PREFACE
Introduction to the Human Body: The Essentials of Anatomy and Physiology,
Seventh Edition, is designed for courses in human anatomy and physiology or in
human biology. It assumes no previous study of the human body. The successful
approach of the previous editions — to provide students with a basic understand-
ing of the structure and functions of the human body with an emphasis on
homeostasis — has been retained. In the development of the seventh edition, we
focused on improving all of the acknowledged strengths of the text.
ORGANIZATION AND CONTENT IMPROVEMENTS
Like previous editions of Introduction to the Human Body, the
seventh edition of the book is divided into 24 chapters. It ap-
proaches the study of the human body system by system, be-
ginning with the integumentary system in Chapter 5, In re-
sponse to feedback from professors and students facing the
challenges of teaching and learning the complexities of the
material in a single semester, this new edition of Introduction
to the Human Body has been streamlined without sacrificing
completeness of coverage. Every chapter in the seventh edi-
tion incorporates improvements to both the text and the art,
many suggested by reviewers, educators, and students.
Some of the significant changes in selected chapters in-
clude the following:
• Chapter 1 Figures 1.1, 1.4, 1.6, and 1.8 have been re-
drawn and a Medical Terminology and Conditions list
has been added.
• Chapter 2 Information on essential fatty acids in health
and disease has been added.
• Chapter 3 Figures 3.8, 3.10, and 3.11 have been re-
drawn.
• Chapter 4 The art in Tables 4.1 and 4.2 has been re-
draw n.
Chapter 5 Information on cosmetic anti-aging treat-
ments has been added to the section on aging.
Chapter 6 The figures illustrating the bones of the
skeletal system have been revised to include new bone
art. A new illustration of intramembranous ossification
has been added.
Chapter 7 This chapter has been reorganized, so that
the types of synovial joints (planar, hinge, pivot, condy-
loid, saddle, and ball-and-socket) are now described after
the types of movement at synovial joints (gliding, flexion,
extension, etc.). In addition, most or the figures have
been redrawn for better clarity and depth.
Chapter 8 Figures 8.2, 8.4, 8.6, 8.7, and 8.11 have been
redrawn and a new figure of ATP production for muscle
contraction has been added.
Chapter 9 Table 9.1 was revised to include new art on
neuroglia and Figures 9.6 and 9.7 were redrawn.
Chapter 10 Figures 10.6 and 10.15 have been redrawn,
'Fables 10.1 and 10.2 have been revised, and a new figure
of the limbic system has been added.
IV
.
•
Chapter 11 Figure 11.1 has been redrawn to include
several examples of autonomic motor neuron pathways.
Chapter 12 The art in Tables 12.2 and 12.3 has been
redrawn.
Chapter 13 Figure 13.3 was revised in order to clarify
the mechanism of action of water-soluble hormones.
Chapter 14 The section on blood groups and blood
types has been revised.
Chapter 15 Figure 15.8 was redrawn and information
on coronary artery disease in the common disorders sec-
tion has been updated.
Chapter 16 Figure 16.3 has been redrawn and informa-
tion on hypertension in the common disorders section
has been updated.
Chapter 17 Figures 17.7, 17.8, 17.9, and 17.10 have
been redrawn
Chapter 18 Figure 18.9 has been revised to include the
values of the lung volumes and lung capacities for
women.
Chapter 19 New to this chapter is the addition of a sec-
tion on phases of digestion that describes the cephalic,
gastric, and intestinal phases of digestion and the major
gastrointestinal hormones.
Chapter 20 Figure 20.1 has been redrawn and updated
to include the new My Pyramid introduced by the
United States Department of Agriculture (USDA).
Chapter 2 1 Figure 2 1 .4 has been redrawn.
Chapter 22 Figure 22.4 has been revised.
Chapter 23 Figures 23.2, 23.3, 23.4, and 23.8 have been
redrawn and a Focus on Homeostasis: The Reproductive
Systems section has been added at the end of the chapter.
Chapter 24 The clinical application on stem cells has
been updated,
On the following pages, the many features of this text are described and illustrated. These
include the "Did You Know" chapter introductions, "Looking Back to Move Ahead" concept
review, Chapter Objectives, Checkpoint Questions, and Clinical Applications. Highly praised features
such as Focus on Wellness and Focus on Homeostasis are also illustrated and explained. The revised
illustration program is presented along with the effective and supportive pedagogy that surrounds
even illustration. An overview of the many ancillarics that support Introduction to the Human Body,
including Wiley PLUS, is provided as well.
Preface
EATURES DESIGNED FOR STUDENT SUCCESS
SOMATIC SENSES
AND SPECIAL SENSES
a
^•^^gr
>
C_/<msider whatwould
happen if yoncouicl n<«
feci die pain of a hot
pot liumlU-iir an in-
flamed appendix, or if you couldno! sec an oncoming
.. smell smoke, taste your lavorit-
edesserr, or maintain your balance on a flight of stairs.
In short, if vim could not "sense" your environment and
make the necessary homeostaric adjustments, you could
not survive very well on your own,
I ~
| Oome things improve vntb age,
but bearing is not otrc of t bent. Damage in the hair
cells that convert sound waves into nerve imputes
accumulates over a lifetime, and by the time bearing
loss is discovered, irreversible damage has already
occurred. Exposure to excessive noise is the most
common cause of bair cell damage. Damage increases
with both the intensity and duration of exposure. The
hair cells appear to he less traumatized by short periods
of loud noise, such as afire alarm going off, than by
chronic exposure to moderately loud noise, such as the
noise of vacuum cleaners, power
tools, engines, and loud music.
DID YOU KNOW?
Each chapter of the 7 th edition is intro-
duced with a short introduction linking
the chapter content to come with some
relevant, everyday scenario. Carefully
crafted by Barbara Brehm, the author of
the very popular Focus on Wellness es-
says, these are designed to pique the
students' curiosity about the contents of
the upcoming- chapter by making con-
nections to issues concerning their own
health. In addition, these chapter-
opening teasers arc linked to web-based
activities that allow students to explore
further the connection of the chapter
content to this particular wellness issue.
Sensory Nerve Endings and Sensory Receptors in the Skin
(page 100}
Somatic Sensory Pathways (page 259)
:
LOOKING BACK TO MOVE AHEAD
Beginning with Chapter 2, chapter-opening pages also include a listing of concepts that were
previously covered, but that will be particularly relevant to understanding the chapter at hand.
Complete with page numbers for easy reference, these background basics allow the student to
make the connections between important concepts developed in earlier chapters that are so
crucial to success in the course.
STRUCTURE AND ORGANIZATION
OFTHE HEART
OBJECTIVES • Describe the Ideation of the heart and
|e Structure and functions of the pericardium.
• Describe the layers of the heart wall and the chambers
of the heart.
, Identify the major blood vessels that enter and exit the
heart.
, Describe the structure and functions of the valves ol
the heart.
■ CHECKPOINT
I. Identify the location < if i he heart.
J, Describe die various layers of the pericardium ami the
f heart wall.
ili) iitria and ventricles differ in structure and function?
4. Which blood vessels that enter and exit the heart carry
lated blood* Which carry deoxygenated blood?
sequence, which heart chambers, heart valves, and
Hood -vessels would a drop uf blood encounter from die time
it flews out of die right atrium until it reaches the aorta?
Ifjrbnn monoxide (CO) is a colorless and odorless gas
lueeo smoke and in exhaust fumes from auto-
,. furnaces, and space heaters. CO hinds to the
■up of hemoglobin, just as O. does, except thai
CO hinds over 200 rimes more strongly, At a concentra-
i ill ns 0. 1%, CO combines with half the available
in molecules and reduces (be oxygen-carrying
i be blood by 50%. Elevated bin id levels of C< >
I nusc carbon monoxide poisoning, which can cause the
i ,ril mucosa to appear bright, cherry-red (the
moglobin with carbon monoxide bound to it).
_§ministeriitg pure oxygen, which speeds up the separa-
tidii of carbon monoxide from hemoglobin, may rescue
FOCUS ON WELLNESS
■\ popular feature of the last four edi-
tions has been the wellness essays, writ-
ten by Barbara Brehin Curtis of Smith
College. These essays increase students'
appreciation of the relevance to the
maintenance of good health to the con-
cepts and details of anatomy and physi-
ology presented in the text. The well-
ness philosophy supports the notion
That lifestyle choices that individuals
make throughout the years have an im-
portant influence on their mental and
physical vvellbemg.
' In addition, each essay includes a
"Think It Over" concept application
exercise. We believe that the informa-
tion contained in these Focus on Well-
ness essays is timely and interesting; we
hope students and instructors continue
to feel this way, too.
Preface VII
CHAPTER OBJECTIVES
Feedback from users indicates that many students do better when the material in
each chapter is developed so that they can focus on fewer learning objectives at a
time. To address this need, chapter objectives are interspersed throughout each
chapter. Each major heading begins with a short, focused list of the important con-
cepts to learn for that section.
CHECKPOINTS
Complementing the format for objectives, Checkpoint Questions appear at strate-
gic intervals within chapters to give students the chance to test their understanding
of what they have just learned. Answers are found easily within the chapter content
immediately preceding the checkpoint; where checkpoints appear within exhibits,
the answers can be found within the same exhibit.
CLINICAL APPLICATIONS
A perennial favorite among students, the intriguing clinical applications in every
chapter explore the clinical, professional, or everyday relevance of a particular
anatomical structure or its related function. A colored screen highlights selected ex-
amples discussing health issues and the treatment of disease.
Adaptive Immunity 431 J
If you want to observe the relationship
bei ween lifestyle and immune (unction,
visit a college campus. As the semester
progresses acid the workload accumu-
lates, an increasing number ol Students
can be found in the waiting rooms of
student health services.
[s Stress the Culprit?
Stress has been implicated as hazardous
to immune function. Researchers in ibe
field of psycbwiciiiviiiiiiilitiiilojQt (PNl)
have found many communication path-
ways that link the nervous, endocrine,
and immune systems, Chronic stress
affects the immune system in severs
ways. For example, Cortisol, a hormone
secreted by the adrenal cortex in asso-
ciation with the stress response, in-
hibits immune system activity, perhaps
one of its energy conservation effects.
PPs'l research supports what many peo-
ple- have observed since the beginning
of rime: Your thoughts, feelings,
moods, and beliefs influence your level
of health and the course of disease, lis-
pecially toxic to the immune system are
feelings of helplessness, hopelessness,
fear, and social isolation.
People resistant to the negative
health effects of stress are more likely
-j, experience a sense of control over
the future, a commitment to their
work, expectations of generally positive
outcomes for themselves, and feelings
of social support. To increase your
stress resistance, cultivate an optimistic
outlook, get involved in your work, mh\
build good relationships with others.
Of b Lifestyle ai Fault?
When work and stress pile up, health
habits can change. Many people smoke
or consume more alcohol when
stressed, two habits detrimental to op-
timal immune function. Under stress.
people are less likely to cat well or ex-
ercise regularly, two habits thai en-
hance immunity;
Adequate sleep and relaxation are
especially important for a healthy im-
mune system. But when there aren'i
enough hours in the day. you may he
tempted to steal some from the night.
While skipping -sleep may give you a
few more hours of productive time in
the short run, in the long run you end
up even farther behind, especially if
gelling sick keeps you out of commis-
sion for several days, blurs your con-
centration, and blocks your creativity.
Even it you make time to gel eight
hours of sleep, stress can cause insom-
nia. If you I'uul yourself tossing and
turning at night, it's time to improve
your stress management and relaxation
skills! Be sure to unwind from the da}
before going to bed.
HI! Preface
FOCUS ON HOMEOSTASIS
Eleven Focus on Homeostasis pages, one each for
he integumentary, skeletal, muscular, nervous, en-
locnne, cardiovascular, lymphatic, respiratory, di-
gestive, urinary, and reproductive systems are in-
luded at the end of the respective system chapters.
ncorporating both graphic and narrative elements,
lese pages explain, clearly and succinctly, how the
litem under consideration contributes to the
Lomeostasis of each of the other body systems. Use
if this feature will enhance student understanding
>f the links among body systems and how interac-
ions among systems contribute to the homeostasis
if die body as a whole.
EXHIBITS
rhe Exhibits are self-contained features designed
o give students the extra help that they need to
earn the numerous structures that constitute cer-
ain body systems — most notably skeletal mus-
ics, articulations, blood vessels, and nerves. Each
"xhibit consists of an overview, a tabular sum-
lary of relevant anatomy, and appropriate illus-
rations. .Many also include a relevant clinical
orrelation. Students will find this clear and con-
ise presentation to be the ideal study vehicle for
•arning anatomically complex body systems.
FOCUS
ON
HOMEOSTASIS
Body System
For all body
systems
Muscular system
The Respiratory System
Contribution of the Respiratory System
Provides oxygen and removes carbon dloiid*. Helps adjust the pH of body fluids through »»■■>■■
Ifitloft 01 carbon dioxide
Increased rats snd depth 01 breaming support Increased activity ol skeletal muscles during
exercise.
Nervous system Nose contains receptors for rne sense ol smell (olfaction) vibration* of Air flowing ■
Endocrine
system
Cardiovascular
system
i ymphatlc
system end
Immunily
Digestive system
Urinnry system
Reproductive
■yitarru
vocal cords produce sounds lor speech.
Angiotensin converting cniymo <ACE) in the lungs pronwlaa formation ol the hormone an'
giotenain II, which In turn stimulates the adrenal gland to release the hormone aldosterone.
During Inhalations, the respiratory pump aids tho return ol venous blood to the heart.
Hairs In the nose, cilia and mucus In the trachea, bronchi and smaller airways, and alveolar
macrophages contribute to nonspecific Immunity to disease. The pharynx (throat), contains lyrr
phalli tissue (tonsils). During Inhalation, ma respiratory pump promotes ma Itovr ol lymph.
forcelul contraction of the respiratory muscle
i assist In defecation
t
Together, the respiratory and urinary systems regulate the pH ol Body fluids.
Increased rale and depth ol breathing support activity during sexual Intercourse. Internal rsspl-
" ration provides oxygen to the developing fetus.
210 Clusters Ihe Mtiscslat System
Exhibit El, 10 MuB'.:losThal Movu the Vortobial Column (Backbone) Ifiguiv B-ii)
objective * Describe the origin, Insertion, and action of the muscles that move the vertebral!
Overview: The erector solrww muscles
foim Bis largest muscular mess ol Ihe back,
lorming a prominent bulge en eiOter side of
the vertebral column (Figure 8 ??). M con-
sists ol Ihree groups ol overlapping muscles:
"Jocosto/i's jroup^il '*-6-lios-TA4a),
f&aoi'ss/mus group ilon'-Jl-si-mus), and
.!■•. :.'.' ■<■■ •''.
that move Ihe vertebral ooTumn Include
the BttrnQClaMoftiastM, gwrrfralue
rVfll0oruni\ rectus abdominis isae Exhibit
n J), psoas major (m« Exhibits it I. and
»l*BU*(See':V bitB II).
Fun flexion at me waist, as in touching
your toes, overstretches the erector
gpnae muscles and muscles that are
ovorslralched cannot contract eHochvaty.
Straightening up Irom such a posibon Is
therefore initiated by the hamstring
muscles on the back of the thigh and the
gluteus moxlmus musclos ol tho
txrilccks,The erector spinae muscle? join
in as the degree ol KeXion decreases.
Improperly lilting a heavy weight.
however, can strain the erector spin no
muscles. The result can be painlul muscle
spasms, tearing ol tendons and ligaments
ol the tower buck, and rupturing of Inter-
vertebral discs. The lumbar muscles are
adapted lor maintaining poatura, not lor
lilting. This is why it is important to krvool
and use Ihe powerful extensor muscles ol
the thvghs and builockc while lilting a
heavy load.
Relating muscles to movements:
Arrange ihB muscles in ihis exhibit according
lo tho following actions on the vertebral
column. (I) flexion and <2| extension.
V. |>. 'I '.. l-i ll| I !■
eiecloi spinas?
*'l..-..- 1
Origin
Inwrt-on
Arflhfl
CfKWr iplnw (tf-REK-toi
AJIrUspIuB
Ocdpi.nl bono.
Extends hwd; wtends arc* fataraSy llewea rtrtebial
. .-. , ,.,.-. ii
cervical, monclc.
'i. i'i.1,-,.1 U. ii il'..
,.. II.MI-
sptnac cmuapuwi
ond (ximbni
and vortobrao.
(Jlocoslala group. bnjjistirnuB
nrtttme
group, and uplnalts group)
9 tarnocU Worn nalol d
Biarnum una
]; ■,!-,■,.- ■--,!' ■
'Jul i ii/' ... .jl ! .jl-i i u:.lIij:. ::...: ■■.-■ ,il :,..il 1 11 n
[liW • no W, -Ito-M A5-1IHC ,
- rvhds
',i'f1iit.r.,| f.ili |-i "in- llr'- mi' r "i.:r '--.:'.-:■ I ,-.( "'
■
ora muselft rotBi&s head io«*aid Side t*npos,nt>
emtio- - cavftte; nmtmt - maswtcJ
connractmg musclo.
psocwaiV lumporal I»ne)
i
Quadra tin ftjmbOrtilin
■ ii
IV.. i'IIi ill. . i.ji .:[...■
Ccnuaciiow ol oolh muscle?* etftvid lurn&ar part ol
IkHod-tV Ms j'i BCtam
en .: 'i ■.. !■_■;
Ihe vertebral column, coneracbon ol one- imisdv "Wo*
ftj mbar port of vtvuwral co In run ,
A.V'iro ■ in-t .' .■-]!- r..
■
Principal Skeletal Muscles 211
1
Flflur* 8.22 Ma|or muscles lhat move Ihe vertebral column (back Lx>f»«)
Tho •r»c1ar splnoo mu»cini «>l«nd tho vertobr ■) column.
Ih ,
aim
Posrmior view ol ewdor spnss musOss
clei conililute the erector tplneoT
Preface IX
AGING
Anatomy and physiology is not static. As the body ages, its
structure and related functions change in subtle and not so
subtle ways. Many students will go on to careers in health
related fields, in which the average age of the client popula-
tion is steadily advancing. For this reason, discussions of
this professionally relevant topic are included in chapters 1,
3,4,7,8, 13, 16, *17, 18, 19, 22, and 23.
AGING AND THE
DIGESTIVE SYSTEM
objective « Describe the effects of aging on the
digestive system.
Changes in Th_ digestive system associated with aging include
decreased secretory mechanisms, decreased motility of the
digestive organs. Kiss of strength and tone of the muscular
tissue and its supporting structures, changes in sensory feed-
back regarding enzyme and hormone release, and diminished
response to pain and internal sensations. In the upper portion
of the GI tract, common changes include reduced sensitivity
to mouth irritations and sores, loss of lasie, periodontal dis-
ease, difficulty in swallowing, hiatal hernia, gastritis, and
peptic ulcer disease. Changes thai may appear in the small
intestine include duodenal ulcers, maldigestion, and malab-
sorption. Other pathologies that increase in incidence with
age are appendicitis, gallbladder problems, jaundice, cirrhosis
of the liver, and acute pancreatitis. Changes in the large in-
testine such as constipation, hemorrhoids, and diverticular
disease may also occur. The incidence of cancer of the colon
or rectum increases with age.
■ CHECKPOINT
25. List several changes in the upper and lower portions of
the CJI tract associated with aging.
_____ _
«y^g> COMMON
COMMON DISORDERS AND MEDICAL TERMINOLOGY AND CONDITIONS
The Common Disorders and Medical Terminology and Conditions sections have
been completely updated and revised for this edition. Marked with distinctive icons,
these sections are located at the ends of appropriate chap-
iters. The problems considered in the Common Disorders
sections are selected to provide a review of normal body
processes and demonstrate the importance of the study of
anatomy and physiology to careers in health-related fields.
The glossaries of selected medical terms and conditions
signed to build vocabulary and enhance understand-
ing. Mirny of the terms include pronunciation guides and
word roots.
DISORDERS
Asthma
jlrtbm* (AZ-i
'In i ■-
teHCtLT-HMIMOLOGY AND CONDITIOKS
/(Mmiurl ihrtsl mmirairr l'ir>i._id procedure tt> clear ihe air-
1 1; objects, h i» performed by applying ■ quick
• iwean the navel ami lower ribs dnl .-.. « ■
I ihc diaphragm and forceful, rapid eapol
be lung-, forcing ti. "in oft-* ii radical ic» eject
wed i.. expel .-aie. from the longs
i ■ ic-.i-.di ui ■ ■ -pun. '.I--.
tl„mf*li auiattnitrt}l\M-\iknu->iOO-vtr).
a^, pulse) Oxygen srarvuiRin due to
ii. rente with i ciiulatiun, tmr-
raon-i, or internal respiration.
Ajfm<ou\ i" p KA-iun) Inhalation into ihc bronchial vm "f »
• Ir, « ' ■ , water, fond, c« a foreign body.
I iiiiution nf die bronchi through i
irM^mfr. an illmnilUHsl, toW* 1mln111u-.1l lll.it U passed
. :,ir*mni--i (or »■»•''. • Imttta Mothi hfondit.
\n inherit-- disease ol secretory cpiihclia ilm
•,. . .11.1 ML'II
ii. .ii of ih<' amy* leads to difficulty
,. | ,■„.,,. i . i.. .1 ■- 1. ii. .ii mf lung tissue.
|^-,-,„ [MM' --nihil, difficult) fain fid «« lal.i '
tyuuui :n i '■ I M- si) Ijms "I blrwl from [lie nine due l"
■ .hgnani growlhs, or Weeding dls-
itcry with silver mil He, elcctro-
laag.AIw called mwMi«f.
^^ helm or under) \ dchci
i liwii I.- I tl .' ii ■'. '•■ ■ "-. bj i m Pi In jrien.il
i- n | ,_i, ,|.. mi, i. . tool edi ii n-iionmg hanojjlobin
inability el' the hi. ■-..
J sum their needs, as in hurl 1.1
10 use I). jvmjK'rly, « in cyanide poisoning.
nbrancs. which canst
e painful when lln- I
■ pUurHh.
in tlie lung* that re*
- due co. the prania
ten
rrnhk-
i if in
v uilhiii ihc bum .hi
Mitlianual miiilaiitm l"hc use of in -uroinaticilly cycling -twice
(ventilator or respirator) ■■' O-rin bi-faihiiui. A plasm Hi'"-' •» ta-
li ii. ' ban riu non 01 mouih ii»*l the tube ii aiiached to a de-
vice tint forms air into the lungs. Kahaltnion occurs psoi-i I)
due in flic elastic recoil of die longs,
Plcurity liilhinuiadon of the pleural mp
Uon during brealhing thai can he qui-
ItH'ntbrane-s ruh -gainst each cirhcr. Als
Krta <RA1-S> Sounds vnnenmes heard
bubhliruj or reeding. OHfcftM rypM a
■boonral type .>r unooni of fluid or r
alveoli, «* lo hrinKho-onsiricti™ th« raiuo turlwlenr airtlon-,
SlSptrmtrj Suni lyaJnme (XI>S) AbrciHhinMdknnleri.rpic
in.iuir. ncwtMinv. in whicii the alveoli do not remain np-n duo
iii .t !ac_ tif Hurfjeuni. Surtactunt redoec* >uiijec ttrmoa .in.l i^
nKcaBiy 111 prcveni (h- .nllipM d _hei.li dunnj; n-h-Jatiarl,
RtspimKry fniht A i.muIhi.hi in which (be respirator) .y.i.in
ELdiec ramot iupply enaugb o : to nuincain m*tabo_jn or
iiiui.u rlimiiiiie enough COj u. pMMU .e-piruiory i-idosi- (a
higlier-lhaii-noriii.il 1 1' level in. inlcr-linal fluid).
Rbiuithii i. ui- inlluniiuuwi i.l"
lln unit. .ii-. BU-mlir,iil- of dH nOM.
SwUrn mfimi death tyndmmr (S1DSI Dcadi ol mfana hei» -en
tlie ages rf I weefc iuiiI I Z mand-i thoughi u> lw dire lo lijTiu-ij
thai iitt-ur. w-hilc Nlceping in .1 priiiu: imsiiion (on the .itonucli)
.. . . 1 . . brcal-ling exhaled air tripped in a depression of the; in«l-
irtv.. It b now NCOmiDCnded thin nonn.it new bum. bg placed
on ihi'ir I ,i I 1 I. |. ij oelllclllber: "b«k i.i.l.cp'l.
Tachypnea (tal'-lp-Nk" -j; U&J I ipiifl Rapid brealhinj rue.
ffQmt (lini'/i A "hiMlnu.!, iqu-al-ng, •« rnu-tail Ugh
mind diinnn breathing reaahiBg from 1 p_n.,i 1. 1
Minalcd airwilv.
1 = [tin ting) ■■ i d-Bf<to(to*- i B---d by -hn_-i_ _i-wiy
uiinn, jiewji liipuiv-nviMiy 10 ,1 wriety ot' stimuli, and airway
mi. The atrv.iv- "Imru-iiiHt may Iw due in uiiihj.Ii mUKto
in llki walls of uiuller bmacfal and bioii.l. .
uf die airwiiys. im-reascil inutiis sect-t-i.in. or dun-Kir n. iIhi l-|i-
uif ihc ilr«ay. Asihtu.1 1^.11 lc.1.1 partially res _i
iji»nuO\ i.r with treamieiil. Il anccn i-S% ofltie US pcniulilkiii -n.l
1 b-cot-_ng inoeas-agb coeutti 1 chfld-cn.
A%ihin.iiiis lyiwcally rcaer 10 tow coiwentratitwis of stimuli thai
lo noi normally cause symptoms in |K.'iiplc wiihuut asiluiu. Swnic-
Igger is an nllerjtcii such as lulleii, dust mitts. UN-ds, ." ■
tcular ftKhl. Othei cOfT-BMM trijigets incIiiiCe eini^iim.il npa^t, ai-
1. stlllitins agents (used III » in- and hcer and 111 _ccp grcciei fresh
alad bars), eienise, and breading cold iii or dnnstte aolofcc
pioill. IIiiI.kIc .1 ■ , ,1,, , I , -.
tncs-, tachycardia, fatigue, i.k.i-1 r.ki.i. an. I .niocli
ronlc Obstructive Pulmonary- DltMM
wn'r tbstrmriir pu/mnmtiy diimt* (COPD) n 1 reapu
char_cteri/ed by chn. nit- t.h.irticlion of airflow. "l"Hc prirH.ip.it
■. ..I I 'OI'll Jie ci..|ih;-*rn.i in] tlm.ni. hiOm llilis. Ill mnsl
iiosi t-ommon cauce js nga-
aioke, Oibsr cnaa meluile
ipanonal eapo-ure to dusts
v I OPDd presxTilable I.. .
OfciAg .'. h.tilhili
polluiinn, pulmnnart' iniis-iinn, nee
gases, and genetic factors.
ipbj/smta
ttpma (em' ii -SK-nn - hli.wnii]inrfuIliifair»isaili-iKile«cJiir-
rizal lay dtainrakiii of the walls uf the alveoli, which produces ib-
nally large air sjiaec- dial lemaiii titles] wjih air daring -thiL-ition.
Il less surface atea fi« gas e.wbonire, 0} eSBumra ati-m die rcsrera-
. 1 . 1. rMli.int. BIibm5 -I. level is MNbicwtul Bow ..
1 ml. I oereivc that novel the LJ.. r-t|tiirein<:iif. uf ihc cell-. It...,-, ll.i
l-jii breathlcrs. A. mutcisiii^ numbcis ofalv_ol.it walls an- .!
; clavtic tccoil ile_reascs due to hiss of clause tibcrs, .tail an tncreas-
aiiiouiii of air Ij-cmnes ira|>|Kil in ihc lungs at die end ui edulaiivn.
tr aeveral yean, advlcil respiraijiry eaeniuii inorases the sin- of ih-
a tape, resulting in a "barrel thest." |.«iph_v*- , ii-i II _ conunon pro-
in the dcvelopiitcni of tung ciutct.
runic Bronchitis
roiTK- frroweWrr- vk - itntasier chllVMerirtst liy cv; .
» l.i.l nv.s-.rv -icamnpaninl by a cmigh. Inlialetl itritaim lead to
inrlamniacton willv an iiscreasc tit tile si_c and number ..i 1
\A ami goblet velk in live airway epnheln'm. Hr ihictrnal and ex-
inrus nroih«-e»t PJITOWS live .itrwav inti Inp-ira the attit-i ol cilia
ilinU.Ht jwihi^ciu Imxt«iic cinbcd-lcd in tktrtf SeCNdQM ind
tiply 1-.1p1.lly. Bcarlca a niagh, «yi np KKm ol chlWJC hrollfhilis arc
tnoaofb-l ! .J.. ,1 , .. ..iiii-ffls-andpulitv-tary-hyyen-t-iiim.
Lung Cancer
hi ilic United State.. Itrng umetr „ she leading came of cancer drarh
in both inalc^ ili.l fcniotcs. At the time of diagnostv. hmg mnei-r is
anally well .itlun.-cl. M...I people ».* lung CUMf .lie within 1 war
,1 A I ... - ...I llie ovctall sivivis'.il rare is only II) I- ',
IS ...il,- dH 10 ranking, anil ihe disease ts III to
Ml rimpi more oommnn In sumters lhan nnnsmoters l-\i«wi>u' ...
iceondhand smukc -also ciiuses lung > in. 1 md heap .l.,.v t Qthaa
eatistrs of htug cancer .10- .iinij.n(r i.i.h.nitin, sueti aea-rays, and inhaled
nrii.in.ty mkIi a. ga h i wm a ind radon gas.
Syanptorm ol hmg .jneer nui include a chronic enugh, spimny
hlewd from ihe rcipitjh.n. n..i. »h,t .'.n h -. •,h..mie» erf breath, cheat
pain, hisarseriess. .tifti-tilty swallouang. Mi'ighl loss, aiuir-sia. faligvie,
hone pain, -tmrnsinn, problems wilh halanvv. headache, aneinu, low
blood phtclei eovini, and nundiie.
Pneumonia
Ptteiimomu 01 pneHMwitis is <Ui attnc inleeooii 01 ii-.ll.ui...
alvi'iili. It Is llie BUM mnmOfl WktiOW tMHO ol ilealh in die Uiuied
Stales, where an csciinaied 4 inillinn cj-cn occul anniuilh. \sTicn ierlai.n
nlivrolie- enter live hmgs of lanccptlble irubwidicik they Iclcjae itainlg-
ing iin.ii-. ■.iiiiiul-iing iiillmiiioaiioii and MiunuiK r_n»ioses that have
damaging side C-fcas. Hie Insula aisj immune res]>iuvw il.lill.1gc alseoli
-n.l bronchial iiiucou. iiifinliranrs inlUnniulion and edema s-auve die
alveoli 10 till wilh detwis anil -' idoa and g»
Bdunge. I tic- must -onunon cause is the hactc-iuiu Smpasaiw jwra-
iwia-W, Inn othei bacwria, vini«_i, or fungi may aly. eaviu: in
Tuberculosis
Hit- riaciennm ,Uivvl\utmmi uiWni-bia pniduee- an info, jo
muni-ahle diaaae called nhmwhuh (TB) thai o
lungs ami the pleurae hut may involve i"l"'' porct ..i the t«"lv- Dbc«
the Iwctena are in-ude ihc hingv, ihci multiply slid cauvr nilt.iniiiii.
u which Miinuliicx ncutrtiphib and iii_cn»ph.igo lo ntlMR lo the
. nj^iir the li.Kleni I-. pt.-.cnl lb.il -.|.l-t.l.l If ti
..V-.I.-HI 1. not iiivp.Hieil. ihr l.acteria may remain duritu.ni for lice. Im-
P 11... I niiiiiiinm nui enbk the baratril IS _w-ape mm Idood and
lymph to In/i-O Other o.yanv. In nt-ny iiewple. qit |"
vitrighl lus-s. lelhaJv!5 , . iimtresin, v l..w vimlc Ivht, iii^Iii .wean, cough,
dyvpiiea, chesi pain, -nil ..pilling hlood (hcmopij-sui— do
.1 ' 1 ., 1 ...... ; In . It.ease is advanced.
Coryza and lnllu*nM
llandtesls uf viruie*. n aueri a uy the ifrwoivntio (rfia- - now/), tan
i-iiu: roijic (ko-kl-<a> lie ihe nlniaan coM. T)|».-l oni/'
elude sncc-in.:. eaocjiivt o-.d secretion, dry cough, and c.wyi'sii.tn
I Ii- 1. i.ii:|.!ic,i.. L .l comnoii told is noi uitialh' accoiii|MHied by a
... 1 I ... |.Il . ■. . i ttl 1 ... .1 h ".-..■:
il a . . .1 l.nilpiliv
lufintma (flu) is alsn caused In- a virus. Its svniplor
lusuallyhia-hcrihan IOI'K.01 H'O. hradaehe, ami n»-
c-ulat aches. CVIdlikc 13 1 .' I il.i' ■<<<< ..iliti.l.--.
Pulmonary Edema
PiiJmmuny erfeww 1- .hi iibnonuil MiniuJantanJ u.iciun.,1 1
illlersiiiial c|«cec and ttaol of lbs lungs. ITic -.tenia may ariw from in-
iltliuj imlimii ni)i i.ipiiiij jainia ilah-ii fjaalmai-rM niigin] .. Ift . .-'
[witnun-in tapillaiy |eev«ire due lo eongcUne lit-arl laduic lOiniW dri-
KiivV The nam eommoft lytnpiom i-. |vunfiil .r Ul.e.-.l lutadiing. Oihet
,ti n| .i 1 hw 1 iH-hitlt- wKi--ing. rs|«d hreailting rate, resiEeauie-s, a Rtlhiui of
1 .. 1 i\.yaiuhkjsitiii-uvin«leie<sMwptripiraliuii.
X Preface
THE ILLUSTRATION PROGRAM
I !'l". r
Beautiful artwork, carefully chosen photographs and photomicrographs and unique pedagogical
enhancements all combine to make the visual appeal and useless of the .lustration program m
Introduction to the Unman Body distinctive. The seventh editi on has been carefully reviewed, revised,
and updated to uphold the standard of excellence that
instructors and students alike have come to expect.
COLOR CODING
Colors arc used in a consistent and meaningful manner
throughout the text to emphasize structural and func-
tional relations. For example, sensory structures, sensory-
neurons, and sensoiy regions of the brain are shades of
blue, whereas motor structures are red. Membrane phos-
pholipids are gray and aqua, the cytosol is sand, and ex-
tracellular fluid is blue. Illustrations of our distinctive
negative and positive feedback loops also use color cues
to aid the students in recognizing and understanding
these concepts.
fhomtal bom
sphenoid bone
:- i I'M'. I "' r
lacrimal bone
'■ja::,'.- qc-ji
Zygomatic aicJi
- ZYGOMATIC BONE
) Antorlor superficial ulew
ID^f
MAX ' ' <•
I.': M.i '■:: i '•-
MAND BLE
II ■ im 1:0- E
i. ; ; '; i I-..-.I .m.i ■■,
(d| Anionor riant' MM |lk>«.»JI
NEW ARTWORK
Exciting new three-dimensional
paintings grace the pages of many
chapters. Many other line drawings
have been newly rendered for this
edition, and nearly every figure has
been revised or improved in some
way. For example, virtually all of the
art" in the chapter on skeletal system
(Chapter 6) has been redrawn.
Preface XI
FEEDBACK LOOP ILLUSTRATIONS
As in past editions, this popular series of illustrations captures
and clarifies the body's dynamic counterbalancing act in
maintaining homeostasis. The feedback loops visually accen-
tuate the roles that receptors, control centers, and effectors
play in modifying a controlled physiological condition.
FUNCTIONS OVERVIEW
The Functions Overview is a feature that juxta-
poses the anatomical components and a brief func-
tional overview for each body system. These func-
"boxes" accompany the first figure of chapters
dealing with body systems. They help students to
itegrate visually the structure and function of a
body system and make the connection between the
interactions of various systems.
Figure 19.1 Orgam ol Iho dlgmtiw syniom «M related structures.
"
Oigira ol IM «MlroinW»1ilMI (W*MI »fO Ihn mouth, phuyni, •■ophagiii. «lom«*h. irtiNI InMsilw. and largi
■Mebllrw. ICMMi d"90Ml»» organ* «r» llnfloolh. longuo. .Olivary gland*. llvor.giMIMaclltOr. and pnocrta*.
MM i It —i.
*ndlr»igue
Functions ol DigtEllvo SysWm
1. Ingoallon: Utting r»o Woiho muM
5. Socnifiwi. rWoaro at mint. add. buffers, and 8iw»ma« Ifllo Inn
lumwi oniM 61 iracl
J, Mixing and preclusion: diuinng and putting Bad Hvougn IU Gl
BBCl
*. OigMton. rnachonol ond chomcul bronkdo*" ol rood
5. AbaorpMn: passage ol mgmiM praduaa Irani in Gl Irnd inlo
M Wood am rympn.
S. Detecaiion oUrninnaon ol leces Irom ine Gl tract
RfH UMnivaM ol head and r»» and arastior view d< vur»
V IrWch ■ccnioff digestive oroons aaelll In 1ll« pl>v>l»l breakdown ol lood?
Soma stimulus
disrupts homuo&insis by
.1! n .i .iii'l i
daoraai ■>.] i
:.:■■■ l;i: ...J '-QIIJ !IC!'
mi.i it i I6y
Ftaccplors
Inpul ll I j Nerve impulses oi
II iihiMiiii i I'in.i : . I i-
ihai receives uie
Inpul and provider
There Is a totum lo
homaostasb
WllBl 1KB lOGpons*
brings the conl/OHed
condition bet* to
normal.
■
lhat bring aboui
a change or
■■i
Mill
: I
R*luifi Bo-homeortaaJftj
t-rhfjn increaMd
««Jlnc WipMt »nd |
ii . ..,: ■.,■] :.,'.:■! ,i
" . .;.' '-'• I'-'i-i.)
|. ■ ,. .
two*, lo ixmnal
."
*^
^'.IL.Ilr.lli.i 1
of Wood
PHrMJVI
1-1 .ll- ,1
ii. i -..-.I ! [.I ■-.'.! r .--.'.,.
ORIENTATION DIAGRAMS
Students sometimes need help figuring out the per-
spective of structural illustrations — descriptions
alone do not always suffice. An orientation diagram
depicting and explaining die perspective of the view
represented in the figure accompanies most anatomy
and histology illustrations. The orientation diagrams
are of three general types: (1) planes indicating
where certain sections are made when a part of the
body is cut; (2) diagrams containing a directional ar-
row and the word "View" to indicate the direction
from which the body part is viewed, e.g. superior,
inferior, posterior, anterior; (3) diagrams with ar-
rows to direct attention to enlarged and detailed
parts of illustrations.
XU Preface
CORRELATION OF SEQUENTIAL PROCESSES
Correlation of sequential processes in text and art is achieved
through the use of numbered lists in the narrative that corre-
spond both visually and numerically to numbered segments
in the accompanying figure. This approach is used exten-
sively throughout the book to lend clarity to the flow of com-
plex processes.
Events at a Synapse
Although the presynaptic and postsynaptic nciiron.s arc in
.Minity at a synapse, their plasma membranes do aol
touch. They arc separated by the synaptic deft, a tiny space
Ma with interstitial fluid. Because nerve impulses cannot
i across the synaptic cleft, an alternate, indirect form
of communication occurs across this space. A typical synapse
operates as follows (Figure '). 7):
f A nerve impulse arrives at 9 synaptic end bulb of a presy-
naptic ax "'.
A The depolarizing phase of the nerve impulse opens
voltage-gated Cif dh-nmch, which are presenl in the
membrane of synaptic end bulbs. Became calcium ions
are more concentrated in
into the synaptic end Inilli tl
£ An. increase in the eoneen
synaptic end bulb triggers
synaptic vesicles, which relc;
initter molecules into the syi
^ The neurotransmitter moJec
tic cleft and bind to M*7»vw|
postsynaptic neuron's plasm
40i Binding of neurotransmitter i
which allows certain ions to II
As ions How through the <>
across the membrane changtl
Figure 9.7 Synaptic transmission at a chemical synapse. Exocytosis of synaptic vesicles Itoma
presynaptic neuron releases neurotransmitter molecules, which bind lo receptors in the plasma membrane ot
the postsynaptic neuron.
At a chemical synapse, a presynaptic electrical signal (nerve Impulse) Is converted into a chemical signal
(neurotransmitter release). The chemical sign*! Is then converted back Into an electrical signal (depolar-
ization or hyperpolarization) in the postsynaptic cell.
Ptesynapl«c neuron
Voltage-gated Ca' '
channel
Synaptic end bulb
ion channel
closed
i' H V
Postsynaplic neuron
ft Depolarization » "JrNerve impulse
What causes the voltage-galed Ca ?1 channels in synaptic end bulbs to open?
KEY CONCEPT STATEMENTS
Included above every figure and de-
noted by the "key" icon, this feature
summarizes an idea that is discussed in
the text and demonstrated in a figure.
A pedagogical feature unique to our
text, these help students keep focused
on the relevance of the figure to their
understanding of specific content.
FIGURE QUESTIONS t
This highly applauded feature asks
readers to synthesize verbal and visual
information, think critically, or draw
conclusions about what they sec in a
figure. Each Figure Question appears
below its illustration and is high-
lighted by a distinctive Question Mark
icon. Answers are located at the end oi
each chapter.
Figure 11.1 Comparison ol somatic and autonomic motor neuron pathways to their effector tissues.
\ Stimulation by the autonomic motor neurons can ell her excite or Inhibit smooth muscle, cardiac muscle.
i - and glands. Stimulation by somatic motor neurons always causes contraction ol skeletal muscle.
ACh:
Skeletal muscle-
contraction
Spinal cord
(a) Somalic nervous system
Autonomic
motor neurons
ACh
?P Postganglionic
•Zi~S sympathetic
Autonomic neuron
■ 1 , 1 1 i'-i
NEorACte
Glands-increased Of
decreased secretions
Smooth muscle [a g
In the urinary bladdei,-
conlraclion or
relaxation
Cardiac muscle (in Ihe
heartHncreased °r
decreased rate and
force of conlraclion
!-.!.; il i .id
Preganglionic
sympattwtlo
ncuro.-i
Adrenal medulla
Spinal cord
Pn»gangi»>"^
parasympathetic
neuron
lonomic '*-'
ganglion Postganglionic
rw.-isympaitiefle
neuron
NE or ACh:
Glands -irveroased or
decreased secretion:
Smoolh musclo (e.g.
in iihi urinaiy bladde
contraction or
relaxation
Cardiac muscle (in V
'h:. iii.i -in wased en
decreased rate and
locos ol conlracl n
(ti) Autonomic nervous syslem
What does "dual Innervation" moan?
Preface XIII
.EARNING AIDS
response to users of the previous edition of Introduction to the Human Body, we have retained the learning aids
at students and instructors find most useful and have tried to improve them wherever possible. Several learning-
is already discussed are the chapter objectives and the checkpoint questions. All learning aids — such as critical
ring questions and end of chapter quizzes — have been revised to reflect the enhancements to the text and art.
CROSS REFERENCES
This new edition features cross-references that guide the
reader to specific pages and figures. Most will help students
relate new concepts to previously learned material. However,
we acknowledge the really ambitious student by including
-loss-references to material that has yet to be consid-
ered.
ANATOMICAL TERMS
The anatomical terms included in the seventh edition have
been updated completely to correspond to the Terminology
'buitoit/iai, the latest word on the use of international
anatomical terminology.
PHONETIC PRONUNCIATIONS
JD WORD ROOTS
Jiave carefully revised all phonetic pronunciations, which
.ear in parentheses after many anatomical and physiologi-
„, terms. The pronunciations are given both in the text,
where the term is introduced, and in the Glossary at the end
• the book. Many new pronunciations have been added to
lis edition. Word roots, derivations designed to provide an
hderstanding of the meaning of new terms, appear in paren-
heses when a term is introduced,
TUDY OUTLINE
ie Study Outline at the end of each chapter summarizes
major topics and includes specific page references so that stu-
dents can easily find full text discussions of the topics they
to review.
SELF-QUIZZES
Self-Quizzes at the end of every chapter include iill-in-the-
blank, multiple choice, and matching questions. These
quizzes are meant not only for students to test their ability to
memorize the facts presented in each chapter, but also to
sharpen their critical thinking skills by applying the concepts
and processes that are part of the way the human body is
structured and how it functions. Answers to the .Sell-Quiz
items arc presented in an appendix at the end ol the book.
CRITICAL THINKING APPLICATIONS
Critical Thinking Applications, included at the end of each
chapter, arc essay-style problems that encourage students to
think about and apply the concepts they have studied. Al-
though there is no single right answer to this type of ques-
tion, suggested answers are available in an appendix at the
end of the text so the students can check to see if they are on
the right track.
GLOSSARY
A full glossary of terms with phonetic pronunciations appears
at the end of the book. It includes over 1700 entries, provid-
ing students with a terrific reference.
INSIDE COVER MATERIALS
The endpapers at the back of this text provide students with
useful information about prefixes, suffixes, word roots, and
combining forms for the terminology used in the study of
anatomy and physiology. At the front of the text, you will
find descriptions of the many supplemental materials avail-
able to support both teaching and study.
XJV Preface
A COMPLETE TEACHING AND LEARNING PACKAGE
The following ancillaries are available to accompany the seventh edition of Introduction to the Unman Body, Each of
our supplementary products is specifically created with one goal in mind: to help teachers teach and students learn.
Please contact your Wiley sales representative for additional information about any of 'the following supplementary products.
Wiley PLUS Helping Teachers Teach and Students Learn
www.wiley.com/college/tortora
This title is available with Wiley PLUS, a powerful online
tool that provides instructors and students with an integrated
suite of teaching and learning resources in one easy to use
Website. Wiley PLUS is organized around the essential activ-
ities you and your students perform in class.
FOR INSTRUCTORS
Prepare & Present: Create class presentations using a
wealth of Wiley-provided resources - such as an online ver-
sion of the textbook, PowerPoint slides, animations,
overviews, and interactive case studies from Interactions, and
images from the Wiley A&P Visual Library - making your
preparation time more efficient. You may easily adapt, cus-
tomize, and add to this content to meet the needs of your
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Create Assignments: Automate the assigning and grading
of homework or quizzes by using Wiley-provided question
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m.itically graded and recorded in your gradebook. Wiley
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tions to the relevant section of the online text> providing stu-
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Track Student Progress: Keep track of your students'
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A "Study and Practice" area links directly to text content,
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swer. Resources include all of the Interactions content, inclu-
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and animated case studies. Also included are practice
quizzes, anatomy drill and practice, a flash card tool, pronun-*
ciation dictionary, web explorations, pre-lecture quizzes, and
other resources for study.
Ail "Assignment" area keeps all the work you want your stu-
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stay "on task". Students will have access to a variety of inter-
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building their confidence and understanding. In addition, all
of the pre-lecture quizzes contain a link to the relevant sec-
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A Personal Gradebook for each student will allow students
to view their results from past assignments at any time.
Please view our online demo at
www.wiley.com/college/wileyplus . Here you will find ad-
ditional information about the features and benefits of Wiley
PLUS, how to request a "test drive" of Wiley PLUS for this
title, and how to adopt it for class use.
Prelace XV
IftTERIALS AVAILABLE FOR INSTRUCTORS
astructor's Companion Website This dedicated website
ravides on-line resources including a chapter-by-chapter
jiopsis, suggested lecture outlines, learning- objectives, and
aching tips. Each chapter also includes a description oi
.at is new to this edition. All of these resources are fully
downloadable. The electronic format provides you with the
pportunity to customize lecture outlines or activities for de-
(rery either in print or electronically to your students. Also
aikble are three sets of PowerPoint Slides to ease in lec-
I presentation - Illustrated Lecture Slides, slides of nil il-
strations in the text by chapter, and slides of all text tables.
Filey's Visual Library for Anatomy & Physiology 3.0
(0-471-736791) This all-new cross-platform DVD includes
ill of the illustrations from the textbook in labeled, unla-
ded, and leader lines only format. In addition, illustrations
rid photographs not included in the text, but which could
bily be added to enhance lecture or lab, are included.
Search for images by chapter, or by using key words. The Vi-
jal Library can also be accessed online at the Instructor's
ompanion Website, or through Wiley PLUS,
J-color Overhead Transparencies (0-471-76103-6) A
et of full-color overheads includes all of the figures in the
text, including' histology micrographs. All transparencies have
been color-enhanced and carefully reviewed to maximize the
labels for clear projection in the classroom.
Test Bank A complete testbank is available on the In-
structor's Companion Website as printable word document.
A variety of formats — multiple choice, short answer, match-
ing and essay -arc provided to accommodate different test-
ing preferences. It is also available as a cross-platform CD-
ROM (0-471-77069-8) or integrated into Wiley PLUS,
users can easily view, edit and add questions. Users can cre-
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Personal Response System A full set of questions to use
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information, see your Wiley representative, or go to
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Faculty Resource Network Wiley's support structure to
help instructors implement the dynamic new media that sup-
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courses. Consult with your Wiley representative for details
about this program or visit www.wherefacultyconnect.com .
MATERIALS AVAILABLE FOR STUDENTS
Jicated Book Companion Website A dynamic website
rich with many activities for review and exploration includes:
japter Overview and Objectives, Self-Quizzes for each
japtcr, Anatomy Drag and Drops, Cadaver Practicals, Pro-
nunciation Dictionary with Flash Card Option and Termi-
nology Quiz, Insights and Explorations - Web-based Activi-
ties, Crossword Puzzles, Disorder Search linked to Chapicr
Content, Weblinks linked to Chapter Content, Medical Tests
and Procedures linked to Chapter Content, Essays on Well-
ness. In addition there are sections on study tips, determin-
ing your learning style, and correlations of what assets will
work best with a specific learning' style.
lustrated Notebook (0-471-76100-4)— Students can or-
. lize their note taking and improve their understanding of
oatomical structures and physiological processes by using
this handy illustrated notebook. Following the illustration se-
quence in the textbook, each left-handed page displays an un-
labeled, black-and-white copy of every text figure. Students
can fill in the labels during lecture or lab at the instructor's
directions and take additional notes on the blank right-hand
pages.
Student Learning Guide (0-471-76105-2)— by Kathleen
Schmidt Prezbindowski, College of Alt. St. Joseph. This
study guide is designed to appeal to a broad range of learn-
ing styles. It includes multiple activities for each chapter, in-
cluding Framework — visual maps of the chapter content;
Wordbytes — to help master vocabulary; Checkpoints — a series
of study activities such as questions to answers, illustrations
to label, tables to complete; Critical Thinking Questions;
Mastery Test,
W THE LABORATORY
ssentials of Anatomy and Physiology Laboratory Man-
ual (0-47 1-465 16-X) by Connie Allen and Valerie Harper,
Edison Community College. This laboratory manual presents
fcaterial covered in the 1 -semester undergraduate anatomy
ami physiology lab course in brief, clear, and concise way.
The manual is very hands-on and contains activities and ex-
periments that enhance students' ability to both visualize
anatomical structures and understand key physiological topics.
Cat Dissection Manual 2e (0-471-70141-6) by Connie
Allen, Edison Community College, and Valerie Harper. This
manual includes photographs and illustrations of the cat
along with guidelines for dissection. All photographs of the
cat dissection, provided by Dennis Strete of McClennan CC,
are new to this edition. It is available independently as well as
bundled with the main manual depending upon your adop-
tion needs.
CONTENTS
t
chapter 1
ORGANIZATION OF
THE HUMAN BODY 1
Anatomy and Physiology Denned 2
Levels of Organization and Body Systems 2
Life Processes 6
Homeostasis: Maintaining Limits 6
Control of Homeostasis: Feedback Systems 7
Negative Feedback Systems 8
Positive Feedback Systems 8
Homeostasis and Disease 8
Aging and Homeostasis 9
Anatomical Terms 9
Names of Body Regions 9
H^H Focus on Wellness:
■B Good Health— Homeostasis Is the Basis 10
Directional Terms 10
Planes and Sections 14
Body Cavities 15
Abdominopelvic Regions and Quadrants 17
Medical Terminology and Conditions 18
Study Outline IS Self-Quiz. 19
Critical Thinking Applications 21
Answers to Figure Questions 2 1
chapter 2
INTRODUCTORY CHEMISTRY 22
Introduction to Chemistry 21
Chemical Elements and Atoms 23
Ions, Molecules, and Compounds 25
Chemical Bonds 25
Ionic Bonds 26
Covalent Bonds 26
Hydrogen Bonds 28
Chemical Reactions 28
Forms of Energy and Chemical Reactions 28
Synthesis Reactions 28
Decomposition Reactions 28
Exchange Reactions 29
Reversible Reactions 29
Chemical Compounds and Life Processes 29
Inorganic Compounds 29
Water 29
Inorganic Acids, Bases, and Salts 30
Acid-Base Balance: the Concept of pH 30
Maintaining pH: Buffer Systems 30
Organic Compounds 3 1
Carbohydrates 31
Lipids 32
Proteins 35
Focus on Wellness:
Herbal Supplements— They're Natural but Are
They Safe? 36
Enzymes 37
Nucleic Acids: Deoxyribonucleic Acid (DNA) and
Ribonucleic Acid (UNA) 38
Adenosine Triphosphate 38
Study Outline 40 Self-Quiz 41
Critical 'Thinking Applications 43
Answers to Figure Questions 43
chapters
CELLS 44
A Generalized View of the Cell 45
The Plasma Membrane 46
Transport across the Plasma Membrane 47
Passive Processes 47
Diffusion: The Principle 47
Osmesis 49
Active Processes 50
Active Transport 50
Transport in Vesicles 5 I
XXII
Contents XXIII
Cytoplasm 52
Cytosol 52
Organelles 52
The Cytoskeleton 53
Centrosome 54
Cilia and Flagella 54
Ribosomes 54
Endoplasmic Reticulum 55
Golgi Complex 56
Lysosomes 56
Peroxisomes 56
Proteasomes 57
Mitochondria 57
Nucleus 57
Gene Action: Protein Synthesis 58
Transcription 58
Translation 60
Somatic Cell Division 62
Interphase 62
Mitotic Phase 62
Nuclear Division: Mitosis 62
Focus on Wellness:
I Phytochemicals— Protecting Cellular Function 64
Cytoplasmic Division: Cytokinesis 64
Aging and Cells 65
Common Disorders 66
Medical Terminology and Conditions 67
Study Outline 61 Self-Quiz 69
Critical Thinking Applications 71
Answers to Figure Questions 71
chapter 4
KSUES 72
Types of Tissues 73
Epithelial Tissue 73
General Features of Epithelial Tissue 73
Covering and Lining Epithelium 73
Simple Epithelium 75
Pseudostratificd Columnar Epithelium 75
Stratified Epithelium 75
Glandular Epithelium 82
Connective Tissue 82
General Features of Connective Tissue 82
Connective Tissue Cells 83
Connective Tissue Extracellular Matrix 83
Ground Substance 83
Fibers 84
Classification of Connective Tissue 84
Loose Connective Tissue 84
Dense Connective Tissue 86
Cartilage 89
Bone Tissue 89
Liquid Connective Tissue 90
Muscular Tissue 90
Nervous Tissue 90
Membranes 90
Mucous Membranes 90
Focus on Wellness:
Excess Adiposity — Too Much ot a Good Thing 91
Serous Membranes 91
Synovial Membranes 91
Tissue Repair: Restoring Homeostasis 92
Aging and Tissues 92
Common Disorders 93
Medical Terminology 7 and Conditions 93
Study Outline 93 Self-Quiz 95
Critical Thinking Applications 96
Answer to Figure Questions 96
chapter 5
THE INTEGUMENTARY SYSTEM 97
Skin 98
Structure of Skin 98
Epidermis 99
Dermis 100
Skin Color 101
Accessory Structures of the Skin 101
Hair 101
Glands 103
Sebaceous (Hands 103
Sudoriferous Clauds 103
Ceruminous Glands 104
Nails 104
Functions of the Skin 104
^^H* Focus on Wellness:
Skin Care for Active Lifestyles 105
Aging and the Integumentary System 106
Common Disorders 107
Medical Terminology and i Conditions 108
Focus on Homeostasis: The Integumentary System 109
Study Outline 110 Self Quiz 110
Critical Thinking Applications 1 12
Answers to Figure Questions 112
chapter 6
THE SKELETAL SYSTEM 113
Functions of Bone and the Skeletal System 114
Types of Bones 114
Structure of Bone 114
Macroscopic Structure of Bone 114
Microscopic Structure of Bone 116
XXIV Contents
Compact Bone Tissue 116
Spongy Bone Tissue 118
Bone Formation 118
Initial Bone Formation in an Embryo and Fetus 118
Intramembranous Ossi fication 118
Endochondral Ossification 120
Bone Growth in Length and Thickness 121
( ■' n >wth i n Len gth 1 2 1
( i it >wth in Thickness 1 2 1
Bone Remodeling 121
Fractures 122
Factors Affecting Bone Growth 122
Bone's Role in Calcium Homeostasis 122
Exercise and Bone Tissue 123
Divisions of the Skeletal System 124
Skull and Hyoid Bone 125
Cranial Bones 127
Facial Bones 129
Unique Features of the Skull 131
Sutures 131
Paranasal Sinuses 1 ? 1
Fontanels 1 32
Hyoid Bone 132
Vertebral Column 133
Regions of the Vertebral Column 133
Normal Curves of the Vertebral Column 134
Vertebrae 134
Thorax 137
Sternum 137
Ribs 138
Pectoral (Shoulder) Girdle 139
Clavicle 139
Scapula 139
Upper Limb 140
Humerus 140
Ulna and Radius 140
Carpals, Metacarpals, and Phalanges 141
Pelvic (Hip) Girdle 143
Lower Limb 144
Femur 144
Patella 144
Tibia and Fibula 145
Tarsals, Metatarsals, and Phalanges 145
Comparison of Female and Male Skeletons 146
Aging and the Skeletal System 147
| Focus on Wellness:
^■r Steps to Healthy Feet 148
Focus on Homeostasis: The Skeletal System 149
Common Disorders 150
Medical Terminology and Conditions 151
Study Outline 152 Self-Quiz 153
Critical Thinking Applications 155
Answers to Figure Questions 1 55
chapter 7
':
JOINTS 156
Joints 157
Fibrous Joints 157 *
Cartilaginous Joints 158
Synovial Joints 158
Structure of Synovial Joints 158
Types of Movements at Synovial Joints 160
Gliding 160
Angular Movements 160
Rotation 161
Special Movements 162
Types of Synovial Joints 1 64
Details of a Synovial Joint: The Knee Joint 165
Aging and Joints 165
Focus on Wellness:
Joint Care: Prevent Repetitive Motion Injury 167
Common Disorders 168
Medical Terminology and Conditions 169
Study Outline 169 Self-Quiz 110
Critical Thinking Applications 111
Answers to Figure Questions 111
chapter 8
THE MUSCULAR SYSTEM 172
Overview of Muscular Tissue 173
Typ es of Mu scula r Tissue 173
Functions of Muscular Tissue 173
Skeletal Muscle Tissue 173
Connective Tissue Components 173
Nerve and Blood Supply 175
Histology 175
Contraction and Relaxation of Skeletal Muscle 177
Sliding- Filament Mechanism 177
Neuromuscular Junction 177
Physiology of Contraction 179
Relaxation 180
Muscle Tone 180
Metabolism of Skeletal Muscle Tissue 180
Energy for Contraction 180
Muscle Fatigue 183
Oxygen Consumption after Exercise 183
Control of Muscle Tension 183
Twitch Contraction 184
Frequency of Stimulation 184
Motor Unit Recruitment 184
Types of Skeletal Muscle Fibers 184
Isometric and Isotonic Contractions 184
Exercise and Skeletal Muscle Tissue 186
Cardiac Muscle Tissue 186
Contents XXV
Smooth Muscle Tissue 186
Aging and Muscular Tissue 188
How Skeletal Muscles Produce Movement 188
Origin and Insertion 188
Group Actions 189
epal Skeletal Muscles 189
[Focus on Wellness:
I Effective Stretching Increases Muscle Flexibility 190
I Focus on Homeostasis: The Muscular System 218
Common Disorders 219
Medical Terminology and Conditions 220
Study Outline 220 Self-Quiz 222
Critical Thinking Applications 224
Answers to Figure Questions 224
chapter 9
NERVOUS TISSUE 225
Overview of the Nervous System 226
Structures of the Nervous System 226
Functions ofthc Nervous System 226
Organization of the Nervous System 227
Histology of Nervous Tissu e 228
Neurons 228
Myelination 228
Gray and White Matter 228
Neuroglia 230
Action Potentials 230
Ion Channels 230
Resting Membrane Potential 232
Generation of Action Potentials 232
Conduction of Nerve Impulses 233
Synaptic Transmission 234
Events at a Synapse 235
■MK Focus on Wellness:
I Neurotransmitters— Why Food Affects Mood 236
Neurotransmitters 237
Common Disorders 237
■ Medical Terminology and Conditions 238
Study Outline 2SS Self-Quiz 239
Critical Thinking Applications 241
. \nswers to Figure Questions 241
chapter 10
CENTRAL NERVOUS SYSTEM f*
SPINAL NERVES, AND CRANIAL NERVES 242
Spinal Cord 243
Protection and Coverings: Vertebral Canal and
Meninges 243
Gross Anatomy of the Spinal Cord 243
Internal Structure of the Spinal Cord 245
Spinal Nerves 246
Spinal Nerve Composition and Coverings 246
Distribution of Spinal Nerves 246
Plexuses 246
247
Spinal Cord Functions
Brain 248
Major Parts and Protective Coverings 248
Brain Blood Supply and the Blood-Brain Barrier 250
Cerebrospinal Fluid 250
Brain Stem 250
Medulla Oblongata 2S0
Pons 253
Midbrain 253
Reticular Formation 253
Diencephalon 254
Thalamus 254
Hypothalamus 254
Pineal Gland 255
Cerebellum 255
Cerebrum 255
Focus on Wellness:
Coffee Nerves— the Health Risks of Caffeine 257
Limbic System 257
Functional Areas of the Cerebral Cortex 258
Somatic Sensory and Somatic Motor Pathways 259
Hemispheric Lateralization 261
Memory 262
Electroencephalogram (EEG) 262
Cranial Nerves 263
Aging and the Nervous System 265
Common Disorders 265
Medical Terminology and Conditions 267
Study Outline 261 Self-Quiz 269
Critical Thinking Applications 210
Answers to Figure Question:; 210
chapter 11
AUTONOMIC NERVOUS
SYSTEM 271
Comparison of Somatic and
Autonomic Nervous Systems 272
Structure of the Autonomic Nervous System 273
Organization of the Sympathetic Division 274
Organization of the Parasympathetic Division 275
Functions of the Autonomic Nervous System 276
ANS Neurotransmitters 276
Activities of the ANS 276
Sympathetic Activities 276
Focus on Wellness:
Mind-Body Exercise— an Antidote to Stress 278
Parasympathetic Activities 278
Common Disorders 280
XXVi Contents
Study Outline ISO Self-Quiz 281
Critical Thinking Applications 283
Answers to Figure Questions 283
| chapter 12
<l
SOMATIC SENSES AND
SPECIAL SENSES 284
Overview of Sensations 285
Definition of Sensation 285
Characteristics of Sensations 285
Types of Sensory Receptors 285
Somatic Senses 286
Tactile Sensations 287
Touch 287
Pressure and Vibration 287
[ten and Tickle 287
Thermal Sensations 287
Pain Sensations 287
■b Focus on Wellness:
I Pain Management— Sensation Modulation 289
Proprioceptive Sensations 289
Special Senses 290
Olfaction: Sense of Smell 290
Structure of the Olfactory Epithelium 290
Stimulation of Olfactory Receptors 290
The Olfactory Pathway 290
Gustation: Sense of Taste 291
Structure of Taste Buds 292
Stimulation of Gustatory Receptors 293
The Gustatory Pathway 293
Vision 293
Accessory Structures of the Eye 293
Layers of the Eyeball 294
Fibrous Tunic 294
Vascular Tunic 294
Retina 296
Interior of the Eyeball 297
Image Formation and Binocular Vision 297
Refraction of Light Rays 297
Accommodation 299
Constriction of the Pupil 300
Convergence 300
Stimulation of Photoreceptors 300
The Visual Pathway 300
Hearing and Equilibrium 301
Structure of the Ear 301
Outer Ear 301
Middle Ear 301
Internal Ear 302
Physiology of Hearing 304
Auditory Pathway 305
Physiology of Equilibrium 305
Static Equilibrium 305
Dynamic Equilibrium 505
Equilibrium Pathways 306
Focus on Homeostasis: The Nervous System 309
Common Disorders 310
Medical Terminology and Conditions 310
Study Outline ill Self-Quiz SI 2
Critical Thinking Application* 314
, inswers to Figure Questions 314
chapter 13
THE ENDOCRINE SYSTEM 315
Introduction 316
Hormone Action 317
Target Cells and Hormone Receptors 317
Chemistry of Hormones 317
Mechanisms of Hormone Action 317
Action of Lipiii-soluble I lormoncs 3 1 7
Action of Water-soluble I form ones 3 1 8
Control of Hormone Secretions 318
Hypothalamus and Pituitary Gland 319
Anterior Pituitary Hormones 320
Human Growth I lonnonc and Insulinlike Growth
Factors 320
Thyroid-stimulating Hormone 3 20
Follicle-Stimulating Hormone and Luteinizing
Hormone 320
Prolactin 320
Adrenocorticotropic Hormone 320
Alelanocyte-stimiihuing Hormone 321
Posterior Pituitary Hormones 321
Oxytocin 322
Antidiuretic Hormone 322
Thyroid Gland 323
Actions of Thyroid Hormones 323
Control of Thyroid Hormone Secretion 325
Calcitonin 325
Parathyroid Glands 325
Pancreatic Islets 327
Actions of Glucagon and Insulin 327
Adrenal Glands 329
Adrenal Cortex Hormones 329
Mineralocorticoids 33 1
Glucocorticoids 331
Focus on Wellness:
Insulin Resistance— a Metabolic Medley 332
Androgens 332
Adrenal Medulla Hormones 333
Ovaries and Testes 333
Pineal Gland 333
Other Hormones 334
Hormones from Other Endocrine Cells 334
Contents XXVII
Prostaglandins and Leukotrienes 334
The Stress Response 335
Aging and the Endocrine System 336
Focus on Homeostasis: The Endocrine System 337
Common Disorders 338
Medical Terminology and Conditions 340
Study Outline 340 Self Quiz 342
Critical Thinking Applications >4 1
Answers to Figure Questions 344
chapter 14
THE CARDIOVASCULAR SYSTEM^
BLOOD 345
Functions of Blood 346
Components of Whole Blood 346
Blood Plasma 346
> Formed Elements 346
Formation of Blood Cells 346
Red Blood Cells 349
White Blood Cells 353
Platelets 353
Hemostasis 354
Vascular Spasm 354
Platelet Ping Formation 354
Blood Clotting 354
Clot Retraction and Blood Vessel Repair 356
Hemostatic Control Mechanisms 357
Clotting in Blood Vessels 357
Blood Groups and Blood Types 357
ABO Blood Group 357
Rh Blood Group 358
Transfusions 358
as Focus on Wellness:
I Lifestyle and Blood Circulation— Let It Flow 359
Common Disorders 360
Medical Terminology' and Conditions 361
Study Outline 361 Self-Quiz 162
Critical Thinking Applications ?63
Answers to Figure Questions 363
chapter 15
THE CARDIOVASCULAR SYSTEM: \
HEART 364
Structure and Organization of the Heart 365
Location and Coverings of the Heart 365
Heart Wall 366
Chambers of the Heart 367
Great Vessels of the Heart 369
Valves of the Heart 369
Blood Flow and Blood Supply of the Heart 371
Blood Flow Through the Heart 371
Blood Supply of the Heart 372
Conduction System of the Heart 372
Electrocardiogram 374
The Cardiac Cycle 374
Heart Sounds 375
Cardiac Output 375
Regulation of Stroke Volume 375
bjbbbb> Focus on Wellness:
I Sudden Cardiac Death During Exercise— What's the Risk? 376
Regulation of Heart Rate 377
Autonomic Regulation of Heart Rate 377
Chemical Regulation of I leart Rate 378
Other Factors in Heart Rate Regulation 378
Exercise and the Heart 378
Common Disorders 379
Medical Terminology and Conditions 381
Study Outline 381 Self Quiz 382
Critical Thinking Applications 384
Answers to Figure Questions )S4
chapter 16
f
THE CARDIOVASCULAR SYSTEM: ^%
BLOOD VESSELS AND CIRCULATION 385
Blood Vessel Structure and Function 386
Arteries and Arterioles 3 86
Capillaries 386
Structure of Capillaries 387
Capillary Exchange 3H7
Venules and Veins 389
Structure of Venules and Veins 389
Venous Return 390
Blood Flow Through Blood Vessels 390
Blood Pressure 390
Resistance 391
Regulation of Blood Pressure and Blood Flow 391
Role of the Cardiovascular Center 391
Hormonal Regulation of Blood Pressure and Blood Flow 593
Checking Circulation 394
Pulse 394
Measurement of Blood Pressure 394
Circulatory Routes 394
Systemic Circulation 394
^■■r Focus on Wellness:
■B: Arterial Health— Undoing the Damage ot Atherosclerosis 410
Pulmonary Circulation 410
Hepatic Portal Circulation 410
Fetal Circulation 412
Aging and the Cardiovascular System 412
Focus on Homeostasis: The Cardiovascular System 414
XXVIII Contents
Common Disorders 415
Medical Terminology and Conditions 415
Study Outline 416 Self-Quiz 417
Critical Thinking Applications 419
Answers to Figure Questions 419
chapter 17
THE LYMPHATIC SYSTEM AND
IMMUNITY 420
Lymphatic System 42 1
Lymphatic Vessels and Lymph Circulation 421
Lymphatic Organs and Tissues 424
Thy iii us 424
Lymph Nodes 424
Spleen 425
Lymphatic Nodules 425
Innate Immunity 425
First Line of Defense: Skin and Mucous
Membranes 425
Second Line of Defense: Internal Defenses 426
Internal Antimicrobial Proteins 426
Phagocytes and Natural Killer Cells 426
Inflammation 426
Fever 427
Adaptive Immunity 428
Maturation of T Cells and B Cells 429
Types of Adaptive Immune Responses 429
Antigens and Antibodies 429
Processing and Presenting Antigens 430
«■«£ Focus on Wellness:
I Lifestyle, Immune Function, and Resistance to Disease 431
T Cells and Cell-mediated Immunity 432
B Cells and Antibody-mediated Immunity 435
Immunological Memory 436
Primary and Secondary Response 436
Naturally \cquired and Artificially Acquired Immunity 437
Aging and the Immune System 437
Focus on Homeostasis: The Lymphatic and
Immune System 438
{ ommon Disorders 439
Medical Terminology and Conditions 441
Study Outlaw 441 Self Quiz 443
Critical Thinking Applications 444
Answers to Figure Questions 444
chapter 18
THE RESPIRATORY SYSTEM 445
Organs of the Respiratory System 446
Nose 447
Pharynx 448
Larynx 448
The Structures of Voice Production 448
Trachea 450
Bronchi and Bronchioles 45 1
Lungs 451
Alveoli 451
Pulmonary Ventilation 453
Muscles of Inhalation and Exhalation 453
Pressure Changes During Ventilation 455
Lung Volumes and Capacities 456
Breathing Patterns and Modified Respirator)
Movements 457
Exchange of Oxygen and Carbon Dioxide 457
External Respiration: Pulmonary Gas Exchange 458
Internal Respiration: Systemic Gas Exchange 459
Transport of Respiratory Gases 459
Oxvgen Transport 459
Carbon Dioxide Transport 461
Control of Respiration 461
Respiratoiy Center 462
Regulation of the Respiratory Center 462
Cortical Influences on Respiration 462
H| Focus on Wellness:
Smoking— a Breathtaking Experience 463
Chemoreceptor Regulation of Respiration 46}
Other Influences on Respiration 464
Exercise and the Respiratory System 465
Aging and the Respiratory System 465
Focus on Homeostasis: The Respiratory System 466
Common Disorders 467
Medical Terminology and Conditions 468
Study Outline 468 Self-Quiz 469
Critical Thinking Applications 411
Answers to Figure Questions 411
chapter 19
THE DIGESTIVE SYSTEM 472 _i_^
Overview of the Digestive System 473
Layers of the GI Tract and the Omentum 474
Month 476
Tongue 477
Salivary Glands 477
Teeth 477
Digestion in the Mouth 478
Pharynx and Esophagus 478
Stomach 480
Structure of the Stomach 481
Digestion and Absorption in the Stomach 482
Pancreas 483
Structure of the Pancreas 483
Pancreatic Juice 484
Liver and Gallbladder 484
Structure of the Liver and Gallbladder 484
Bile 484
Contents XXIX
Functions of the Liver 485
Small Intestine 486
Structure of the Small Intestine 486
Intestinal Juice 488
Mechanical Digestion in the Small Intestine 488
Chemical Digestion in the Small Intestine 488
Absorption in the Small Intestine 488
Absorption of Monosaccharides 488
Absorption of Amino Acids 489
Absorption of Ions and Water 489
Absorption of Lipids and Bile Salts 489
Absorption of Vitamins 491
Large Intestine 491
Structure of the Large Intestine 491
Digestion and Absorption in the Large Intestine 493
The Defecation Reflex 493
Phases of Digestion 493
Cephalic Phase 493
m Focus on Wellness:
I Emotional Eating— Consumed by Food 494
Gastric Phase 494
Intestinal Phase 494
Aging and the Digestive System 495
Focus on Homeostasis: The Digestive System 496
Common Disorders 497
Medical Terminology find Conditions 498
Study Outline 498 Self-Quiz 500
Critical Thinking Applications SOI
Answers to Figure Questions 502
chapter 20
NUTRITION AND
METABOLISM 503
Nutrients 504
Guidelines for Healthy Eating 504
Minerals 504
Vitamins 505
Metabolism 507
Carbohydrate Metabolism 510
Glucose C la ta bol i sm 5 1
Glucose Anabolism 5 1 1
Lipid Metabolism 512
Lipid Catabolism 512
Lipid Anabolism 512
Lipid Transport in Blood 5 1 2
Protein Metabolism 514
Protein Catabolism 514
Protein Anabolism 514
Metabolism and Body Heat 515
Measuring Heat 515
Body Temperature Homeostasis 515
Body Heat Production 5 1 5
Body Heat Loss 516
Regulation of Body Temperature 5 1 6
Focus on Wellness:
Exercise Training— Metabolic Workout 518
Common Disorders 519
Medical Terminology and Conditions 519
Study Outline 519 Self-Quiz 521
Critical Thinking Applications 522
Answers to Figure Questions 522
chapter 21
THE URINARY SYSTEM 523
Overview of the Urinary System 524
Structure of the Kidneys 525
External Anatomy of the Kidneys 525
Internal Anatomy of the Kidneys 526
Renal Blood Supply 526
Nephrons 526
Functions of the Nephron 528
Glomerular Filtration 530
Net Filtration Pressure 530
Glomerular Filtration Rate 53 1
Tubular Reabsorption and Secretion 531
Hormonal Regulation of Nephron Functions 533
Components of Urine 533
Focus on Wellness:
! Infection Prevention for Recurrent UTIs 535
Transportation, Storage, and Elimination
of Urine 535
Ureters 535
Urinary Bladder 536
Urethra 536
Micturition 537
Aging and the Urinary System 537
Focus on Homeostasis: The Urinary System 538
Common Disorders 539
Medical Terminology and Conditions 539
Study Outline 540 Self-Quiz 541
Critical Thinking Applications 542
Answers !u Figure Questions 542
chapter 22
FLUID, ELECTROLYTE,
AND ACID-BASE
BALANCE 543
Fluid Compartments and Fluid Balance 544
Sources of Body Water Gain and Loss 545
Regulation of Body Water Gain 545
Regulation of Water and Solute Loss 545
Movement of Water Between Fluid
Compartments 547
XXX Contents
Electrolytes in Body Fluids 548
Acid-Base Balance 550
The Actions of Buffer Systems 550
Protein Buffer System 550
Carbonic Acid-Bicarbonate Buffer System 550
Phosphate Buffer System 550
Focus on Wellness:
Prolonged Physical Activity— a Challenge to Fluid
and Electrolyte Balance 551
Exhalation of Carbon Dioxide 551
Kidney Excretion of H + 552
Acid-Base Imbalances 552
Aging and Fluid, Electrolyte, and Acid-Base
Balance 553
Study Outline 553 Self-Quiz 554
Critical Thinking Applications 555
Answers to Figure Questions 555
chapter 23
THE REPRODUCTIVE SYSTEMS 556
Male Reproductive System 557 p.
Scrotum 557
Testes 558
Spermatogenesis 558
Sperm 560
Hormonal Control of the 'testes 561
Ducts 562
Epididymis 562
Ductus Deferens 562
Ejaculatory Ducts 562
Urethra 562
Accessory Sex Glands 562
Semen 563
Penis 563
Female Reproductive System 564
Ovaries 564
Oogenesis 565
Uterine Tubes 566
Uterus 566
Vagina 568
Perineum and Vulva 568
Mammary Glands 569
The Female Reproductive Cycle 570
Hormonal Regulation of the Female Reproductive
Cycle 570
Phases of the Female Reproductive Cycle 572
Menstrual Phase 572
Preovulatory Phase 572
Ovulation 572
Postovulatory Phase 572
Birth Control Methods and Abortion 574
Surgical Sterilization 574
Hormonal Methods 574
i \ *
Intrauterine Devices 575
Spermicides 575
Barrier Methods 575
Periodic Abstinence 575
Focus on Wellness:
The Female Athlete Triad— Disordered Eating, Amenorrhea,
and Premature Osteoporosis 576
Abortion 577
Aging and the Reproductive Systems 577
Focus on Homeostasis: The Reproductive Systems 578
Common Disorders 579
Medical Terminology and Conditions 581
Study Outline 5S1 Self-Quiz 583
Critical Thinking Applications 584
Answers to Figure Questions 585
chapter 24
DEVELOPMENT AND
INHERITANCE 586
Embryonic Period 587
First Week of Development 587
Fertilization 5K7
Early Embryonic Development 588
Second Week of Development 590
Third Week of Development 592
G astipulation 592
Development of the Allantois, Chorionic Villi,
and Placenta 592
Fourth Through Eighth Weeks of Development 594
Fetal Period 596
Maternal Changes During Pregnancy 600
Hormones of Pregnancy 600
Changes during Pregnancy 600
Exercise and Pregnancy 601
Labor and Delivery 601
Lactation 602
Focus on Wellness;
Breast Milk— Mother Natures Approach to Infection
Prevention 603
Inheritance 604
Genotype and Phenotype 604
Autosomes and Sex Chromosomes 605
Common Disorders 607
Medical Terminology and Conditions 607
Study Outline 608 Self-Quiz 610
Critical Thinking Applications 6 1 1
Answers to Figure Questions 61 1
Answers to Self-Quizzes and
Critical Thinking Applications A 1
Glossary G-1
Credits C-1
Index M
2 Chapter 1 Organization ol the Human Body
ANATOMY AND PHYSIOLOGY
DEFINED
objective • Define anatomy and physiology.
The sciences of anatomy and physiology are the foundation
for understanding the structures and functions of the human
body. Anatomy (a-NAT-6-me; am- = up; -tomy = process of
cutting) is the science of structure and the relationships
among sniictures. Physiology (fiz'-e-OL-o-je; physio- = na-
ture, -kgy - study of) is the science of body functions, that is,
how the body parts work. Because function can never be sepa-
rated completely from structure, we can understand the hu-
man body best by studying anatomy and physiology together.
We will look at how each structure of the body is designed to
carry out a particular function and how the structure of a part
often determines the functions it can perform. The bones of
die skull, for example, arc tightly joined to form a rigid case
that protects the brain. The bones of the fingers, by contrast,
are more loosely joined, which enables them to perform a vari-
ety of movements, such as turning die pages of this book.
■ CHECKPOINT
1 . What is the basic difference between anatomy and physi-
ology?
2. Give your own example of how the structure of a part of
the body is related to its function.
LEVELS OF ORGANIZATION
AND BODY SYSTEMS
OBJECTIVES • Describe the structural organization
of the human body.
• Define the body systems and explain how they relate
to one another.
The structures of the human body are organized on several
levels, similar to the way letters of the alphabet, words,
sentences, and paragraphs make up language. Listed here,
from smallest to largest, are the six levels of organization of
the human body, chemical, cellular, tissue, organ, system, and
organismal (Figure !.l).
The chemical level, which can be compared to letters of
the alphabet, includes atoms, the smallest units ol matter
that participate in chemical reactions, and molecules, two
or more atoms joined together. Certain atoms, such as
carbon (C), hydrogen (H), oxygen (O), nitrogen (N),
calcium (Ca), and others, are essential for maintaining
life. Familiar examples of molecules found in die body
are DNA (deoxyribonucleic acid), the genetic material
passed on from one generation to another; hemoglobin,
which carries oxygen in the blood; glucose, commonly
known as blood sugar; and vitamins, which are needed
for a variety of chemical processes. Chapters 2 and 20
focus on the chemical level of organization.
Molecules combine to form structures at the next level of j
organization — the cellular level. Cells are the basic
structural and functional units of an organism. Just as
words are the smallest elements of language, cells are the
smallest living units in die human body. Among the
many types of cells in your body are muscle cells, nerve
cells, and blood cells. Figure 1.1 shows a smooth muscle
cell, one of three different kinds of muscle cells in
your body. As you will see in Chapter 3, cells contain
specialized structures called organelles, such as the
nucleus, mitochondria, and lysosomes, that perform
specific functions.
The tissue level is the next level of structural organiza-
tion. Tissues are groups of cells and the materials
surrounding them that work together to perform a
particular function, similar to the way words are put
together to form sentences. The four basic types of tissue
in your body are epithelial tissue, connective tissue, museum
tissue, and nervous tissue. The similarities and differences
among the different types of tissues are the focus of
Chapter 4. Note in Figure 1.1 that smooth muscle tissue
consists of tightly packed smooth muscle cells.
At the organ level y different kinds of tissues join together
to form body structures. Similar to the relationship
between sentences and paragraphs, organs usually have a
recognizable shape, are composed of two or more differ-
ent types of tissues, and have specific functions. Examples
of organs are the stomach, heart, liver, lungs, and brain.
Figure 1.1 shows several tissues that make up the stom-
ach. The serous membrane is a layer around the outside of
the stomach that protects it and reduces friction when
the stomach moves and rubs against other organs.
Underneath the serous membrane are the miooth muscle
tissue layers, which contract to churn and mix food and
push it on to the next digestive organ, the small intestine,
The innermost lining of the stomach is an epithelial tissue
layer, which contributes fluid and chemicals that aid
digestion.
The next level of structural organization in the body is
the system level. A system (or chapter in our analogy)
consists of related organs (paragraphs) that have a
common function. The example shown in Figure 1.1 is
the digestive system, which breaks down and absorbs
molecules in food. In the chapters that follow, we will
explore the anatomy and physiology of each of the
body systems. Table 1.1 on pages 4-5 introduces the
Levels of Organization and Body Systems 3
Figure 1.1 Levels of structural organization in the human body.
£ The levels of structural organization are the chemical, cellular, tissue, organ, system, and organismal.
CELLULAR LEVEL
Q CHEMICAL LEVEL
J& ^r ^ > ~^^^A © T,SSUE LEVEL
• of
Serous
membrane
Smooth muscli
tissue layers
Q ORGANISMAL LEVEL
I Which level of structural organization usually has a recognizable shape arid is composed of two or more
different types of tissues that have a specific function?
components and functions of these systems. As you study
the body systems, you will discover how they work to-
gedier to maintain health, protect you from disease, and
allow for reproduction of the species.
© The organismal level is the largest level of organization.
All the systems of the body combine to make up an
organism,, that is, one human being. An organism can be
compared to a book in our analogy.
Table 1 .1 Components and Functions of the Eleven Principal Systems of the Human Body
1. Integumentary System
(Chapter 5)
Components:
Skin and structures
derived from it,
such as hair, nails,
and sweat and oil
glands.
Functions:
Helps regulate
body temperature;
protects the body;
eliminates some
wastes; helps make
vitamin D; detects
sensations such
as touch, pressure,
pain, warmth,
and cold.
Skin and
associated
glands
2. Skeletal System
(Chapters 6 and 7)
Components:
All the bones and
joints of the body
and their associated
cartilages.
Functions:
Supports and
protects the body,
provides a specific
area for muscle
attachment,
assists with
body movements,
stores cells that
produce blood cells,
and stores minerals
and lipids (fats).
Bone
3. Muscular System
(Chapter 8)
Components:
Specifically refers to
skeletal muscle tissue,
which is muscle
usually attached to
bones (other muscle
tissues include
smooth and cardiac) -
Functions:
Participates in
bringing about body
movements, maintains
posture, and produces
heat.
4. Nervous System
(Chapters 9-12)
Components:
Brain, spinal cord,
nerves, and sense
organs such as the
eyes and ears,
Functions: Regulates
body activities through
nerve impulses by
detecting changes in the
environment, interpreting
the changes, and
responding to the
changes by bringing
about muscular
contractions or
glandular secretions.
Spinal
cord
Nerve
5. Endocrine System
(Chapter 1 3)
Components:
All glands and
tissues that
produce chemical
regulators of
body functions,
called hormones.
Functions:
Regulates body
activities through
hormones
transported by the
blood to various
target organs.
Pituitary
gland
Thymus
6. Cardiovascular System
(Chapters 14-16)
Components:
Blood, heart, and
blood vessels.
Functions: Heart
pumps blood through
blood vessels; blood
carries oxygen and
nutrients to cells and
carbon dioxide and
wastes away from
cells, and helps
regulate acidity,
temperature, and
water content of body
fluids; blood components
help defend against
disease and mend
damaged blood vessels.
7. Lymphatic System and Immunity
(Chapter 17)
Com,
Thymus
Thoracic
duct
Components:
Lymphatic fluid
and vessels; spleen,
thymus, lymph
nodes, and
tonsils: cells that
carry out immune
responses (B
cells, T cells,
and others).
Functions:
Returns proteins
and fluid to blood;
carries lipids from
gastrointestinal tract
to blood; contains
siles of maturation and
proliferation of B cells and
T cells that protect against
disease-causing microbes.
[.Respiratory System
(Chapter 18)
Components:
Lungs and air
passageways
such as the
pharynx (throat),
larynx (voice box),
trachea (windpipe),
and bronchial tubes
leading into and out
of them.
Functions:
Transfers oxygen from
inhaled air to blood
and carbon dioxide from
blood to exhaled air; helps
regulate acidity of
body fluids; air flowing
out of lungs through vocal
cords produces sounds.
9. Digestive System
(Chapter 19)
Components:
Tonsil Organs of
gastrointestinal tract,
including the mouth,
pharynx (throat),
esophagus, stomach,
small and large
intestines, rectum, and
anus; also includes
accessory digestive
organs that assist in
digestive processes,
such as the salivary
glands, liver, gallbladder,
and pancreas.
Functions: Achieves
physical and chemical
breakdown of food; ab-
Lymphatic sorbs nutrients; eliminates
vessel solid wastes.
Mouth
Salivary
gland
Pharynx
(throat)
= — Spleen
Lymph
node
Stomach
Pancreas
(behind
stomach)
Larynx
(voice box)
Trachea
(windpipe)
Pharynx
(throat)
Bronchus
Lung
10. Urinary System
(Chapter 21)
Components:
Kidneys, ureters,
urinary bladder,
and urethra.
Functions:
Produces, stores,
and eliminates urine;
eliminates wastes
and regulates volume
and chemical com-
position of blood;
helps regulate
acidity of body fluids;
maintains body's
mineral balance; helps
regulate red blood
cell production.
Prostate
11. Reproductive Systems
(Chapter 23)
Components:
Gonads (testes or ovaries)
and associated organs:
uterine tubes, uterus, and
vagina in females, and
epididymis, ductus (vas)
deferens, and penis in
males. Also, mammary
glands in females.
Functions:
Gonads produce gametes
(sperm or oocytes) that
unite to form a new
organism and release
hormones that regulate
reproduction and other
body processes; associated
organs transport and store
gametes. Mammary glands
produce milk.
■ CHECKPOINT
3. Define the following terms: atom, molecule, cell, tissue,
organ, system, and organism.
4. Referring to Table 1.1, which body systems help elimi-
nate wastes?
LIFE PROCESSES
OBJECTIVE • Define the important life processes of
humans. ___^_ .
All living organisms have certain characteristics that set them
apart from nonliving things. The following are six important
life processes of humans:
1. Metabolism (me-TAB-6-iizm) is the sum of all the
chemical processes that occur in the body. It includes the
breakdown of large, complex molecules into smaller,
simpler ones and the building up of complex molecules
from smaller, simpler ones. For example, proteins in food
are split into amino acids, which are the building blocks
of proteins. These amino acids can then be used to build
new proteins that make up muscles and bones.
2. Responsiveness is the body's ability to detect and respond
to changes in its internal (inside the body) or external
(outside the body) environment. Different cells in the
body detect different sorts of changes and respond in
characteristic ways. Nerve cells respond to changes in the
environment by generating electrical signals, known as
nerve impulses. Muscle cells respond to nerve impulses
by contracting, which generates force to move body
parts.
3. Movement includes motion of the whole body, individual
organs, single cells, and even tiny organelles inside cells.
For example, the coordinated action of several muscles
and bones enables you to move your body from one
place to another by walking or running. After you eat a
meal that contains fats, your gallbladder (an organ) con-
tracts and squirts bile into the gastrointestinal tract to
help in the digestion of fats. When a body tissue is dam-
aged or infected, certain white blood cells move from
the blood into the affected tissue to help clean up and
repair the area. And inside individual cells, various parts
move from one position to another to carry out their
functions.
4. Growth is an increase in body size. It may be due to an
increase in (1) the size of existing cells, (2) the number of
cells, or (3) the amount of material surrounding cells.
5. Differentiation (dif'-er-en-she-A-shun) is the process
whereby unspecialized cells become specialized cells.
Specialized cells differ in structure and function from the
unspecialized cells that gave rise to them. hor example,
specialized red blood cells and several types of white
blood cells differentiate from die same unspecialized cells
in bone marrow. Similarly, a single fertilized egg cell
undergoes tremendous differentiation to develop into a
unique individual who is similar to, yet quite different
from, either of the parents.
6. Reproduction refers to either (1) the formation of new
cells for growth, repair, or replacement or (2) the pro-
duction of a new individual.
Although not all of these processes are occurring in cells
throughout the body all of the rime, when they cease to
occur properly cell death may occur. When cell death is
extensive and leads to organ failure, the result is death ol the
organism.
■ CHECKPOINT
5. What types of movement can occur in the human body?
HOMEOSTASIS:
MAINTAINING LIMITS
OBJECTIVES • Define homeostasis and explain its
importance.
• Describe the components of a feedback system.
• Compare the operation of negative and positive feed-
back systems.
• Distinguish between symptoms and signs of a disease. I
The trillions of cells of die human body need relatively stable
conditions to function effectively and contribute to the sur-
vival of the body as a whole. The maintenance of relatively
stable conditions is called homeostasis (ho -me-o-STA-sis;
bomeo- = sameness; -stasis = standing still). Homeostasis
ensures that the body's internal environment remains sLc:i<]\
despite changes inside and outside the body. A large part of
the internal environment consists of the fluid surround-
ing body cells, called interstitial fluid. Homeostasis keeps the
interstitial fluid at a proper temperature of 37° Celsius
(98.6° Fahrenheit) and maintains adequate nutrient and oxy-
gen levels for body cells to flourish.
Each body system contributes to homeostasis in some
way. For instance, in the cardiovascular system, alternating
contraction and relaxation of the heart propels blood
throughout the body's blood vessels. As blood flows through
the blood capillaries', the smallest blood vessels, nutrients and
oxygen move into interstitial fluid and wastes move into the
blood. Cells, in turn, remove nutrients and oxygen from and
release their wastes into interstitial fluid. Homeostasis is
dynamic) that is, it can change over a narrow range that is
compatible with maintaining cellular life processes. For exam-
ple, die level of glucose in the blood is maintained within a
narrow range. It normally does not fall too low between meals
or rise too high even after eating a high-glucose meal. The
brain needs a steady supply of glucose to keep funcrioning — a
low blood glucose level may lead to unconsciousness or even
death. A prolonged high blood glucose level, by contrast,
can damage blood vessels and cause excessive loss of water in
the urine.
Homeostasis: Maintaining Limits 7
Figure 1.2 Parts of a feedback system. The dashed return
arrow symbolizes negative feedback.
\^ The three basic elements of a feedback system are the receptor,
control center, and effector.
Some stimulus
disrupts homeostasis by
\&
Control of Homeostasis: Feedback Systems
Fortunately, every body structure, from cells to systems, has
one or more homeostatic devices that work to keep the inter-
nal environment within normal limits. The homeostatic
mechanisms of the body are mainly under the control of two
systems, the nervous system and the endocrine system. The
nervous system detects changes from die balanced state and
semis messages in the form of nerve impulses to organs that
counteract the change. For example, when body temper-
ature rises, nerve impulses cause sweat glands to release
more sweat, which cools the body as it evaporates. The en-
docrine system corrects changes by secreting molecules
called hormones into the blood. Hormones affect specific body
cells where they cause responses that restore homeostasis.
For example, the hormone insulin reduces blood glucose
level when it is too high. Nerve impulses typically cause rapid
corrections; whereas hormones usually work more slowly.
Homeostasis is maintained by means of many feedback
systems, k feedback system or feedback loop is a cycle of events
in which a condition in the body is continually monitored,
evaluated, changed, remonitored, reevaluated, and so on.
Each monitored condition, such as body temperature, blood
pressure, or blood glucose level, is termed a controlled
miditivii. Any disruption that causes a change in a controlled
condition is called a stimulus. Some stimuli come from the
external environment, such as intense heat or lack of oxygen.
Others originate in the internal environment, such as a blood
thicose level that is too low. Homeostatic imbalances may
|so occur clue to psychological stresses in our social
environment — the demands of work and school, for example.
]n most cases, the disruption of homeostasis is mild and
temporary, and the responses of body cells quickly restore
balance in the internal environment. In other cases, the dis-
ruption of homeostasis may be intense and prolonged, as in
poisoning, overexposure to temperature extremes, severe in-
fection, or death of a loved one.
Three basic components make up a feedback system: a
receptor, a control center, and an effector (Figure 1 .2).
1. A receptor is a body structure that monitors changes in a
controlled condition and sends information called the
input to a control center. Input is in the form of nerve
impulses or chemical signals. Nerve endings in the skin
Increasing or
decreasing a
Controlled condition
that is monitored by
X
Nerve impulses or
I chemical signals to a
J*
ontrol center
that receives the
input and provides
There is a return to
homeostasis
when the response
brings the controlled
condition back to
normal.
Nerve impulses or
chemical signals to
Effectors
that bring about
a change or
I
Response that alters the
controlled condition
V
What is the basic difference between negative and positive feed-
back systems?
that sense temperature are one of the hundreds of
different kinds of receptors in the body.
2. A control center in the body, for example, the brain, sets
the range of values within which a controlled condition
should be maintained, evaluates the input it receives from
receptors, and generates output commands when they
are needed. Output is information, in the form of nerve
8 Chapter 1 Organization of the Human Body
impulses or chemical signals, that is relayed from the
control center to an effector.
3. An effector is a body structure that receives output from
the control center and produces a response that changes
the controlled condition. Nearly every organ or tissue in
the body can behave as an effector. For example, when
your body temperature drops sharply, your brain (control
center) sends nerve impulses to your skeletal muscles
(effectors) that cause you to shiver, which generates heat
and raises your temperature.
Feedback systems can be classified as either negative
feedback systems or positive feedback systems.
Negative Feedback Systems
/V negative feedback system reverses a change in a controlled
condition. Consider one negative feedback system that helps
regulate blood pressure. Blood pressure (BP) is the force exerted
by blood as it presses against the walls of blood vessels. When
the heart beats faster or harder, BP increases. If a stimulus
causes blood pressure (controlled condition) to rise, the fol-
lowing sequence of events occurs (Figure 1.3). The higher
pressure is detected by baroreceptors, pressure-sensitive nerve
cells located in the walls of certain blood vessels (the
receptors). The baroreceptors send nerve impulses (input) to
the brain (control center), which interprets the impulses and
responds by sending nerve impulses (output) to the heart (the
effector). Heart rate decreases, which causes blood pressure
to decrease (response). This sequence of events returns the
controlled condition— blood pressure^to normal, and
homeostasis is restored. This is a negative feedback system
because the activity of the effector produces a result, a drop
in blood pressure, that reverses the effect of the stimulus.
Negative feedback systems tend to regulate conditions in
the body that are held fairly stable over long periods of
time, such as blood pressure, blood glucose level, and body-
temperature.
Positive Feedback Systems
A positive feedback systetn strengthens a change in a con-
trolled condition. Normal positive feedback systems tend to
reinforce conditions that don't happen very often, such as
childbirth, ovulation, and blood clotting. Because a positive
feedback system continually reinforces a change in a con-
trolled condition, it must be shut off by some event outside
the system. If the action of a positive feedback system isn't
stopped, it can "run away" and produce life-threatening
changes in the body.
Homeostasis and Disease
As long as all of the body's controlled conditions remain
within certain narrow limits, body cells hinction efficiently,
homeostasis is maintained, and the body stays healthy-
Figure 1.3 Homeostasis of blood pressure by a negative
feedback system. Note that the response is ted back into the sys-
tem, and the system continues to lower blood pressure until there is
a return to normal blood pressure (homeostasis).
\ If the response reverses a change in a controlled condition, a
r^fe— » system is operating by negative feedback.
Some stimulus
disrupts homeostasis by
Increasing
Blood pressure
eceptor
Baroreceptors in
certain blood
vessels send
<s^
I
I
Return to homeostasis
when response brings
blood pressure
back to normal
A decrease in heart rate
decreases blood pressure
I
I
I
I
What would happen to the heart rate if some stimulus caused
' blood pressure to decrease? Would this occur by positive or nega-
tive feedback?
Anatomical Terms 9
Should one or more components of the body lose their abil-
ity to contribute to homeostasis, however, the normal balance
pong all of the body's processes may be disturbed. If the
bomeostatic imbalance is moderate, a disorder or disease may
occur; if it is severe, death may result.
A disorder is any abnormality of structure and/or func-
tion. Disease is a more specific term for an illness character-
ized by a recognizable set of symptoms and signs. Symptoms
ire subjective changes in body functions that are not apparent
to an observer, for example, headache or nausea. Signs are
objective changes that a clinician can observe and measure,
such as bleeding, swelling, vomiting, diarrhea, fever, a rash,
or paralysis. Specific diseases alter body structure and func-
tion in characteristic ways, usually producing a recognizable
set of symptoms and signs.
Diagnosis (di'-ag-NO-sis; din- = through; -gnosis = knowl-
edge) is the identification of a disease or disorder based on a
scientific evaluation of the patients symptoms and signs,
medical history, physical examination, and sometimes data
in. in laboratory tests. Taking a medical history consists of col-
lecting information about events that might be related to a
patient's illness, including the chief complaint, history
of present illness, past medical problems, family medical
problems, and social history. A physical examination is an
orderly evaluation of the body and its functions. This
process includes inspection (looking at or into the body with
various instruments), palpation (feeling body surfaces with
the hands), auscultation (listening to body sounds, often us-
ing a stethoscope), percussion (tapping on body surfaces and
listening to the resulting echo), and measuring vital signs
(temperature, pulse, respiratoiy rate, and blood pressure).
Some common laboratory tests include analyses of blood
and urine.
I CHECKPOINT
6. What types of disturbances can act as stimuli that initiate
a feedback system?
7. How are negative and positive feedback systems similar?
How are they different?
8. Contrast and give examples of symptoms and signs of a
disease.
AGING AND HOMEOSTASIS
objective • Describe some of the ef fects of aging.
iu will see later, aging is a normal p>rocess character-
ized by 7 a progressive decline in the body's ability to restore
homeostasis. Aging produces observable changes in struc-
ture and function and increases vulnerability to stress and
disease. The changes associated with aging are apparent in
all body systems. Examples include wrinkled skin, gray hair,
loss of bone mass, decreased muscle mass and strength, di-
minished reflexes, decreased production of some hormones,
increased incidence of heart disease, increased susceptibility
to infections and cancer, decreased lung capacity, less effi-
cient functioning of die digestive system, decreased kidney
function, menopause, and enlarged prostate. These and other
effects of aging will be discussed in detail in later chapters.
■ CHECKPOINT
9. What are some of the signs of aging?
ANATOMICAL TERMS
OBJECTIVES • Describe the anatomical position.
• Identify the major regions of the body and relate the
common names to the corresponding anatomical
terms for various parts of the body.
• Define the directional terms and the anatomical
planes and sections used to locate parts of the human
body.
The language of anatomy and physiology is very precise.
When describing where the wrist is located, is it correct to
say "the wrist is above the fingers"? This description is true
if your arms are at your sides. But if you hold your hands up
above your head, your fingers would be above your wrists.
To prevent this kind of confusion, scientists and health-care
professionals refer to one standard anatomical position and
use a special vocabulary for relating body parts to one an-
other.
In the study of anatomy, descriptions of any part of the
human body assume that the body is in a specific stance
called the anatomical position. In the anatomical position,'
the subject stands erect facing the observer, with the head
level and the eyes facing forward. The feet are flat on the
floor and directed forward, and the arms arc- at the sides with
the palms turned forward (Figure 1 .4 on page 11).
Names of Body Regions
The human body is divided into several major regions that
can be identified externally. These are the head, neck, trunk,
upper limbs, and lower limbs (Figure 1.4). The head consists
of the skull and face. The skull is the part of the head that en-
closes and protects the brain, and the face is the front portion
of the head drat includes the eyes, nose, mouth, forehead,
cheeks, and chin. The neck supports the head and attaches it
to the trunk. The trunk consists of the chest, abdomen, and
pelvis. Each upper limb is attached to the trunk and consists
Focus ON
Good He
Homeostasis Is
the Basis
You've seen homeostasis defined as a
condition in which the body's internal
environment remains relatively stable.
What does this mean to you in your
everyday life?
Homeostasis: The Power to Heal
The body's ability to maintain home-
ostasis gives it tremendous healing
power and a remarkable resistance to
abuse. The physiological processes re-
sponsible for maintaining homeostasis
are in large part also responsible for
your good health.
For most people, lifelong good
health is not something that just hap-
pens. Two of the many factors in this
balance called health arc the environ-
ment and your own behavior. Also im-
portant is your genetic makeup. Your
body's homeostasis is affected by the air
you breathe, the food you eat, and even
the thoughts you think. The way you
live your life can either support or in-
terfere with your body's ability to
maintain homeostasis and recover from
the inevitable stresses life throws your
way.
Let's consider the common cold.
You support your natural healing
processes when you take care of your-
self. Plenty of rest, fluids, and chicken
soup allow the immune system to do its
job. The cold runs its course, and you
are soon back on your feet. If, instead
of taking care of yourself, you continue
to smoke two packs of cigarettes a day,
skip meals, and pull several all nighters
studying for an anatomy and physiol-
ogy exam, you interfere with the im-
mune system's ability to fend off attack-
ing microbes and bring the body back
to homeostasis and good health. Other
infections take advantage of your weak-
ened state, and pretty soon the cold has
"turned into" bronchitis or pneumonia.
Homeostasis and Disease Prevention
Many diseases are the result of years of
poor health behavior that interferes
with the body's natural drive to main-
tain homeostasis. An obvious example
is smoking-related illness. Smoking to-
bacco exposes sensitive lung tissue to a
multitude of chemicals that cause can-
cer and damage the lungs ability to re-
pair itself. Because diseases such as em-
physema and lung cancer are difficult
to treat and very rarely cured, it is
much wiser to quit smoking— or never
start — than to hope a doctor can fix
you once you are diagnosed with a lung
disease. Developing a lifestyle that
works with, rather than against, your
body's homeostatic processes helps you
maximize your personal potential for
optimal health and well-being.
► Thin
What health habits have you developed over the past several years to
prevent disease or enhance your body's ability to maintain health and
homeostasis?
of the shoulder, armpit, arm (portion of the limb from the
shoulder to the elbow), forearm (portion of die limb from the
elbow to the wrist), wrist, and hand. Each lower limb is also
attached to the trunk and consists of the buttock, thigh
(portion of the limb from the hip to the knee), leg (portion o I
the limb from the knee to the ankle), ankle, and foot. The
rroin is the area on the front surface of the body, marked by a
ncase on each side, where the trunk attaches to the thighs.
In Figure 1.4, the corresponding anatomical adjective for
each part of the body appears in parentheses next to the com-
mon name. For example, if you receive a tetanus shot in your
buttock, it is a gluteal injection. The descriptive form of a body
part is based on a Greek or Latin word or "root" for the same
part or area. The Latin word for armpit is axilla (ak-SIL-a),
for example, and thus one of the nerves passing within the
armpit is named the axillary nerve. You will learn more about
the word roots of anatomical and physiological terms as you
read this book.
Directional Terms
To locate various body structures, anatomists use specific
directional terms, words that describe the position of one
body part relative to another. Several directional terms can be
grouped in pairs that have opposite meanings, for example,
anterior (front) and posterior (back). Study Exhibit LI on
page 12 and Figure 1.5 on page 13 to determine, among
other things, whether your stomach is superior to your lungs.
10
Anatomical Terms
Figure 1.4 The anatomical position. The common names and corresponding anatomical terms (in parentheses)
indicate specific body regions. For example, the head is the cephalic region.
I '"
In the anatomical position, the subject stands erect tacing the observer, with the head level and the eyes facing forward.
Trie feet are flat on the floor and directed forward, and the arms are at the sides with the palms facing forward.
Foot —
(pedal)
Eye (orbital)
Ear (otic)
Nose (nasal)
Mouth (oral)
Breastbone
(sternal)
Breast (mammary)
Navel
umbilical)
Hip (coxal)
Groin
inguinal)
Pubis
(pubic)
HEAD
(CEPHALIC
NECK
(CERVICAL
UPPER
LIMB
- LOWER
LIMB
(plantar)
(b) Posterior view
Heel
(calcaneal)
Where is a plantar wart located?
12 Chapter 1 Organization of the Human Body
Exhibit 1.1 Directional Terms (Figure 1. 5)
1
OBJECTIVE • Define each directional term used to describe the human body.
Most of the directional terms used to
describe the human body can be grouped
into pairs that have opposite meanings. For
example, superior means toward the upper
part of the body, and inferior means toward
the lower part of the body. It is important to
understand that directional terms have
relative meanings; they only make sense
when used to describe the position of one
structure relative to another. For example,
your knee is superior to your ankle, even
though both are located in the inferior half
of the body Study the directional terms
and the example of how each is used. As
you read each example, refer to Figure 1.5
to see the location of the structures
mentioned.
■ CHECKPOINT
Which directional terms can be used to spec-
ify the relationships between (1) the elbow
and the shoulder, (2) the left and right shoul-
ders, (3) the sternum and the humerus, and
(4) the heart and the diaphragm?
Directional Term
Definition
Example of Use
Superior (soo'-PEER-e-or)
(cephalic or cranial)
Inferior (in'-FEER-e-or) (caudal)
Anterior (an-TEER-e-or) (ventral]
Posterior (pos-TEER-e-or) (dorsal)
Medial (ME-de-al)
Lateral (LAT-er-al)
Proximal (PROK-si-mal)
Distal (DIS-tal)
Superficial (soo'-per-FISH-al)
Deep (DEP)
Toward the head, or the upper part of a structure.
Away from the head, or the lower part of a structure.
Nearer to or at the front of the body.
Nearer to or at the back of the body.
Nearer to the midline 1 or midsagittal plane.
Farther from the midline or midsagittal plane.
Nearer to the attachment of a limb to the trunk;
nearer to the point of origin or the beginning.
Farther from the attachment of a limb to the trunk;
farther from the point of origin or the beginning.
Toward or on the surface of the body.
Away from the surface of the body.
The heart is superior to the liver.
The stomach is inferior to the lungs.
The sternum (breastbone) is anterior to heart.
The esophagus (food tube) is posterior to the trachea
(windpipe).
The ulna is medial to the radius.
The lungs are lateral to the heart. ,
The humerus is proximal to the radius.
The phalanges are distal to the carpals.
The ribs are superficial to the lungs.
The ribs are deep to the skin of the chest and back.
'The midline is an imaginary vertical line that divides the body into equal right and left sides.
Anatomical Terms 1 3
* Figure 1.5 Directional terms.
Directional terms precisely locate various parts of the body in relation to one another.
LATERAL <-
>- MEDIAL-^
Midline
-*~ LATERAL
Esophagus (food tube)
Trachea (windpipe)
Diaphragm
SUPERIOR
Urinary bladder
NFERIOR
Anterior view of trunk and right upper limb
Is the radius proximal to the humerus? Is the esophagus anterior to the trachea? Are the ribs superficial to the lungs? Is the
urinary bladder medial to the ascending colon? Is the sternum lateral to the descending colon?
1 4 Chapter 1 Organization of the Human Body
Planes and Sections
You will also study parts of the body in four major planes,
that is, imaginary flat surfaces that pass through the body
parts (Figure 1.6): sagittal, frontal, transverse, and oblique. A
sagittal plane (SAJ-i-tal; sagitt- = arrow) is a vertical plane
that divides the body or an organ into right and left sides.
More specifically, when such a plane passes through the
midline of the body or organ and divides it into equal right
and left sides, it is called a midsagittal plane. If the sagittal
plane does not pass through the midline but instead divides
the body or an organ into unequal right and left sides, it is
called * parasagittal plane (para- = near). A frontal plane or
coronal plane divides the body or an organ into anterior (front)
and posterior (back) portions. A transverse plane divides
the body or an organ into superior (upper) and inferior
(lower) portions. A transverse plane may also be termed a
cross-sectional or horizontal plane. Sagittal, frontal, and trans-
Figure 1.6 Planes through the human body.
^ Frontal, transverse, sagittal, and oblique planes divide the body
;;.'■•> in specific ways.
Frontal plane
Oblique plane
j — Parasagittal
plane
dsagittal plane
Right anterolateral view
verse planes are all at right angles to one another. An oblique
plane, by contrast, passes through the body or an organ at an
angle between the transverse plane and a sagittal plane or
between the transverse plane and the frontal plane.
When you study a body region, you will often view it in
section, meaning that you look at only one flat surface of the
three-dimensional structure. It is important to know the
plane of the section so you can understand the anatomical
relationship of one part to another. Figure L7 indicates how
Figure 1.7 Planes and sections through different parts of the
brain. The diagrams (left) show the planes, and the photographs
(right) show the resulting sections. (Note: The "view" arrows in the
diagrams indicate the direction from which each section is viewed.
This aid is used throughout the book to indicate viewing
perspective.)
Planes divide the body in various ways to produce sections.
Transverse section
(b)
Frontal plane
Frontal section
(c)
dsagittal plane
Midsagittal section
' Which plane divides the heart into anterior
•
ior and posterior portions? > Which plane divides the brain into equal right and left sides?
Body Cavities 1 5
ree different sections — a transverse (cross) section, a frontal
tioii, and a midsagittal section — provide different views of
he brain.
■ CHECKPOINT
10. Describe the anatomical position and explain why it is
used.
11. Locate each region on your own body, and then identify
it by its common name and the corresponding anatomi-
cal descriptive form.
12. For each directional term listed in Exhibit 1.1 on page
12, provide your own example.
13. What are the various planes that may be passed through
die body? Explain how each divides the body.
BODY CAVITIES
objectives • Describe the principal body cavities
and the organs they contain,
• Explain why the abdominopelvic cavity is divided into
regions and quadrants.
Spaces within the body that contain, protect, separate, and
support internal organs are called body cavities. 1 1 ere we
discuss several of the larger body cavities (Figure \ .8).
The cranial cavity is formed by the cranial (skull) bones
and contains the brain. The vertebral (spinal) cavity is
formed by the bones of the vertebral column (backbone) and
contains the spinal cord.
The major body cavities of the trunk are the thoracic and
abdominopelvic cavities. The thoracic cavity (thor-AS-ik;
Figure 1.8 Body cavities. The dashed lines indicate the border between the abdominal and
pelvic cavities.
The major body cavities of the trunk are the thoracic and abdominopelvic cavities.
"
;a} Right lateral view
Cranial —
cavity
Vertebral
cavity
v. m
_
Thoracic —
cavity
Diaphragm
Abdominopelvic
cavity:
Abdominal
cavity
Pelvic
cavity
W
(b) Anterior view
CAVITY
Cranial cavity
Vertebral cavity
Thoracic cavity*
Pleural cavity
Pericardial cavity
Mediastinum
Abdominopelvic
cavity
Abdominal cavity
Pelvic cavity
Formed by cranial bones and contains brain.
Formed by vertebral column and contains spinal
cord and the beginnings of spinal nerves.
Chest cavity; contains pleural and pericardial
cavities and mediastinum.
Each surrounds a lung; the serous membrane of
the pleural cavities is the pleura.
Surrounds the heart; the serous membrane ot the
pericardial cavity is the pericardium.
Central portion of thoracic cavity between the
lungs; extends trom sternum to vertebral column
and from neck to diaphragm; contains heart,
thymus, esophagus, trachea, and several large
blood vessels,
Subdivided into abdominal and pelvic cavities.
Contains stomach, spleen, liver, gallbladder,
small intestine, and most of large intestine; the
serous membrane of the abdominal cavity is
the peritoneum.
Contains urinary bladder, portions of large intestine,
and internal organs of reproduction.
See Figure 1 .9 for details of the thoracic cavity.
In which cavities are the following organs located: urinary bladder, stomach, heart, small intestine, lungs,
internal female reproductive organs, thymus, spleen, liver? Use the following symbols for your response:
T = thoracic cavity, A = abdominal cavity, or P = pelvic cavity.
16 Chapter 1 Organization ol the Human Body
9 The thoracic cavity. The dashed iines indicate the borders o« the mediastinum. Notice tha, the pen=a«W cav.y
F ' 9Ur l the hear anXuhe pleural cavit.es surround the lungs.
■:,'■'■-.-."■■
Right pleural cavity
Parietal pleura
Visceral pleura
Diaphragm
Mediastinum
Pericardial cavity
^ AjA Parietal pericardium
■W "*■ ^ Visceral pericardium
jj/X \!0 — - Left pleural cavity
Anterior view
Fi9ure11 The nine re^ons o, the a^minopeMc oavit, The mternai reproductive or 9 ans in the peivic cav.ty are shown in
Figures 23.1 on page 557 and 23.6 on page 564.
The nine-region designation is used tor anatomical studies.
Clavicles
Midclavicular lines
i — ' — i
Left
Right
RIGHT
HYPOCHONDRIA
REGION
RIGHT'".
LUMBAR
REGION
EPIGASTRIC-
REGION
Diaphragm
Hypochondriac
|4lEGlON
RIGHT INGUINAL
(ILIAC) REGION
UMBILICAL LEFT
EGION ' LUMBAR
REGION
POGAS-
TRIC (PUBIC)
REGION
KHFT INGUINAL
^lAC) REGION
Gallbladder
Large intestine -
(ascending colon)
Small intestine -
Appendix
Large intestine
(transverse colon)
Urinary bladder
(a) Anterior view showing location of abdominopelvic regions
*? ,n which abdominopelvic region is each of the following found: most
(b) Anterior superficial view of organs in abdominopelvic regions
of the liver, ascending colon, urinary bladder, appendix?
Body Cavities 17
umc- = chest) is the chest cavity. Within the thoracic cavity
_re three smaller cavities: die pericardial cavity (per'-i-KAR-
[de-al; peri- = around; -cardial = heart), a fluid-filled space
bar surrounds the heart, and two pleural cavities (PLOOR-
pkitr- = rib or side), each of which surrounds one lung
|d contains a small amount of fluid (Figure 1.9 on page 16).
ie mural portion of the thoracic cavity is called the niedi-
wm (me'-de-a-STI-mim; media- = middle; -stinum = par-
tion). It is between the lungs, extending from the sternum
breastbone) to the vertebral column (backbone), and from
jj£ neck to the diaphragm (Figure 1.9). The mediastinum
bntains all thoracic organs except the lungs themselves.
[Anion" - the structures in the mediastinum are the heart,
[esophagus, trachea, and several large blood vessels. The
tinpbragm (Dl-a-fram = partition or wall) is a dome-shaped
muscle that powers breathing and separates the thoracic
cavity from the abdominopelvic cavity.
The abdominopelvic cavity (ab-donV -i-no-PEL-vic) ex-
tends from the diaphragm to the groin. As the name sug-
ests, die abdominopelvic cavity is divided into two por-
[tions, although no wall separates them (see Figure 1.8). The
portion, the abdominal cavity (abdomin- = belly)
contains the stomach, spleen, liver, gallbladder, small intes-
tine, and most of the large intestine. The lower portion, the
pelvic cavity (pelv- = basin) contains the urinary bladder,
portions of the large intestine, and internal organs of the
reproductive system. The pelvic cavity is located below the
il line in Figure 1 .8. Organs inside the thoracic and
abdominopelvic cavities are called viscera (VIS-e-ra).
I Abdominopelvic Regions and Quadrants
| To describe the location of the many abdominal and pelvic
organs more precisely, the abdominopelvic cavity may be
ed into smaller compartments. In one method, two
horizontal and two vertical lines, like a tic-tac-toe grid,
partition die cavity into nine abdominopelvic regions (Fig-
10 on page 16). The names of the nine abdominopelvic
regions are the tight hypochondriac (hi'-po-KON-dre-ak), epigas-
p-i-CAS-trik), 'left hypochondriac, right lumbar, umbilical
(um-BIL-i-kal), left lumbar, right inguinal (iliac) (IL-e-ak),
Uypog/ixtric (hl'-po-GAS-trik), and left inguinal (iliac). In
another method, one horizontal and one vertical line passing
through the umbilicus (um-BlL-i-kus or um-bi-Ll-kus;
umhilic- = navel) or belly button divide the abdominopelvic
cavity into quadrants (KWOD-rantz; quad- = one-fourth)
[(Figure 1.11). The names of the abdominopelvic quadrants
e right upper quadrant (R UQ), left upper quadrant (L UQ),
haver quadrant (RLQ), and left lower quadrant (LLQ).
Figure 1-11 Quadrants of the abdominopelvic cavity. The two
lines cross at right angles at the umbilicus (navel).
| The quadrant designation is used to locate the site of pain, a
mass, or some other abnormality.
RIGHT UPPER -
QUADRANT
(RUQ)
RIGHT LOWER
QUADRANT
(RLQ)
LEFT UPPER
QUADRANT
(LUQ)
LEFT LOWER
QUADRANT
(LLQ)
Anterior view showing location of abdominopelvic quadrants
' . In which abdominopelvic quadrant would the pain from appen-
i dicitis (inflammation of the appendix) be felt?
The nine-region division is more widely used for anatomical
studies, and quadrants are more commonly used by clinicians
to describe the site of an abdominopelvic pain, mass, or other
abnormality.
■ CHECKPOINT
14. What landmarks separate the various body cavities from
one another?
15, Locate the nine abdominopelvic regions and the lour ab-
dominopelvic quadrants on yourself, and list some of the
organs found in each.
We will next examine the chemical level of organization
in Chapter 2. You will learn about the various groups of
chemicals in your body, how they function, and how they
contribute to the homeostasis of your body.
1 8 Chapter 1 Organization of the Human Body
MEDICAL TERMINOLOGY AND CONDITIONS
Most chapters in this text are followed by a glossary of key medical
terms that include both normal and pathological conditions. You
should familiarize yourself with these terms because they will play
,,, essential role in your medical vocabulary.
Some of these conditions, as well as ones discussed in the text,
are referred to as local or systemic. A local disease is one that affects
one part or a limited area of the body. A systemic disease affects the
entire body or several parts.
Epidemiology (ep'-i-de-me-OL-o-je; epi- = upon; -Ami = people)
The science that deals with why, when, and where diseases
occur and how they are transmitted within a defined human
population.
Geriatrics (jer'-e-AT-riks; ger- = old; -tames = medicine) The : sci-
ence that deals with the medical problems and care ol elderly
persons.
Pathology (pa-THOL-6-je; patho- = disease) The science that deals
with the nature, causes, and development of abnormal conditions
and the structural and functional changes that diseases produce.
Pharmacology (far-ma-KOL-6-je; pharmm- = drug) The science that
deals with the effects and use of drugs in the treatment of disease.
TUDY
OUTLINE
Anatomy and Physiology Defined (p. 2)
1. Anatomy is the science of structure and the relationships
among structures.
2. Physiology is the science of how body structures function.
Levels of Organization and Body Systems (p. 2)
1. The human body consists of six levels of organization: chemi-
cal, cellular, tissue, organ, system, and organisms!,
2. Cells are the basic structural and functional units of an organ-
ism and the smallest living units in the human hotly-
3 Tissues consist of groups of cells and the materials surround-
ing them that work together to perform a particular function.
4 Organs usually have recognizable shapes, are composed of two
or more different types of tissues, and have specific functions,
5. Systems consist of related organs that have a common function.
6 Table 1.1 on pages 4-5 introduces the eleven systems of
the human body: integumentary, skeletal, muscular, nervous,
endocrine, cardiovascular, lymphatic, respiratory, digestive,
urinary, and reproductive.
7. The human organism is a collection of structurally and func-
tionally integrated systems.
8. Body systems work together to maintain health, protect against
disease, and allow for reproduction of the species.
s have certain characteristics that set them
Life Processes (p. 6)
1. All living organisms
apart from nonliving things.
2 Among the life processes in humans are metabolism, respon-
siveness, movement, growth, differentiation, and reproduction.
Homeostasis: Maintaining Limits (p. 6)
1. Homeostasis is a condition in which the internal environment
of the body remains stable, within certain limits.
2. A large part of the body's internal environment is interstitial I
fluid, which surrounds all body cells.
3. Homeostasis is regulated by the nervous and endocrine systems
acting together or separately. The nervous system delects body
changes and sends nerve impulses to maintain homeostasis. ! he
endocrine system regulates homeostasis by secreting hormones.
4 Disruptions of homeostasis come from external and internal
stimuli and from psychological stresses. When disruption ot
homeostasis is mild and temporary, responses ol body cells
quickly restore balance in die internal environment. It disruption
is extreme, the body's attempts to restore homeostasis may hub
5. A feedback system consists of (1) receptors that monitor
changes in a controlled condition and send input to (2) a
control center that sets the value at which a controlled condi-
tion should be maintained, evaluates the input it receives,
and generates output commands when they are needed, and
(3) effectors that receive output from the control center and
produce a response (effect) that alters the controlled condition.
6. if a response reverses a change in a controlled condition, the
system is called a negative feedback system. If a response
Strengthens a change in a controlled condition, the system is
referred to as a positive feedback system.
7. One example of negative feedback is the system that regulates
blood pressure. If a stimulus causes blood pressure (controlled
condition) to rise, baroreceptors (pressure-sensitive nerve cells,
the receptors) in blood vessels send impulses (input) to the brain
(control center). The brain sends impulses (output) to the heart
Self-Quiz 19
(effector). As n result, heart rate decreases (response), and blood
pressure drops back to normal (restoration of homeostasis).
8. Disruptions of homeostasis — homeostatic imbalances — can
lead to disorders, disease, and even death.
9. A disorder is any abnormality of structure and/or function.
Disease is a more specific term for an illness with a definite set
of signs and symptoms.
10. Symptoms are subjective changes in body functions that are not
apparent to an observer, whereas signs are objective changes
that can be observed and measured,
11. Diagnosis of disease involves identification of symptoms and
signs, a medical history, physical examination, and sometimes
laboratory tests.
Aging and Homeostasis (p. 9)
I. Aging produces observable changes in structure and function
and increases vulnerability to stress and disease.
I 2. Changes associated with aging occur in all body systems.
Anatomical Terms (p. 9)
1. Descriptions of any region of the body assume the body is in
the anatomical position, in which the subject stands erect fac-
ing the observer, with the head level and the eyes facing for-
ward, the feet flat on die floor and directed forward, and the
arms at the sides, with die palms turned forward.
2. The human body is divided into several major regions: die head,
neck, trunk, upper limbs, and lower limbs.
3. Within bodv regions, specific body parts have common names
and corresponding anatomical descriptive forms (adjectives). Ex-
amples are chest (thoracic), nose (nasal), and wrist (carpal).
4. Directional terms indicate the relationship of one part of the
body to another. Exhibit 1.1 on page 12 summarizes commonly
used directional terms.
5. Planes are imaginary flat surfaces that divide the body or or-
gans into two parts. A midsagittal plane divides the body or an
organ into equal right and left sides. A parasagittal plane di-
vides the body or an organ into unequal right and left sides. A
frontal plane divides the body or an organ into anterior and
posterior portions. A transverse plane divides the body or an
organ into superior and inferior portions. An oblique plane
passes through the body or an organ at an angle between a
transverse plane and a sagittal plane, or between a transverse
plane and a frontal plane,
6. Sections result from cuts through body structures. They are
named according to the plane on which the cut is made: trans-
verse, frontal, or sagittal.
Body Cavities (p. 15)
1. Spaces in the body that contain, protect, separate, and support
internal organs are called body cavities.
2. The cranial cavity contains the brain, and the vertebral cavity
contains the spinal cord.
3. The thoracic cavity is subdivided into three smaller cavities: a
pericardial cavity, which contains the heart, and two pleural
cavities, which each contain a lung.
4. The central portion of the thoracic cavity is the mediastinum.
It is located between the lungs and extends from the sternum to
the vertebral column and from die neck to the diaphragm. It
contains all thoracic organs except the lungs.
5. The abdominopelvic cavity is separated from the thoracic cav-
ity by the diaphragm and is divided into a superior abdominal
cavity and an inferior pelvic cavity.
6. Organs in the thoracic and abdominopelvic cavities are called
viscera.
7. Viscera of the abdominal cavity include the stomach, spleen,
liver, gallbladder, small intestine, and most of the large intestine.
8. Viscera of die pelvic caviry include the urinary bladder, por-
tions of the large intestine, and internal organs of the repro-
ductive system.
9. To describe the location of organs easily, the abdominopelvic
cavity may be divided into nine abdominopelvic regions by two
horizontal and two vertical lines.
10. The names of the nine abdominopelvic regions are right
hypochondriac, epigastric, left hypochondriac, right lumbar, um-
bilical, left lumbar, right inguinal, hypogastric, and left inguinal.
11. The abdominopelvic cavity may also be divided into quadrants
by passing one horizontal and one vertical line through die
umbilicus (navel).
12. The names of the abdominopelvic quadrants are right upper
quadrant (RUQ), left upper quadrant (LUQ), right lower
quadrant (RLQ), and left lower quadrant (LLQ).
1. To properly reconnect die disconnected bones of a human
skeleton, you would need to have a good understanding of
a. physiology
b. homeostasis
c. chemistry
d. anatomy
e. feedback systems
2. Which of the following best illustrates the idea of increasing
levels of organizational complexity?
a. chemical — ► tissue — » cellular -^ organ -> organismal -> system
b. chemical -^ cellular — > tissue —*■ organ — » system — * organismal
c. cellular — » chemical — » tissue -» organismal -* organ -> system
d. chemical -* cellular — » tissue — > system — * organ —> organismal
e. tissue — » cellular —* chemical — > organ — ► system — > organismal
20 Chapter 1 Organization of the Human Body
3. Match the following:
a. transports oxygen,
nutrients, and carbon
dioxide
b. breaks down and
-absorbs food
c. functions in body
movement, posture,
and heat production
d. regulates body activities
through hormones
. e. supports and protects
the body
_ f. eliminates wastes and
regulates the chemical
composition and volume
of blood
g. protects the body, detects
sensations, and helps
regulate body temperature
4. Fill in the missing blanks in the following table.
A. urinary system
B. digestive system
C. endocrine
system
D. integumentary
system
E. muscular system
F. skeletal system
G. cardiovascular
system
System
a
Functions
Regulates body
activities by nerve
impulses
Major Organs
b
c Lymph vessels, spleen, d
thymus, tonsils,
lymph nodes
e f Supplies oxygen
to cells, elimi-
nates carbon
dioxide, regulates
acid-base balance
Reproductive g 1l —
5. Homeostasis is
a. the sum of all of the chemical processes in the body
b. the sign of a disorder or disease
c. the combination of growth, repair, and energy release that is
basic to lite
d. the tendency to maintain constant, favorable internal body
conditions
e. caused by stress
6. Which of the following is NOT true concerning the life
processes?
a. The pupils of your eyes becoming smaller when exposed to
strong light is an example of differentiation.
b. The ability to walk to your car following class is a result of
the life process called movement.
c. Hie repair of injured skin would involve the life process of
reproduction.
d. Digesting and absorbing food is an example of metabolism.
e. Sweating on a hot summer day invokes responsiveness.
7. Tn a negative feedback system,
a. the controlled condition is never disrupted
b. there tends to lie a "runaway" body response
C, the change in the controlled condition is reversed
d. the body part that responds to the output is known as the
receptor
e. the response results in a reinforcement of the original
stimulus
8. The part of a feedback system that receives the input and gen-
erates the output command is the
a. effector b. receptor c. feedback loop
d. response e. control center
9. Match the following:
a. observable, measurable change A. systemic
b. abnormality of function B. symptom
c. affects the entire body C. sign
d. subjective changes that aren't D, disorder
easily observed
10. An itch in your axillary region would cause you to scratch
a. your armpit b. the front of your elbow
c. von r neck d. the top of your head e. your calf
11. If you were facing a person who is in the correct anatomical
position, you could observe the
a. crural region b. lumbar region c. gluteal region
d. popliteal region e. scapular region
12. Where would you look for the femoral artery?
a. wrist b. forearm c. face
d, thigh e. shoulder
13. The right ear is to the right nostril.
a. intermediate b. inferior c. lateral
d. distal e. medial
14. Your chin is in relation to your lips.
a. lateral b. superior c. deep
d. posterior e. inferior
15. Your skull is . in relation to your brain.
a. intermediate b. superior c. deep
d. superficial e. proximal
16. A magician is about to separate his -.issistant's body into supe-
rior and inferior portions. The plane through which he will
pass his magic wand is the
a. midsagittal b. frontal C. transverse
d. parasagittal e. oblique
17. Which statement is NOT true of body cavities?
a. The diaphragm separates the thoracic and abdominopelvic
cavities.
b. The organs in the cranial and vertebral cavities are called
viscera.
c. The urinary bladder is in the pelvic cavity.
d. The abdominal cavity is below the thoracic cavity.
e. The pelvic cavity terminates below the gnmi.
Answers to Figure Questions 21
18, If Jamie is having her appendix removed, the
would prepare which area for surgery?
a. right upper quadrant
b. right lower quadrant
c. left upper quadrant
d. left lower quadrant
e. left hypochondriac region
19. In lind die Liriiinry bladder, you would look in the
a. hypochondriac region
b. umbilical region
c. epigastric region
d. iliac region
e. hypogastric region
surgeon 20. Match the following:
a, contains the urinary bladder
and reproductive organs
b. contains the brain
c. contains the heart
d. region between the lungs,
from the breastbone to
the backbone
e. separates the thoracic and
abdominal cavities
f. contains a lung
g. contains the spinal cord
_ h. contains the stomach and liver
A. cranial cavity
B. abdominal cavity
C. vertebral cavity
D. pelvic cavity
E. pleural cavity
R mediastinum
G. diaphragm
H. pericardial cavity
I
■
CRITICAL THINKING APPLICATIONS
1. Taylor was going for the playground record for the longest
upside-down hang from the monkey bars. She didn't make it
and may have broken her arm. The emergency room techni-
cian would like an x-ray film of Taylor's arm in the anatomical
position. Use the proper anatomical terms to describe the posi-
tion of Taylor's arm in the x-ray film.
2. Imagine that a manned space flight lands on Mars. The astro-
naut life specialist observes lumpy shapes that may be life
forms, What are some characteristics of living organisms that
may help the astronaut determine if these are life forms or mud
balls?
3. f my was trying to impress Jenna with a tale about his last rugby
match. "The coach said I suffered a caudal injur,- to the dorsal
sural in my groin." Jenna responded, "I think either you or
your coach suffered a cephalic injury." Why wasn't Jenna im-
pressed by Guy's athletic prowess?
4. There's a special fun-house mirror that hides half your body
and doubles the image of your other side. In the mirror, you
can do amazing feats such as lifting both tegs off the ground.
Along what plane is the mirror dividing your body? A different
mirror in the next room shows your reflection with two heads,
four arms and no legs. Along what plane is this mirror dividing
your body?
/ANSWERS TO FIGURE QUESTIONS
1.1 Organs have a recognizable shape and consist of two or more
different types of tissues that have a specific function.
1.2 The basic difference between negative and positive feedback
systems is that in negative feedback systems, the response re-
verses a change in a controlled condition, and in positive
feedback systems, the response strengthens the change in a
controlled condition.
1.3 If a stimulus caused blood pressure to decrease, the heart
rate would increase due to die operation of this negative
feedback system.
1.4 A plantar wart is found on the sole.
1.5 No, the radius is distal to die humerus; No, the esophagus is
posterior to the trachea; Yes, the ribs are superficial to the
lungs; Yes, the urinary bladder is medial to the ascending
colon; No, the sternum is medial to the descending colon.
1.6 The frontal plane divides the heart into anterior and
posterior portions.
1.7 The midsagittal plane divides the brain into equal tight and
left sides.
Urinary bladder = P, stomach = A, heart = T, small
intestine = A, lungs = T, internal female reproductive
organs = P, thymus = T, spleen = A, liver = A.
Some structures in the mediastinum arc the heart, esopha-
gus, and aorta,
1.10 The liver is mostly in the epigastric region; the ascending
colon is in the right lumbar region; the urinary bladder is in
the hypogastric region; the appendix is in the right inguinal
region.
1.11 The pain associated with appendicitis would be felt in the
right lower quadrant (RLQ).
1.8
1.9
.
chapter 2
INTRODUCTORY CHEMISTRY
did you know?
L±ow often have you heard people
talk about dietary fat? You have probably
heard many debates regarding the health benefits
ofmonoimsaturated and polyunsaturated verms
saturated fats (fatty acids). The chemistry of fatty
acids is responsible for the physiological roles they play.
A great deal of research has focused on the behavior
of the various kinds of fatty acids in the body. At one
time many scientists thought that total fat intake
should be kept low to prevent heart disease. Now
scientists believe that certain types of unsaturated
fatly acids, such as those found in
fish oils, may actually reduce heart
disease risk.
Focus on Wellness, page 36
www.wiley.com/college/apcentral
1 V/ any common substances we
eat and drink— water, sugar, table
salt, proteins, starches, fats — play
vital roles in keeping us alive. In
this chapter, you will learn how these
substances function in your body. Because
your body is composed of chemicals and all body
activities are chemical in nature, it is important to
become familiar with the language and basic ideas of
chemistry to understand human anatomy and physiology;
looking back to move ahead .
Levels of Organization and Body Systems (p, 2)
22
INTRODUCTION TO CHEMISTRY
OBJECTIVES * Define a chemical element, atom, ion,
molecule, and compound.
« Explain how chemical bonds form.
• Describe what happens in a chemical reaction and
explain why it is important to the human body.
Chemistry (KEM-is-trc) is the science of the structure and
interactions of matter, which is anything that occupies space
and has mass. Mass is the amount of matter in any living
organism or nonliving thing.
Chemical Elements and Atoms
All forms of matter are made up of a limited number of
building blocks called chemical elements, substances that
cannot be broken down into a simpler form by ordinary
chemical means. At present, scientists recognize 112 different
elements. Each element is designated by a chemical symbol,
one or two letters of the element's name in English, Latin, or
Introduction to Chemistry 23
another language. Examples are H for hydrogen, C for
carbon, O for oxygen, N for nitrogen, K tor potassium, Na
for sodium, Fe for iron, and Ga for calcium.
Twenty-six different elements normally are present in
your body. Just four elements, called the major daiients,
constitute about 96% of the body's mass: oxygen, carbon,
hydrogen, and nitrogen. Eight others, the ksser dements-, con-
tribute 3.8% of the body's mass: calcium (Ca), phosphorus
(P), potassium (K), sulfur (S), sodium (Na), chlorine (CI),
magnesium (Mg), and iron (Fe). An additional 14 elements —
die trace dements — are present in tiny amounts. Together,
they account for the remaining 0.2% of the body's mass. Sev-
eral trace elements have important functions in the body, For
example, iodine (!) is needed to make thyroid hormones. The
functions of some trace elements are unknown. Table 2.1 lists
the main chemical elements of the human body-
Each element is made up of atoms, die smallest units of
matter that retain the properties and characteristics of the
element. A sample of the element carbon, such as pure coal,
contains only carbon atoms, and a tank of helium gas con-
tains only helium atoms.
Chemical Element
(Symbol)
MAJOR ELEMENTS
Oxygen (0)
Carbon (C)
Hydrogen (H)
Nitrogen (N)
LESSER ELEMENTS
Calcium (Ca)
TRACE ELEMENTS
Table 2.1 Main Chemical Elements In the Body
% of Total
Body Mass
65.0
18.5
9.5
3.2
1.5
Phosphorus (P)
1.0
Potassium (K)
0.35
Sulfur (S)
0.25
Sodium (Na)
0.2
Chlorine (C!>
0.2
Magnesium (Mg)
0.1
Iron (Fe)
0.005
0.2
Significance
Part of water and many organic (carbon-containing) molecules; used to generate ATP, a molecule used by
cells to temporarily store chemical energy.
Forms backbone chains and rings of all organic molecules: carbohydrates, lipids (fats), proteins, and nucleic
acids (DNA and RNA).
Constituent of water and most organic molecules; ionized form (H ) makes body fluids more acidic.
Component of all proteins and nucleic acids.
Contributes to hardness of bones and teeth; ionized form (Ca 2+ ) needed for blood clotting, release of
hormones, contraction of muscle, and many other processes.
Component of nucleic acids and ATP; required for normal bone and tooth structure.
Ionized form (K + ) is the most plentiful cation (positively charged particle) in intracellular fluid; needed to gener-
ate action potentials.
Component of some vitamins and many proteins,
Ionized form (Na' ) is the most plentiful cation in extracellular fluid; essential for maintaining water balance;
needed to generate action potentials.
Ionized form (CI ) is the most plentiful anion (negatively charged particle) in extracellular fluid; essential
for maintaining water balance.
Ionized form (Mg 2 ' ) needed for action of many enzymes, mofecules that increase the rate of chemical
reactions in organisms.
Ionized forms (Fe 2 ^ and Fe 3 ^) are part of hemoglobin (oxygen-carrying protein in red blood cells) and some
enzymes (proteins that catalyze chemical reactions in living cells).
Aluminum (Al), Boron (B), Chromium (Cr), Cobalt (Co), Copper (Cu) f Fluorine (F), Iodine (I), Manganese (Mn)
Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), and Zinc (Zn).
24 Chapter 2 Introductory Chemistry
Figure 2.1 Two representations of the structure of an atom.
Electrons move about the nucleus, which contains neutrons and
protons, (a) In the electron cloud model of an atom, the shading
represents the chance of finding an electron in regions outside the
nucleus, (b) In the electron shell model, filled circles represent
individual electrons, which are grouped into concentric circles
according to the shells they occupy. Both models depict a carbon
atom, with six protons, six neutrons, and six electrons.
An atom consists of two basic parts: a nucleus and one or
more electrons (Figure 2.1). The centrally located nucleus
contains positively charged protons (p + ) and uncharged
(neutral) neutrons («°). Because each proton has one positive
charge, the nucleus is positively charged. The electrons (e )
are tiny, negatively charged particles that move about in a
large space surrounding the nucleus. They do not follow a
fixed pad! or orbit but instead form a negatively charged
"cloud" that surrounds the nucleus (Figure 2.1a). The
number of electrons in an atom equals die number of
protons. Because each electron carries one negative charge,
the negatively charged electrons and the positively charged
protons balance each other. As a result, each atom is electri-
cally neutral, meaning its total charge is zero.
The number of protons in the nucleus of an atom is
called the atom's atomic number. The atoms of each differ-
> r
An atom is the smallest unit of matter that retains the properties
and characteristics of its element
Nucleus
Protons (p + )
Neutrons (n°)
• Electrons (e~)
v
(a) Electron cloud model (b) Electron shell model
What is the atomic number of carbon?
ent kind of element have a different number of protons in die
nucleus: A hydrogen atom has 1 proton, a carbon atom has
6 protons, a sodium atom has 1 1 protons, a chlorine atom has
17 protons, and so on (figure 2.2). Thus, each type of atom,
or element, has a different atomic number. The total number
Figure 2.2 Atomic structures of several atoms that have important roles in the human body.
The atoms of different elements have different atomic numbers because they have different numbers of protons.
First
electron
shell
Second
electron
shell
Hydrogen (H)
Atomic number = 1
Mass number = 1
•
Carbon (C)
Atomic number = 6
Mass number = 12
Nitrogen (N)
Atomic number = 7
Mass number = 14
Oxygen (O)
Atomic number = 8
Mass number = 1 6
Third
electro
she!
o o
U P n" ♦♦
Sodium (Na)
Atomic number = 11
Mass number = 23
• • •
17P
18iV
Fourth
electron
shell
• •
•
Chlorine (CI)
Atomic number = 17
Mass number = 35
Potassium (K)
Atomic number = 1 9
Mass number = 39
Atomic number = number of protons in an atom
Mass number = number of protons and neutrons in an atom
Which four of these elements are most abundant in living organisms?
of protons plus neutrons in an atom is its mass number. For
nsi nice, an atom of sodium, with II protons and 12
neutrons in its nucleus, has a mass number of 23,
Even though their exact positions cannot be predicted,
specific groups of electrons are most likely to move about
in certain regions around the nucleus. These regions are
called electron shells, which are depicted as circles in Figures
Mli and 2.2 even though some of their shapes are not
spherical, The electron shell nearest the nucleus — the first
iiiti shell — can hold a maximum of 2 electrons. The sec-
ond electron shell can hold a maximum of 8 electrons, and
the third can hold up to 18 electrons. Higher electron shells
re are as many as seven) can contain many more elec-
trons. The electron shells are filled with electrons in a spe-
cific order, beginning with the first shell.
Ions, Molecules, and Compounds
The atoms of each element have a characteristic way of los-
ing gaining, or sharing their electrons when interacting with
other atoms. If an atom either gives up or gains electrons, it
becomes an ion (I-on), an atom that has a positive or nega-
fee charge due to unequal numbers of protons and electrons.
An ion of an atom is symbolized by writing its chemical sym-
bol followed by the number of its positive (+) or negative (-)
charges* For example, Ca 2+ stands for a calcium ion that has
two positive charges because it has given up two electrons.
Refer to Table M on page 23 for the important functions ol
several ions in the body.
In contrast, when two or more atoms share electrons, the
resulting combination of atoms is called a molecule (MC)L-e-
I ill), A molecular formula indicates the number and type of
atoms that make up a molecule, A molecule may consist of
two or more atoms of the same element, such as an oxygen
i oleeule or a hydrogen molecule, or two or more atoms of
different elements, such as a water molecule (Figure IS).
The molecular formula for a molecule of oxygen is () 2 . The
script 2 indicates there are two atoms of oxygen in the
ixyjren molecule. In the water molecule, H 2 0, one atom of
oxy
gen shares electrons with two atoms of hydrogen. Notice
Figure 2.3 Molecules.
$*fe^
A molecule may consist of two or more atoms of the same
element or two or more atoms of different elements.
+
Combine
to form
2 Hydrogen
molecules
(21-y
1 Oxygen
molecule
(CU
2 Water
molecules
(2 H 2 0)
Introduction to Chemistry 25
that two hydrogen molecules can combine with one oxygen
molecule to form two water molecules (Figure 2*3).
A compound is a substance containing atoms of two or
more different elements. Most of the atoms in your body are
joined into compounds, for example, water (ILO). A mole-
cule of oxygen (O?) is not a compound because it consists of
atoms of only one element,
kfree radical is an electrically charged ion or molecule
that has an unpaired electron in its outermost shell. (Most of
an atom's electrons associate in pairs,) A common example of
a free radical is superoxide^ which is formed by the addition
of an electron to an oxygen molecule. Having an unpaired
electron makes a free radical unstable and destructive to
nearby molecules. Free radicals break apart important body
molecules by either giving up their unpaired electron to or
taking on an electron from another molecule.
In our bodies, several processes can generate free radicals.
They may result from exposure to ultraviolet radiation in
sunlight or to x-rays. Some reactions that occur during
normal metabolic processes produce free radicals. More-
over, certain harmful substances, such as carbon tetrachlo-
ride (a solvent used in dry cleaning), give rise to free
radicals when they participate in metabolic reactions in the
body. Among the many disorders and diseases linked to
oxygen-derived free radicals are cancer, the buildup of
fatty materials in blood vessels (atherosclerosis), Alzheimer
disease, emphysema, diabetes mellitus, cataracts, macular
degeneration, rheumatoid arthritis, and deterioration
associated with aging. Consuming more antioxidants —
substances that inactivate oxygen-derived free radicals — is
thought to slow die pace of damage caused by free
radicals. Important dietary antioxidants include selenium,
zinc, beta-carotene, and vitamins C and E.
n
Which of the molecules shown here is a compound?
Chemical Bonds
The forces that bind the atoms of molecules and compounds
together, resisting their separation, are chemical bonds. The
chance that an atom will form a chemical bond with another
atom depends on the number of electrons in its outermost
shell, also called die valence shell. An atom with an outer
shell holding eight electrons is chemically stable, which means
it is unlikely to torm chemical bonds with other atoms.
Neon, for example, has eight electrons in its outer shell, and
for this reason it rarely forms bonds with other atoms.
The atoms of most biologically important elements do
not have eight electrons in their outer shells. Given the right
conditions, two or more such atoms can interact or bond in
w^ays that produce a chemically stable arrangement of eight
electrons in die outer shell of each atom (octet ride). Three
general types of chemical bonds are ionic bonds, covalcnt
bonds, and hydrogen bonds.
26 Chapter 2 Introductory Chemistry
Ionic Bonds
Positively charged ions and negatively charged ions are
attracted to one another. This force of attraction between
ions of opposite charges is called an ionic bond. Consider
sodium and chlorine atoms to see how an ionic bond forms
(Figure 2.4). Sodium has one outer shell electron (Figure
ka). If a sodium atom loses this electron, it is left with the
eight electrons in its second shell. However, the total number
i it protons (1 1) now exceeds the number of electrons (10). As
Figure 2.4 Ions and ionic bond formation, (a) A sodium atom
can attain the stability of eight electrons in its outermost shell by
losing its one valence electron; it then becomes a sodium ion, Na .
(b) A chlorine atom can attain the stability of eight electrons in its
outermost shell by accepting one electron; it then becomes a
chloride ion, CI, (c) An ionic bond holds Na' and CI together in the
ionic compound sodium chloride, NaCl.The electron that is donated
or accepted is colored red.
An ionic bond is the force of attraction that holds together
oppositely charged ions.
Atom
+ *
^ Electron
donated
(a) Sodium: 1 valence electron
Electron
accepted
« o
• 9
m m
Atom
Ion
(b) Chlorine: 7 valence electrons
• *
O Q
CI
• Q
(c) Ionic bond in sodium chloride (NaCI)
' Will the element potassium (K) be more likely to form an anion
[ or a cation? Why? (Hint: Look back to Figure 2.2 for the atomic
structure of K.)
a result, the sodium atom becomes a cation (KAT-T-on), a
positively charged ion. A sodium ion has a charge of 1+ and
is written NV . On the other hand, chlorine has seven outer
shell electrons (Figure 2,4b), too many to lose. But if chlorine
accepts one electron from a neighboring atom, it will have
eight electrons in its third electron shell. When this happens,
the total number of electrons (18) exceeds the number
of protons (.17), and the chlorine atom becomes an anion
(AN-I-on), a negatively charged ion. The ionic form of
chlorine is called a chloride ion. It has a charge of 1— and is
written CI". When an atom of sodium donates its sole outer
shell electron to an atom of chlorine, the resulting positive
and negative charges attract each other to form an ionic bond
(Figure 2.4c), The resulting ionic compound is sodium
chloride, written NaQ.
In the body, ionic bonds are found mainly in teeth and
bones, where they give great strength to the tissue. Most
other ions in the body are dissolved in body fluids, An ionic
compound that breaks apart into cations and anions when
dissolved is called an electrolyte (e-LEK-tro-lit) because the
solution can conduct an electric current. As you will see in
later chapters, electrolytes have many important functions.
For example, they are critical for controlling water move-
ment within the body, maintaining acid- base balance, and
producing nerve impulses.
Covalent Bonds
When a covalent bond forms, neither of the combining
atoms loses or gains electrons. Instead, the atoms form a
molecule by sharing one, two, or three pairs of their outer
shell electrons. The greater the number of electron pairs
shared between two atoms, the stronger the covalent bond,
Covalent bonds are the most common chemical bonds in the
body, and the compounds that result from them form most of
the body's structures. Unlike ionic bonds, most covalent
bonds do not break apart when the molecule is dissolved in
waiter.
It is easiest to understand the nature of covalent bonds by
considering those that form between atoms of the same
element (Figure 2.5). A single covalent bond results when two
atoms share one electron pair. For example, a molecule of
hydrogen forms when two hydrogen atoms share their single
valence electrons (Figure 2.5a), which allows both atoms to
have a full valence shell. (Recall that the first electron shell
holds only two electrons.) A double covalent bond (Figure 2.5b)
or a triple covalent bond (Figure 2.5c) results when two atoms
share two or three pairs of electrons. Notice the structural
formulas for covalently bonded molecules in Figure 2.5. The
number of lines between the chemical symbols for two atoms
indicates whether the bond is a single (-), double (=), or
triple (=) covalent bond.
The same principles of covalent bonding that apply to
atoms of the same element also apply to covalent bonds
between atoms of different elements. Methane (CH 4 ), a gas,
Introduction to Chemistry 27
Figure 2,5 Covalent bond formation. The red electrons are shared equally in (a)-(d) and unequally in (e).To the right are
simpler ways to represent these molecules. In a structural formula, each covalent bond is denoted by a straight line between
the chemical symbols for two atoms. In a molecular formula, the number of atoms in each molecule is noted by subscripts.
; >- ln
in a covalent bond, two atoms share one, two, or three pairs of electrons in the outer shell.
DIAGRAMS OF ATOMIC AND MOLECULAR STRUCTURE
®
+
9
H
(a)
Hydrogen atoms
(b)
+
Oxygen atoms
* (-3
Hydrogen molecule
Oxygen molecule
STRUCTURAL MOLECULAR
FORMULA FORMULA
H — H
=
H ?
o,
(c)
+
Nitrogen atoms
Nitrogen molecule
N^M
N s
fr
(d)
C
Carbon atom
« +
H
O O
Hydrogen atoms
„ C °H
Q O
Methane molecule
H
I
H — C
I
H
— H
CH.
(e)
Oxygen atom
+
Hydrogen atoms
■** h
Water molecule
What is the main difference between an ionic bond and a covalent bond?
O
/
i
H
H
H.O
28 Chapter 2 Introductory Chemistry
contains four separate single covalent bonds; each hydrogen atom
shares one pair of electrons with the carbon atom (Figure 2.5d).
In some covalent bonds, atoms share the electrons
equally— one atom does not attract the shared electrons
more strongly than the other atom. This is called a nonpolar
covalent bond. The bonds between two identical atoms always
are nonpolar covalent bonds (Figure 2.5a -c). Another exam-
ple of a nonpolar covalent bond is the single covalent bond
that forms between carbon and each atom of hydrogen in a
methane molecule (Figure 2.5d).
In a polar covalent bond, the sharing of electrons between
atoms is unequal — one atom attracts the shared electrons
more strongly than the other. The partial charges are indi-
cated by a lowercase Greek delta (5) with a minus or plus
sign. For example, when polar covalent bonds form, the
resulting molecule has a partial negative charge, written
S~ t near die atom that attracts electrons more strongly. At
least one other atom in the molecule then will have a partial
positive charge, written S+. A very important example of a
polar covalent bond in living systems is the bond between
oxygen and hydrogen in a molecule of water (Figure 2.5e).
Hydrogen Bonds
The polar covalent bonds that form between hydrogen atoms
and odier atoms can give rise to a third type of chemical bond,
a hydrogen bond. A hydrogen bond forms when a hydrogen
atom with a partial positive charge (8 + ) attracts die partial neg-
ative charge (S~) of neighboring electronegative atoms, most
often oxygen or nitrogen. Thus, hydrogen bonds result from
attraction of oppositely charged parts of molecules rather
than from sharing of electrons as in covalent bonds. Hydro-
gen bonds are weak when compared to ionic and covalent
bonds. Thus, they cannot bind atoms into molecules. How-
ever, hydrogen bonds do establish important links between
molecules or between different parts of a large molecule,
such as deoxyribonucleic acid (DNA). See Figure 2.15.
Chemical Reactions
A chemical reaction occurs when new bonds form and/or old
bonds break between atoms. Through chemical reactions,
body structures are built and body functions are carried out,
processes diat involve transfers of energy
Forms of Energy and Chemical Reactions
Energy (en- = in; -ergy = work) is the capacity to do work.
The two main forms of energy are potential energy, energy
stored by matter due to its position, and kinetic energy, the
energy of matter in 'motion. For example, the energy stored in
a battery or in a person poised to jump down some steps is
potential energy. When the battery is used to run a clock or
the person jumps, potential energy is converted into kinetic
energy. Chemical energy is a form of potential energy that is
stored in the bonds of molecules. In your body, chemical en-
ergy in the foods you eat is eventually converted into various
forms of kinetic energy* such as mechanical energy, used to
walk and talk, and heat energy, used to maintain body tem-
perature. In chemical reactions, breaking old bonds requires
an input of energy and forming new bonds releases energy.
Because most chemical reactions involve both breaking old
bonds and forming new bonds, the overall reaction may either
release energy or require energy.
Synthesis Reactions
When two or more atoms, ions, or molecules combine to
form new and larger molecules, the process is a synthesis
reaction. The word synthesis means "to put together." Synthe-
sis reactions can be expressed as follows:
A
+
B
Combine to form
Atom, ion, Atom, ion,
or molecule A or molecule B
*■ AB
New molecule AE
An example of a synthesis reaction is the synthesis of wa-
ter from hydrogen and oxygen molecules (see Figure 2,3):
2H-
+
o 7
Combine to form
^ 2 H,()
Two hyd n i g en ( )n e oxygen
molecules molecule
Two water
molecules
All the synthesis reactions that occur in your body are col-
lectively referred to as anabolism (a-N/VB-o-lizm). Combining
simple molecules like amino acids (discussed shortly) to form
large molecules such as proteins is an example of anabolism.
Decomposition Reactions
In a decomposition reaction, a molecule is split apart. The
word decompose means to break down into smaller parts.
Large molecules are split into smaller molecules, ions, or
atoms. A decomposition reaction occurs in this way:
AB
Molecule AB
Breaks down into
A
+
B
Atom, ion, or Atom, ion, or
molecule A molecule B
For example, under the proper conditions, a methane mole-
cule can decompose into one carbon atom and two hydrogen
molecules:
CH 4
One methane
molecule
Breaks down in in
c +
One carbon
2H 2
Two hydrogen
molecules
The decomposition reactions that occur in your body arc
collectively referred to as catabolism (ka-TAB-o-lizm). The
breakdown of large starch molecules into many small glucose
molecules during digestion is an example of cataholism.
In general, energy-releasing reactions occur as nutrients,
such as glucose, are broken down via decomposition reac-
, Some of the energy released is temporarily stored in a
al molecule called adenosine triphosphate (ATP), which
be discussed more fully later in this chapter. The energy
sferred to the ATP molecules is then used to drive the
rgy-requiring synthesis reactions that lead to die building
dy structures such as muscles and bones,
'change Reactions
[any reactions in the body are exchange reactions; they con-
£ of both synthesis and decomposition reactions. One type
exchange reaction works like this;
AB + CD — + AD + BC
The bonds between A and B and between C and D break
iomposition), and new bonds then form (synthesis)
reen A and D and between B and CI An example of an
lange reaction is:
HC1 + NaHC0 3 — * H : C0 3 + NaCl
Hydrochloric Sodium Carbonic Sodium
acid bicarbonate add chloride
Notice that the ions in both compounds have "switched
iers": The hydrogen ion (H + ) from HC1 has combined
the bicarbonate ion (HCO3 ) from NaHCO^, and the
him ion (Na + ) from NaHCO,? has combined with the
jride ion (CI) from II CI.
Reactions
Some chemical reactions proceed in only one direction, as
jreviously indicated by the single arrows. Other chemical
tactions may be reversible, Reversible reactions can go in
icr direction under different conditions and are indicated
half arrows pointing in opposite directions:
AB
Breaks down into
Combine lo form
= A + B
Some reactions arc reversible only under special condi-
. .. Water _
AB ^ A 4- B
Heat
Whatever is written above or below the arrows indicates
1 condition needed for the reaction to occur In these reac-
ts, AB breaks down into A and B only when water is added,
A and B react to produce AB only when heat is applied.
CHECKPOINT
Compare the meanings of atomic number, mass number,
ion, and molecule.
What is die significance of the valence (outer) electron
shell of an atom?
t Distinguish among ionic, covalent, and hydrogen bonds.
I. Explain the difference between anabolism and catabo-
lism. Which involves synthesis reactions?
Chemical Compounds and Life Processes 29
CHEMICAL COMPOUNDS
AND LIFE PROCESSES
objectives • Discuss the functions of water and
inorganic acids, bases, and salts.
• Define pH and explain how the body attempts to keep
pH within the limits of homeostasis.
• Discuss the functions of carbohydrates, lipids, and
proteins.
• Explain the importance of deoxyribonucleic acid
(DNA), ribonucleic acid (RNA), and adenosine triphos-
phate (ATP).
Chemicals in the body can be divided into two main classes
of compounds: inorganic and organic. Inorganic compounds
usually lack carbon, are structurally simple, and are held
together by ionic or covalent bonds. They include water,
many salts, acids, and bases. Two inorganic compounds that
contain carbon are carbon dioxide (CO?) and bicarbonate ion
(HCO} - ). Organic compounds, by contrast, always contain
carbon, usually contain hydrogen, and always have covalent
bonds. Examples include carbohydrates, lipids, proteins,
nucleic acids, and adenosine triphosphate (ATP). Organic
compounds arc discussed in detail in Chapters 19 and 20.
Large organic molecules called ?nacnmiol varies are formed by
covalent bonding of many identical or similar building-block
subunits termed monomers.
Inorganic Compounds
Water
Water is the most important and most abundant inorganic
compound in all living systems, making up 55% to 60% of
body mass in lean adults. With few exceptions, most of the
volume of cells and body fluids is water. Several of its proper-
ties explain why water is such a vital compound for life.
1. Water is an excellent solvent. A solvent is a liquid or
gas in which some other material, called a solute, has
been dissolved. The combination of solvent plus solute is
called a solution. Water is the solvent that carries
nutrients, oxygen, and wastes throughout the body. The
versatility of water as a solvent is due to its polar covalent
bonds and its "bent" shape (see Figure 2.5c), which allow
each water molecule to interact with several neighboring
ions or molecules. Solutes that are charged or contain
polar covalent bonds are hydrophilic (hydro- = water;
-philic - loving), which means they dissolve easily in
water. Common examples of hydrophilic solutes are
sugar and salt. Molecules that contain mainly nonpolar
covalent bonds, by contrast, are hydrophobic (-phobic —
fearing). They are not very water soluble. Examples of
hydrophobic compounds include animal tats and
vegetable oils.
30 Chapter 2 Introductory Chemistry
2. Water participates in chemical reactions. Because water
can dissolve so many different substances, it is an ideal
medium for chemical' reactions. Water also is an active par-
ticipant in some decomposition and synthesis reactions.
Daring digestion, for example, decomposition reactions
break down large nutrient molecules into smaller mole-
cules by die addition of water molecules. This type of reac-
tion is 'called hydrolysis (hi-DROL-i-sis; -lysis = to loosen
or break apart) (see Figure 2.8). Hydrolysis reactions en-
able dietary nutrients to be absorbed into die body.
3. Water absorbs and releases heat very slowly. Tn com-
parison to most other substances, water can absorb or
release a relatively large amount of heat with only a slight
change in its own temperature. The large amount of
water in the body thus moderates the effect of changes in
the environmental temperature, thereby helping main-
tain the homeostasis of body temperature.
4. Water requires a large amount of heat to change
from a liquid to a gas. When the water in sweat evapo-
rates from the skin surface, it takes with it large quanti-
ties of heat and provides an excellent cooling mechanism.
5. Water serves as a lubricant. Water is a major part of
saliva, mucus, and other lubricating fluids. Lubrication is
especially necessary in the thoracic and abdominal cavi-
ties, where internal organs touch and slide over one an-
other. It is also needed" at joints, where bones, ligaments,
and tendons rub against one another.
Inorganic Acids, Bases, and Salts
Many inorganic compounds can be classified as acids, bases,
or salts. An acid is a substance that breaks apart or dissociates
(dis-SQ-se-ats') into one or more hydrogen ions (H + ) when it
dissolves in water (Figure 2.6a). A base, by contrast, usually
dissociates into one or more hydroxide ions (OH") when it
dissolves in water (Figure 2.6b). A salt, when dissolved m
water, dissociates into cations and anions, neither of which is
H u or OH" (Figure 2.6c).
Acids and bases react with one another to form salts, tor
example, die reaction of hydrochloric acid (HC1) and potas-
sium hydroxide (KOH), a base, produces the salt potassium
chloride (KC1), along with water (FFO). This exchange reac-
tion can be written as follows:
HC1 + KOH
Add Base
KC1 + H 2
Salt Water
Acid- Base Balance: The Concept ofpH
To ensure homeostasis, body fluids must contain almost bal-
anced quantities of acids and bases. The more hydrogen ions
(H + ) dissolved in a solution, the more acidic the solution;
conversely, the more hydroxide ions (OH"), the more basic
(alkaline) the solution, the chemical reactions that take place
in the body are very sensitive to even small changes in the
Figure 2.6 Acids, bases, and salts, (a) When placed in water,
hydrochloric acid (HC!) ionizes into H 4 and CI/, (b) When the base
potassium hydroxide (KOH) is placed in water, it ionizes into OH
and K-. (c) When the salt potassium chloride (KCI) is placed in wa-
ter, it ionizes into positive and negative ions (K* and CI ), neither of
which isH + or OH .
Ionization is the separation of inorganic acids, bases, and salts
into ions in a solution.
,, ,„,
(a) Acid
(b) Base
(c) Salt
* The compound CaC0 3 (calcium carbonate) dissociates into a cal-
[ cium ion (Ca 2+ ) and a carbonate ion <C0 3 2 ). Is it an acid, a base, or
a salt? What about H 2 S0 4 , which dissociates into two H + and one
SO d 2 ~?
.
acidity or alkalinity of the body fluids in which they occur.
Any departure from the narrow limits of normal H + and
OH concentrations greatly disrupts body functions.
A solution's acidity or alkalinity is expressed on the pH
scale, which extends from to 14 (Figure 2.7). This scale is
based on the number of hydrogen ions in a solution. '1 he
midpoint of the pH scale is 7, where the numbers of H + and
OH" are equal. A solution with a pH of 7, such as pure wa-
ter, is neutral — neither acidic nor alkaline. A solution that
has more H + than OH" is acidic and has a pH below 7. A
solution that has more OH" than H H is basic (alkaline) and
has a pH above 7. A change of one whole number on the pH
scale represents a 10-fold change in the number of H'. At a
pH of 6, there are 10 times more H + than at a pH of 7. Put
another way, a pll of 6 is 10 times more acidic than a pH
of 7, and a pH of 9 is 100 times more alkaline than a pi I of 7,
Maintaining pH: Buffer Systems
Although the pH of various body fluids may differ, the nor-
mal limits for each are quite narrow. Table 2.2 shows the pH
values for certain body fluids compared with those of com-
mon household substances. Homeostatic mechanisms main-
tain the pH of blood between 7.35 and 7.45, so that it is
slightly more basic than pure water. Even though strong
acids and bases may be taken into the body or be formed by
body cells, the pH* of fluids inside and outside cells remains
almost constant. One important reason is the presence of
buffer systems, in which chemical compounds called buffed
convert strong acids or bases into weak acids or bases. (More
will be said about buffers in Chapter 22.)
Chemical Compounds and Life Processes 31
Figure 2.7 The pH scale. A pH below 7 indicates an acidic solution, or more H + than
OH .The lower the numerical value of the pH, the more acidic the solution because the
H concentration becomes progressively greater. A pH above 7 indicates a basic (alkaline)
solution; that is, there are more OH than H . The higher the pH, the more basic the solution.
At pH 7 (neutrality), the concentrations of H + and OH are equal.
[OH ]
10
,"14 1Q -13 10 -.2 10 11 10 -tO 1Q 9 1(r 8 1Q -7 |0 -6 1Q -S ]Q A 1() -a jqI
(moles/liter)
[K
, i
10 g 10 10"' 10
*-3
|ij l 10 ■' 10"* 10 7
10"° 10" 10
pH 1
MORE
ACIDIC
6 7 8
- NEUTRAL ■
10 11 12 13 14
MORE
BASIC (ALKALINE)
Which pH is more acidic, 6.82 or 6.91? Which pH is closer to neutral, 8.41 or 5.59?
rganic Compounds
Carbohydrates
Carbohydrates include sugars, glycogen, starches, and cellu-
ose. The elements present in carbohydrates are carbon, hy-
rogen, and oxygen. The ratio of hydrogen to oxygen atoms
sually 2:1, as in water (H 2 0), and the number of carbon
ml oxygen atoms is the same or nearly the same. For exam-
le, die molecular formula for die small carbohydrate glucose
C 6 H 12 6 . Carbohydrates are divided into three major
groups based on their size: monosaccharides, disaccharides,
nd polysaccharides. Monosaccharides and disaccharides are
rmed simple sugars, and polysaccharides are also known as
omplex carbohydrates.
Monosaccharides (mon'-6-SAK-a-rids; mono- : : one;
mchar- = sugar) are the building blocks of carbohy-
drates, in your body, the principal function of the
monosaccharide glucose is to serve as a source of chemical
energy for generating the ATP that fuels metabolic reac-
tions, Ribose and deoxyribose are monosaccharides used
to make ribonucleic acid (RNA) and deoxyribonucleic acid
(UNA), which are described on pages 38-39.
2. Disaccharides (df-SAK-a-rfds; di- = two) are simple
sugars that consist of two monosaccharides joined by a
alent bond. When two monosaccharides (smaller
molecules) combine to form a disaccharide (a larger
molecule), a molecule of water is formed and re-
moved. Such a reaction is called dehydration synthesis
Table 2.2 pH Values of Selected Substances
Substance*
pH Value
Gastric juice (digestive juice of the stomach)
1.2-3,0
Lemon juice
2.3
Grapefruit juice, vinegar, wine
3.0
Carbonated soft drink
3.0-3.5
Orange juice
3.5
Vaginal fluid
3.5-4,5
Tomato juice
4.2
Coffee
5.0
Urine
4.6-8.0
Saliva
6.35-6.85
Cow's milk
6.8
Distilled (pure) water
7,0
Blood
7.35-7,45
Semen (fluid containing sperm)
7.20-7.60
Cerebrospinal fluid (fluid associated with the nervous system)
7.4
Pancreatic juice (digestive juice of the pancreas)
7.1-8.2
Bile (liver secretion that aids fat digestion)
7,6-8,6
Milk of magnesia
10.5
Lye
14.0
Substances in the human body are highlighted in gold.
32 Chapter 2 Introductory Chemistry
(de- = from, down, or out; hydra- = water). Sucli reac-
tions occur during synthesis of large molecules. For
example, the monosaccharides glucose and fructose
combine to form the disaecharide sucrose (table sugar) as
shown in Figure 2.8. Disaccharides can be split into
monosaccharides by adding a molecule of water, a hy-
drolysis reaction. Sucrose, for example, may be hy-
drolyzed into its components of glucose and fructose by
the addition of water (Figure 2.8). Other disaccharides
include maltose (glucose + glucose), or malt sugar, and
lactose (glucose + galactose), the sugar in milk
3, Polysaccharides (pol'-e-SAK-a-rids; poly- = many) are
large, complex carbohydrates that contain tens or hun-
dreds of monosaccharides joined through dehydration syn-
thesis reactions. Like disaccharides, polysaccharides can be
broken down into monosaccharides through hydrolysis re-
actions. The main polysaccharide in die human body is
glycogen, which is made entirely of glucose units joined to-
gether in branching chains (Figure :,9). Glycogen is stored
in cells of the liver and in skeletal muscles. If energy de-
mands of the body are high, glycogen is broken down into
glucose; when energy demands are low, glucose is built
back up into glycogen. Starches are also made of glucose
units and are polysaccharides made mostly by plants. We
digest starches to glucose as another energy source. Cellu-
lose is a polysaccharide found in plant cell walls, Although
humans cannot digest cellulose, it does provide bulk
(roughage or fiber) that helps move feces through the large
intestine. Unlike simple sugars, polysaccharides usually are
not soluble in water and do not taste sweet.
Lipids
Like carbohydrates, lipids (lip- = fat) contain carbon, hydro-
gen, and oxygen. Unlike carbohydrates, they do not have a 2:1
ratio of hydrogen to oxygen. The proportion of oxygen atoms
in lipids is usually smaller than in carbohydrates, so there are
fewer polar covalent bonds. As a result, most lipids are hy-
drophobic; that is, they are insoluble in water (see page 2 { )).
The diverse lipid family includes triglycerides (tats and
oils), phospholipids (lipids that contain phosphorus), steroids,
fatty acids, and fat-soluble vitamins (vitamins A, D, E,
andK).
The most plentiful lipids in your body and in your diet
are the triglycerides (tn-GLLcer-ldes; tri- = three). At n
temperature, triglycerides may be either solids (fats) or
liquids (oils). They are the body's most highly concentrated
form of chemical energy, storing more than twice as much
chemical energy per gram as carbohydrates or proteins. Our
capacity to store triglycerides in fat tissue, called adipose
tissue, for all practical purposes, is unlimited. Excess dietary
carbohydrates, proteins, fats, and oils all have the same fate:
They are deposited in adipose tissue as triglycerides.
Figure 2.8 Dehydration synthesis and hydrolysis of a molecule of sucrose. In the dehydration
synthesis reaction (read from left to right), two smaller molecules, glucose and fructose, are joined to
form a larger molecule of sucrose. Note the loss of a water molecule. In the hydrolysis reaction (read
from right to left), the larger sucrose molecule is broken down into two smaller molecules, glucose and
fructose. Here, a molecule of water is added to sucrose for the reaction to occur
Monosaccharides are the building blocks of carbohydrates.
CH.OH
ChLGH
HOCH
iH
HO
OH HO
H
'CH.OH
01 I
H
Dehydration
synthesis
Hydrolysis
CH K OH
hLO
Glucose
(C 5 H 12 6 )
Fructose
(C 6 H 52 6 )
Sucrose
(C^H^O^)
Water
(a) Dehydration synthesis and hydrolysis of sucrose
H
H-C-OH
h 9 —
/h
l\.i
HO 6 —
I
II
CH 2 OH
m oh
OH
O
OH
HO
OH
All atoms written out
OH
Standard shorthand
v
(b) Alternate chemical structures of organic molecules (shown here is glucose)
How many carbons are there in fructose? in sucrose?
jure 2.9 Part of a glycogen molecule, the main
jlysaccharide in the human body.
Glycogen is made up of glucose units and is the storage form
k of carbohydrate in the human body.
Which body cells store glycogen?
A triglyceride consists of two types oi building blocks:
tigle glycerol molecule and three fatty acid molecules,
jree-carbon glycerol molecule forms die backbone of a
iglyceride (Figure 2.10), 'Three fatty acids are attached, by
^hydration synthesis reactions, one to each carbon of the
Ivcnol backbone. The Bitty acid chains of a triglyceride
ay be saturated, monounsaturated, or polyunsaturated.
Chemical Compounds and Life Processes 33
Saturated fats contain only single covaknt bonds between fatty
acid carbon atoms. Because they do not contain any double
bonds between fatty acid carbon atoms, each carbon atom is
saturated with hydrogen atoms (see palmitic acid and stearic
acid in Figure 2.10). Triglycerides with mainly saturated fatty
acids are solid at room temperature and occur mostly in
meats (especially red meats) and nonskim dairy products
(whole milk, cheese, and butter). They also occur in a few
tropical plants, such as cocoa, palm, and coconut. Diets that
contain large amounts of saturated fats arc associated with
disorders such as heart disease and colorectal cancer.
Monounsaturated fats (mono- = one) contain fatty acids with
dm double covaknt bond between two fatty acid carbon atoms
and thus are not completely saturated with hydrogen atoms
(see oleic acid in Figure 2.10). Olive oil, peanut oil, canola
oil, most nuts, and avocados are rich in triglycerides with
monounsaturated fatty acids. Monosaturated fats are thought
to decrease the risk of heart disease. Polyunsaturated fats
(poly- = many) contain more than one double covaknt bond
between fatty acid carbon atoms. Corn oil, safflower oil,
sunflower oil, soybean oil, and fatty fish (salmon, tuna, and
mackerel) contain a high percentage of polyunsaturated tatty'
acids. Poly saturated tats are also believed to decrease the risk of
heart disease. However, when products such as margarine and
vegetable shortening are made from polyunsaturated lats, com-
pounds called tram fatty acids are produced. Trans fatty acids,
like saturated fiats, increase the risk of cardiovascular disease.
A group of fatty acids called essential fatty acids (EFAs)
are essential to human health. However, they cannot be made
by the human body and must be obtained from foods or
Figure 2.10 Triglycerides consist of three fatty acids attached to a glycerol backbone. The fatty acids
vary in length and the number and location of double bonds between carbon atoms (C=C). Shown here is a
triglyceride molecule that contains two saturated fatty acids and one monounsaturated fatty acid.
A triglyceride consists of two types of building blocks; a single glycerol molecule and three fatty acid molecules.
Glycerol
molecule
Three fatty acid molecules
ir
H
H
OHHHHHHHHHHHHHH
II I I I l I I I l I I I I I
H-C-O-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H Palmitic acid (C t5 H 31 COOH)
I I
H H
O H H H
H
H H
H H
H H H H H
(saturate*
H H H
H H H . H H H
I ! I I I 1 I I
H-C-0-C-C-C-C-C-G-C-C-C-G-C-C-C-C-C-C-C-C-H Stearic acid (C^H^COOH
H H
H H H H H H
H
H H
(saturated)
H
OHHHHHHH
if i l l l l I i I h .
H-C-O-C-C-C-C-C-C-C-C-CV' P jl
H H H H H H H / °- n / fi ,
h
fi
V
Oleic acid (C 17 H 33 COOH)
(monounsaturated)
How many double bonds are there in a monounsaturated fatty acid?
34 Chapter 2 introductory Chemistry
supplements. Among the more important EFAs are owega-1
fatty acids, omega-6 fatty acids, and cis-fatty acids,
Omega-3 and omega-6 fatty acids are polyunsaturated fatty
acids that may have a protective effect against heart disease and
stroke by lowering total cholesterol, raising HDL (high-density
lipoproteins or "good cholesterol") and lowering LDL (low-
density lipoproteins or "bad cholesterol"). In addition, they de-
crease bone loss; reduce symptoms of arthritis due to inflamma-
tion; promote wound healing; improve certain skin disorders
(psoriasis, eczema, and acne); and improve mental functions.
Primary sources of omega-3 fatty acids include flaxseed, fatty
fish, oils that have large amounts of polyunsaturated fats, fish
oils, and walnuts. Primary sources of omega-6 fatty acids in-
clude most processed foods (cereals, breads, white rice), eggs,
baked goods, oils with large amounts of polyunsaturated fats,
and meats (especially organ meats, such as liver).
Cfr-fatty acids are nutritionally beneficial monosaturated
fatty acids that are used by the body to produce hormone-like
regulators and cell membranes. However, when or-fatty acids
are heated, pressurized, and combined with a catalyst (usually
nickel) in a process called hydrogmation, they are changed to
unhealthy tram fatty acids. Hydrogenadon is used by manufac-
turers to make vegetable oils solid at room temperature and less
likely to turn rancid. Hydrogenated or trans fatty acids are
common in commercially baked goods (crackers, cakes, and
cookies), salty snack foods, some margarines, and fried foods
(donuts and french fries). If a product label contains the words
hydrogenated or partially hydrogenated, then the product con-
tains trans tatty acids. Among die adverse effects of trans fotty
acids are an increase in total cholesterol, a decrease in HDL, an
increase in LDL, and an increase in triglycerides. These effects,
which can increase die risk of heart disease and other cardiovas-
cular diseases, are similar to those caused by saturated fats.
Like triglycerides, phospholipids have a glycerol back-
bone and two fatty acids attached to the first two carbons
(Figure 2.11a). Attached to the third carbon is a phosphate
Fiaure 2 11 Phospholipids, (a) In the synthesis of phospholipids, two fatty acids attach to the first two carbons of the glycerol
EScb^e A phosphate group links a small charged group to the third carbon in glycerol. In (b), the circle represents the po.ar head re.
gion, and the two wavy lines represent the two nonpolar tails.
| Phospholipids are the main lipids in cell membranes.
Polar head
OHHHHHHHHHHHHHHHHH
c-c-c-c-C'C-c-c-c-c-c-c-c-c-
HHHHHHHHHHHHHHH H H
OHHHHHHHH
11 i i I I i I I H
■c-c-c-c-c-c-c-c-CsV ft j
I 1 I 1 I I I
H H H H H H H
Nonpolar tails
(a) Chemical structure of a phospholipid
Phosphate group
Polar head
Polar
heads
Nonpolar tails
Polar
heads
Cell membrane
Nonpolar tails
(c) Arrangement of phospholipids
in a portion of a cell membrane
(b) Simplified way to draw a phospholipid
* How does a phospholipid differ from a triglyceride?
jgure2.12 Steroids. All steroids have four rings of carbon atoms.
Cholesterol is the starting material for synthesis of other
steroids in the body.
(a) Cholesterol (b) Estradiol (an estrogen or
female sex hormone)
Which dietary lipids are thought to contribute to atherosclerosis?
roup (P0 4 3_ ) that links a small charged group to the glyc-
erol backbone. Whereas the nonpolar fatty acids form the
■ophobic "tails" of a phospholipid, the polar phosphate
i and charged group form die hydrophilic "head"
Jgure 2. 1 I b). Phospholipids line up tails-to-tails in a double
I to make up much of the membrane that surrounds each
|[ (Figure 2.11c).
The structure of steroids, with their four rings of carbon
fas, differs considerably from that of the triglycerides and
Chemical Compounds and Life Processes 35
phospholipids. Cholesterol (Figure 2.12a), which is needed for
membrane structure, is the steroid from which other steroids
may be synthesized by body cells. For example, cells in the
ovaries of females synthesize estradiol (Figure 2.12b), which is
one of the estrogens or female sex hormones. Estrogens regu-
late sexual functions. Other steroids include testosterone (die
main male sex hormone), which also regulates sexual functions;
Cortisol, which is necessary for maintaining normal blood
sugar levels; bile salts, which are needed for lipid digestion and
absorption; and vitamin D, which is related to bone growth.
Proteins
Proteins are large molecules that contain carbon, hydrogen,
oxygen, and nitrogen; some proteins also contain sulfur.
Much more complex in structure than carbohydrates or
lipids, proteins have many roles in the body and are largely
responsible for the structure of body cells. Tor example, pro-
teins termed enzymes speed up particular chemical reactions,
other proteins are responsible for contraction of muscles,
proteins called antibodies help defend the body against
invading microbes, and some hormones are proteins.
Amino acids (a -MR -no) are the building blocks of
proteins. All amino acids have an ammo group ( — NH 2 ) at one
end and a carhoxyl group (— -COOHj at the other end. Each of
the 20 different amino acids has a different side chain (R
group) (Figure 2.13a). The covalent bonds that join amino
acids together to form more complex molecules are called
peptide hands (Figure 2.13b).
Figure 2.13 Amino acids, (a) In keeping with their name, amino acids have an amino group (shaded
blue) and acarboxyl (acid) group (shaded red). The side chain (R group) is shaded gold and is different in
each type of amino acid, (b) When two amino acids are chemically united by dehydration synthesis (read
from left to right), the resulting covalent bond between them is called a peptide bond. The peptide bond is
formed at the point where water is lost. Here, the amino acids glycine and alanine are joined to form
the dipeptide glycylalanine. Breaking a peptide bond occurs by hydrolysis (read from right to left).
Amino acids are the building blocks of proteins.
Side chain
Amino
group
Carboxyl
group
(a) Structure of an amino acid
Glycine
Dehydration
synthesis
Hydrolysis
Peptide bond
H
+ H,0
(b) Protein formation
How many peptide bonds would there be in a tripeptide?
Glycylalanine
(a dipeptide)
Water
Focus ON Welln
Herbal Si
They're Natural but
Are They Safe?
Sales of herbal supplements are boom-
ing. Preparations of ginseng and echi-
nacea stand next to bottles of vitamin C
and aspirin in medicine cabinets across
North America. But beware: Although
some herbal supplements are helpful
for specific problems, others are a
waste of money, and many can be
harmful to your health.
Does Natural Mean Safe?
Herbal supplements are preparations
made from the leaves, flowers, bark,
berries, or roots of plants. Herbal
preparations have been used through-
out the ages in cultures around the
world to relieve pain, heal wounds,
chase away evil spirits, and even to kill.
Many of die active ingredients in drugs
we use today were originally isolated
from herbs. For example, the heart drug
digitalis comes from the foxglove plant.
Anyone who knows some chem-
istry can understand why "natural"
does not necessarily mean "safe."
Natural chemicals are still chemicals.
They participate in chemical reactions
in your body. They have chemical ef-
fects in the same way that manufac-
tured drugs do.
Herbal products can't be effective
and harmless at the same time because
anything that has a physiological effect
can be harmful at some dose. All drugs
become toxic if you take too much of
them.
Handle with Care
If you want to use herbal supplements,
you must also use your head. Because
regulation of these supplements is cur-
rently fairly loose in most countries,
you can't believe everything the manu-
facturer says on the label or in advertis-
ing literature, If a product sounds too
good to be true, beware!
Tlcalth-care professionals are espe-
cially concerned about the lack of data
on the long-term safety of many herbal
products. Scientists are just beginning
to investigate the use of herbs, and our
understanding of these remedies is still
in its infancy.
Talk to Your Doctor
If you decide to try herbal supplements
for an ailment, talk to your health-care
provider to be sure you are not over-
looking beneficial medical treatments.
If you are taking any medications, ask
your pharmacist whether you should be
concerned about possible interactions
between the supplement and your
drugs. For example, it is dangerous to
lake ginkgo biloba and aspirin together,
because both have potent blood-thin-
ning effects that can lead to dangerous
bleeding.
Women who are pregnant, in-
tending to become pregnant, or nurs-
ing a baby should avoid supplements
in the same way that they avoid
drugs.
► Thin -
Your Aunt Mary tells you she is taking an herbal weight-loss supplement.
"It's natural, so it's safe, " she says, hi fact, it's not working as well as it was
ttvo weeks ago, so she is now taking double the recommended dose. What
would you say to her?
_
The union of two or more amino acids produces a
peptide (PEP-tid). When two amino acids combine, the
molecule is called a dipeptide (Figure 2.13b). Adding another
amino acid to a dipeptide produces a tripeptide. A polypeptide
contains a large number of amino acids. Proteins are
polypeptides that contain as few as 50 or as many as 2000
amino acids. Because each variation in the number ami
sequence of amino acids produces a different protein, a great
variety of proteins is possible. The situation is similar to
using an alphabet of 20 letters to form words. Each letter
would be equivalent to an amino acid, and each word would
be a different protein.
36
An alteration in the sequence of amino acids can have
I serious consequences. For example, a single substitution of
an amino acid in hemoglobin, a blood protein, can result
in a deformed molecule that produces sickle-cell disease
(page 360).
A protein may consist of only one polypeptide or sev-
eral intertwined polypeptides. A given type of protein has a
unique three-dimensional shape because of the ways that
each individual polypeptide twists and folds as associated
polypeptides come together. If a protein encounters a hos-
environment in which temperature, pH, or ion concen-
tration is significantly altered, it may unravel and lose
characteristic shape. This process is called denatiirafion
i-na'-chur-A-shun), Denatured proteins are no longer
functional A common example of denaturation is seen
in frying an egg. In a raw egg, the egg-white protein
(albumin) is soluble and the egg w r hite appears as a clear,
viscous fluid. When heat is applied to the egg, however, the
albumin denatures; it changes shape, becomes insoluble, and
\ bite.
Enzymes
we have seen, chemical reactions occur when chemical
is ire made or broken as atoms, ions, or molecules col-
with one another. At normal body temperature, such coi-
ns occur too infrequently to maintain life. Enzymes (EN-
zlnis) are the living cell's solution to this problem, because
they speed up chemical reactions by increasing the frequency
of collisions and by properly orienting the colliding mole-
les. Substances such as enzymes that can speed up chemical
factions without themselves being altered are called cata-
Lfr (KAT-n-lists). In living cells, most enzymes are proteins.
The names of enzymes usually end in -ase. All enzymes can
rouped according to the types of chemical reactions they
catalyze. For example, oxidases add oxygen, kinases add phos-
phate, dehydrogenases remove hydrogen, anhydrases remove
water ATPases split ATP, proteases break down proteins, and
breakdown lipids.
Enzymes catalyze selected reactions with great efficiency
and with many built-in controls. Three important properties
nes are their specificity, efficiency, and control.
1. Specificity* Enzymes are highly specific. Each particular
enzyme catalyzes a particular chemical reaction that
involves specific substrates, the molecules on whieh
the enzyme acts, and that gives rise to specific products,
the molecules produced by the reaction. In some cases,
the enzyme fits the substrate like a key fits in a lock. In
other cases, the enzyme changes its shape to fit snugly
around the substrate once the substrate and enzyme
come together. Each of the more than 1000 known
izymes in your body has a characteristic three-
dimensional shape with a specific surface configuration
that allows it to fit specific substrates.
2. Efficiency. Under optimal conditions, enzymes can
catalyze reactions at rates that are millions to billions of
times more rapid than those of similar reactions occur-
ring without enzymes. A single enzyme molecule can
convert substrate molecules to product molecules at rates
as high as 600,000 per second.
\, Control. Enzymes are subject to a variety of cellular
controls. Their rate of synthesis and their concentration
at any given time are under the control of a cell's genes.
Substances within the cell may either enhance or inhibit
Chemical Compounds and Life Processes 37
activity of a given enzyme. Many enzymes exist in both
active and inactive forms within the cell. The rate at
which the inactive form becomes active or vice versa is
determined by the chemical environment inside the cell.
Many enzymes require a nonprotein substance, known as
a cofactor or coenzyme, to operate properly. Ions of iron,
zinc, magnesium, or calcium are cofactors; niacin or
riboflavin, derivatives of 13 vitamins, act as coenzymes.
Figure 2.14 illustrates the actions of an enzyme.
The substrates attach to the active site of the enzyme
molecule, the specific part of the enzyme that catalyzes
the reaction, forming a temporary compound called
the enzyme -substrate complex. In this reaction, the
substrates are the disaccharide sucrose and a molecule of
water.
The substrate molecules are transformed by the re-
arrangement of existing atoms, the breakdown of the
substrate molecule, or the combination of several sub-
strate molecules into products of the reaction. Here die
products are mo monosaccharides: glucose and fructose.
After the reaction is completed and the reaction products
move away from the enzyme, the unchanged enzyme is
free to attach to another substrate molecule.
Figure 2.14 How an enzyme works.
/V An enzyme speeds up a chemical reaction without being altered
^— or consumed.
Substrates
Sucrose and
Water
Active site
of enzyme
Enzyme and substrate
come together at active
site of enzyme, forming an
enzyme-substrate complex
Products
Glucose
Fructose
When reaction is complete, Enzyme catalyzes
enzyme is unchanged and reaction and transforms
free to catalyze same reaction substrate into products
again on a new substrate
What part of an enzyme combines with its substrate?
T
38 Chapter 2 Introductory Chemistry
Enzyme deficiencies may lead to certain disorders. For ex-
ample, some people do not produce enough lactase, an en-
zyme that breaks down the disaccharide lactose into the
monosaccharides glucose and galactose. This deficiency
causes a condition called lactose intolerance, in which
undigested lactose retains fluid in the feces, and bacterial
fermentation of lactose results in the production of gases.
Symptoms of lactose intolerance include diarrhea, gas,
bloating, and abdominal cramps after consumption of milk
and other dairy products. The severity of symptoms varies
from relatively minor to sufficiently serious to require
medical attention. Persons with lactose intolerance can
take dietary enzyme supplements to aid in the digestion of
lactose.
Nucleic Acids: Deoxyribonucleic Acid (DNA)
and Ribonucleic Acid (RNA)
Nucleic acids (noo-KLE-ic), so named because they were first
discovered in die nuclei of cells, are huge organic molecules
that contain carbon, hydrogen, oxygen, nitrogen, and phos-
phorus. The Wo kinds of nucleic acids are deoxyribonucleic
acid (DNA) (de-ok'-se-ri'-bo-noo-KLE-ik) and ribonucleic
acid (RNA).
A nucleic acid molecule is composed of repeating build-
ing blocks called nucleotides. Each nucleotide of DNA
consists of three parts (Figure 2.15a):
■ One of four different nitrogenous bases, ring-shaped
molecules that contain atoms of C, H, O, and N.
■ A five-carbon monosaccharide called deoxyrihose.
■ A phosphate group (P0 4 3 " ).
In DNA, the four bases are adenine (A), thymine (T),
cytosine (C), and guanine (G). Figure 2.15b shows the
following structural characteristics of the DNA molecule:
1, The molecule consists of two strands, with crossbars.
The strands twist about each other in the form of a
double helix so that the shape resembles a twisted rope
ladder.
2, The uprights (strands) of the DNA ladder consist of al-
ternating phosphate groups and the deoxyribose portions
of the nucleotides.
3, The rungs of the ladder contain paired nitrogenous
bases, which are held together by hydrogen bonds.
Adenine always pairs with thymine, and cytosine always
pairs with guanine.
About 1000 rungs of DNA comprise a gene, a portion of
a DNA strand that performs a specific function, for example,
providing instructions to synthesize the hormone insulin.
Humans have about 30,000 genes. Genes determine which
traits we inherit, and they control all the activities that take
place in our cells throughout a lifetime. Any change that oc-
curs in die sequence of nitrogenous bases of a gene is called a
mutation. Some mutations can result in the death of a cell,
cause cancer, or produce genetic defects in future generations.
RNA, the second kind of nucleic acid, is copied from
DNA but differs from DNA in several respects. DNA is
double-stranded, RNA is single-stranded. The sugar in the
RNA nucleotide is ribose, and RNA contains the nitrogenous
base uracil (U) rather than thymine. Cells contain three dif-
ferent kinds of RNA: messenger RNA, tibosomal RNA, and
transfer RNA. Each has a specific role to perform in carrying
out the instructions encoded in DNA, as will be described in
Chapter 3 .
Adenosine Triphosphate
Adenosine triphosphate (a-DEN-6-sen tn-FOS-fat) or AT?
is the "energy currency" of living organisms. As you learned
earlier in the chapter, ATP transfers energy from energy-
releasing reactions to energy-requiring reactions that main-
tain cellular activities. Among these cellular activities ad
contraction of muscles, movement of chromosomes during
cell division, movement of structures within cells, transport
of substances across cell membranes, and synthesis of larger
molecules from smaller ones.
Structurally, ATP consists of three phosphate groups at-
tached to adenosine, which is composed of adenine and ri-
bose (Figure 2.16), The energy-transferring reaction occua
via hydrolysis: Removal of the last phosphate group (P0 4 3 ),
symbolized by (P) in die following discussion, by addition of
a water molecule liberates energy and leaves a molecule
called adenosine diphosphate (ADP). The enzyme that cat-
alyzes the hydrolysis of ATP is called ATPasc. This reaction
may be represented as follows:
ATP + H 2
Adenosine Water
triphosphate
ATPasc
+ K
Phosphate Energy
group
The energy released by the breakdown of ATP into ADP
is constantly being used by the cell. As die supply of ATP at
any given time is limited, a mechanism exists to replenish it:
The enzyme ATP synthase promotes the addition of a phos-
phate group to ADP. The reaction may be represented as
follows:
ADP +
Adenosine
diphosphate
i K
Phosphate Energy
group
. I TPsvntbuse
ATP
Adenosine
triphosphate
+ 11,0
Water
As you can see from this reaction, energy is required to pro-
duce ATE. The energy needed to attach a phosphate group to
ADP is supplied mainly by the breakdown of glucose in a
process called cellular respiration, which you will learn more
about in Chapter 20.
Chemical Compounds and Life Processes 39
Figure 2.15 DNA molecule, (a) A nucleotide consists of a nitrogenous base, a five-carbon
sugar, and a phosphate group, (b) The paired nitrogenous bases project toward the center of the
double helix. The structure is stabilized by hydrogen bonds (dotted lines) between each base
pair. There are two hydrogen bonds between adenine and thymine and three between cytosine
and guanine.
\ Nucleotides are the building blocks of nucleic acids.
Phosphate
group
O"
O H-N
N-H
O
OH Thymine (T)
Deoxyribose
H Adenine (A)
sugar
H H
(a) Components of
nucleotides
O
f-LC — 0~P=0
o-
Key to bases:
MB = Adenine
= Guanine
= Thymine
= Cytosine
Phosphate group
Deoxyribose sugar
Hydrogen bond
Strand 1 Strand 2
(b) Portion of a DNA molecule
Which nitrogenous base is not present in RNA? Which nitrogenous base is not present in DNA?
40 Chapter 2 Introductory Chemistry
Figure 2.16 Structure of ATP and ADP. The two phosphate
bonds that can be used to transfer energy are indicated in red. Most
often energy transfer involves hydrolysis of the terminal phosphate
bond of ATP.
v. AT
ATP transfers chemical energy to power cellular activities.
Adenosine
I
Q
Ribose
Phosphate groups
Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)
' What are some cellular activities that depend on energy supplied
[ by ATP?
■ CHECKPOINT
5. How do inorganic compounds differ from organic com-
pounds?
6. What functions does water perform in the body?
7. Distinguish among saturated, luonounsaturated, and
polyunsaturated fats.
8. What are the important properties of enzymes?
9. How do DNA and RNA differ?
10. Why is ATP important? |
In Chapter 1, you learned that the human body is com-
prised of various levels of organization and that the chemical
level consists of atoms and molecules. Now that you have an
understanding of die chemicals in the body, you will see in
the next chapter how they are organized to form the struc-
tures of cells and perform the activities of cells that con-
tribute to homeostasis.
STUDY OUTLINE
Introduction to Chemistry (p. 23)
1. Chemistry is the science of the structure and interactions of
matter, which is anything that occupies space and has mass.
Matter is made up of chemical elements.
2. The elements oxygen (O), carbon (C), hydrogen (H), and ni-
trogen (N) make up 96% of the body's mass.
3. Each element is made up of units called atoms, which consist of
a nucleus that contains protons and neutrons, and electrons
that move about die nucleus in electron shells. The number of
electrons is equal to the number of protons in an atom.
4. The atomic number, the number of protons, distinguishes the
atoms of one element from those of another element.
5. The combined total of protons and neutrons in an atom is its
mass number.
6. An atom that gives up or gains electrons becomes an ion — an
atom that has a positive or negative charge due to having
unequal numbers of protons and electrons.
7. A molecule is a substance that consists of two or more chemi-
cally combined atoms. The molecular formula indicates the
number and type of atoms that make up a molecule.
8. A compound is a substance that can be broken down into two
or more different elements by ordinary chemical means.
9. A free radical is a destructive, electrically charged ion or mold
cule that has an unpaired electron in its outermost shell.
10. Chemical bonds hold die atoms of a molecule together,
11. Electrons in die valence (outermost) shell are the parts of an
atom that participate in chemical reactions.
12. When outer shell electrons arc transferred from one atom
to another, the transfer forms ions, whose unlike charges at-
tract each other and form ionic bonds. Positively char
ions are called cations; negatively charged ions are called
anions.
13. In a eovalent bond, pairs of outer shell electrons are shared be-
tween two atoms.
14. Hydrogen bonds arc weak bonds between hydrogen and cer-
tain other atoms within large complex molecules such as pro-
teins and nucleic acids. They add strength and stability and
help determine the molecule's three-dimensional shape.
15. Energy is the capacity to do work. Potential energy is energy
stored by matter due to its position. Kinetic energy is the en-
ergy of matter in motion. Chemical energy is a form of poten-
tial energy stored in the bonds of molecules.
16. In chemical reactions, breaking old bonds requires energy and
forming new bonds releases energy
17, In a synthesis (anabolic) reaction, two or more atoms, ions, or
molecules combine to form a new and larger molecule. In a de-
composition (catabolic) reaction, a molecule is split apart into
smaller molecules, ions, or atoms.
18, When nutrients, such as glucose, are broken down via decom-
position reactions, some of the energy released is temporarily
stored in adenosine triphosphate (ATP) and then later used to
drive energy-requiring synthesis reactions that build body
structures, such as muscles and bones.
19; Exchange reactions are combination synthesis and decomposi-
tion reactions, Reversible reactions can proceed in both direc-
tions under different conditions.
Chemical Compounds and Life Processes (p. 29)
1, Inorganic compounds usually are structurally simple and lack
carbon. Organic substances always contain carbon, usually con-
tain hydrogen, and always have covalent bonds.
I Water is the most abundant substance in the body. It is an ex-
cellent solvent, participates in chemical reactions, absorbs and
releases heat slowly, requires a large amount of heat to change
from a liquid to a gas, and serves as a lubricant.
3, Inorganic acids, bases, and salts dissociate into ions in water. An
acid ionizes into hydrogen ions (H~); a base usually ionizes into hy-
droxide ions (OH ' ). A salt ionizes into neither H 4 nor OI I ions.
4, The pH of body fluids must remain fairly constant for the body
to maintain homeostasis. On the pi I scale, 7 represents neu-
trality Values below 7 indicate acidic solutions, and values
above 7 indicate alkaline solutions.
5, Buffer systems help maintain pH by converting strong acids or
bases into weak acids or bases.
Self-Quiz 41
6, Carbohydrates include sugars, glycogen, and starches. They
may be monosaccharides, di saccharides, or polysaccharides.
Carbohydrates provide most of the chemical energy needed to
generate ATP, Carbohydrates, and other large, organic mole-
cules, are synthesized via dehydration synthesis reactions, in
which a molecule of water is lost. In the reverse process, called
hydrolysis, large molecules are broken down into smaller ones
upon the addition of water.
7. Lipids are a diverse group of compounds that include triglyc-
erides (fats and oils), phospholipids, and steroids. Triglycerides
protect, insulate, provide energy, and are stored in adipose tis-
sue. Phospholipids are important membrane components.
Steroids are synthesized from cholesterol.
8- Proteins are constructed from amino acids. They give structure
to the body, regulate processes, provide protection, help mus-
cles to contract, transport substances, and serve as enzymes.
9. Enzymes are molecules, usually proteins, that speed up chemi-
cal reactions and are subject to a variety of cellular controls.
10. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are
nucleic acids consisting of nitrogenous bases, five-carbon sug-
ars, and phosphate groups. DNA is a double helix and is the
primary chemical in genes. RNA differs in structure and chem-
ical composition from DNA; its main function is to carry out
the instructions encoded in DNA.
11, Adenosine triphosphate (ATP) is the principal energy- transfer-
ring molecule in living systems. When it transfers energy, ATP
is decomposed by hydrolysis to adenosine diphosphate (ADP)
and (P) . ATP is synthesized from ADP and (P) using primarily
the energy supplied by the breakdown of glucose.
C
SELF-QUIZ
1. A substance that dissociates in water to form H + is called
a. a base b. a salt c. a buffer d, an acid
e, a nucleic acid
2. Ionic bonds are characterized by
a, sharing electrons between atoms
b. their ability to form strong, stable bonds
c, atoms giving away and taking electrons
d. die type of bonding formed in most organic compounds
c. an attraction between water molecules
J, If an atom has two electrons in its second electron shell and its
first electron shell is filled, it will tend to
a. lose two electrons from its second electron shell
b. lose the electrons from its first electron shell
c. lose all of die electrons from its first and second electron
shells
d. gain six electrons in its second electron shell
e. share two electrons in its second electron shell
4. Matter that cannot be broken down into simpler substances by
chemical reactions is known as
a. a molecule b. an antioxidant
c. a compound, d. a buffer e. a chemical element
5. Chlorine (CI) has an atomic number of 17. An atom of chlorine
may become a chloride ion (CI) by
a. losing one electron b. losing one neutron
c, gaining one proton d. gaining one electron
e. gaining two electrons
6. Which of the following is NOT true?
a. A substance that separates in water to form some cation
other than l\ + and some anion other than OH is known as
a salt.
b. A solution that has a pH of 9.4 is acidic,
t\ A solution with a pi I of 5 is 100 times more acidic than
distilled water, which has a pH of 7.
d, Buffers help to make the body's pF I more stable,
e, Amino acids are linked by peptide bonds.
42 Chapter 2 Introductory Chemistry
7. Which of the following organic compounds are NOT paired
with their correct sub units (building blocks)?
a. glycogen, glucose
h. proteins, monosaccharides
c. DNA, nucleotides
d. lipids, glycerol and fatty acids
e. ATP, ADP and P
8. The type of reaction by which a disaccharide is formed from
two monosaccharides is known as a
a. decomposition reaction
b. hydrolysis reaction
c dehydration synthesis reaction
d. reversible reaction
e. dissociation reaction
9. Which of die following contains die genetic code in human
cells?
a. DNA b* enzymes c. RNA d. glucose
e. ATP
10. What is the principal energy-transferring molecule in the
body?
a. ADP b. RNA c. DNA d. ATP e. NAD
11. Which of the following statements about water is NOT true?
a. It is involved in many chemical reactions in the body.
b. It is an important solvent in the human body.
c. It helps lubricate a variety of structures in the body.
d. It can absorb a large amount of heat without changing its
temperature.
e. It requires very little heat to change from a liquid to a gas.
12. The difference in H concentration between solutions widi
a pi I of 3 and a pll of 5 is that the solution with the pH of
3 has f-r.
a. 2 times more
b. 5 times more
c. 10 times more
d. 1 00 times more
e. 200 times less
13. Which of the following is NOT a true statement about enzyme
activity?
a. Enzymes form a temporary complex with their substrates
b. Enzymes arc not permanently altered by the chemical
reactions they catalyze.
c. All proteins are enzymes.
d. Enzymes are considered to be organic catalysts.
e. Enzymes are subject to cellular control.
14. For each item in the following list, place an R if it applies i
RNA or a D if it refers to DNA; use R and D if it applies to
both RNA and DNA, |
a. composed of nucleotides
b. forms a double helix
c. contains thymine
. d* contains the sugar ribose
c. contains the nitrogenous base uracil
f. is the hereditary material of cells
g. contains the sugar deoxyribose
h. is single-stranded
L contains adenine
j. contains phosphate groups
15. An organic compound that consists of C, H, and O and that
may be broken down into glycerol and fatty acids is a
a. tridveeride b, nucleic acid c. monosaccharide
d. carbohydrate e. protein
16. Why is it important to consume foods that contain antioxidants?
a. They provide an energy source for the body.
b. They help inactivate damaging free radicals.
c. They make up the body's genes.
d. They act as buffers to help maintain the blood's pH.
e. They are important solvents in the body,
17. If an enzyme is exposed to an extremely high temperature, it
wilt
a. divide b. release energy c. become an electrolyte
d* form hydrogen bonds c\ denature
18. In what form are lipids stored in the adipose (hit) tissue of the
body?
a. triglycerides b. glycogen c. cholesterol
dt polypeptides e. di saccharides
19. Approximately 96% of your body's mass is composed of which of
the following elements? Place an X beside each correct answerj
nitrogen
chlorine
sulfur
magnesium
calcium
iron
phosphorus
ci] r h ii i
sodium
oxygen
potass iu
hvdrogen
20. Match the following:
m
. a. inorganic compound
A.
glycogen
b, monosaccharide
B.
enzyme
c. polysaccharide
C
glucose
d. component of triglycerides
D.
water
e. lipase
E.
glycerol
r
CRITICAL THINKING APPLICATIONS
I,
While having a tea party, your three -year-old cousin Sabrma
added milk, lemon juice,' and lots of sugar to her tea. The tea
now has strange white lumps floating in it. What caused the
milk to curdle?
Joy is very proud of her healthy diet. "I drink only pure spring
water and eat organic foods. I have a chemical-free body,"
Sonia replied, "Ever hear of I1 2 0?" Explain the error in Joy's
reasoning.
Albert, Jr., was trying out the new Super Genius I tome Chem-
istry Kit diat he got for his birthday He decided to cheek the
Answers to Figure Questions 43
4.
pH of his secret formula: lemon juice and diet cola. The pi I
was 2.5. Next he added tomato juice. Now he has a really
disgusting mixture with a pH of 3.5. "Wow! That's twice
as strong!" Does Albert, Jr., have the makings of a "Super
Genius"? Explain.
During chemistry lab, Maria places sucrose (table sugar) in a
glass beaker, adds water, and stirs. As the table sugar disap-
pears, she loudly proclaims that she has chemically broken
down the sucrose into fructose and glucose. Ts Maria's chemical
analysis correct?
^ANSWERS TO FIGURE QUESTIONS
2.1 The atomic number of carbon is 6.
U The four most plentiful elements in living organisms are
oxygen, carbon, hydrogen, and nitrogen.
23 Water is a compound because it contains atoms of both
hydrogen and oxygen.
2.4 K is an electron donor; when it ionizes, it becomes a cation,
K , because losing one electron from the fourth electron
shell leaves eight electrons in the third shell.
2.5 An ionic bond involves the loss and gain of electrons; a cova-
lent bond involves the sharing of pairs of electrons.
2.6 CaC0 3 is a salt, and TI 2 S0 4 is an acid.
J. 7 \ pll of 6.82 is more acidic than a pi I of 6.91 . Both
pH - 8.41 and pH = 5.59 are 1.41 pH units from neutral
(pH = 7).
2,8 There are 6 carbons in fructose, 12 in sucrose.
2.9 Glycogen is stored in liver and skeletal muscle cells.
2.10 A monounsaturated fatty acid has one double bond.
2.1 1 A triglyceride has three fatty acid molecules attached to a
glycerol backbone, and a phospholipid has two fatty acid tails
and a phosphate group attached to a glycerol backbone.
2.12 The dietary lipids thought to contribute to atherosclerosis
are cholesterol and saturated fats.
2.13 A tripeptide would have two peptide bonds, each linking two
amino acids.
2.14 The enzyme's active site combines with die substrate.
2.15 Thymine is present in DNA but not in RNA, and uracil is
present in RNA but not in DNA.
2.16 A few cellular activities that depend on energy supplied by
ATP are muscular contractions, movement of chromosomes,
transport of substances across cell membranes, and synthesis
reactions.
chapter 3
CELLS
did you know?
WW by is it so important to eat a
variety of fruits and vegetables? Because your parents
wouldn't let you have dessert unless you did? Another
good reason to eat plenty of fruits and vegetables is
that these foods contain important compounds, known
as phytochemicals (literally, "plant chemicals"), which
help to keep cells healthy. Some phytochemicals block
chemicals that can came damage to cells. Others
enhance your body's production of enzymes that render
potentially cancer- causing substances harmless.
Collectively, the actions of phytochemicals promote
healthy cellular function, and prevent the types of
cellular damage associated with cancer,
aging, and heart disease.
Focus on Wellness, page 64
www.wiIey.com/college/apcentral
A
** <r
bout 200 different
types of cells compose your
body. Each cell is a living
structural and functional unit that is enclosed by a
membrane. All cells arise from existing cells by the process
of cell division, in which one cell divides into two new
cells. In your bod)', different types of cells fulfill unique
roles that support homeostasis and contribute to the
many functional capabilities of the human organism.
Cell biology is the study of cellular structure and
function. As you study the various parts of a cell
and their relationships to each other, you will learn
that cell structure and function are intimately related.
looking back to move ahead
Levels of Organization and Body Systems (page 2)
Free Radicals (page 25)
Carbohydrates (page 31)
Lipids (page 32)
Proteins (page 35)
Nucleic Acids: Deoxyribonucleic Acid (DNA) and Ribonucleic
Acid (RNA) (page 38)
A GENERALIZED VIEW
OF THE CELL
OBJECTIVE • Name and describe the three main parts
of a ce 1 1 .
Figure 3.1 is a generalized view of a cell that shows the main
cellular components. Though some body cells lack some cel-
lular structures shown in this diagram, many body cells in-
clude most of these components. For case of study; we can
divide a cell into 3 main parts: the plasma membrane, cyto-
plasm, and nucleus.
I The plasma membrane forms a cell's outer surface, sepa-
rating the cell's internal environment (inside the cell)
from its external environment (outside the cell). It regu-
lates the flow of materials into and out of a cell to main-
tain the appropriate environment for normal cellular ac-
tivities. The plasma membrane also plays a key role in
A Generalized View of the Cell 45
communication among cells and between cells and their
external environment.
■ The cytoplasm (SI-to-plazm; -plasm = formed or molded)
consists of all the cellular contents between the plasma
membrane and die nucleus, This compartment can he di-
vided into two components: cytosol and organelles, Cy-
tosol (SI-to-sol) is the fluid portion of cytoplasm that con-
sists mostly of water plus dissolved solutes and suspended
particles. Within the cytosol are several different types of
organelles (or-ga-NELZ = little organs), each of which
has a characteristic structure and specific functions.
■ The nucleus (NOO-kle-us = nut kernel) is the largest
organelle of a cell. The nucleus acts as the control cen-
ter for a cell because it contains the genes, which con-
trol cellular structure and most cellular activities.
■ CHECKPOINT
1. What are the general functions of the three main parts
of a cell?
Figure 3.1 Generalized view of a body cell.
The cell is the basic, living, structural and functional unit of the body.
Flagellum
Ciliurn
Cytoskeleton:
Microtubu!
Microfilament
Intermediate filament
Microvilli
Centrosome:
Pericentriolar
material
Centrioies
PLASMA
MEMBRANE
Lysosorne
Smooth
endoplasmic
reticulum
Peroxisome
Mitochondrion
NUCLEUS:
Chromatin
Nuclear
envelope
Nucleolus
CYTOPLASM
cytosol plus
organelles except
the nucleus)
Rough
endoplasmic
reticulum
Ribosome
Gotgi complex
i \
What are the three principal parts of a cell?
Sectional view
46 Chapter 3 Cells
THE PLASMA MEMBRANE
OBJECTIVE • Describe the structure and functions of
the plasma membrane.
The plasma membrane is a flexible yet sturdy barrier that
consists mostly of phospholipids (lipids that contain phos-
phorus) and proteins. Virtually all membrane proteins are
glycoproteins, proteins with attached carbohydrates. Other
molecules present in lesser amounts in the plasma membrane
are cholesterol and glycolipids (lipids with attached carbohy-
drates). The basic framework of die plasma membrane is die
lipid bilayer, t%vo back-to-back layers made up of three types
of lipid molecules: phospholipids, cholesterol, and glycolipids
(Figure 3.2). The proteins in a membrane are of two types—
integral and peripheral (Figure 3.2). Integral proteins extend
into or through die lipid bilayer among the fatty acid tads.
Peripheral proteins are loosely attached to the exterior or in-
terior surface of the membrane. Although many of the pro-
teins can float laterally in the lipid bilayer, each individual
protein has a specific orientation with respect to the "inside"
and "outside" faces of the membrane.
The plasma membrane allows some substances to move
into and out of the cell but restricts the passage of other sub-
stances. This property of membranes is called selective per-
meability (per'-me-a-BIL-i-te). The lipid bilayer part of the
membrane is permeable to water and to nonpolar (lipid-soluble)
molecules, such as fatty acids, fat-soluble vitamins, steroids,
oxygen, and carbon dioxide. The lipid bilayer is not perme-
able to ions and large, uncharged polar molecules such as
glucose and amino acids. These small and medium-sized
water-soluble materials may cross the membrane with the as-
sistance of integral proteins. Some integral proteins form ion
channels through which specific substances can move into
and out of cells (Figure 3.2). Other membrane proteins act as
transporters, which change shape as diey move a substance
from one side of the membrane to the other. Large molecules
such as proteins are unable to pass through the plasma mem-
brane except by transport within vesicles (discussed later in
this chapter).
Most functions of the plasma membrane depend on the
types of proteins that are present. Integral proteins called
receptors recognize and bind a specific molecule that governs
some cellular function, for example, a hormone such as in-
sulin. Some integral and peripheral proteins act as enzymes,
speeding up specific chemical reactions. Membrane glyco-
proteins and glycolipids often are cell identity markers. Tliey
enable a cell to recognize other cells of its own kind during
tissue formation, or «i recognize and respond to potentially
dangerous foreign cells.
Figure 3.2 Chemistry and structure of the plasma membrane.
IN*
The plasma membrane consists mostly of phospholipids, arranged in a bilayer, and proteins, most of which are glycoproteins.
Channel protein
Extracellular
fluid
rl
Glycoprotein:
Carbohydrate
Protein
Peripheral protein
Glycolipid:
Carbohydrate
Lipid
Phospholipids
Head
Fatty acid
tails
Head
— Lipid
bilayer
Integral proteins
Peripheral protein
Cholesterol
N Hume several functions carried out by membrane proteins.
I CHECKPOINT
2. What molecules make up the plasma membrane and
what are their functions?
3, What is meant by selective permeability?
TRANSPORT ACROSS THE
PLASMA MEMBRANE
OBJECTIVE • Describe the processes that transport
substances acro ss the plasma membrane.
Movement of materials across its plasma membrane is essen-
to the life of a cell. Certain substances must move into
the cell to support metabolic reactions. Other materials must
noved out because they have been produced by the cell
for export or are cellular waste products. Before discussing
materials move into and out of a cell, we need to under-
.,] what exactly is being moved as well as the form it needs
I e to make its journey.
About two-thirds of the fluid in your body is contained
jnside body cells and is called intracellular fluid or ICF
ra- = within). ICF is actually the cytosol of a cell. Fluid
outside body cells is called extracellular fluid or ECF {extra-
- outside). The ECF in the microscopic spaces between the
cells of tissues is interstitial fluid (in'-ter-STISH-al; inter- =
between). The ECF in blood vessels is called plasma, and
that in lymphatic vessels is called lymph.
Materials dissolved in body fluids include gases, nutrients,
ions, and other substances needed to maintain life. Any mater-
ia] dissolved in a fluid is called a solute, and die fluid in which it is
wived is the solvent. Body fluids arc dilute solutions in which
a variety of solutes are dissolved in a very familiar solvent, water,
amount of a solute in a solution is its concentration. A con-
tration gradient is a difference in concentration between two
different areas, for example, the ICF and ECE Solutes moving
i n high-concentration area (where there are more of diem)
i low-concentration area (where there are fewer of them) are
to move dawn or with the concentration gradient. Solutes
moving from a low-concentration area to a high-concentration
are said to move up or against the concentration gradient.
Substances move across cellular membranes by passive
processes and active processes. Passive processes, in which a
stance moves down its concentration gradient through
the membrane, using only its own energy of motion (kinetic
energy), include simple diffusion and osmosis. In active
pwesses, cellular energy, usually in the form of ATP, is used
push" the substance through the membrane "uphill"
| against its concentration gradient. An example is active trans-
port. Another way that some substances may enter and leave
an active process in which tiny membrane sacs re-
ferred to as vesicles are used (see Figure 3.10),
Transport Across the Plasma Membrane 47
Passive Processes
Diffusion: The Principle
Diffusion (di-FU-zhun; difftis- = spreading) is a passive
process in which a substance moves from one place to an-
other due to the substance's kinetic energy. If a particular
substance is present in high concentration in one area and in
low concentration in another area, more particles oi the sub-
stance diffuse from the region of high concentration to the
region of low concentration than diffuse in the opposite di-
rection. The diffusion of more molecules in one direction
than the other is called net diffusion. Substances undergoing
net diffusion move from a high to a low concentration, or
down their concentration gradient. After some time, equilib-
rium (e'-kwi-LIB-re-um) is reached: The substance becomes
evenly distributed throughout the solution and the concen-
tration gradient disappears.
Placing a crystal of dye in a water-filled container pro-
vides an example of diffusion (Figure 3.3). At the beginning,
the color is most intense just next to the crystal because the
crystal is dissolving and the dye concentration is greatest there.
At increasing distances, the color is lighter and lighter because
the dye concentration is lower and lower The dye molecules
undergo net diffusion, down their concentration gradient, un-
til they are evenly mixed in the water. At equilibrium the solu-
tion has a uniform colon Tn the example of dye diffusion, no
membrane was involved. Substances may also diffuse across a
membrane, if die membrane is permeable to them.
Figure 3.3 Principle of diffusion. A crystal of dye placed in a
cylinder of water dissolves (beginning), and there is net diffusion
from the region of higher dye concentration to regions of lower dye
concentration (intermediate). At equilibrium, dye concentration is
uniform throughout the solution.
^ At
At equilibrium, net diffusion stops but random movements
continue.
v
nning Intermediate Equilibrium
(a) (b) (c)
How does simple diffusion differ from facilitated diffusion?
48 Chapter 3 Cells
Now that you have a basic understanding of die nature of
diffusion, we will consider two types of diffusion: simple dif-
fusion and facilitated diffusion.
Simple Diffusion In simple diffusion, substances diffuse
across a membrane in one of two ways: lipid-soluble substances
diffuse through the lipid bilayer, and ions diffuse dirough pores
of ion channels formed by integral proteins (Figure 3.4), Lipid-
soluble substances that move across membranes by simple dif-
fusion through die lipid bilayer include oxygen, carbon dioxide,
and nitrogen gases; fatty acids; steroids; and fat-soluble vita-
mins (A, D, E, and K). Polar molecules such as water and urea
also move through the lipid bilayer. Simple diffusion through
the lipid bilayer is important in die exchange of oxygen and
carhon dioxide between blood and body cells and between
blood and air within die lungs during breathing. It also is the
transport method for absorption of lipid-soluble nutrients and
release of some wastes from body cells.
Most membrane channels are ion channels, which allow a
specific type of ion to move across the membrane by simple
diffusion 'through the channel's pore. In typical plasma mem-
branes, die most common ion channels are selective for K +
(potassium ions) or CI (chloride ions); fewer channels are
available for Na + (sodium ions) or Ca 2 ' (calcium ions). Many
ion channels are gated; that is, a portion of die channel pro-
tein acts as a "gate," moving in one direction to open the
pore and in another direction to close it (Figure 3.5). When
Figure 3.4 Simple diffusion. Lipid-soluble molecules may dif-
fuse through the lipid bilayer, and ions may diffuse through pores of
ion channels in integral proteins. Plasma membranes have channels,
formed by integral proteins, that are selective for potassium ions (K + ),
sodium ions (Na~), calcium ions (Ca 2 ), and chloride ions (CI ).
. ,
In simple diffusion there is a net (greater) movement of sub-
stances from a region of their higher concentration to a re-
gion of their lower concentration.
Extracellular fluid
Concentration
gradient
Plasma membrane
Cytosol
Ion channel o Pore
o
o Ion
O Lipid-soluble molecule
What are some examples of substances that diffuse through the
lipid bilayer?
Figure 3-5 Diffusion of potassium ions (K + ) through a gated
K + channel. A gated channel is one in which a portion of the chan-
nel protein acts as a gate to open or close the channel's pore to the
passage of ions.
& a
Channels are integral membrane proteins that allow specific
small, inorganic ions to pass across the membrane by simple
diffusion.
Extracellular fluid
Plasma membrane
Cytosol
Channel protein
Gate open
Gate closed
Details of the K + channel
Is the concentration of K + In body cells higher in the cytosol or
n the extracellular fluid?
the gates are open, ions diffuse into or out of cells, down
their concentration gradient. Gated channels are important
for the production of electrical signals by body cells.
Facilitated Diffusion Some substances that cannot dif-
fuse through the lipid bilayer or through ion channels do
cross the plasma membrane by a passive process called facili-
tated diffusion. In this process, an integral membrane protein
assists a specific substance across the membrane, The sub!
stance binds to a specific transporter on one side of the mem-
brane and is released on the other side after the transporter
undergoes a change in shape. As is true for simple diffusion,
facilitated diffusion moves a substance down a concentration
gradient — from a region of higher concentration to a region
of lower concentration — and does not require cellular en-
ergy in the form of ATP.
Substances that move across plasma membranes by facili-
tated diffusion include glucose, fructose, galactose, and some
vitamins. Glucose enters many body cells by facilitated diffu-
sion as follows (Figure 3,6):
Glucose binds to a glucose transporter protein on the
outside surface of the membrane.
As the transporter undergoes a change in shape, glucose
passes through the membrane.
The transporter releases glucose on the odier side of die
membrane.
Figure 3.6 Facilitated diffusion of glucose across a plasma
membrane. The transporter protein binds to glucose in the extra-
cellular fluid and releases it into the cytosol.
Facilitated diffusion across a membrane requires a transporter
fc— protein but does not use ATP.
Extracellular fluid
Glucose
■
» Plasma membrane
Cytosol
Glucose
transporter
0>
Glucose
gradient
O
Transport Across the Plasma WlemhTane 49
(Figure 3.7a). Notice that the cellophane now separates two
fluids having different water concentrations. As a result, wa-
ter begins to move by osmosis from the region where its con-
centration is higher (100% water in the beaker) through the
cellophane to where its concentration is lower (80% water
inside the sac). Because the cellophane is not permeable to
sucrose, however, all die sucrose molecules remain inside the
sac. As water moves into the sac, the volume of the sucrose
solution increases and the fluid rises into the glass tube (Fig-
ure 3.7b). As the fluid rises in the tube, its water pressure
forces some water molecules from the sac back into the
beaker. At equilibrium, just as many water molecules are
moving into the beaker due to the water pressure as are mov-
ing into the sac due to osmosis.
A solution containing solute particles that cannot pass
through a membrane exerts a pressure on the membrane,
called osmotic pressure. The osmotic pressure of a solution
depends on the concentration of its solute particles — the
higher the solute concentration, die higher the solution's os-
motic pressure. Because the osmotic pressure of cytosol and
How does insulin alter glucose transport by facilitated diffusion?
The selective permeability of the plasma membrane is of-
regulated to achieve homeostasis. For example, die hor-
mone insulin promotes the insertion of glucose transporters
into the plasma membranes of certain cells. Thus, the effect
iisiilin is to increase entry of glucose into body cells by
mi 1 1 of facilitated diffusion,
Osmosis
Osmosis (oz-MO-sis) is a passive process in which there is a
net movement of water through a selectively permeable
membrane. Water moves by osmosis from an area of higher
vster concentration to an area of lower water conceiitnttion (or
bm an area of lower solute concentration to an area of higher
>e concentration). Water molecules pass through plasma
membranes in two places: through the lipid bilayer and
through integral membrane proteins that function as Water
innels.
The device in Figure 3.7 demonstrates osmosis, A sac
made of cellophane, a selectively permeable membrane that
permits water but not sucrose (sugar) molecules to pass, is
filled with a solution that is 20% sucrose and 80% water,
upper part of the cellophane sac is wrapped tightly
about a stopper through which a glass tube is fitted. The sac
is then placed into a beaker containing pure (100%) water
Figure 3.7 Principle of osmosis, (a) At the start of the experi-
ment, a cellophane sac— a selectively permeable membrane that
permits water but not sucrose molecules to pass— containing a 20%
sucrose solution is immersed in a beaker of pure (100%) water.
Osmosis begins (arrows) as water moves down its concentration
gradient into the sac. (b) As the volume of the sucrose solution
increases, the solution moves up the glass tubing, The added fluid in
the tube exerts a pressure that drives some water molecules back
into the beaker. At equilibrium, osmosis has stopped because the
number of water molecules entering and the number leaving the
cellophane sac are equal.
Osmosis is the net movement of water molecules through a se-
lectively permeable membrane.
Glass tube
Rubber
stopper
Sucrose
molecules
Selectively
permeable
membrane
Water
molecules
(a) At start of experiment
(b) At equilibrium
/
Will the fluid level in the tube continue to rise until the sucrose
concentrations are the same in the beaker and in the sac?
50 Chapter 3 Cells
interstitial fluid is the same, cell volume remains constant.
Cells neither shrink clue to water loss by osmosis nor swell
due to water g;ain by osmosis.
Any solution in which cells maintain their norma] shape
and volume is called an isotonic solution {ho- = same; tomc-
= tension) (Figure 3.8). This is a solution in which the con-
centrations of solutes are the same on both sides. For exam-
ple, a 0.9% NaCl (sodium chloride, or table salt) solution,
called a normal saline solution, is isotonic for red blood cells.
When red blood cells are bathed in 0.9% NaCl, water mole-
cules enter and exit the cells at the same rate, allowing the
red blood cells to maintain their normal shape and volume.
If red blood cells are placed in a hypotonic solution (hypo-
= less than), a solution that has a lower concentration of"
solutes (higher concentration of water) than the cytosol in-
side the red blood cells (Figure 3.8), water molecules enter
the cells by osmosis taster than they leave. This situation
causes the red blood cells to swell and eventually to burst.
Rupture of red blood cells is called hemolysis (he-MOL-i-
sis). A hypertonic solution {hyper- = greater than) has a higher
concentration of solutes (lower concentration of water) than
does the cytosol inside red blood cells (Figure 3.8). When
cells are placed in a hypertonic solution, water molecules
Figure 3.8 Principle of osmosis applied to red blood cells
(RBCs). The arrows indicate the direction and degree ol water
movement into and out of the ceils. One example of an isotonic
solution for RBCs is 0.9% NaCl.
An isotonic solution is one in which cells maintain their norma!
shape and volume.
Isotonic
solution
Hypotonic
solution
Hypertonic
solution
(a) Illustrations showing direction of water movement
Normal RBC
shape
RBC undergoes
hemolysis
RBC undergoes
crenation
5 )
(b) Scanning electron micrographs (all 800x)
Will a 2% solution of NaCl cause hemolysis or crenation of
move out of the cells by osmosis faster than they enter, caus-
ing the cells to shrink Such shrinkage of red blood cells is
called crenation (kre-NA-shun).
RBCs and other body cells may be damaged or destroyed
if exposed to hypertonic or hypotonic solutions. For this
reason, most intravenous (IV) solutions, liquids infused
into the blood of a vein, are isotonic. Examples are iso-
tonic saline (0.9% NaCl) and D5W, which stands for dex-
trose 5% in water. Sometimes infusion of a hypertonic so-
lution is useful to treai patients who have cerebral edema,
excess interstitial fluid in the brain. Infusion of such a so-
lution relieves fluid overload by causing osmosis of water
from interstitial fluid into the blood. The kidneys then ex-
crete the excess water from the blood into the urine.
Hypotonic solutions, given eidier orally or through an IV,
can be used to treat people who are dehydrated. The water
in the hypotonic solution moves from the blood into inter-
stitial fluid and then into body cells to rehydrate diem. Wa-
ter and most sports drinks diat you consume to "rehydrate"
after a workout are hypotonic relative to your body cells.
RBCs?
Active Processes
Active Transport
Active transport is an active process in which cellular ener^v
is used to transport substances across die membrane against a
concentration gradient (from an area of low to an area of
high concentration).
Energy derived from splitting ATP changes the shape of |
a transporter protein, called a pump, which moves a sub-
stance across a cellular membrane against its concentration
gradient A typical body cell expends about 40% of its AIT
on active transport. Drugs that turn off ATP product inn.
such as the poison cyanide, are lethal because they shut down
active transport in cells throughout the body. Substances
transported across the plasma membrane by active transport
are mainly ions, primarily Na\ K + , H ' , Ca 2 ' , I~, and CI .
The most important active transport pump expels
sodium ions (Na 4 ) from cells and brings in potassium ions
(K 1 ). The pump protein also acts as an enzyme to split ATP,
Because of the ions it moves, this pump is called the sodium-
potassium (Na + /K 4 ) pump. All cells have thousands of
sodium-potassium pumps in their plasma membranes. These
pumps maintain a low concentration of sodium ions in the
cytosol by pumping Na + into die extracellular fluid against
the Na 4 concentration gradient. At the same time, the pump
moves potassium ions into cells against the K H concentration
gradient. Because K + and Na 4 slowly leak back across the
plasma membrane down their gradients, the sodium-
potassium pumps must operate continually to maintain a low
concentration of Na 1 and a high concentration ofK 1 in the
cytosol. These differing concentrations are crucial for osmotic
nee of die two fluids and also for the ability of some cells
^generate electrical signals such as action potentials.
Figure 3.9 shows how the sodium-potassium pump
operates.
Three sodium ions (Na + ) in the cytosol bind to the
pump protein.
A NV binding triggers the splitting of ATP into ADP plus
a phosphate group ((?)), which also becomes attached to
the pump protein. This chemical reaction changes the
shape of the pump protein, expelling the three Na ' into
the extracellular fluid. The changed shape of the pump
protein then favors binding of two potassium ions (K + ) in
the extracellular fluid to the pump protein.
The binding of K f causes the pump protein to release
the phosphate group, which causes the pump protein to
return to its original shape,
A As the pump protein returns to its original shape, it re-
leases the two IC into the cytosoL At this point, the
pump is ready again to bind Na + , and the cycle repeats.
Transport in Vesicles
A vesicle (VES-i-kul) is a small round sac formed by budding
I off from an existing membrane. Vesicles transport substances
from one structure to another within cells, take in substances
from extracellular fluid, and release substances into extracel-
lular fluid. Movement of vesicles requires energy supplied by
ATP and is therefore an active process. The two main types
I of transport in vesicles between a cell and the extracellular
fluid that surrounds it are (1) endocytosis (endo- = within), in
Transport Across the Plasma Membrane 51
which materials move into a cell in a vesicle formed from the
plasma membrane, and (2) exocytosis (exo~ « out), in which
materials move out of 'a cell by the fusion of a vesicle formed
inside a cell with the plasma membrane,
ENDOCYTOSIS Substances brought into the cell by endocy-
tosis are surrounded by a piece of the plasma membrane,
which buds off inside the cell to form a vesicle containing die
ingested substances. The two types of endocytosis we will
consider are phagocytosis and bulk-phase endocytosis.
1. Phagocytosis, In phagocytosis (fag'-6-si-TO-sis; phago-
- to eat), large solid particles, such as whole bacteria or
viruses or aged or dead cells, are taken in by the cell (Fig-
ure 3.10), Phagocytosis begins as the particle binds to a
plasma membrane receptor, causing the cell to extend
projections of its plasma membrane and cytoplasm, called
pseudopods (SOO-do-pods; pseudo- = false; -pods = feet).
Two or more pseudopods surround the particle, and por-
tions of their membranes fuse to form a vesicle that en-
ters the cytoplasm. The vesicle fuses with one or more
Ivsosomes. and lysosomal enzymes break down the in-
gested material. In most cases, any undigested materials
remain indefinitely in a vesicle called a residual body.
Phagocytosis occurs only in phagocytes, cells that are
specialized to engulf and destroy bacteria and other for-
eign substances. Phagocytes include certain types of
white blood cells and macrophages, which are present in
most body tissues. The process of phagocytosis is a vital
defense mechanism that helps protect the body from
disease.
Figure 3.9 Operation of the sodium-potassium pump. Sodium ions (Na + ) are expelled from the cell,
and potassium ions (K~) are imported into the cell. The pump does not work unless Na and ATP are present In
the eytosof and K ( is present in the extracellular fluid.
| The sodium-potassium pump maintains a low intracellular concentration of Na + .
Na +
gradient
Extracellular fluid
NaVK + ATPase
3 Na + expelled
V,
gradient
2K 1
imported
What is the role of ATP in the operation of this pump?
j
52 Chapters Cells
Figure 3.10 Phagocytosis.
\ phagocytosis is a vital defense mechanism that helps protect
/ the body from disease.
Plasma membrane
Pseudopods
Microbe
Receptor
Digestive
enzymes
Fusion of lysosome
and vesicle
Digestion by
lysosomal enzymes
/
Residual body
5 )
What triggers pseudopod formation'
2* Bulk-phase Endocytosis. In hulk-phase endocytosis
(pinocytosisjy cells take up tiny droplets of extracellular
fluid. The process occurs in most body cells and takes in any
and all solutes dissolved in the extracellular fluid. During
bulk-phase endocytosis the plasma membrane folds inward
and tonus a vesicle containing a droplet of extracellular fluid.
The vesicle detaches or "pinches off' from the plasma
membrane and enters the cytosol. Within the cell, the
vesicle fuses with a lysosome, where enzymes degrade the
engulfed solutes. The resulting smaller molecules, such
as amino acids and fatty acids, leave the lysosome to be
used elsewhere in the cell.
EXOCYTOSIS In contrast with endocytosis, which brings
materials into a cell, exocytosis results in secretion, the libera-
tion of materials from a cell. All cells carry out exocytosis, but
it is especially important in two types of cells: (1) secretory
cells that liberate digestive enzymes, hormones, mucus, or
other secretions; (2) nerve cells that release substances
called neurotransmitters via exocytosis (see Figure " on
page 235). During exocytosis, membrane-enclosed vesicles
called secretory vesicles form inside the cell, fuse with the
plasma membrane, and release their contents into the extra-
cellular fluid.
Segments of the plasma membrane lost through endocy-
tosis are recovered or recycled by exocytosis. The balance be-
tween endocytosis and exocytosis keeps the surface area ol a
cell's plasma membrane relatively constant.
Table 3.1 summarizes the processes by which materials
move into and out of cells.
■ CHECKPOINT
4. What is the key difference between passive and active
processes?
5. How does diffusion dirough membrane channels com-
pare to facilitated diffusion :
6. In what ways are endocytosis and exocytosis similar ;md
different?
CYTOPLASM
OBJECTIVE • Describe the structure and functions of
cytoplasm, cytosol, and or ganelles.
Cytoplasm consists of all of the cellular contents between the
plasma membrane and the nucleus and includes both cytosol
and organelles.
Cytosol I
The cytosol (intracellular fluid) is the fluid portion of the r,
toplasm that surrounds organelles and accounts lor about
55% of the total cell volume. Although cytosol varies in com-
position and consistency from one part of a cell to another,
typically it is 75% to 90% water plus various dissolved
solutes "and suspended particles. Among these are variojJ
ions, glucose, amino acids, fatty acids, proteins, lipids, ATP,
and waste products. Some cells also contain lipid droplets ili.i:
contain triglycerides and glycogen granules, clusters of glycogen
molecules. The cytosol is die site of many of the chemical reac-
tions diat maintain cell structures and allow cellular growth.
Organelles ]
Organelles are specialized structures inside cells that have
characteristic shapes and specific functions. Each type of
organelle is a functional compartment where specific
processes take place, and each has its own unique set of en-
zymes.
Transport Process
Passive Processes
Diffusion
Simple diffusion
Diffusion through the
lipid bilayer
Diffusion through
membrane channels
Facilitated diffusion
Osmosis
Active Processes
Active Transport
Transport in Vesicles
Endocytosis
Phagocytosis
Bulk-phase endocytosis
Exocytosis
Cytoplasm 53
Table 3.1 Transport of Materials Into and Out of Cells
Description
Movement of substances down a concentration gradient until equilibrium is
reached; do not require cellular energy in the form of ATP.
Passive movement of a substance through the lipid bilayer of the plasma
membrane.
Passive movement of a substance down its gradient through channels that
span a lipid bilayer; some channels are gated.
Passive movement of a substance down its concentration gradient aided by
membrane proteins known as transporters.
Movement of water molecules across a selectively permeable membrane
from an area of higher water concentration to an area of lower water
concentration.
Movement of substances against a concentration gradient; requires cellular
energy in the form of ATP.
Transport in which cell expends energy to move a substance across the
membrane against its concentration gradient aided by membrane proteins
that act as pumps; these integral membrane proteins use energy supplied
by ATP.
Movement of substances into or out of a cell in vesicles that bud from the
plasma membrane; requires energy supplied by ATR
Movement of substances into a cell in vesicles.
"Cell eating"; movement of a solid particle into a cell after pseudopods
engulf it.
"Cell drinking"; movement of extracellular fluid into a cell by infolding of
plasma membrane.
Movement of substances out of a cell in secretory vesicles that fuse with
the plasma membrane and release their contents into the extracellular fluid.
Substances Transported
Lip id -soluble molecules: oxygen, carbon
dioxide, and nitrogen gases; fatty acids,
steroids, and fat-soluble vitamins (A, D, E,
K). Polar molecules: water and urea.
Mainly ions: K\ CI", Na\ and Ca 2 '. Water.
Glucose, fructose, galactose, and some
vitamins.
Water.
Na + , K\ Ca 2 \ H+, 1 , CI", and other ions.
Bacteria, viruses, and aged or dead cells.
Solutes in extracellular fluid.
Neurotransmitters, hormones, and digestive
enzymes.
The Cytoskeleton
ending throughout the cytosol, the cytoskeleton is a net-
work of three different types of protein filaments: microfila-
ments, intermediate filaments, and microtubules (Figure 3.1 1).
The thinnest elements of the cytoskeleton are the micro-
foments, which are concentrated at the periphery ol a cell
and contribute to the cells strength and shape (Figure 3.1 la).
Microfilaments have two general functions: providing me-
chanical support and helping generate movements. They also
anchor the cytoskeleton to integral proteins in the plasma
membrane and provide support for microscopic, fingerlike
projections of the plasma membrane called microvilli (micro-
small; -villi = tufts of hair; singular is 'microvillus). Because
they greatly increase the surface area of the cell, microvilli
are abundant on cells involved in absorption, such as the cells
that line the small intestine. Some microfilaments extend be-
yond die plasma membrane and help cells attach to one an-
other or to extracellular materials.
With respect to movement, microfilaments are involved
in muscle contraction, cell division, and cell locomotion.
AUcrofilament-assisted movements include the migration of
embryonic cells during development, the invasion of tissues
by white blood cells to fight infection, and the migration of
skin cells during wound healing.
As their name suggests, intermediate filaments are
thicker than microfilaments but thinner than microtubules
(Figure 3.1 lb). They are found in parts of cells subject to
tension (such as stretching), help hold organelles such as the
nucleus in place, and help attach cells to one another.
The largest of the cytoskeletal components, micro-
tubules are long, hollow tubes (Figure 3.1 lc). Microtubules
help determine cell shape and function in both the move-
ment of organelles, such as secretory vesicles, within a cell
and the migration of chromosomes during cell division.
They also are responsible for movements of cilia and ia-
gella.
54 Chapter 3 Cells
Figure 3.11 Cytoskeleton.
Extending throughout the cytoplasm, the cytoskeleton is a net-
. work of three kinds of protein filaments: microfilaments, in-
termediate filaments, and microtubules.
Microvillus
MICROFILAMENTS ^Jji
Nucleus
a) Microfilament
INTERMEDIATE
FILAMENTS
(b) Intermediate filament
MICROTUBULES
Centrosome
kK>
(c) Microtubule
Which eytoskeietal components help form the structure of centri-
j oles, cilia, and ffagella?
Centrosome
The centrosome i located near the nucleus, lias two compo-
nents — a pair of centrioles and pericentriolar material
(Figure 3.12). The two centrioles are cylindrical structures,
each of which is composed of nine clusters of three micro-
tubules (a triplet) arranged in a circular pattern. Surrounding
the centrioles is die pericentriolar materia/ (per'-e-sen'-tre-O-
lar), containing hundreds of ring-shaped proteins called tubu-
lins. The tubulins are the organizing centers for growth of
die mitotic spindle, which plays a critical role in cell division,
and for microtubule formation in nondividing cells.
Cilia and Flagella
Microtubules are the main structural and functional compo-
nents of cilia and flagella, both of which are motile projec-
tions of die cell surface. Cilia (SIL-e-a; singular is cilium =
eyelash) are numerous, short, hairlike projections that extend
from the surface of the cell (see Figure 3.1). In die human
body, cilia propel fluids across the surfaces of cells that are
firmly anchored in place. The coordinated movement of
many cilia on the surface of a cell causes a steady movement
of fluid along die cells surface. Many cells of die respiratory
tract, for example, have hundreds of cilia that help sweep for-
eign particles trapped in mucus away from the lungs. Their
movement is paralyzed by nicotine in cigarette smoke. For this
reason, smokers cough often to remove foreign particles from
their airways. Cells that line the uterine (fallopian) tubes also
have cilia that sweep oocytes (egg cells) toward the uterus.
Flagella (fla-JEL-a; singular is fJ&geUum = whip) are sim-
ilar in structure to cilia but are much longer (see Figure 5.1),
Flagella usually move an entire cell. The only example of a
flagelluni in die human body is a sperm cell's tail, which pro-
pels the sperm toward its possible union with an oocyte.
Ribosomes
Ribosomes (Rl-bo-soms; -somes = bodies) are the sites of pro-
tein synthesis. Ribosomes are named for their high content of
r/Aonucleic acid (RNA). Besides ribosomal RNA (rRNA),
these tiny organelles contain ribosomal proteins. Structurally,
a ribosome consists of two subunits, large and small, one
about half the size of the other (Figure 3. 1 3). The large and
Figure 3.12 Centrosome.
The pericentriolar material of a centrosome organizes the mitotic
pBV^ spindle during cell division.
Pericentriolar material
Centrioles
Microtubules (triplets)
T)
What are the components of the centrosome?
Figure 3.13 Ribosomes,
Rjbosomes, the sites of protein synthesis, consist of a large sub-
kk unit and a small subunit.
j
▼
Large subunit Small subunit
Complete
functional
ribosome
Where are ribosomal subunits synthesized and assembled?
Cytoplasm 55
incorporated into organelle membranes or the plasma mem-
brane. Thus, rough ER is a factory for synthesizing secretory
proteins and membrane molecules.
Smooth ER extends from the rough ER to form a net-
work of membranous tubules (Figure 3.14). As you may al-
ready have guessed, smooth ER appears "smooth" because it
lacks ribosomes. Smooth ER is where fatty acids and steroids
such as estrogens and testosterone are synthesized. In liver
cells, enzymes of the smooth ER also help release glucose
into the bloodstream and inactivate or detoxify a variety of
drugs and potentially harmful substances, including alcohol,
pesticides, and carcinogens (cancer-causing agents).
One of the functions of smooth ER, as noted earlier, is to
detoxify certain drugs. Individuals who repeatedly take
such drugs, such as the sedative phenobarbital, develop
changes in the smooth ER in their liver cells. Prolonged
administration of phenobarbital results in increased toler-
ance to the drug; the same dose no longer produces the
same degree of sedation. With repeated exposure to the
drug, the amount of smooth ER and its enzymes increases
to protect the cell from its toxic effects. As the amount of
smooth ER increases, higher and higher dosages of the
drug are needed to achieve die original effect.
••:• ■ ".
small subunits arc made in the nucleolus of the nucleus.
Later, they exit the nucleus and are assembled in the cyto-
plasm, where they form a functional ribosome*
Some ribosomes are attached to the outer surface of the
nuclear membrane and to an extensively folded membrane
called the endoplasmic reticulum. These ribosomes synthe-
size proteins destined for specific organelles, tor insertion in
the plasma membrane, or for export from the cell. Other ri-
bosomes are "free" or unattached to other cytoplasmic struc-
tures. Free ribosomes synthesize proteins used in the cytosol,
Ribosomes are also located within mitochondria, where they
synthesize mitochondrial proteins.
Endoplasmic Reticulum
The endoplasmic reticulum (en'-do-PLAS-mik rc-TIK-u-
luni; -pliismic = cytoplasm; reticulum = network) or ER is a
network of folded membranes (Figure 3.14). The ER extends
throughout the cytoplasm and is so extensive that it consti-
tutes more than half of the membranous surfaces within the
cytoplasm of most cells.
Cells contain two distinct forms of ER that differ in
structure and function. Rough ER extends from the nuclear
envelope (membrane around the nucleus) and appears
hough" because its outer surface is studded with ribosomes.
Proteins synthesized by ribosomes attached to rough ER en-
ter the spaces within the ER for processing and sorting.
These molecules (glycoproteins and phospholipids) may be
Figure 3.14 Endoplasmic reticulum (ER).
V, The ER is a network of folded membranes that extend through-
js. out the cytoplasm and connect to the nuclear envelope.
Nuclear
envelope
Rough ER
Smooth ER
< \
How do rough ER and smooth ER differ structurally and
functionally?
56 Chapter 3 Cells
Golgi Complex
After proteins are synthesized on a ribosome attached to
rough ER, they usually are transported to another region of
the cell. The first step in the transport pathway is through an
organelle called the Golgi complex (GOL-je). It consists of 3
to^20 cisterns (SIS-terns = cavities), flattened membranous
sacs with bulging edges, piled on each other like a stack of
pita bread (Figure 3.15). Most cells have several Golgi com-
plexes. The Golgi complex is more extensive in cells that se-
crete proteins.
The main function of the Golgi complex is to modify and
package proteins. Proteins synthesized by ribosomes on
rouoh ER enter the Golgi complex and are modified to form
glycoproteins and lipoproteins. Then, they are sorted and
packaged. Some of the processed proteins are discharged
from the cell by exocytosis. Certain cells of the pancreas re-
lease the hormone insulin this way. Other processed proteins
become part of the plasma membrane as existing parts of the
membrane are lost. Still other processed proteins become in-
corporated into organelles called lysosomes.
Lysosomes
Lysosomes (Ll-so-soms; fyso- = dissolving; -somes = bodies)
are membrane-enclosed vesicles (see Figure 3.1) that may
contain as many as 60 different digestive enzymes; these en-
Figure 3.15 Golgi complex.
Most proteins synthesized by ribosomes attached to rough ER
pass through the Golgi complex for processing.
Cistern
Transfer vesicle
* What types of body cells are likely to have extensive Golgi com-
plexes?
zymes can break down a wide variety of molecules once die
lysosome fuses with vesicles formed during endocytosis. The
lysosomal membrane allows the final products of digestion,
such as monosaccharides, fatty acids, and amino acids, to be
transported into the cytosol.
Lysosomal enzymes also help recycle worn-out struc-
tures. A lysosome can engulf another organelle, digest it, and
return the digested components to the cytosol for reuse. Tn
this way, old organelles are continually replaced. The process
by which worn-out organelles are digested is called an-
tophagy (aw-TOF-a-je; auto- = self; -pbagy = eating). Dur-
ing autophagy, the organelle to be digested is enclosed by a
membrane derived from the ER to create a vesicle that then
fuses with a lysosome. In this way, a human liver cell, for ex-
ample, recycles about half its contents every week. Lysosomal
enzymes may also destroy the entire cell, a process known as
autolysis (aw-TOL-i-sis). Autolysis occurs in some patholog-
ical conditions and also is responsible for the tissue deteriora-
tion that occurs just after death.
Some disorders are caused by faulty or absent lysosomal
enzymes, For instance, Tay-Sachs disease, which most
often affects children of Ashkenazi (eastern European Jew-
ish) descent, is an inherited condition characterized by the
absence of a single lysosomal enzyme. This enzyme nor-
mally breaks down a membrane glycolipid called ganglio-
side Gm2 that is especially prevalent in nerve cells. As the
excess ganglioside G M2 accumulates, because it is not bro-
ken down, the nerve cells function less efficiently. Chil-
dren with Tay-Sachs disease typically experience seizures
and muscle rigidity. They gradually become blind, de-
mented, and uncoordinated and usually die before the age
of 5. Tests can now reveal whether an adult is a carrier of
the defective gene.
Peroxisomes
Another group of organelles similar in structure to lyso-
somes, but smaller, are called peroxisomes (per-OK-si-soms;
peroxi- = peroxide; see Figure 5.1). Peroxisomes contain sev-
eral oxidases, which are enzymes that can oxidize (remove hy-
drogen atoms from) various organic substances. For example,
amino acids and fatty acids are oxidized in peroxisomes as
part of normal metabolism. In addition, enzymes in peroxi-
somes oxidize toxic substances. Thus, peroxisomes are very
abundant in the liver, where detoxification of alcohol and
other damaging substances takes place. A byproduct of the
oxidation reactions is hydrogen peroxide (H2O2), a poten-
tially toxic compound. However, peroxisomes also contain an
enzyme called attahise that decomposes the H 2 C> 2 . Because
the generation and degradation of H 2 2 occurs within the
same organelle, peroxisomes protect other parts of the cell
from the toxic effects of HjOj.
Proteasomes
iough lysosomes degrade proteins delivered to them in
ides, proteins in the eytosol also require disposal at cer-
tain limes in the life of a cell Continuous destruction of un-
tied, damaged, or faulty proteins is die function of tiny
barrel-shaped structures called proteasomes (PRO-te-a-s5mes
• protein bodies). A typical body cell contains many thou-
of proteasomes, in both the eytosol and the nucleus.
Proteasomes were so named because they contain myriad pro-
,-ff, enzymes that cut proteins into small peptides. Once the
enzymes of a proteasome have chopped up a protein into
smaller chunks, odier enzymes then break down die peptides
into amino acids, which can be recycled into new proteins.
Mitochondna
they arc the site of most ATP production, the
lowerhouses" of a cell are its mitochondria (ml-to-KON-
Igure 3.16 Mitochondrion,
Within mitochondria, chemical reactions generate most of a
,: cells ATP.
Outer mitochondrial membrane
Inner mitochondrial membrane
Matrix
Cristae
Enzymes
Nucleus 57
dre-a; mito- - thread; -chomdria = granules; singular is mito-
chondrion). A cell may have as few as one hundred or as many
as several thousand mitochondria, depending on how active
the cell is. For example, active cells such as those found in
muscles, the liver, and kidneys use ATP at a high rate and
have large numbers of mitochondria, A mitochondrion con-
sists of two membranes, each of which is similar in structure
to the plasma membrane (Figure 3.16). The miter mitochon-
drial membrane is smooth, but the inner mitochondrial mem-
brane is arranged in a series of folds called cristae (KRIS-te;
singular is crista = ridge). The large central fluid-filled cavity
of a mitochondrion, enclosed by the inner membrane and
cristae, is the matrix. The elaborate folds of die cristae pro-
vide an enormous surface area for a series of chemical reac-
tions that provide most of a cell's ATP. Enzymes that catalyze
these reactions arc located in the matrix and on the cristae.
Mitochondria also contain a small number of genes and a few
ribosomes, enabling them to synthesize some proteins.
■ CHECKPOINT
7. What does cytoplasm have that eytosol does not?
8. What is an organelle?
9. Describe the structure and function of ribosomes, the
Golgi complex, and mitochondria.
NUCLEUS
OBJECTIVE • Describe the structure and functions of
the nucleus.
How do the cristae of a mitochondrion contribute to its
ATP-producing function?
The nucleus is a spherical or oval structure that usually is the
most prominent feature of a cell (Figure J. 17). Most body
cells have a single nucleus, although some, such as mature
red blood cells, have none. In contrast, skeletal muscle cells
and a few other types of cells have several nuclei. A double
membrane called the nuclear envelope separates the nucleus
from the cytoplasm. Both layers of the nuclear envelope are
lipid bilayers similar to the plasma membrane. The outer
membrane of the nuclear envelope is continuous with the
rough endoplasmic reticulum and resembles it in structure.
Many openings called nuclear pores pierce the nuclear enve-
lope. Nuclear pores control the movement of substances be-
tween the nucleus and the cytoplasm.
Inside the nucleus are one or more spherical bodies
called nucleoli (noo'-KLE-6-li; singular is nucleolus). These
clusters of protein, DNA, and RNA are the sites of assembly
of ribosomes, which exit the nucleus through nuclear pores
and participate in protein synthesis in the cytoplasm. Cells
that synthesize large amounts of protein, such as muscle and
liver cells, have prominent nucleoli.
58 Chapters Cells
Figure 3.17 Nucleus.
The nucleus contains most of a cell's genes, which are located on chromosomes.
Chromatin Nuclear envelope
Rough endoplasmic
reticulum
Nuclear
envelope
Nuclear pore
Details ot the nucleus
Details of the nuclear envelope
r
What are the functions of nuclear genes?
Also within the nucleus are most of the cell's hereditary
units, called genes, which control cellular structure and di-
rect most cellular activities. The nuclear genes arc
arranged along chromosomes (chromo- = colored) (see Fig-
ure 3.21). Human somatic (body) cells have 46 chromosomes,
23 inherited from each parent In a cell that is not dividing, the
46 chromosomes appear as a diffuse, granular mass, which is
called chromatin (Figure 3.17). The total genetic information
carried in a cell or organism is called its genome.
In the last decade of die twentieth century, the genomes
of humans, mice, fruit flies, and more than 50 microbes were
sequenced. As a result, research in the field of genomics, the
study of the relationships between die genome and the bio-
logical functions of an organism, has flourished. The Human
Genome Project began in 1990 as an effort to sequence all of
the nearly 3.2 billion nucleotides of our genome and was
completed in April 2003, Scientists now know that the total
number of genes in the human genome is about 30,000, In-
formation regarding the human genome and how it is af-
fected by the environment seeks to identify and discover the
functions of the specific genes that play a role in genetic dis-
eases. Genomic medicine also aims to design new drugs and
to provide screening tests to enable physicians to provide
more effective counseling and treatment for disorders with
significant genetic components such as hypertension (high
blood pressure), obesity, diabetes, and cancer.
The main parts of a cell and their functions are summa-
rized in Table 3.2.
■ CHECKPOINT
10. Why is the nucleus so important in the life of a cell?
GENE ACTION: PROTEIN SYNTHESIS
OBJECTIVE • Outline the sequence of events involved
in protein synthesis.
Although cells synthesize many chemicals to maintain homer'
sis, much of the cellular machinery is devoted to protein produc-
tion. Cells constantly synthesize large numbers of diverse pro-
teins. The proteins, in turn, determine the physical and chemical
characteristics of cells and, on a larger scale, of organisms.
The DNA contained in genes provides the instructions for
making proteins. To synthesize a protein, die information con-
tained in a specific region of DNA is first transcribed (copied) to
produce a specific molecule of RNA (ribonucleic acid). The RNA
then attaches to a ribosome, where the information contained in
die RNA is translated into a corresponding specific sequence of
amino acids to form a new protein molecule (Figure 3,18 on
page 60).
Information is stored in DNA in four types of nucleotides,
die repeating units of nucleic acids (see Figure 2, 1 5 on page 39).
Each sequence of three DNA nucleotides is transcribed as a
complementary (corresponding) sequence of three RNA nu-
cleotides. Such a sequence of three successive DNA nucleotides
is called a base triplet. Each DNA base triplet is transcribed as a
complementary sequence of three successive RNA nucleotides,
The three successive RNA nucleotides are called a codon. Wild
translated, a given codon specifies a particular amino acid.
Transcription
During transcription, which occurs in the nucleus, the ge-
netic information in DNA base triplets is copied into a com-
Part
Plasma Membrane
Cytoplasm
Cytosol
Organelles
Cytoskeleton
Centrosome
Cilia and flagella
Ribosome
Endoplasmic
reticulum (ER)
Golgj complex
Lysosome
peroxisome
Proteasome
Mitochondrion
Nucleus
Gene Action: Protein Synthesis 59
Table 3.2 Cell Parts and Their Functions
Structure
Functions
Composed of a lipid bilayer consisting of
phospholipids, cholesterol, and glycolipids with
various proteins inserted; surrounds cytoplasm.
Protects cellular contents; makes contact with other cells; contains
channels, transporters, receptors, enzymes, and cell-identity
markers; mediates the entry and exit of substances.
Cellular contents between the plasma membrane
and nucleus, including cytosol and organelles.
Composed of water, solutes, suspended particles,
lipid droplets, and glycogen granules.
Specialized cellular structures with characteristic
shapes and specific functions.
Network composed of three protein filaments:
microfilaments, intermediate filaments, and
microtubules.
Paired centrioles plus pericentriolar material.
Motile cell surface projections with inner core of
microtubules.
Composed of two subunits containing ribosomal
RNA and proteins; may be free in cytosol or
attached to rough ER.
Membranous network of folded membranes.
Rough ER is studded with ribosomes and is
attached to the nuclear membrane; smooth ER
lacks ribosomes.
A stack of 3-20 flattened membranous sacs
called cisterns.
Vesicle formed from Golgi complex; contains
digestive enzymes.
Vesicle containing oxidative enzymes.
Tiny structure that contains proteases, enzymes
that cut proteins.
Consists of an outer and inner membranes, cristae,
and matrix.
Site of all intracellular activities except those occurring in the
nucleus.
Medium in which many of the cell's chemical reactions occur.
Each organelle has one or more specific functions.
Maintains shape and general organization of cellular
contents; responsible for cell movements.
Pericentriolar material is organizing center for microtubules and
mitotic spindle.
Cilia move fluids over a cell's surface; a flagellum moves an
entire cell.
Protein synthesis.
Rough ER is the site of synthesis of glycoproteins and
phospholipids; smooth ER is the site of fatty acid and steroid
synthesis. Smooth ER also releases glucose into the bloodstream,
inactivates or detoxifies drugs and potentially harmful substances,
and stores calcium ions for muscle contraction.
Accepts proteins from rough ER; forms glycoproteins and
lipoproteins; stores, packages, and exports proteins.
Fuses with and digests contents of vesicles; digests
worn-out organelles (autophagy), entire cells (autolysis),
and extracellular materials.
Detoxifies harmful substances.
Degrades unneeded, damaged, or faulty proteins by cutting them
into small peptides.
Site of reactions that produce most of a cell's ATP.
Consists of nuclear envelope with pores, nucleoli,
and chromatin (or chromosomes).
Contains genes, which control cellular structure and direct
most cellular activities.
Flagellum
Cilium
Intermediate
filament
Centrosome
Lysosome
Smooth ER
Peroxisome
%.-*
Microtubule
PLASMA MEMBRANE
CYTOPLASM
NUCLEUS
Ribosome on rough ER
Golgi complex
Mitochondrion
Microfilament
60 Chapters Cells
plementary sequence of codons in a strand of RNA, Tran-
scription of DNA is catalyzed by the enzyme RNA polymerase,
which must be instructed where to start the transcription
process and where to end it. The segment of DNA where RNA
polymerase attaches to it is a special sequence of nucleotides
called a promoter, located near die beginning of a gene (Figure
3.19a). Three kinds of RNA are made from DNA;
■ Messenger RNA (mRNA) directs synthesis of a protein.
■ Rihosomal RNA (rRNA) joins with ribosomal proteins
to make ribosomes.
■ Transfer RNA (tRNA) binds to an amino acid and holds
it in place on a ribosome until it is incorporated into a
protein during translation. Each of the more than 20 dif-
ferent types of tRNA binds to only one of the 20 differ-
ent amino acids.
During transcription, nucleotides pair in a complementary
manner; The nitrogenous base cytosine (C) in DNA dictates the
complementary nitrogenous base guanine (G) in the new RNx\
strand, a G in DNA dictates a C in RNA, a thymine (T) in DNA
dictates an adenine (A) in RNA and an A in DNA dictates a
uracil (U) in RNA As an example, if a segment of DNA had the
base sequence ATGCAT, the newly transcribed RNA strand
would have the complementary base sequence UACGUA
Transcription of DNA ends at another special nucleotide
sequence on DNA called a terminator, which specifies the
end of the gene (Figure 3.19a> Upon reaching the termina-
tor, RNA polymerase detaches from the transcribed RNA
Figure 3.18 Overview of transcription and translation.
Transcription occurs in the nucleus; translation takes place in
the cytoplasm.
Nucleus
DNA
Nuclear pore
RNA
Plasma
membrane
Cytoplasm
RNA
Ribosome
Protein
Figure 3.19 Transcription.
During transcription, the genetic information in DNA is copied to
RNA,
'a) Overview
DNA
Promoter
Terminator
(b) Details
RNA
polymerase
Codon
Newly synthesized
pre-mRNA
RNA nucleotides
Key:
G
DNA strand
being
transcribed
mRNA
Adenine
Guanine
Thymine
Cytosine
Uracil
Cytoplasm
Why are proteins important in the lite of a cell?
J What enzyme catalyzes transcription of DNA?
molecule and the DNA strand. Once synthesized, mRNA,
rRNA (in ribosomes), and tRNA leave the nucleus of the cell
by passing through a nuclear pore. In the cytoplasm, they
participate in the next step in protein synthesis, translation.
Translation I
Translation is the process in which mRNA associates with ribo-
somes and directs synthesis of a protein by converting the se-
quence of nucleotides in mRNA into a specific sequence of amino
acids. Translation occurs in the following way (Figure 320);
Gene Action; Protein Synthesis 61
Figure 3.20 Protein elongation and termination of protein synthesis during translation.
During protein synthesis the ribosomal subunits join, but they separate when the process is complete.
Large
subunit
nitiatortRNA
Amino acid
tRNA
Small
subunit
Anticodon
Amino acid
(methionine)
Large and small ribosomal subunits
join to form a functional ribosome
and initiator tRNA fits into position
on the ribosome.
Initiator tRNA
mRNA
Codons
O
Anticodon of incoming tRNA pairs
with next mRNA codon beside
initiator tRNA,
mRNA
binding
site
Small
subunit
Start
codon
Initiator tRNA
attaches to a
start codon.
New
peptide
bond
Stop
codon
Q Protein synthesis stops when
the ribosome reaches stop
codon on mRNA,
Amino acid on initiator tRNA
forms a peptide bond with
amino acid beside it.
mRNA
movement
Key:
= Adenine
= Guanine
s Cytosine
= Uracil
Q tRNA leaves the ribosome;
ribosome shifts by one codon;
tRNA binds to newly exposed
codon; steps A - A repeat.
Growing
mRNA protein
^•°uomplete protein
£ tRNA
Summary of movement of ribosome along mRNA
< i
What is the function of a stop codon?
62 Chapters Cells
An m RN A molecule binds to die small ribosomal subunit,
and a special tRNA, called initiator tRNA, binds to the
start codon (AUG) on mRNA, where translation begins.
The large ribosomal subunit attaches to the small sub-
unit, creating a functional ribosome. The initiator tRNA
firs into position on the ribosome. One end of a tRNA
carries a specific amino acid, and the opposite end con-
sists of a triplet of nucleotides called an anticodon. By
pairing between complementary nitrogenous bases, the
tRNA anticodon attaches to the mRNA codon. For ex-
ample, if the mRNA codon is AUG, then a tRNA with
the anticodon UAC would attach to it.
ft The anticodon of another tRNA with its amino acid at-
taches to the complementary mRNA codon next to the
initiator tRNA.
A peptide bond is formed between the amino acids car-
ried by the initiator tRNA and the tRNA next to it.
After the peptide bond forms, the tRNA detaches from
the ribosome, and the ribosome shifts the mRNA strand
by one codon. As the tRNA bearing the newly forming
protein shifts, another tRNA with its amino acid binds to
a newly exposed codon. Steps through repeat again
and again as the protein lengthens.
Protein synthesis ends when the ribosome reaches a stop
codon, at which time die completed protein detaches
from the final tRNA. When the tRNA vacates the ribo-
some, the ribosome splits into its large and small subunits.
Protein synthesis progresses at a rate of about 1 5 amino
acids per second. As the ribosome moves along the mRNA
and before it completes synthesis of the whole protein, an-
other ribosome may attach behind it and begin translation of
die same mRNA strand. In this way, several ribosomes may
be attached to the same mRNA, an assembly called a polyri-
bosome. The simultaneous movement of several ribosomes
along the same mRNA strand permits a large amount of pro-
tein to be produced from each mRNA.
■ CHECKPOINT
11. Define protein synthesis.
12. Distinguish between transcription and translation.
SOMATIC CELL DIVISION
OBJECTIVE • Discuss the stages, events, and signifi-
cance of somatic cell division.
As body cells become damaged, diseased, or worn out, they
are replaced by cell division, the process whereby cells repro-
duce themselves. The two types of cell division are reproduc-
tive cell division and somatic cell division. Reproductive cell
division or meiosis is the process that produces gametes —
sperm and oocytes — the cells needed to form the next gener-
ation of sexually reproducing organisms. This is described in
Chapter 23; here we will focus on somatic cell division.
All body cells, except the gametes, are called somatic
(soma — body) cells. In somatic cell division, a cell divides
into two identical cells. An important part of somatic cell di-
vision is replication (duplication) of the DNA sequences tliat
make up genes and chromosomes so that the same genetic
material can be passed on to the newly formed cells. Alter so-
matic cell division, each newly formed cell has the same
number of chromosomes as the original cell. Somatic cell di-
vision replaces dead or injured cells and adds new ones for
tissue growth. For example, skin cells are continually re-
placed by somatic cell divisions.
The cell cycle is the name for the sequence of changes that
a cell undergoes from the time it Forms until it duplicates its
contents and divides into two cells. In somatic cells, the cell cy-
cle consists of two major periods: interphase, when a cell is not
dividing, and die mitotic (M) phase, when a cell is dividing.
Interphase
During interphase the cell replicates its DNA. It also manu-
factures additional organelles and eytosolic components in
anticipation of cell division. Interphase is a state of high
metabolic activity, and during this time die cell does most of
its growing.
A microscopic view of a cell during interphase shows a
clearly defined nuclear envelope, a nucleolus, and a tangled
mass of chromatin (Figure 3.21a). Once a cell completes its
replication of DNA and other activities oi interphase, the mi-
totic phase begins.
Mitotic Phase
The mitotic phase (ml-TOT-ik) of the cell cycle consists o)
mitosis, division of die nucleus, foLlowed by cytokinesis, division
of the cytoplasm into two cells. The events that take place dur-
ing mitosis and cytokinesis are plainly visible under a micro-
scope because chromatin condenses into chromosomes.
Nuclear Division: Mitosis
During mitosis (nii-TO-sis; mhos = thread), the duplicated
chromosomes become exactly segregated, one set into each
of two separate nuclei. For convenience, biologists divide the
process into four stages: prophase, metaphase, anaphase, and
telophase. However, mitosis is a continuous process, with one
stage merging imperceptibly into the next.
Prophase During early prophase, the chromatin fibers
condense and shorten into chromosomes that are visible un-
der the light microscope (Figure 3.21b). The condensation
process may prevent entangling of the long DNA strands as
they move during mitosis. Recall that DNA replication took
place during interphase. Thus, each prophase chromosome
consists of a pair of identical, double-stranded chromatids. A
Somatic Cell Division 63
Figure 3.21 Cell division: mitosis and cytokinesis. Begin the sequence at (a) at the top of the figure and read
clockwise until you complete the process.
| In somatic cell division, a single cell divides to produce two identical cells.
all at 700x
(a) INT IPHASE
Centrosome:
- Centrioles
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
^
•
•4
I 2
at
Kinetochore
Mitotic spindle
(microtubules)
Fragments of
nuclear envelope
Chromosome
)
Early
(d) ANAPHASE
When does cytokinesis begin?
Focus on Wellness
Phytochemicals
Protecting Cellular
Function
Many studies over the years have
shown that people who consume plenty
of plant foods, including vegetables,
beans, fruits, and grains, have a lower
risk of cancer and heart disease than
their nieat-and-pota to-eating peers.
Scientists are just beginning to uncover
the biochemical explanations for these
associations. Their investigations have
led to the discovery of compounds in
plants that appear to promote healthy
cellular function, and to prevent the
types of cellular damage associated with
cancer, aging, and heart disease. Collec-
tively, these compounds are called phyto-
chemicals, literally "plant chemicals. 11
A Radical Notion?
Phytochemicals appear to protect cells
and interrupt cancerous tumor growth
in a number of interesting ways. Some
phytochemicals block chemicals that
can cause oxidative damage to cells.
You will learn about the process of oxi-
dation in Chapter 20 when you read
about metabolism. Oxidative damage
commonly occurs in cells when
byproducts of metabolism, known as
oxygen free radicals, "steal" electrons
from other molecules. This electron
theft causes chain reactions of electron
transfers that can damage cell mem-
branes, the membranes of cellular or-
ganelles, and even the cells' genetic
material.
Some phytochemicals act as anti-
oxidants, donating electrons to free
radical molecules, thus protecting cel-
lular structures. Antioxidants include
polyphenols, which are found in green
tea, and lycopenes, which are found in
tomato products.
Disabling the Opponent
Many substances entering the body are
potentially carcinogenic, depending
upon their interaction w r ith certain en-
zymes in the liver. Some phytochemi-
cals, such as the allyl sulfides in garlic
and onions, enhance the production of
enzymes that may render potentially
carcinogenic substances harmless. The
sulforaphane in broccoli, cauliflower,
and other cruciferous vegetables per-
forms a similar function.
Promoting Health
Some phytochemicals protect against
cancer by blocking the action of sub-
stances called promoters, Promoters
encourage the aggressive cellular divi-
sion of cells that have undergone
cancer-causing genetic changes. For
example, estrogens are hormones thai
promote the division of cancerous ct
in the breast. Isoflavonoids, found in
soy products, weaken the action ot es-
trogens in breast tissue.
Variety is the key to consuming
more phytochemicals. Try to eat two to
four servings of fruit and three to five
servings of vegetables each day
► Think It Over
What are some dietary changes you could make that would increase your in-
take of helpful phytochemicals?
constricted region of the chromosome, called a centromere y
holds the chromatid pair together.
Later in prophase, die pericentriolar material of the two
centrosomes starts to form the mitotic spindle, a football-
shaped assembly of microtubules (Figure 3.21b). Lengthen-
ing of die microtubules between centrosomes pushes the
centrosomes to opposite poles (ends) of the cell. Finally, the
spindle extends from pole to pole. Then the nucleolus and
nuclear envelope break down.
METAPHASE During metaphase, the centromeres of the
chromatid pairs are aligned along the microtubules of the mi-
totic spindle at the exact center of the mitotic spindle (Figure
3.2 lc) This midpoint region is called the metaphase plate.
ANAPHASE During anaphase the centromeres split, separat-
ing the two members of each chromatid pair, which move to
opposite poles of the cell (Figure 3.2 Id). Once separated, the
chromatids are called chromosomes. As the chromosomes are
64
pulled by the microtubules of the mitotic spindle during
anaphase, they appear V-shaped because the centromeres
lead the way and seem to drag the trailing arms of the chro-j
mosomes toward the pole.
Ti l A m lASE The final stage of mitosis, telophase, begins af-
ter chromosomal movement stops (Figure 3.2 le). The identi-
cal sets of chromosomes, now at opposite poles of the eel
uncoil and revert to the threadlike chromatin form. A til
nuclear envelope forms around each chromatin mass, nuck
oli appear, and eventually the mitotic spindle breaks up.
Cytoplasmic Division: Cytokinesis
Division of a cell's cytoplasm and organelles is called cytoki-
nesis (sf-to4d-NE-sis; -kinesis = motion). This process usu-
ally begins late in anaphase with formation of a cleavm
furrow, a slight indentation of the plasma membrane, that
extends around the center of the cell (Figure 3.2 1 d,e). Mien
Aging and Cells 65
-, «
laments in the cleavage furrow pull the plasma membrane
jogressively inward, constricting the center of the cell like a
Jelt around* a waist, and ultimately pinching it in two. After
cytokinesis there are two new and separate cells, each with
qual portions of cytoplasm and organelles and identical sets
f chromosomes. When cytokinesis is complete, interphase
gins (Figure 3.211),
One of the distinguishing features of cancer cells is un-
controlled division. The mass of cells resulting from this di-
on is called a neoplasm or tumor. One of the ways to treat
(nicer is by chemotherapy, the use of anticancer drugs. Some
)f these drugs stop cell division by inhibiting the formation
the mitotic spindle. Unfortunately, these types of anti-
tcer drugs also kill all types of rapidly dividing cells in the
body, causing side effects such as nausea, diarrhea, hair loss,
fatigue, and decreased resistance to disease.
I CHECKPOINT
13. Distinguish between somatic and reproductive cell divi-
sion. Why is each important?
[l4. What are the major events of each stage of the mitotic
se?
AGING AND CELLS
ECTIVE • Describe the cellular changes that occur
with aging.
jing is a normal process accompanied by a progressive al-
teration of the body's homeostatic adaptive responses. It pro-
■es observable changes in structure and function and in-
sis vulnerability to environmental stress and disease. The
specialized branch of medicine that deals with the medical
problems and care of elderly persons is geriatrics (jer'-e-AT-
r- = old age; -iatrics = medicine). Gerontology (jer'-
on-TOL-6-je) is the scientific study of the process and prob-
lems associated with aging.
Although many millions of new cells normally are pro-
d each minute, several kinds of cells in the body--skele-
muscle cells and nerve cells — do not divide. Experiments
hown that many other cell types have only a limited ca-
pability to divide, Normal cells grown outside the body di-
vide only a certain number of times and then stop. These ob-
servations suggest that cessation of mitosis is a normal,
genetically programmed event. According to this view, "aging
lenes" are part of the genetic blueprint at birth. These genes
have an important function in normal cells, but their activi-
ties slow over time. They bring about aging by slowing down
for hairing processes vital to life.
Another aspect of aging involves telomeres (TE-lo-
fcerz), specific DNA sequences found only at the tips of each
chromosome. These pieces of DNA protect the tips of chro-
mosomes from erosion and from sticking to one another.
ei; in most normal body cells each cycle of cell divi-
sion shortens die telomeres. Eventually, after many cycles of
cell division, the telomeres can be completely gone, and even
some of the functional chromosomal material may be lost.
These observations suggest that erosion of DNA from the
tips of our chromosomes contributes greatly to the aging and
death of cells.
Glucose, the most abundant sugar in the body, plays a
role in the aging process. It is haphazardly added to proteins
inside and outside cells, forming irreversible cross-links be-
tween adjacent protein molecules. With advancing age, more
cross-links form, which contributes to the stiffening and loss
of elasticity that occur in aging tissues.
Free radicals produce oxidative damage in lipids, pro-
teins, or nucleic acids. Some effects are wrinkled skin, stiff
joints, and hardened arteries. Naturally occurring en^yrhes in
peroxisomes and in the cytosol normally dispose of free radi-
cals. Certain dietary substances, such as vitamin E, vitamin C,
beta carotene, and selenium, are antioxidants that inhibit free
radical formation.
Some theories of aging explain the process at the cellular
level, while others concentrate on regulatory mechanisms op-
erating within the entire organism. For example, the immune
system may start to attack the body's own cells. This autoim-
mune response might be caused by changes in certain plasma
membrane glycoproteins and glycol ipids (cell-identity mark-
ers) that cause antibodies to attach to and mark the cell for
destruction. As changes in the proteins on the plasma mem-
brane of cells increase, the autoimmune response intensifies,
producing the well-known signs of aging.
Progeria (pro-JER-e-a) is a disease characterized by nor-
mal development in the first year of life followed by rapid
aging. It is caused by a genetic defect in which telomeres
are considerably shorter than normal. Symptoms include
dry and wrinkled skin, total baldness, and birdlike racial
features. Death usually occurs around age 13.
Werner syndrome is a rare, inherited disease that
causes a rapid acceleration of aging, usually while the per-
son is only in his or her twenties. It is characterized by
wrinkling of the skin, graying of the hair and baldness,
cataracts, muscular atrophy, and a tendency to develop di-
abetes mellitus, cancer, and cardiovascular disease. Most
afflicted individuals die before age 50. Recently, the gene
that causes Werner syndrome has been identified. Re-
searchers hope to use the information to gain insight into
the mechanisms of aging, as well as to help those suffering
from the disorder.
I
■ CHECKPOINT
15. Briefly outline the cellular changes involved in aging.
Next, in Chapter 4, we will explore how cells associate to
form the tissues and organs diat we will discuss later in the text.
66 Chapter 3 Cells
tOMMON
DISORDERS
Cancer
Cmeer is a group of diseases characterized by uncontrolled or ab-
normal cell proliferation. When cells in a part of the body divide
without control, the excess tissue that develops is called a tumor or
neoplasm (NE-6-plazm; neo- = new). The study of tumors is called
oncology (on-KOL-6-je; onco- ■ swelling or mass). Tumors may be
cancerous and often fatal, or they may be harmless. A cancerous
neoplasm is called a malignant tumor or malignancy. One prop-
erty of most malignant tumors is their ability to undergo metastasis
(me-TAS-ta-sis), the spread of cancerous cells to other parts of the
body A benign tumor is a neoplasm that does not metastasize. An
example is a wart. Most benign tumors may be surgically removed it
diis interferes with normal body function or they become disfigur-
ing. Some can lie inoperable and perhaps fatal.
Growth and Spread of Cancer
Cells of malignant tumors duplicate rapidly and continuously. As
malignant cells invade surrounding tissues, they often trigger an-
giomnesis, the growth of new networks of blood vessels. As the can-
cer grows, it begins to compete with normal tissues for space and
nutrients. Eventually, the normal tissue decreases in size and dies.
Some malignant cells may detach from the initial (primary) tumor
and invaded body cavity or enter the blood or lymph, then circulate
to and invade other body tissues, establishing secondary tumors.
The pain associated with cancer develops when die tumor presses
on nerves or blocks a passageway in an organ so that secretions
build up pressure.
Causes of Cancer
Several factors may trigger a normal cell to lose control and become
cancerous. One cause is environmental agents: substances in the air
we breathe, the water we drink, and the food we eat. A chemical
agent or radiation diat produces cancer is called a carcinogen (car-
slN-o-ien). Carcinogens induce mutations, permanent changes in
the DNA base sequence of a gene. The World Health Organization
estimates that carcinogens are associated with 60-90% of -all hu-
man cancers, Examples of carcinogens are hydrocarbons found in
cigarette tar, radon gas from the eardi, and ultraviolet (UV) radia-
tion in sunlight. .
Intensive research efforts are now directed toward studying
cancer-causing genes, or oncogenes (ON-ko-jenz). Wren inappro-
priately activated, these genes have die ability to transform a nor-
mal cell into a cancerous cell. Most oncogenes derive from normal
.rencs called proto-oncogenes that regulate growth and develop-
ment. The proto-oncogene undergoes some change that either
causes it to be expressed inappropriately or make its products in s
ccssive amounts or at the wrong time. Some oncogenes cause exces
sive production of growth factors, chemicals that stimulate cell
growth. Others may trigger changes in a cell-surface receptor, cans
ing it to send signals as though it were being activated by a groutli
factor. As a result, the growth pattern of the cell becomes abnormal
Some cancers have a viral origin. Viruses are tiny packages of
nucleic acids, either RNA or DNA, that can reproduce only while
inside the cells they infect. Some viruses, termed oncogenic viruses,
cause cancer by stimulating abnormal proliferation of cells, lor in-
stance, the human papillomavirus (HPV) causes virtually all cervical
cancers in women.
Recent studies suggest that certain cancers may be linked to a
cell having abnormal numbers of chromosomes. As a result, the cell
could potentially have extra copies of oncogenes or too tew copies
of tumor-suppressor genes, which in either case could lead to un-
controlled cell proliferation. There is also some evidence suggesting
that cancer may be caused by normal stem cells that develop into
cancerous stcm'cells capable of forming malignant tumors.
Carcinogenesis: A Multistep Process
Carcinogenesis (kar'-si-no-JEN-e-sis), the process by which cancer
develops, is a multistep process in which as many as 10 distinct mu-
tations may have to accumulate in a cell before it becomes cancer-
ous. In colon cancer, the tumor begins as an area of increased cell
proliferation that results from one mutation. This growth then p
gresses to abnormal, but noncancerous, growths called adenomas.
After several more mutations, a carcinoma develops. The fact diat
so many mutations arc needed for a cancer to develop indicates that
cell growth is normally controlled with many sets of checks and hal
ances.
Treatment of Cancer
Many cancers are removed surgically. However, when cancer is
widely distributed diroughout the body or exists in organs such as
the brain whose functioning would be greatly harmed by surge
chemotherapy and radiation therapy may be used instead. Some-
times surgery, chemotherapy, and radiation therapy are used in
combination." Chemotherapy involves administering drugs that
cause the death of cancerous cells. Radiation therapy breaks chro-
mosomes, thus blocking cell division. Because cancerous cells divide
rapidly, they are more vulnerable to the destructive effects of
chemotherapy and radiation therapy than are normal cells. Unfor-
tunately for the patients, hair follicle cells, red bone marrow cells,
and cells lining die gastrointestinal tract also are rapidly dividing.
Hence, the side effects of chemotherapy and radiation therapy in-
clude hair loss due to death of hair follicle cells, vomiting and nau-
sea due to death of cells lining the stomach and intestines, and sus-
ceptibility to infection due to slowed production of white blood
cells in red bone marrow.
Study Outline 67 |
f^—f TVj
DICAL TERMINOLOGY AND CONDITIONS
ipksia (an'-a-PLA-ze-a; an- = not; -pltisia = to shape) The
lass of tissue differentiation and function that is characteristic
ill most malignancies.
Apoptom (ap'-op-TO-sis; a falling off, like dead leaves from a
tree) An orderly, genetically programmed cell death in which
"cell-suicide" genes become activated. Enzymes produced by
these genes disrupt the cytoskeleton and nucleus; the cell
shrinks and pulls away from neighboring cells; die DNA within
the nucleus fragments; and die cytoplasm shrinks, although the
plasma membrane remains intact, Phagocytes in the vicinity'
then ingest the dying cell. Apoptosis removes unneeded cells
during development before birth and continues after birth both
to regulate the number of cells in a tissue and to eliminate po-
tentially dangerous cells such as cancer cells.
Atrophy (AT-ro-fe; //- = without; -trophy = nourishment) A de-
crease in the size of cells with subsequent decrease in the size of
die affected tissue or organ; wasting away.
Biopsy (ET-op-se; bio- = life; -opsy = viewing) The removal and
microscopic examination of tissue from the living body for di-
agnosis.
dysplasia (dis-PLA-ze-a; dys- = abnormal) Alteration in the size,
shape, and organization of cells due to chronic irritation or in-
flammation; may progress to a neoplasm (tumor formation,
usually malignant) or revert to normal if the irritation is re-
moved.
Hyperplasia (hl'-per-PLA-ze-a; hyper- = over) Increase in the
number of cells of a tissue due to an increase in the frequency
of cell division.
Hypertrophy (hi-PER-tro-fe) Increase in die size of cells in a tis-
sue without cell division.
Metaplasia (met'-a-PLA-ze-a; meta- = change) The transforma-
tion of one type of cell into another.
Necrosis (ne-KRO-sis = death) A pathological type of cell death,
resulting from tissue injury, in which many adjacent cells swell,
burst, and spill their cytoplasm into the interstitial fluid; the
cellular debris usually stimulates an inflammatory response,
which does not occur in apoptosis.
Progeny (PROJ-e-ne; pro- = forward; -gmy - production) Off-
spring or descendants.
Proteomics (pro'-te-O-miks; proteo- = protein) The study of the
proteome (all of an organism's proteins) in order to identify all
the proteins produced; it involves determining how the pro-
teins interact and ascertaining the three-dimensional structure
of proteins so that drugs can be designed to alter protein activ-
ity to help in the treatment and diagnosis of disease.
Tumor marker A substance introduced into circulation by tumor
cells that indicates the presence of a tumor, as well as the spe-
cific type. Tumor markers may be used to screen, diagnose,
make a prognosis, evaluate a response to treatment, and moni-
tor for recurrence of cancer.
STUDY OUTLINE
Introduction (p. 44)
I. A cell is die basic, living, structural and functional unit of the
body.
I Cell biology is the study of cell structure and function,
A Generalized View of the Cell (p. 45)
1, .lire 3.1 on page 45 shows a generalized view of a cell that is
a composite of many different cells in the body.
I The principal parts of a cell are the plasma membrane; die cy-
toplasm, which consists of cytosol and organelles; and the nu-
cleus.
The Plasma Membrane (p. 46)
■1, The plasma membrane surrounds and contains the cytoplasm
i cell; it is composed of proteins and lipids.
2, The lipid bilayer consists of two back-to-back layers of phos-
pholipids, cholesterol, and glycolipids.
3- Integral proteins extend into or through the lipid bilayer; pe-
ripheral proteins associate with the inner or outer surface oi
the membrane.
4. The membrane's selective permeability permits some sub-
stances to pass across it more easily than others. The lipid bi-
layer is permeable to water and to most lipid-soluble mole-
cules. Small- and medium-sized water-soluble materials may
cross the membrane with the assistance of integral proteins.
5. Membrane proteins have several functions. Channels and
transporters are integral proteins that help specific solutes
across the membrane; receptors serve as cellular recognition
sites; some membrane proteins are enzymes; and others are cell
identity markers.
Transport Across the Plasma Membrane (p. 47)
1, Fluid inside body cells is called intracellular fluid (TCF); fluid
r
outside body cells is extracellular fluid (ECF). The ECF in the
microscopic spaces between the cells of tissues is interstitial
68 Chapters Ceils
fluid. The ECF in blood vessels is plasma, and that in lym-
phatic vessels is lymph*
2. Any material dissolved in a fluid is called a solute, and the fluid
that dissolves materials is the solvent. Body fluids arc dilute so-
lutions in which a variety of solutes art* dissolved in the solvent
water,
3. The selective permeability of the plasma membrane supports
the existence of cone e titration gradients, differences in the con-
centration of chemicals between one side of the membrane and
the other.
4. Materials move through cell membranes by passive processes
or by active processes, In passive processes, a substance moves
down its concentration gradient across the membrane. In active
transport, cellular energy is used to drive the substance "uphill"
a gai n s t i ts co neen tra ti on gra d lent,
5. In transport in vesicles, tiny vesicles either detach from the
plasma membrane while bringing materials into the cell or
merge with the plasma membrane to release materials from the
cell.
6. Diffusion is the movement of substances due to their kinetic-
energy. In net diffusion, substances move from an area of
higher concentration to an area of lower concentration until
equilibrium is reached, At equilibrium the concentration is the
same throughout the solution.
7. In simple diffusion, substances move through the lipid bilayer
or through channels in integral proteins. Ion channels selective
For K + , CI , Na 1 , and Ca 2H allow these ions to diffuse across
the plasma membrane by simple diffusion, In facilitated diffu-
sion, substances cross the membrane with the assistance of
transporters, which bind to a specific substance on one side of
the membrane and release it on the other side after the trans-
porter undergoes a change in shape,
8. Osmosis is the movement of water molecules through a selec-
tively permeable membrane from an area of higher to an area
of lower water concentration.
9. In an isotonic solution, red blood cells maintain their normal
shape; in a hypotonic solution, they gain water and undergo
hemolysis; in a hypertonic solution, they lose water and un-
dergo crenation .
10. With the expenditure of cellular energy, usually in the form of
ATP, solutes can cross the membrane against their concentra-
tion gradient by means of active transport. Actively transported
solutes include several ions such as Na' 1 , K \ H + » Ca- ' , I , and
CI ; amino acids; and monosaccharides.
11. The most important active transport pump is the sodium-potas-
sium pump, which expels Na from cells and brings K ' in,
12. Transport in vesicles includes both endocytosis (phagocytosis
and bulk-phase endocytosis) and exocytosis.
13. Phagocytosis is the ingestion of solid particles. It is an impor-
tant process used by some white blood cells to destroy bacteria
that enter the body. Bulk-phase endocytosis is the ingestion of
extra eel 1 ular f! uid.
14. Exocytosis involves movement of secretory or waste products
out of a cell bv fusion of vesicles with the plasma membrane.
Cytoplasm (p. 52)
I. Cytoplasm includes all the cellular contents between the
plasma membrane and nucleus; it consists of cytosol and
organelles.
2* The fluid portion of cytoplasm is cytosol, composed mostlj rij
water, plus ions, glucose, amino acids, fatty acids, proti
lipids, ATP, and waste products; the cytosol is the site of many
chemical reactions required for a cell's existence.
3. Organelles are specialized cellular structures with characteristic
shapes and specific functions,
4. The cytoskeleton is a network of several kinds of protein hli-
ments that extend throughout die cytoplasm; they provide ,i
structural framework for the cell ami generate movements,
Components of the cytoskeleton include microfilaments, inter-
mediate filaments, and microtubules.
5. The centrosome consists of two centrioles and pencentriokr
material. The centrosome serves as a center for organizing mi-
crotubules in interphase cells and the mitotic spindle during
cell division,
6. Cilia and flagella arc motile projections of the cell surface. Glial
move fluid along the ceil surface; a ftagellum moves an entire
cell.
7. Ribosomes, composed of ribosomal RNA and ribosomal pro-
teins, consist of two submits and are the sites of protein syn-
thesis.
8. Endoplasmic reticulum (ER) is a network of membranes thai
extends from the nuclear envelope throughout the cytoplasm,
9. Rough ER is studded with ribosomes. Proteins synthesized on
the ribosomes enter the ER for processing and sorting. The
ER is also where glycoproteins and phospholipids form.
10. Smooth ER lacks ribosomes. It is the site where forty acids and
steroids are synthesized. Smooth ER also participates in relead
ttig glucose from the liver into the bloodstream, inactivating ot
detoxifying drugs and other potentially harmful substances, and
releasing calcium ions that trigger contraction in muscle cells.
II. The Golgi complex consists of Rattened sacs called cisterns
that receive proteins synthesized in the rough ER. Within the
Golgi cisterns the proteins are modi lied, sorted, and packaged
into vesicles for transport to different destinations. Some
processed proteins leave the cell in secretory vesicles, some arc
incorporated into the plasma membrane, and some enter lyso-
somes.
12. Lysosomes are membrane-enclosed vesicles that contain digd
tive enzymes. They function in digestion of worn-out or-
ganelles (autophagy) and even in digestion of their own cell
(autolysis).
13. Peroxisomes are similar to lysosomes but smaller. They oxidize
various organic substances such as amino acids, fatty acids, and
toxic substances and, in the process, produce hydrogen perox-
ide. The hydrogen peroxide is degraded by an enzyme in per*
oxisomes called catalase.
14. Froteasomes contain proteases that continually degrade im
needed, damaged, or faulty proteins,
[5. Mitochondria consist of a smooth outer membrane, an inner
membrane containing cristae, and a fluid-filled cavity called the
affix. They arc called "powerhouses" of the cell because they
produce most of a cells ATP.
Nucleus (p. 57)
1 The nucleus consists of a double nuclear envelope; nuclear
pores, which control the movement of substances between the
nucleus and cytoplasm; nucleoli, which produce ribosomes; and
genes arranged on chromosomes,
2. Most body cells have a single nucleus; some (red blood cells)
have none, and others (skeletal muscle cells) have several.
3. Genes control cellular structure and most cellular functions.
Gene Action: Protein Synthesis (p. 58)
I, VIost of the cellular machinery is devoted to protein synthesis.
I Cells make proteins by transcribing and translating the genetic
information encoded in the sequence of four types of nitroge-
nous bases in DNA.
[j, la transcription, genetic information encoded in die DNA base
sequence is copied into a complementary sequence of bases in a
strand of messenger RNA (mRNA). Transcription begins on
DMA in a region called a promoter.
[4. Translation is the process in which in RNA associates with ribo-
somes and directs synthesis of a protein, converting the nu-
cleotide sequence in mRNA into a specific sequence of amino
acids.
5, In translation, mRNA binds to a ribosome, specific amino acids
attach to tRNA, and anticodons of tRNA bind to eodons of
mRNA, bringing specific amino acids into position on a grow-
ing protein,
6. Translation begins Lit the start codon and terminates at the stop
codon.
Self-Quiz 69
Somatic Cell Division (p. 62)
1. Cell division is the process by which cells reproduce them-
selves.
2. Cell division that results in an increase in die number of body
cells is called somatic cell division; it involves a nuclear division
called mitosis plus division of cytoplasm, called cytokinesis.
3. Cell division that results in the production of sperm and
oocytes is called reproductive cell division.
4. The cell cycle is an orderly sequence of events in which a cell
duplicates its contents and divides in two. It consists of inter-
phase and a mitotic phase.
5. Before the mitotic phase, the DNA molecules, or chromo-
somes, replicate themselves so that identical chromosomes can
be passed on to the next generation of cells.
6. A cell that is between divisions and is carrying on every life
process except division is said to be in interphase.
7. Mitosis is the replication and distribution of two sets of chro-
mosomes into separate and equal nuclei; it consists of prophase,
rnetaphase, anaphase, and telophase.
8. Cytokinesis usually begins late in anaphase and ends in
telophase.
9. A cleavage furrow forms and progresses inward, cutting
through the cell to form two separate identical cells, each with
equal portions of cytoplasm, organelles, and chromosomes.
Aging and Ceils (p. 65)
1.
2.
Aging is a normal process accompanied by progressive alter-
ation of the body's homeostatic adaptive responses.
Many theories of aging have been proposed, including geneti-
cally programmed cessation of cell division, shortening of
telomeres, addition of glucose to proteins, buildup of free radi-
cals, and an intensified autoimmune response.
SELF-QUI
H the extracellular fluid contains a greater concentration of
solutes than the cytosol of the cell, die extracellular fluid is said
p be
a, isotonic b. hypertonic c* hypotonic
d, cytotonic e. epi tonic
The proteins found in the plasma membrane
a. are primarily glycoproteins
b. allow die passage of many substances into the cell
c. allow cells to recognize other cells
d. help anchor cells to each other
e. have all of the above functions
3. To enter many body cells, glucose must bind to a specific mem-
brane transport protein, which assists glucose to cross the
membrane without using ATR This type of movement is
known as
a. facilitated diffusion b. simple diffusion
c. vesicular transport d. osmosis e. active transport
4. A red blood cell placed in a hypotonic solution undergoes
a. hemolysis b, crenation c. equilibrium
d. a decrease in osmotic pressure e. shrinkage
5. Which of the following normally pass through the plasma
membrane only by transport in vesicles?
a. water molecules b. sodium ions c. proteins
d. oxygen molecules e + hydrogen ions
70 Chapter 3 Cells
6« Which of the following statements concerning diffusion is
NOT true?
a. Diffusion speeds up as body temperature rises.
b. A small surface area slows down the rate of diffusion.
c. A low-weight particle diffuses faster than a high-weight
particle.
d. It moves materials from an area of low concentration to an
area of high concentration by kinetic energy.
e. Diffusion over a greater distance takes longer than diffusion
over a short distance.
7. Which of the following processes requires ATP?
a. diffusion b. active transport c, osmosis
d. facilitated diffusion e. net diffiision
8. Nicotine in cigarette smoke interferes with the ability of cells
to rid the breathing passageways of debris. Which organelles
are "paralyzed" by nicotine?
a. flagella b. ribosomes c. microfilaments
d. cilia e. lysosomes
9. Many proteins found in the plasma membrane are formed by
the and packaged by the
a. ribosomes, Golgi complex
b. smooth endoplasmic reticulum, Golgi complex
c. Golgi complex, lysosomes
d. mitochondria, Golgi complex
e. nucleus, smooth endoplasmic reticulum
10. Match the following:
a. cellular movement A. centrosome
b. selective permeability B. cytoskeleton
. c. protein synthesis C, Golgi complex
. d. lipid synthesis, detoxification D. lysosomes
e. packages proteins and lipids E. mitochondria
f. ATP production F. plasma membrane
g, digest bacteria and worn-out G. ribosomes
organelles H- smooth ER
h. forms mitotic spindle
11. If die smooth endoplasmic reticulum were destroyed, a cell
would not be able to
a. form lysosomes b. synthesize certain proteins
c. generate energy d. phagocytize bacteria
e. synthesize fatty acids and steroids
12. Water moves into and out of red blood cells through the
process of
a. endocytosis b, phagocytosis t\ osmosis
d. active transport e, facilitated diffusion
13. A cell undergoing mitosis goes through the following stages in
which sequence?
a. interphase, metaphase, prophase, cytokinesis
b. interphase, prophase, cytokinesis, telophase
c. anaphase, metaphase, prophase, telophase
d. anaphase, metaphase, prophase, cytokinesis
e. prophase, metaphase, anaphase, telophase
14. Transcription involves
a. transferring information from die mRNA to tRN A
b. codon binding with anticodons c joining amino acids
by peptide bonds d. copying information contained in the
DNA to mRNA e. synthesizing the protein on the
ribosome
IS* If a DNA strand has a nitrogenous base sequence TACGA, then
the sequence of bases on the corresponding mRNA would be
a. ATGCT b, AUGCU c. GUACU d. CTG VI
e. AUCUG
16. Place the following events of protein synthesis in die proper
order.
1, DNA uncoils and mRNA is transcribed. 2. tRNA with
an attached amino acid pairs with mRNA. 3. mRNA
passes from the nucleus into the cytoplasm and attaches to a
ribosome, 4, Protein is formed. 5, 1 wo amino acids
are linked by a peptide bond.
a. 1,2,3,4,5 b. 1,3,2,5,4 c, 1,2,3,5,4
d. 1,5,3,2,4 e. 2, 1,3,4,5
17. Match the following descriptions with the phases shown.
_ a, nuclear envelope (membrane) and nucleoli reappear
b. centromeres of the chromatid pairs line up in the
center of the mitotic spindle
c, DNA duplicates
d. cleavage furrow splits cell into two identical cells
e> chromosomes move toward opposite poles of cell
f. chromatids are attached at centromeres; mitotic spindle
forms
A. prophase
B. cytokinesis
C. telophase
D. anaphase
E. metaphase
F. interphase
18. In which phase is a cell highly active and growing?
a. anaphase b. prophase c> metaphase
d. telophase e. interphase
19* If a virus were to enter a cell and destroy its ribosomes, hoi,
would the cell be affected?
a. It would be unable to undergo mitosis.
b. It could no longer produce ATR
c. Movement of the cell would cease.
d. Tt would undergo autophagy.
e. It would be unable to synthesize proteins.
20. Which of the following statements concerning cancer is NO]
true?
a. A benign tumor is noncancerous.
b. When a cancerous growth presses on nerves, it can cause pain,]
c. Angiogenesis is the spread of cancerous cells to other parts
of the body
d. Ultraviolet radiation and radon gas are carcinogens.
e. Cancer is uncontrolled mitosis in abnormal cells.
Answers to Figure Questions 7'
RITICAL THINKING APPLICATIONS
One of your bones' functions is to store minerals, especially
ilcium. The bone tissue must lie dissolved to release the cal-
cium for use by die body's systems. Which organelle would be
involved in breaking down bone tissue?
In your dream, you're floating on a raft in the middle of the
an. The sun's hot, you're very thirsty, and you're sur-
mded by water. You want to take a long, cool drink of seawa-
but something you learned in A&P (you knew that was
coming) stops you from drinking and saves your lite! Why
shouldn't vou drink seawater?
4,
Mucin is a glycoprotein present in saliva. When mixed with
water, mucin becomes the slippery substance known as mucus.
Trace the route taken by mucin through the cells of the salivary
glands, starting with the organelle where it is synthesized and
ending with its release from the cells.
Jethra loves his french fries super-sized with extra salt He
dropped A&P last semester but remembers something about a
pump, "Hey, I'm a big guy. I need the extra salt to power my
sodium pump." How well does jethro remember his A&P?
r>
ANSWERS TO FIGURE QUESTIONS
3.2
5,4
3,6
37
3.8
1.10
The three main parts of a cell are the plasma membrane
eytoplasm, and nucleus.
Some integral proteins function as channels or transporters
to move substances across membranes. Other integral pro-
teins function as receptors. Membrane glyeolipids and glyco-
proteins are involved in cellular recognition.
In simple diffusion, substances cross a membrane through
the lipid bilayer and pores of ion channels; in facilitated dif-
fusion, transporters are involved.
Oxygen, carbon dioxide, fatty acids, fat-soluble vitamins, and
steroids can cross the plasma membrane by simple diffusion
through die lipid bilayer.
The concentration of K is higher in the cytosol of body
cells than in extracellular fluids.
Insulin promotes insertion of glucose transporters in the
plasma membrane, which increases cellular glucose uptake
by facilitated diffusion.
\,.. the water concentrations can never be the same because
the beaker always contains pure (100%) water and the sac
contains a solution that is less than 100% water.
M% solution of NaCl will cause cremation of RBCs because
it is hypertonic*
ATP adds a phosphate group to the pump protein, which
changes the pump's three-dimensional shape,
The trigger that causes pseudopod extension is binding of a
particle to a membrane receptor.
3.11 Clusters of microtubules form the structure of centrioles,
cilia, and flagella.
3.12 The components of the centrosome are two centrioles and
the pericentriolar material.
3.13 Large and small ribosomal subunits are synthesized in a
nucleolus in the nucleus and then join together in the
cytoplasm.
3.14 Rough ER has attached ribosomes where proteins that will
be exported from the cell are synthesized; smooth ER lacks
ribosomes and is associated with lipid synthesis and other
metabolic reactions.
3.15 Cells diat secrete proteins into extracellular fluid have exten-
sive Golgi complexes.
3.16 Mitochondrial cristae provide a large surface area for chemi-
cal reactions and contain enzymes needed for ATP produc-
tion.
3.17 Nuclear genes control cellular structure and direct most cel-
lular activities.
3.18 Proteins determine the physical and chemical characteristics
of cells.
3.19 RNA polymerase catalyzes transcription of DNA.
3.20 WheP a ribosome encounters a stop eodon in niRNA, the
completed protein detaches from die final tRNA,
3.21 Cytokinesis usually begins late in anaphase.
TISSUES
did you know?
Aeople who have never taken
biology courses have been known to remark, "I don y t
want to lift weights, because if I build muscular tissue,
I am afraid it will turn to fat when I stop lifting. n Of
course, muscular tissue is specialized for its contractile
Junction, and does not "turn into" fat tissue, which is
specialized for energy storage. As people age, skeletal
muscles do atrophy, or shrink, over the years. Adipose
tissue tends to grow. While some of these changes in
body composition appear to be an inevitable part of the
aging process, scientists believe much of
the loss of muscular tissue can be
prevented with exercise training.
Focus on Wellness, page 91
www.wiley.com/college/apcentral
jf± s you
learned in the
previous chapter,
cells are highly
organized living units,
but they typically do not function alone. Instead, cells
work together in groups called tissues. A tissue is a
group of similar cells, usually with a common embryonic
origin, that function together to carry out specialized
activities. Histology (hiss-TOL-6-je; hist- = tissue;
-fagy = study of) is the science that deals with the study
of tissues. A pathologist (pa-THOL-6-gist; jtwrfw- =
disease) is a physician who specializes in laboratory
studies of cells and tissues to help other physicians mak<
accurate diagnoses. One of the principal functions of a
pathologist is to examine tissues for any changes that
might indicate disease.
looking back to move ahead . .
Levels of Organization and Body Systems (page 2)
A Generalized View of the Cell (page 45)
Phagocytosis (page 51)
Cytosol (page 52)
Organelles (page 52)
Cilia (page 54)
72
PES OF TISSUES
IBJECT1VE * Name four basic types of tissue that
lake up the human body and state die characteristics of
each.
Body tissues are classified into four basic types based on their
ictureand functions:
L Epithelial tissue (ep'-i-THE-le-al) covers body surfaces;
lines body cavities, hollow organs, and ducts (tubes); and
forms glands.
2. Connective tissue protects and supports the body and its
organs, binds organs together, stores energy reserves as
fat, and provides immunity.
}, Muscular tissue generates the physical force needed to
make body structures move,
4. Nervous tissue detects changes inside and outside the
body and initiates and transmits nerve impulses (action
potentials) that coordinate body activities to help main-
tain homeostasis.
Epithelial tissue and most types of connective tissue are
seel in detail in this chapter. The structure and fimc-
Ls of bone tissue and blood (connective tissues), muscular
feue, and nervous tissue are examined in detail in later
chapters.
Most epithelial cells and some muscle and nerve cells are
Igbtlv joined into functional units by points of contact be-
Ben their plasma membranes called cell junctions. Some
II junctions fuse cells together so tightly that they prevent
Instances from passing between the cells. This fusion is very
Important for tissues that line the stomach, intestines, and
urinary bladder because it prevents the contents of these or-
pins hum leaking out. Other cell junctions hold cells to-
gether so that they don't separate while performing their
factions. Still other cell junctions form channels that allow
and molecules to pass between cells. This permits cells
[ill a tissue to communicate with each other and it also enables
pen'e or muscle impulses to spread rapidly among cells.
I CHECKPOINT
1, Define a tissue. What are the four basic types of body
tissues?
I Whv are cell junctions important?
EPITHELIAL TISSUE
OBJECTIVES • Discuss the general features of epitlie-
[lial tissue,
1 1 Describe the structure, location, and function of the
[wious types of epithelial tissue.
Epithelial Tissue 73
Epithelial tissue, or more simply epithelium (plural is epithe-
lm% may be divided into two types: (1) covering and lining
epithelium and (2) glandular epithelium. As its name suggests,
covering and lining epithelium forms the outer covering of
the skin and the outer covering of some internal organs. It
also lines body cavities; blood vessels; ducts; and the interiors
of the respiratory, digestive, urinary, and reproductive systems.
It makes up, along with nervous tissue, die parts of the sense
organs for hearing, vision, and touch. Glandular epithelium
makes up die secreting portion of glands, such as sweat glands.
General Features of Epithelial Tissue
As you will see shortly, there are many different types of ep-
ithelia, each with characteristic structure and functions.
However, all of the different types of epithelial tissue also
have features in common. General features of epithelial tissue
include the following:
1. Epithelium consists largely or entirely of closely packed
cells with little extracellular material between them, and
the cells are arranged in continuous sheets, in either
single or multiple layers.
2. Epithelial cells have an apical (free) surface, which is exposed
to a body cavity, lining of an internal organ, or die exterior
of the body; lateral surfaces, which face adjacent cells on ei-
ther side; and a basal smjace, which is attached to a base-
ment membrane. In discussing epithelia with multiple lay-
ers, the term apical layer refers to the most superficial layer
of cells, whereas the term basal layer refers to the deepest
layer of cells. The basement membrane is a diin extracellu-
lar structure composed mostly of protein fibers. It is lo-
cated between the epithelium and die underlying connec-
tive tissue layer and helps bind and support the epithelium.
3. Epithelia are avascular (a- = without; vascular • blood
vessels); that is, they lack blood vessels. The vessels that
supply nutrients to and remove wastes from epithelia are
located in adjacent connective tissues. The exchange of
materials between epithelium and connective tissue oc-
curs by diffusion.
4. Epithelia have a nerve supply.
5. Because epithelium is subject to a certain amount of wear
and tear and injury, it has a high capacity for renewal by
cell division.
Covering and Lining Epithelium
Covering and lining epithelium, which covers or lines various
parts of the body, is classified according to the arrangement
of cells into layers and the shape of the cells (Figure 4.1):
1. Arrangement of cells in layers. The cells of covering and
lining epithelia are arranged in one or more layers de-
pending on the functions the epithelium performs:
74 Chapter 4 Tissues
Figure 4.1 Cell shapes and arrangement of layers for covering and lining epithelium.
Cell shapes and arrangement of layers are the bases for classifying covering and lining epithelium.
> c "
Arrangement
of layers
Simph
1
Stratified
*
Basement
membrane
Cell shape
?
Squamous
Cuboidal
Columnar
Basement
membrane
Which cell shape is best adapted for the rapid movement of substances from one cell to another?
2.
a. Simple epithelium is a single layer of cells that functions
in diffusion, osmosis, filtration, secretion, and absorp-
tion. Secretion is the production and release of sub-
stances such as mucus, sweat, or enzymes. Absorption
is the intake of fluids or other substances such as di-
gested food from the intestinal tract.
b, Pseudostratified epithelium {psendo- = false) appears to
have multiple layers of cells because the cell nuclei lie
at different levels and not all cells reach the apical sur-
face. Cells that do extend to the apical surface may
contain cilia; others (goblet cells) secrete mucus.
Pseudostratified epithelium is actually a simple ep-
ithelium because all its cells rest on the basement
membrane.
C, Stratified epithelium (stratum = layer) consists of two
or more layers of cells that protect underlying tissues
in locations where there is considerable wear and tear*
Cell shapes.
a. Squamous cells (SKWA-mus = flat) arc arranged like
floor tiles and are thin, which allows for the rapid pas-
sage of substances.
b. Cuboidal cells are as tall as they are wide and are
shaped like cubes or hexagons. They may have mi-
crovilli at their apical surface and function in either
secretion or absorption.
c. Columnar cells are much taller than they are wide, like
columns, and protect underlying tissues. Their apical
surfaces may have cilia or microvilli, and they often
are specialized for secretion and absorption.
d. Transitional cells change shape, from flat to cuboidal
as organs such as the urinary bladder stretch (dis-
tend) to a larger size and then collapse to a smaller
size.
Combining the two characteristics (arrangements of layers
and cell shapes), the types of covering and lining epithelia are
as follows:
I, Simple epithelium
A* Simple squamous epithelium
B. Simple cuboidal epithelium
C. Simple columnar epithelium (nonciliated and ciliated)
D. Pseudostratified columnar epithelium (nonciliated and
ciliated)
II. Stratified epithelium
A. Stratified squamous epithelium (keratinized and
nonkeratini/.ed)*
B. Stratified cuboidal epithelium*
C. Stratified columnar epithelium*
D. Transitional epithelium
"This classification is based on the shape of the cells in the|
apical layer.
Each of these covering and lining epithelia is described in
| following sections and illustrated in Tabic 4.L The illus-
ion of each type consists of a photomicrograph, a corre-
iponding diagram, and an inset that identifies a major location
|f the tissue in the body. Descriptions, locations, and functions
^fthe tissues accompany each illustration.
miple Epithelium
>LE Squamous Epitiiklium This tissue consists of a
ingle layer of flat cells that resembles a tiled floor when
[viewed from its apical surface (Table 4.1 A). The nucleus of
ich cell is a flattened oval or sphere and is centrally located.
2 squamous epithelium is found in parts of the body
(be" filtration (kidneys) or diffusion (lungs) are priority
Lcesses. It is not found in body areas that are subjected to
bear and tear.
The simple squamous epithelium that lines the heart,
llood vessels, and lymphatic vessels is known as endothelium
Jo- = within; -thelium = covering); the type that forms
idielial layer of serous membranes, such as the peri-
toneum, is called mesothelium (mem- = middle).
Lple Cuboidal Epithelium The cuboidal shape of the
lis in this tissue (Table 4. IB) is obvious only when the tis-
L is sectioned and viewed from the side. Cell nuclei are
II, round and centrally located. Simple cuboidal epithe-
, is found in organs such as the thyroid gland and kidneys
performs the functions of secretion and absorption.
Slwlk Columnar Epithelium When viewed from the
the cells of simple columnar epithelium appear like
columns with oval nuclei near the base of the cells. Simple
columnar epithelium exists in two forms: nonciliated
simple columnar epithelium and ciliated simple columnar
epithelium.
Nonciliated simple columnar epithelium contains two types
of cells- columnar epithelial cells with microvilli at their api-
cal surface, and goblet cells (Table 4.1C). Microvilli, micro-
tic fingerlike projections, increase the surface area of the
plasma membrane (see Figure 3.1 on page 45), thus in-
creasing the rate of absorption by the cell. Goblet ceUs are
modified columnar cells that secrete mucus, a slightly sticky
fluid at their apical surfaces. Before it is released, mucus ac-
cumulates in the upper portion of die cell, causing that area
dge out. The whole cell then resembles a goblet or wine
<fes. Secreted mucus serves as a lubricant for the linings of
the digestive, respiratory, reproductive, and most of the un-
v tracts. Mucus also helps to trap dust entering the respi-
iry tract, and it prevents destruction of the stomach lining
I iv acid secreted by the stomach.
Ciliated simple columnar epithelium (Table 4. ID) contains
Us with cilia at their apical surface. In a few parts of the up-
respiratory tract, ciliated columnar cells are interspersed
Epithelial Tissue 75
with goblet cells. Mucus secreted by die goblet cells forms a
film over the respiratory surface that traps inhaled foreign
particles. The cilia wave in unison and move die mucus and
any trapped foreign particles toward the throat, where it can
be coughed up and swallowed or spit out. Cilia also help to
move oocytes expelled by the ovaries through the uterine
tubes nun the uterus.
Pseudostratified Columnar Epithelium
As noted earlier, pseudostratified columnar epithelium ap-
pears to have several layers because the nuclei of the cells are
at various depths (Table 4. IE). Even though all the cells are
attached to the basement membrane in a single layer, some
cells do not extend to the apical surface. When viewed from
the side, these features give the false impression of a multi-
layered tissue- — thus the name pseudomm&ed epithelium
(psemlo- = false). In pseudostratified ciliated columnar epithelium,
the cells that extend to the surface either secrete mucus
(goblet cells) or bear cilia. The secreted mucus traps for-
eign particles and the cilia sweep away mucus for eventual
elimination from the body. Pseudostratified nmciliated colum-
nar epithelium contains cells without cilia and lacks goblet
cells.
Stratified Epithelium
Stratified epithelium contains two or more layers of cells
used for protection of underlying tissues in areas where there
is considerable wear and tear. Some cells of stratified epithe-
lia also produce secretions. The name of the specific kind ol
stratified epithelium depends on the shape of the cells in the
apical layer.
Stratified Squamous Epithelium Cells in the apical
layer of this type of epithelium are flat; those in the deep lay-
ers vary in shape from cuboidal to columnar (Table 4. IF).
The basal (deepest) cells continually undergo cell division. As
new cells grow, die cells of the basal layer are pushed upward
toward the surface. As they move farther from the deeper
layers and from their blood supply in the underlying connec-
tive tissue, they become dehydrated, shrunken, and harder.
At the apical layer, the cells lose their cell junctions and are
sloughed off, but they are replaced as new cells continually
emerge from the basal cells.
Stratified squamous epithelium exists in both keratinized
and nonkeratinized forms. In keratinized stratified squamous
epithelium, a tough layer of keratin is deposited in the apical
layer and several layers deep to it. Keratin is a tough protein
that helps protect the skin and underlying tissues from mi-
crobes, heat, and chemicals. Nmkeratinized stratified squamous
epithelium, which is found, for example, lining the mouth,
does not contain keratin in the apical layer and several layers
deep to it and remains moist. Stratified squamous epithelium
forms the first line of defense against microbes.
76 Chapter 4 Tissues
Table 4.1 Epithelial Tissues
Covering and Lining Epithelium
Simple Epithelium
A. Simple squamous
epithelium
Description; Single layer of flat cells; centrally located nucleus.
Location: Lines heart, blood vessels, lymphatic vessels, air sacs of lungs, glomerular (Bowman's) capsule of kidneys, and
inner surface of the tympanic membrance (eardrum); forms epithelial layer of serous membranes, such as the peritoneum.
Function: Filtration, diffusion, osmosis, and secretion in serous membranes.
Surface view of simple squamous epithelium
of mesothefial lining of peritoneum
Small
intestine
«*>
• •
Sectional view of simple squamous epithelium of small intestine
Flat nucleus of simple
squamous cell
Connective tissue
Muscular tissue
<z>
Simple squamous
cell
Basement membrane
Connective tissue
Simple squamous epithelium
ial Tissue 77
Covering and Lining Epithelium
. Simple cuboidal Description: Single layer of cube-shaped cells; centrally located nucleus.
elium Location: Covers surface of ovary, lines anterior surface of capsule of the lens of the eye, forms the pigmented epithelium at
the posterior surface of the eye, lines kidney tubules and smaller ducts of many glands, and makes up the secreting portion of
some glands such as the thyroid gland.
Function: Secretion and absorption.
Pancreas
Bfcm
Duodenum
Conciliated simple
columnar epithelium
Sectional view of simple cuboidal epithelium
of intralobular duct of pancreas
Simple
cuboidaf
epithelium
Nucleus of
simple cuboidal
cell
Lumen
of duct
Connective
tissue
Simple cuboidal eel
Basement
membrane
Connective
tissue
Simple cuboidal epithelium
Description: Single layer of nonciliated column-like cells with nuclei near bases of cells; contains goblet cells and cells
with microvilli in some locations.
Location: Lines most of the gastrointestinal tract (from the stomach to the anus), ducts of many glands,
and gallbladder.
Function: Secretion and absorption.
Small
intestine
Mucus in
goblet ce
Nucleus of
goblet cell
Nucleus of
absorptive ce
Connective
tissue
Lumen of Microvilli
jejunum
Sectional view of nonciliated simple columnar
epithelium of lining of jejunum of small intestine
Nonciliated
simple
columnar
epithelium
.«:■,
v
lh
Microvilli
Mucus in
* goblet cell
Absorptive
cell
F-* Basement
membrane
Connective
tissue
Nonciliated simple columnar epithelium
(continues)
78 Chapter 4 Tissues
Table 4.1 Epithelial Tissues (continued)
Covering and Lining Epithelium .
D. Ciliated simple Description: Single layer of ciliated column-like cells with nuclei near bases; contains goblet cells in some
columnar epithelium locations.
Location; Lines a few portions of upper respiratory tract, uterine (fallopian) tubes, uterus, some paranasal sinuses, and
central canal of spinal cord.
Function: Moves mucus and other substances by ciliary action.
Uterine tube
E. Pseud ostratified
columnar epithelium
Sectional view of ciliated simple columnar
epithelium of uterine tube
Lumen of
uterine tube
Cilia
Nucleus of
ciliated simple
columnar cell
Ciliated simple
columnar
epithelium
Connective
tissue
*»•»»,••■.'••
Cilia
Mucus in
goblet cell
- Basement
membrane
Connective
tissue
Ciliated simple columnar epithelium
Description: Mot a true stratified tissue; nuclei of cells are at different levels; all cells are attached to basement
membrane, but not all reach the apical surface.
Location: Pseudostratified ciliated columnar epithelium lines the airways of most of upper respiratory tract; pseudostratified
nonciliated columnar epithelium lines larger ducts of many glands, epididymis, and part of male urethra.
Function: Secretion and movement of mucus by ciliary action.
Nucleus
of ciliated
**^ ^x\ columnar cell
Trachea
Nucleus of
goblet cell
Nucleus of
basal cell
Connective
tissue
Mucus in Cilia Lumen of
goblet cell
trachea
Sectional view of pseudostratified ciliated columnar
epithelium of trachea
Pseudostratified ciliated columnar epithelium
Mucus in
goblet cell Ciliated columnar cell
r m
Cilia
i
9
8 9
r
»
f- — Basement
membrane
Basal cell
Connective
tissue
Pseudostratified ciliated columnar
epithelium
elial Tissue 79
Covering and Lining Epithelium
Stratified Epithelium
F. Stratified squamous
epithelium
Description: Several layers of cells; cuboidal to columnar shape in deep layers; squamous cells form the apical layer and
several layers deep to it; cells from the basal layer replace surface cells as they are lost.
Location: Keratinized variety forms superficial layer of skin; nonkeratinized variety lines wet surfaces, such as lining of the
mouth, esophagus, part of epiglottis, part of pharynx, and vagina, and covers the tongue.
Function: Protection,
-
<^>^
i
I m&
20Qx
Stratified -
squamous
epithelium
Connective
tissue
Flattened
squamous
cell at
apical
surface
Basement
membrane
Connective
tissue
Sectional view of stratified squamous epithelium of vagina
Stratified squamous epithelium
G, Stratified cuboidal
epithelium
Description: Two or more layers of cells in which cells in the apical layer are cube-shaped.
Location: Ducts of adult sweat glands and esophageal glands and part of male urethra.
Function: Protection and limited secretion and absorption.
Esophagus
Nucleus of stratified
cuboidal cell
Lumen of duct
Sectional view of stratified cuboidal epithelium
of the duct of an esophageal gland
Stratified cuboidal
epithelium
Connective tissue
r qg
Q Q
Stratified cuboidal epithelium
Apical
surface
Basement
membrane
Connective
tissue
(continues)
80 Chapter 4 Tissues
Table 4,1 Epithelial Tissues (continued)
Covering and Lining Epithelium
H. Stratified columnar
epithelium
Description: Several layers of irregularly shaped cells; only the apical layer has columnar cells.
Location: Lines part of urethra, large excretory ducts of some glands such as esophageal glands, small areas in anal mucous
membrane, and a part of the conjunctiva of the eye.
Function: Protection and secretion.
Esophagus
^300x
Sectfonal view of stratified columnar
epithelium Ol the duct Of an esophageal gland
Stratified columnar
epithelium
Lumen of duct
Nucleus of stratified
columnar cell
Connective tissue
Apical
surface
Basement
membrane
Connective
tissue
Stratified columnar epithelium
Transitional
epithelium
Description: Appearance is variable (transitional); shape of cells in apical layer ranges from squamous (when stretched) to
cuboidal (when relaxed).
Location: Lines urinary bladder and portions of ureters and urethra.
Function: Permits distention.
Urinary bladder
Lumen of
urinary
bladder
Nucleus of
transitional
cell
' * ; * , c — Transitional
epithelium
Connective
tissue
Sectional view of transitional epithelium of urinary
bladder in relaxed state
- Apical
surface
Basement
membrane
Connective
tissue
Relaxed transitional epithelium
Epithelial Tissue 81
rering and Lining Epithelium
ilandular Epithelium
j, Endocrine glands
Description: Secretory products (hormones) diffuse into blood after passing through interstitial fluid.
Location: Examples include pituitary gland at base of brain, pineal gland in brain, thyroid and parathyroid glands near larynx
(voice box), adrenal glands superior to kidneys, pancreas near stomach, ovaries in pelvic cavity, testes in scrotum, and thymus
in thoracic cavity.
Function: Produce hormones that regulate various body activities.
c\
w
Thyroid
gland
Thyroid
follicle
500x
Blood vessel
Hormone-producing
(epithelial) cell
Stored precursor
of hormone
Sectional view of endocrine gland (thyroid gland)
Thyroid
follicle
Endocrine gland (thyroid gland)
K. Exocrine glands
Description: Secretory products released into ducts.
Location: Sweat, oil, and earwax glands of the skin; digestive glands such as salivary glands, which secrete into mouth
cavity, and pancreas, which secretes into the small intestine.
Function: Produce substances such as sweat, oil, earwax, saliva, or digestive enzymes.
Skin
Secretory
portion of
sweat gland
300x
Sectional view of the secretory portion of an
exocrine gland (sweat gland)
Lumen of duct
of sweat gland
Nucleus of
secretory
cell of
sweat gland
Basement
membrane
Exocrine gland
(sweat gland)
82 Chapter 4 Tissues
A Papanicolaou test (pa-pa-NI-ko-lo), also called a Pap
test or Pap smear, involves collection and microscopic
examination of epithelial cells that have been scraped off
the apical layer of a tissue. A very common type of Pap test
involves examining the cells from the nankeratinized strat-
ified squamous epithelium of the vagina and cervix (inte-
rior portion) of the uterus. This type of Pap test is per-
formed mainly to detect early changes in the cells of the
trmak: reproductive system that may indicate cancer or a
precancerous condition. In performing a Pap smear, a
physician collects cells, which are then smeared on a mi-
croscope slide. The slides are then sent to a laboratory for
analysis, An annual Pap test is recommended for all
women as part of a routine pelvic exam.
Stratified Cuboidal Epiti [ELIUM This fairly rare type of
epithelium sometimes consists of more than two layers of
cells (Table 4.1G). Cells in the apical layer Lire cuboidal. Its
function is mainly protective; in some locations it also func-
tions in secretion and absorption.
Stratified Columnar Epithelium This type of tissue
also is uncommon. Usually the basal layer or layers consist of
shortened, irregularly shaped cells; only the apical layer of
cells is columnar in form (Table 4. III). This type of epithe-
lium functions in protection and secretion.
Transitional EPITHELIUM This type of stratified epithe-
lium is variable in appearance, depending on whether the
organ it lines is unstretched or stretched. In its unstrctched
state (Tabic 4.11), transitional epithelium looks similar to
stratified cuboidal epithelium, except that the cells in the
apical layer tend to be large and rounded. As the cells are
stretched, they become flatter, giving die appearance of "strat-
ified squamous epithelium. Because of its elasticity, transitional
epithelium lines hollow structures that are subjected to expan-
sion from within, such as die urinary bladder. It allows organs
to stretch to hold a variable amount of fluid without rapturing.
Glandular Epithelium
The function of glandular epithelium is secretion, which is
accomplished by glandular cells that often lie in clusters deep
to the covering and lining epithelium. A gland may consist of
one cell or a group of highly specialized epithelial cells that
secrete substances into ducts (tubes), onto a surface, or into
the blood. All glands of the body are classified as either
endocrine or exocrine.
The secretions of endocrine glands (endo- = within;
-mm = secretion) (Table 4.1J) enter the interstitial fluid and
then diffuse into the bloodstream without flowing through a
duct. These secretions, called hormones, regulate many meta-
bolic and physiological activities to maintain homeostasis.
The pituitary, thyroid, and adrenal glands are examples of
endocrine glands. Endocrine glands will be described in
detail in Chapter 13.
Exocrine glands (exo- = outside; Table 4. IK) secrete
their products into ducts that empty at the surface of cove
ing and lining epithelium such as the skin surface or die lu-
men (interior space) of a hollow organ. The secretions ol d
ocrine glands include mucus, perspiration, oil, earwax, milk,
saliva, and digestive enzymes. Examples of exocrine glands
are sweat glands, which produce perspiration to help lower
body temperature, and salivary glands, which secrete mucus
and digestive enzymes. As you will see later, some glands of]
the body, such as the pancreas, ovaries, and testes, contain
both endocrine and exocrine tissue.
■ CHECKPOINT
3. What characteristics are common to all epithelial tissues?!
4. Describe the various cell shapes and layering arrange-
ments of epithelium.
5. Explain how the structure of the following kinds of ep-
ithelium is related to the functions of each: simple squa-
mous, simple cuboidal, simple columnar (nonciliated and
ciliated), pseudostratified columnar (nonciliated and cili-
ated), stratified squamous (keratinized and nonkeratinized),
stratified cuboidal, stratified columnar, and transitional.
CONNECTIVE TISSUE
OBJECTIVES
• Discuss the general features of connective tissue.
• Describe the structure, location, and function of the
various types of connective tissue,
Connective tissue is one of the most abundant and widely
distributed tissues in the body In its various forms, connec-
tive tissue has a variety of (unctions. It binds together, sup-
ports, and strengthens other body tissues; protects and insu-
lates internal organs; compartmentalizes structures such as
skeletal muscles; is the major transport system within the]
body (blood, a fluid connective tissue); is the major site oi
stored energy reserves (adipose, or fat tissue); and is the main
site of immune responses-
General Features of Connective Tissue
Connective tissue consists of two basic elements: cells and ex-
tracellular matrix. A connective tissue's extracellular matrix
is the materia] between its widely spaced cells. The extracel-
lular matrix consists of protein fibers and ground substance,
the material between the cells and die fibers. The extracellu-
lar matrix is usually secreted by the connective tissue cells
and determines the tissue's qualities. For instance, in cartilage,
Connective Tissue 83 f
i
I Figure 4.2 Representative cells and fibers present in connective tissues.
fc Fibroblasts are usually the most numerous connective tissue cells.
Macrophage
Ground
substance
Reticular
fiber
Adipocyte
Collagen
fiber
Blood vessel
<®|jg^
Eosinophil
Fibroblast
Elastic
fiber
Plasma cell
Neutrophil
Mast cell
What is the function of fibroblasts?
die extracellular matrix is firm but pliable. The extracellular
matrix of bone, by contrast, is hard and not pliable.
In contrast to epithelia, connective tissues do not usually
occur on bodv surfaces. Also, unlike epithelia, connective tis-
, usually are highly vascular; that is, they have a rich blood
supply Exceptions include cartilage, which is avascular, and
tendons, with a scanty blood supply. Except for cartilage,
connective tissues, like epithelia, are supplied with nerves.
Connective Tissue Cells
; types of connective tissue cells vary according to the
.type of tissue and include the following (Figure 4.2):
1 Fibroblasts (Fl-bro-blasts; fibre- = fibers) are large, flat
' cells with branching processes. They are present in sev-
I eral connective tissues, and usually are the most numer-
ous. Fibroblasts migrate through the connective tissue,
secreting the fibers and ground substance of the extracel-
lular matrix.
I Macrophages (MAK-ro-fa-jez; macro- = large; -phages =
eaters) develop from monocytes, a type of white blood
cell. Macrophages have an irregular shape with short
branching projections and are capable of engulfing bacte-
ria and cellular debris by phagocytosis.
3 Plasma cells are small cells that develop from a type of
' ' white blood cell called a B lymphocyte. Plasma cells se-
crete antibodies, proteins that attack or neutralize foreign
substances in the body. Thus, plasma cells are an impor-
tant part of the body's immune response.
4, Mast cells are abundant alongside die blood vessels that
supply connective tissue. They produce histamine, a
chemical that dilates small blood vessels as part of the fo-
il) minatory response, the body's reaction to injury or in-
fection. Mast cells can also kill bacteria.
5. Adipocytes, also called tat cells or adipose cells, are con-
nective tissue cells that store triglycerides (fats). They are
found below the skin and around organs such as the heart
and kidneys.
Connective Tissue Extracellular Matrix
Each type of connective tissue has unique properties, based
on the 'specific extracellular materials between the ceils. The
extracellular matrix consists of a fluid, gel, or solid ground
substance plus protein fibers.
Ground Substance
Ground substance, the component of a connective tissue be-
tween the cells and fibers, supports cells, binds them to-
gether, and provides a medium through which substances are
exchanged between the blood and cells. The ground sub-
stance plays an active role in how tissues develop, migrate,
proliferate, and change shape, and in how they carry out their
metabolic functions.
Ground substance contains water and an assortment of
large organic molecules, many of which are complex combi-
nations of polysaccharides and proteins. For example,
hyaluronic acid (hi'-a-loo-RON-ik) is a viscous, slippery sub-
stance that binds cells together, lubricates joints, and helps
maintain the shape of the eyeballs. It also appears to play a role
in helping phagocytes migrate through connective tissue dur-
ing development and wound repair. White blood cells, sperm
cells, and some bacteria produce byalurmuduse, an enzyme
84 Chapter 4 Tissues
that breaks apart hyaluronic acid and causes the ground sub-
stance of connective tissue to become watery. The ability to
produce hyaluronidase enables white blood cells to move
through connective tissues to reach sites of infection and
sperm cells to penetrate the ovum during fertilization. Tt also
accounts for how bacteria spread through connective tissues.
Fibers
Fibers in the extracellular matrix strengthen and support
connective tissues. Three types of fibers arc embedded in the
extracellular matrix between the cells: collagen fibers, elastic
fibers, and reticular fibers.
Collagen fibers {calk = glue) are very strong and resist
pulling forces, but they are not stiff, which promotes tissue
flexibility. These fibers often occur in bundles lying parallel
to one another (Figure 4.2), The bundle arrangement affords
great strength. Chemically, collagen fihers consist of the pro-
tein collagen. This is the most abundant protein in your body,
representing about 25% of total protein. Collagen fibers are
found in most types of connective tissues, especially bone,
cartilage, tendons, and ligaments.
Despite their strength, ligaments may be stressed beyond
their normal capacity. This results in sprain, a stretched or
torn ligament. The ankle joint is most frequently sprained.
Because of their poor blood supply, the healing of even
partially torn ligaments is a very slow process; completely
torn ligaments require surgical repair.
Elastic fihers, which are smaller in diameter than colla-
gen fibers, branch and join together to form a network within
a tissue. An elastic fiber consists of molecules of a protein
called elastin surrounded by a glycoprotein named fibrillin,
which is essential to the stability of an elastic fiber. Elastic
fibers are strong but can be stretched up to one-and-a-half
times dieir relaxed length without breaking. Equally impor-
tant, elastic fibers have the ability to return to their original
shape after being stretched, a property called elasticity. Elastic
fibers are plentiful in skin, blood vessel walls, and lung tissue.
Marfan syndrome (MAR-fan) is an inherited disorder
caused by a defective fibrillin gene. The result is abnormal
development of elastic libers. Tissues rich in elastic fibers
are malformed or weakened. Structures affected most seri-
ously are the covering layer of bones (periosteum), the lig-
ament that suspends the lens of the eye, and the walls of
the large arteries. People with Marfan syndrome tend to
be tall and have disproportionately long arms, legs, fin-
gers, and toes. A common symptom is blurred vision
ised by displacement of the lens of the eye. The most
life-threatening complication of Marfan syndrome is
weakening of the aorta (the main artery that emerges from
the heart), which can suddenly burst.
Reticular fibers (reficul- = net), consisting of collagen and
a coating of glycoprotein, provide support in the walls of
blood vessels and form branching networks around fat cells,
nerve fibers, and skeletal and smooth muscle cells. Produced
by fibroblasts, they are much thinner than collagen fibers.
Like collagen fibers, reticular fibers provide support and
strength and also form the stroma (= bed or covering) oj
supporting framework of many soft organs, such as the
spleen and lymph nodes. These fibers also help form the
basement membrane.
Classification of Connective Tissues |
Because of the diversity of cells and extracellular matrix and
the differences in their relative proportions, the classification
of connective tissues is not always clear-cut. We offer the id-
lowing scheme:
L Loose connective tissue
A. Areolar connective tissue
B. Adipose tissue
C. Reticular connective tissue
II. Dense connective tissue
D. Dense regular connective tissue
E. Dense irregular connective tissue
K Elastic connective tissue
III. Cartilage
(j. Hyaline cartilage
H. Fibrocartilage
L Elastic cartilage
IV. Bone tissue
V. Liquid connective tissue (blood tissue and lymph)
Loose Connective Tissue
The fibers in loose connective tisme are loosely intertwined]
among the many cells. The types of loose connective tissue
are areolar connective tissue, adipose tissue, and reticular
connective tissue.
Akkolar Connective Tissue One of the most widely dis-
tributed connective tissues in die body is areolar connective
tisme (a-RE-o-lar; areol- = a small space). It contains several
kinds of cells, including fibroblasts, macrophages, plasma
cells, mast cells, adipocytes, and a few white blood cells
(Table 4.2A). All three types of fibers — collagen, elastic, andj
reticular — are arranged randomly throughout the tissue.
Combined with adipose tissue, areolar connective tissue
forms the subcutaneous layer, the layer of tissue that attach.
the skin to underlying tissues and organs.
ADIPOSE TISSUE Adipose tissue is a loose connective tissue
in which the cells, called adipocytes (adipo- = fat), are special-
ized for storage of triglycerides (fats) (Table 4.2 B). Because
the cell fills up with a single, large triglyceride droplet, the
Connective Tissue 85
Loplasm and nucleus are pushed to the periphery of the cell.
Adipose tissue is found wherever areolar connective tissue is
ml, Adipose tissue is a good insulator and can therefore
nee heat loss through the skin. It is a major energy reserve
generally supports and protects various organs. As the
ount of adipose tissue increases with weight gain, new
blood vessels form. Thus, an obese person has many more
blood vessels than does a lean person, a situation that can
cause high blood pressure, since the heart has to work harder.
A surgical procedure, called liposuction {lip- ■ fat) or suc-
tion lipectomy (rectomy = to cut out), involves suctioning
out small amounts of adipose tissue from various areas of
the body. The technique can be used as a body-contouring
procedure in regions such as the thighs, buttocks, arms,
breasts, and abdomen. Postsurgical complications that may
develop include fat emboli (clots), infection, fluid depletion,
injury to internal structures, and severe postoperative pain.
Table 4.2 Connective Tissues
Loose Connective Tissue
A. Areolar connective
tissue
Skin
Description: Consists of fibers (collagen, elastic, and reticular) and several kinds of ceils (fibroblasts, macrophages,
plasma cells, adipocytes, and mast cells) embedded in a semifluid ground substance.
Location: Subcutaneous layer deep to skin; superficial region of dermis of skin; lamina propria of mucous membranes; and
around blood vessels, nerves, and body organs.
Function: Strength, elasticity, and support.
Macrophage
Mast cell
Collagen
fiber
Fibroblast
Plasma ce
Elastic
fiber
Reticular
fiber
Subcutaneous
layer
Sectional view of subcutaneous areolar
connective tissue
Areolar connective tissue
B, Adipose tissue
Heart
Description: Consists of adipocytes, cells specialized to store triglycerides (fats) as a large centrally located droplet;
nucleus and cytoplasm are peripherally located.
Location: Subcutaneous layer deep to skin, around heart and kidneys, yellow bone marrow, and padding around joints
and behind eyeball in eye socket.
Function: Reduces heat loss through skin, serves as an energy reserve, supports, and protects.
Nucleus of
adipocyte
Cytoplasm
Fat-storage area
of adipocyte
Blood vessel
Plasma
membrane
of adipocyte
Adipose tissue
Sectional view of adipose tissue
showing adipocytes of white fat
(continues)
86 Chapter 4 Tissues
Table 4.2 Connective Tissues (continued)
Loose Connective Tissue
C. Reticular connective
tissue
Description: A network of interlacing reticular fibers and reticular cells.
Location: Stroma (supporting framework) of ,iver, spieen, iymph nodes; red bone marrow, which g,ves nse to blood ceiis,
refcuar lamina of the basement membrane; and around blood vessels and muscles.
Function: Forms stroma of organs; binds together smooth muscle tissue cells; filters and removes worn-ou, blood ce.,s j
the spleen and microbes in lymph nodes.
Nucleus of
reticular cell
Reticular fiber
Lymph node
Sectional view of reticular connective tissue
of a lymph node
Reticular connective tissue
Dense Connective Tissue
D. Dense regular
connective tissue
Description: Extracellular matrix looks shiny white; consists mainly of collagen fibers regularly arranged in bund.es;
fibroblasts present in rows between bundles.
Lotion: Forms tendons (attach muscle to bone), most .igaments (attach bone to bone), and aponeuroses (sheets ,e,
dons that attach muscle to muscle or muscle to bone).
Function: Provides strong attachment between various structures.
Nucleus of
fibroblast
Collagen
fiber
Sectional view of dense regular connective
tissue of a tendon
Dense regular connective tissue
REcncuLAK Connective Tissue Reticular connective tis-
sue consists of fine interlacing reticular fibers and reticular
cells (Table 4.2C). Reticular connective tissue forms the
stroma (supporting framework) of certain organs, helps bind
together smooth muscle cells, and filters worn-out blood
cells and bacteria.
Dense Connective Tissue
Dense connective tissue contains more numerous, thicker,
and denser fibers but fewer cells than loose connective
tissue. There are three types: dense regular connecth
tissue, dense irregular connective tissue, and elastic con-
nective tissue.
Dense Regular Connective Tissue In this tissue, bun-
dles of collagen libers are arranged regularly in parallel
terns that provide the tissue with great strength (TabJ
4.2D). The tissue structure withstands pulling along the
of die fibers. Fibroblasts, which produce the fibers mt
ground substance, appear in rows between the fibers. IT"
Connective Tissue 87
Loose Connective Tissue
E. Dense irregular
connective tissue
Skin
Dermis
F, Elastic connective
tissue
Heart
Description: Consists predominantly of collagen fibers randomly arranged and a few fibroblasts.
Location: Fasciae (tissue beneath skin and around muscles and other organs), deeper region of dermis of
skin, periosteum of bone, perichondrium of cartilage, joint capsules, membrane capsules around various organs
(kidneys, liver, testes, lymph nodes), pericardium of the heart, and heart valves.
Function: Provides strength.
Collagen
fiber
Fibroblast
z^W^^^i
Blood
vessel
Sectional view of dense irregular connective
tissue of reticular region of dermis
Dense irregular connective tissue
Description: Consists predominantly of freely branching elastic fibers; fibroblasts are present in spaces between fibers.
Location: Lung tissue, walls of elastic arteries, trachea, bronchial tubes, true vocal cords, suspensory ligament of
penis, and ligaments between vertebrae.
Function: Allows stretching of various organs.
Nucleus of
fibroblast
Elastic lamellae
(sheets of
elastic material)
Sectional view of elastic connective tissue
of aorta
Elastic connective tissue
(continues)
tissue is silvery white and tough, yet somewhat pliable. Ex-
amples are tendons and most ligaments,
Dknsi Irregular Connective Tissuk This tissue con-
, : I- collagen fibers that are packed more closely together
than in loose connective tissue and are usually irregularly
arranged (Table 4.2E). It is found in parts of the body where
pulling forces are exerted in various directions. The tissue
I usually occurs in sheets, such as in the dermis of the skin,
Rich underlies the epidermis. Heart valves, the perichon-
drium (the membrane surrounding cartilage), and the pe-
riosteum (the membrane surrounding bone) are considered
dense irregular connective tissues, despite a fairly orderly
arrangement of their collagen fibers.
Elastic Connective Tissue Branching elastic fibers
predominate in elastic connective tissue (Table 4.2F), giving
the unstained tissue a yellowish color. Fibroblasts are pre-
sent in the spaces between the fibers. Elastic connective tis-
sue is quite strong and can recoil to its original shape alter
Chapter 4 Tissues
Cartilage
G. Hyaline cartilage
Table 4.2 Connective Tissues (continued)
Description: Consists of a bluish-white, shiny ground substance with fine collagen fibers and many chondrocytes; most
abundant type of cartilage.
Location: Ends of long bones, anterior ends of ribs, nose, parts of larynx, trachea, bronchi, bronchial tubes, and embryonic
and fetal skeleton,
Function: Provides smooth surfaces for movement at joints, as well as flexibility and support.
Fetus
H. Fibrocartilage
450x
Sectional view of hyaline cartilage of a
developing fetal bone
Perichondrium
Lacuna
containing
chondrocyte
Nucleus of
chondrocyte
Ground
substance
Hyaline cartilage
Description: Consists of chondrocytes scattered among bundles of collagen fibers within the extracellular matrix.
Location: Pubic symphysis (point where hip bones join anteriorly), intervertebral discs (discs between vertebrae), menisci
(cartilage pads) of knee, and portions of tendons that insert into cartilage.
Function: Support and fusion.
Tendon of
quadriceps
femoris muscle
Patella
(knee cap)
■MOOx
Sectional view of fibrocartilage of tendon
Nucleus of
chondrocyte
Collagen fibers
in ground
substance
Lacuna
containing
chondrocyte
Fibrocartilage
Portion of
right lower limb
Connective Tissue 89
Description: Consists of chondrocytes located in a threadlike network of elastic fibers within the extracellular matrix.
Location: Lid on top of larynx (epiglottis), part of external ear (auricle), and auditory (eustachian) tubes.
Function: Gives support and maintains shape.
Perichondrium
Nucleus of
chondrocyte
Lacuna
containing
chondrocyte
Elastic fiber
in ground
substance
-:?:; ix
Sectional view of elastic cartilage of auricle of ear
Elastic cartilage
luiim stretched. Elasticity is important to the normal func-
tioning of lung tissue, which recoils as you exhale, and elastic
arteries, whose recoil between heart beats helps maintain
blood flow.
Cartilage
Cartilage consists of a dense network of collagen fibers and
elastic fibers firmly embedded in chondroitin sulfate, a rub-
bery component of the ground substance. Cartilage can en-
dure considerably more stress than loose and dense connec-
M tissues. While the strength of cartilage is due to its
collagen fibers, its resilience (ability to assume its original
|rape after deformation) is due to chondroitin sulfate.
The cells of mature cartilage, called chondrocytes
■6-sits; cbondro- = cartilage), occur singly or in groups
within spaces called lacunae (la-KOO-ne = little lakes; sin-
gular is lacuna) in the extracellular matrix. The surface of
st cartilage is surrounded by a membrane of dense irregu-
lar connective tissue called the perichondrium (per'-i-KON-
lim . p er i- = around). Unlike other connective tissues,
cartilage has no blood vessels or nerves, except in the peri-
ndrium. Since cartilage has no blood supply it heals
poorly following an injur}?. The three types of cartilage are
hyaline cartilage, fibrocartilage, and elastic cartilage.
HYALINE CARTILAGE This type of cartilage contains a re-
silient gel as its ground substance and appears in the body as
luish-white, shiny substance. The fine collagen libers are
risible with ordinary staining techniques, and prominent
chondrocytes are found in lacunae (Table 4.2G). iVlost
hyaline cartilage is surrounded by a perichondrium. The ex-
ceptions are the articular cartilage in joints and the epiphy-
seal plates, the regions where bones lengthen as a person
grows. Hyaline cartilage is die most abundant cartilage in the
body It affords flexibility and support and, at joints, reduces
friction and absorbs shock. Hyaline cartilage is the weakest of
the three types of cartilage.
FiBROCARTli AGE Chondrocytes are scattered among clearly
visible bundles of collagen libers widiin the extracellular ma-
trix of this type of cartilage (Table 4.211). Fibrocartilage lacks a
perichondrium. This tissue combines strength and rigidity and
is die strongest of die three types of cartilage. One location of
fibrocartilage is in the discs between vertebrae (backbones).
Elastic: Cartilage In elastic cartilage, chondrocytes are
located within a direadlike network of elastic fibers within the
extracellular matrix (fable 4.21). A perichondrium is present.
Elastic cartilage provides strength and elasticity and maintains
the shape of certain structures, such as the external ear
Bone Tissue
Bones are organs composed of several different connective
tissues, including bone or osseous tissue (OS-e-us). Bone tissue
has several functions. It supports soft tissues, protects delicate
structures, and works with skeletal muscles to generate
movement. Bone stores calcium and phosphorus; stores red
hone marrow, which produces blood cells; and houses yellow r
bone marrow, a storage site for triglycerides. The details of
bone tissue are presented in Chapter 6.
90 Chapter 4 Tissues
The technology of tissue engineering has allowed scientists
to grow new tissues in die laboratory to replace damaged tis-
sues in the body. Tissue engineers have already developed
laboratory-grown versions of skin and cartilage. In the pro-
cedure, scaffolding beds of biodegradable synthetic materials
or collagen are used as substrates that permit body cells such
as skin cells or cartilage cells to be cultured, As the cells di-
vide and assemble, the scaffolding degrades, and the new,
permanent tissue is then implanted in the patient. Other
structures being developed by tissue engineers include
bones, tendons, heart valves, bone marrow, and intestines.
Work is also underway to develop insulin-producing cells for
diabetics, dopamine-producing cells for Parkinson disease
patients, and even entire livers and kidneys.
Liquid Connective Tissue
Blood Tissue Blood tissue (or simply blood) is a connective
tissue with a liquid extracellular matrix called blood plasma, a
pale yellow fluid that consists mostly of water with a wide va-
riety of dissolved substances: nutrients, wastes, enzymes, hor-
mones, respiratory gases, and ions. Suspended in the plasma
are red blood cells, white blood cells, and platelets. Red blood
cells transport oxygen to body cells and remove carbon diox-
ide from them. White blood cells are involved in phagocytosis,
immunity, and allergic reactions. Platelets participate in blood
clotting. The details of blood are considered in Chapter 14.
LYMPH Lymph is a fluid that flows in lymphatic vessels. It is a
connective tissue diat consists of several types of cells in a clear
extracellular matrix similar to blood plasma but with much less
protein. The details of lymph are considered in Chapter 17.
■ CHECKPOINT
6. What are the features of the cells, ground substance, and
fibers that make up connective tissue?
7. How are the structures of the following connective tis-
sues related to their functions: areolar connective tissue,
adipose tissue, reticular connective tissue, dense regular
connective tissue, dense irregular connective tissue, elas-
tic connective tissue, hyaline cartilage, fibrocartilage,
elastic cartilage, bone tissue, blood tissue, and lymph?
MUSCULAR TISSUE
OBJECTIVES • Describe the functions of muscular
tissue.
• Contrast the locations of the three types of muscular
tissue.
Muscular tissue consists of elongated cells called muscle fibers
that are highly specialised to generate force. As a result of
this characteristic, muscular tissue produces motion, maintains
posture, and generates heat It also offers protection. Based on
its location and certain structural and functional characteris-
tics, muscular tissue is classified into diree types; skeletal, car-
diac, and smooth. Skeletal muscle tissue is named for its loca-
tion — it is usually attached to the bones of die skeleton
Cardiac muscle tissue forms the bulk ol the wall of the hc;irt,
Smooth muscle tissue is located in the walls of hollow internal
structures such as blood vessels, airways to the lungs, the stom-
ach, intestines, gallbladder, and urinary bladder. The details of
muscular tissue are presented in Chapter 8,
■ CHECKPOINT I
8. What are the functions of muscular tissue?
9. Name the three types of muscular tissue.
NERVOUS TISSUE
objective • Describe the functions of nervous tissue.
Despite the awesome complexity of the nervous system, it con-
sists of only two principal types of cells: neurons and neu-
roglia. Neurons (new- = nerve, nerve tissue, nervous system)
or nerve cells, are sensitive to various stimuli. They convert
stimuli into nerve impulses (action potentials) and conduct
these impulses to other neurons, to muscle libers, or to glands.
Neuroglia (noo-ROG-lc-a; -glia = glue) do not generate or
conduct nerve impulses, but they do have many other impor-
tant supportive functions. The detailed structure and function
of neurons and neuroglia are considered in Chapter 9.
■ CHECKPOINT
10. How do neurons differ from neuroglia?
MEMBRANES
OBJECTIVES • Define a membrane,
• Describe the classification of membranes.
Membranes are flat sheets of pliable tissue that cover or li
a part of the body. The combination of an epithelial layer and
an underlying connective tissue layer constitutes an epithelial
membrane. The principal epithelial membranes of die bodj
are mucous membranes, serous membranes, and the cuts
neons membrane, or skin. (Skin is discussed in detail in
Chapter 5 and will not be discussed here,) Another kind o^
membrane, a synovial membrane, lines joints and contains
connective tissue but no epithelium.
Mucous Membranes
A mucous membrane or mucosa (mu-KO-sa) lines a bod;
cavity that opens directly to die exterior. Mucous membranj
line the entire digestive, respiratory, and reproductive systei
and much of die urinary system. The epithelial layer ol
^
focus on Wellness
Membranes 91
Excess Adiposity —
Too Much of a Good
Thing
jipose tissue contains adipocytes,
Is specialized for die function of en-
storage. Adequate energy storage
been vital to the survival of our
;cies dirough the ages. But what
ippens when we have too much of a
h.!i,I tiling?
tcess Adiposity: Too Much Fat
jjposity becomes too much of a good
prig when it leads to health problems,
jfhich can include hypertension (high
bod pressure), poor blood sugar regu-
aion (including type 2 diabetes), heart
lease, certain cancers, gallstones,
itis, and lower backaches. In gen
, the risk of health problems associ-
I with excess adipose tissue increases
a dose-dependent fashion: The
iter die excess weight, the greater the
People with a great deal of excess
% have a much higher risk for health
jblems than people who are only
rhtly too fat. But die health effects of
tat depend on several important
[dors hesides quantity of adipose tissue.
Location of Adipose Tissue
People who carry extra fat on the torso
are at greater risk for hypertension,
type 2 diabetes, and artery disease than
people whose extra fat resides in the
hips and thighs- Especially risky is ex-
cess fat stored around the viscera (such
as the abdominal organs). Adipocytes
in this area appear to be more "meta-
bolically active" than those under the
skin. Visceral fat affects blood sugar
and blood fat regulation, which in turn
can lead to the health problems men-
tioned above.
Family Medical History
and Age
Excess body fat is especially risky
for people who have already developed
fat-related health problems, or who
have a family history of these disorders.
On the other hand, people over 70
years old may benefit from a little extra
adipose tissue. Many health profession-
als recommend an extra l(.) or 15
pounds for people over 70 to help them
resist wasting if they should become ill.
Beware the Deadly Sins: Gluttony
and Sloth
People with a moderate amount of ex-
cess adipose tissue who eat a healthy diet
and exercise regularly have health risks
similar to those of their leaner peers.
This observation suggests that some of
the health risks seen in overweight peo-
ple may he caused by poor health habits
(such as too much food, too much alco-
hol, or too little exercise) rather than by
die presence of excess adipose tissue.
Why do you think body weight alone is not always a good measure of
adiposity, or a good predictor of health risks associated with excess
adipose tissue?
ucous membrane secretes mucus, which prevents the cavi-
from drying out. It also traps particles in the respiratory
jjgsageways, lubricates and absorbs food as it moves through
istrointestinal tract, and secretes digestive enzymes. The
fenective tissue layer helps bind the epithelium to the un-
tying structures. It also provides the epithelium with oxy-
mand nutrients and removes wastes via its blood vessels.
(erous Membranes
serom membrane (serous - watery) lines a body cavity that
not open directly to the exterior, and it also covers the
ins that lie within the cavity. Serous membranes consist of
parts: a parietal layer and a visceral layer. The parietal
(pa-RI-e-tal; pariet- = wall) is the part attached to the
i,, wall, and the visceral layer (viscer- = body organ) is
e part that covers and attaches to the organs inside these
ities. Each layer consists of areolar connective tissue cov-
ered by wesothelhmi. Mesothelium is a simple squamous ep-
ithelium. It secretes serous fluid, a watery lubricating fluid
that allows organs to glide easily over one another or to slide
against the walls of cavities.
The serous membrane lining the thoracic cavity and cov-
ering the lungs is the pleura. The serous membrane lining
the heart cavity and covering the heart is the pericardium.
The serous membrane lining die abdominal cavity and cover-
ing the abdominal organs is the peritoneum.
Synovial Membranes
Synovial membranes (sin-O-ve-al) line the cavities ot some
joints. They are composed of areolar connective tissue and
adipose tissue with collagen fibers; they do not have an ep-
ithelial layer. Synovial membranes contain cells (synovio-
cytes) which secrete synovial fluid. This fluid lubricates the
ends of bones as they move at joints, nourishes the cartilage
92 Chapter 4 Tissues
covering the bones, and removes microbes and debris from
the joint cavity.
■ CHECKPOINT
11. Define the following kinds of membranes: mucous,
serous, cutaneous, and synovial.
12. Where is each type of membrane located in the body?
What are their functions?
TISSUE REPAIR: RESTORING
HOMEOSTASIS
OBJECTIVE • Describe the role of tissue repair in
restoring homeostasis.
Tissue repair is the process that replaces worn-out, damaged,
or dead cells. New cells originate by cell division from
the stroma, the supporting connective tissue, or from the
parenchyma, cells that constitute the functioning part of the
tissue or organ. In adults, each of the four basic tissue types
(epithelial, connective, muscular, and nervous) has a different
capacity for replenishing parenchymal cells lost by damage,
disease, or other processes.
Epithelial cells, which endure considerable wear and tear
(and even injury) in some locations, have a continuous capac-
ity for renewal. In some cases, immature, undifferentiated
cells called stem cells divide to replace lost or damaged cells.
For example, stem cells reside in protected locations in the
epithelia of the skin and gastrointestinal tract to replenish
cells sloughed from the apical layer.
Some connective tissues also have a continuous capacity
for renewal. One example is bone, which has an ample blood
supply. Other connective tissues such as cartilage can replen-
ish cells less readily in part because of a poor blood supply
Muscular tissue has a relatively poor capacity for renewal
of lost cells. Cardiac muscle fibers can be produced from
stem cells under special conditions (see page 367). Skeletal
muscle tissue does not divide rapidly enough to replace ex-
tensively damaged muscle fibers. Smooth muscle fibers can
proliferate to some extent, but they do so much more slowly
than the cells of epithelial or connective tissues.
Nervous tissue has the poorest capacity for renewal. Al-
though experiments have revealed the presence of some stem
cells in the brain, they normally do not undergo mitosis to
replace damaged neurons.
If parenchymal cells accomplish the repair, tissue regen-
eration is possible, and a near-perfect reconstruction of the
injured tissue may occur. However, if fibroblasts of the stroma
are active in the repair, the replacement tissue will be a new
connective tissue. The fibroblasts synthesize collagen and
other extracellular matrix materials that aggregate to form
scar tissue, a process known as fibrosis. Because scar tissue is
not specialized to perform the functions of the parenchyii
tissue, the original function of the tissue or organ is impaired
Scar tissue can form adhesions, abnormal joining of tis-
sues. Adhesions commonly form in the abdomen around a
site of previous inflammation such as an inflamed appen-
dix, and they can develop after surgery. Although adhe-
sions do not always cause problems, they can decrease tis- '
sue flexibility, cause obstruction (such as in die intestines
and make a subsequent operation more difficult:.
■ CHECKPOINT |
13. How are stromal and parenchymal repair of a tissi
different?
AGING AND TISSUES
objective • Describe the effects of aging on tissues
Generally tissues heal faster and leave less obvious scars in
young than in the aged. In fact, surgery performed on fe
leaves no scars. The younger body is generally in a better n
tritional state, its tissues have a better blood supply, and i
cells have a higher metabolic rate. Thus, cells can synthd
needed materials and divide more quickly The extracellul
components of tissues also change with age. Glucose, the in
abundant sugar in the body, plays a role in die aging proc
Glucose is haphazardly added to proteins inside and outsi
cells, forming irreversible cross-links between adjacent protei
molecules. With advancing age, more cross-links form, whi
contributes to the stiffening and loss of elasticity that occur!
aging tissues. Collagen fibers, responsible for the strength
tendons, increase in number and change in quality with agii
Elastin, another extracellular component, is responsible for
elasticity of blood vessels and skin. It thickens, fragments, i
acquires a greater affinity for calcium with age- -changes |
may also be associated with the development of atheroscle
sis, the deposition of fatty materials in arterial walls.
■ CHECKPOINT
14. What common changes occur in epithelial and connec
rive tissues with aging?
Now that you have an understanding of tissues, we wi
look at the organization of tissues into organs and orgj
into systems. In the next chapter we will consider how
skin and other organs function as components of the intei
mentary system.
Study Outline 93
COMMON
DISORDERS
Sjogren's Syndrome
Sjogren's syndrome (SI IO-grenz) is a common autoimmune disease
that causes inflammation and destruction of exocrine glands, espe-
u:ilk i he lacrimal (tear) glands and salivary glands. Signs of Sjo-
u's syndrome include dryness of the eyes, mouth, nose, ears,
and vagina, and salivary gland enlargement Systemic effects
iiile fatigue, arthritis, difficulty in swallowing, pancreatitis (in-
umation of the pancreas), pleuritis (inflammation of the pleurae
ill the lungs), and muscle and joint pain. The disorder affects fe-
males more than males by a ratio of 9 to I. About 20% of older
adults experience some signs of Sjogren's syndroms. Treatment is
iportive, including using artifical tears to moisten the eyes, sip-
ping fluids, chewing sugarless gum, using a saliva substitute to
moisten the month, and using moisturing creams for the skin.
Systemic Lupus Erythematosus
ystemic lupus erythematosus (er-i-the-ina- TO-sus), SLE, or sim-
fapfff, is a chronic inflammatory disease of connective tissue oc-
curring mostly in nonwhite women during their childbearing years.
It is an autoimmune disease that can cause tissue damage in every
body system. The disease, which can range from a mild condition in
most patients to a rapidly fetal disease, is marked by periods of exac-
erbation and remission. Although the cause of SI, I 7 is unknown, ge-
netic, environmental, and hormonal factors all have been impli-
cated. The genetic component is suggested by studies of twins and
himily history. Environmental factors include viruses, bacteria,
chemicals, drugs, exposure to excessive sunlight, and emotional
stress, Sex hormones, such as estrogens, may also trigger SI J
Signs and symptoms of SLE include painful joints, low-grade
fever, fatigue, mouth ulcers, weight loss, enlarged lymph nodes and
spleen, sensitivity to sunlight, rapid loss of large amounts of scalp
hair, and anorexia. A distinguishing feature of lupus is an eruption
across die bridge of the nose and cheeks called a "butterfly rash."
Other skin lesions may occur, including blistering and ulceration.
The erosive nature of some SLE skin lesions was thought to resem-
ble the damage inflicted by the bite of a wolf- -thus, the name lupus
(= wolf). The most serious complications of the disease involve in-
llainmation of the kidneys, liver, spleen, lungs, heart, brain, and
gastrointestinal tract. Because there is no cure for SLE, treatment is
supportive, including anti-inflammatory drugs, such as aspirin, and
i mmunosu ppressi ve drugs.
IEDICAL TERMINOLOGY AND CONDITIONS
Tisstte rejection An immune response of the body directed at for-
eign proteins in a transplanted tissue or organ; immunosup-
pressive drugs, such as cyclosporins, have largely overcome tis-
sue rejection in heart-, kidney-, and liver- transplant patients.
Tissue transplantation The replacement of a diseased or injured
tissue or organ; the most successful transplants involve use of a
person's own tissues or those from an identical twin.
Xenotransplantation (zen'-o-trans'-plan-TA-shun; xeno- = strange,
foreign) The replacement of a diseased or injured tissue or organ
with cells or tissues from an animal. Only a few cases of "success-
ful xenotransplantation exist to date.
a
STUDY OUTLINE
Types of Tissues (p. 73)
(issue is a group of similar cells that usually has a similar em-
bryological origin and is specialized for a particular function.
The various tissues of the body are classified into four basic
tvpes: epithelial, connective, muscular, and nervous.
Ihelial Tissue (p. 73)
1. The general types of epithelia include covering and lining
epithelium and glandular epithelium.
, Some general characteristics of epithelium: It consists mostly
cells with little extracellular material, is arranged in sheets, is
attached to connective tissue by a basement membrane, is avas-
cular (no blood vessels), has a nerve supply, and can replace
itself.
3. Epithelial layers can be simple (one layer) or stratified (several
layers). The cell shapes may be squamous (flat), cuboidal (cube-
like), columnar (rectangular), or transitional (variable).
4. Simple squamous epithelium consists of a single layer of flat
cells (Table 4. 1 A). It is found in parts of the body where filtra-
tion or diffusion are priority processes. One type, endothelium,
lines die heart and blood vessels. Another type, mesotheliuni,
forms the serous membranes that line the thoracic and abdomi-
nal cavities and cover the organs within them.
94 Chapter 4 Tissues
5. Simple cuhoidal epithelium consists of a single layer of cube-
sJiaped cells that function in secretion and absorption (Table
4.113). It is found covering the ovaries, in the kidneys and eyes,
and lining some glandular ducts.
6. Noneiliated simple columnar epithelium consists of a single
layer of noneiliated rectangular cells (Table 4.1C). It lines most
of the gastrointestinal tract. Specialized cells containing mi-
crovilli perform absorption. Goblet cells secrete mucus,
7. Ciliated simple columnar epithelium consists of a single layer
of ciliated rectangular cells (Table 4. ID). It is found in a few
portions of the upper respiratory tract, where it moves foreign
particles trapped in mucus out of the respiratory tract.
8. Pseudostra titled columnar epithelium has only one layer but
gives the appearance of many (Table 4, IE).
9. Stratified squamous epithelium consists of several layers of
cells; cells in die apical layer and several layers deep to it are
flat (Table 4. IF). It is protective, A nonkeratinized variety lines
the mouth; a keratinized variety forms the epidermis, the most
superficial layer of the skin.
10. Stratified cuhoidal epithelium consists of several layers of cells;
cells in the apical layer are cube-shaped (Table 4.1(0. It is
found in adult sweat glands and a portion of the male urethra.
IL Stratified columnar epidielium consists of several layers of
cells; cells in the apical layer are column-shaped (Tabic 4.1H).
It is found in a portion of the male urethra and large excretory
ducts of some glands.
12. Transitional epithelium consists of several layers of cells whose
appearance varies with the degree of stretching (Table 4.11). It
lines the urinary bladder.
13. A gland is a single cell or a group of epithelial cells adapted for
secretion,
14. Endocrine glands secrete hormones into interstitial fluid and
then the blood (Table 4.1J).
15. Exocrine glands (mucous, sweat, oil, and digestive glands) se-
crete into ducts or directly onto a free surface (Table 4.1K).
Connective Tissue (p. 82)
1. Connective tissue is one of the most abundant body tissues,
2. Connective tissue consists of cells and an extracellular matrix of
ground substance and fibers; it has abundant matrix with rela-
tively few cells. It does not usually occur on free surfaces, has a
nerve supply (except for cartilage), and is highly vascular (ex-
cept for cartilage, tendons, and ligaments).
3. Cells in connective tissue include fibroblasts (secrete matrix),
macrophages (perform phagocytosis), mast cells (produce hista-
mine), and adipocytes (store fat).
4. The ground substance and fibers make up the extracellular
matrix.
5. The ground substance supports and binds cells together, pro-
vides a medium for the exchange of materials, and is active in
influencing cell functions.
6. The fibers in the extracellular matrix provide strength and sup-
port and are of three types: (a) collagen fibers (composed of
collagen) are found in large amounts in bone, tendons, and lig-
aments; (b) elastic fibers (composed of elastixi, fibrillin, and
other glycoproteins) are found in skin, blood vessel walls, and
lungs; and (c) reticular fibers (composed of collagen and glyco-
protein) are found around fat cells, nerve fibers, and skeletal
and smooth muscle cells.
7. Connective tissue is subdivided into loose connective tissue,
dense connective tissue, cartilage, bone tissue, and liquid con-
nective tissue (blood tissue and lymph).
8. Loose connective tissue includes areolar connective tissue, nli
pose tissue, and reticular connective tissue.
9. Areolar connective tissue consists of the three types or ill
several cells, and a semifluid ground substance (Table 4.2A). It
is found in the subcutaneous layer; in mucous membranes; and
around blood vessels, nerves, and body organs.
10. Adipose tissue consists of adipocytes, which store triglyccrni^
(Table 4«2B). It is found in die subcutaneous layer, around or*
gans, and in the yellow bone marrow.
11. Reticular connective tissue consists of reticular fibers and retic-
ular cells and is found in the liver, spleen, and lymph nodes
(Table 4.2Q. '
12. Dense connective tissue includes dense regular connective tis-
sue, dense irregular connective tissue, and clastic connc
tissue.
13. Dense regular connective tissue consists of parallel bundles
collagen fibers and fibroblasts (Table 4.2D). It forms tendons]
most ligaments, and aponeuroses.
14. Dense irregular connective tissue consists of usually randomly
arranged collagen fibers and a few fibroblasts (Table 4.2E). It i
found in fasciae, die dermis of skin, and membrane capsule!
around organs.
15. Elastic connective tissue consists of branching elastic fibers a
fibroblasts (Table 4.2 F). It is found in the walls of large arteriesj
lungs, trachea, and bronchial tubes.
16. Cartilage contains chondrocytes and has a rubbery matrii
(chondroitin sulfate) containing collagen and elastic fibers.
17. Hyaline cartilage is found in the embryonic skeleton, at the
ends of bones, in the nose, and in respiratory structures (Taj
4,2(7). It is flexible, allows movement, and provides support.
18. Fibrocartilage is found in the pubic symphysis, inrerverteb
discs, and menisci (cartilage pads) of the knee joint (Tab!
4.2H).
19. Elastic cartilage maintains the shape of organs such as
epiglottis of the larynx, audi tow (eustachian) tubes, and e
nal ear (Tabic 4,21).
20. Bone or osseous tissue supports, protects, helps provide rnov
merit, stores minerals, and houses blood-forming tissue.
21. Blood tissue is liquid connective tissue that consists of hi
plasma and formed elements — red blood cells, white bl
cells, and platelets. Its cells transport oxygen and carbon di
ide, carry on phagocytosis, participate in allergic reactions, p
vide immunity, and bring about blood clotting. Lymph, the
traccllular fluid that flows in lymphatic vessels, is also a liq
connective tissue. It is a clear fluid similar to blood plasma bd
with less protein.
I Muscular Tissue (p. 90)
1. Muscular tissue consists of cells (called muscle fibers) that are
specialized for contraction. It provides motion, maintenance of
posture, heat production, and protection.
I Skeletal muscle tissue is attached to bones, cardiac muscle tis-
forms most of the heart wall, and smooth muscle tissue is
found in the walls of hollow internal structures (blood vessels
and viscera).
irvous Tissue (p. 90)
The nervous system is composed of neurons (nerve cells) and
neuroglia (protective and supporting cells).
Neurons are sensitive to stimuli, convert stimuli into nerve im-
pulses, and conduct nerve impulses.
Membranes (p. 90)
1, An epithelial membrane consists of an epithelial layer overlying
a connective tissue layer. Examples are mucous, serous, and cu-
taneous membranes.
Self-Quiz 95
2. Mucous membranes line cavities that open to the exterior, such
as the gastrointestinal tract.
3. Serous membranes line closed cavities (pleura, pericardium,
peritoneum) and cover the organs in the cavities. These mem-
branes consist of parietal and visceral layers.
4. Synovial membranes line joint cavities, bursae, and tendon
sheaths and consist of areolar connective tissue instead of ep-
ithelium.
Tissue Repair: Restoring Homeostasis (p. 92)
L Tissue repair is the replacement of worn-out, damaged, or dead
cells by healthy ones.
2, Stem cells may divide to replace lost or da maged cells.
Aging and Tissues (p. 92)
1. Tissues heal faster and leave less obvious scars in the young
than in the aged; surgery performed on fetuses leaves no scars,
2. The extracellular components of tissues, such as collagen and
elastic fibers, also change with age.
1
s^ SELF-QUIZ
5,
Epithelial tissue functions in
a. conducting nerve impulses b. storing tat
c. covering and lining the body and its parts
(1. movement e. storing minerals
Epithelial tissue is classified according to
a. its location
b. its function
c. the composition of the extracellular matrix
d. the shape and arrangement of its cells
c. whether it is under voluntary or involuntary control
Mucous membranes arc
a. composed of three layers
b. found in body cavities that open to the body's exterior
C. located at the ends of bones
d. found lining the thoracic cavity
c. capable of producing synovial fluid
Which of the following is NOT a type of connective tissue?
a, blood b. adipose c. reticular
d. simple cuboidal e. cartilage
hich of die following is true concerning connective tissue?
,i Except for cartilage, connective tissue has a rich blood
supply
b, Connective tissue is classified according to cell shape and
arrangement.
C. The cells of connective tissue are generally closely joined.
i | oose connective tissue consists of many fibers arranged in
a regular pattern,
e. The fibers in connective tissue are composed of lipids.
6. Match the following tissue types with their descriptions.
A. simple cuboidal
epithelium
B. simple squamous
epithelium
C* adipose
D. fibrocartilage
E. reticular connective
E smooth muscle
G. keratinized stratified
squamous epithelium
H. bone
a. fat storage
_ b. waterproofs the skin
c. forms the stroma
(framework)
of many organs
d* composes the
intervertebral
discs
e. stores red bone marrow,
protects, supports
£ found in the walls of
hollow organs
g. found in lungs, involved
in diffusion
h. found in kidney
tubules, involved in
absorption
7. Tf you were going to design a hollow organ that needed to ex-
pand and have stretchability, which of the following epithelial
and connective tissues might you use?
a. transitional epithelium and elastic connective tissue
b. stratified columnar epithelium and adipose tissue
c. simple columnar epithelium and dense regular connective
tissue
d. simple squamous epithelium and hyaline cartilage
e. transitional epithelium and reticular connective tissue
96 Chapter 4 Tissues
8. Which of the following statements is NOT true concerning
epithelial tissue?
a. The cells of epithelial tissue are closely packed.
b. The basal layer of cells rests on a basement membrane.
c. Epithelial tissue has a nerve supply.
d. Epithelial tissue undergoes rapid rates of cell division.
e. Epithelial tissue is well supplied with blood vessels.
9. Where would you find smooth muscle tissue?
a. the heart b. attached to bones c. in joints
cL in the discs between the vertebrae e. in the walls of
hollow organs
10. A connective tissue with a liquid extracellular matrix is
a. elastic cartilage b. blood c. areolar d. reticular
e. osseous
11. The interior of your nose is lined with
a. a mucous membrane
b. smooth muscle tissue
c* a synovial membrane
d. keratinized stratified squamous epithelium
e. a serous membrane
12. The four main types of tissue are
a. epithelial, embryonic, blood, nervous
b. blood, connective, muscular, nervous
c. connective, epithelial, muscular, nervous
d. stratified, muscular, striated, nervous
e* epithelial, connective, muscular, membranous
13. Which of the following materials would NOT be found in the
extracellular matrix of connective tissue?
a. collagen fibers b. elastic fibers c. keratin
d. reticular fibers e. hyaluronic acid
14. Which connective tissue cells secrete antibodies?
a. mast cells b. adipocytes c\ macrophages
d. plasma cells e. chondrocytes
15. Modified columnar epithelial cells that secrete mucus di
cells.
a, ciliated b« keratinized c, mast d. fibroblast
e. goblet
16. Which tissue forms the bulk of the heart wall?
a. skeletal muscle b. nervous c. bone
d. cardiac muscle e. smooth muscle
17. Stratified squamous epithelium functions in
a. protection and secretion b. contraction c. absorptioi
d. stretching e. transport
18. What tissue type is found in tendons?
a. dense irregular connective tissue b. elastic connective
tissue e. dense regular connective tissue
d, pseudostratified epithelium e. areolar tissue
19. Tn what tissue type would you find stores of calcium ant
phosphorus?
a. bone b> hyaline cartilage c. fibrocartilage
d. dense irregular connective tissue e. elastic cartilage
20. Which of die following statements is true concerning glanduj
tissue?
a. Endocrine glands are composed of connective tissue;
exocrine glands arc composed of modified epithelium,
b. Endocrine gland secretions diffuse into the bloodstream;
exocrine gland secretions enter ducts.
c. A sweat gland is an example of an endocrine gland.
d. Endocrine glands contain ducts; exocrine glands
do not,
e. Exocrine glands produce substances known as hormones.
■
CRITICAL THINKING APPLICATIONS
Your young nephew can't wait to get his eyebrow pierced like
his big brother Tn the meantime, he's walking around with
sewing needles stuck through his fingertips. There is no visible
bleeding. What type of tissue has he pierced? (Be specific.)
How do you know?
Collagen is the new "miracle" cosmetic. It's advertised to give
you shiny hair and glowing skin, and can be injected to reduce
wrinkles. What is collagen? If you wanted to launch your own
line of cosmetics, what tissue or structure would supply you
with -abundant collagen?
Your lab partner Samir put a tissue slide labeled uterine tffl
under the microscope. He focused the slide and exclaunt
"Look! It's all hairy," Explain to Samir what the "hair" really
You've gone out to cat at your favorite last-food join-
body's Fried Chicken Emporium. A health-food zealot grf
your chicken leg and declares, "This is all fat!" Using yoi
knowledge of tissues, defend your dinner choice.
£ ANSWERS TO FIGURE QUESTIONS
4.1
Substances would move most rapidly through squamous cells
because thev are so thin.
Fibroblasts secrete the fibers and ground substance of thee
traccllular matrix.
THE INTEGUMENTARY SYSTEM
chapter 5
x rotecting skin from the
sun's damaging ultraviolet (UV) rays helps
tent premature aging and cancers of the skin.
Avoiding direct sunlight is the best strategy, but
when not practical, a sunscreen should be used
on exposed skim These do not shield the skin
completely, but they do reduce the damaging
tcts of the ultraviolet rays. Evidence suggests
that the skin can repair some damage when
sunscreens are applied consistently. But
researchers warn that mnsct~eens can provide a
false sense of security. Because they prevent
mng, sunscreens may lull us into thinking the
is not hurting us, while damage is occurring.
Focus on Wellness, page 105
www.wJley.CQm/college/apcentral
C/f all the body's organs, none is
more easily inspected or more exposed
to infection, disease, and injury than die skin,
Because of its visibility, skin reflects our emotions and some as-
pects of normal physiology, as evidenced by frowning, blushing,
and sweating. Changes in skin color or condition may indicate
homeostatic imbalances in the body. For example, a skin rash
such as occurs in chickenpox reveals a systemic infection, but a
yellowing of the skin is an indication of jaundice, usually due to
disease of the liver, an internal organ, Other disorders may be
limited to die skin, such as warts, age spots, or pimples. The
skin ? s location makes it vulnerable to damage from trauma, sun-
light, microbes, or pollutants in the environment. Major dam-
age to the skin, as occurs in third-degree burns, can be life
threatening due to the loss of die protective skin functions.
Many interrelated factors may affect both the appearance
and heakh of the skin, including nutrition, hygiene, circulation,
age, immunity, genetic traits, psychological state, and drugs. So
important is the skin to body image that people spend much
time and money to restore it to a more youthful appearance.
Dermatology (der'-ma-TOL-6-je; dennato- = skin; -logy =
study of) is the branch of medicine that specializes in diagnos-
ing and treating skin disorders.
looking back to move ahead . . .
• Types of Tissues (page 73)
• General Features of Epithelial Tissue (page 73)
• Stratified Squamous Epithelium (page 75)
• General Features of Connective Tissue (page 82)
• Areolar Connective Tissue (page 84)
• Dense Irregular Connective Tissue (page 87)
97
98 Chapter 5 The Integumentary System
SKIN
OBJECTIVES • Describe the structure and functions
of the skin.
• Explain the basis for different skin colors.
Recall from Chapter 1 that a system consists of a group of
organs working together to perform specific activities.
The integumentary system (in-teg-u-VlK\-i;u-c; inte- —
whole; -gament = body covering) is composed of organs such
as the skin and hairs, and other structures such as nails. The
skin or cutaneous membrane covers the external surface of
the body. Tt is the largest organ of the body in surface
area and weight. In adults, the skin covers an area ii
about 2 square meters (22 square feet) and weighs 4. 5 -5k
(10-11 lb), about 16% of total body weight.
Structure of Skin
Structurally, the skin consists of two main parts (Figure 5.11
The superficial, thinner portion, which is composed ofep-
Figure 5.1 Components of the integumentary system. The skin consists of a thin, superficial epidermis and a deep, thicker
dermis. Deep to the skin is the subcutaneous layer, whfch attaches the dermis to underlying organs and tissues.
The integumentary system includes the skin and its accessory structures — hair, nails, and glands — along with associated
muscles and nerves.
Epidermal ridge
Dermal papilla
Capillary loop
Sweat pore
Sebaceous (oil) gland
Corpuscle of touch
(Meissner corpuscle
Arrector pili muscle
Hair follicle
Hair root
Eccrine sweat gland
Apocrine sweat gland
Lamellated (pacinian)
corpuscle
Sensory nerve
Adipose
tissue
Hair shaft
Free nerve ending
- EPIDERMIS
Outer
region
— DERMIS
Inner
region
Subcutaneous
layoi
Blood vessels:
Vein
Artery
Sectional view of skin and subcutaneous layer
What types of tissues make up the epidermis and the dermis?
Functions of Skin
1. Body temperature regulation.
2. Reservoir for blood.
3. Protection from external environment.
4. Cutaneous sensations.
5. Excretion and absorption.
6. Vitamin D synthesis.
MIL
i;lr
/ tissue, is the epidermis (ep'-i-DERM-is; epi- —
)ve). The deeper, thicker connective tissue portion is the
is.
Deep to the dermis, but not part of the skin, is the
wtoneous (suhQ) layer. Also called the bypodermis
Ip- = below), this layer consists of areolar and adipose ris-
es. Fibers that extend from the dermis anchor the skin to
subcutaneous layer, which, in turn, attaches to underlying
gsues and organs. The subcutaneous layer serves as a stor-
depot for fat and contains large blood vessels that supply
skin. This region (and sometimes the dermis) also con-
ins nerve endings called lameUated (pacinian) corpuscles
-SEM-e-an) that are sensitive to pressure (Figure 5.1 .).
lidermis
ie epidermis is composed of keratinized stratified squa-
ms epithelium. It contains four principal types of cells:
sratinocytes, melanocytes, Langerhans cells, and Merkel
(see Figure 5.1). About 90% of epidermal cells are ker-
imuytes (ker-a-TIN-o-sIts; keratino- = hornlike; -cytes
Skin 99
cells), which are arranged in four or five layers and produce
the protein keratin. Recall from Chapter 4 that keratin is a
tough, fibrous protein that helps protect the skin and
underlying tissues from heat, microbes, and chemicals.
Keratinocytes also produce lamellar granules, which release a
water-repellent sealant.
About 8% of the epidermal cells are melanocytes (MEL-
a-no-sits; melano- — black), which produce the pigment
melanin. Their long, slender projections extend between the
keratinocytes and transfer melanin granules to them.
Melanin is a yellow-red or brown-black pigment that con-
tributes to skin color and absorbs damaging ultraviolet (UV)
light. Although keratinocytes gain some protection from
melanin granules, melanocytes themselves are particularly
susceptible to damage by UV light.
Langerhans cells (LANG-er-hans) participate in immune
responses mounted against microbes that invade the skin.
Langerhans cells, macrophages, and B cells help other cells
of the immune system recognize an antigen (foreign microbe
or substance) so that it can be destroyed (Chapter 17).
Langerhans cells are easily damaged by UV light.
Hire 5.2 Layers of the epidermis.
The epidermis consists of keratinized stratified squamous epithelium.
stum — —
leum
Dead
keratinocytes Superficial
Lamellar granules
Keratinocyte
Langerhans cell
Merkel cell
Tactile disc
Sensory neuron
Melanocyte
Dermis
Deep
f
^
240x
Epidermis:
Stratum
corneum
Stratum
lucid urn
Stratum
granulosum
Stratum
spinosum
Stratum
basale
Dermis
(a) Four principal cell types in epidermis
(b) Photomicrograph of a portion of the skin
Which epidermal layer includes stem cells that continually undergo cell division?
1 00 Chapter 5 The Integumentary System
Merkel cells contact the flattened process of a sensory
neuron (nerve cell), a structure called a tactile (Merkel) disc.
Merkel cells and tactile discs detect different aspects of touch
sensations.
Several distinct layers of keratinocytes in various stages
of development form the epidermis (Figure 5.2). Tn most re-
gions of the body the epidermis has four strata or layers —
stratum basale, stratum spinosum, stratum granulosum, and a
thin stratum corneum. This is called thm skin. Where expo-
sure to friction is greatest, such as in die fingertips, palms,
and soles, die epidermis has five layers — stratum basale, stra-
tum spinosum, stratum granulosum, stratum lueidum, and a
thick stratum corneum. This is referred to as thick skin.
The deepest layer of the epidermis is the stratum basale
(ba-SA-le; basal- = base), composed of a single row of
cuboidal or columnar keratinocytes. Some cells in this layer
are stem cells that undergo cell division to continually produce
new keratinocytes.
New skin cannot regenerate if an injury destroys the stra-
tum basale and its stem cells. Skin wounds of this magni-
tude require skin grafts in order to heal. A skin graft is the
transfer of a patch of healthy skin taken from a donor site
to cover a wound. To avoid tissue rejection, the trans-
planted skin is usually taken from the same individual {au-
tograft) or an identical twin (isograft). If skin damage is so
extensive that an autograft would cause harm, a self-
donation procedure called autologous skin transplantation
(aw-TOL-6-gus) may be used. In this procedure, per-
formed most often for severely burned patients, small
amounts of an individual's epidermis are removed, and the
keratinocytes are cultured in the laboratory to produce
thin sheets of skin. The new skin is transplanted back to
the patient so that it covers the burn wound and generates
a permanent skin. Also available as skin grafts are products
grown in the laboratory from the foreskins of circumcised
infants, and synthetic materials, which are products of tis-
sue engineering.
Superficial to the stratum basale is the stratum spinosum.
(spi-NO-sum; spinas- = thornlike), where 8 to 10 layers of
many-sided keratinocytes fit closely together. Cells in the
more superficial portions of this layer become somewhat flat-
tened.
At about the middle of the epidermis, the stratum gran-
ulosum (gran-u-LQ-sum; granulos- = little grains) consists of
diree to five layers of ilattened keratinocytes that are under-
going apoptosis, genetically programmed cell death in which
the nucleus fragments before die cells die. The nuclei and
other organelles of these cells begin to degenerate. A distinc-
tive feature of cells in this layer is the presence of keratin.
Also present in the keratinocytes are membrane-enclosed
lamellar granules, which release a Iipid-rich secretion that
acts as a water-repellent sealant, retarding loss of body fluids
and entry of foreign materials.
The stratum lucidum (LOO-si-dum; lucid- = clear) is
present only in the thick skin of the fingertips, palms, and
soles. It consists of three to live layers ot ilattened clear, dead
keratinocytes that contain large amounts of keratin.
The stratum corneum (COR-ne-um; come- - horn or
horny) consists of 25 to 30 layers of flattened dead ker-
atinocytes. These cells are continuously shed and replacej
by cells from the deeper strata, The interior of the eel
contains mostly keratin. Its multiple layers of dead cells
help to protect deeper layers from injury and microbial in
vasion. Constant exposure of skin to friction stimulates
formation of a callus, an abnormal thickening ol the strat
corneum.
Newly formed cells in the stratum basale are slow!
pushed to the surface. As the cells move from one epiden
layer to the next, they accumulate more and more keratin
a process called kemtimzation (ker'-a-tin-i-ZA-shun). Even-
tually the keratinized cells slough off and are replaced by un
deriving cells that, in turn, become keratinized. The w
process by which cells form in the stratum basale, rise to the
surface, become keratinized, and slough off, takes about four
weeks in an average epidermis of 0.1 mm (0.004 in.) thick]
ness. An excessive amount of keratinized cells shed from the
skin of the scalp is called dandruff.
Dermis
The second, deeper part of the skin, the dermis, is compost
mainly of connective tissue containing collagen and elastic
fibers. The superficial part of the dermis makes up i
one-fifth of the thickness of the total layer (see Figure 5.1).
consists of areolar connective tissue containing fine elast
fibers. Its surface area is greatly increased by small, fingerlil
projections called dermal papillae (pa-PIL-e = nipples
These nipple-shaped structures indent the epidermis. Some
contain capillary loops (blood capillaries). Other dermal papil-
lae also contain tactile receptors called corpuscles of toad
Meissner corpuscles, nerve endings that are sensitive to touch. J
Also present in the dermal papillae are free nerve endings ths
are associated with sensations of warmth, coolness, pain, tick-
ling, and itching.
The deeper part of the dermis, which is attached to thj
subcutaneous layer, consists of dense irregular connective ti<
sue containing bundles of collagen and some coarse elastic
fibers. Adipose cells, hair follicles, nerves, oil glands, an|
sweat glands are found between the fibers.
The combination of collagen and elastic fibers in
deeper part of the dermis provides the skin with strength,
tensibility (ability to stretch), and elasticity (ability to return
original shape after stretching). The extensibility of skin
readily be seen in pregnancy and obesity. Extreme stretchim
kowever, may produce small tears in the dermis, causing
toe(STRI~e = streaks), or stretch marks, that are visible as
red or silvery white streaks on the skin surface.
Skin Color
nut, hemoglobin, and carotene are three pigments that
impart a wide variety of colors to skin. The amount of
melanin causes the skin's color to vary from pale yellow to
red to tan to black. Melanocytes are most plentiful in the epi-
dermis of the penis, nipples of the breasts, the area just
ind die nipples (areolae), face, and limbs. They are also
present in mucous membranes. Because the number of
melanocytes is about the same in all people, differences in
skin color are due mainly to the amount of pigment the
mocytes produce and transfer to keratinocytes. In some
people, melanin accumulates in patches called freckles. As a
puson grows older, age (liver) spots may develop, These flat
blemishes look like freckles and range in color from light
town to black. Like freckles, age spots are accumulations of
melanin. A round, flat, or raised area that represents a benign
lized overgrowth of melanocytes and usually develops in
jldhood or adolescence is called a nevus (NE-vus), or a
mole.
Exposure to UV light stimulates melanin production.
Both die amount and darkness of melanin increase, which
the skin a tanned appearance and further protects the
body against UV radiation. Thus, within limits, melanin
Irves a protective function. Nevertheless, repeatedly expos-
ing the skin to UV light causes skin cancer. A tan is lost when
le melanin-containing keratinocytes are shed from the stra-
ta corneum. Albinism (AL-bin-izm; alhin- = white) is the
inherited inability of an individual to produce melanin. Most
albinos (al-BI-nos), people affected by albinism, do not have
melanin in their hair, eyes, and skin.
Dark-skinned individuals have large amounts of melanin
ie epidermis. Consequently, the epidermis has a dark pig-
mentation and skin color ranges from yellow to red to tan to
black. Light-skinned individuals have little melanin in the
dermis. Thus, the epidermis appears translucent and skin
r ranges from pink to red depending on the amount and
-en content of the blood moving through capillaries in
dermis. The red color is due to hemoglobin, the oxygen-
ing pigment in red blood cells.
Carotene (KAR-6-ten; carot = carrot) is a yellow-orange
| pigment diat gives egg yolk and carrots their colon This pre-
or of vitamin A, which is used to synthesize pigments
Leded for vision, accumulates in the stratum corneum and
forty areas of the dermis and subcutaneous layer in response
excessive dietary intake. In fact, so much carotene may be
Heposited in the skin after eating large amounts of carotene-
rich foods that the skin color actually turns orange, which is
especially apparent in light-skinned individuals.
Accessory Structures of the Skin 101
The color of skin and mucous membranes can provide
clues for diagnosing certain conditions. When blood is not
picking up an adequate amount of oxygen in the lungs, as
in someone who has stopped breathing, the mucous
membranes, nail beds, and skin appear bluish or cyanotic
(sI-a-NOT-ik; cyan- = blue). Jaundice QON-dis;jamd- =
yellow) is due to a buildup of the yellow pigment bilirubin in
die skin. This condition gives a yellowish appearance to die
skin and the whites of the eyes, and usually indicates liver
disease. Erythema (er-i-THE-ma; eryth- - red), redness
of the skin, is caused by engorgement of capillaries in the
dermis with blood due to skin injury, exposure to heat, in-
fection, inflammation, or allergic reactions. Pallor (PAL-
or), or paleness of the skin, may occur in conditions such as
shock and anemia. All skin color changes are observed most
readily in people with lighter-colored skin and may be more
difficult to discern in people with darker skin. However, ex-
amination of the nail beds and gums can provide some in-
formation about circulation in individuals with darker skin.
■ CHECKPOINT
1. What structures are included in the integumentary
system?
2. What are the main differences between the epidermis
and dermis of the skin?
3. What are the three pigments found in the skin, and how
do thev contribute to skin color?
ACCESSORY STRUCTURES
OF THE SKIN
OBJECTIVE m Describe the structure and functions of
hair, skin glands, and nails.
Accessory structures of the skin that develop from the epider-
mis of an embryo — hair, glands, and nails- -perform vital
functions. Hair and nails protect the body. Sweat glands help
regulate body temperature,
Hair
Hairs, or pili (PI-le), are present on most skin surfaces except
the palms, palmar surfaces of the fingers, soles, and plantar
surfaces of the toes. In adults, hair usually is most heavily dis-
tributed across the scalp, over the brows of the eyes, and
around the external genitalia. Genetic and hormonal influ-
ences largely determine the thickness and pattern of distribu-
tion of hair. Hair on the head guards the scalp from injury
and the sun's rays; eyebrows and eyelashes protect the eyes
1 02 Chapter 5 The Integumentary System
from foreign particles; and hair in the nostrils protects
against inhaling insects and foreign particles.
Each hair is a thread of fused, dead, keratinized cells that
consists of a shaft and a root (Figure 5.3). The shaft is the
superficial portion, most of which projects above the surface
of the skin. The root is the portion below the surface that
penetrates into the dermis and sometimes into the subcuta-
neous layer. Surrounding the root is the hair follicle, which is
composed of two layers of epidermal cells: external and inter-
nal root sheaths surrounded by a connective tissue sheath. Sur-
rounding each hair follicle are nerve endings, called hair root
plexuses, that are sensitive to touch. If a hair shaft is moved, its
hair root plexus responds.
The base of each follicle is enlarged into an onion-
shaped structure, the bulk In the bulb is a nipple-shaped
indentation, the papilla of the hah; that contains many blood
vessels and provides nourishment for die growing hair. The
bulb also contains a region of cells called the matrix, which
produces new hairs by eell division when older hairs are slid.
Chemotherapy is die treatment of disease, usually cancer,
by means of chemical substances or drugs. Chemotherapeu-
tic agents interrupt the life cycle of rapidly dividing cancer
cells. Unfortunately, the drugs also affect other rapidly divid-
ing cells in the body, such as the matrix cells of a hair. It is
for this reason that individuals undergoing chemotherapy
experience hair loss. Since about 15% of the matrix cells of
scalp hairs are hi die resting stage, these cells are not affected
by chemotherapy. Once chemotherapy is stopped, the matrix
cells replace lost hair follicles and hair growth resumes.
Figure 5.3 Hair.
Hairs are growths of epidermis composed of dead, keratinized cells.
... H.
Hair root;
Sebaceous gland
Hair root plexus
Bulb
Papilla of the hair
Apocrine sweat gland
Hair follicle:
Internal root
sheath
External root
sheath
Blood vessels
Melanocyte
Papilla of the hair
Blood vessels
Hair foot
(b) Frontal section of hair root
External
root sheath
Connective
tissue sheath
,c) Transverse section of hair root
?
Which part of a hair produces a new hair by ceil division?
Sebaceous (oil) glands (discussed shortly) and a bundle of
Loath muscle cells are also associated with hairs. The
Smooth muscle is called arrector pili (a-RKK-tor PI-le; arrcct
= to raise). It extends from the upper dermis to the side of
L hair follicle. In its normal position, hair emerges at an an-
He to the surface of the skin. Under stress, such as cold or
■ght, nerve endings stimulate the arrector pili muscles to
contract, which pulls the hair shafts perpendicular to the skin
surface. This action causes "goose bumps" because the skin
[around die shaft forms slight elevations.
The color of hair is due to melanin. It is synthesized by
[melanocytes in the matrix of the bulb and passes into cells of
pe root and shaft. Dark-colored hair contains mostly true
melanin. Blond and red hair contain variants of melanin in
Rich there is iron and more sulfur. Gray hair occurs with a
Lline in the synthesis of melanin. White hair results from
■^cumulation of air bubbles in the hair shaft.
At puberty, when the testes begin secreting significant
Lntities of androgens (masculinizing sex hormones),
Lies develop the typical male pattern of hair growth, in-
Linga beard and a hairy chest. In females at puberty, the
.varies and the adrenal glands produce small quantities of
Ldroefens, which promote hair growth in the axillae and
Kubic region. Occasionally, a tumor of the adrenal glands,
or ovaries produces an excessive amount of androgens.
■he result in females or prepubertal males is hirsutism
; HI: :i iizm; birsut- = shaggy), a condition of excessive
\ hair.
Surprisingly, androgens also must be present for occur-
rence of the most common form of baldness, androgenic
akpecui ur male-pattern baldness. In genetically predisposed
faults, androgens inhibit hair growth. On men, hair loss is
Lt obvious at the temples and crown. Women are more
Rely to have thinning of hair on top of the head. The first
Lg approved for enhancing scalp hair growth was minoxidil
une®)* It causes vasodilation (widening of blood vessels),
i is increasing circulation. In about a third of the people
lo try it, minoxidil improves hair growth, causing scalp fol-
lies to enlarge and lengthening the growth cycle. For many,
jnrevcr, the hair growth is meager. Minoxidil does not help
jcople who already are bald.
glands
Recall from Chapter 4 that glands are single or groups of ep-
Llial cells that secrete a substance. The glands associated
with the skin include sebaceous, sudoriferous, and cerumi-
ius glands.
acvous Glands
com glands (se-BA-shus; sebace- = greasy) or oil
ohsnh, with few exceptions, are connected to hair follicles
Accessory Structures of the Skin 1 03
(Figure 5.3a). The secreting portions of the glands lie in the
dermis and open into the hair follicles or directly onto a skin
surface. There are no sebaceous glands in the palms and
soles.
Sebaceous glands secrete an oily substance called sebum
(SE-bum). Sebum keeps hair from drying out, prevents
excessive evaporation of water from the skin, keeps the skin
soft, and inhibits the growth of certain bacteria.
When sebaceous glands of the lace become enlarged
because of accumulated sebum, blackheads develop. Because
sebum is nutritive to certain bacteria, pimples or boils often
result. The color of blackheads is due to melanin and oxi-
dized oil, not dirt. Sebaceous gland activity increases during
adolescence.
Sudoriferous Glands
There are three to four million sudoriferous glands (soo'-
dor-IF-er-us; siulori- = sweat; -ferom = bearing), or sweat
glands, divided into two main types: eccrine and apocrine.
Eccrine sweat glands (eccrine = secreting outwardly)
are much more common than apocrine sweat glands. They
are distributed throughout the skin of most parts of the
body, except for the margins of the lips, nail beds of the
fingers and toes, glans penis, glans clitoris, labia minora,
and eardrums. Eccrine sweat glands are most numerous in
the skin of the forehead, palms, and soles; their density can
be as high as 450 per square centimeter (3000 per square
inch) in the palms. The secretory portion of eccrine sweat
glands is located mostly in the deep dermis (sometimes in
the upper subcutaneous layer). The excretory duct projects
through the dermis and epidermis and ends as a pore at the
surface of the epidermis (see Figure 5,1). The sweat pro-
duced by eccrine sweat glands (about 600 niL per day)
consists of water, ions (mostly Na' and CI), urea, uric
acid, ammonia, amino acids, glucose, and lactic acid. The
main function of eccrine sweat glands is to help regulate
body temperature through evaporation. As sweat evapo-
rates, large quantities of heat energy leave the body sur-
face.
Apocrine sweat glands are found mainly in the skin of
the axilla (armpit), groin, areolae (pigmented areas around
the nipples) of the breasts, and bearded regions of the face in
adult males. The secretory portion of these sweat glands is
located mostly in the subcutaneous layer, and the excretory
duct opens into hair follicles (see Figure 5.1). Their secretory
product is slightly viscous compared to eccrine secretions and
contains the same components as eccrine sweat plus lipids
and proteins. Eccrine sweat glands start to function soon af-
ter birth, but apocrine sweat glands do not begin to function
until puberty. Apocrine sweat glands are stimulated during
emotional stress and sexual excitement; these secretions are
commonly known as a "cold sweat,"
1 04 Chapter 5 The Integumentary Syste
Cemiminous Glands
Ceruminous glands (sc-ROO-mi-nus; cer- = wax) are pre-
sent in die external auditory canal, the outer ear canal The
combined secretion of the ceruminoiis and sebaceous glands
is called cerumen or earwax. Cerumen and the hairs in the
external auditory meatus provide a sticky barrier against
foreign bodies.
■ CHECKPOINT
4. Describe the structure of a hair. What causes "goose
bumps"?
5. Contrast the locations and functions of sebaceous (oil)
glands and sudoriferous (sweat) glands.
6. Describe the parts of a nail.
Nails
Nails are plates of tightly packed, hard, dead, keratinized
cells of the epidermis. Each nail (Figure 5.4) consists of a nail
body, a free edge, and a nail root. The nail body is the
portion of the nail that is visible; the free edge is the part of
the body that extends past the end of the finger or toe; the
nail root is die portion that is not visible. Most of the nail
body is pink because of the underlying blood capillaries. The
whitish semilunar area near the nail root is called the lunula
(LOO-nyu-la = little moon). It appears whitish because the
vascular tissue underneath does not show through due to the
thickened stratum basale in the area. Nail growth occurs by
the transformation of superficial cells of the nail matrix into
nail cells. The average growth of fingernails is about 1 mm
(0.04 inch) per week. The cuticle consists of stratum
corneum.
Functionally, nails help us grasp and manipulate small
objects, provide protection to the ends of die fingers and
toes, and allow us to scratch various parts of the body.
FUNCTIONS OF THE SKIN
OBJECTIVE • Describe how the skin contributes to the
regulation of body temperature, protection, sensation, ex-
cretion and absorption, and synthesis of vitamin D.
Following are the major functions of die skin:
1. Body temperature regulation. The skin contributes to j
die homeostatic regulation of body temperature by liber-
ating sweat at its surface and by adjusting the flov,
blood in the dermis (discussed in detail in Chapter 20)
2. Protection, Keratin in die skin protects underlying
from microbes, abrasion, heat, and chemicals, and thi
tightly interlocked keratinocytes resist invasion by
crobes. Lipids released by lamellar granules inhibit evap-
oration of water from the skin surface, dius protectinj
the body from dehydration. Oily sebum prevents has
from drying out and contains bactericidal chemicals that
Figure 5.4- Nails. Shown is a fingernail.
\ Nail cells arise by transformation of superficial cells of the nail matrix into nail cells.
Nail root Cuticle Lunula Nail body
Free edge
Nail body
Lunula
Cuticle
Nail root
M
i-%>#^
Free edge
of nail
. .
m
Epidermis
Dermis
Phalanx
(finger
bone)
Nail matrix
(a) Dorsal view
Why are nails so hard?
->
(b) Sagittal section showing internal detail
ocus on Wellness
Lifestyles
Physical activity is good for your skin.
During exercise, the body shunts blood
the skin to help release excess heat
oduced by the contracting muscles.
is increased blood flow provides the
with nutrients and gets rid of
Bes.
in the Sun
ram your skin's point of view, the
in problem with exercise is that it
en occurs outdoors, where sun expo-
e over the years can lead to wrinkles,
e spots, and cancers of the skin. To
event these, do what you can to min-
ze sun exposure. The most effective
(an protection is some form of sun
lock. Tightly woven clothing (hold it
to a light and see how much shines
ough) helps keep the sun's rays from
aching the skin, and wide-brimmed
ts provide some protection. Zinc ox-
e blocks the sun and is good for noses
lips when long-term exposure is
avoidable.
V
Functions of the Skin 105
When a sun block is not practical, a
sunscreen should be used. These do
not shield the skin completely, but they
do reduce the damaging effects of the
ultraviolet rays. Evidence suggests that
the skin can repair some damage when
sunscreens are consistently applied. But
researchers warn that sunscreens can
provide a false sense of security Be-
cause they prevent burning, sunscreens
may lull us into thinking the sun is not
hurting us, while damage may still be
occurring.
Barriers to Skin Protection
Chemists have yet to invent a sun-
screen that is fun to wear. Many exer-
cisers can't take the grease, especially,
as an avid bicyclist put it, "as it mingles
with sweat and dead bugs." Advice for
heavy sweaters is to exercise in the
early or late part of the day, take as
shady a route as possible, wear a hat
and protective clothing, and use as
much sunscreen as you can tolerate.
Swimmers should note that "water-
proof" sunscreen stays on for only
about 30 minutes in the water and
should be reapplied at that time.
Dry Skin Care
Although not life threatening, dry skin
can be very uncomfortable. Frequent
showers and water exposure can strip
the skin of its natural protective oils.
The only solution is frequent moistur-
izing. Use of a good moisturizing
cream immediately after drying off will
counteract the drying effect of a "wash-
and-wear" lifestyle.
► Think It
Imagine yon have a friend who is training for a marathon and must exercise
outdoors for an hour or more on most days. He has fair skin and a family
history of skin cancer What advice would yon give him for minimizing sun
exposure while continuing his training?
surface bacteria. The acidic pi I of perspiration re-
tards the growth of some microbes. Melanin provides
some protection against the damaging effects ot UV
lieht. Hair and nails also have protective functions.
I, Cutaneous sensations. Cutaneous sensations are those
that arise in the skin. These include tactile sensations —
touch, pressure, vibration, and tickling — as well as ther-
mal sensations such as warmth and coolness. Another
cutaneous sensation, pain, usually is an indication of im-
pending or actual tissue damage. Chapter 12 provides
mure details on the topic of cutaneous sensations.
Excretion and absorption. The skin normally has a
small role in excretion, the elimination of substances from
the body and absorption, the passage of materials from the
external environment into body cells.
Most drugs are either absorbed into die body through the
digestive system or injected into subcutaneous tissue or mus-
cle. An alternative route, transdermal (transcutaneous)
drug administration, enables a drug contained within an
adhesive skin patch to pass across die epidermis and into the
blood vessels of the dermis. The drug is released continu-
ously at a controlled rate over one to several days. A growing
number of drugs are available for transdermal administra-
tion, including nitroglycerin, for prevention of angina pec-
toris (chest pain associated with heart disease); scopolamine,
for motion sickness; estradiol, used for estrogen -replacement
therapy during menopause; ethinyl estradiol mt\ norelge-
stromin in contraceptive patches; nicotine, used to help peo-
ple stop smoking; and fentanyl, used to relieve severe pain in
cancer patients.
1 06 Chapter 5 The Integumentary System
5. Synthesis of vitamin D. Exposure of the skin to ultravi-
olet radiation activates vitamin D. Ultimately vitamin D
is converted to its active form, a hormone called eal-
citriol, that aids in die absorption of calcium and phos-
phorus from the gastrointestinal tract into the hlood.
People who avoid sun exposure and individuals who live in
colder, northerti climates may experience vitamin D defi-
ciency if it is not included in their diet or as supplements.
■ CHECKPOINT
7. In what two ways does the skin help regulate body tem-
perature?
8. In what ways does the skin serve as a protective barrier?
9. What sensations arise from stimulation of neurons in the
skin?
AGING AND THE
INTEGUMENTARY SYSTEM
OBJECTIVE • Describe the effects of aging on the in-
tegumentary system.
Most infants and children encounter relatively few problems
with die skin as it ages. With the arrival of adolescence, how-
ever, some teens develop acne. The pronounced effects of
skin aging do not become noticeable until people reach their
late forties. Most of the age-related changes occur in the der-
mis. Collagen fibers in the dermis begin to decrease in num-
ber, stiffen, break apart, and disorganize into a shapeless,
matted tangle. Elastic fibers lose some of their elasticity,
thicken into clumps, and fray, an effect that is greatly acceler-
ated in the skin of smokers. Fibroblasts, which produce both
collagen and elastic fibers, decrease in number. As a result,
the skin forms the characteristic crevices and furrows known
as wrinkles.
With further aging, Langerhans cells dwindle and
macrophages become less-efficient phagocytes, thus decreas-
ing the skin's immune responsiveness. Moreover, decreased
size of sebaceous glands leads to dry and broken skin that is
more susceptible to infection. Production of sweat dimin-
ishes, which probably contributes to the increased incidence
of heat stroke in the elderly. There is a decrease in the num-
ber of functioning melanocytes, resulting in gray hair and
atypical skin pigmentation. An increase in the size of some
melanocytes produces pigmented blotching (age spots). Walls
of blood vessels in the dermis become thicker and less per-
meable, and subcutaneous fat is lost. Aged skin (especially the
dermis) is thinner than young skin, and the migration of cells
from the basal layer to the epidermal surface slows consider-
h With the onset of old age, skin heals poorly and be-
comes more susceptible to pathological conditions such as
skin cancer, itching, and pressure ulcers.
Growth of nails and hair begins to slow during the sec-
ond and third decades of life. The nails also may become
more brittle with age, often due to dehydration or repeated
use of cuticle remover or nail polish.
Several cosmetic anti-aging treatments are available to
diminish the effects of aging or sun-damaged skin, including
topical products that bleach the skin to tone down blotches
and blemishes (hydroquinone) or decrease fine wrinkles and
roughness (retinoic acid); ntia^odermahrasion (mi-kro-DER-
ma-bra-zhun; mikros- = small, derm = skin; -abrasio • to
wear away), the use of tiny crystals under pressure to remove
and vacuum the skin's surface cells to improve skin texture
and reduce blemishes; chemical peel, the application of a mill
acid (such as glycolic acid) to the skin to remove surface cells
to improve skin texture and reduce blemishes; laser resurfac-
ing, the use of a laser to clear up blood vessels near the skL
surface, even out blotches and blemishes, and decrease fin
wrinkles; dermal fillers, injections of collagen from cows
hyaluronic acid, or calcium hydroxylapatite that plumps
the skin to smooth out wrinkles and fill in furrows, such
those around the nose and mouth and between the eyebrows
fat transplantation, in which fat from one part of the body!
injected into another location such as around the eyes; hotit-
liniim toxin or Botox®, a diluted version of the toxin that
causes food poisoning, which is injected into the skin to para-
lyze muscles that cause the skin to wrinkle; radio frequency
nonsurgical facelift, the use of radio frequency emissions to
tighten skin of the jowls, neck, and sagging eyebrows am
eyelids; and facelift, hrowlift, or necklift, invasive surgery
which loose skin and fat are removed surgically and the un
derlying connective tissue and muscle are tightened,
■ CHECKPOINT
10. Which portion of the skin is involved in most age-rek|
changes? Give several examples.
To appreciate the many ways that skin contributes
homeostasis of other body systems, examine the Focus on]
Homeostasis: The Integumentary System on page 109. This |
focus box is the first often, found at the end of selected chapl
ters, that explain how the body system under consideration
contributes to homeostasis of all the other body systems. The
Focus on Homeostasis feature will help you understand hod
the individual body systems interact to contribute to the
homeostasis of the entire body. Next, in Chapter 6, we wi|
explore how bone tissue is formed and how bones are assem-
bled into the skeletal system, which protects many of our in-
ternal organs.
Aging and the Integumentary System 1 07
COMMON
DISORDERS
Skin Cancer
essive exposure to the sun causes virtually all of the one million
leases wfskhi cancer diagnosed annually in die United States, There
hi three common forms of skin cancer. Basal celt carcinomas ac-
count for about 78% of all skin cancers. The tumors arise from cells
in the stratum basale of the epidermis and rarely metastasize, Squa-
wvs cell carcinomas, which account for about 20% of ail skin can-
arise from squamous cells of the epidermis, and they have a
sble tendency to metastasize. Most arise from preexisting le-
sions of damaged tissue on sun-exposed skin. Basal and squamous
Bell carcinomas are together known as n&nmelanoma skin ameer,
v are 50% more common in males than in females.
Malignant melanomas arise from melanocytes and account
bout 2% of all skin cancers. They are the most prevalent
1 1 ihreatening cancer in young women. The estimated lifetime
{risk of developing melanoma is now I in 75, double the risk only
IS years ago. In part, this increase is due to depletion of the
../.ale layer, which absorbs some UV light high in the atmos-
phere. But the main reason for the increase is that more people
arc spending more time in the sun and in tanning beds. Malig-
nant melanomas metastasize rapidly and can kill a person within
Months of diagnosis.
Che key to successful treatment of malignant melanoma is
early detection. The early warning signs of malignant melanoma
are identified by the acronym ABO) (Figure 5.5), A is for asym-
\wtiy; malignant melanomas tend to lack symmetry. B is for hor-
malignant melanomas have irregular — notched, indented,
scalloped, or indistinct — borders. C is for color; malignant
melanomas have uneven coloration and may contain several col-
ls. D is for diameter; ordinary moles typically are smaller than
igure 5.5 Comparison of a normal nevus (mole) and a
lalignant melanoma.
Excessive exposure to the sun is the cause of most skin
cancers.
(a) Normal nevus (mole;
(b) Malignant melanoma
Which type of skin cancer is the most common type?
6 mm (0,25 in.), about the size of a pencil eraser. Once a malig-
nant melanoma has the characteristics of A, B, and C, it is usually
larger than 6 mm.
Among the risk factors for skin cancer are the following:
1. Skin type. Individuals with light-colored skin who never tan
but always burn are at high risk
2. Sun exposure* People who live in areas with many days of sun-
light per year and at high altitudes (where ultraviolet light is
more intense) have a higher risk of developing skin cancer. Like-
wise, people who engage in outdoor occupations and those who
have suffered three or more severe sunburns have a higher risk,
3. Family history. Skin cancer rates are higher in some families
than in others.
4. Age. Older people are more prone to skin cancer owing to
longer total exposure to sunlight.
5. Immunological status* Individuals who are immunositppressed
have a higher incidence of skin cancer.
Sun Damage
Although basking in the warmth of the sun may feel good, it is not a
healthy practice. There are two forms of ultraviolet radiation that
affect the health of the skin. Longer-wavelength ultraviolet A
(UVA) rays make up nearly 95% of the ultraviolet radiation that
reaches the earth. UVA rays are not absorbed by the ozone layer.
They penetrate the furthest into the skin, where they are absorbed
by melanocytes and thus are involved in sun tanning. UVA rays also
depress the immune system. Shorter-wave length ultraviolet B
(UVB) rays are partially absorbed by the ozone layer and do not
penetrate the skin as deeply as UVA rays, UVB rays cause sunburn
and are responsible for most of the tissue damage (production of
oxygen free radicals that disrupt collagen and elastic libers) that re-
sults in wrinkling and aging of the skin and cataract formation*
Both UVA and UVB rays are thought to cause skin cancer. Long-
term overexposure to sunlight results in dilated blood vessels, age
spots, freckles, and changes in skin texture.
Exposure to ultraviolet radiation (either natural sunlight or the
artificial light of a tanning booth) may also produce photosensitiv-
ity, a heightened reaction of the skin after consumption of certain
medications or contact with certain substances. Photosensitivity is
characterized by redness, itching, blistering, peeling, hives, and
even shock. Among the medications or substances that may cause a
photosensitivity reaction are certain antibiotics (tetracycline), non-
steroidal anti-inflammatory drugs (ibuprofen or naproxen), certain
herbal supplements (St. John's Wort), some birth control pills, some
high blood pressure medications, some antihistamines, and certain
artificial sweeteners, perfumes, aftershaves, lotions, detergents, and
medicated cosmetics.
Burns
A burn is tissue damage caused by excessive heat, electricity, ra-
dioactivity, or corrosive chemicals that denature the proteins in the
1 08 Chapter 5 The Integumentary System
skin cells. Burns destroy some of the skin s important contributions
to homeostasis— protection against microbial invasion and desicca-
tion, and regulation of body temperature.
Burns are graded according to their severity, k first-degree bum
involves only the epidermis. Tt is characterized by mild pain and
redness but no blisters. Skin functions remain intact. A second-degree
hum destroys a portion of the epidermis and part of the dermis.
Some skin functions are lost. In a second-degree burn there is red-
ness, blister formation, edema, and pain, and scarring may result.
First- and second-degree burns arc collectively referred to as par-
tial-thickness hums*
A third-degree burn or full-thickness hum destroys the epidermis,
the underlying dermis, and subcutaneous layer. Most skin functions
are lost. Skin grafting may be required to promote healing and to
minimize scarring.
The seriousness of a burn is determined by its depth and ex-
tent of area involved, as well as the person's age and general
health. According to the American Burn Association's classifica-
tion of burn injury, a major burn includes third-degree burns over
10% of body surface area; or second-degree burns oyer 25% of
body surface area; or any third-degree burns on the face, hands,
feet, or perineum (per-i-NE-urn, which includes the anal and uro-
genital regions). When the burn area exceeds 70% T more than half
the victims die.
MEDICAL TERMINOLOGY AND CONDmONS
Abrasion (a-BRA-shun; ab- = away; -niison = scraped) A portion
of the epidermis that has been scraped away,
Athletes (KVR-\ets)foot A superficial fungus infection of the skin
of the foot.
Blister A collection of serous iluid within the epidermis or between
the epidermis and dermis, due to short-term but severe
friction.
Cold sore A lesion, usually in the oral mucous membrane, caused
by type 1 herpes simplex virus (IISV) transmitted by oral or
respiratory routes. The virus remains dormant until triggered
by factors such as ultraviolet light, hormonal changes, and
emotional stress. Also called _a fever blister:
Contact dermatitis (der'-ina-TI-tis; dermat- = skin; -his = inflam-
mation) Inflammation of the skin characterized by redness, itch-
ing, and swelling and caused by exposure of the skin to chemicals
it bring about an allergic reaction, such as poison ivy toxin.
Corn (KORN) A painful thickening of the stratum corneum of
the epidermis found principally over toe joints and between the
toes, often caused by friction or pressure. Corns may be hard
or soft, depending on their location. Hard corns are usually
found over toe joints, and soft corns are usually found between
the fourth and filth toes.
Hemangioma (he-man'-je-6-ma; hem- = blood; -angi blood
vessel; -oma = tumor) Localized tumor of the skin and subcuta-
neous layer that results from an abnormal increase in
blood vessels. One typ e \szport~wine stain, a flat pink, red, or
purple lesion present at birth, usually at the nape of the neck.
Pressure Ulcers
Pressure ulcers, also known as decubitus ulcers (de-KU-bi-tus) or be
sores, are a shedding of 'epithelium caused by a constant deficiency
blood flow to tissues. Typically the affected tissue overlies a bonj
projection that has been subjected to prolonged pressure against
object such as a bed, cast, or splint. If the pressure is relieved in
few hours, redness occurs but no lasting tissue damage results. Pro^
longed pressure causes tissue ulceration. Small breaks in die epider-;
mis become infected, and the sensitive subcutaneous layer and]
deeper tissues are damaged. Eventually, the tissue dies. Pressure ul-
cers occur most often in bedridden patients. With proper care,
pressure ulcers are preventable.
Acne
Acne is an inflammation of sebaceous glands that usually begins at
puberty, when the sebaceous glands grow in size and increase thei
production of sebum. Androgens from the testes, ovaries,
adrenal glands play the greatest role in stimulating sebaceod
glands, Acne occurs predominantly in sebaceous follicles that havt
been colonized by bacteria, some of which thrive in the lipid-nV
sebum. The infection may cause a c\st (sac of connective tissuj
cells) to form, which can destroy and displace epidermal cells, Tl
condition, called cystic acne, can permanently scar the epidermis.
Hives (IlfVZ) Skin condition marked by reddened elcvatt
patches that are often itchy. Most commonly caused by ii
tions, physical trauma, medications, emotional stress, food at
ditives, and certain food allergies.
Impetigo (im'-pe-TT-go) Superficial skin infection caused
Staphylococcus bacteria; most common in children.
Intradermal (in-tra-DER-mal; intra- = within) Within die
Also called intracutaneous.
Keratosis (ker'-a-TO-sis; kera- = horn) Formation of a hardened
growth of epidermal tissue, such as a solar keratosis, a prema-
lignant lesion of the sun-exposed skin of the face and hands.
Laceration (las-er-A-shun; lacer- = torn) An irregular tear of the
•-.kin.
Psoriasis (so-RI-a-sis, psora = itch) A common, chronic skin
order in which keratinocytcs divide and move more quicU
than normal from the stratum battle to the stratum cornet
and form flaky scales, most often on the knees, elbows
scalp.
Pruritus (proo-RI-tus; prim- = to itch) Itching, one of the most
common dermatological disorders. It may be caused by slai
disorders (infections), systemic disorders (cancer, kidnq
failure), psychogenic factors (emotional stress), or allei
reactions.
Topical Refers to a medication applied to the skin surface ratha
than ingested or injected.
Wart Mass produced by uncontrolled growth of epidielial !
cells, caused by a papilloma virus. Most warts are noncancerous,
The Integumentary System
For all body
systems
Contribution of the Integumentary System
The skin and hair provide barriers that protect all internal organs from damaging agents in the
external environment; sweat glands and skin blood vessels help regulate body temperature,
needed for proper functioning of other body systems.
Skeletal system
luscular system
The skin helps activate vitamin D, needed for proper absorption of dietary calcium and phospho-
rus to build and maintain bones.
Through activation of vitamin D, the skin helps provide calcium ions, needed for muscle contrac-
tion; the skin also rids the body of heat produced by muscular activity.
lervous system
Nerve endings in the skin and subcutaneous tissue provide input to the brain for touch, pres-
sure, thermal, and pain sensations.
idocrine
/stem
Keratinocytes in the skin help activate vitamin P, initiating its conversion to calcitriol, a hormone
that aids absorption of dietary calcium and phosphorus.
irdiovascular
rtem
Local chemical changes in the dermis cause widening and narrowing of skin blood vessels,
which help adjust blood flow to the skin.
(mphatic
tern and
imunity
spiratory
tern
Igestive system
The skin is the "first line of defense" in immunity, providing mechanical barriers and chemical
secretions that discourage penetration and growth of microbes; Langerhans cells in the epider-
mis participate in immune responses by recognizing foreign antigens for destruction by immune
cells.
Hairs in the nose filter dust particles from inhaled air; stimulation of pain nerve endings in the
skin may alter breathing rate.
The skin helps activate vitamin D to become the hormone ealcitriol, which promotes absorption
of dietary calcium and phosphorus in the small intestine.
■rlnary system
roductive
■systems
Kidney cells receive partially activated vitamin D hormone from the skin and convert it to cal-
citriol; some waste products are excreted from the body in sweat, contributing to excretion by
the urinary system.
Nerve endings in the skin and subcutaneous tissue respond to erotic stimuli, thereby contribute
■%*■» Z&to^ in 9 t0 sexual pleasure; suckling of a baby stimulates nerve endings in the skin, leading to milk
ejection; mammary glands (modified sweat glands) produce milk; the skin stretches during preg-
nancy as the fetus enlarges.
110 Chapter 5 The Integumentary System
STUDY OUTLINE
2.
3.
Skin (p. 98)
I. The skin and hairs and other structures such as nails constitute
the integumentary system.
The principal parts of the skin are die outer epidermis and in-
ner dermis. The dermis overlies and attaches to the subcuta-
neous layer.
Epidermal cells include keratinocytes, melanocytes, Langer-
hans cells, and Merkel cells. The epidermal layers, from deep-
est to most superficial, arc the stratum basale, stratum spin-
osum, stratum granulosum, stratum lucidtim, and stratum
corneum. The stratum basale undergoes continuous cell divi-
sion and produces all other layers.
The dermis consists of two regions. The superficial region is
areolar connective tissue containing blood vessels, nerves, hair
follicles, dermal papillae, and corpuscles of touch (Mcissner cor-
puscles). The deeper region is dense, irregularly arranged con-
nective tissue containing adipose tissue, hair follicles, nerves, se-
baceous (oil) glands, and ducts of sudoriferous (sweat) glands.
Skin color is due to die pigments melanin, carotene, and hemo-
globin.
4.
5.
Accessory Structures of the Skin (p. 101)
1. Accessory structures of the skin develop from the epidermis of
an embryo.
2. They include hair, skin glands (sebaceous, sudoriferous, and
ceruminous), and nails,
3. Hairs are threads of fused, dead keratinized cells that function
in protection.
4. Hairs consist of a shaft above the surface, a root that penetrates
the dermis and subcutaneous layer, and a hair follicle.
5. Associated with hairs are bundles of smooth muscle called
arrector pili and sebaceous (oil) glands,
6. Sebaceous (oil) glands are usually connected to hair follicles;
they are absent in the palms and soles. Sebaceous glands pro-
duce sebum, which moistens hairs and waterproofs the skin,
7. There are two types of sudoriferous (sweat) glands: eccrine and
apocrine. Kccrine sweat glands have an extensive distribution;
their duets terminate at pores at the surface of the epidermis,
and their main function is to help regulate hotly temperature,
Apocrine sweat glands are limited in distribution, and their
ducts open into hair follicles. They begin lunctioiting at pu-
berty and arc stimulated during emotional stress and sexual
excitement.
8. Ceruminous glands are modified sudoriferous glands that se-
crete cerumen. They are found in the external auditory canal
9. Nails are hard, dead, keratinized epidermal cells covering th<
terminal portions of the fingers and toes.
10. The principal parts of a nail are the body, free edge, root,
lunula, cuticle, and matrix. Oil division of the matrix cells pro-
duces new r nails.
Functions of the Skin (p. 104)
1. Skin functions include body temperature regulation, protecl
tion, sensation, excretion and absorption, and synthesis of
vitamin D.
2. The skin participates in body temperature regulation by liber-
ating sweat at its surface and by adjusting the How of blood w
the dermis.
3. The skin provides physical, chemical, and biological barriers]
that help protect the body.
4. Cutaneous sensations include tactile sensations, thermal sei
tions, and pain.
Aging and the Integumentary System (p. 106)
1, Most effects of aging occur when an individual reaches the lat
forties.
2. Among the effects of aging are wrinkling, loss of subcutaneous]
fat, atrophy of sebaceous glands, and decrease in the numherof]
melanocytes and Langerhans cells.
'Q
SELF-QUIZ
Hair follicles
a. consist of dead cells
b* extend above the surface of the skin
c. can increase in number as you age
d. contain cells undergoing mitosis
e. are another name for arrector pili muscles
Skin coloration
a. is due to melanin found in the subcutaneous laj ei
b. in European- Americans is due mainly to carotene
c. is related to apocrine glands
d. is stimulated by exposure to the sun
e. is produced by Merkel cells
3. In which portion of the skin will you find dermal papillae?
a, superficial region of the dermis b* epidermis
c. hypodermis d. stratum spinosum
e. deeper region of the dermis
4. If you pricked your fingertip with a needle, the first 1
epidermis that it would penetrate is the
a. stratum basale b. stratum spinosum
c. stratum granulosum d. stratum lucidum
e* stratum corneum
5. A person with albinism has a defect in the production of
a. carotene b. keratin c. collagen d. cerumen
e. melanin
ii, The red or pink tones seen in some skin are due to
a. hemoglobin in the blood moving through capillaries in die
dermis
h. the presence of carotene
c. the lack of oxygen
d. a buildup of bilirubin in the blood
e. an increased production of melanin
When you have your hair cut, scissors are cutting through the
bair
a. follicle b. root c. shaft d, papilla e. bulb
\\ Inch of die following is NOT true concerning eccrine sweat
glands?
a. They are most numerous on the palms and the soles,
b. They help regulate body temperature.
c. They produce a viscous secretion.
d. They function throughout life.
e. They terminate at pores on the skin's surface.
I Which tissue is the main type found in the inner region of the
dermis?
a, dense irregular connective b. stratified squamous
epithelium c. smooth muscle d. nervous
e. cartilage
10. Winch of the following is NOT a function of skin?
a, calcium production b. vitamin I) synthesis
c. protection d. immunity e. temperature regulation
11, Which of the following is NOT true concerning hair?
a. I lair is mainly composed of keratin.
b. Hirsutism is another name for male-pattern baldness.
c. Hair color is due to melanin.
d. Sebaceous glands are associated with hair.
e. Contraction of the arrector pili muscles makes bair stand
erect,
\l Sebaceous glands
a. secrete an oily substance
b. are located on the palms and soles
c. are responsible for breaking out in a "cold sweat"
d. me involved in body temperature regulation
e. are found in the external auditory meatus
.. keratinocytes in die stratum basale are pushed toward die
skin's surface, they
a. begin to divide more rapidly b> become more elastic
c, begin to die d. lose their melanin
e. begin to assume a columnar shape
Self-Quiz 111
14. lb produce vitamin D, the skin cells need to be exposed to
a. calcium and phosphorus b. ultraviolet light
c. heat d. pressure c. keratin
15. To prevent an unwanted hair from growing back, you must
destroy which structure?
a. shaft 1>. root sheath e. lunula d. hair matrix
e. arrector pili
16. Aging can result in
a. an increase in collagen and elastic fibers in the skin
b. a steady increase in the activity of sudoriferous glands
c\ a greater immune response from Langerhans cells
d. more efficient activity by macrophages
e. a decline in the activity of sebaceous glands
17. The portion of die nail that is responsible for nail growth is the
a. cuticle b. nail matrix c, lunula d. nail body
e. nail root
18. Match the following:
a. Langerhans cell A. earwax
b, Merkel cell B. silvery white streaks
c. keratin C. yellow-orange precursor
d. melanin of vitamin A
e. lamellated (pacinian) D - function in immune
corpuscle responses
f cerumen E. protective protein of
skin, bair
E touch receptor found in
epidermis
g. carotene
h. striae
l. corpuscle ol touch
,., . ix G. yellow to black pigment
(Meissner corpuscle) - r °]
H. nerve endings sensitive
to pressure
I. touch receptor found in
dermal papillae
19. Which of the following is NOT an accessory structure of the
skin?
a. dermal papillae b. sudoriferous glands
c. sebaceous glands d. ceruminous glands e. nails
20* What is the response by effectors when the body temperature
is elevated?
a. Blood vessels in die dermis constrict.
b. Sweat glands increase production of sweat.
c. Skeletal muscles begin to contract involuntarily.
d. The body's metabolic rate increases.
e* The ceruminous glands increase production.
1 2 Chapter 5 The Integumentary System
%
CRITICAL THINKING APPLICATIONS
1. Three-year-old Michael was having his first haircut. As the 3,
barber started to snip his hair, Michael cried, "Stop! You're
killing it!" He then pulled his own hair, yelling, "Ouch! See! It's
alive!" Is Michael right about his hair?
2. Michael's twin sister Michelle scraped her knee at the play- 4.
ground, She told her mother that she wanted "new skin that
doesn't leak,'' Her mother promised that new skin would soon
appear under die bandage. I low does new skin grow?
Andrew is training for the Mega man triathlon. After hours
running shoes and damp locker rooms, his feet are a mess!
has calluses, warts, and athlete's foot. What are the causes of 1
misery?
Fifteen -year-old Jeremy has a bad case of "blackheads." Ac-
cording to his Aunt Frieda, Jeremy s skin problems are fro
too much late-night TV, frozen pizza, and cheddar popco
Explain die real cause of blackheads to Aunt Frieda.
% ANSWERS TO FIGURE QUESTIONS
5.1
5.2
5.3
The epidermis is made up of epithelial tissue, and the dermis
is composed of connective tissue.
The stratum basale is the layer of the epidermis that contains
stem cells that continually undergo cell division.
The matrix produces a new hair by cell division*
5.4 Nails are hard because they are composed of tightly packed,
hard, dead keratinized epidermal cells.
5.5 Basal cell carcinoma is the most common type of skin can
THE SKELETAL SYSTEM
i
chapter 6
\V-
idyou know?
JTeople are encouraged to limit
I food intake and exercise regularly to prevent
)benty and stay healthy. But people who go to extremes
can compromise the health of their bones. Premature
mrosis can occur in young women who experience
prolonged menstrtial irregularity, which is often
mused by extreme dieting and/or excessive exercise.
These women have low levels of the estrogens,
hormones which help to keep bones strong. Extreme
dieting behavior may mean a minimal calcium intake,
which then limits the body's bone-building ability.
People who build strong bones during adolescence and
young adulthood reduce their likelihood of developing
osteoporosis later in life.
Focus on Wellness, page 148
www.wiley.com/college/apcentral
JL/espite its simple
appearance, bone is a complex
and dynamic living tissue that is
remodeled continuously — new
bone is built while old bone is
broken down. Each individual bone is an organ coin-
posed of several different tissues working together:
bone, cartilage, dense connective tissues, epithelium,
blood-forming tissue, adipose tissue, and nervous tissue*
The entire framework of bones and their cartilages con-
stitute the skeletal system. The study of bone structure
and the treatment of bone disorders is termed osteology
(os'-te-OL-6-je; osteo- = bone; -logy = study of).
looking back to move ahead
• Connective Tissue Extracellular Matrix (page 83)
• Cartilage (page 89)
• Bone Tissue (page 89)
• Collagen Fibers (page 84)
• Dense Irregular Connective Tissue (page 87)
113
114 Chapter 6 The Skeletal System
FUNCTIONS OF BONE AND THE
SKELETAL SYSTEM
objective • Discuss the functions of bone and the
skeletal system.
Bone tissue and the skeletal system perform several basic
functions:
1. Support* The skeleton provides a structural framework
for the body by supporting soft tissues and providing
points of attachment for most skeletal muscles.
2. Protection. The skeleton protects many internal organs
from injury. For example, cranial bones protect the brain,
vertebrae (backbones) protect the spinal cord, and the rib
cage protects the heart and lungs.
3. Assisting in movement. Because most skeletal muscles
attach to bones, when muscles contract, they pull on
bones. Together bones and muscles produce movement.
This function is discussed in detail in Chapter 8.
4. Mineral homeostasis. Bone tissue stores several miner-
als, especially calcium and phosphorus. On demand, bone
releases minerals into the blood to maintain critical min-
eral balances (homeostasis) and to distribute the minerals
to other parts of the body.
5. Production of blood cells. Within certain bones a con-
nective tissue called red bone marrow produces red
blood cells, white blood cells, and platelets, a process
called hemopoiesis (htmi-6-poy-E-sis; hemo- = blood;
poiesis = making). Red bone marrow consists of develop-
ing blood cells, adipocytes, fibroblasts, and macrophages.
It is present in developing bones of the fetus and in some
adult bones, such as the pelvis, ribs, sternum (breast-
bone), vertebrae (backbones), skull, and ends of the arm
bones and thigh bones.
6. triglyceride storage. Yellow bone marrow consists
mainly of adipose cells, which store triglycerides. The
stored triglycerides are a potential chemical energy re-
serve. Yellow bone marrow also contains a few blood
cells. In the newborn, all bone marrow is red and is in-
volved in hemopoiesis. With increasing age, much of the
bone marrow changes from red to yellow.
■ CHECKPOINT
1 . What kinds of tissues make up the skeletal system?
2. How do red and yellow bone marrow differ in composi-
tion, location, and function?
TYPES OF BONES
OBJECTIVE • Classify bones on the basis ot their
shape and location.
Almost all the bones of the body may he classified into four
main types based on their shape: long, short, flat, or irregular.
Long bones have greater length than width and consist of a
shaft and a variable number of ends. They are usually some-
what curved for strength. Long bones include those in the
thigh (femur), leg (tibia and fibula), arm (humerus), forearm
(ulna and radius), and fingers and toes (phalanges).
Short bones are somewhat cube-shaped and nearly equal
in length and width. Examples of short bones include most
wrist and ankle bones.
Flat hones are generally thin, afford considerable protec-
tion, and provide extensive surfaces for muscle attachment.
Bones classified as flat bones include the cranial bones, which
protect die brain; the sternum (breastbone) and ribs, which
protect organs in the thorax; and die scapulae (shoulder blades),]
Irregular bones have complex shapes and cannot be
grouped into any of the previous categories. Such bones in-
clude the vertebrae and some fecial bones.
■ CHECKPOINT
3, Give several examples of long, short, flat, and irregular
bones.
STRUCTURE OF BONE
objectives • Describe the parts of a long bone.
• Describe the histological features of bone tissue.
We will now explore the structure of bone at both the macro-
scopic and microscopic levels.
Macroscopic Structure of Bone
The structure of a bone may be analyzed by considering the
parts of a long bone, for instance, the humerus (the ai
bone), as shown in Figure 6.1. A typical long bone consists
the following parts;
1. The diaphysis (dT-AF-i-sis = growing between) is the
bone's shaft or body — the long, cylindrical, main portioq
of the bone.
2. The epiphyses (e-PIF-i-sez = growing over; singular |
epiphysis) are the distal and proximal ends of the bone.
Structure of Bone
Figure 6-1 Parts of a long bone: epiphysis, metaphysis, and diaphysis. The spongy
bone of the epiphysis and metaphysis contains red bone marrow, and the medullary cavity of
Ihe diaphysis contains yellow bone marrow in an adult.
A long bone is covered by articular cartilage at its proximal and distal epiphyses and by
p periosteum around the remainder of the bone.
Proximal
epiphysis
Metaphysis
Diaphysis
Metaphysis
Distal
epiphysis
Articular cartilage
Spongy bone
Red bone marrow
Epiphyseal line
Endosteum
Compact bone
Medullary cavity
Nutrient artery
Periosteum
Humerus
Articular cartilage
(a) Partially sectioned humerus (arm bone)
Proximal —
epiphysis
Spongy bone
Metaphysis
Medullary cavity
in diaphysis
Compact bone
Partially sectioned femur (thigh bone)
Femur
Functions of Bone Tissue
1. Supports soft tissues and provides attachment for skeletal muscles.
2. Protects internal organs.
3- Assists in movement together with skeletal muscles.
4. Stores and releases minerals.
5. Contains red bone marrow, which produces blood cells.
6. Contains yellow bone marrow, which stores triglycerides (fats), a
potential chemical energy source.
) Which part of a bone reduces friction at joints? Produces blood cells? Lines the medullary cavity?
i
116 Chapter 6 The Skeletal System
3. The metaphyses (me-TAF-i-sez; meta- - between; sin-
gular is metaphysis) are the regions in a mature bone where
the diaphysis joins die epiphyses. In a growing hone, each
metaphysis contains an epiphyseal plate (ep'-i-FIZ-e-al), a
layer of hyaline cartilage that allows the diaphysis of the
bone to grow in length (described later in the chapter).
When bone growth in length stops, the cartilage in the
epiphyseal plate is replaced by bone and the resulting
bony structure is known as the epiphyseal line.
4. The articular cartilage is a thin layer of hyaline cartilage
covering the part of the epiphysis where the bone forms
an articulation (joint) with another bone, Articular carti-
lage reduces friction and absorbs shock at freely movable
joints. Because articular cartilage lacks a perichondrium,
repair of damage is limited.
5. The periosteum (per'-e-OS-te-um; peri- = around) is a
tough sheath of dense irregular connective tissue that
surrounds die bone surface wherever it is not covered by
articular cartilage. The periosteum contains bone-form-
ing cells that enable bone to grow in diameter or thick-
ness, but not in length. It also protects the bone, assists
in fracture repair, helps nourish bone tissue, and serves as
an attachment point for ligaments and tendons.
6. The medullary cavity (iVLED-u-lar'-e; medulla- = mar-
row, pith) or marrow cavity is a hollow, cylindrical space
within the diaphysis that contains fatty yellow bone mar-
row in adults.
7. The endosteum (end-OS-te-um; endo- = within) is a thin
membrane diat lines the medullary cavity It contains a
single layer of bone-forming cells.
Microscopic Structure of Bone
Like other connective tissues, bone, or osseous tissue (OS-e-us)
contains abundant extracellular matrix that surrounds widely
separated cells. The extracellular matrix is about 25% water,
25% collagen fibers, and 50% crystallized mineral salts. As
these mineral salts are deposited in die framework formed by
the collagen fibers of the extracellular matrix, they crystallize
and the tissue hardens. This process of calcification is initiated
by osteoblasts, the bone-building cells.
Although a bone's hardness depends on the crystallized in-
organic mineral salts, a bone's flexibility depends on its colla-
gen fibers. Like reinforcing metal rods in concrete, collagen
fibers and other organic molecules provide tensile strength,
which is resistance to being stretched or torn apart.
Four major types of cells are present in bone tissue:
osteogenic cells/ osteoblasts, osteocytes, and osteoclasts
(Figure 6.2a).
1. Osteogenic celh (os-te-o-JEN-ik; -gem = producing) are
unspecialized stem cells derived from mesenchyme, die tis-
sue from which all connective tissues are formed. They are
the only bone cells to undergo cell division; the resulting
cells develop into osteoblasts. Osteogenic cells are found
along die inner portion of the periosteum, in the endosteum,
and in the canals within bone that contain blood vessels.
2. Osteoblasts (OS-te-6-blasts'; -blasts = buds or sprouts)
are bone-building cells. They synthesize and secrete col-
lagen fibers and odier organic components needed to
build the extracellular matrix of bone tissue. As osteoblasts
surround themselves with matrix, they become trapped in
their secretions and become osteocytes. (Note: Blasts m
bone or any other connective tissue secrete matrix.)
3. Osteocytes (OS-te-6-sfts'; -cytes = cells), mature bon
cells, are the main cells in bone tissue and maintain its;
daily metabolism, such as the exchange of nutrients an
wastes with the blood. Like osteoblasts, osteocytes do no
undergo cell division. (Note: Cytes in bone or any oth
tissue maintain the tissue.)
4. Osteoclasts (OS-te-6-clasts'; -dm = break) are huge eel!
derived from the fusion of as many as 50 monocyte
type of white blood cell) and are concentrated in the t
dosteum. They release powerful lysosomal enzymes
acids that digest the protein and mineral components
the bone extracellular matrix. This breakdown of bone ex-
tracellular matrix, termed resorption, is part of die norm
development, growth, maintenance, and repair of boi
(Note; Clasts in bone break down extracellular matrix.)
Bone is not completely solid but has many small spac
between its cells and extracellular matrix components. So:
spaces are channels for blood vessels that supply bone ce
with nutrients. Other spaces are storage areas for red '
marrow. Depending on the size and distribution of
spaces, the regions of a bone may be categorized as compa
or spongy (see Figure 6,1). Overall, about 80% of the skd
ton is compact bone and 20% is spongy bone.
Compact Bone Tissue
Compact bone tissue contains few spaces and is arranged in
pcating units called osteons or haversian systems (Figure fi
Each osteon consists of a central (haversian) canal with its co
centrically arranged lamellae, lacunae, osteocytes, and can
culi. A central or haversian (ha-VER-shun) canal is a chann
that contains blood vessels, nerves, and lymphatic vessels. "
central canals run longitudinally through the bone. Around
canals are concentric lamellae (la-MEL-e) — rings of hard,
cified extracellular matrix. Between the lamellae are si
spaces called lacunae (la-KOO-ne = little lakes; singular is
cma% which contain osteocytes. Radiating in all directions
from the lacunae are tiny canaliculi (kan'-a-LIK-u-lI : - si
channels), which are filled with extracellular fluid. Inside
canaliculi are slender fingerlike processes of osteocytes (see i
set at right of Figure 6.2c). The canaliculi connect lacuna
with one another and with the central canals. Thus, an intii
cate, miniature canal system throughout the bone provid
many routes for nutrients and oxygen to reach the osteocj
and for wastes to diffuse away This is very important hea
diffusion through the lamellae is extremely slow.
Structure of Bone 17
Figure 6.2 Histology of bone.
* Osteocytes lie in lacunae arranged in concentric circles around a central (haversian) canal in compact bone, and
in lacunae arranged irregularly in the trabecule of spongy bone.
i
i ■ i
=>
i>
Osteogenic cell
(develops into an
iast)
Osteoblast
(forms bone
extracellular
matrix)
Osteocyte
(maintains
bone tissue)
{a) Types of cells in bone tissue
Osteoclast
(functions in resorption, the
breakdown of bone matrix)
! '%u
m
Canaliculi
— Central
(haversian)
canal
— Lacuna
550x
Concentric
lamellae
(b) Sectional view of an osteon (haversian system)
Compact
bone
ingy
bone
periosteum
Medullary
cavity
Concentric lamellae
Blood vessels
Lymphatic vessel
Osteocyte
Medullary cavity
Trabecule
Periosteum
Central canal
Perforating canal
Spongy bone
Compact bone
(c) Osteons (haversian systems) in compact bone and trabeculae in spongy bone
As people age, some
central (haversian) canals may become blocked. What effect wouid this have on the osteocytes?
118 Chapter 6 The Skeletal System
Blood vessels, lymphatic vessels, and nerves from the pe-
riosteum penetrate the compact bone through transverse
perforating (valkmann's) canals. The vessels and nerves of
the perforating canals connect with those of the medullary
cavity, periosteum, and central (haversian) canals.
Compact bone tissue contains few spaces. It is found be-
neath the periosteum of all bones and makes up the bulk of
the diaphyses of long bones. Compact bone tissue provides
protection and support and resists the stresses produced by
weight and movement.
Spongy Bone Tissue
In contrast to compact bone tissue, spongy hone tissue does
not contain osteons. As shown in Figure 6.2c it consists of
units called trabecular (tra-BKK-u-le = little beams; singular
is trabecule), an irregular latticework of thin columns of bone.
The macroscopic spaces between the trabeculae of some
bones are filled with red bone marrow. Within each trabecule
are osteocytes that lie in lacunae. Radiating from the lacunae
are canaliculi.
Spongy bone tissue makes up most of the bone tissue of
short, flat, and irregularly shaped bones. It also forms most of
the epiphyses of long bones and a narrow rim around the
medullar}? cavity of the diaphysis of long bones.
Spongy bone tissue is different from compact bone tissue
in two respects. First, spongy bone tissue is light, which re-
duces the overall weight of a bone so that it moves more
readily when pulled by a skeletal muscle. Second, the trabec-
ulae of spongy bone tissue support and protect the red bone
marrow. The spongy bone tissue in the hip bones, ribs, breast-
bone, backbones, and the ends of long bones is the only site
where red bone marrow is found and, thus, the site of blood
cell production in adults.
In a bone scan, a small amount of a radioactive tracer
compound that is readily absorbed by bone is injected in-
travenously. The degree of uptake of the tracer is related
to die amount of blood flow to the bone, Normal bone tis-
sue is identified by a consistent gray color throughout be-
cause of its uniform uptake of the radioactive tracer.
Darker or lighter areas may indicate bone abnormalities.
Darker areas called "hot spots" are areas of increased me-
tabolism that absorb more of the radioactive tracer due to
increased blood flow. Hot spots may indicate bone cancer,
abnormal healing of fractures, or abnormal bone growth.
Lighter areas called "cold spots" are areas of decreased
metabolism that absorb less of the radioactive tracer due
to decreased blood flow. Cold spots may indicate problems
such as degenerative bone disease, decalcified bone, frac-
tures, bone infections, Paget's disease, or rheumatoid
arthritis. A bone scan detects abnormalities 3 to 6 months
sooner than standard x-ray procedures and exposes the patient
to less radiation. A bone scan is the standard test for bone
density screening, particularly for osteoporosis in females.
■ CHECKPOINT
4. Diagram the parts of a long bone, and list the fund
of each part.
5. What are the four types of cells in bone tissue?
6. How are spongy and compact bone tissue different inj
terms of their microscopic appearance, location, and
function?
BONE FORMATION
OBJECTIVES • Explain the importance of bone for-
mation during different phases of a person's lifetime.
• Describe die factors that affect bone growth during a
person's lifetime.
The process by which bone forms is called ossification (os'
i-fi-KA-shmr, ossi- = bone; -fication = making). Bone for-
mation occurs in four principal situations: (1) the initial
formation of bones in an embryo and fetus, (2) the growth
of bones during infancy, childhood, and adolescence unl
their adult sizes are reached, (3) the remodeling of
(replacement of old bone tissue by new bone tissd
throughout life); and (4) the repair of fractures (breaks ii
bones) throughout life.
Initial Bone Formation
in an Embryo and Fetus
We will first consider the initial formation of bone in an ei
bryo and fetus. The embryonic "skeleton" is at first
posed of mesenchyme shaped like bones and are the sit
where ossification occurs. These "bones" provide the tem-
plate for subsequent ossification, which begins during
sixth week of embryonic development and follows one of
patterns.
The two methods of bone formation, which both invol
the replacement of a preexisting connective tissue with bom
do not lead to differences in the structure of mature bom
but are simply different methods of bone development
the first type of ossification, called intramemhranons ossifi-i
cation (in'-tra-MEM-bra-nus; intra- = within; membramM
membrane), bone forms directly within mesenchyme
arranged in sheetlike layers that resemble membranes. In the
second type, endochondral ossification (en'-do-KON-dra
endo- = within; -chondral = cartilage), bone forms withir
hyaline cartilage that develops from mesenchyme.
Intramemhranons Ossification
Intramemhranons ossification is the simpler of die
methods of bone formation. The flat bones of the skull and
mandible (lower jawbone) are formed in this way Also,
pots" that help the fetal skill pass through the birth
canal later harden as they undergo intramembranous ossifica-
te, which occurs as follows (Figure 6.3):
Development of the ossification center. At the site where
bone will develop, called the ossification center, cells in
mesenchyme cluster together and differentiate, first into
osteogenic cells and then into osteoblasts. Osteoblasts se-
crete the organic extracellular matrix of bone,
Calcification. Next, the secretion of extracellular matrix
stops and die cells, now called osteocytes, lie in lacunae
Bone Formation 119
and extend their narrow cytoplasmic processes into
canaliculi that radiate in all directions. Within a few days,
calcium and other mineral salts are deposited and the ex-
tracellular matrix hardens or calcifies (calcification),
© Formation of trabecular. As die bone extracellular ma-
trix forms, it develops into trabeculae that fuse with one
another to form spongy bone. Blood vessels grow into
the spaces between the trabeculae. Connective tissue that
is associated with the blood vessels in the trabeculae dif-
ferentiates into red bone marrow.
Figure 6.3 Intramembranous ossification. Illustrations ©and ® show a smaller field of vision at higher
magnification than illustrations ©and ©.
Intramembranous ossification involves the formation of bone within mesenchyme arranged in sheetlike layers that
» resemble membranes.
Flat bone
of skull
Mandible
Blood capillary
- Ossification center
Mesenchymal cell
Osteoblast
Collagen fiber
A Development of ossification center
Osteocyte in lacuna
Canaliculus
Osteoblast
Newly calcified bone
extracellular matrix
Mesenchyme
condenses
Blood vessel
Spongy bone
trabeculae
Osteoblast
A Calcification
A Formation of trabeculae
0\
Wt
"- ' C -
^MsU&^ES&lgF iiljfXglj& l
O Development of the periosteum
Which bones of the body develop by intramembranous ossification?
Periosteum
Spongy bone tissue
Compact bone tissue
1 20 Chapter 6 The Skeletal System
Development of the periosteum. At the periphery of the
bone, the mesenchyme condenses and develops into the
periosteum. Eventually, a thin layer of compact bone re-
places the surface layers of the spongy bone, but spongy
bone remains in the center.
Endochondral Ossification
The replacement of cartilage by bone is called endochondral
ossification, Most bones of the body are formed in this way,)
but as shown in Figure 6.4, this type of ossification is bes
observed in a long bone:
Figure 6.4 Endochondral ossification of the tibia (shin bone).
During endochondral ossification, bone gradually replaces a cartilage model.
Proximal
epiphysis
/
Diaphysis
Distal
epiphysis
Perichondrium
Hyaline
cartilage
.
Uncatcified -
matrix
Calcified
matrix
*
Nutrient
artery
Periosteum
Primary
ossification
center
Spongy
bone
Uncalcified
matrix
Calcified
matrix
Periosteum -
Medullary
cavity
®
A Development of
cartilage model
A Growth of
cartilage model
A Development of
primary ossification
center
A Development of
the medullary
(marrow) cavity
Articular cartilage
Secondary
ossification
center
Uncalcified
matrix
©Development of secondary
A
/
ossification center
A Formation of articular cartilage
and epiphyseal plate
Spongy bone
Epiphyseal plate
) Which structure signals that bone growth in length has stopped?
Development of the cartilage model. At the site where
the bone is going to form, cells in mesenchyme crowd
together in the shape of the future bone and then de-
velop into chondroblasts. The chondroblasts secrete car-
tilage extracellular matrix, producing a cartilage model
consisting of hyaline cartilage. A membrane called the
pmcfjondrium (per'-i-KON-dr£-um) develops around
the cartilage model.
Growth of the cartilage model Once chondroblasts
become deeply buried in cartilage extracellular matrix,
they are called chondrocytes. As the cartilage model con-
tinues to grow, chondrocytes in its mid-region increase in
size and the surrounding extracellular matrix begins to
calcify- Other chondrocytes within the calcifying carti-
lage die because nutrients can no longer diffuse quickly
enough through the extracellular matrix. As chondro-
cytes die, lacunae form and eventually merge into small
cavities.
Development of the primary ossification center.
Primary ossification proceeds imvard from the external
surface of the bone. A nutrient artery penetrates the peri-
chondrium and the calcifying cartilage model in the mid-
region of the cartilage model, stimulating osteogenic
cells in the perichondrium to differentiate into os-
teoblasts. Once the perichondrium starts to form bone, it
is known as the periosteum. Near the middle of the
model, blood vessels grow into the disintegrating calci-
fied cartilage and induce growth oi&primmy ossification
center, a region where bone tissue will replace most of
die cartilage. Osteoblasts then begin to deposit bone ex-
tracellular matrix over the remnants of calcified cartilage,
forming spongy bone trabeculae.
As the primary ossification center grows toward the ends
of die bone, osteoclasts break down some of the newly
formed spongy bone trabeculae. This activity leaves a
cavity, the medullary (marrow) cavity, in the diaphysis
(shaft). The medullary cavity then fills with red bone
marrow. Most of the wall of the diaphysis is replaced by
compact bone.
Development of the secondary ossification centers.
(When blood vessels enter the epiphyses, secondary ossifi-
cation centers develop, usually around the time of birth.
Bone formation is similar to that in primary ossification
centers except that spongy bone remains in the interior
of the epiphyses (no medullary cavities are formed there).
Secondary ossification proceeds outward from the center
of the epiphysis toward the outer surface of the bone.
Formation of articular cartilage and the epiphyseal
plate. The hyaline cartilage that covers the epiphyses
becomes the articular cartilage. Prior to adulthood,
hyaline cartilage remains between the diaphysis and epi-
physis as the epiphyseal plate, which is responsible for
the lengthwise growth of long bones.
Bone Formation 121
Bone Growth in Length and Thickness
During infancy, ehildood, and adolescence, long 1 bones grow
in length and thickness.
Growth in Length
Bone growth in length is related to the activity of the epiphy-
seal plate. Within the epiphyseal plate is a group of young
chondrocytes that are constantly dividing. As a bone grows in
length, new chondrocytes are formed on the epiphyseal side
of the plate, while old chondrocytes on the diaphyseal side of
the plate are replaced by bone, hi this way the thickness of
the epiphyseal plate remains relatively constant, but the bone
on the diaphyseal side increases in length. When adolescence
comes to an end, the formation of new cells and extracellular
matrix decreases and eventually stops between ages 18 and
25. At this point, bone replaces all the cartilage, leaving a
bony structure called the epiphyseal line. With the appear-
ance of the epiphyseal line, bone growth in length stops. If a
bone fracture damages the epiphyseal plate, the fractured
bone may be shorter than normal once adult stature is
reached. This is because damage to cartilage, which is avas-
cular, accelerates closure of the epiphyseal plate, thus inhibit-
ing lengthwise growth of the bone.
Growth in Thickness
As long bones lengthen, they also grow in thickness (width).
At the bone surface, cells in the perichondrium differentiate
into osteoblasts, which secrete bone extracellular matrix.
Then the osteoblasts develop into osteocytes, lamellae are
added to the surface of the bone, and new osteons of compact
bone tissue are formed. At the same time, osteoclasts in the
endosteum destroy the bone tissue lining the medullary cav-
ity; Bone destruction on the inside of the bone by osteoclasts
occurs at a slower rate than bone formation on the outside of
the bone. Thus, the medullary cavity enlarges as the bone in-
creases in thickness.
Bone Remodeling
Like skin, bone forms before birth but continually renews it-
self thereafter, Bone remodeling is the ongoing replacement
of old bone tissue by new bone tissue. It involves bone re-
sorption, the removal of minerals and collagen fibers from
bone by osteoclasts, and hone deposition, the addition of
minerals and collagen fibers to bone by osteoblasts. Thus,
bone resorption results in the destruction of bone extracellu-
lar matrix, while bone deposition results in the formation of
bone extracellular matrix. Remodeling takes place at different
rates in different regions of the body. Even after bones have
reached their adult shapes and sizes, old bone is continually
destroyed and new bone is formed in its place. Remodeling
also removes injured bone, replacing it with new bone tissue.
Remodeling may be triggered by factors such as exercise,
sedentary lifestyle, and changes in diet.
1 22 Chapter 6 The Skeletal System
Orthodontics (or-tho-DON-tiks) is the branch of den-
tistry concerned with the prevention and correction of
poorly aligned teeth. The movement of teeth by braces
places a stress on the bone that forms the sockets that an-
chor the teeth. In response to this artificial stress, osteo-
clasts and osteblasts remodel the sockets so that the teeth
align properly.
A delicate balance exists between the actions of osteo-
clasts and osteoblasts. Should too much new tissue he
formed, the bones become abnormally thick and heavy K too
much mineral material is deposited in the bone, the surplus
may form thick bumps, called spurs, on the bone that inter-
fere with movement at joints. Excessive loss of calcium or
tissue weakens the bones, and they may break, as occurs in
osteoporosis, or they may become too flexible, as in rickets
and osteomalacia. (For more on these disorders, see the
Disorders section at the end of the chapter,) Abnormal accel-
eration of the remodeling process results in a condition
called Paget's disease, in which the newly formed bone, espe-
cially that of the pelvis, limbs, lower vertebrae, and skull, be-
comes hard and brittle and fractures easily.
Fractures
k fracture is any break in a bone. Types of fractures include
the following;
1. Partial: an incomplete break across the bone, such as a
crack,
2. Complete: a complete break across the bone; that is, the
bone is broken into two or more pieces.
3. Closed (simple): the fractured bone does not break
through the skin.
4. Open (compound): the broken ends of the bone pro-
trude through the skin.
Repair of a fracture involves several steps. First, phago-
cytes begin to remove any dead bone tissue. Then, chon-
droblasts form fibrocartilage at the fracture site and this
bridges the broken ends of the bone. Next, the fibrocartilage
is converted to spongy bone tissue by osteoblasts. Finally,
bone remodeling occurs, in which dead portions of bone are
absorbed by osteoclasts and spongy bone is converted to
compact bone.
Although bone has a generous blood supply healing
sometimes takes months. The calcium and phosphorus
needed to strengthen and harden new bone are deposited
only gradually, and bone cells generally grow and reproduce
slowly. The temporary disruption in their blood supply also
helps explain the slowness of healing of severely fractured
hones.
Factors Affecting Bone Growth
Bone growth in the young, bone remodeling in the adult, inJ
the repair of fractured bone depend on several factors. Thesf
include (1) adequate minerals, most importantly ealeiuinj
phosphorus, and magnesium; (2) vitamins A, C, and D;
several hormones; and (4) weight-bearing exercise (exei
that places stress on bones). Before puberty, the main hoi
mones that stimulate bone growth are human growth hoi
nione (hGH), which is produced by the anterior lobe of thj
pituitary gland, and insulinlike growth factors (IGFs), whidj
are produced locally by bone and also by the liver in respoi
to hGH stimulation. Oversecretion of hGH produces
antism, in which a person becomes much taller and heavM
than normal, and undersecretion of hGH produces dwarfisi
(short stature). Thyroid hormones, from the thyroid gin
and insulin, from the pancreas, also stimulate normal boi
growth. At puberty, estrogens (sex hormones produced
the ovaries) and androgens (sex hormones produced by
testes in males and the adrenal glands in both sexes) start
be released in larger quantities, These hormones are respoi
sible for the sudden growth spurt that occurs during
teenage years. Estrogens also promote changes in the skeletc
that are typical of females, for example, widening of die peh
Bone's Role in Calcium Homeostasis
Bone is the major reservoir of calcium, storing 99% of
total amount of calcium present in the body. Calcium (CI
becomes available to other tissues when bone is broken di
during remodeling. However, even small changes in blo<
calcium levels can be deadly— the heart may stop (cardiac
rest) if the level is too high or breathing may cease (rcspii
tory arrest) if the level is too low. In addition, most fiinctiof
of nerve cells depend on just the right level of Ca 2+ , mi
enzymes require Ca 2 as a cofactor, and blood clotting
quires Ca 2 + . The role of bone in calcium homeostasis is
"buffer" the blood calcium level, releasing Ca 2 to the blr
when the blood calcium level falls (using osteoclasts) and
positing Ca 2 ' back in bone when the blood level rises (usi
osteoblasts).
The most important hormone that regulates Ca
change between bone and blood is parathyroid hormt
(PTH), secreted by the parathyroid glands (see Figure 11
on page 327), PTII secretion operates via a negative kt
back system (Figure 6.5). If some stimulus causes blood Ca
level to decrease, parathyroid gland cells (receptors) det
this change and increase their production of a molej
known as cyclic adenosine monophosphate (cyclic AM
The gene for PTH within the nucleus of a parathyroid gl
cell, which acts as the control center, detects the increas
production of cyclic AMP (the input). As a result, PTH
thesis speeds up, and more PTH (the output) is released i
Figure 6.5 Negative feedback system for the regulation of
blood calcium (Ca 2+ ) level.
Release of calcium from bone extracellular matrix and retention
. of calcium by the kidneys are the two main ways that blood
calcium level can be increased.
Some stimulus
disrupts homeostasis by
Decreasing
2+v
Biood calcium (Ca ) level
ncreased production
of cyclic AMP
ol center
PTH gene 'turned on"
Output
Increased
release of PTH
ectors
Osteoclasts Kidneys re-
increase tain Ca +
bone in blood
resorption and
produce
calcitriol
Return to homeostasis
when response brings
blood Ca z+ level back
to normal
a
Increase in blood
Ca 2+ level
/ What body functions depend on proper levels of Ca 2+ ?
Exercise and Bone Tissue 1 23
the blood. The presence of higher levels of PTH increases
the number and activity of osteoclasts (effectors), which step
up the pace of bone resorption. The resulting release of Ca 2
from bone into blood returns the blood Ca 2H level to normal.
PTH also decreases loss of Ca 2 ' in the urine, so more is
retained in the blood, and it stimulates formation of cal-
citriol, a hormone that promotes absorption of calcium from
the gastrointestinal tract. Both of these effects also help ele-
vate the blood Ca 2 " 1 level.
As you will learn in Chapter 13, another hormone in-
volved in calcium homeostasis is calcitonin (CT). This hor-
mone is produced by the thyroid gland and decreases blood
Ca 24 level by inhibiting the action of osteoclasts, thus de-
creasing bone resorption,
■ CHECKPOINT
7. Distinguish between intramembranous and endochon-
dral ossification.
8. Explain how bones grow in length and thickness.
9. What is bone remodeling? Why is it important?
10. Define a fracture and explain how fracture repair occurs.
11. What factors affect bone growth?
12. What are some of the important functions of calcium in
the body?
% EXERCISE AND BONE TI SSUE
OBJECTIVE • Describe how exercise and mechanical
stress affect bone tissue.
Within limits, bone tissue has the ability to alter its strength
in response to mechanical stress. When placed under stress,
bone tissue becomes stronger through increased deposition
of mineral salts and production of collagen fibers. Without
mechanical stress, bone does not remodel normally because
resorption outpaces hone formation* The absence of me-
chanical stress weakens bone through decreased numbers of
collagen fibers and demineralization, loss of bone minerals,
The main mechanical stresses on bone are those that re-
sult from the pull of skeletal muscles and the pull of gravity.
If a person is bedridden or has a fractured bone in a cast, the
strength of the unstressed bones diminishes. Astronauts sub-
jected to the weightlessness of space also lose bone mass. In
both cases, the bone loss can be dramatic, as much as 1% per
week. Bones of athletes, which are repetitively and highly
stressed, become notably thicker than those of nonathletes.
Weight-bearing activities, such as walking or moderate
weightlifting, help build and retain bone mass. Adolescents
and young adults should engage in regular weight-bearing
exercise prior to the closure of the epiphyseal plates to help
build total mass before its inevitable reduction with aging.
124 Chapter 6 The Skeletal System
However, the benefits of exercise do not end in young adult-
hood. Even elderly people can strengthen their bones by en-
caging in weight-bearing exercise.
Table 6. 1 summarizes the factors that influence bone me-
tabolism: growth, remodeling, and repair of fractured bones.
■ CHECKPOINT
13, What types of mechanical stress may be used to
strengthen bone tissue?
DIVISIONS OF THE SKELETAL
SYSTEM
objective • Group the bones of the body into axial
and appendicularjliroions.
Because the skeletal system forms the framework of the body
a familiarity with the names, shapes, and positions of individ-
ual bones will help you locate other organs. For example, the
radial artery, the site where die pulse is usual y taken, j
named for its closeness to the radius, the lateral bone ot the
forearm. The ulnar nerve is named for its closeness to die ulna,
the medial hone of die forearm. Hie frontal lobe of the brail
lies deep to the frontal (forehead) bone. The tibialis anterior
muscle lies along the anterior surface of the tibia (shin bone).
The adult human skeleton consists of 206 bones grou]
in two principal divisions: 80 in the axial skeleton and 126 in
the appendicular skeleton (Table 6.2 and Figure 6.6). The ,,
Lai skeleton consists of the bones that lie around the longitrf
dinal axis of the human body, an imaginary line that ,
through die body's center of gravity from the head to
space between die feet: the bones of the skull, auditory os^
cles (ear bones), hvoid bone, ribs, sternum, and vertebra
The appendicular skeleton contains the bones ot the uppi
and lower limbs plus the bone groups called girdles that con
nect the limbs to the axial skeleton. The skeletons of intent
and children have more than 206 bones because some of
bones, such as die hip bones and vertebrae, fuse later in lite,
■ CHECKPOINT
14. How are the limbs connected to the axial skeleton
Table 6.1 Summary of Factors That Influence Bone Metabolism
Factor
Minerals
Calcium and phosphorus
Magnesium
Vitamins
Vitamin A
Vitamin C
Vitamin D
Hormones
Human growth hormone (hGH)
Insulinlike growth factors (IGFs)
Insulin
Thyroid hormones
(thyroxine and triiodothyronine)
Parathyroid hormone (PTH)
Calcitonin (CT)
Comment
Make bone extracellular matrix hard.
Needed for normal activity of osteoblasts.
Needed for the activity of osteoblasts during remodeling of bone: deficiency stunts bone growth; toxic in high do-
He'ps maintain bone extracellular matrix; deficiency leads to decreased collagen production. wh,ch slows down
hone arowth and delays repair of broken bones.
osteoporosis but is toxic if taken in high doses,
Secreted by the anterior lobe of the pituitary gland; promotes genera, growfh of a„ body tissues, including bone,
mainlv bv stimulating production of insulinlike growth factors,
Z tedbt the live bones, and other tissues upon s , mU ,ationby human growth hormone; stimulate the uptake,
amino acids and synthesis of proteins; promote tissue repair and bone growth. |
Secreted by the pancreas; promotes normal bone growth.
Secreted by thyroid gland; promote normal bone growth.
Secreted by the parathyroid glands; promotes bone resorption by osteoclasts; enhances recovery of G*< from
urine; promotes formation of the active form of vitamin D (calc.tnol).
Secreted by the thyroid gland; inhibits bone resorption by osteoclasts.
Exercise
Weight-bearing activities help build thicker, stronger bones and retard the loss of bone mass that occurs as
people age,
Figure 6.6 Divisions of the skeletal system. The axial
pSeton is indicated in green, (Note the position of the hyoid bone in
Figure 6.7b.)
The adult human skeleton consists of 206 bones grouped into
axial and appendicular divisions.
SKULL:
Cranial bones
Skull and Hyoid Bone 1 25
Table 6.2 The Bones of the Adult Skeletal System
Division of the
Skeleton
Facial bones
VERTEBRAL
COLUMN
PELVIC
(HIP)
GIRDLE
PECTORAL
(SHOULDER)
GIRDLE:
Clavicle
Scapula
THORAX:
Sternum
Ribs
UPPER LIMB:
Humerus
Appendicular
Skeleton
Ulna
Radius
Carpal s
Phalanges
LOWER LIMB:
Femur
Patella
Tibia
Fibula
Metatarsals
Phalanges
Anterior view
Identify each of the following bones as part of the axial skeleton
-j or the appendicular skeleton: skull, clavicle, vertebral column,
shoulder girdle, humerus, pelvic girdle, and femur.
Structure
Number
of Bones
Axial Skeleton
Skull
C£
Cranium
Face
Hyoid
Auditory ossicles
i^3^«
Vertebral column
Thorax
'■i * Jx ^\
Sternum
'I I*
Ribs
8
14
1
6
26
1
24
Subtotal
= 80
Pectoral (shoulder) girdles
Clavicle
2
Scapula
2
Upper limbs
Humerus
2
Ulna
2
Radius
2
CarpaJs
16
Metacarpals
10
Phalanges
28
Pelvic (hip) girdle
Hip or pelvic bone
2
Lower limbs
Femur
2
Patella
2
Fibula
2
Tibia
2
Tarsals
14
Metatarsals
10
Phalanges
28
Subtotal ■
126
Total =
206
SKULL AND HYOID BONE
objective • Name the cranial and facial bones and
indicate their locations and major structural features.
The skull, which contains 22 bones, rests on top of the verte-
bral column. It includes two sets of bones; cranial bones and
facial bones. The eight cranial hones form the cranial cavity
that encloses and protects the brain. They are the frontal
bone, two parietal bones, two temporal bones, occipital bone,
1 26 Chapter 6 The Skeletal System
Figure G.7 Skull. Although the hyoid bone is not part of the skull, it is included in (b) and (c) for reference.
The skull consists of two sets of bones: Eight cranial bones form the cranial cavity and fourteen facial bones
form the face.
FRONTAL BONE
PARIETAL BONE
Squamous suture
SPHENOID BONE
Orbit
ETHMOID BONE
LACRIMAL BONE
Perpendicular plate
of ethmoid bone
INFERIOR NASAL
CONCHA
VOMER
Mental foramen
Sagittal suture
— Coronal suture
Optic foramen (canalfj
TEMPORAL BONE
NASAL BONE
Middle nasal concha
ZYGOMATIC BONE
MAXILLA
MANDIBLE
(a) Anterior view
Coronal suture
PARIETAL BONE
Squamous suture
TEMPORAL BONE
Mandibular fossa
Lambdoid suture
OCCIPITAL BONE
External auditory
meatus
Mastoid process
Styloid process
Foramen magnum
FRONTAL BONE
SPHENOID BONE
ETHMOID BONE
LACRIMAL BONE
NASAL BONE
Zygomatic arch
ZYGOMATIC BONE
Condylar process
of mandible
MAXILLA
Mental foramen
MANDIBLE
HYOID BONE
(b) Right lateral view
Skull and Hyoid Bone 127
PARIETAL BONE
Squamous suture
Lambdoid suture
TEMPORAL BONE
OCCIPITAL BONE
floid process -
(c) Medial view of sagittal section
What are the names of the cranial bones?
FRONTAL BONE
Coronal suture
Hypophyseal fossa
of sphenoid
Crista galli
of ethmoid
Cribriform plate
of ethmoid
Frontal sinus
Perpendicular plate
of ethmoid
NASAL BONE
SPHENOID BONE
Sphenoidal sinus
INFERIOR NASAL
CONCHA
VOMER
MAXILLA
PALATINE BONE
Alveolar process
of mandible
MANDIBLE
HYOID BONE
enoid bone, and ethmoid bone. Fourteen facial hones
mi the face: two nasal bones, two maxillae, two zygomatic
ties, the mandible, two lacrimal bones, two palatine bones,
\) inferior nasal conehae, and the vomer. Figure 6.7 shows
se bones from three different viewing- directions to permit
iu to view all of the bones from their best perspective.
The cranial hones have functions besides protection of
brain. Their inner surfaces attach to membranes
■cringes) that stabilize the positions of the brain, blood
Is, and nerves. Their outer surfaces provide large areas
I attachment for muscles that move various parts of the
Besides forming die framework of the face, the facial
foes protect and provide support for the entrances to the
rive and respiratory systems. The facial bones also pro-
e attachment for some muscles that are involved in pro-
cbg various facial expressions. Together, the cranial and
fial bones protect and support the delicate special sense or-
s for vision, taste, smell, hearing, and equilibrium (balance).
tranial Bones
(e frontal bone forms the forehead (the anterior part of the
iflium), die roofs of the orbits (eye sockets; Figure 6.7a),
and most of the anterior (front) part of the cranial floor. The
frontal sinuses lie deep within the frontal bone (Figure 6.7c).
These mucous membrane-lined cavities act as sound cham-
bers that give the voice resonance. Other functions of die si-
nuses are given on page 131.
The two parietal bones (pa-RI-e-tal; parkt- = wall) form
most of die sides and roof of the cranial cavity (Figure 6.7).
The two temporal bones (tempor- = temples) form the
inferior (lower) sides of the cranium and part of the cranial
floor. In the lateral view of the skull (Figure 6.7b), note that
the temporal and zygomatic bones join to form the zygomatic
arch. The mandibular fossa (depression) forms a joint with a
projection on the mandible (lower jawbone) called the
condylar process to form the temporomandibular pmt (TMJ).
The mandibular fossa can be seen in Figure 6.8. The externa!
auditory meatus is the canal in the temporal bone that leads to
the middle ear. The mastoid process (mastoid ; breast-shaped;
see Figure 6.7b) is a rounded projection of the temporal bone
posterior to (behind) the external auditory meatus. It serves
as a point of attachment for several neck muscles. The styloid
process (styl- = stake or pole; see Figure 6.7b) is a slender pro-
jection that points downwtitd from the undersurface ol die
temporal bone and serves as a point of attachment for mus-
1 28 Chapter 6 The Skeletal System
cles and ligaments of the tongue and neck. The carotid foramen
(Figure 6.8) is a hole through which the carotid artery passes.
"The occipital hone (ok-SIP-i-tal; occipit- = back of head)
forms the posterior part and most of the base of the cranium
(Figures 6.7b, c and 6.8), The foramen magnum (jnagnttm =
large), the largest foramen in the skull, passes through the
occipital bone (Figures 6.7b and 6,8). Within this foramen
are the medulla oblongata of the brain, connecting to the
spinal cord, and the vertebral and spinal arteries. The occipital
condyles are oval processes, one on either side of the foramen
magnum (Figure 6.8), that articulate (connect) with the first
cervical vertebra.
The sphenoid hone (SFE-noyd - wedge-shaped) lies at
the middle part of the base of the skull (Figures 6. 7, 6.8, and
6.9). This bone is called the keystone of the cranial floor be-
cause it articulates with all the other cranial bones, holding
them together. The shape of the sphenoid bone resembles a
bat with outstretched wings. The cubelike central portion of
.'
the sphenoid bone contains the sphenoidal ] sinuses, which drain
into the nasal cavity (see Figures 67a and 6.11). On the
superior surface of the sphenoid is a depression called tlu
hypophyseal fossa (hi-pQ-FlZ-e-al), which contains the pitu-
itary gland. Two nerves pass through foramina in the sphe-
noid bone: the mandibular nerve through the foramen
and the optic nerve through the optic foremen (canal).
The ethmoid hone (ETH-moid = sievelike) is spongelike
in appearance and is located in the anterior part of the cranial
floor between the orbits (Figure 6.10 on page 130). It forms
part of the anterior portion of the cranial floor, the medial
wall of the orbits, the superior portions of the nasal septum, a
partition that divides the nasal cavity into right and left sides,
and most of the side walls of the nasal cavity. The ethmoid
bone contains 3 to 18 air spaces, or "cells," that give this
bone a sievelike appearance. The ethmoidal cells together
form the ethmoidal sinuses (see Figure 6.11). The perpendiculi
plate forms the upper portion of die nasal septum. The cribri
Figure 6.8 Skull.
The occipital bone forms most of the posterior and inferior portion of the cranium.
ncisor teeth
MAXILLA
ZYGOMATIC BONE
Zygomatic arch
VOMER
Foramen ovale
Mandibular fossa
Carotid foramen
Occipital condyle
TEMPORAL BONE
OCCIPITAL BONE
) What is the largest foramen in the skult?
nteriorview, mandible removed
PALATINE BONE
Middle nasal concha
SPHENOID BONE
Styloid process
Mastoid process
Foramen magnum
PARIETAL BONE
Lambdoid suture
Figure 6.9 Sphenoid bone.
The sphenoid bone is called the keystone of the cranial floor because it articulates with all other cranial bones,
.">■'" - holding them together.
Skull and Hyoid Bone 129
Corona! suture
Foramen ovale
Transverse plane
Foramen magnum
OCCIPITAL BONE
FRONTAL BONE
ETHMOID BONE:
Crista galli
Olfactory foramina
Cribriform plate
SPHENOID BONE:
Optic foramen
Hypophyseal fossa
Squamous suture
TEMPORAL BONE
PARIETAL BONE
Lambdoid suture
Viewed from above in floor of cranium
* Starting at the crista galli of the ethmoid bone and going in a clockwise direction, what are the names
of the bones that articulate with the sphenoid bone?
(KRIB-ri-forrn) forms the roof of the nasal cavity
10), It contains the olfactory foramina (olfact- = to
, holes through which fibers of the olfactory nerves
i e Figure 6.9). Projecting upward from the cribriform
it. is a triangular process called the crista galli (= cock's
Lb), which serves as a point of attachment for the mem-
, (meninges) that cover the brain (Figure 6. 1 0).
o part of the ethmoid bone are two thin, scroll-shaped
on cither side of the nasal septum. These are called die
i&r nasal concha (KONG-ka; conch- = shell) and the mid-
d concha. The plural is conchae (KONG-ke). The eon-
jhae cause turbulence in inhaled air, which results in many in-
hled particles striking and becoming trapped in the mucus that
pes the nasal passageways. This turbulence thus cleanses the
[haled air before it passes into the rest of the respiratory tract.
Facial Bones
The shape of die face changes dramatically during the first
two years after birth. The brain and cranial bones expand,
the teeth form and erupt (emerge), and the paranasal sinuses
increase in size. Growth of the face ceases at about 16 years
of age.
The paired nasal bones form part of the bridge of the
nose (see Figure 6.7a). The rest of die supporting tissue of
the nose consists of cartilage.
The paired maxillae (mak-SIL-e = jawbones; singular is
maxilla) unite to form the upper jawbone and articulate with
every bone of the face except the mandible (lower jawbone)
(see Figure 6.7). Each maxilla contains a maxillary sinus that
empties into the nasal cavity (see Figure 6.1 1), The alveolar
130 Chapter 6 The Skeletal System
Figure 6.10 Ethmoid bone.
The ethmoid bone is the major supporting structure of the nasal cavity.
View *~~\
- Sagittal
plane
(a) Sagittal section
ETHMOID BONE:
Crista galli
Olfactory foramen
Cribriform plate
Superior nasal concha
Middle nasal concha
Sphenoidal sinus
Inferior nasal concha
Palatine bone
Maxilla
Crista galli
Left orbit
Perpendicular
plate
Superior n?
concha
Middle nasal
concha
(b) Anterior view of position of ethmoid bone in skull
' What part of the ethmoid bone forms the top part of the nasal septum?
proem (al-VE-6-lar; alveol- = small cavity) of the maxilla is an
afeh that contains the alveoli (sockets) for the maxillary
(upper) teeth. The maxilla forms the anterior three-quarters
of the hard palate.
Usually the left and right mamillary bones unite during
weeks 1 to 12 of embryonic development. Failure to do
so can result in one type of cleft palate. The condition
may also involve incomplete fusion of the palatine bones
(see Figure 6*8). Another form of this condition, called
cleft lip, involves a split in the upper lip. Cleft lip and cleft
palate often occur together. Depending on the extent and
position of the cleft, speech and swallowing may be
fected. Facial and oral surgeons recommend closure
cleft lip during die first few weeks following birth, ai
surgical results are excellent. Repair of cleft palate
callyis completed between 12 and 18 months of age, i
ally before the child begins to talk. Because die pake
important for pronouncing consonants, speech thera]
may be required, and orthodontic therapy may be neel
to align the teeth. Again, results are usually excellei
Supplementation with folic acid (one of the B vitamj
during pregnancy decreases the incidence of cleft palai
and cleft lip.
■ t r.
Skull And Hvoid Bone 1 31
The two L-shaped palatine bones (PAL-a-tin; palat- =
,i Of mouth) lire fused and form the posterior portion of
I the hard palate, part of the floor and lateral wall of the nasal
Brity, and a small portion of the floors of the orbits (see Fig-
Hi). In cleft palate, the palatine bones may also be in-
completely fused.
The mandible (inaml- - to chew), or lower jawbone, is
I the largest, strongest facial bone (see Figure 6.7b). It is the
Kily movable skull bone. Recall from our discussion of the
I temporal bone that die mandible has a condylar process (KC)N-
di-br). This process articulates with the mandibular fossa of
the temporal bone to form the temporomandibular joint.
The mandible, like die maxilla, has an alveolar proms contain-
ing the alveoli (sockets) for the mandibular (lower) teeth (see
ILre 6.7c). The mental foramen {went- = chin) is a hole in
mandible that can be used by dentists to reach the mental
nerve when injecting anesthetics (see Figure 6.7a).
One problem associated with the temporomandibular joint
II) is temporomandibular joint (TMJ) syndrome. It
is characterized by dull pain around the ear, tenderness of
the jaw muscles, a clicking or popping noise when opening
or dosing die mouth, limited or abnormal opening of the
mouth, headache, tooth sensitivity, and abnormal wearing
of the teedi, TMJ syndrome can be caused by improperly
ted teeth, grinding or clenching the teeth, trauma to
head and neck, or arthritis. Treatments include
applying moist heat or ice, eating a soft diet, taking pain
such as aspirin, muscle retraining, adjusting or
reshaping the teeth, orthodontic treatment, or surgery.
The two zygomatic bones {zygo- = like a yoke), com-
monly called cheekbones, form the prominences of die
:eksand part of the lateral wall and floor of each orbit (see
Figure 6.7a, b). They articulate with the frontal, maxilla,
| sphenoid, and temporal bones.
The paired lacrimal bones (LAK-ri-mal; lucrim- =
teardrop), the smallest bones of the face, are thin and roughly
| resemble a fingernail in size and shape. The lacrimal bones
en be seen in the anterior and lateral views of the skull in
ts a and b of Figure 6.
The two inferior nasal conchae are scroll-like bones that
I project into the nasal cavity below the superior and middle
nasal conchae of the ethmoid bone (see Figures 6.7a, c and
BO), They serve the same function as the other nasal con-
the filtration of air before it passes into the lungs.
The vomer (VO-mer = plowshare) is a roughly triangular
Bone on die floor of the nasal cavity that articulates interiorly
with both the maxillae and palatine bones along the midline of
Be skull. The vomer, clearly seen in the anterior view of the
stall in Figure 6.7a and die inferior view in Figure 6.8, is one of
^components of die nasal septum, a partition that divides the
Lai cavity into right and left sides. The nasal septum is
formal by*" the vomer, septal cartilage, and the perpendicular
plate of the ethmoid bone (see Figure 6.7a and c). The anterior
border of the vomer articulates with the septal cartilag^hyaline
cartilage) to form die anterior portion of the septum. The upper
border of the vomer articulates with die perpendicular plate of
the ethmoid bone to form the remainder of die nasal septum.
A deviated nasal septum is one that does not run along
the midline of die nasal cavity. It deviates (bends) to one
side. Septal deviations may occur due to a developmental
abnormality or trauma. If die deviation is severe, it may
block the nasal passageway entirely. Even a partial blockage
may lead to infection. If inflammation occurs, it may cause
nasal congestion, blockage of the paranasal sinus openings,
chronic sinusitis, headache, and nosebleeds. The condition
usually can be corrected, or at least improved, surgically.
Unique Features of the Skull
Now that you are familiar with the names of the skull bones,
we will take a closer look at three unique features of the skull:
sutures, paranasal sinuses, and fontanels.
Sutures
A suture (SOO-chur - seam) is an immovable joint in an adult
that is found only between skull bones. Sutures hold skull
bones together. Of die many sutures that are found in the skull,
we will identify only four prominent ones (see Figure 6.7):
L The coronal suture (ko-RO-nal; coron- = crown) unites
the frontal bone and two parietal bones,
2. The sagittal suture (SAJ-i-tal; sagitt- = arrow) unites the
two parietal bones.
3* The Imnbdoid suture (LAM-doyd; so named because its
shape resembles the Greek letter lambda, A) unites the
parietal bones to the occipital bone.
4. The squamous sutures (SKWA-mus; squam- Bat) unite
the parietal bones to the temporal bones,
Paranasal Sinuses
Paired cavities, the paranasal sinuses {para- = beside), are lo-
cated in certain skull bones near the nasal cavity (Figure 6J I).
The paranasal sinuses are lined with mucous membranes that
are continuous with the lining of the nasal cavity. Skull bones
containing paranasal sinuses include die frontal bone {frontal
sinus), sphenoid bone {sphenoid shuts), ethmoid bone {ethmoidal
sinuses), and maxillae (pmxittmy sinuses). Besides producing mu-
cus, the paranasal sinuses serve as resonating chambers, pro-
ducing die unique sounds of each of our speaking and singing
voices, and lighten the weight of the skull.
Secretions produced by the mucous membranes of die
paranasal sinuses drain into the nasal cavity. An inflamma-
tion of die membranes due to an allergic reaction or infec-
tion is called sinusitis. If the membranes swell enough to
block drainage into the nasal cavity, fluid pressure builds
up in the paranasal sinuses, resulting in a sinus headache.
1 32 Chapter 6 The Skeletal System
Figure 6-11 Paranasal sinuses.
Paranasal sinuses are mucous membrane-lined spaces in the
frontal, sphenoid, ethmoid, and maxillary bones that connect
to the nasal cavity.
Frontal sinus
Ethmoidal cells
Sphenoidal sinus
Maxillary sinus
Right lateral view
1 What are two main functions of the paranasal sinuses?
Fontanels
Recall that the skeleton of a newly formed embryo consists o
cartilage or mesenchyme arranged like membranes shaf
like bones. Gradually, ossification occurs- -bone replaces the
cartilage or mesenchyme, Mesenchyme-filled spaces called
fontanels (fonta-NELZ = little fountains) or "soft spots" are
found between cranial bones at birth. They include the ante-
rior fontanel, the posterior fontanel, the anterolate
fontanels, and the posterolateral fontanels. These areas o:
unossified mesenchyme will eventually be replaced with bora
by intraniembranous ossification and become sutures. Func-
tionally, the fontanels enable the fetal skull to be compressed
as it passes through the birth canal and permit rapid gn
of the brain during infancy The form and location of several
fontanels are shown and described in Table 6.3.
Hyoid Bone
The single hyoid hone (Hl-oyd = U-shaped) is a uniq
component of the axial skeleton because it does not artic
with or attach to any other bone. Rather, it is suspended tin
the styloid processes of the temporal bones by ligaments am
muscles. The hyoid bone is located in the neck between
mandible and larynx (see Figure 6.7b). It supports the ton
and provides attachment sites for some tongue muscles ai|
for muscles of the neck and pharynx. The hyoid bone., as uj
Fontanel
Anterior
Posterior
Table 6.3 Fontanels
Location
Between the two parietal bones and the frontal bone.
Between the two parietal bones and the occipital bone.
Anterior
Posterior
Anterolateral
Posterolateral
One on each side of the skull between the frontal,
parietal, temporal, and sphenoid bones.
One on each side of the skull between the parietal,
occipital, and temporal bones.
Anterolateral
Description
Roughly diamond-shaped, the largest of the fontanels; usually clos
18-24 months after birth.
Diamond-shaped, considerably smaller than the anterior
fontanel; generally closes about 2 months after birth.
Small and irregular in shape; normally close about 3 months
after birth.
Irregularly shaped; begin to close 1 or 2 months after birth, but
closure is generally not complete until 12 months.
Posterolateral
as the cartilage of the larynx and trachea, is often fractured
during strangulation. As a result, they are carefully examined
pan autopsy when strangulation is suspected.
I CHECKPOINT
1 15. Describe the general features of the skull
16, Define the following; suture, foramen, nasal septum*
paranasal sinus, and fontanel,
VER TEBRAL COLUMN
JECTIVE • Identify the regions and normal curves
the vertebral column and describe its structural and
kctional features.
fe vertebral column, also called the spine, spinal column, or
Mom, is composed of a series of bones called vertebrae
IR-te-bre; singular is vertebra). The vertebral column
prions as a strong, flexible rod that can rotate and move
iure6.12 Vertebral column.
The adult vertebral column typically contains 26 vertebrae.
Vertebral Column 133
forward, backward, and sideways. It encloses and protects the
spinal cord, supports the head, anoVserves as a point of attach-
ment for the ribs, pelvic girdle, and't'he muscles of the back.
Regions of the Vertebral Column
The total number of vertebrae during early development is
33. Then, several vertebrae in the sacral and coccygeal regions
fuse. As a result, the adult vertebral column typically contains
26 vertebrae (Figure 6.12). These are distributed as follows:
■ 7 cervical vertebrae {cervic- = neck) in the neck region
■ 12 thoracic vertebrae (thorax = chest) posterior to the
thoracic cavity
■ 5 lumbar vertebrae {lamb- = loin) supporting the lower
back
■ 1 sacrum (SA-krum = sacred bone) consisting of five
fused sacral vertebrae
■ I coccyx (KOK-siks = cuckoo, because the shape resem-
bles the bill of a cuckoo bird) usually consisting of four
Fused coccygeal vertebrae (kok-SIJ-e-al)
POSTERIOR
Intervertebral
disc
Intervertebral
foramen
Sacrum
Coccyx
ANTERIOR
Cervical curve (formed by 7
cervical vertebrae)
Thoracic curve (formed by 12
thoracic vertebrae)
Lumbar curve (formed by 5
lumbar vertebrae)
Sacral curve (formed by 5
fused sacral vertebrae)
(a) Right lateral view showing four
normal curves
5)
(
Which curves are concave {relative to the front of the body)?
Single curve in fetus Four curves in adult
(b) Fetal and adult curves
Functions of the Vertebral Column
1. Permits movement.
2. Encloses and protects the spinal cord.
3. Serves as a point of attachment for the ribs and muscles of the back.
1 34 Chapter 6 The Skeletal System
The cervical, thoracic, and lumbar vertebrae are mov-
able] but the sacrum and coccyx are immovable. Between ad-
jacent vertebrae from the second cervical vertebra to the
sacrum are intervertebral discs (inter- = between). Each disc
has an outer ring of fibrocartikge and a soft, pulpy, highly elas-
tic interior. The discs form strong joints, permit various move-
ments of die vertebral column, and absorb vertical shock.
Normal Curves of the Vertebral Column
When viewed from the side, the vertebral column shows four
slight bends called normal curves (Figure 6. 1 2), Relative to
the front of the body, the cervical and lumbar curves arc
convex (bulging out), and the thoracic and sacral curves are
concave (cupping in). The curves of the vertebra! column in-
crease its strength, help maintain balance in the upright posi-
tion, absorb shocks during walking and running, and help
protect the vertebrae from breaks.
In die fetus, there is a single concave curve (Figure 6.12b).
At about die third month after birth, when an infant begins to
hold its head erect, the cervical curve develops. Later, when the
child sits up, stands, and walks, the lumbar curve develops.
Vertebrae
Vertebrae in different regions of die spinal column vary in
shape, and detail, but they are similar enough that we can dis
the structure and functions of a typical vertebra (Figure 6, 1 J)i
1. The body, the thick, disc-shaped front portion, is
weight-bearing part of a vertebra.
2. The vertebral arch extends backwards from the body
the vertebra. It is formed by two short, thick proces
the pedicles (PED-i-kuls = little feet), which project ba
ward from the body to unite with the laminae. The lad
me (LAM-i-ne = thin layers) are the flat parts of the arJ
and end in a single sharp, slender projection called wspk
ons process. The hole between the vertebral arch and b
contains the spinal cord and is known as the verti
foramen. Together, the vertebral foramina of all vertebn
form the vertebral cavity. When the vertebrae are st
on top of one another, there is an opening between
joining vertebrae on both sides of the column. I
opening, called an intervertebral foramen, permits the pa;
sage of a single spinal nerve.
Figure 6.13 Structure of a typical vertebra, as illustrated by a thoracic vertebra. (Note the facets
for the ribs, which vertebrae other than the thoracic vertebrae do not have.) In (b), only one spinal nerve has
been included, and it has been extended beyond the intervertebral foramen for clarity.
> A
A vertebra consists of a body, a vertebral arch, and several processes.
ANTERIOR
POSTERIOR
Location of
thoracic vertebrae
Facet for rib
Facet of superior
articular process
Spinal cord
Vertebral foramen
ANTERIOR
(a) Superior view
POSTERIOR
Spinous process
Transverse
process
Vertebral arch:
Lamina
Pedicle
Facet for rib
Body
Spinous
process
(b) Right posterolateral view
What are the functions of the vertebral and intervertebral foramina?
ANTERIOR
Spinal cord
Facet of superior
articular process
Pedicle
Spinal nerve
ntervertebral dis
Intervertebral
foramen
Facets for rib
Body
Inferior articu ! ar
process
1, Seven processes arise from the vertebral arch. At the
point where a lamina and pedicle join, a transverse process
extends laterally on each side. A single spinous process
(spine) projects from the junction of the laminae. These
three processes serve as points of attachment for muscles.
The remaining four processes form joints with other ver-
tebrae above or below. The two superior articular processes
of a vertebra articulate with the vertebra immediately
Vertebral Column 135
above them. The two inferior wticuhir processes of a verte-
bra articulate with the vertebra immediately below them.
The smooth articulating surfaces of the articular
processes are called facets (= little feces), which are cov-
ered with hyaline cartilage.
Vertebrae in each region are numbered in sequence from
top to bottom. The seven cervical vertebrae are termed CI
through C7 (Figure 6.14). The spinous processes of the
Figure 6.14 Cervical vertebrae.
The cervical vertebrae are found in the neck region.
POSTERIOR
Vertebral foramen
Transverse foramen
ANTERIOR
Groove for vertebral
artery and first cervical
spinal nerve
Transverse process
Superior articular
facet
;a) Superior view of the atlas (C1
Location of
cervical vertebrae
Atlas
Axis
Typical
cervical
vertebra
ANTERIOR
POSTERIOR
Lamina
Vertebral
foramen
Transverse
foramen
ANTERIOR
POSTERIOR
Lamina
Vertebral foramen
Transverse foramen
Transverse process
ANTERIOR
(b) Superior view of the axis {02)
Spinous process
Transverse process
Superior articular facet
Dens
Bifid spinous process
Superior articular facet
Pedicle
Body
(c) Superior view of a typical cervical vertebra
Which bones permit the movement of the head to signify "no"?
136 Chapter 6 The Skeletal System
second through sixth cervical vertebrae are often bifid, or split
into two parts (Figure 6,14b, c). All cervical vertebrae have
three foramina; one vertebral foramen and two transverse
foramina. Each cervical transverse process contains a trans-
verse foramen through which blood vessels and nerves pass.
The first two cervical vertebrae differ considerably from
the others. The first cervical vertebra (CI), the atlas, sup-
ports die head and is named for the mythological Atlas who
supported the world on his shr .alders. The atlas lacks a body
and a spinous process. The upper surface contains superior ar-
ticular facets that articulate with the occipital bone of the
skull. This articulation permits you to nod your head to indi-
cate "yes." The inferior surface contains inferior articular
facets that articulate with the second cervical vertebra.
The second cervical vertebra (C2), the axis, does have a
body and a spinous process. A tooth-shaped process called
the dens (= tooth) projects up through the vertebral foramen
of the atlas. The dens is a pivot on which the atlas and head
move, as in side-to-side movement of the head to signify
"no."
The third through sixth cervical vertebrae (C3 through
C6), represented by the vertebra in Figure 6.14c, correspond
to the structural pattern of the typical cervical vertebra de-
scribed previously. The seventh cervical vertebra (C7), called
the vertebra prominens, is somewhat different. It is marked by
a single, large spinous process that can be seen and felt at the
base of the neck.
Thoracic vertebrae (Tl through T12) are considerably
larger and stronger than cervical vertebrae. Distinguishing
features of the thoracic vertebrae are their facets for articu-
lating with the ribs (see Figure 6.13). Movements of the tho-
racic region are limited by the attachment of the ribs to the
sternum.
The lumbar vertebrae (LI through L5) are the largest
and strongest in the column (Figure 6.15). Their various!
projections are short and thick, and the spinous proce
are well adapted for the attachment of the large back!
muscles.
The sacrum is a triangular bone formed by the fusion of
five sacral vertebrae, indicated in Figure 6.16 as SI through
S5. The fusion of the sacral vertebrae begins between ages 16
and 18 years and is usually completed by age 30. The sacrum
serves as a strong foundation for the pelvic girdle. It is posi-
tioned at the back of the pelvic cavity medial to the two hip
bones.
The anterior and posterior sides of the sacrum contain
four pairs of sacral foramina. Nerves and blood vessels pass
through the foramina. The sacral canal is a continuation of
the vertebral cavity. The lower entrance is called the sa
hiatus (hl-A-tus = opening). The anterior top border of the
sacrum has a projection, called the sacral promontory (PROM-
on-to'-re), which is used as a landmark for measuring the
pelvis prior to childbirth.
Anesthetic agents that act on the sacral and coecv
nerves are sometimes injected through die sacral hiatus, a
procedure called caudal anesthesia or epidural block.
Figure 6.15 Lumbar vertebrae,
^ Lumbar vertebrae are found in the lower back.
POSTERIOR
ANTERIOR
Location of
lumbar vertebrae
Lamina
Pedicle
ANTERIOR
Spinous process
Superior articular facet
Transverse process
Vertebral foramen
Body
Superior view
■ Why are the lumbar vertebrae the largest and strongest in the vertebral column?
j
JTie procedure is used most often to relieve pain during
!il: or and to provide anesthesia to the perineal area. Anes-
Jietic agents may also be injected through the posterior
sacral foramina.
Thorax 137
the sternum, costal cartilages, ribs, and the bodies of the tho-
racic vertebrae (Figure 6,17). The thoracic cage encloses and
protects the organs in the thoracic cavity and upper abdomi-
nal cavity. It also provides support for the bones of the shoul-
der girdle and upper limbs.
The coccyx, like the sacrum, is triangular in shape and is
formed by the fusion of the four coccygeal vertebrae. These
Ire indicated in Figure 6.16 as Col through Co4. The top of
coccyx articulates with the sacrum.
| CHECKPOINT
17. What are the functions of the vertebral column?
|8< What are the main distinguishing characteristics of the
bones of the various regions of the vertebral column?
THORAX
[BJECTIVE • Identify
ieir principal markings.
the bones of the thorax and
Je term thorax refers to the entire chest. The skeletal por-
L of the thorax, the thoracic cage, is a bony cage formed by
Sternum
The sternum, or breastbone, is a flat, narrow bone located
in the center of the anterior thoracic wall and consists of
three parts that usually fuse by age 25 (Figure 6.17). The
upper part is the manubrium (ma-NOO-bre-um : handle-
like); the middle and largest part is the body; and the low-
est, smallest part is the xiphoid process (Zl-foyd = sword-
shaped).
The manubrium articulates with the clavicles and the
first and second ribs. The body of the sternum articulates di-
rectly or indirectly with the second through tenth ribs. The
xiphoid process consists of hyaline cartilage during infancy
and childhood and does not ossify completely until about age
40. It has no ribs attached to it but provides attachment for
some abdominal muscles. If the hands of a rescuer are incor-
rectly positioned during cardiopulmonary resuscitation
(CPRJ, there is danger of fracturing the xiphoid process and
driving it into internal organs.
Figure 6.16 Sacrum and coccyx.
The sacrum is formed by the union of five sacral vertebrae, and the coccyx is formed by the union of usually
four coccygeal vertebrae.
Superior articular process Superior articular facet
ANTERIOR
Sacra
promontory
Sacral
foramen
Location of
I sacrum and coccyx
Sacrum
Sacral hiatus
Coccyx.
Sacraf
canal
Sacral
foramen
(a) Anterior view
(b) Posterior view
I
What is the function of the sacral foramina?
1 38 Chapter 6 The Skeletal System
Figure 6.17 Skeleton of the thorax.
The bones of the thorax enclose and protect organs in the thoracic cavity and upper abdominal cavity.
; ,, ™
STERNUM:
Manubrium
Body
Xiphoid
process
Costal
cartilage
Intercostal
space
L2
Which ribs are true ribs? False ribs? Floating ribs?
Anterior view
Ribs
Twelve pairs of ribs make up the sides of the thoracic cavity
(Figure 6.17). The ribs increase in length from the first
through seventh ribs, then decrease in length to the twelfth
rib. Each rib articulates posteriorly with its corresponding
thoracic vertebra,
The first through seventh pairs of ribs have a direct ante-
rior attachment to the sternum by a strip of hyaline cartilage
called costal cartilage (cost- = rib). These ribs are called true
ribs. The remaining five pairs of ribs are termed fake ribs be-
cause their costal cartilages either attach indirectly to the
sternum or do not attach to die sternum at all. The cartilages
of die eighth, ninth, and tenth pairs of ribs attach to each
other and then to the cartilages of the seventh pair of ribs.
The eleventh and twelfth false ribs are also known as floating
ribs because the costal cartilage at their anterior ends does
not attach to the sternum at all. Floating ribs attach only pos-
teriorly to the thoracic vertebrae. Spaces between ribs, calk
intercostal spaces, are occupied by intercostal muscles, bloc
vessels, and nerves.
Rib fractures are the most common chest injuries, and
they usually result from direct blows, most often from ira
pact with a steering wheel, falls, and crushing injuries
die chest. In some cases, fractured ribs may puncture i
heart, great vessels of die heart, lungs, trachea, bronchi
esophagus, spleen, liver, and kidneys. Rib fractures are
usually quite painful. Rib fractures are no longer bound
with bandages because of the pneumonia that would result
from lack of proper lung ventilation.
■ CHECKPOINT
19. What are the functions of the bones of the thorax?
20. What are die parts of the sternum?
PECTORAL (SHOULDER) GIRDLE
BJECTIVE • Identify the bones of the pectoral
(shoulder) girdle an d their principal markings.
[The pectoral girdles (PEK-to-ral) or shoulder girdles at-
tach the hones of the upper limbs to the axial skeleton
re 6.18). The right and left pectoral girdles each con-
of two bones: a clavicle and a scapula. The clavicle, the
anterior component, articulates with the sternum^ and the
btpula, the posterior component, articulates with the clav-
icle and the humerus. The pectoral girdles do not articu-
with the vertebral column. The joints of the shoulder
s are freely movable and thus allow movements in
■any directions.
[Clavicle
ach clavicle (KLAV-i-kul = key) or collarbone is a long,
ider S-shaped bone that is positioned horizontally above
first rib. The medial end of the clavicle articulates w r ith
sternum, and the lateral end articulates with the
jmion of the scapula (Figure 6. IS). Because of its position,
Pectoral (Shoulder) Girdle 139
die clavicle transmits mechanical force from the upper limb
to the trunk. If the force transmitted to the clavicle is exces-
sive, as when you fall on your outstretched arm, a fractured
clavicle may result.
Scapula
Each scapula (SCAF-yu-la), or shoulder blade, is a large, flat,
triangular bone situated in the posterior part of the thorax
(Figure 6. 18). A sharp ridge, the spine, runs diagonally across
the posterior surface of the flattened, triangular body of the
scapula. The lateral end of the spine, the acromion (a-KRO-
me-on; acrwn- = topmost), is easily felt as the high point of
the shoulder and is the site of articulation with the clavicle.
Inferior to the acromion is a depression called the glenoid
cavity. This cavity articulates with die head of the humerus
(arm bone) to form the shoulder joint. Also present on the
scapula is a projection called the coracoid process (KOR-a-koyd
= like a crow's beak) to which muscles attach.
■ CHECKPOINT
21. What bones make up the pectoral girdle? What is the
function of the pectoral girdle?
igure 6.18 Right pectoral (shoulder) girdle.
The pectoral girdle attaches the bones of the upper limb to the axial skeleton.
Pectoral girdle:
Clavicle
Scapula
CLAVICLE
CLAVICLE
Acromion
Coracoid process
Glenoid cavity
Humerus
SCAPULA
SCAPULA:
Acromion
- Spine
Body
[a) Anterior view
(b) Posterior view
5>
l
Which bones make up a pectoral girdle?
1 40 Chapter 6 The Skeletal System
UPPER LIMB
OBJECTIVE • Identify the bones of the upper limb
and their principal markings.
Each upper limb consists of 30 bones. Each upper limb in-
cludes a humerus in the arm; ulna and radius in the forearm;
and 8 earpals (wrist bones), 5 metacarpals (palm hones), and
14 phalanges (finger bones) in the hand (see Eigure 6.6).
Humerus
The humerus (HU-mer-us), or arm bone, is the longest and
largest bone of the upper limb (Figure 6.19). At the shoulder
it articulates with the scapula, and at the elbow it articulates
with both the ulna and radius. The proximal end of the
humerus consists of a bead that articulates with the glenoid
cavity of the scapula, It also has an anatomical neck, the former
site of the epiphyseal plate, which is a groove just distal to
the head. The body of the humerus contains a roughened,
V-shaped area called the deltoid tuberosity where the deltoid
muscle attaches. At the distal end of the humerus, the capitn-
lum (ka-PIT-u-hnn = small head), is a rounded knob that
articulates with the head of the radius. The radial fossa is i
depression that receives the head of the radius when the fore-
arm is flexed (bent). The trochlea (TROK-le-a) is a spool-
shaped surface that articulates with the ulna. The coronM
fossa (KOR-o-noyd = crown-shaped) is a depression that re-
ceives paft of the ulna when the forearm is flexed. The olecri
non fossa (6-LEK-ra-non) is a depression on the back of the
bone that receives the olecranon of the ulna when the 6
arm is extended (straightened).
Ulna and Radius
The ulna is on the medial aspect (little-finger side) of th<
forearm and is longer than the radius (Figure 6.20). At th<
proximal end of the ulna is the olecranon, which forms tb.
prominence of the elbow. The coronoid process, together wil
the olecranon, receives the trochlea of the humerus. Th
trochlea of the humerus also fits into the trochlear notch\
large curved area between the olecranon and the corn run
process. The radial notch is a depression for the head of th«
radius, A styloid process is at the distal end of the ulna.
The radius is located on the lateral aspect (thumb side
of the forearm. The proximal end of die radius has a disc-
Figure 6.19 Right humerus in relation to the scapula, ulna, and radius.
The humerus is the longest and largest bone of the upper limb.
Radial fossa
Capitulum
Head
Anatomical
neck
Scapula
- HUMERUS
Deltoid
tuberosity
Body
Coronoid
fossa
Trochlea
Ulna —
Radius
Olecranon
fossa
Anterior view
With which part of the scapula does the humerus articulate?
Posterior view
Figure 6.20 Right ulna and radius in relation to the humerus
and carpais.
In the forearm, the longer ulna is on the medial side, and the
|k-. radius is on the lateral side.
Humerus
Capitulum
Trochlea
Coronoid
process
Radial
tuberosity
RADIUS
Nutrient
foramina
Head
VI —
Styloid process
of radius
ULNA
Styloid process
of ulna
Carpais
(a) Anterior view
Olecranon
Ulna
Trochlear
notch
Coronoid
process
Radial
notch
(hi Lateral view of proximal end of uina
/ What part of the ulna is called the elbow?
Upper Limb 141
shaped bead that articulates with the capitulum of the
humerus and radial notch of the ulna. It has a raised, rough-
ened area called the radial Tuberosity that provides a point of
attachment for the biceps brachii muscle. The distal end of
the radius articulates with three carpal bones of the wrist.
Also at the distal end is a styloid process. Fracture of die distal
end of the radius is the most common fracture in adults older
than 50 years.
Carpais, Metacarpals, and Phalanges
The carpus (wrist) of the hand contains eight small hones,
die carpais, held together by ligaments (Figure 6.21). The
carpais are arranged in two transverse rows, with four bones
in each row, and they are named for their shapes. In the
anatomical position, the carpais in the top row, from the
Figure 6.21 Right wrist and hand in relation to the ulna and
radius.
| The skeleton of the hand consists of the carpais, metacarpals,
- and phalanges.
Carpais
- Metacarpals
— Phalanges
CARPALS:
Scaphoid
Trapezium
Trapezoid
Sesamoid
bones
METACARPAL
LATERAL
Radius
Ulna
CARPALS:
Lunate
Triquetrum
Pisiform
Capitate
Hamate
Base
Body
Head
Base
Body
Head
PHALANGES -
Little finger
MEDIAL
Index finger
K \
•
Ring finger
Middle finger
Anterior view
What part of which bones are commonly called the knuckles?
1 42 Chapter 6 The Skeletal System
Figure 6.22 Female pelvic (hip) girdle,
-\ The hip bones are united in front at the pubic symphysis and in back at the sacrum.
Greater (false) pelvis
RIGHT
HIP BONE -
Ilium
Ischium
Iliac crest
Sacroiliac joint
Sacrum
Pelvic brim
Coccyx
Acetabulum
Obturator foramen
Pubic symphysis
(a) Anterior view
Midsagittal
plane
WVj
Sacrum
True pelvis
Coccyx
Plane of
pelvic outlet
False pelvis
Abdominal wall
Plane of pelvic brim
Pelvic axis
- Pubic symphysis
(b) Midsagjttal section indicating locations of true and false pelves
) What part of the pelvis surrounds the pelvic organs in the pelvic cavity?
I
lateral to medial position, are die scaphoid (SKAF-oid -
boatlike), Innate (LOO-nat = moon-shaped), triquetrum
(trl-KWE-trum = three cornered), and pisiform (Pi-si-form
= pea-shaped). In about 70% of carpal fractures, only the
scaphoid is broken because of the force transmitted through
it to the radius. The carpal s in the bottom row, from the lat-
eral to medial position, are the trapezium (tra-PE-ze-um
four-sided figure with no two sides parallel), trapezn
(TRAP-e-zoid = four-sided figure with two sides parallel
capitate (KAP-i-tat = head-shaped; the largest carpal bonj
whose rounded projection, die head, articulates with the
nate), and hamate (HAM-it = hooked; named for a la|
hook-shaped projection on its anterior surface). Together,
concavity formed by the pisiform and hamate (on the ulna
side) and the scaphoid and trapezium (on the radial side) consti-
tute a space called the carpal tunnel Through it pass the long
iexor tendons of the digits and thumb and the median nerve.
farrowing of the carpal tunnel gives rise to a condition
[called carpal tunnel syndrome, in which the median
e is compressed. The nerve compression causes pain,
[numbness, tingling, and muscle weakness in the hand.
The metacarpus (palm) of the hand contains five bones
died metacarpals (meta- = after or beyond). Each metacarpal
m consists of a proximal base, an intermediate body, and a
;tal bead. The metacarpal bones arc numbered I through V
(or 1 to 5), starting with the lateral bone in the thumb. The
jeais of the metacarpals are commonly called die "knuckles"
id are readily visible in a clenched fist.
The phalanges (fa-LAN-jez = battle lines) are the bones
f the fingers. They number 14 in each hand. Like the
rpals, the phalanges are numbered T through V (or I
5), beginning with the thumb. A single bone of a finger or
is termed a phalanx (FA-lanks). Like the metacarpals, each
|alanx consists of a proximal base, an intermediate body, and
festal bead. There are two phalanges (proximal and distal) in
J thumb and three phalanges (proximal, middle, and distal)
each of the other four digits, In order from the thumb,
iese other four digits are commonly referred to as the
[dex finger, middle finger, ring finger, and little finger
8gure6.21).
I CHECKPOINT
22. What bones form the upper limb, from proximal to
distal?
PELVIC (HIP) GIRDLE
OBJECTIVE • Identify the bones of the pelvic (hip)
girdle and the ir principal markings.
The pelvic (hip) girdle consists of the two hip hones, also
i weal hones (Figure 6.22 on page 142). The pelvic gir-
irovides a strong, stable support for the vertebral column,
jtects the pelvic viscera, and attaches the lower limbs to the
ill skeleton. The hip bones are united to each other in front
i joint called the pubic symphysis (PU-bik SIM-fi-sis); pos-
iiui.i k they unite with the sacrum at the sacroiliac joint.
Together with the sacrum and coccyx, the two hip bones
j the pelvic girdle form a basinlike structure called the pelvis
ispelvises or pelves). In turn, the bony pelvis is divided
upper and lower portions by a boundary called the pelvic
n (Figure 6.22). The part of the pelvis above the pelvic
Pelvic (Hip) Girdle 143
brim is called the false (greater) pelvis. The false pelvis is ac-
tually part of the abdomen and does not contain any pelvic
organs, except for the urinary bladder, when it is foil, and the
uterus during pregnancy. The part of the pelvis below the
pelvic brim is called the true (lesser) pelvis. The true pelvis
surrounds the pelvic cavity (see Figure LB on page 15). The
upper opening of the true pelvis is called the pelvic inlet, and
the lower opening of the true pelvis is called the pelvic outlet.
The pelvic axis is an imaginary curved line passing through
the true pelvis; it joins the central points of the planes of die
pelvic inlet and outlet. During childbirth, the pelvic axis is
the course taken by the baby's head as it descends through
the pelvis.
Pelvimetry is the measurement of die size of the inlet and
| outlet of the birth canal, which may be done by ultra-
sonography or physical examination. Measurement of the
pelvic outlet in pregnant females is important because it
must become large enough for the fetus to pass through at
birth.
Each of the two hip bones of a newborn is composed of
three parts; the ilium, the pubis, and the ischium (Figure
6.23). The ilium (= Hank) is the largest of the three subdivi-
sions of the hip bone. Its upper border is the iliac crest. On
Figure 6.23 Right hip bone. The lines of fusion of the ilium, is-
chium, and pubis are not always visible in an adult hip bone,
(3^ The two hip bones form the pelvic girdle, which attaches the
. lower limbs to the axial skeleton and supports the vertebral
column and viscera.
SUPERIOR
Iliac crest
Greater
sciatic
notch
POSTERIOR
Acetabulum
Obturator foramen
ANTERIOR
f
Lateral view
Which bone fits into the socket formed by the acetabulum?
1 44 Chapter 6 The Skeletal System
the lower surface is the grater sciatic notch (sT-AT-ik) through
which the sciatic nerve, the longest nerve in the body, passes.
The ischium (IS-ke-um = lip) is the lower, posterior part of
the hipbone. The pubis (PU~bis = pubic hair) is the lower,
anterior part of the hipbone. By age 23 years, the three sepa-
rate bones have Rised into one. The deep fossa (depression)
where the three bones meet is the acetabulum (as-e-TAB-u-
l imi = vinegar cup). It is the socket for the head of the femur.
The ischium joins with the pubis, and together they surround
the obturator foramen (OB-too-ra-ter), the largest foramen in
the skeleton.
■ CHECKPOINT
23. What bones make up the pelvic girdle? What is the func-
tion of the pelvic girdle?
LOWER LIMB
OBJECTIVE • List the skeletal components of the
lower limb and their principal m arkings.
Each lower limb is composed of 30 bones: the femur in the
thigh; die patella (kneecap); the tibia and fibula in the leg
(the part of the lower limb between the knee and the ankle);
and 7 tarsals (ankle bones), 5 metatarsals, and 14 phalanges
(toes) in the foot (see Figure 6,6).
Femur
The femur (thigh bone) is the longest, heaviest, and
strongest bone in the body (Figure 6.24). Its proximal end ar-
ticulates with the hip bone, and its distal end articulates with
the tibia and patella. The body of the femur bends medially,
and as a result, the knee joints are brought nearer to the mid-
line of the body. The bend is greater in females because the
female pelvis is broader,
The head of the femur articulates with the acetabulum
of the hip bone to form the hip joint. The neck of the femur
is a constricted region below the head. A fairly common
fracture in the elderly occurs at the neck of the femur,
which becomes so weak that it fails to support the weight
of the body. Although it is actually the femur that is frac-
tured, this condition is commonly known as a broken hip.
The greater trochanter (tro-KAN-ter) is a projection felt
and seen in front of the hollow on the side of the hip. It is
where some of the thigh and buttock muscles attach and
serves as a landmark for intramuscular injections in the
thigh.
The distal end of the femur expands into the medial
condyle and lateral condyle, projections which articulate with
the tibia. The patellar surface is located on the anterior surface
of the femur between the condyles.
Figure 6.24 Right femur in relation to the hip bone
tibia, and fibula.
The head o1 the femur articulates with the acetabulum of the
bone to form the hip joint.
Hip bone
Greater
trochanter
- FEMUR
Femur
Medial cor
Patella
Fibu'ia
Tibia
v
Anterior view
With which bones does the distal end of the femur articulate?
J
Patella
The patella (= little dish), or kneecap, is a small, triangv
bone in front of the joint between the femur and tibia, coi
monly known as the knee joint (Figure 6.24). The patella '
velops in the tendon of the quadriceps femoris muscle,
functions are to increase the leverage of the tendon, maim
the position of the tendon when the knee is flexed, and pi
tect the knee joint. During normal flexion and extension
the knee, the patella tracks (glides) up and down in
groove between the two femoral condyles.
In "runner's knee," or patellofemoral stress syndrom*
normal tracking does not occur. Instead, the patella traf
laterally, and the increased pressure of abnormal trackii
causes die associated pain. A common cause of ninnei
knee is constantly walking, running, or jogging on dj
same side of the road. Because roads are high in the mi(
die and slope down on the sides, the slope stresses *
knee that is closer to the center of the road.
Tibia and Fibula
[The tibia, or shin bone, is the larger, medial, weight-bear-
bone of the leg (Figure 6.25). The tibia articulates at
proximal end with the femur and fibula, and at its distal
end with the fibula and talus of the ankle. The proximal
jend of the tibia expands into a lateral condyle and a medial
pndyky projections which articulate with the condyles of
the femur to form the knee joint. The tibial tuberosity is on
ill anterior surface below the condyles and is a point of
attachment for the patellar ligament. The medial surface
,,| the distal end of the tibia forms the medial malleolus
LE-6-lus = little hammer), w r hich articulates with the
is of the ankle and forms the prominence that can be
felt on the medial surface of your ankle.
[Shin splints is the name given to soreness or pain along
\t tibia. Probably caused by inflammation of die perios-
im brought about by repeated tugging of the attached
roscles and tendons, it is often the result of walking or
tnning up and down hills.
gure 6.25 Right tibia and fibula in relation to the femur,
, and talus.
The tibia articulates with the femur and fibula proximally and
s with the fibula and talus distal ly, while the fibula articulates
proximally with the tibia below the knee joint and distally with
the talus.
Patella
Lateral condyle
Head —
•>3
Fibular notch
Lateral malleolus
Femur
Medial condyle
Tibial tuberosity
TIBIA
FIBULA
Medial malleolus
Talus
Anterior view
/ Which leg bone bears the weight of the body?
Lower Limb 145
The fibula is parallel and lateral to the tibia (Figure
6.25) and is considerably smaller than the tibia. The head of
the fibula articulates with the lateral condyle of the tibia be-
low the knee joint. The distal end has a projection called the
lateral malleolus that articulates with the talus of the ankle.
This forms the prominence on the lateral surface of the an-
kle. As shown in Figure 6.25, the fibula also articulates with
the tibia at the fibular notch.
Tarsals, Metatarsals, and Phalanges
The tarsus (ankle) of the foot contains seven bones, the
tarsals, held together by ligaments (Figure 6.26), Of these,
the talus (TA-lus - ankle bone) and calcaneus (kal-KA-ne-
us = heel bone) are located on the posterior part of die foot.
The anterior part of the ankle contains the cuboid (KU-
boyd), navicular (na-VIK-u-lar), and three cuneiform bones
(KU-ne-i-form) called the firsts second, and third cuneiforms.
The talus is the only bone of the foot that articulates with
the fibula and tibia. It articulates medially with the medial
malleolus of the tibia and laterally with the lateral malleolus
of the fibula. During walking, the talus initially bears the en-
tire weight of the body. About half the weight is then trans-
Figure 6.26 Right foot.
k The skeleton of the foot consists of the tarsals, metatarsals, and
., - phalanges.
LATERAL
TARSALS:
Calcaneus
Cuboid
POSTERIOR
MEDIAL
IETATARSAL:
Base
Body
Head
View
TARSALS:
Talus
Navicular
Third cuneiform
Second cuneiform
First cuneiform
Tarsals
Metatarsals
Phalanges
PHALANGES:
Proximal
Middle
Distal
Great (big) toe
Superior view
Which tarsal bone articulates with the tibia and fibula?
J
1 46 Chapter 6 The Skeletal System
minted to the calcaneus. The remainder is transmitted to the
other tarsal bones. The calcaneus is the largest and strongest
of the tarsals.
Five bones called metatarsals and numbered I to V (or 1
to 5) from the medial to lateral position form die skeleton of
the metatarsus. Like the metacarpals of the palm, each
metatarsal consists of a proximal base, an intermediate body,
and a distal head. The first metatarsal, which is connected to
die big toe, is thicker than the others because it bears more
weight.
The phalanges of the foot resemble those of the hand
both in number and arrangement Each also consists of a
proximal base, an intermediate body, and a distal head. The
great or big toe (hallux) has two large, heavy phalanges-
proximal and distal The other four toes each have three pha-
langes—proximal, middle, and distal.
The bones of the foot are arranged in two arches (Figure
6,27), These arches enable the foot to support the weight of
the body, provide an ideal distribution of body weight over
the hard and soft tissues of the foot, and provide leverage
while walking. The arches are not rigid— they yield as
weight is applied and spring back when the weight is lifted,
thus helping to absorb shocks. The longitudinal arch extends
from the front to the back of the foot and has two parts, me-
dial and lateral. The transverse arch is formed by the navicu-
lar, three cuneiforms, and the bases of the five metatarsals.
The bones composing the arches are held in position by
ligaments and tendons. If these ligaments and tendons are
weakened by excess weight, postural abnormalities, or ge-
netic predisposition, the height of the medial longitudinal
arch may decrease or "fall." The result is a condition
called flatfoot.
■ CHECKPOINT
24. What bones form die lower limb, from proximal
distal?
25. What are die functions of the arches of the foot?
COMPARISON OF FEMALE AND
MALE SKELETONS
OBJECTIVE • Identify the principal structural differ-
ences between female and male skeletons.
The bones of a male are generally larger and heavier
those of a female. The articular ends are thicker in relation t<
the shafts. In addition, because certain muscles of the male
are larger than those of the female, the points of muscle ad
tachment— tuberosities, lines, and ridges- -are larger in the
male skeleton.
Many significant structural differences between the
skeletons of females and males are related to pregnancy nil
childbirth. Because the female's pelvis is wider and shallowd
than the male's, there is more space in die true pelvis of the
female, especially in die pelvic inlet and pelvic outlet, whichj
accommodate the passage of die infant's head at birth. Sev-
eral of the significant differences between the female s
male pelves are shown in Table 6.4.
■ CHECKPOINT
26, Explain die major structural differences between female
and male skeletons related to pregnancy and childbirri
Figure 6.27 Arches of the right foot.
Arches help the foot support and distribute the weight of the body and provide leverage during walking.
lalus
Navicular
Cuneiforms
Metatarsals
Lateral malleolus
of fibula
MEDIAL PART OF
LONGITUDINAL ARCH
Cuboid
Calcaneus
TRANSVERSE ARCH
Lateral view
What structural aspect of the arches allows them to absorb shocks?
LATERAL PART OF
LONGITUDINAL ARCH
AGING AND THE
IKELETAL SYSTEM
OBJECTIVE • Describe the effects of aging on the
tal system .
M birth through adolescence, more hone is produced
in is lost during bone remodeling. In young adults, the
if bone production and loss are about the same. As the
Ms of sex steroids diminish during middle age, especially
., mien after menopause, a decrease in bone mass occurs
mse bone destruction outpaces bone formation. Because
ben's bones generally are smaller than men's bones to be-
;with, loss of bone mass in old age typically causes greater
jblems in women. These factors contribute to a higher in-
lencc of osteoporosis in women.
Aging has two main effects on the skeletal system: Bones
in; ine more brittle and lose mass. Bone brittleness results
jm a decrease in the rate of protein synthesis and in the
reduction of human growth hormone, which diminishes the
Jduction of the collagen fibers that give bone its strength
[i flexibility. As a result, inorganic minerals gradually con-
itute a greater proportion of the bone extracellular matrix,
Aging and the Skeletal System 1 47
Loss of bone mass results from demineralization and usually
begins after age 30 in females, accelerates greatly around age
45 as levels of estrogens decrease, and continues until as
much as 30% of the calcium in bones is lost by age 70, Once
bone loss begins in females, about 8% of bone mass is lost
every 10 years. In males, calcium loss from bone typically
does not begin until after age 60, and about 3% of bone mass
is lost every 10 years. The loss of calcium from bones is one
of the problems in osteoporosis (described on page 150).
Loss of bone mass also leads to bone deformity, pain, stiff-
ness, some loss of height, and loss of teeth,
■ CHECKPOINT
27. How does aging affect the brittleness of bone and the
loss of bone mass?
To appreciate the many ways that the skeletal system
contributes to homeostasis of other body systems, examine
Focus on Homeostasis: The Skeletal System on page 149.
Next, in Chapter 7, we will see how joints both hold the
skeleton together and permit it to participate in movements.
Point of Comparison
General structure
False (greater) pelvis
Pelvic inlet
Acetabulum
Obturator foramen
pubic arch
Table 6.4 Comparison of the Pelvis in Females and Males
Female
Male
Light and thin.
Shallow.
Larger and more oval
Small and faces anteriorly,
Oval.
Greater than 90° angle.
Heavy and thick.
Deep.
Smaller and heart-shaped.
Large and faces laterally.
Round.
Less than 90° angle.
Putnc arch (wider)
False (greater)
pelvis
Pelvic inlet
Acetabulum
Obturator
foramen
False (greater)
pelvis
Pelvic inlet
Acetabulum
Obturator
foramen
Pubic arch (narrower)
Anterior views
Focus on Well
■
Steps to
Healthy
Feet
Vie take the structure and function of
our feet for granted — until they start
to hurt* And even then we often con-
tinue to mistreat them, cramming them
into shoes that are too tight, and then
walking on concrete sidewalks and tak-
ing long shopping expeditions. No
wonder foot problems are such a com-
mon complaint! Fortunately, most foot
problems are preventable by under-
standing the foot's structure and func-
tion and then using good footwear to
support them in their work.
These Feet Were Made for Walking
Each time you take a step, your heel
strikes the ground first Then you roll
through the arches, over the ball of
your foot, and onto your toes. Your
arches flatten slightly as they absorb
the weight of your body. One foot con-
tinues to bear your weight until the
heel of the other foot touches the
ground. As you walk, your big toe
maintains your balance while the other
toes give your foot some resiliency.
The two outer metatarsals move to ac-
commodate uneven surfaces, while die
inner three stay rigid for support.
The most common cause of foot
problems is ill-fitting shoes, which
stress the structure and interfere with
the function of the foot. The high heel
is a case in point, which explains why
80% of those suffering from foot prob-
lems are women. Although many peo-
ple think high heels look good and are
fun to wear, they should not be used
for walking because they make the
body's weight fall onto the forefoot.
Thus, the arches of the foot are not al-
lowed to absorb the force of the body's
weight. This unnatural stress can injure
soft-tissue structures, joints, and bones.
Good Shoes for Happy Feet
Choosing shoes that are "good" to your
feet can prevent many foot problems,
an especially important consideration it
you are doing any amount of walking,
A good shoe has a sole that is strong
and flexible and provides a good grip-
ping surface. Cushioned insoles help
protect feet from hard surfaces. Arch
supports help distribute weight over a
broader area, just like the arches in
your foot
Many people spend a great deal of
time researching which brand of shoes
► Think It Over
but
to buy but do not spend adequate timi
evaluating whether or not the sb
suit their feet, A high-quality shoe i
only worth buying if it tits! Shop to
shoes in the late afternoon when yo
feet are at their largest. One foot is i
ten bigger than the odier; always
for the bigger foot. The shoes you
on should feel comfortable immedi
atcly — don't plan on shoes stretchin
with wear. The heel should lit snugl
and the instep should not gape ope
The toe box should be wide enough
wiggle all your toes.
r ■■' -
m
X
Why do you think excess body weight is associated with an increasi
risk of foot problems?
148
ocus
IN
IOMEOSTASIS m
Aging and the Skeletal System 1 49
System
I sy
or all body
stems
The Skeletal System
Contribution Of The Skeletal System
Bones provide support and protection for internal organs; bones store and release calcium,
which is needed for proper functioning of most body tissues.
•
Integumentary
system
[Muscular system
n
Bones provide strong support for overlying muscles and skin; joints provide flexibility while skin
compensates for the change in joint angle.
Bones provide attachment points for skeletal muscles and leverage for the muscles to bring
about body movements; contraction of skeletal muscle requires calcium ions.
Nervous system
-^•T
The skull and vertebrae protect the brain and spinal cord; a normal blood level of calcium is
needed for normal functioning of neurons and neuroglia.
Endocrine
system
Bones store and release calcium, needed for normal actions of many hormones.
Cardiovascular
system
w
Red bone marrow carries out hemopoiesis (blood cell formation); rhythmic beating of the heart
requires calcium ions.
Lymphatic
system and
immunity
Respiratory
system
Digestive system
Irinary system
u>
f-
Reproductive
systems
v , /
Red bone marrow produces white blood cells involved in immune responses.
The axial skeleton of the thorax protects the lungs; rib movements assist breathing; some mus-
cles used for breathing attach to bones by means of tendons.
Teeth masticate (chew) food; the rib cage protects the esophagus, stomach, and liver; the pelvis
protects portions of the intestines.
Ribs partially protect the kidneys, and the pelvis protects the urinary bladder and urethra.
The pelvis protects the ovaries, uterine (fallopian) tubes, and uterus in females and part of the
ductus (vas) deferens and accessory glands in males; bones are an important source of calcium
needed for milk synthesis during lactation.
1 50 Chapter 6 The Skeletal System
COMMON
DISORDERS
Osteoporosis
Osteoporosis (os'-te-o-po-RO-sisjjfrar- = passageway; -osis "■ condi-
tion) is literally a condition of porous bones (Figure 628). The ba-
sic problem is that bone destruction outpaces bone formation. In
large part this is due to depletion of calcium from the body — more
calcium is lost in urine, feces, and sweat than is absorbed from the
diet. Bone mass becomes so depleted that bones fracture, often
spontaneously, under die mechanical stresses of everyday living. For
example, a hip fracture might result from simply sitting down too
quickly. In the United States, osteoporosis causes more than a mil-
lion fractures a year, mainly in the hip, wrist, and vertebrae. Osteo-
porosis afflicts the entire skeletal system. In addition to fractures,
osteoporosis causes shrinkage of vertebrae, height loss, hunched
backs, and bone pain.
Thirty million people in die United States suffer from osteo-
porosis. The disorder primarily affects middle-aged and elderly peo-
Figure 6.28 Comparison of spongy bone tissue from (a) a
normal young adult and (b) a person with osteoporosis. Notice
the weakened trabeculae in (b). Compact bone tissue is similarly af-
fected by osteoporosis.
In osteoporosis, bone resorption outpaces bone formation, so
bone mass decreases.
••_. r ■ -•.;.,
(a) Normal bone
(b) Osteoporotic bone
If you wanted to develop a drug to lessen the effects of osteo-
porosis, would you look for a chemical that inhibits the activity of
osteoblasts or that of osteoclasts?
pie, 80% of them women. Older women suffer from osteoporosi
more often than men for two reasons: Women's bones are less nil
sive than men's bones, and production of estrogens in women dt
dines dramatically at menopause; production oi die main androgen]
testosterone, in older men wanes gradually and only slightly. Estrft
»ens and testosterone stimulate osteoblast activity and syndics
bone extracellular matrix. Besides gender, risk factors for developing
osteoporosis include a family history of the disease, European or
Asian ancestry, thin or small body build, an inactive lifestyle, i
rette smoking, a diet low in calcium and vitamin D, more dian
alcoholic drinks a day, and the use of certain medications.
In postmenopausal women, treatment of osteoporosis may in-
clude estrogen replacement therapy (ERT; low doses of estrogens}
or hormone replacement therapy (HRT; a combination of estrogei
and progesterone, another sex steroid). Although such uv
help combat osteoporosis, they increase a woman's risk of breasl
cancer. The drug Raloxifene® (Evista) mimics the beneficial effects]
of estrogens on bone without increasing the risk of breast ear
Another drug that may be used is die nonhormone drug Alenl
dronate (Fosamax®), which blocks resorption of bone by osteoclasts,
Perhaps more important than treatment is prevention. Aik
quate calcium intake and weight-bearing exercise in her early yea
may be more beneficial to a woman than drugs and calcium supply
merits when she is older.
Rickets and Osteomalacia
Rickets and osteomalacia (os'-te-6-ma-LA-she-ah; -malaria : = sol
ness) are disorders in which bone calcification fails. The buiu
become soft or rubbery and are easily deformed. Rickets affects
growing bones of children, hut osteomalacia affects the bones
adults.
Herniated Disc
If the ligaments of the intervertebral discs become injured or wa
ened, die resulting pressure may be great enough to rupture
surrounding fibrocartilage. When this occurs, the material insK
may herniate (protrude). This condition is called a bernm
(slipped) disc, Tt occurs most often in the lumbar region becai
that part of the vertebral column bears much of the weight of
body and is the region of the most bending.
Spina Bifida
Spina bifida (SPI-na BIF-i-da) is a congenital defect of the vet
bral column in which laminae fail to unite at the midline. In serit
cases, protrusion of the membranes (meninges) around the sp|
the spinal cord itself may produce partial or complete paral-
1, partial or complete loss of urinary bladder control, and the
knee of reflexes. Because an increased risk of spina bifida is asso-
kd with a low level of folic acid (one of the B vitamins) early in
icy, all women who might become pregnant are encouraged
[take folic acid supplements.
Up Fracture
Bough any region of the hip girdle may fracture, die term hip
'arc most commonly applies to a break in the bones associated
„ the hip joint— the head, neck, or trochanteric regions of the
gur, or die bones that form the acetabulum. In the United States,
ii'li:(l to 500,000 people sustain hip fractures each year. The inci-
if hip fractures is increasing, in part due to longer life spans.
Common Disorders
Decreases in bone mass due to osteoporosis and an increased ten-
dency to fall predispose elderly people to hip fractures.
Hip fractures often require surgical treatment, the goal of
which is to repair and stabilize the fracture, increase mobility and
decrease pain. Sometimes the repair is accomplished by using surgi-
cal pins, screws, nails, and plates to secure the head of the femur. In
severe hip fractures, the femoral head or the acetabulum of the hip
bone may be replaced by prostheses (artificial devices), The proce-
dure of replacing either the femoral head or the acetabulum is hemi-
arthroplasty (hem-e-AR-thro-plas-tc; hemi- = one half; -a/thro- :
joint; -plasty = molding). Replacement of both the femora] head
and acetabulum is total hip arthroplasty. The acetabular prosthesis is
made of plastic, and the femoral prosthesis is metal; both are
designed to withstand a high degree of stress. The prostheses are
attached to healthy portions of bone with acrylic cement and
screws.
miCALTERMINOLOGY AND CONDITIONS
L (BUN-yun) A deformity of the great toe that typically is
caused by wearing tightly fitting shoes. The condition produces
inflammation of bursae (fluid-filled sacs at the joint), bone
spurs, and calluses.
vfoot A condition in which the medial part of the longitudinal
arch is abnormally elevated. It is often caused by muscle defor-
mities, such as may result from diabetes.
Iwis (^i-PO-sis; kypho- = bent; -wis = condition) An exag-
geration of the thoracic curve of the vertebral column. In the
elderly, degeneration of the intervertebral discs leads to kypho-
I sis; it may also be caused by osteoporosis, rickets, and poor
posture.
Mosis (lor-DO-sis; lord- = bent backward) An exaggeration of
ihc lumbar curve of the vertebral column, also called hollow
I Iwk. It may result from increased weight of the abdomen as in
I pregnancy or extreme obesity, poor posture, rickets, or tuber-
, cubsis of the spine.
ntbritis (os'-te-6-ar-THRl-tis; arthr = joint) The degener-
ation of articular cartilage such that the bony ends touch; the
resulting friction of hone against bone worsens the condition.
tally associated with theelderly.
rente sarcoma (os'-te-O-JKN-ik sar-KO-ma; sarcoma
unective tissue tumor) Bone cancer that primarily affects os-
ohlasts and occurs most often in teenagers during their
i growth spurt; the most common sites are the metaphyses of the
thigh bone (femur), shin bone (tibia), and arm bone (humerus).
Metastases occur most often in lungs; treatment consists of
multidrug chemotherapy and removal of the malignant growth,
or amputation of die limb.
Osteomyelitis (os'-te-o-mi-e-LI-tis) An infection of bone charac-
terized by high fever, sweating, chills, pain, nausea, pus forma-
tion, edema, and warmth over the affected bone and rigid over-
lying muscles- Bacteria, usually Staphylococcus aureus, often cause
it. The bacteria may reach the bone from outside the bod]
(through open fractures, penetrating wounds, or orthopedic
surgical procedures); from other sites of infection in the body
(abscessed teeth, burn infections, urinary tract infections, or up-
per respiratory infections) via the blood; and from adjacent soft
tissue infections (as occurs in diabetes mcllitus),
Osteopenia (os'-te-d-PE-ne-aj penia = poverty) Reduced bone
mass due to a decrease in the rate of bone synthesis to a level in-
sufficient to compensate for normal bone resorption; any de-
crease in bone mass below normal An example is osteoporosis,
Scoliom (sko'-le-O-sis; scolio- = crooked) A sideways bending of
the vertebral column, usually in the thoracic region. It may re-
sult from congenitally (present at birth) malformed vertebrae,
chronic sciatica, paralysis of muscles on one side of the vertebral
column, poor posture, or one leg being shorter than the other.
Wbiplasb injury Injury to the neck region due to severe hyperex-
tension (backward tilting) of the head followed by severe hyper-
flexion (forward tilting) of the head, usually associated with a
rear-end automobile collision. Symptoms are related to stretch-
ing and tearing of ligaments and muscles, vertebral fractures,
and herniated vertebral discs.
152 Chapter 6 The Skeletal System
STUDY OUTLINI
1.
2,
Functions of Bone and the Skeletal System (p, 114)
The skeletal system consists of all bones attached at joints and
cartilage between joints,
The functions of the skeletal system include support, protec-
tion, movement, mineral homeostasis, housing blood-forming
tissue, and storage of energy.
Types of Bones (p. 1 1 4)
1. On the basis of shape, bones are classified as long, short, flat, or
irregular.
Structure of Bone (p. 114)
1. Parts of a long bone include the diaphysis (shaft), epiphyses
(ends), metaphysis, articular cartilage, periosteum, medullary
(marrow) cavity, and endosteum.
2. The diaphysis is covered by periosteum.
3. Bone tissue consists of widely separated cells surrounded by
large amounts of extracellular matrix (intercellular substance).
The four principal types of cells are osteogenic cells, os-
teoblasts, osteocytes, and osteoclasts, The extracellular matrix
contains collagen fibers (organic) and mineral salts that consist
mainly of calcium phosphate (inorganic).
4. Compact (dense) bone tissue consists of osteons (haversian sys-
tems) with little space between them. Compact bone composes
most of die bone tissue of die diaphysis. Functionally, compact
bone protects, supports, and resists stress.
5. Spongy bone tissue consists of trabeculae surrounding many
red bone marrow-filled spaces. Tt forms most of the structure
of short, flat, and irregular bones and the epiphyses of long
bones. Functionally, spongy bone stores red bone marrow and
provides some support.
Bone Formation (p. 1 1 8)
L Bone forms by a process called ossification.
2, Bone formation in an embryo or fetus occurs by intramembra-
nous and endochondral ossification, which involve the replace-
ment of preexisting connective tissue with bone.
3, Intramembranous ossification occurs within mesenchyme
arranged in sheetlike layers that resemble membranes.
4, Endochondral ossification occurs within a hyaline cartilage de-
rived from mesenchyme- The primary ossification center of a
long bone is in the diaphysis. Cartilage degenerates, leaving
cavities that merge to form the medullary (marrow) cavity. Os-
teoblasts lay down bone. Next, ossification occurs in the epi-
physes, where bone replaces cartilage, except for articular carti-
lage and the epiphyseal plate.
5* Because of die activity of the epiphyseal plate, the diaphysis of
a bone increases in length.
6* Bone grows in diameter as a result of the addition of new bone
tissue around the outer surface of die bone.
7. Old bone is constantly destroyed by osteoclasts, white n<
bone is constructed by osteoblasts. This process is called r
modeling.
8* A fracture is any break in a bone. Fracture repair involves
modeling.
9. Normal growth depends on minerals (calcium, phosphor
magnesium), vitamins (A, C, D), and hormones (human grcn
hormone, insulinlike growth factors, insulin, thyroid h(
manes, sex hormones, and parathyroid hormone).
10. Bones store and release calcium and phosphate, control!*
mainly by parathyroid hormone (PTH). PTH raises blood
cium level.
11, Calcitonin (CT) lowers blood calcium level.
Exercise and Bone Tissue (p. 123)
1. Mechanical stress increases bone strength by increasing depos
tion of mineral salts and production of collagen fibers.
2. Removal of mechanical stress weakens bone through deiiiim
ali/.aiion and collagen fiber reduction.
Divisions of the Skeletal System (p. 124)
1, The axial skeleton consists of bones arranged along the long
tudinal axis of die body. The parts of the axial skeleton are
skull, hyoid bone, auditory ossicles, vertebral column, sterni
and ribs.
2. The appendicular skeleton consists of the bones of the gin
and the upper and lower limbs. The parts of the appends
skeleton are the pectoral (shoulder) girdles, bones of the up
limbs, pelvic (hip) girdle, and bones of the lower limbs.
Skull and Hyoid Bone (p. 125)
1. The skull consists of cranial hones and facia] bones.
2. The eight cranial bones include the frontal (1), parietal
temporal (2), occipital (1), sphenoid (1), and ethmoid (1).
3. The 14 facial bones are the nasal (2), maxillae (2), zygon|
(2), mandible (1), lacrimal (2), palatine (2), inferior nasal cj
chae (2), and vomer (1).
4. The hyoid bone, a U-shaped bone that does not articulate
any other bone, supports the tongue and provides attache
for some of its muscles as well as some neck muscles,
5. Sutures are immovable joints between bones of the skull.
amples are the coronal, sagittal, lambdoid, and squamous
tares,
6. Paranasal sinuses are cavities in bones of the skull that coi
nicate with the nasal cavity They are lined by mucous me
branes. Cranial bones containing paranasal sinuses are
frontal, sphenoid, ethmoid, and maxillae.
7. Fontanels are mescnchynie-filled spaces between die
bones of fetuses and infants. The major fontanels are the ant
rior, posterior, anterolaterals, and posterolaterals.
Vertebral Column (p. 133)
Hrhc bones of the adult vertebral column are the cervical verte-
brae (7), thoracic vertebrae (12), lumbar vertebrae (5), the
Sacrum (5, fused), and the coccyx (4, fused).
The vertebral column contains normal curves that give
strength, support, and balance.
The vertebrae are similar in structure, each consisting of a
body, vertebral arch, and seven processes. Vertebrae in the
different regions of the column vary in size, shape, and de-
tail.
(fix (p. 137)
The thoracic skeleton consists of the sternum, ribs, costal carti-
lages, and thoracic vertebrae.
The thoracic cage protects vital organs in the chest area,
toral (Shoulder) Girdle (p. 139)
I livh pectoral (shoulder) girdle consists of a clavicle and
scapula.
i attaches an upper limb to the trunk.
>erLimb(p. 140)
There are 30 bones in each upper limb.
The upper limb bones include the humerus, ulna, radius,
Earpals, metacarpals, and phalanges.
Self-Quiz 153
Pelvic (Hip) Girdle (p. 143)
1. The pelvic (hip) girdle consists of two hip bones.
2. It attaches the lower limbs to the trunk at die sacrum,
3. Each hip hone consists of three fused components: ilium, pu-
bis, and ischium.
Lower Limb (p. 144)
L There are 30 bones in each lower limb,
2. The lower limb bones include the femur, patella, tibia, fibula,
tarsals, metatarsals, and phalanges.
3, The bones of the foot are arranged in two arches, the longitu-
dinal arch and the transverse arch, to provide support and
leverage.
Comparison of Female and Male Skeletons (p. 146)
1, Male bones are generally larger and heavier than female bones
and have more prominent markings for muscle attachment.
2. The female pelvis is adapted for pregnancy and childbirth. Dif-
ferences in pelvic structure are listed in Table 6.4 on page 147,
Aging and the Skeletal System (p. 147)
1. The main effect of aging is a loss of calcium from hones, which
may result in osteoporosis.
2. Another effect of aging is a decreased production of extracellu-
lar matrix proteins (mostly collagen fibers), which makes bones
more brittle and thus more susceptible to fracture*
■
SELF-QUIZ
Match the following cell types to their functions:
L a. chondroblasts A. mature bone cells
. b, osteoclasts
c. chondrocytes
I d. osteocytes
e. osteoblasts
B. cells that form bone
C. secrete cartilage matrix
D. mature cartilage cells
E. involved in bone resorption
lum trying to locate a foramen in a bone, you would look tor
a. a large, rough projection
b. a ridge
c. a rounded projection
i a shallow depression
I e. an opening or hole
| The ribs articulate with the
I a, thoracic vertebrae
l b. sacrum
c. cervical vertebrae
J, lumbar vertebrae
is and axis
4. Match the following:
a. run lengthwise
A. lamellae
R. lacunae
C. perforating (volk-
mann's) canal
D. canaliculi
E. central (haversian) canal
through bone
b. connect central
canals with lacunae
c. concentric rings of
matrix
d. connect nutrient
arteries and nerves from
the periosteum to the
central canals
e. spaces that contain
osteocytes
5, The presence of an epiphyseal line in a long bone indicates that
the bone
a. is undergoing resorption
b. has stopped growing in length
c. is growing in diameter
d. is still capable of growing in length
e. is broken
1 54 Chapter 6 The Skeletal System
6. The hyoid bone is unique because it
a. is the smallest bone in the skull
b. can malform causing a cleft palate
c. forms the paranasal sinuses
d. is often broken when an individual falls forward
e. does not articulate with any other bone
7. The bones that form the pectoral girdle are the
a. clavicle and scapula b. scapula and sternum
c, humerus and scapula d. clavicle and humerus
e. cov.il hones
8* The main hormone that regulates the Ca 2H balance between
bone and blood is
a, parathyroid hormone b. insulin c. testosterone
d, insiilinlike growth factors e. human growth hormone
9. Spongy bone differs from compact bone because spongy bone
a. is made up of numerous osteons
b. is found primarily in the diapfayses of long bones
c. has latticework walls known as trabeculae
d. contains few, small spaces known as lacunae
e. has lamellae arranged in concentric rings
10. In which of the following individuals might you expect to find
the smallest bone mass?
a. 20-year-old male weightlifter
b. 45-year-old female weightlifter
c. 45-year-old male astronaut
d. 80-year-old bedridden female
e. 65-year-old bedridden male
11. Place the following steps of endochondral ossification in the
correct order:
1. Hyaline cartilage remains on the articular surfaces and
epiphyseal plates
2. Chondroblasts produce a growing hyaline cartilage model
surrounded by the perichondrium
3. Osteoblasts in perichondrium produce compact bone
4. Secondary ossification centers form
5. Primary ossification center and medullary cavity form
a. 2,3,4,5,1 b. 2,3,5,4,1 c. 5,2,1,3,4
d. 3,2,5,4,1 e, 5,3,2, 1,4
12* Match each bone to its shape:
a. humerus A. Hat
b. carpus B. irregular
c. vertebra C, long
d. sternum D. short
13. Where long bones form joints, the epiphyses are covered
a. yellow bone marrow b. osteoclasts c. periosteum
d. endosteum e. hyaline cartilage
14. What substance in bone contributes to its tensile strength?
a. red bone marrow
b. collagen
c. yellow bone marrow
d. calcium phosphate
e. loose fibrous connective tissue
1 5. The skeletal system is responsible tor
a. protecting internal organs from injury
b. producing movement
c. providing a supporting framework for the body
d. hemopoiesis
e. all of the above
16. For each of the following bones, place an AX in the blank
belongs to the axial skeleton and an AP in the blank if it is
of the appendicular skeleton.
a. lacrimal L. metatarsals ___
b. clavicle m. temporal —
n. metacarpals
c. radius
d. mandible
e. patella
f. car nals
_ g, scapula
_ h. sternum
i, phalanges
j. tarsals
k. ethmoid
o. vomer
p. fibula
q, palatine
r. hyoid
5, tibia
t, sphenoid
u. vertebrae
v. coxal
w, maim
x, front
y. infej
m
com
z. hurad
aa. ulna
bb. ferai
cc. ribs
dd. o<
Answers to Figure Questions 1 55
I
r*
RITICAL THINKING APPLICATION
J,R. was riding his motorcycle across the Big Span Bridge when
he had a collision with a nearsighted sea gull. In the resulting
erash, J.R. crushed his left leg, fracturing both leg bones;
snapped the pointy distal end of his lateral forearm bone; and
broke the most lateral and proximal bone in his wrist. The sea
gull flew off when the ambulance arrived. Name the bones that
JJL broke.
While investigating her new baby brother, a 4-year-old girl dis-
covers a soft spot on the baby's skull and announces that the
I ilii needs to go back because "it's not finished yet." Explain
the presence of soft spots in the infant's skull and the lack of
soft spots in yours.
3. Old Grandma Olga is a tiny, stooped woman with a big sense
of humor. Her favorite movie line is from The Wizard of Qz
when the wicked witch says "I'm melting." "That's me," laughs
Olga, "melting away, getting shorter every year." What is hap-
pening to Grandma Olga?
4. During the volleyball game, Kate jumped, twisted, spiked,
scored, and screamed! She couldn't put any weight on her left
leg and her left knee swelled rapidly to twice its usual size. X-
rays revealed a fracture of the proximal tibia. In layman s terms,
what is the location of Kate's fracture? What caused the rapid
swelling? What are die body's requirements for bone healing?
ANSWERS TO FIGURE QUESTION
6.1 The articular cartilage reduces friction at joints; red bone
marrow produces blood cells; and the endosteurn lines the
medullary cavity,
6.2 Because the central canals are the main blood supply to the
osteocytes, their blockage would lead to death of osteocytes.
6.3 The flat bones of the skull and mandible develop by in-
tramembranous ossification,
6.4 The epiphyseal lines are indications of growth zones that
have ceased to function.
6.5 1 leartbeat, respiration, nerve cell functioning, enzyme func-
tioning, and blood clotting arc all processes that depend on
proper levels of calcium.
I 6.6 Axial skeleton; skull and vertebral column. Appendicular
skeleton: clavicle, shoulder girdle, humerus, pelvic girdle,
and femur.
6.7 The cranial bones are the frontal, parietal, occipital, sphe-
noid, ethmoid, and temporal bones.
6.8 The foramen magnum is the largest foramen in the skull.
Crista galli of ethmoid bone, frontal, parietal, temporal, oc-
cipital, temporal, parietal, frontal, and crista galli of ethmoid
bone articulate in clockwise order with the sphenoid bone.
, Hi The perpendicular plate of the ethmoid bone forms the top
part of the nasal septum.
Ml The paranasal sinuses produce mucus and serve as resonat-
ing chambers for vocalization.
6,12 The thoracic and sacral curves are concave.
i J] The vertebral foramina enclose the spinal cord, and the in-
rvcrtebral foramina provide spaces for spinal nerves to exit
the vertebral column.
6.14 The atlas and axis permit movement of the head to signify
6.15
6.16
6.17
6.18
6.19
6.20
6.21
6.22
6.23
6.24
6.25
6.26
6.27
6.28
"no."
The lumbar vertebrae support more weight than the tho-
racic and cervical vertebrae.
The sacral foramina are passageways for nerves and blood
vessels.
The true ribs are pairs 1 through 7; the false ribs are pairs 8
dirough 12; and the floating ribs are pairs 1 1 and 12.
A pectoral girdle consists of a clavicle and a scapula.
The glenoid cavity of the scapula articulates with the
humerus.
The "elbow" part of the ulna is the olecranon.
The knuckles are the heads of the metacarpals.
The true pelvis surrounds the pelvic organs in the pelvic
cavity.
The femur tits into the acetabulum.
The distal end of the femur articulates with the tibia and die
patella.
The tibia is the weight-bearing bone of the leg.
The talus articulates widi the tibia and fibula.
The arches are not rigid, yielding when weight is applied
and springing back when weight is lifted to allow r them to
absorb the shock of walking and running.
A drug that inhibits the activity of osteoclasts might lessen
the effects of ostcop< in >sis.
JOINTS
did you know?
£* or many years, people believed
that exercise accelerated joint degeneration, and that
people with arthritis should avoid physical activity.
Scientists now believe that a sedentary lifestyle leads to
loss of strength in muscles, tendons, ligaments, and
other joint structures, which makes movement even
more painful and difficult When muscles and joints
| atrophy, the resulting weakness makes joints less stable,
I and more vulnerable to injury. Physical activity helps
to strengthen joint structures and delay the progress of
arthritis, Low- or non-impact activities such as
strength training, swimming, and cycling can improve
^^^^^^ fitness, functional status, and quality
XT^H of life for people with arthritis.
Focus on Wellness, page 167
www.wiley.com/college/apcentral
JLJones are too rigid
to bend without being
damaged. Fortunately, flexible
connective tissues form joints that hold
bones together while in most cases permitting some
degree of movement. If you have ever damaged these
areas, you know how difficult it is to walk with a cast
over your knee or to turn a doorknob with a splint on
your finger. A joint (also called an articulation) is a
point of contact between bones, between cartilage and
bones, or between teeth and bones. When we say one
bone articulates with another bone, we mean that die
two bones form a joint, Anhrology (ar-THROL-6-je;
ar thr- = joint; -fogy = study of) is the scientific study of
joints. Many joints of the body permit movement. The
study of motion of the human body is called kinesiolm
(ld-ne'-se-OL-6-j£;.iK»c«- = movement).
looking back to move ahead
Collagen Fibers (page 84)
Dense Regular Connective Tissue (page 86)
Cartilage (page 89)
Synovial Membranes (page 91)
Divisions of the Skeletal System (page 124)
156
JOINTS
)BJECTIVES • Describe how the structure of a joint
etermines its function.
Describe the structural and functional classes of
joints.
loint's structure determines its combination of strength and
ibility. At one end of the spectrum Lire joints that permit
movement and are thus vety strong, but inflexible. In eon-
(t, other joints afford fairly free movement and are thus
but not as strong. In general, the closer the fit at the
t of contact, the stronger the joint. At tightly fitted
movement is obviously more restricted. The looser
fit, the greater the movement. However, loosely fitted
its are prone to displacement of the articulating bones
their normal positions (dislocation). Movement at joints
termined by (I) the shape of the articulating bones,
I die flexibility (tension or tautness) of the ligaments that
id the bones together, and (3) the tension of associated
ides and tendons. Joint flexibility may also be affected by
pones. For example, toward the end of pregnancy, a hor-
called relaxin increases the flexibility of the fibrocarti-
ftlie pubic symphysis and loosens die ligaments be-
en the sacrum and hip bone. These changes enlarge the
itlet, which assists in delivery of die baby.
|oinrs are classified structurally, based on their anatomi-
tl characteristics, and functionally, based on the type of
merit they permit.
The structural classification of joints is based on two
I) the presence or absence of a space between the
ilating bones, called a synovial cavity, and (2) the type of
tainective tissue that holds the bones together. Structurally;
classified as one of the following types:
Fibrous joints (Fl-brus): There is no synovial cavity and
the bones are held together by fibrous connective tissue
that is rich in collagen fibers.
I Cartilaginous joints (kar-ti-LAJ-i-nus): There is no
synovial cavity and the bones are held together by carti-
ge.
I Synovial joints (si-NO-ve-al): The bones forming the
joint have a synovial cavity and are united by the dense
pilar connective tissue of an articular capsule, and
pften by accessory ligaments.
The functional classification of joints relates to the de-
movement they permit. Functionally, joints are classi-
ng of the following types:
wrthrosis (sin'-ar-THRO-sis; $yn- = together): An
f immovable joint. The plural is synarthroses.
Amphiarthrosis (ani'-fe-ar-THRO-sis; amply- = on bodi
sides): A slightly movable joint. The plural is irrnphicinhroses.
Fibrous Joints 157
■ Diarthrosis (dl'-ar-THRO-sis = movable joint): A
freely movable joint. The plural is di arthroses. All di-
arthroses are synovial joints. They have a variety of
shapes and permit several different types of movements.
The following sections present die joints of the body ac-
cording to their structural classification. As we examine the
structure of each type of joint, we will also explore its func-
tional attributes.
■ CHECKPOINT
1 . What factors determine movement at joints?
FIBROUS JOINTS
objective • Describe the structure and functions of
the three types of fibrous joints.
Fibrous joints permit little or no movement. The three types
of fibrous joints are (1) sutures, (2) syndesmoses, and (3)
gom phoses.
1. A suture (SOO-cher; sutur- = seam) is a fibrous joint
composed of a thin layer of dense fibrous connective tis-
sue. Sutures unite the bones of the skull. An example is
the coronal suture between the frontal and parietal bones
(Figure 7.1a). The irregular, interlocking edges of sutures
give them added strength and decrease their chance of
fracturing. Because a suture is immovable, it is classified
functionally as a synarthrosis.
2. A syndesmosis (sin'-dez-MO-sis; syndesmo- ■ ■ band or
ligament) is a fibrous joint in which the distance between
the articulating bones and the amount of dense fibrous
connective tissue is greater than in a suture (Figure 7.1b).
One example of a syndesmosis is the distal articulation
between the tibia and fibula where the anterior tibio-
fibular ligament connects the bones. Because it permits
slight movement, a syndesmosis is classified functionally
as an amphiarthrosis.
3. A gompbosis (gom-FO-sis; gompiro- = a bolt or nail;
plural is gomphoses) is a type of fibrous joint in which a
cone-shaped peg fits into a socket. The only gomphoses
in the human body are the articulations of the roots oi
the teeth with die sockets of the alveolar processes of the
maxillae and mandible (Figure 7.1c). The dense fibrous
connective tissue between die root of a tooth and its
socket is the periodontal ligament. A gomphosis is classi-
fied functionally as a synarthrosis, an immovable joint.
■ CHECKPOINT
2. Which fibrous joints are synarthroses? Which are am-
phiarthroses?
158 Chapter 7 Joints
Figure 7.1 Fibrous joints.
At a fibrous joint, the bones are held together by connective
tissue containing many collagen fibers.
Inner compact bone
Spongy bone
Outer compact
bone
Coronal suture
(a) Suture between skull bones
interosseous membrane
Anterior
tibiofibular
ligament
(b) Syndesmosis between distal tibia and fibula
Socket of
alveolar
process
Periodontal
ligament
Root of
tooth
rii ;
;c) Gomphosis between tooth and
socket of alveolar process
' Functionally, why are sutures classified as synarthroses and
j syndesmoses classified as amphiarthroses?
CARTILAGINOUS JOINTS
OBJECTIVE • Describe the structure and functions
the two types of cartilaginous joints, j
1.
Like a fibrous joint, a cartilaginous (car-ti-LAJ-i-nus) jm
allows little or no movement. Here the articulating bones
tightly connected by either fibrocartaiage or hyaline cartita
The two types of cartilaginous joints are synchondroses
symphyses.
A synchondrosis (sin'-kon-DRO-sis; chondro- = eartila
is a cartilaginous joint in which the connecting material
hyaline cartilage. An example of a synchondrosis is
epiphyseal plate that connects the epiphysis and diapl|
of an elongating bone (Figure 7.2a). Functionally, a
chondrosis is a synarthrosis, an immovable joint,
bone growth stops, bone replaces the hyaline cartilage.
A symphysis (SIM-fi-sis = growing together) is a
laffinous joint in which die ends of the articulating bom
are covered with hyaline cartilage, but the bones areco
nected by a broad, flat disc of fibrocartilage. The pu
symphysis between the anterior surfaces of the hip horn
is one example of a symphysis (figure 7.2b). This type
joint is also found at the intervertebral joints bed
bodies of vertebrae. Functionally, a symphysis is m
phiarthrosis, a slightly movable joint.
■ CHECKPOINT \
3. Which cartilaginous joints are syn arthroses? Which ai
amphiarthroses?
2.
SYNOVIAL JOINTS
OB J ECTI VE • Describe the structure of synovial joi
Structure of Synovial Joints
Synovial joints (si-NO-ve-al) have certain characterist
that distinguish them from other joints. The unique chat
teristic of a synovial joint is the presence of a space callc|
synovial (joint) cavity between the articulating bones (Fij
7.3). The synovial cavity allows a joint to be freely mova!
Hence, all synovial joints are classified functionally as
arthroses. The bones at a synovial joint are covered
articular cartilage, which is hyaline cartilage. Articular
lage reduces friction between bones in the joint during id
ment and helps to absorb shock.
A sleeve like articular capsule surrounds a synovial joi;
encloses the synovial cavity, and unites the articulating boi
Figure 7.2 Cartilaginous joints.
At a cartilaginous joint, the bones are held firmly together by
f> cartilage-
Epiphyseal plates
-"/£■
Epiphysis
• . ■■-.
Epiphysis
iff . r **« IT ' -
Diaphysis
(a) Synchondrosis
Pubic
symphysis
(b) Symphysis
I What is the structural difference between a synchondrosis and a
{ symphysis?
articular capsule is composed of two layers, an outer
fibrous capsule and an inner synovial membrane (Figure 7.3).
Hie outer layer, the fibrous capsule, usually consists of dense
irregular connective tissue that attaches to the periosteum of
irticulating bones. The fibers of some fibrous capsules
t arranged in parallel bundles that are highly adapted for
Listing strains Such fiber bundles are called ligaments
= bound or tied) and are one of the main mechanical
irs that hold bones close together in a synovial joint. The
'inner layer of the articular capsule, the synovial membrane,
iposed of areolar connective tissue with elastic fibers. At
synovial joints the synovial membrane includes accu-
i.ihiiivns of adipose tissue, called articular fat pads (see Fig-
,10c).
Hie synovial membrane secretes synovial fluid (ov- =
which forms a thin film over the surfaces within the ar-
j. Lir capsule. This viscous, clear or pale yellow fluid was
Led for its similarity in appearance and consistency to
Looked egg white (albumin). Its several functions include
reducing friction by lubricating the joint, and supplying
{nutrients to and removing metabolic wastes from the chon-
drocytes within articular cartilage. When a synovial joint is
Synovial Joints 159
immobile for a time, the fluid is quite viscous (gel-like), but
as joint movement increases, the fluid becomes less viscous.
One of the benefits of a warm-up before exercise is that it
stimulates the production and secretion of synovial fluid.
More fluid means less stress on the joint during exercise.
Many synovial joints also contain accessoiy ligaments
that lie outside and inside the articular capsule. Examples of
accessoiy ligaments outside the articular capsule are the fibu-
lar (lateral) and tibial (medial) collateral ligaments of the knee
joint (see Figure 7.l0d). Examples of accessory ligaments in-
side the articular capsule are the anterior and posterior cruci-
ate ligaments of the knee joint (see Figure 7. 1 Od).
Inside some synovial joints, such as the knee, are pads of
fibrocartilage that lie between the articular surfaces of die
bones and are attached to the fibrous capsule. These pads are
called articular discs or menisci (me-NIS-si; singular is
meniscus). Figure 7.IOd depicts the lateral and medial menisci
in the knee joint. By modifying the shape of the joint surfaces
of the articulating bones, articular discs allow two bones of
different shapes to (it more tightly. Articular discs also help
to maintain the stability of the joint and direct the flow ot
synovial fluid to the areas of greatest friction.
Figure 7.3 Structure of a typical synovial joint. Note the two
layers of the articular capsule: the fibrous capsule and the synovial
membrane. Synovial fluid fills the synovial cavity which is located
between the synovial membrane and the hyaline articular cartilage.
The distinguishing feature of a synovial joint is the synovial
(joint) cavity between the articulating bones.
1' '/'/''
— Frontal
Articulating
bone
Synovial (joint)
cavity (contains
synovial fluid)
Articular
cartilage
Periosteum
Articular
capsule:
Fibrous
capsule
Synovial
membrane
1 v
r
Articulating
bone
Frontal section
What is the functional classification of synovial joints?
1 60 Chapter 7 Joints
The tearing of articular discs (menisci) in the knee, com-
monly called torn cartilage, occurs often among athletes.
Such damaged cartilage will begin to wear and may pre-
cipitate arthritis unless it is surgically removed (meniscec-
tomy). Surgical repair of the torn cartilage is required
because of the avascular nature of cartilage and may be
assisted by arthroscopy (ar-TIlROS-ko-pe; -scopy = ob-
servation), the visual examination of the interior of a joint,
usually the knee, with an arthroscope, a lighted, pencil-thin
instrument, Arthroscopy is used to determine the nature
and extent of damage following knee injury and to moni-
tor the progression of disease and the effects of therapy. In
addition, the insertion of surgical instruments through the
arthroscope or other incisions enables a physician to re-
move torn cartilage and repair damaged cruciate liga-
ments in the knee; to remodel poorly formed cartilage; to
obtain tissue samples for analysis; and to perform surgery
on other joints, such as the shoulder, elbow, ankle, and
wrist.
The various movements of the body create friction
between moving parts. Saclike structures called bursae
(BER-se = purses; singular is bursa) are strategically situ-
ated to reduce friction in some synovial joints, such as the
shoulder and knee joints (see Figure 7.10c). Bursae are
not strictly part of synovial joints, but do resemble joint
capsules because their walls consist of connective tissue
lined by a synovial membrane. They are also filled with a
fluid similar to synovial fluid. Bursae are located between
the skin and bone in places where skin rubs over bone.
They are also found between tendons and bones, muscles
and bones, and ligaments and bones. The fluid-filled bur-
sal sacs cushion the movement of one body part over an-
other.
An acute or chronic inflammation of a bursa, for example
in die shoulder and knee, is called bursitis. The condition
may be caused by trauma, by an acute or chronic infection
(including syphilis and tuberculosis), or by rheumatoid
arthritis (described on page 168). Repeated, excessive exer-
tion of a joint often results in bursitis, with local inflam-
mation and the accumulation of fluid. Symptoms include
pain, swelling, tenderness, and limited movement. Treat-
ment may include oral anti-inflammatory agents and injec-
tions of cortisol-like steroids.
■ CHECKPOINT
4, How does the structure of synovial joints classify them as
diarth roses?
5, What are the functions of articular cartilage, the articular
capsule, synovial fluid, articular discs, and bursae?
TYPES OF MOVEMENTS AT
SYNOVIAL JOINTS
OBJECTIVE • Describe the types of movements that
can occur at synovial joints.
Anatomists, physical therapists, and kinesiologists use spetifil
terminology to designate specific types of movement that can
occur at a synovial joint. These precise terms indicate die
form of motion, die direction of movement, or the relation*
ship of one body part to another during movement. Move-
ments at synovial joints are grouped into four main cate-
gories: (1) gliding, (2) angular movements, (3) rotation, and
(4) special movements. The last category includes move-
ments that occur only at certain joints.
Gliding
Gliding is a simple movement in which relatively flat bom
surfaces move back-and-forth and side-to-side relative to one
another. This can be illustrated between the acromion of the
scapula and clavicle by placing your upper limb at your side,|
rotating it about your head, and lowering it again (see Figure]
7.7b). Gliding movements are limited in range due to
loose-fitting structure of the articular capsule and associated
ligaments and bones.
Angular Movements j
In angular movements, there is an increase or a decrease n
the angle between articulating bones. The principal angularl
movements are flexion, extension, hyperextension, abduction,
adduction, and circumduction and are discussed with respt
to the body in the anatomical position. In flexion (FLEK-
snun = to bend), there is a decrease in die angle between ai
ticulating bones; in extension (eks-TEN-shun = to strew
out), there is an increase in the angle between articulatii
bones, often to restore a part of the body to the anatomii
position after it has been flexed (Figure 7,4). Examples
flexion include bending die head toward the chest (Fi|
7.4a); moving the humerus forward at the shoulder joint as
swinging the arms forward while walking (Figure 7.4b); mm
ing the forearm toward the arm (Figure 7,4c); moving
palm toward the forearm (Figure 7.4d); moving the femur
ward, as in walking (Figure 7.4e); and bending the knee (Fig
7.4f ). Extension is simply die reverse of these movements.
Continuation of extension beyond the anatomical pos
tion is called hyperextension (byper- = beyond or excessive)
Examples of hyperextension include bending the head bat
ward (Figure 7.4a); moving the humerus backward, as
swinging die arms backward while walking (Figure 741
moving the palm backward at the wrist joint (Figure
rfc
Types of Movements
at Synovial Joints 161
Figure 7.4 Angular movements at synovial joints: flexion, extension, and hyperextension.
^ In angular movements, there is an increase or decrease in the
angle between articulating bones.
(a) Joints between atlas and occipital bone and
between cervical vertebrae
(b) Shoulder joint
(c) Elbow joint
(d) Wrist joint
(e) Hip joint
(f) Knee joint
What prevents hyperextension at some synovial joints?
B moving the femur backward, as in walking (Figure 7.4*).
Encrextension of other joints, such as the elbow, intcrpha-
Igeal joints (fingers and toes), and knee joints, is usually
nted by the arrangement of ligaments and bones,
| Abduction (alvDUK-shun; ah- = away; -duct = to lead)
movement of a bone away from the midline, and ad-
kction (ad-D UK-shun; ad- = toward) is the movement of a
L toward the midline. Examples of abduction include lat-
eral movement of the humerus upward (Figure 7.5a), lateral
ovement of die palm away from the body (Figure 7.5b),
[and lateral movement of the femur away from the body (Fig-
Ic). Movement in the opposite direction (medially) in
, case produces adduction (Figure 7.5).
Circumduction (ser-kum-DUK-shun; tin- = circle) is
movement of the distal end of a part of the body in a circle
L-un ) Fxamples of joints that allow circumduct! on
include the humerus at the shoulder joint (making a circle with
your arm) and the femur at the hip joint (making a circle with
your leg). Circumduction is more limited at die hip due to
greater tension on the ligaments and muscles.
Rotation
In rotation (ro-TA-shun; rota- = to revolve) a hone revolves
around its own longitudinal axis. An example is aiming die head
from side to side, as in signifying "no" (Figure 7.7a on page 163).
In the limbs, rotation is defined relative to the midline. If die an-
terior surface of a bone of the limb is turned toward the midline,
the movement is called medial (internal) romhih You can medially
rotate die humerus at the shoulder joint as follows; Starting in
die anatomical position, flex your elbow and then draw your
palm across die chest (Figure 7.7b). If the anterior surface of the
162 Chapter 7 Joints
Figure 7.5 Angular movements at synovial joints: abduction and adduction.
Condyloid, saddle, and ball-and-socket joints permit abduction and adduction.
(a) Shoulder joint
(b) Wrist joint
(c) Hip joint
J ^ One way to remember what adduction means is use of the phrase "adding your limb to your trunk." Why is this an effective learning device?
bone of a limb is turned away from the midline, die movement is
called lateral (external) ivtation (see Figure 7.7b).
Special Movements
The special movements that occur only at certain joints in-
clude elevation, depression, protraction, retraction, inversion,
aversion, dursi flexion, plantar flexion, supination, and prona-
tion (Figure 7.8).
■ Elevation (el'-e-VA-shun - to lift up) is the upward
movemeiit of a part of the body, such as closing the
mouth to elevate the mandible (Figure 7.8a) or shrugging
the shoulders to elevate the scapula.
■ Depression (de-PRESH-un - to press down) is the
downward movement of a part of die body, such as open-
ing the mouth to depress the mandible (Figure
returning shrugged shoulders to the anatomical positiouj
to depress the scapula.
Protraction (pro-TRAK-shun = to draw forth) is
movement of a part of die body forward, You can pi
tract your mandible by thrusting it outward (Figure 7.!
or protract your clavicles by crossing your arms.
Retraction (re-TRAK-shun = to draw back) is the move-
ment of a protracted part of the body back to
anatomical position (Figure 7.8d).
Inversion (in-VER-zhun = to turn inward) is movement
the soles medially so that they face each other (Figure 7.1
Eversion (e-VER-zJnm = to turn outward) is moveraj
of the soles laterally so that they face away from eat
other (Figure 7.81).
Figure 7.6 Angular movements at synovial joints: circumduction.
Circumduction is the movement of the distal end of a body part in a circle.
(a) Shoulder joint
List two joints where circumduction can occur.
(b) Hip joint
Wgfi
'#//)
Types of Movements at Synovial Joints 1 63
Figure 7.7 Rotation at synovial joints.
In rotation, a bone revolves around its own longitudinal axis.
v
(a) Atlantoaxial joint
How do medial and lateral rotation differ?
I Dorsiflexion (dor'-si-FLEK-shun) is bending of the foot
in the direction of the dorsum (superior surface), as when
you stand on your heels (Figure 7.8g).
Plantar flexion involves bending of the foot in the direc-
tion of the plantar surface (Figure 7.8g), as when stand-
ing on your toes.
Supination (soo'-pi-NA-shun) is movement of die forearm
so that the palm is turned forward (Figure 7.8h). Supina-
(b) Shoulder joint
tion of the palms is one of the defining features of the
anatomical position (see Figure 1 .4 on page 1 1).
■ Pronation (pro-NA-shun) is movement of the forearm so
that die palm is turned backward (Figure 7,8h).
■ CHECKPOINT
6. Define each of the movements at synovial joints just de-
scribed and give an example of each.
jure 7.8 Special movements at synovial joints.
Special movements occur only at certain synovial joints.
(a) Temporomandibular joint
(b)
(c)
Temporomandibular joint
(e) fntertarsal joints (f) (g) Ankle joint
/ What movement of the shoulder girdle is involved in bringing the arms forward until the elbows touch?
(h) Radioulnar ioint
164 Chapter? Joints
TYPESOF SYNOVIAL JOINTS
OBJECTIVE • Describe the six subtypes of synovial
joints.
Although all synovial joints have a similar structure, the
shapes of the articulating surfaces vary and thus various types
of movement are possible. Accordingly synovial joints are di-
vided into six subtypes; planar, hinge, pivot, condyloid, sad-
dle, and ball-and-socket joints.
1. The articulating surfaces of bones in planar joints ad
flat or slightly curved (Figure 7.9a). Some example- 4
planar joints are the intercarpal (between carpal bones at
the wrist), intertarsal (between tarsal bones at the ankle),
sternoclavicular (between the sternum and die clavicle),
and acromioclavicular (between the acromion of the
scapula and the clavicle) joints. Planar joints primariW
permit gliding movements.
2. In binge joints, the convex surface of one bone fits
into the concave surface of another bone (Figure 7
Figure 7.9 Types of synovial joints. For each subtype, a drawing of the actual joint and a simplified diagram are shown.
> Synovial joints are classified into subtypes on the basis of the shapes of the articulating bone surfaces.
Navicular
Second
cuneiform
Third
cuneiform
(a) Planar joint between the navicular and second
and third cuneiforms of the tarsus in the foot
Head of
radius
Annular
ligament
,_
!
Radial
notch
Ulna
Radius
L
If
[c) Pivot joint between head of
radius and radial notch of ulna
\
Humerus
Trochlea
Ulna
Trochlear
notch
ir
(b) Hinge joint between trochlea of humerus
and trochlear notch of ulna at the elbow
Radius
Scaphoid
Ulna
Lunate
(d) Condyloid joint between radius and scaphoid
and lunate bones of the carpus (wrist)
Radius
Trapezium
Metacarpal
of thumb
V
W
Acetabulum
of hip bone
(e) Saddle joint between trapezium of carpus (wrist)
and metacarpal of thumb
* Which joints permit the greatest range of motion?
! |.:ad of
femur
(f) Ball-and-socket joint between head of tin
femur and acetabulum of the hip bone
3,
i
Examples of hinge joints are the knee, elbow, ankle, and
interphalangeal joints (between the phalanges of the fin-
gers and toes). As die name implies, hinge joints produce
an angular, opening-and-closing motion like that of a
hinged door. I Tinge joints permit only flexion and
extension.
In pivot joints, the rounded or pointed surface of one
ic articulates with a ring formed partly by another
bone and partly by a ligament (Figure 7.9c). A pivot joint
allows rotation around its own longitudinal axis. Exam-
ples of pivot joints are the atlantoaxial joint, in which the
atlas rotates around the axis and permits you to turn your
head from side to side as in signifying "no," and the ra-
dioulnar joints that allow you to move your palms for-
ward and backward.
joints (KON-di-loyd = knucklelike), the
com
convex oval-shaped projection of one bone tits into the
concave oval-shaped depression of another bone (Figure
|9d). Examples are the wrist and metacarpophalangeal
joints (between the metacarpals and phalanges) of the
cotid through fifth digits. A condyloid joint permits
flexion, extension, abduction, adduction, and circumduc-
tion.
In saddle joints, the articular surface of one bone is
;i Idle-shaped, and the articular surface of the other bone
fits into the saddle like a rider sitting on a horse (Figure
be). An example of a saddle joint is the carpometacarpal
joint between the trapezium of the carpus and metacarpal
Bthe thumb. Saddle joints permit flexion, extension, ab-
duction, adduction, and circumduction.
^In ball-and-socket joints, the ball-like surface of one
bone fits into a cuplike depression of another bone
(Figure 7.9f). Ball-and-socket joints permit movement in
several directions (flexion, extension, abduction, adduc-
circumduction, and rotation); the only examples in
ik human body are the shoulder and hip joints.
I CHECKPOINT
Where in the body can each subtype of synovial joint be
nd?
DETAILS OF A SYNOVIAL JOINT:
THE KNEE JOINT
OBJECTIVE • Describe the principal structures and
functions of the knee joint.
ou an idea of the complexity of a synovial joint, we
.mine some of the structural features of the knee
the largest and most complex joint in the body.
Aging and Joints 165
Among the main structures of the knee joint are the follow-
ing (Figure 7,10).
1* The articular capsule is strengthened by muscle tendons
surrounding the joint.
2. The patellar ligament extends from the patella to the
tibia and strengthens the anterior surface of the joint.
3. The oblique popliteal ligament (pop-LIT-e-al) strength-
ens the posterior surface of die joint,
4. The arcuate popliteal ligament strengthens the lower
lateral part of the posterior surface of the joint.
5. The tibial (medial) collateral ligament strengthens the
medial aspect of the joint
6. The fibular (lateral) collateral ligament strengthens the
lateral aspect of the joint,
7. The anterior cruciate ligament (ACL) extends posteri-
orly and laterally from die tibia to the femur. The A( T is
stretched or torn in about 70% of all serious knee in-
juries.
8. The posterior crnciate ligament (PCL) extends anteri-
orly and medially from the tibia to die femur. The ACL
and PCL limit anterior and posterior movement of the
femur and maintain the alignment of the femur with the
tibia.
9* The menisci, fihrocartilage discs between the tibial and
femoral condyles, help compensate for die irregular
shapes of the articulating bones. The two menisci of the
knee joint are the medial meniscus, a semicircular piece of
fihrocartilage on the medial aspect of die knee, and the
lateral meniscus, a nearly circular piece of fihrocartilage on
the lateral aspect of the knee.
10. The hursae, saclike structures filled with fluid, help re-
duce friction.
■ CHECKPOINT
8. Which ligaments strengthen the posterior aspect of the
knee joint?
AGING AND JOINTS
OBJECTIVE • Explain the effects of aging on joints,
Aging usually results in decreased production of synovial
fluid in joints. In addition, the articular cartilage becomes
thinner with age, and ligaments shorten and lose some of
dieir flexibility. The effects of aging on joints are influenced
by genetic factors and by wear and tear, and vary consider-
ably from one person to another. Although degenerative
changes in joints may begin as early as age 20, most changes
do not occur until much later. By age 80, almost everyone de-
166 Chapter 7 Joints
Figure 7,1 Structure of the right knee joint.
Femur
The knee joint is the largest and most complex joint in the body.
Quadriceps
femoris tendon
Patella
Fibula
FIBULAR
COLLATERAL
LIGAMENT
BURSA
BURSA
ARTICULAR
CAPSULE
TIBIAL
COLLATERAL
LIGAMENT
Articular
fat pad
PATELLAR
LIGAMENT
Tibia
Femur
Gastrocnemius
muscle
TIBIAL
Tibia
COLLATERAL
LIGAMENT
ARTICULAR
CAPSULE
OBLIQUE
POPLITEAL
LIGAMENT
ARCUATE
POPLITEAL
LIGAMENT
FIBULAR
COLLATERAL
LIGAMENT
Fibula
(a) Anterior superficial view
(b) Posterior deep view
LATERAL
MENISCUS
Gastrocnemius
muscle
(c) Sagittal section
Quadriceps
femoris tendon
Patella
Articular
fat pad
BURSA
PATELLAR
LIGAMENT
Femur
ANTERIOR
CRUCIATE
LIGAMENT
(ACL)
LATERAL
MENISCUS
FIBULAR
Fibula
COLLATERAL
LIGAMENT
POSTERIOR
CRUCIATE
LIGAMENT
(PCL)
MEDIAL
MENISCUS
TIBIAL
COLLATERAL
LIGAMENT
Tibia
v
What structures are damaged in the knee injury called torn cartilage?
(d) Anterior deep view (flexed)
ocus on Wellness
reven
D
throses (freely movable joints) al-
xtensive movement. But the hu-
man bodv is not a machine, and di-
tthroses were not designed to
tand the repetition of a given mo-
,-ni, over and over and over again, all
L long. When you repeat the same
p t j Qn for extended periods of time,
pi may overstress the joint or joints
|jesponsible for that motion and the as-
sociated soft-tissue structures, such as
particular capsule, ligaments, bursae,
;cles, tendons, and nerves. Repeated
,des of mechanical stress can
lead to the development of repetitive
■ km injuries.
eat That?
drive motion injuries are a type of
mnidative trauma disorder (CTD),
!i group of disorders character-
\v, ongoing damage to soft tissues,
drive motion injuries are the most
nan type of CTD, but CTDs may
i wl l trauma due to exposure to
„r hot temperatures, certain types
king, vibration, and so forth.
■litive motion injuries are similar
nany ways to the overuse injuries
iletes often experience. Just as
lis players may develop epicondyli-
Aoing and Joints 167
tis (tennis elbow), so too may construc-
tion workers who perform repeated
elbow flexion and extension in their
work and students who spend hours a
day using their computer mouse
("mouse elbow"),
Repetitive motions alone may
cause repetitive motion injuries. Risk
increases when repetitive motions are
coupled with poor posture and biome-
chanics, which put excess strain on
joints. Joint stress also increases when a
person must apply force with the mo-
tion, such as when gripping or lifting
heavy objects. The joints at highest risk
are those that are the weakest. Wrists,
backs, elbows, shoulders, and necks are
the most common sites of repetitive
motion injury.
Repetitive motion injuries usually
develop slowly over a long period of
time. They typically begin with mild to
moderate discomfort in the affected
joints, especially at night. Other symp-
toms include swelling in the joint, mus-
cle fatigue, numbness, and tingling.
Symptoms may come and go at first,
but then become constant. Symptoms
of more advanced damage include
more intense pain, muscle weakness,
and nerve problems. If left untreated,
repetitive motion injuries can be ex-
tremely painful. They also may se-
verely limit a joint's range of motion.
Fortunately, because they develop
slowly, most repetitive motion injuries
are discovered earl) enough to be suc-
cessfiillj treated.
Carpal tunnel syndrome is a repetitive motion injury in which pressure de-
velops on the median nerve as it passes through the carpal tunnel, a narrow
tunnel of hone and ligament at the wrist Pressure on this nerve causes
numbness, tingling, and pain in some or all of the fingers. What kind of
workers do you think might be most at risk for the development of carpal
tunnel syndrome?
vel.ips some type of degeneration in the knees, elbows, hips,
shoulders. It is also common for elderly individuals to
op degenerative changes in the vertebral column, result-
hunched-over posture and pressure on nerve roots.
arthritis, called osteoarthritis, is at least partially;
Nearly everyone over age 70 has evidence of
losteoarthritic changes. Stretching and aerobic exercises
Httempt to maintain full range of motion are helpful in
nil/nig the effects of aging. They help to maintain the
functioning of ligaments, tendons, muscles, synovial
,,,| articular cartilage.
CHECKPOINT
Which joints show evidence of degeneration in nearly all
individuals as aging progresses?
Now that you have a basic understanding of bones and
joints, we will examine the structure and functions of muscu-
lar tissue and muscles. In this way you will understand how
bones, joints, and muscles work together to produce various
movements.
168 Chapter? Joints
■
COMMON
DISORDERS
Common Joint Injuries
Rotator cuff injury is a strain or tear in the rotator cuff muscles (see
Figure 8.19 on page 205) and is a common injury among baseball
pitchers and volleyball players, racket sports players, swimmers, and
violinists, due to shoulder movements that involve vigorous circum-
duction. It also occurs as a result of wear and tear, aging, trauma,
poor posture, improper lifting, and repetitive motions in certain
jobs, such as placing items on a shelf above your head. Most often,
there is tearing of the supraspinal muscle tendon of the rotator
cuff. This tendon is especially predisposed to wear-and-tear because
of its location between die head of the humerus and acromion of
the scapula, which compresses the tendon during shoulder move-
ments.
A separated shoulder is an injury of the acromioclavicular joint,
the joint formed by the acromion of the scapula and the acromial
end of the clavicle. It most often happens with forceful trauma, as
may happen when the shoulder strikes the ground in a fall.
Tennis elbow most commonly refers to pain at or near the lat-
eral epicondyle of the humerus, usually caused by an improperly ex-
ecuted backhand. The extensor muscles strain or sprain, resulting in
pain. Little-league elbow typically develops because of a heavy
pitching schedule or throwing many curve balls, especially in
j .-. urngsters. In this injury, the elbow may enlarge, fragment, or sep-
arate.
A dislocation of the radial head is the most common upper
limb dislocation in children. In this injury, the head of the radius
slides past or ruptures die ligament that forms a collar around the
head of the radius at the proximal radioulnar joint. Dislocation is
most apt to occur when a strong pull is applied to the forearm while
it is extended and supinated, for instance while swinging a child
around with outstretched arms.
The knee joint is the joint most vulnerable to damage because
it is a mobile, weight-bearing joint and its stability depends almost
entirely on its associated ligaments and muscles* Further, there is no
correspondence of the articulating bones. A swollen knee may occur
immediately or hours after an injury. The initial swelling is due to
escape of blood from damaged blood vessels adjacent to areas in-
volving rupture of the anterior cruciate ligament, damage to syn-
ovial membranes, torn menisci, fractures, or collateral ligament
sprains. Delayed swelling is due to excessive production of synovial
fluid, a condition commonly referred to as "water on the knee." A
common type of knee injury in football is rupture of the tibial col-
lateral ligaments, often associated with tearing of the anterior cru-
ciate ligament and medial meniscus (torn cartilage). Usually, a hard
blow to the lateral side of the knee while the foot is fixed on the
ground causes the damage. A dislocated knee refers to die displace-
ment of the tibia relative to the femur. The most common type is
dislocation anteriorly, resulting from hyperextension of the knee. A
frequent consequence of a dislocated knee is damage to the
popliteal artery.
Rheumatism and Arthritis
Rheumatism (ROO-ma-tizm) is any painful disorder of the si
porting structures of the body — bones, ligaments, tendons, or mil*
cles — that is not caused by infection or injury 7 . Arthritis is a form
rheumatism in which the joints are swollen, stiff, and painful. If
fiicts about 45 million people in the United States, and is the li
ing cause of physical disability among adults over age 65.
Rheumatoid arthritis (RA) is an autoimmune disease in whi<
the immune system of the body attacks its own tissues — in
case, its own cartilage and joint linings. The primary symptom
RA is inflammation of the synovial membrane, RA is charactoej
by inflammation of the joint, which causes redness, m
swelling, pain, and loss of function.
Osteoarthritis (os'-te-o-ar-THRI-tis) is a degenerate
disease in which joint cartilage is gradually lost. It results Iron
combination of aging, irritation of the joints, muscle weakne
wear and abrasion. Commonly known as "wear-and-tear" arthril
osteoarthritis is the most common type of arthritis. A major disti
don between osteoarthritis and rheumatoid arthritis is thai
teoarthritis strikes the larger joints (knees, hips) first, and rheui
toid arthritis first strikes smaller joints such as those in the Sn|
A relatively new treatment for osteoarthritis of some joints is
viscm&ppkmentatitm, in which hyaluronic acid is injected into
to improve lubrication. Results are usually as good as those in i
inff corticosteroids.
In gouty anhritis (GOVV-te), sodium urate crystals
posited in the soft tissues of the joints. The crystals irritate
erode the cartilage, causing inflammation, swelling, and acute j
If die disorder is not treated, the ends of the articulating bones
and the joint becomes immovable.
Joints that have been severely damaged by diseases such
arthritis, or by injury, may be replaced surgically with artiflcai j(
in a procedure referred to as arthroplasty (AR-thra-plas'
artbr- = joint; -plasty = plastic repair of). Although most joint
the body can undergo arthroplasty; the ones most commonly
placed are the hips, knees, and shoulders. During the pro<
the ends of the damaged bones are removed and the metal, cer
or plastic components are fixed in place. The goals of art limp'
are to relieve pain and increase range of motion
Sprain and Strain
A sprain is the forcible wrenching or twisting of a joint
stretches or tears its ligaments but does not dislocate the boa
occurs when die ligaments are stressed beyond their normal
ity. Sprains also may damage surrounding blood vessels, mi
tendons, or nerves* Severe sprains may he so painful that the
cannot be moved. There is considerable swelling, which |
from hemorrhage of ruptured blood vessels. The ankle joint is
often sprained; die lower back is another frequent location
sprains. A strain is a stretched or partially torn muscle. It ofw
curs when a muscle contracts suddenly and powerfully— for
pie, in sprinters when they accelerate quickly.
Study Outline 169
MEDICAL TERMINOLOGY AND CONDITIONS
'hraigiti (ar-TI [RAL-je-a; artbr- = joint; -algia « pain) Pain
in a joint.
hrsectmny (bur-SEK-to-me; -ectorny = to cut out) Removal of a
bur
Bwfoto (kon-DRI-tis; chondro- = cartilage) Inflammation of
cartilage.
Dislocation (dis- = apart) or luxation (luks-A-slum; lux- = dislo-
cation) The displacement of a bone from a joint with tearing of
ligaments, tendons, and articular capsules. A partial or incom-
plete dislocation is called a subluxation.
Synovitis (sin'-6-VI-tis) Inflammation of a synovial membrane in
a joint
;
STUDY OUTLINE
Joints (p. 157)
■\ joint (articulation) is a point of contact between two bones,
curtilage and bone, or teeth and bone.
\ joint's structure determines its combination of strength and
flexibility.
Itructiiral classification is based on the presence or absence of a
novial cavity and the type of connecting tissue. Structurally,
joints are classified as fibrous, cartilaginous, or synovial.
4 Functional classification of joints is based on die degree of move-
ment permitted. Joints may be synarthroses (immovable), am-
phia throses (slightly movable), or diarthroses (freely movable).
Fibrous Joints (p- 157)
I, There is no joint cavity and the bones are held together by fi-
brous connective tissue in fibrous joints.
,. joints include immovable sutures (found between skull
ones), slightly movable syndesmoses (such as the distal joint
between the tibia and fibula), and immovable gomphoses (roots
.lit' teeth in alveoli of the mandible and maxilla).
Cartilaginous Joints (p. 158)
There is no joint cavity and the bones arc held together by car-
tilage in cartilaginous joints.
These joints include immovable synchondroses united by hya-
line cartilage (epiphyseal plates) and slightly movable symphy-
united by fibrocarrjlage (pubic symphysis).
Synovial Joints (p. 158)
I \ synovial joint contains a synovial cavity .All synovial joints
are diarthroses.
Other characteristics of a synovial joint are die presence of ar-
ticular cartilage and an articular capsule, made up of a fibrous
ipsule and a synovial membrane.
[Tie synovial membrane secretes synovial fluid, which forms a
viscous film over the surfaces within the articular capsule.
4, V novial joints also contain accessory ligaments and ar-
ticular disc
Bursae are saclike structures, similar in structure to joint capsules,
ill, reduce friction in joints such as die shoulder and knee joints.
Types of Movements at Synovial Joints (p. 160)
|. In a gliding movement, the nearly flat surfaces of bones move
bad-aiitl-forth and side-to-side.
2. In angular movements, there is a change in the angle
between bones. Examples are flexion -extension, hyperexten-
sion, abduction -adduction, and circumduction.
3. In rotation, a bone moves around its own longitudinal axis,
4. Special movements occur at specific synovia] joints in the body.
Examples are as follows: elevation -depression, protraction-
retraction, inversion -evasion, dorsi flexion -plantar flexion, and
supination - pronation.
Types of Synovial Joints (p. 164)
1. Types of synovial joints are planar, hinge, pivot, condyloid, sad-
dle, and ball-and-socket.
2. In a planar joint, the articulating surfaces are flat; examples are
joints between carpals and tarsals*
3. In a hinge joint, the convex surface of one hone fits into the
concave surface of another; examples are the elbow, knee, and
ankle joints.
4. In a pivot joint, a round or pointed surface of one bone fits into
a ring formed by another bone and a ligament; examples are
the atlantoaxial and radioulnar joints.
5. In a condyloid joint, an oval-shaped projection of one bone fits
into an oval cavity of another; examples are the wrist joint and
metacarpophalangeal joints for the second through fifth digits,
6. In a saddle joint, the articular surface of one bone is shaped like
a saddle, and the other bone fits into the "saddle" like a rider
oji a horse; an example is the carpometacarpal joint between
the trapezium and the metacarpal of the thumb.
7. In a ball-and-socket joint, the ball-shaped surface of one bone
fits into the cuplike depression of another; examples are die
shoulder and hip joints.
Details of a Synovial Joint: The Knee Joint (p. 165)
1. The knee joint is a diarthrosis that illustrates the complexity of
this type of joint.
2. It contains an articular capsule, several ligaments within and
around the outside of the joint, menisci, and bursae.
Aging and Joints (p. 165)
1. With aging, a decrease in synovial fluid, thinning of articular
cartilage, and decreased flexibility of ligaments occur,
2. Most individuals experience some degeneration in the knees,
elbows, hips, and shoulders due to the aging process.
170 Chapter 7 Joints
SELF-QUIZ
1. A joint that has a fit offers a great amount of move-
ment and is likely to become dislocated.
a. tight, less b. tight, more c. loose, less
d. loose, more e. flexible, less
2. An example of a fibrous joint in which the bones are immov-
able is a
a. suture b. syndesmosis c, synovial d. symphysis
e. synchondrosis
3. Pulling out a tooth would disarticulate which type of joint?
a. symphysis b. synovial c. gomphosis
d. cartilaginous e. suture
4. Which of the following is NOT a function of synovial fluid?
a. It acts as a lubricant.
b. It helps strengthen the joint
c. It removes microbes and debris from the joint.
d. It provides nutrients to the tissues around the joints.
e. It removes metabolic wastes,
5. Articular cartilage and bursae would most likely be found in
which of the following?
a. a gomphosis b. a suture c. the pubic symphysis
d* the knee e. a synchondrosis
6. Which of the following structures provides flexibility to a joint
while also preventing dislocation?
a. bursae b. articular cartilage c, synovial fluid
d. muscles e. articular capsule
7. The joints between the vertebrae and the joint between the hip
bones are examples of which joint type?
a, synovial b. symphysis c, fibrous
d* synchondrosis e. suture
8. Match the following:
a. the joint between the A, planar joint
atlas and axis B hinge joint
_ b. allows gliding movements Q ball-and-socket joint
c, the joint between the q pivot joint
carnal and metacarpal of ^ , „ ' . ,
' , , E. saddle joint
the thumb
d. hip joint
e. knee joint
9. Which of the following diarthrotk joints allows for the gn
degree of movement?
a. ball-and-socket b, hinge c. condyloid
d. pivot c. saddle
10- Moving the femur forward when walking is an example i if
a. abduction b, circumduction c. flexion
d. gliding e. inversion
11. When a gymnast performs the "splits," the primary m:
at the hip joint is
a. rotation b. adduction c. extension d. tjjidinj
e, abduction
12. In the anatomical position, the palms are
a. supinated b. flexed c. inverted d, profited
e. protracted
13. A fluid-rilled sac found between skin and bone that lu
duce friction between the skin and bone is a
a, meniscus b, bursa c. ligament
d. articular capsule e, synovial membrane
14. Nodding your head "yes" in response to a question invuh
a. abduction and adduction b. circumduction
c. extension and hyperextension d. rotation
e. flexion and extension
15. Match the following:
a. movement of a bone
around its own axis
b. movement away from
the midline of the body
c. turning the palm so it faces
forward
d. downward movement
of a body part
e. movement toward the
midline of the body
f. movement of the mandible
or shoulder backward
g. turning the palm so it faces
backward
h. upward movement of a
body part
i. movement of the distal end
of a body part in a circle
j, movement beyond the
pi a n e o f extension
A. rotation
B. supination
C> depress!'; hi
D. adducti
E. retraction
F. pronation
G. abduction
H. hype rex
I. eireuimluctiol
J. elevation
h
RITICAL THINKING APPLICATIONS
After your second A & F exam, you dropped to one knee,
ripped your head back, raised one arm over your head,
clenched your fist, pumped your arm up and down, and yelled
Res!" Use die proper terms to describe the movements under-
taken by the various joints.
Amu Rosa's hip has been bothering her for years, and now she
can hardly walk. Her doctor suggested a hip replacement. "It's
one of those synonymous joints," Aunt Rosa explained. What
type of joint is the hip joint? What types of movements can it
perform?
AW'
" ■ '. 7
Answers to Figure Questions 1 7"
3. Remember Kate, the volleyball player from Chapter 6? Her
cast finally came off today. The orthopedist tested her knee's
range of motion and declared that the ACL appeared to be in-
tact. What is the ACL? How does the ACL contribute to the
kn ee joint's sta bi I i ty?
4. Drew got slammed by a wave while bodysurfmg. Now his arm
feels useless, he's got an odd bump on his shoulder, and his
shoulder really hurts! What happened to Drew's shoulder?
iNSWERSTO FIGURE QUESTIONS
ii
7.5
Sutures are synarthroses because they are immovable; syn-
desmoses are classified as amphiarthroscs because they are
slightly movable.
Hyaline cartilage holds a synchondrosis together, and fibro-
cartilage holds a symphysis together.
Synovial joints are diarthroses, freely movable joints.
The arrangement of ligaments and bones prevents hyperex-
,-ion at some synovial joints.
When you adduct your arm or leg, you bring it closer to the
midline of the body, thus "adding" it to the trunk.
7.6 Circumduction can occur at the shoulder joint and at the hip
joint.
7.7 The anterior surface of a bone or limb rotates toward the
midline in medial rotation, and away from the midline in lat-
eral rotation.
7.8 Bringing the arms forward until the elbows touch is an ex-
ample of protraction.
7.9 Ball-and-socket joints permit the greatest range of move-
ment.
7.10 In torn cartilage injuries of the knee, the menisci are
damaged.
THE MUSCULAR SYSTEM
■■^■nwai^aH
did you know?
Strength training exercise results
not only in stronger muscles, but in many other health
benefits as well Strength training helps to increase
bone strength, increasing the deposition of bone
minerals in young adults and helping to prevent, or at
least slow, their loss in later life. By increasing muscle
mass, strength training raises resting metabolic rate,
the amount of energy expended at rest, so you can
eat more food without gaining weight. Strength
training helps to prevent back injury and injury from
participation in sports and other physical activities.
Psychological benefits include reductions in feelings
of stress and fatigue.
Focus on Wellness, page 190
www.wiley.com/college/apcentral
>
ovements such as throwing a
ball, biking, and walking require an
interaction between bones and muscles.
To understand how muscles produce
different movements, you will learn
where the muscles attach on individual bones and the
types of joints acted on by the contracting muscles.
The bones, muscles, and joints together form an
integrated system called the musculoskeletal system,
The scientific study of muscles is known as myolo^
(ml -GL-o-je; my- = muscle; -logy = study of). The
branch of medical science concerned with the
prevention or correction of disorders of the muscu-
loskeletal system is called orthopedics (or'-tho-PE-d
ortho- = correct; pedi = child).
lonl i ig li ■■ ■ to o i/e ilie a<
• MuscularTissue(page90)
• Adenosine Triphosphate (page 38}
• Divisions of the Skeletal System (page 1 24)
• Joints (page 157)
• Types of Movements at Synovial Joints (page 160)
172
IVERVIEW OF MUSCULAR
ISSUE
fBJECTlVE • Describe the types and functions of
luscular tissue.
Types of Muscular Tissue
iscular tissue constitutes about 40% to 50% of the total
t weight and is composed of highly specialized cells. Re-
jall from Chapter 4 that the three types of muscular tissue
^■skeletal, cardiac, and smooth. As its name suggests, most
ktalmiisde tissue is attached to hones and moves parts of
k skeleton. It is striated; that is, striatiom, or alternating
and dark bands, are visible under a microscope. Because
skeletal muscle can be made to contract and relax by con-
control, it is voluntary* Due to the presence of a small
Liber of cells that can undergo cell division, skeletal mus-
ic has a limited capacity for regeneration.
Cardiac muscle tissue, found only in die heart, forms the
I ilk of the heart wall. The heart pumps blood through blood
to all parts of the body Like skeletal muscle tissue,
cardiac muscle tissue is striated. However, unlike skeletal
muscle tissue, it is involuntary: Its contractions are not under
conscious control. Cardiac muscle can regenerate under cer-
Eji conditions. This will be explained in Chapter 1 5.
Smooth muscle tissue is located in the walls of hollow in-
ternal structures, such as blood vessels, airways, the stomach,
and the intestines. It participates in internal processes such as
Irestion and the regulation of blood pressure. Smooth mus-
mmstriated (lacks striations) and involuntary (not un-
onscious control). Although smooth muscle tissue has
derable capacity to regenerate when compared with
muscle tissues, this capacity is limited when compared
1 1 r types of tissues, for example, epithelium.
Functions of Muscular Tissue
Through sustained contraction or alternating contraction
mi relaxation, muscular tissue has live key functions: pro-
king body movements, stabilizing body positions, regulat-
ion volume,, moving substances within the body, and
ngheat.
Producing body movements. Body movements such as
balking, running, writing, or nodding die head rely on
p integrated functioning of skeletal muscles, bones, and
joints.
Stabilizing body positions. Skeletal muscle contractions
stabilize joints and help maintain body positions, such as
standing or sitting. Postural muscles contract continuously
when a person is awake; for example, sustained contrac-
of your neck muscles hold your head upright.
Skeletal Muscle Tissue 1 73
3. Regulating organ volume. Sustained contractions of
ringlike bands of smooth muscles called sphincters prevent
outflow of the contents of a hollow organ. Temporary
storage of food in the stomach or urine in the urinary
bladder is possible because smooth muscle sphincters
close off the outlets of these organs.
4. Moving substances within the body. Cardiac muscle
contractions pump blood through the body's blood
vessels. Contraction and relaxation of smooth muscle in
the walls of blood vessels helps adjust their diameter and
thus regulate blood How. Smooth muscle contractions
also move food and other substances through the gas-
trointestinal tract, push gametes (sperm and oocytes)
through the reproductive system, and propel urine
through die urinary system. Skeletal muscle contractions
aid the return of blood to the heart,
5. Producing heat. As muscular tissue contracts, it
produces heat. Much of die heat released by muscles is
used to maintain normal body temperature. Involuntary
contractions of skeletal muscle, known as shivering, can
help warm the body by greatly increasing the rate of heat
production.
■ CHECKPOINT
1, What features distinguish the three types of muscular
tissue?
2. What are the general functions of muscular tissue?
SKELETAL MUSCLE TISSUE
OBJECTIVES • Explain the relation of connective
tissue components, blood vessels, and nerves to skeletal
muscles.
• Describe the histology of a skeletal muscle fiber.
Each skeletal muscle is a separate organ composed of
hundreds to thousands of cells, which are called muscle fibers
because of their elongated shapes. Connective tissues
surround muscle fibers and whole muscles, and blood vessels
and nerves penetrate muscles.
Connective Tissue Components
Several connective tissue coverings are associated with
skeletal muscle (Figure 8.1). The entire muscle is wrapped in
epimysium (ep'-i-MIZ-e-um; epi- = upon). Perimysium
(per'-i-MIZ-e-um; peri- = around) surrounds bundles of
10 to 100 or more muscle fibers called fascicles (FAS-i-kuls =
little bundle). Finally, endomysium (en ' -do-MIZ-e-um;
endo- = within) wraps each individual muscle liber. Epimy-
sium, perimysium, and endomysium extend beyond the
muscle as a tendon — a cord of dense regular connective
tissue composed of parallel bundles of collagen fibers. Its
174 Chapters The Muscular System
Figure 8.1 Organization of skeletal muscle and its connective tissue coverings.
A skeletal muscle consists of individual muscle fibers (cells) bundled into fascicles and surrounded by three
connective tissue layers.
Transverse
plane
Bone
Fascicle —
Transverse sections
Periosteum
Tendon
m
Skeletal
muscle
Perimysium
Epimysium
Fascicle
Perimysium
Muscle
fiber (cell)
Myofibril
Perimysium
Endomysium
Motor neuron
Blood capillary
Endomysium
- Nucleus
Muscle fiber
Striations
Sarcoplasm
Sarcolemma
Myofibril
Filament
Functions of Muscles
1. Produces body motions.
2. Stabilizes body positions.
3. Regulates organ volume.
4. Moves substances within the body.
5. Produces heat.
Starting with the connective tissue that surrounds an individual muscle fiber (cell) and working
I toward the outside, list the connective tissue layers in order.
ion is to attach a muscle to a bone, An example is the
■ttneal (Achilles) tendon of the gastrocnemius muscle
jure 8,24a).
Nerve and Blood Supply
!etal muscles are well supplied with nerves and blood
Rsseis (l ; mL::iT 8.1), both of which are directly related In
(contraction, the chief characteristic of muscle. Muscle
contraction also requires a good deal of ATP and therefore
amounts of nutrients and oxygen for AIP synthesis.
over, the waste products of these ATP-producing
ions must be eliminated. Thus, prolonged muscle action
depends on a rich blood supply to deliver nutrients and
iv j,en and to remove wastes.
Generally, an artery and one or two veins accompany
each nerve that penetrates a skeletal muscle. Within the en-
Liysium, microscopic blood vessels called capillaries are
ibutetl so that each muscle fiber is in close contact with
■rmore capillaries. Each skeletal muscle fiber also makes
ntactwith the terminal portion of a neuron.
Histology
Microscopic examination of a skeletal muscle reveals that it
of thousands of elongated, cylindrical cells called
de fibers arranged parallel to one another (Figure 8.2a).
, muscle fiber is covered by a plasma membrane
I the sarcolemma {sarco- = flesh; -lemma = sheath).
Transverse tubules (T tubules) tunnel in from the surface to-
:nter of each muscle fiber. Multiple nuclei lie at
periphery of the fiber, next to the sarcolemma. The
:le liber's cytoplasm, called sarcoplasm, contains many
chondria that produce large amounts of ATP during
k contraction. Extending throughout the sarcoplasm is
oplasmic reticulum (sar'-ko-PLAZ-mik re-TIK-ii-lum),
[network of fluid-filled membrane-enclosed tubules (similar
nooth endoplasmic reticulum) that stores calcium ions
red for muscle contraction. Also in the sarcoplasm are
emus molecules of myoglobin (mi'-o-GLO-bin), a red-
pigment similar to hemoglobin in blood. In addition to
aracteristic color it lends to skeletal muscle, myoglobin
oxygen until it is needed by mitochondria to generate
ffP.
Extending along the entire length of the muscle fiber are
idrical structures called myofibrils. Each myofibril, in
consists of two types of protein filaments called thin
id thick filaments (Figure 8.2b), which do not
,1 the entire length of a muscle fiber. Filaments overlap
.edfic patterns and form compartments called sarcomeres
parts), the basic functional units of striated muscle
c 8.2b, c). Sarcomeres are separated from one
her h) zig-zagging zones of dense protein material called
r,v, Within each sarcomere a darker area, called the A
land, extends the entire length of the thick filaments. At the
mi' each A band is a narrow H zone, which contains
Skeletal Muscle Tissue 1 75
only the thick filaments. At both ends of the A band, thick
and thin filaments overlap. A lighter-colored area to either
side of the A band, called the J band, contains the rest of die
thin filaments but no thick filaments. Each I band extends
into two sarcomeres, divided in half by a Z disc (see Figure
8.4a). The alternating darker A bands and lighter 1 bands
give the muscle fiber its striated appearance.
Thick filaments are composed of the protein myosin, which
is shaped like two golf clubs twisted together (Figure 8.3a on
page 177). The -myosin tails (golf club handles) are arranged par-
allel to each other, forming the shaft of the thick filament. The
heads of the golf clubs project outward from the surface of the
shaft. These projecting heads are referred to as myosin heads.
Thin filaments are anchored to the Z discs. Their main
component is the protein actin. Individual actin molecules
join to form an actin filament that is twisted into a helix
(Figure 8.3b). Each actin molecule contains a myosin-binding
site, where a myosin head can attach. The thin filaments
contain two other proteins, tropomyosin and troponin. In a
relaxed muscle, myosin is blocked from binding to actin
because strands of tropomyosin cover die myosin-binding sites
on actin. The tropomyosin strands, in turn, are held in place
by troponin molecules.
Muscular atrophy (A-tro-fe; a- = without, -trophy :
nourishment) is a wasting away of muscles. Individual
muscle fibers decrease in size because of progressive loss of
myofibrils. The atrophy that occurs if muscles are not used
is termed disuse atrophy. Bedridden individuals and people
with casts experience disuse atrophy because the number
of nerve impulses to inactive muscle is greatly reduced. If
the nerve supply to a muscle is disrupted or cut, the mus-
cle undergoes denervation atrophy. In about 6 months to 2
| years, the muscle will be one-quarter of its original size,
and the muscle fibers will be replaced by fibrous connec-
tive tissue. The transition to connective tissue, when com-
plete, cannot be reversed.
Muscular hypertrophy (hi-PER-tro-fe; hyper- ' above
or excessive) is an increase in muscle fiber diameter owing
to the production of more myofibrils, mitochondria, sar-
coplasmic reticulum, etc. It results from very forceful,
repetitive muscular activity, such as strength training. Be-
cause hypcrtrophied muscles contain more myofibrils,
they are capable of contractions that are more forceful.
■ CHECKPOINT
3. What type of connective tissue coverings are associated
with skeletal muscle?
4. Why is a rich blood supply important for muscle
contraction?
5. What is a sarcomere? What does a sarcomere contain?
Figure 8.2 Organization of skeletal muscle from gross to molecular levels.
The structural organization of a skeletal muscle from macroscopic to microscopic is as follows: skeletal
, muscle, fascicle (bundle of muscle fibers), muscle fiber, myofibril, and thin and thick filaments.
Triad:
Skeletal muscle
fiber
Striations
Which filaments are part of the A band and I band?
Figure 8.3 Detailed structure of filaments, (a) About 300
myosin molecules compose a thick filament. The myosin tails all
point toward the center of the sarcomere, (b) Thin filaments contain
acta troponin, and tropomyosin,
ils contain thick and thin filaments.
Thick filament
Myosin tail
-rrrr*"*""""'
Myosin lie ads
(a) One thick filament (above) and a myosin molecule (below)
Actin
Troponin
Tropomyosin
Myosin-binding site (covered by tropomyosh
(b) Portion of a thin filament
What proteins are present in the A band and in the I band?
CONTRACTION AND RELAXATION
OF SKELE TAL MUSCLE
OBJECTIVE * Explain how skeletal muscle fibers
contract and relax.
Sliding-Filament Mechanism
During muscle contraction, myosin heads of the thick fila-
rntspull on the thin filaments, causing the thin filaments to
■e toward the center of a sarcomere (Figure 8.4a, b). As the
, ilnnents slide, the I bands and H zones become nar-
B(l :.4b) and eventually disappear altogether when
muscle is maximally contracted (Figure 8,4c).
The thin filaments slide past the thick filaments because
Imyosin heads move like the oars of a boat, pulling on the
loleoiles of the thin filaments. Although the sarco-
shortens because of die increased overlap of thin and
i filaments, the lengths of the thin and thick filaments do
I change. The sliding of filaments and shortening of sar-
in turn cause the shortening of the muscle fibers.
tlis process, the sliding- filament mechanism of muscle
ion, occurs only when the level of calcium ions
Contraction and Relaxation of Skeletal Muscle 1 77
(Ca 2+ ) is high enough and ATP is'uvailable, for reasons you
will see shortly.
Neuromuscular Junction
Before a skeletal "muscle fiber can contract, it must be stimu-
lated by an electrical signal called a muscle action potential
delivered by its neuron called a motor neuron. A single
motor neuron along with all the muscle fibers it stimulates is
called a motor unit. Stimulation of one motor neuron causes
all the muscle fibers in that motor unit to contract at the
same time. Muscles diat control small, precise movements,
such as the muscles that move the eyes, have 10 to 20 muscle
libers per motor unit. Muscles of the body that are responsi-
ble for large, powerful movements, such as the biceps brachii
in the arm and gastrocnemius in the leg, have as many as
2000 to 3000 muscle fibers in some motor units.
As the axon (long process) of a motor neuron enters a
skeletal muscle, it divides into branches called axon terminals
that approach — but do not touch --the sarcolemma of a
muscle fiber (Figure 8.5a, b). The ends of the axon terminals
Figure 8.4. Sliding-fiiament mechanism of muscle
contraction.
| During muscle contraction, thin filaments move inward toward
'-'" * " -"~y
the H zone.
2 Sarcomeres
Thick filament
Z disc Thin filament Z disc
(a) Relaxed muscle
M line
Z disc
(b) Partially contracted muscle
< >
(c) Maximally contracted muscle
What happens to the I bands as muscle contracts? Do the
lengths of the thick and thin filaments change during contraction?
1 78 Chapter 8 The Muscular System
enlarge into swellings known as synaptic cud hulks, which eon-
mnsynaptic vesicles filled with a chemical neurotransmitter. The
region of the sarcolennm near the axon terminal is called the
motor end plate. The space between the axon terminal and
sarcolemma is the synaptic cleft. The synapse formed between
the axon terminals of a motor neuron and the motor end plate
of a muscle fiber is known as the neuromuscular junction
(NMJ). At the NMJ, a motor neuron excites a skeletal muscle
fiber in die following way (Figure 8.5c):
Release of acetylcholine. Arrival of the nerve inipuU
at the synaptic end bulbs triggers release of the neural
transmitter acetylcholine (ACb) (as'-e-til-KO-len). A(l
then diffuses across the synaptic cleft between the motri
neuron and the motor end plate.
Activation of ACh receptors. Binding of ACh to its if
ceptor in the motor end plate opens ion channels that
low small cations, especially sodium ions (Na 1 ), to
across the membrane
Figure 8.5 Neuromuscular junction,
A neuromuscular junction includes the axon terminal of a motor neuron plus the motor end plate of a muscle fiber.
Axon of motor neuron
Sarcolemma
Axon terminal
Synaptic
end bulb
Neuromuscular
junction (NMJ)
Motor end plate
Sarcolemma
Myofibril
(a) Neuromuscular junction
Q ACh released
from synaptic vesicle
Synaptic cleft
(space)
© Binding of ACh to
ACh receptors opens
cation channel
IV
♦*
9 »
Axon terminal
Nerve impuls
Synaptic vesk
containing
acetylcholine
(ACh)
Synaptic
end bulb
Synaptic els
(space)
R^
(b) Enlarged view of the
neuromuscular junction
Synaptic end bulb
A ACh broken down
Motor end plate
9
Q Muscle action
potential produced
What is the motor end plate?
(c) Binding of acetylcholine to ACh receptors in the motor end plate
I Generation of muscle action potential. The inflow
[ofW (down its concentration gradient) generates a
muscle action potential. The muscle action potential
■then travels along the sarcolemma and through the T
tubules. Each nerve impulse normally elicits one mus-
cle action potential If another nerve impulse releases
more acetylcholine, then steps and © repeat. See
chapter 9 for the details of nerve impulse generation.
A Breakdown of ACh. The effect of ACh lasts only briefly
because the neurotransmitter is rapidly broken down in
naptic cleft by an enzyme called acetylcholinesterase
0Cfr£)(as'-e-til-k6'-lin-ES-ter-as).
ictioning of the NMJ can be altered by several toxins
U drags. Botulinum toxin, produced by the bacterium
m botulinum, blocks release of ACh. As a result,
jBsde contraction does not occur. The bacteria prolifer-
ffa m improperly canned foods, and their toxin is one of
most lethal chemicals known. A tiny amount can cause
by paralyzing the diaphragm, the main muscle that
Ewers breathing. Yet, it is also the first bacterial toxin to
, used as a medicine (Botox®). Injections of Botox into
ilu affected muscles can help patients who have strabismus
d eyes) or blepharospasm (uncontrollable blinking).
so used as a cosmetic treatment to relax muscles that
Contraction and Relaxation of Skeletal Muscle 1 79
cause facial wrinkles and to alleviate chronic back pain due
to muscle spasms in the lumbar region.
Physiology of Contraction
Both Ca 2+ and energy in the form of ATP, are needed for
muscle contraction. When a muscle fiber is relaxed (not
contracting), there is a low concentration of Ca 2 * 1 in the
sarcoplasm because the membrane of the sarcoplasmic reticu-
lum contains Ca 2+ active transport pumps that continually
transport Ca 2+ from the sarcoplasm into the sarcoplasmic
reticulum (see Figure H.7^). However, when a muscle
action potential travels along the sarcolemma and into the
transverse tubule system, Ca 24 release channels open
(see Figure 8.70), allowing Ca 2 " to escape into the sar-
coplasm. The Ca 2 ^ binds to troponin molecules in the thin
filaments, causing the troponin to change shape. This change
in shape releases the troponin -tropomyosin complex from
the myosin-binding sites on actin (see Figure 8.7©).
Once the myosin-binding sites are uncovered, the
contraction cycle — the repeating sequence of events that
causes the filaments to slide — begins, as shown in Figure 8.6:
Splitting ATP. The myosin heads contain ATPase, an
enzyme diat splits ATP into ADP (adenosine diphos-
Figure 8.6 The contraction cycle. Sarcomeres shorten through repeated cycles in which the myosin
heads (crossbridges) attach to actin, rotate, and detach.
During the power stroke of contraction, crossbridges rotate and move the thin filaments past the thick
^^r- filaments toward the center of the sarcomere.
Q Myosin heads
hydrolyze ATP and
become reoriented
and energized
© Myosin heads
bind to actin,
forming
crossbridges
Contraction cycle continues if
ATP is available and Ca 2+ level in
the sarcoplasm is high
As myosin heads
bind ATP, the
crossbridges detach
from actin
Myosin crossbridges
rotate toward center of the
sarcomere (power stroke)
?
What causes crossbridges to detach from actin?
180 Chapter 8 The Muscular System
phate) and P (a phosphate group). This splitting reaction
transfers energy to the myosin head, although ADP and
P remain attached to it.
Forming crossbridges. The energized myosin heads at-
tach to the myosin-binding sites on actin, and release the
phosphate groups. When myosin heads attach to actin
during contraction, they are referred to as crossbridges.
Power stroke. After the crossbridges form, the power
stroke occurs. During the power stroke, the crossbridge
rotates or swivels and releases the ADP. The force pro-
duced as hundreds of crossbridges swivel slides the thin
filament past the thick filament toward the center of the
sarcomere.
Binding ATP and detaching. At the end of the power
stroke, the crossbridges remain firmly attached to actin.
When they bind another molecule of ATP, the myosin
heads detach from actin.
As the myosin ATPase again splits ATP, the myosin head
is reoriented and energized, ready to combine with another
myosin-binding site farther along the thin filament. The con-
traction cycle repeats as long as ATP and Ca 2 + are available
in the sarcoplasm. At any one instant, some of the myosin
heads are attached to actin, forming crossbridges and gener-
ating force, and other myosin heads are detached from actin
and getting ready to bind again. During a maximal contraction,
the sarcomere can shorten by as much as half its resting length.
merits slip back to their relaxed positions. Figure u
rizes the events of contraction and relaxation in
fiber.
Muscle Tone
Even when a whole muscle is not contracting, a small
her of its motor units are involuntarily activated to produc
sustained contraction of their muscle fibers. This pi
results in muscle tone (tonos = tension). To sustain mi
tone, small groups of motor units are alternate!) active
inactive in a constantly shifting pattern. Muscle tone
skeletal muscles firm, but it does not result in a com
strong enough to produce movement. For example, th<
of muscles in the back of the neck keeps the head upi
prevents it from slumping forward on the chest. Rei
skeletal muscle contracts only after it is activated by a<
choline released by nerve impulses in its motor nu
Hence, muscle tone is established by neurons in the
and spinal cord that excite the muscle's motor m
When the motor neurons serving a skeletal muscle are
aged or cut, the muscle becomes flaccid (FLAS-id :: Hat
a state of limpness in which muscle tone is lost.
■ CHECKPOINT
6. Explain how a skeletal muscle contracts and relaxes,
7. What is the importance of the neuromuscular juncA
After a person dies, Ca 2 '' begins to leak out of the sar-
coplasmic reticulum and binds to troponin, causing the
thin filaments to slide. ATP production has ceased, how-
ever, so the crossbridges cannot detach from actin. The re-
sulting stiffness of the muscles is termed rigor mortis,
rigidity of death. It begins 3-4 hours after death, lasts
about '24 hours, and then disappears as enzymes from
lysozymes digest crossbridges.
METABOLISM OF SKELETAL
MUSCLE TISSUE
OBJECTIVES • Describe the sources of ATP and
gen for muscle contraction.
• Define muscle fatigue and list its possible causes.
Relaxation
Two changes permit a muscle fiber to relax after it has con-
tracted. First, the neurotransmitter acetylcholine is rapidly
broken down by the enzyme acetylcholinesterase (AChE).
When nerve action potentials cease, release of ACh stops,
and AChE rapidly breaks down the ACh already present m
the synaptic cleft. This ends the generation of muscle action
potentials, and the Ca 2 ' release channels in the sarcoplasmic
reticulum membrane close.
Second, calcium ions are rapidly transported from the
sarcoplasm into the sarcoplasmic reticulum, As the level of
Ca 2+ in the sarcoplasm falls, the tropomyosin -troponin
complex slides back over the myosin-binding sites on actin.
Once the myosin-binding sites are covered, the thin fila-
Energy for Contraction
Unlike most cells of the body, skeletal muscle fibers
switch between virtual inactivity, when they are relaxed
using only a modest amount of ATP, and great activity,
they are contracting and using ATP at a rapid pace. How*
the ATP present inside muscle fibers is enough to
contraction for only a few seconds. If strenuous exercise!
continue, additional ATP must be synthesized. Muscle!
have three sources for ATP production: (1) creatine 1
phate, (2) anaerobic cellular respiration, and (3) aerobic
hilar respiration.
While at rest, muscle fibers produce more ATP than
need. Some of the excess ATP is used to make creatine pi
ate, an energy-rich molecule that is unique to im
Metabolism of Skeletal Muscle Tissue 1 81
Figure 8.7 Summary of the events of contraction and relaxation in a skeletal muscle fiber.
Acetylcholine released at the neuromuscular junction triggers a muscle action potential, which leads
to muscle contraction.
Nerve
impulse
^
Nerve impulse arrives at
axon terminal of motor
neuron and triggers release
of acetylcholine (ACh).
Muscle action
potential
Q ACh diffuses across
synaptic cleft, binds
to its receptors in the
motor end plate, and
triggers a muscle
action potential (AP),
I
ACh receptor
\
Synaptic vesicle
filled with ACh
ffk Acetylcholinesterase
in
t
Transverse tubule
o
c
O s* ~ ©
Ai- Q Muscle AP traveling along
i transverse tubule opens Ca 2+
9
synaptic cleft destroys
ACh so another muscle
action potential does not
arise unless more ACh is
released from motor neuron.
release channels in the
sarcoplasmic reticulum (SR)
o membrane, which allows calcium
ions to flood into the sarcoplasm.
I ° ^ o
a
t
Q Muscle relaxes.
BWIMM
•?_t.rU-r.; M
Troponin-tropomyosin
complex slides back
into position where it
blocks the myosin
binding sites on actin.
Ca~ binds to troponin on
the thin filament, exposing
the binding sites for myosin.
Elevated Ca 2+
Ca active
transport pumps o
o o o
Ca 2 " release channels in o
SR close and Ca 2+ active
transport pumps use ATP
to restore low level of
Ca £+ in sarcoplasm.
>
Q Contraction: power strokes
use ATP; myosin heads bind
to actin, swivel, and release;
thin filaments are pulled toward
center of sarcomere.
°n O ° rt °
o o
o o
o o
- 1 The power stroke occurs during which numbered step in this figure?
182 Chapter 8 The Muscular System
fibers (Figure 8.8a). One of AXP's high-energy phosphate
groups is transferred to creatine, forming creatine phosphate
and ADP (adenosine diphosphate). Creatine is a small, amino
acid-like molecule that is synthesized in die liver, kidneys,
and pancreas and derived from certain foods (milk, red meat,
fish), then transported to muscle fibers. While muscle- is con-
tracting, the high-energy phosphate group can be transferred
from creatine phosphate back to ADP, quickly forming new
ATP molecules. Together, creatine phosphate and ATP pro-
vide enough energy for muscles to contract maximally for
about 15 seconds. This energy is sufficient for short bursts of
intense activity, for example, running a 100-meter dash.
Adults need to synthesize and ingest a total of a hoi
2 grams of creatine daily to make up for the urinary loss
creatinine, die breakdown product of creatine. Some
studies have demonstrated improved performance during
intense exercise in subjects who had ingested creal
supplements. For example, college football players who
received supplements of 15 grams per day for 28
gained more muscle mass and had larger gains in lif
power and sprinting performance than the control subje
Other studies, however, have failed to find a performance-
enhancing effect of creatine supplementation. In addition,'
Figure 8.8 Production of ATP for muscle contraction.
(a) Creatine phosphate, formed from ATP while the muscle is relaxed, transfers a high-energy phosphate group to ADR
forming ATP, during muscle contraction, (b) Breakdown of muscle glycogen into glucose and production of pyruvic acid
from glucose via glycolysis produce both ATP and lactic acid. Because no oxygen is needed, this is an anaerobic pathway.
(c) Within mitochondria, pyruvic acid, fatty acids, and amino acids are used to produce ATP via aerobic cellular respiration,
an oxygen-requiring set of reactions.
,>- : Dl
During a long-term event such as a marathon race, most ATP is produced aerobically.
Muscle glycogen
Creatine
i ADP
Creatine
phosphate
Energy
for muscle
contraction
ADP
From
blood
Glucose
i zn
Relaxed
muscle
Contracting
muscle
i --]
^7
Glycolysis
2 <TATP J> (net gain)
2 Pyruvic acid
(a) ATP from creatine phosphate
actic acid
^>
Into blood
(b) ATP from anaerobic glycolysis
Fatty acids liberated
from adipose cells
Pyruvic acid
from glycolysis
Amino acids from
protein breakdown
^ i
;
Cellular respiration
in mitochondria
r
Oxygen from
hemoglobin in blood
or from myoglobin
in muscle fibers
Heat
(c) ATP from aerobic cellular respiration
Where inside a skeletal muscle fiber are the events shown here occurring?
lesting extra creatine decreases the body's own synthesis
nine, and it is not known whether natural synthesis
lovers after long-term creatine supplementation. Further
fcearch is needed to determine both the long-term safety
andrhc value of creatine supplementation.
hen muscle activity continues past the 15-second
the supply of creatine phosphate is depleted. The next
force of AIT is glycolysis, a series of cytosolic reactions that
produces 2 ATPs by breaking down a glucose molecule to
a, vie acid. Glucose passes easily from the blood into con-
r^iin. muscle libers and also is produced within muscle
Ls by breakdown of glycogen (Figure 8.8b). When oxygen
are low us a result of vigorous muscle activity, most of
vruvic acid is converted to lactic acid, a process called
robic cellular respiration because it occurs without us-
irip oxygen. Anaerobic cellular respiration can provide
igh energy for about 30 to 40 seconds of maximal muscle
Together, conversion of creatine phosphate and
lysis can provide enough ATP to run a 400-meter race.
'In ile activity that lasts longer than half a minute depends
asingly on aerobic cellular respiration, a series of oxygen-
ring reactions that produce ATP in mitochondria. Muscle
have two sources of oxygen: (1) oxygen that diffuses into
foem from die blood and (2) oxygen released by myoglobin in
tsarcoplasm. Myoglobin is an oxygen-binding protein found
fay in muscle fibers" It binds oxygen when oxygen is plentiful
bl releases oxygen when it is scarce. If enough oxygen is pre-
sent, pyruvic acid enters the mitochondria, where it is com-
idized in reactions that generate ATP, carbon dioxide,
and heat (Figure 8.8c). In comparison with anaerobic
cellular respiration/ aerobic cellular respiration yields much
ATP, about 36 molecules of ATP from each glucose mol-
ole.In activities that last more than 10 minutes, aerobic eel-
respiration provides most of the needed AI P.
Muscle Fatigue
n'lity of a muscle to contract forcefully after pro-
ductivity is called muscle fatigue. One important factor
uscle fatigue is lowered release of calcium ions from the
iplasmic reticulum, resulting in a decline of Ca 2+ level in
ism. Other factors that contribute to muscle fa-
include depletion of creatine phosphate, insufficient
,.. depletion of glycogen and other nutrients, buildup of
id and ADP, and failure of nerve impulses in the mn-
•uron to release enough acetylcholine.
Oxygen Consumption After Exercise
mii prolonged periods of muscle contraction, increases in
thing and blood flow enhance oxygen delivery to rcrascu-
After muscle contraction has stopped, heavy
Control of Muscle Tension 1 83
breathing continues for a period of time, and oxygen con-
sumption remains above the resting level The term oxygen
debt refers to the added oxygen, over and above the oxygen
consumed at rest, that is taken into die body after exercise.
This extra oxygen is used to "pay back" or restore metabolic
conditions to the resting level in three ways: (I) to convert
lactic acid back into glycogen stores in the liver, (2) to resyn-
thesize creatine phosphate and ATP, and (3) to replace the
oxygen removed from myoglobin.
The metabolic changes that occur during everase, how-
ever, account for only some of the extra oxygen used after ex-
ercise. Only a small amount of resynthesis of glycogen occurs
from lactic acid. Instead, glycogen stores are replenished
much later from dietary carbohydrates. Much of the lactic
acid that remains after exercise is converted back to pyruvic
acid and used for ATP production via aerobic cellular respi-
ration. Ongoing changes after exercise also boost oxygen use.
First, the elevated body temperature after strenuous exercise
increases the rate of chemical reactions throughout the body.
Faster reactions use ATP more rapidly, and more oxygen is
needed to produce ATP. Second, the heart and muscles used
in breathing are still working harder than they were at rest,
and thus they consume more ATP Third, tissue repair
processes are occurring at an increased pace. For these rea-
sons, recovery oxygen uptake is a better term than oxygen
debt for the elevated use of oxygen after exercise.
■ CHECKPOINT
8. What are the sources of ATP for muscle fibers?
9. What factors contribute to muscle fatigue?
10. Why is the term recovery oxygen uptake more accurate
than oxygen debt}
CONTROL OF MUSCLE TENSION
OBJECTIVES • Explain the three phases of a twitch
contraction.
• Describe how the frequency of stimulation and motor
unit recruitment affect muscle tension.
• Compare the three types of skeletal muscle fibers.
• Distinguish between isotonic and isometric contrac-
tions.
The contraction that results from a single muscle action po-
tential, a muscle twitch, has significantly smaller force than
the maximum force or tension the liber is capable of produc-
ing. The total tension that a single muscle fiber can produce
depends mainly on the rate at which nerve impulses arrive at
its neuromuscular junction. The number of impulses per
second is die frequency of stimulation. When considering die
contraction of a whole muscle, the total tension it can produce
1 84 Chapter 8 The Muscular System
depends on the number of muscle fibers that are contracting
in unison.
Twitch Contraction
A twitch conn-action is a brief contraction of all the muscle
fibers in a motor unit in response to a single action potential
in its motor neuron. Figure 8.9 shows a recording of a muscle
contraction, called a myogram. Note that a brief delay; called
the latent period, occurs between application of the stimulus
(time zero on the graph) and the beginning of contraction.
During the latent period, the muscle action potential sweeps
over the sarcolemma and calcium ions are released from
the sarcoplasmic reticulum. During the second phase, the
contraction period (upward tracing), repetitive power strokes
are occurring, generating tension or force of contraction. In
the third phase, the relaxation period (downward tracing),
power strokes cease because the level of Ca 2 "* in the
sarcoplasm is decreasing to the resting level. (Recall that
calcium ions are actively transported back into the sarcoplas-
mic reticulum.)
Frequency of Stimulation
If a second stimulus occurs before a muscle fiber has com-
pletely relaxed, the second contraction will be stronger than
the first because the second contraction begins when die
fiber is at a higher level of tension (Figure 8.10a, b). This
phenomenon, in which stimuli arriving one after the odier
cause larger contractions, is called wave summation. When a
skeletal muscle fiber is stimulated at a rate of 20 to 30 times
per second, it can only partially relax between stimuli. The
result is a sustained but wavering contraction called unfused
(incomplete) tetanus (reran- = rigid, tense; Figure 8.10c).
When a skeletal muscle liber is stimulated at a higher rate of
Figure 8.9 Myogram of a twitch contraction. The arrow indi
cates the time at which the stimulus occurred.
§k A myogram is a record of a muscle contraction.
g
£
c
o
5
o
2
Contraction
period
10 20 30 40 50
Time in milliseconds (msec)
During which period do sarcomeres shorten?
80 to 100 times per second, it does not relax at all. The rea
is fused (complete) tetanus, a sustained contraction in whfc
individual twiches cannot be detected (Figure B.lOd).
Motor Unit Recruitment
The process in which the number of contracting motor
is increased is called motor unit recruitment. Normally,
various motor neurons to a whole muscle lire asynchrorA
(at different times): While some motor units are contracth
others are relaxed. This pattern of motor unit activity del
muscle fatigue by allowing alternately contracting mc
units to relieve one another, so that the contraction can
sustained for long periods.
Recruitment is one factor responsible for prodw
smooth movements rather than a series of jerky movemt
Precise movements are brought about by small chan
muscle contraction. Typically, the muscles that produce
cise movements are composed of small motor units. In
way, when a motor unit is recruited or turned off, only slii
changes occur in muscle tension. On the other hand, h
motor units are active where large tension is needed and
cision is less important.
Types of Skeletal Muscle Fibers j
Skeletal muscles contain three types of muscle fibers,
are present in varying proportions in different muscle
the body: The fiber types are (1) slow oxidative fibers, (2)
oxidative -glycolytic fibers, and (3) fast glycolytic fibers.
Slow oxidative (SO) fibers or red fibers are small in
eter and appear dark red because they contain a large aim
of myoglobin. Because they have many large mitochom
SO fibers generate ATP mainly by aerobic cellular respi
tioiij which is why they are called oxidative fibers,
fibers are said to be "slow" because the contraction cycle
ceeds at a slower pace than in "fast" fibers. SO fibers are
resistant to fatigue and are capable of prolonged, sustaij
contractions.
Fast oxidative -glycolytic (FOG) fibers are interml
in diameter between the other two types. Like slow nil
fibers, they contain a large amount of myoglobin, and
appear dark red. FOG fibers can generate considerable
by aerobic cellular respiration, which gives them a mojj
ately high resistance to fatigue. Because their glycogen
tent is high, they also generate ATP by anaerobic glycol]
These fibers are "fast" because they contract and relax nx
quickly than SO fibers.
Fast glycolytic (FG) fibers or white fibers arc Lirjft
diameter, contain die most myofibrils, and generate the
powerful and most rapid contractions. They have a low
globin content and few mitochondria. FG fibers col
large amounts of glycogen and generate ATP mainly
anaerobic glycolysis. They are used for intense movement
short duration, but they fatigue quickly Strength-mil
Control of Muscle Tension 1 85
Figure 8.10 Myograms showing the effects of different frequencies of stimulation, (a) Single twitch, (b) When a second
stimulus occurs before the muscle has relaxed, wave summation occurs, and the second contraction is stronger than the first.
(The dashed line indicates the force of contraction expected in a single twitch.) (c) In unfused tetanus, the curve looks jagged due
to partial relaxation of the muscle between stimuli, (d) In fused tetanus, the contraction force is steady and sustained.
Due to wave summation, the tension produced during a sustained contraction is greater than during a single twitch.
E
n
H
c
5
'-■
**-
o
03
c
i_.
O
(a) Single twitch (b) Wave summation
(c) Unfused tetanus
Time (msec) ^
(d) Fused tetanus
v
What frequency of stimulation is needed to produce fused tetanus?
Bpams that engage a person in activities requiring great
ngth for short times produce increases in the size,
and glycogen content of F( i libers.
lost skeletal muscles are a mixture of all three types of
I muscle fibers, about half of which are SO fibers. The
feorrions vary somewhat, depending on the action of the
die person's training program, and genetic factors.
nuple, the continually active postural muscles of the
., and legs have a high proportion of SO fibers.
Its 'I the shoulders and arms, in contrast, are not
Itantly active but are used intermittently and briefly to
e amounts of tension, such as in lifting and
ig. These muscles have a high proportion of FG
jb. Leg muscles, which not only support the body but are
used for walking and running, have large numbers of
Band FOG fibers.
Jven though most skeletal muscles are a mixture of all
ii s of skeletal muscle fibers, the skeletal muscle fibers
riven motor unit are all of the same type. The differ-
ur units in a muscle are recruited in a specific order.
need. For example, if weak contractions suffice
nil a task, only SO motor units are activated. If more
led, the motor units of FOG fibers are also re-
Kinally, if maximal force is required, motor units of
m are also called into action.
Isometric and Isotonic Contractions
Muscle contractions are classified as either isotonic or iso-
metric. In an isotonic contraction (iso- - equal; -tonic = ten-
sion), the tension (force of contraction) developed by the
muscle remains almost constant while die muscle changes its
length. Isotonic contractions are used For body movements
and for moving objects. For example, picking up a book from
a table involves isotonic contractions of die biceps brachii
muscle in the arm.
In an isometric contraction {-metro = measure or length),
die tension generated is not enough to exceed the resistance
of the object to be moved and the muscle does not change its
length. Isometric contractions occur when you try to lift a
box but the box does not move because it is too heavy. Iso-
metric contractions are important for maintaining posture
and supporting objects in a fixed position.
■ CHECKPOINT
11. Define the following terms: myogram, twitch contrac-
tion, wave summation, unfused tetanus, and fused
tetanus.
12. What characteristics distinguish the three types of
skeletal muscle fibers?
13. Provide examples of isometric and isotonic contractions.
1 86 Chapter 8 The Muscular System
EXERCISE AND SKELETAL
MUSCLE TISSUE
OBJECTIVE • Describe the effects of exercise on skele-
tal muscle tissue.
The relative ratio of fast glycolytic (FG) and slow oxidative
(SO) fibers in each muscle is genetically determined and
helps account for individual differences in physical perfor-
mance. For example, people with a higher proportion of FG
fibers often excel in activities that require periods of intense
activity, such as weight lifting or sprinting. People with
higher percentages of SO fibers are better at activities that
require endurance, such as long-distance running.
Although the total number of skeletal muscle fibers usually
does not increase, the characteristics of those present can
change to some extent. Various types of exercises can induce
changes in the fibers in a skeletal muscle. Endurance-type (aer-
obic) exercises, such as miming or swimming, cause a gradual
transformation of some FG fibers into fast oxidative-glycolytic
(FOG) fibers. The transformed muscle fibers show slight in-
creases in diameter, number of mitochondria, blood supply,
and strength. Endurance exercises also result in cardiovascular
and respiratory changes that cause skeletal muscles to receive
better supplies of oxygen and nutrients but do not increase
muscle mass. By contrast, exercises that require great strength
for short periods produce an increase in the size and strength
of FG fibers. The increase in size is due to increased synthesis
of thick and thin filaments. The overall result is muscle en-
largement (hypertrophy), as evidenced by the bulging muscles
of body builders.
■ CHECKPOINT
14. Explain how the characteristics of skeletal muscle fibers
may change with exercise.
CARDIAC MUSCLE TISSUE
OBJECTIVE • Describe the structure and function of
cardiac muscle tissue.
Most of the heart consists of cardiac muscle tissue. Like
skeletal muscle, cardiac muscle is also striated, but its action is
involuntaryi Its alternating cycles of contraction and
relaxation are not consciously controlled. Cardiac muscle
fibers often are branched; are shorter in length and larger in
diameter than skeletal muscle fibers; and have a single,
centrally located nucleus (see Figure 15.2b on page 366).
Cardiac muscle fibers interconnect with one another by
irregular transverse thickenings of the sareolemma called
intercalated discs (in-TER-ka-lat-ed = to insert between).
The intercalated discs hold the fibers together anil o ffl
gap junctions, which allow muscle action potentials to \
quickly from one cardiac muscle fiber to another.
A major difference between skeletal muscle ami cm
muscle is the source of stimulation. We have sei
skeletal ""muscle tissue contracts oniv when stimulate
acetylcholine released by a nerve impulse in a motor
In contrast, the heart: beats because some of the
muscle fibers act as a pacemaker to initiate each cardii
traction. The built-in or intrinsic rhythm of heart
m
turns is called autorhythmicity (avv-t6-rith-MIS-i-te).|
hormones and neurotransmitters can increase or I
heart rate by speeding or slowing the heart's pacemaker.
Under normal resting conditions, cardiac iiuincIc |
contracts and relaxes an average of about 75 times i
Thus, cardiac muscle tissue requires a constant supplj
gen and nutrients. The mitochondria in cardiac inn .
are larger and more numerous than in skeletal musdj
and produce most of the needed ATP via aerobic eellulaj;
piration. In addition, cardiac muscle fibers tin n
released by skeletal muscle fibers during exercise, to
ATE
■ CHECKPOINT
15, What are the major structural and functional differ
between cardiac and skeletal muscle tissue?
SMOOTH MUSCLE TISSUE
OBJECTIVE • Describe the structure and functii
smooth muscle tissue.
Smooth muscle tissue is found in many internal organs
blood vessels, kike cardiac muscle, smooth muscle is
tary t Smooth muscle fibers are considerably smaller in
and diameter than skeletal muscle fibers and are tag
both ends. Within each fiber is a single, oval, cent
cated nucleus (Figure 8.11). In addition to thick
filaments, smooth muscle fibers also contain intern
filaments. Because the various filaments have no regi
tern of overlap, smooth muscle fibers lack alternai
and light bands and thus appear nomtriated, or smool
In smooth muscle fibers, the thin filaments m
structures called dense bodies, which are functionally!
to Z discs in striated muscle fibers. Some dense hodi<
dispersed throughout the sarcoplasm; others are attacbj
the sareolemma. Bundles of intermediate filaments
attach to dense bodies and stretch from one dense bi
another, During contraction, the sliding filament
involving thick and thin filaments generates tension
Figure 8.11 Histology of smooth muscle tissue. A smooth
muscle fiber is shown in the relaxed state (left) and the contracted
slate (right).
Smooth muscle lacks striations— it looks "smooth"— because
^ the thick and thin filaments and intermediate filaments are ir-
regularly arranged.
Nucleus of
Smooth
jflcell)
smooth
fiber
Sarcolemma
Intermediate
tL filament
long^udinal section
tf smooth muscle tissue
1 — Thick filament
Thin filament
Relaxed
Contracted
' Which type of smooth muscle is found in the walls of hollow or-
gans?
transmitted to intermediate filaments. These, in turn, pull on
dense bodies attached to die sarcolemma, causing a
lengthwise shortening of the muscle fiber.
[There are two kinds of smooth muscle tissue, visceral
and multiunit. The more common type is visceral (single-
Bit) muscle tissue. It is found in sheets that wrap around to
part of the walls of small arteries and veins and hollow
i such as the stomach, intestines, uterus, and urinary
x The fibers in visceral muscle tissue are tightly bound
wther in a continuous network. Like cardiac muscle,
bceral smooth muscle is autorhythmic. Because the fibers
•ect to one another by gap junctions, muscle action
trials spread throughout the network. When a neuro-
transmitter, hormone, or autorhythmic signal stimulates one
the muscle action potential spreads to neighboring
which then contract in unison, as a single unit.
The second kind of smooth muscle tissue, multiunit
oth muscle tissue, consists of individual fibers, each with
Urn motor nerve endings. Unlike stimulation of a single
i muscle fiber, which causes contraction of many adja-
i fibers, stimulation of a single multiunit smooth muscle
Aging and Muscular Tissue 1 87
fiber causes contraction of that fiber only. Multiunit smooth
muscle tissue is found in the walls of large arteries, in large
airways to the lungs, in the arrector pili muscles attached to
hair follicles, and in the internal eye muscles.
Compared with contraction in a skeletal muscle fiber,
contraction itra smooth muscle fiber starts more slowly and
lasts much longer. Calcium ions enter smooth muscle fibers
slowly and also move slowly out of the muscle fiber when
excitation declines, which delays relaxation. The prolonged
presence of Ca 2 + in the cytosol provides for smooth muscle
tone, a state of continued partial contraction. Smooth muscle
tissue can thus sustain long-term tone, which is important in
the walls of blood vessels and in the walls of organs that
maintain pressure on their contents. Finally, smooth muscle
can both shorten and stretch to a greater extent than other
muscle types. Stretchiness permits smooth muscle in the wall
of hollow organs such as the uterus, stomach, intestines, and
urinary bladder to expand as their contents enlarge, while
still retaining the ability to contract.
Most smooth muscle fibers contract or relax in response to
nerve impulses from the autonomic (involuntary) nervous sys-
tem. In addition, many smooth muscle fibers contract or relax
in response to stretching; hormones; or local factors such as
changes in pi I, oxygen and carbon dioxide levels, temperature,
and ion concentrations. For example, the hormone epineph-
rine, released by die adrenal medulla, causes relaxation of
smooth muscle in the airways and in some blood vessel walls.
Table 8.1 presents a summary of the major characteristics
of the three types of muscular tissue.
■ CHECKPOINT
16. How do visceral and multiunit smooth muscle differ?
17. What are the major structural and functional differences
between smooth and skeletal muscle tissue?
AGING AND MUSCULAR TISSUE
objective • Explain the effects of aging on skeletal
muscle.
Beginning at about 30 years of age, humans undergo a slow,
progressive loss of skeletal muscle mass that is replaced
largely by fibrous connective tissue and adipose tissue. In
part, this decline is due to decreased levels of physical activ-
ity. Accompanying the loss of muscle mass is a decrease in
maximal strength, a slowing of muscle reflexes, and a loss of
flexibility, hi some muscles, a selective loss of muscle fibers of
a given type may occur. With aging, the relative number ul
slow oxidative fibers appears to increase. This could be due
either to atrophy of the other fiber types or their conversion
into slow oxidative fibers. Whether this is an effect of aging
1 88 Chapter 8 The Muscular System
Table 8.1 Summary of the Principal Features of Muscular Tissue
Characteristics
Cell Appearance and Features
Skeletal Muscle
Cardiac Muscle
Smooth Muscle
Long cylindrical fiber with many
peripherally located nuclei;
striated; unbranched
Location
Fiber Diameter
Fiber Length
Sarcomeres
Transverse Tubules
Speed of Contraction
Nervous Control
Capacity for Regeneration
Primarily attached to
bones by tendons
Very large (lO-IOO^m)'
Very large (100 ^m-30 cm)
Yes
Yes, aligned with each
A- 1 band junction
Fast
Voluntary
Limited
Branched cylindrical fiber, usually
with one centrally located nucleus;
intercalated disc? join neighboring
fibers; striated
Heart
Large (10-20 /xm)
Small (50-100 ^m)
Yes
Yes, aligned with each Z
disc
Moderate
Involuntary
Limited
Fiber is thickest in the middle,
tapered at each end, has
one centrally located nucleus;
not striated
Walls of hollow viscera, airways, blood
vessels, iris and ciliary body of the
eye, arrector pili of hair follicles
Small (3-8 ju.m)
Intermediate (30-200 /im)
No
No
Slow
Involuntary
Considerable compared with other
muscle tissues, but limited compared
with tissues such as epithelium
r 1 micrometer (jim) - 1/25,000 of an inch.
itself or mainly reflects the more limited physical activity of
older people is still an unresolved question. Nevertheless,
aerobic activities and strength training programs are effective
in older people and can slow or even reverse the age-associ-
ated decline in muscular performance.
■ CHECKPOINT
18. Why docs muscle strength decrease with aging?
HOW SKELETAL MUSCLES
PRODUCE MOVEMENT
OBJECTIVE • Describe how skeletal muscles cooperate
to produce movement.
Now that you have a basic understanding of the structure and
functions of muscular tissue, we will examine how skeletal
muscles cooperate to produce various body movements.
Origin and Insertion
Based on the description of muscular tissue, we can define a
skeletal muscle as an organ composed of several different
types of tissues. These include skeletal muscle tissue, vasci
tissue (blood vessels and blood), nervous tissue (motor n<
rons), and several types of connective tissues.
Skeletal muscles are not attached directly to bones; the
produce movements by pulling on tendons, which, in
pull on bones. Most skeletal muscles cross at least one joii
and are attached to the articulating bones that form the jok
(Figure 8.12). When the muscle contracts, it draws one
toward the other. The two bones do not move equally One
held nearly in its original position; the attachment of a mi
cle (by means of a tendon) to die stationary hone is callei
origin. The other end of the muscle is attached by means o^
tendon to the movable bone at a point called the imertm
The fleshy portion of the muscle between the tendons of i
origin and insertion is called the belly, A good analogy |
spring on a door. The part of the spring attached to the d<
represents the insertion, die part attached to the frame is
origin, and the coils of the spring are the belly.
Tenosynovitis (ten'-o-sin-o-VI-tis), commonly known
tendinitis, is a painful inflammation of the ten Jo
tendon sheaths, and synovial membranes of joints,
tendons most often affected are at the wrists, shou
elbows (resulting in tennis elbow), finger joints (resulting
trigger finger), ankles, and feet. The affected sheaths sons
jure 8-12 Relationship of skeletal muscles to bones.
Metal muscles produce movements by pulling on tendons at-
hed to bones.
In the limbs, the origin of a muscle is proximal and the insertion
is distal.
Shoulder joint
Scapula
ORIGINS
from scapula .
and humerus
BELLY
ORIGINS
from scapula
Tendons
of triceps
brach
muscle
BELLY
of biceps
brachii
muscle
Humerus
INSERTION
on ulna
Elbow joint
lend on
INSERTION
on radius
Radius
Origin and insertion of a skeletal muscle
Which muscle produces the desired action?
become visibly swollen due to fluid accumulation.
The joint is tender, and movement of the body part often
s pain. Trauma, strain, or excessive exercise may
use tenosynovitis. For instance, tying shoelaces too
V may cause tenosynovitis of the dorsum of the foot.
gymnasts are prone to developing the condition he-
mic, repetitive, and maximum hyperextension
. wrists.
[Group Actions
ovements occur because several skeletal muscles are
i groups rather than individually. Also, most skeletal
Principal Skeletal Muscles 1 89
muscles are arranged in opposing pairs at joints, that is,
flexors -extensors, abductors— adductors, and so on. A muscle
that causes a desired action is referred to as the prime mover or
agonist ( - leader). Often, another muscle, called die antag-
onist (ant- = against), relaxes while the prime mover contracts.
The antagonist has an effect opposite to diat of the prime
mover; drat is, the antagonist stretches and yields to die move-
ment of the prime mover. When you bend (flex) your elbow,
the biceps brachii is die prime mover. While die biceps brachii
is contracting, the triceps brachii, the antagonist, is relaxing
(see Figure 8.20). Do not assume, however, that the biceps
brachii is always the prime mover and the triceps brachii is al-
ways the antagonist. For example, when straightening (extend-
ing) the elbow, the triceps brachii serves as the prime mover
and the biceps brachii functions as die antagonist. If the prime
mover and antagonist contracted together widi equal force,
there would be no movement, as in an isometric contraction.
Most movements also involve muscles called synergists
(SIN-er-gists; syn- = together; erg- - work), which help the
prime mover function more efficiently by reducing unneces-
sary movement. Some muscles in a group also act as fixators,
stabilizing die origin of die prime mover so diat the prime
mover can act more efficiently, Under different conditions and
depending on the movement, many muscles act at various times
as prime movers, antagonists, synergists, or fixators,
■ CHECKPOINT
19. Distinguish between the origin and insertion of a skeletal
muscle.
20. Explain why most body movements occur because several
skeletal muscles act in groups rather than individually.
PRINCIPAL SKELETAL MUSCLES
OBJECTIVES • List and describe the ways that skele-
tal muscles are named-
• Describe the location of skeletal muscles in various
regions of the body and identify their functions.
The names of most of the nearly 700 skeletal muscles are
based on specific characteristics. Learning die terms used to
indicate specific characteristics will help you remember the
names of the muscles (Table 8,2 on page 191).
Exhibits 8.1 through 8.13 list the principal skeletal mus-
cles of the body with their origins, insertions, and actions.
(By no means have all the muscles of die body been in-
cluded.) For each exhibit, an overview section provides a gen-
eral orientation to die muscles and their functions or unique
characteristics. To make it easier for you to learn to say the
names of skeletal muscles and understand how they are named,
we have provided phonetic pronunciations and word roots that
Focus on Wellness
Increases Muscle
Flexibility
A certain degree of elasticity is an im-
portant attribute of skeletal muscles
and their connective tissue attach-
ments. Greater elasticity contributes to
a greater degree of flexibility, increas-
ing the range of motion of a joint. A
joint's range of motion (ROM) is the
maximum ability to move the bones
about the joint through an arc of a cir-
cle. For example, a person may nor-
mally be able to extend the knee joint
from 30° when it is maximally flexed to
170° when fully extended. The ROM
or degree of flexibility is then 170 -
30° = 140°. Physical therapists mea-
sure improvements in flexibility by in-
creases in ROM .
Stretching It
When a relaxed muscle is physically
stretched, its ability to lengthen is lim-
ited by connective tissue structures,
such as fasciae. Regular stretching
gradually lengthens these structures,
but the process occurs very slowly. To
see an improvement in flexibility,
stretching exercises must be performed
regularly — daily, i f possible — for m any
weeks.
Tissues stretch best when slow,
gentle force is applied at elevated tissue
temperatures. An external source ot
heat, such as hot packs or ultrasound,
can be used. But 10 or more minutes of
muscular contraction is also a good way
to raise muscle temperature. Exercise
heats die muscle more deeply and thor-
oughly. That's where the term "warm-
up" comes from. It's important to warm
up before stretching, not vice versa.
Stretching cold muscles does not in-
crease flexibility and may even cause
injury.
Just Relax . . ■
The easiest and safest way to increase
flexibility is with static stretching. A
good static stretch is slow and gentle.
After warming up, you get into a com-
fortable stretching position and relax.
Continuing to relax and breathe deeply,
you reach just a little farther, and a lit-
tle farther, holding the stretch for at
least 30 seconds, Tf you have difficulty
relaxing, you know you have stretched
too far. Ease up until you feel a stretch
but no strain.
When stretching, it is important to
relax. Sounds simple, right? But if you
► Thin
ever visit an exercise class, you'll noti(
some people who are all tense, m
and hunched up, because the stretchii
positions are uncomfortable. As a re;
their muscles tighten up in prott
These people figure they'd better push!
little harder, and they tense up
more. They are unintentionally acri™
ing the motor neurons that initiate mi
pilar contraction in the very mus<
they are supposed to be relaxing, v. hi.,
of course interferes with the musdc
ability to elongate and stretch.
hing the information presented in t
cles are being stretched when you
a bar or chair.
is chapter, tty to figure out which n
one foot (keep that leg straight) itpm
indicate how the muscles are named (refer also to Table 8.2).
Once you have mastered the naming of the muscles, their ac-
tions will have more meaning and be easier to remember.
The muscles are divided into groups according to die part of
the body on which they act. Figure 8.13 on pages 192-193 shows
genera! anterior and posterior views of the muscular system. As
you study groups of muscles in the following exhibits, refer to
Figure 8.1 3 to see how each group is related to all others.
To appreciate the many ways that the muscular sysB
contributes to homeostasis of other body systems, examine Fi
cus on Homeostasis: The Muscular System on page 218. }
in Chapter 9, we will see how the nervous system is org
how neurons generate nerve impulses that activate musde
sues as well as other neurons, and how synapses function.
190
Table 8.2 Characteristics Used to Name Skeletal Muscles
Name
Meaning
Example
Direction: Orientation of muscle fibers relative to the body's midline
Rectus Parallel to midline Rectus abdominis
Transverse Perpendicular to midline Transverse abdominis
Oblique Diagonal to midline External oblique
Size: Relative size of the muscle
Maximus
Largest
Minimus
Smallest
Longus
Longest
Latissimus
Widest
Longissimus
Longest
Magnus
Large
Major
Larger
Minor
Smaller
Vastus
G real
Shape: Relative shape of the muscle
Deltoid
Trapezius
Serratus
Rhomboid
Orbicularis
Pectinate
Piriformis
Platys
Quadratus
Gracilis
Triangular
Trapezoid
Saw-toothed
Diamond-shaped
Circular
Comblike
Pear-shaped
Flal
Square
Slender
Action: Principal
Flexor
Extensor
Abductor
Adductor
Levator
Depressor
Supinator
Pronator
Sphincter
Tensor
action of the muscle
Decreases joint angle
Increases joint angle
Moves bone away from midline
Moves bone closer to midline
Produces superior movement
Produces inferior movement
Turns palm anteriorly
Turns palm posteriorly
Decreases size of opening
Makes a body part rigid
Number of Origins: Number of tendons of origin
Biceps Two origins
Triceps Three origins
Quadriceps Four origins
Principal Skeletal Muscles 1 91
Figure
8.16b
8.16b
8.16a
Gluteus maximus
8.23b
Gluteus minimus
8,23b
Adductor longus
8,23a
Latissimus dorsi
8,13b
Longissimus muscles
8.22
Adductor magnus
8.23b
Pectoral is major
8.13a
Pectoralis minor
8.19a
Vastus lateralis
8.23a
Deltoid
8.13b
Trapezius
8.13b
Serratus anterior
8.13a
Rhomboid major
8.18b
Orbicularis oculi
8.14
Pectineus
8,23a
Piriformis
8.23b
Platysma
8.13a
Quadratus lumborum
8.17b
Gracilis
8.23a
Flexor carpi radialis
8.21a
Extensor carpi ulnaris
8.21b
Abductor poflicis longus
8.21b
Adductor longus
8.23a
Levator scapulae
8.18
Depressor labii inferioris
Supinator
Pronator teres
8.21a
External anal sphincter
19.15b
Tensor fasciae latae
8.23a
Biceps brachii
8.20a
Triceps brachii
8.20b
Quadriceps femoris
8.23a
Location: Structure near which a muscle is found
Example: Temporalis, a muscle near the temporal bone (Figure 8.14).
Origin and Insertion: Sites where muscle originates and inserts
Example: Brachioradialis, originating on the humerus and inserting on the radius (Figure 8.21a).
1 92 Chapter 8 The Muscular System
Figure 8,13 Principal superficial skeletal muscles.
Most movements require contraction of several skeletal muscles acting in groups rather than individually.
Epicranial aponeurosis
Occipitofrontalis (frontal belly) - j Temporalis
H — - j-MM Orbicularis oculi
Bel
Orbicularis oris
Sternocleidomastoid
Latissimus dorsi
Rectus abdominis
External oblique
Brachioradialis
Extensor carpi radialis
long us
Extensor digitorum
Tensor fasciae latae
lliacus
Psoas major
Pectineus
Adductor longus
Sartorius
Adductor magnus
Gracilis
Vastus lateralis
Rectus femoris
Vastus medialis
Tendon of
quadriceps
femoris
Patella
Gastrocnemius
Soleus
Tibia
Flexor digitorum longus
Pectoralis major
Serratus anterior
Extensor carpi radialis
longus and brevis
Brachioradialis
■ Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
Abductor potlicis longus
Thenar muscles
Hypothenar muscles
Patellar ligament
Tibialis anterior
Fibularis longus
Hbia
T>j9MK
(a) Anterior view
Principal Skeletal Muscles 1 93
Epicranial aponeurosis
Occipitofrontalis (occipital belly)
Occlpitofrontalis (frontal belly)
Temporalis
Biceps brachii
Brachialis
Triceps brachii
Brachioradialis
Extensor carpi
radialis brevis
Extensor digitorum
Extensor carpi ulnaris
Flexor carpi ulnaris
Infraspinatus
Teres minor
Teres major
Latissimus dorsi
External oblique
Gluteus medsus
Flexor carpi ulnaris
Extensor carpi ulnaris
Tensor fasciae
latae
Gluteus maximus
Gastrocnemius
Vastus lateralis
Gracilis
Adductor magnus
Semitendinosus
Biceps femoris
liotibial tract
Semimembranosus
Sartorius
Soleus
FibuJaris longus
Flexor digitorum
longus
Calcaneal
(Achilles) tendon
Fibularis longus
Soleus
Extensor digitorum longus
j>/?/y/L
(b) Posterior view
nich is an example of a muscle named for the following characteristics: direction of fibers, shape, action, size,
gin and insertion, location, and number of origins?
194 Chapters The Muscular System
Exhibit 8.1 Muscles of Facial Expression (Figure 8.14)
OBJECTIVE • Describe the origin, insertion, and action of the muscles of facial expression.
Overview: The muscles of facia! expres-
sion provide humans with the ability to
express a wide variety of emotions, including
displeasure, surprise, fear, and happiness.
The muscles themselves lie within the layers
of superficial fascia (connective tissue be-
neath the skin). As a rule, their origins are in
the fascia or in the bones of the skull, with
insertions into the skin. The "movable bone"
in this case is the skin rather than a joint.
Bell's palsy, also known as facial
paralysis, is a one-sided paralysis of the
muscles of facial expression as a result of
damage or disease of the facia! (VII)
nerve. Although the cause is unknown, a
relationship between the herpes simplex
virus and inflammation of the facial nerve
has been suggested. In severe cases, the
paralysis causes the entire side of the face
to droop, and the person cannot wrinkle
the forehead, close the eye, or pucker the
lips on the affected side. Drooling and diffi-
culty in swallowing also occur. Eighty per-
cent of patients recover completely within
a few weeks to a few months. For others,
paralysis is permanent.
Relating muscles to movements:
the muscles in this exhibit into two groups:
(1) those that act on the mouth and (2) those]
that act on the eyes.
■ CHECKPOINT
What muscles would you use to show sur-
prise, express sadness, show your upper
teeth, pucker your lips, squint, and blow up.
balloon?
Muscle
Origin
Insertion
Action
Occipitofrontalis
(ok-sip-i-to -f run-TA-l is)
Frontal belly
Occipital belly
(occipit- ■ base of skull)
(See Figure 8.13b.)
Orbicularis oris (or-bi;-ku-LAR-is
OR-is; -orb - circular; or = mouth)
Zygomaticus major (zT-go-MA-ti-
kus; zygomatic = cheek bone;
major - greater)
Buccinator (BUK-si~na'-tor;
bucia = cheek)
Platysma (pla-TIZ-ma; platys = flat)
Orbicularis oculi (OK-u-IT;
oculi = eye)
Levator palpebrae superior! s
(le-VA-tor PAL-pe-bre soo-per'-e-
OR-is; palpebrae - eyelids)
(see Figure 8.15.)
Epicranial aponeurosis
(ap'-o-noo-RO-sis)
(flat tendon that attaches
to the frontalis and occipitalis
muscles).
Occipital and temporal
Muscle fibers surrounding
opening of mouth.
Zygomatic bone.
Maxilla and mandible.
Fascia over deltoid and
pectoralis major muscles.
Medial wall of orbit.
Roof of orbit.
Skin superior to orbit.
Epicranial aponeurosis,
Skin at corner of
mouth.
Skin at angle of mouth
and orbicularis oris.
Orbicularis oris.
Mandible, muscles
around angle of mouth,
and skin of lower face.
Skin of upper eyelid.
Draws scalp forward, raises eyebrows,
and wrinkles skin of forehead horizontally as in a
look of surprise.
Draws scalp backward.
Closes and protrudes lips, compresses
lips against teeth, and shapes lips during speech
Draws angle of mouth upward and outward,
as in smiling or laughing.
Presses cheeks against teeth and lips, as in
whistling, blowing, and sucking; draws corner of
mouth laterally; assists in mastication (chewing) I
keeping food between the teeth (and not between
teeth and cheeks).
Draws outer part of lower lip downward and
backward as in pouting; depresses mandible.
Circular path around orbit. Closes eye.
Elevates upper eyelid (opens eye]
Principal Skeletal Muscles
Figure 8.14- Muscles of facial expression. In this and subsequent figures in the chapter the
muscles indicated in all uppercase letters are the ones specifically referred to in the corresponding
exhibit.
V- * 1^£
When they contract, muscles of facial expression move the skin rather than a joint.
Epicranial aponeurosis
TEMPORALIS
OCC I PITO FRONTALIS
(OCCIPITAL BELLY)
MASSETER
Sternocleidomastoid
OCCIPITOFRONTAL^
(FRONTAL BELLY)
ORBICULARIS OCULI
ZYGOMATICUS MAJOR
BUCCINATOR
ORBICULARIS ORIS
Depressor labii inferioris
PLATYSMA
Right lateral superficial view
Which muscles of facial expression cause smiling, pouting, and squinting?
Exhibit 8.2 Muscles That Move the Mandible (Lower Jaw) (See Figure 8.14)
OBJECTIVE • Describe the origin, insertion, and action of the muscles that move the mandible.
Overview: Muscles that move the
ile (lower jaw) are also known as
msdesof mastication (mas'-ti-KA-shun -
i because they are involved in biting
owing. These muscles also assist in
Ifflsech.
Relating muscles to movements: Arrange
the muscles in this exhibit and the previous
exhibit according to their actions on the
mandible: (1) elevation, (2) depression, and
(3) retraction. The same muscle may be
mentioned more than once.
■ CHECKPOINT
What would happen if you lost tone in the
masseter and temporalis muscles?
Origin
Insertion
Action
«B$eter(MA-se-ter;
chewer) See Figure 8.14.
mporalis (tem'-por-A-lis;
temples) See Figure 8.14.
Maxilla and zygomatic arch,
Temporal bone.
Mandible,
Mandible.
Elevates mandible as in closing mouth.
Elevates and retracts (draws back) mandible.
1 96 Chapter 8 The Muscular System
Exhibit 8.3 Muscles That Move the Eyeballs: Extrinsic Muscles (Figure 8.15)
OBJECTIVE • Describe the origin, insertion, and action of the extrinsic muscles of the eyeballs.
Overview: Two types of muscles are
associated with the eyeball, extrinsic and
intrinsic. Extrinsic muscles originate outside
the eyeball and are inserted on its outer
surface (sclera). They move the eyeballs in
various directions. Intrinsic muscles originate
and insert entirely within the eyeball. They
move structures within the eyeballs, such as
the iris and the lens.
Movements of the eyeballs are controlled
by three pairs of extrinsic muscles: (1 ) supe-
rior and inferior recti, (2) lateral and medial
recti, and (3) superior and inferior obliques.
Two pairs of rectus muscles move the eyeball
in the direction indicated by their respective
names: superior, inferior, lateral, and medial.
One pair of muscles, the oblique muscles —
superior and inferior — rotate the eyeball on
its axis. The extrinsic muscles of the eyeballs
are among the fastest contracting and most
precisely controlled skeletal muscles of the
body.
Strabismus is a condition in which .the
two eyes are not properly aligned. A
lesion of the oculomotor (III) nerve, which
controls the superior, inferior, and medial
recti and the inferior oblique muscles,
causes the eyeball to move laterally when
at rest. The person cannot move the eye-
ball medially and interiorly. A lesion in the
abducens (VI) nerve, which innervates the
lateral rectus muscle, causes the eyeball
to move medially when at rest with inabil-
ity to move the eyeball laterally.
Relating muscles to movements:
Arrange the muscles in this exhibit according]
to their actions on the eyeballs: (1) elevation,)
(2) depression, (3) abduction, (4) adduction,
(5) medial rotation, and (6) lateral rotation.
The same muscle may be mentioned more
than once.
■ CHECKPOINT
Which muscles contract and relax in each
eye as you gaze to your left without moving
your head?
Muscle
Origin
Insertion
Action
Superior rectus (REK4us;
superior - above; reel- = straight;
here, muscle fibers that are parallel
to long axis of eyeball)
Inferior rectus (inferior = below)
Lateral rectus
Medial rectus
Superior oblique (6-BLEK;
oblique - slanting; here, muscle
fibers run diagonally to long axis
of eyeball)
Inferior oblique
Tendinous ring attached
to bony orbit around optic
foramen.
Same as above.
Same as above.
Same as above.
Same as above.
Maxilla.
Superior and central
part of eyeball.
Inferior and central part
of eyeball.
Lateral side of eyeball.
Medial side of eyeball.
Eyeball between superior and
lateral recti The muscle moves
through a ring of fibrocarti-
laginous tissue called
the trochlea {trochlea = pulley).
Eyeball between inferior and
lateral recti.
Moves eyeball upward (elevation) and medially
(adduction), and rotates it medially.
Moves eyeball downward (depression) and
medially (adduction), and rotates it medially.
Moves eyeball laterally (abduction).
Moves eyeball medially (adduction).
Moves eyeball downward (depression)
and laterally (abduction), and rotates it mediallyl
Moves eyeball upward (elevation) and laterally
(abduction), and rotates it laterally.
7', :v
Principal Skeletal Muscles 197
Figure 8.15 Extrinsic muscles of the eyeballs.
The extrinsic muscles of the eyeball are among the fastest contracting
and most precisely controlled skeletal muscles in the body.
SUPERIOR OBLIQUE
Levator palpebrae superioris
SUPERIOR RECTUS
MEDIAL RECTUS
Optic nerve
INFERIOR
RECTUS
LATERAL
RECTUS
INFERIOR
OBLIQUE
Lateral view of right eyebal
Which muscle passes through the trochlea?
Trochlea
Eyeba!
lly.
ly
198 Chapter 8 The Muscular System
Exhibit 8.4 Muscles That Act on the Anterior Abdominal Wall (Figure s.w)
OBJECTIVE Describe the o rigin, insertion, and action of the muscles that act on the anterior abdominal wall.
Overview: The anterior abdominal wall is
composed of skin; fascia; and four pairs of
muscles: rectus abdominis, external oblique,
internal oblique, and transverse abdominis.
A hernia is a protrusion of an organ
through a structure that normally contains
it, which creates a lump that can be seen
or felt through the skin's surface. The
inguinal region is a weak area in the
abdominal wall. It is often the site of an
inguinal hernia, a rupture or separation
of a portion of the inguinal area of the
abdominal wall resulting in the protrusion
of a part of the small intestine. Hernia is
much more common in males than in
females because the inguinal canals in
males are larger to accommodate the
spermatic cord and ilioinguinal nerve.
Treatment of hernias most often involves
surgery. The organ that protrudes is
"tucked" back into the abdominal cavity
and the defect in the abdominal muscles
is repaired. In addition, a mesh is often
applied to reinforce the area of weakness.
Relating muscles to movements:
Arrange the muscles in this exhibit accordir
to the following actions on the vertebral
column: (1) flexion, (2) lateral flexion,
(3) extension, and (4) rotation. The same
muscle may be mentioned more than once.
■ CHECKPOINT
Which muscles do you contract when you
"suck in your tummy" thereby compressing
the anterior abdominal wall?
Muscle
Origin
Insertion
Action
Rectus abdominis (REK-tus
ab-DOM-in-is; red- « straight,
fibers parallel to midline;
abdomin- = abdomen)
External oblique (6-BLEK;
external = closer to surface;
oblique = slanting; here, fibers
that are diagonal to midline)
Internal oblique (internal = farther
from surface)
Transverse abdominis
{transverse - fibers that are
perpendicular to midline)
Pubis and pubic
symphysis.
Lower eight ribs.
Ilium, inguinal ligament,
and thoracolumbar
fascia.
Ilium, inguinal ligament,
lumbar fascia, and
cartilages of last six ribs.
Cartilage of fifth to seventh
ribs and xiphoid process of
sternum.
Crest of ilium and Jinea alba
(a tough connective tissue band
that runs from the xiphoid
process of the sternum to the
pubic symphysis).
Cartilage of last three or four
ribs and linea alba.
Xiphoid process of sternum
linea alba, and pubis.
Flexes vertebral column, and compresses abdor
to aid in defecation, urination, forced expiration,
and childbirth.
Contraction of both external obliques compresses
abdomen and flexes vertebral column; contraction
of one side alone bends vertebral column
and rotates it.
Contraction of both internal obliques compresses
abdomen and flexes vertebral column; contract
one side atone bends vertebral column laterally
and rotates it.
Compresses abdomen.
Figure 8.16 Muscles of the male anterolateral abdominal wall
The inguinal ligament separates the thigh from the body wall.
Principal Skeletal Muscles
Linea alba
EXTERNAL OBLIQUE
EXTERNAL OBLIQUE
RECTUS ABDOMINIS
TRANSVERSE
ABDOMINIS
INTERNAL OBLIQUE
[a) Anterior superficial view
(b) Anterior deep view
Which abdominal muscle aids in urination?
200 Chapters The Muscular System
Exhibit 8.5 Muscles Used in Breathing (Figure 8.17)
OBJECTIVE • Describe the origin, insertion, and action of the muscles used in breathing.
Overview: The muscles described here
alter the size of the thoracic cavity so that
breathing can occur. Inhalation (breathing in)
occurs when the thoracic cavity increases in
size, and exhalation (breathing out) occurs
when the thoracic cavity decreases in size.
The dome-shaped diaphragm is the most
important muscle that powers quiet breath-
ing. The external intercostals, located be-
tween the ribs, assist the diaphragm during
quiet breathing. The internal intercostals,
also between the ribs, run at right angles to
the external intercostals.
Relating muscles to movements;
Arrange the muscles in this exhibit accor
to the following actions on the size of the
thorax: (1) increase in vertical dimension,
(2) increase in lateral and anteroposterior
dimensions, and (3) decrease in lateral a
anteroposterior dimensions.
■ CHECKPOINT
What situations would require forceful
breathing?
Muscle
Diaphragm (Dl -a-fram;
die = across; -phragm = wall)
External intercostals
(in'-ter-KOS-tals;
external - closer to surface;
inter- = between; costa = rib)
Internal intercostals
(interna! = farther from surface)
Origin
Insertion
Xiphoid process of the sternum
costal cartilages of the inferior
six ribs, lumbar vertebrae, and
twelfth rib.
Inferior border of rib above.
Central tendon.
Superior border of rib below.
Superior border of
rib below.
Inferior border of rib
above.
Action
Contraction of the diaphragm causes it to flatten an
increases the vertical (top-to-bottom) dimension of j
thoracic cavity, resulting in inhalation; relaxation o1
the diaphragm causes it to move superiorly and
decreases the vertical dimension of the thoracic
cavity, resulting in exhalation.
Contraction elevates the ribs and increases the
anteroposterior (front-to-back) and lateral
(side-to-side) dimensions of the thoracic cr
resulting in inhalation; relaxation depresses (her
and decreases the anteroposterior and lateral
dimensions of the thoracic cavity, resulting in
exhalation.
Contraction draws adjacent ribs together to further
decrease the anteroposterior and lateral dimensi
of the thoracic cavity during forced exhalation.
Principal Skeletal Muscles 201
Figure 8.17 Muscles used in breathing.
The muscles used in breathing alter the size of the thoracic cavity.
Sternum
INTERNAL
INTERCOSTALS
EXTERNAL
INTERCOSTALS
Pectoralis minor (cut)
External oblique (cut)
Rectus abdominis (cut)
Ribs
[a) Anterior superficial view
Which muscles contract during a normal quiet inhalation?
(b) Anterior deep view
EXTERNAL
INTERCOSTALS
INTERNAL
INTERCOSTALS
DIAPHRAGM
Quadratus lumborum
202 Chapters The Muscular System
Exhibit 8,6 Muscles That Move the Pectoral (Shoulder) Girdle (Figure 8.18)
OBJECTIVE • Describe the origin, insertion, and action of the muscles that move the pectoral girdle.
Overview: Muscles that move the pectoral
(shoulder) girdle originate on the axial skele-
ton and insert on the clavicle or scapula, The
main action of the muscles is to hold the
scapula in place so that it can function as a
stable point of origin for most of the muscles
that move the humerus (arm bone),
Relating muscles to movements:
Arrange the muscles in this exhibit according
to the following actions on the scapula:
(1) depression, (2) elevation, (3) lateral and
forward movement, and (4) medial and
backward movement. The same muscle
may be mentioned more than once.
■ CHECKPOINT
Which muscle in this exhibit not only moves
the pectoral girdle but also assists m tou»S
inhalation?
Muscle
Origin
Insertion
Action
Pectoralis minor (pek'-tor-A-lis;
pect- = breast, chest, thorax;
minor = lesser)
Serratus anterior (ser-A-tus;
serratus = saw-toothed;
anterior = before)
Trapezius (tra-PE-ze-us;
trapezi- - trapezoid-shaped)
(See also Figure 8.13b.)
Levator scapulae (le-VA-tor
SKA-pu-le; levator = to raise;
scapulae = of the scapula)
Rhomboid major (rom-BOYD);
rhomboid - rhomboid or
diamond-shaped)
Third through fifth ribs.
Upper eight or nine ribs.
Occipitaf bone and spines
of seventh cervical and all
thoracic vertebrae.
Upper four or five cervical
vertebrae.
Spines of second to fifth
thoracic vertebrae.
Scapula,
Scapula.
Clavicle and
scapula.
Scapula.
Scapula.
Depresses scapula, moves it laterally and forward,
and rotates it downward (movement of glenoid cavily
upward); elevates third through fifth ribs during forced
inhalation when scapula is fixed.
Moves scapula laterally and forward, and rotates it
upward (movement of glenoid cavily downward);
elevates ribs when scapula is fixed; known as "boxer's
muscle" because it is important in horizontal arm
movements such as punching and pushing.
Elevates clavicle; moves scapula medially and
backward, rotates it upward, and elevates or
depresses it; extends head.
Elevates scapufa and rotates it downward.
Elevates scapula, moves it medially and backward,
and rotates it downward.
Principal Skeletal Muscles 203
Figure 8.18 Muscles that move the pectoral (shoulder) girdle.
Muscles that move the pectoral girdle originate on the axial skeleton and insert on the clavicle or scapula.
LEVATOR SCAPULAE
Clavicle
TRAPEZIUS
PECTORALIS
MINOR
Humerus
SERRATUS
ANTERIOR
External
intercostals
Internal
intercostals
Rectus
abdominis
(cut)
(a) Anterior deep view
Which muscles originate on the ribs? The vertebrae?
JD/M/L
(b) Anterior deeper view
RHOMBOID
MAJOR
SERRATUS
ANTERIOR
Ribs
204 Chapter 8 The Muscular System
Exhibit 8.7 Muscles That Move the Humerus (Arm Bone) (Figure 8.19)
OBJECTIVE • Describe the origin, insertion, and action of the muscles that move the humerus.
Overview: Of the nine muscles that
cross the shoulder joint, only two of them
(pectoralis major and latissimus dorsi) do not
originate on the scapula.
The strength and stability of the shoulder
joint are provided by four deep muscles of
the shoulder and their tendons: subscapu-
lar^ supraspinatus, infraspinatus, and teres
minor. The tendons are arranged in a nearly
complete circle around the joint, like the cuff
on a shirt sleeve. This arrangement is called
the rotator cuff.
One of the most common causes of
shoulder pain and dysfunction in athletes
is known as impingement syndrome.
The repetitive movement of the arm over
the head that is common in baseball,
overhead racquet sports, lifting weights
over the head, spiking a volleyball, and
swimming puts these athletes at risk for
developing this syndrome. It may also be
caused by a direct blow or stretch injury.
Continual pinching of the supraspinatus
tendon as a result of overhead motions
causes it to become inflamed and results
in pain. If movement is continued despite
the pain, the tendon may degenerate near
the attachment to the humerus and
ultimately may tear away from the bone
(rotator cuff injury). Treatment consists of
resting the injured tendons, strengthening
the shoulder through exercise, and
surgery if the injury is particularly severe.
Relating muscles to movements;
Arrange the muscles in this exhibit accc
to the following actions on the humerus!
the shoulder joint: (1) flexion, (2) exter
(3) abduction, (4) adduction, (5) medii
rotation, and (6) lateral rotation. The same
muscle may be mentioned more than on
■ CHECKPOINT
What is the rotator cuff?
Muscle
Origin
Insertion
Action
Pectoralis major (pek'-to-RA-lis;
pector- = chest; major = greater)
(See also Figure 8.13a.)
Latissimus dorsi (la-TIS-i-mus
DOR-sT; latissimus ~ widest;
dorsi = of the back)
(See also Figure 8.13b.)
Deltoid (DEL-toyd;
deltoid = triangularly shaped)
(See also Figure 8.13a, b.)
Subscapularis (sub-scap'-u-LA-ris;
sub- - below; scapularis = scapula)
Supraspinatus (soo'-pra-spi-NA-tus;
supra- ■ above; spina- = spine
of scapula)
Clavicle, sternum, cartilages of
second to sixth ribs.
Spines of lower six thoracic
vertebrae, lumbar vertebrae,
sacrum and ilium, lower
four ribs.
Clavicle and scapula.
Scapula,
Scapula.
Humerus.
Humerus.
Humerus,
Humerus.
Humerus.
Adducts and rotates arm medially at shoulder joirt
flexes and extends arm at shoulder joint,
Extends, adducts, and rotates arm medially at
shoulder joint; draws arm downward and bacto
Abducts, flexes, extends, and rotates arm at she
Rotates arm medially at shoulder joint.
Assists deltoid muscle in abducting arm at shoud
joint.
Coracobrachialis
(kor'-a-ko-bra-ke-A-lis; coraco =
coracoid process; brachi- =■ arm)
scapula.
numeius.
rtCAca di iu auuuoio at 1 1 r ui ji iuuiu^i juitu.
Principal Skeletal Muscles 205
Figure 8.19 Muscles that move the humerus (arm bone).
£ The strength and stability of the shoulder joint are provided by the tendons of the muscles that form
90fe^ the rotator cuff.
DELTOID (cut)
SUPRASPINOUS
SUBSCAPULAR IS
PECTORALIS ■
MAJOR (cut)
TERES MAJOR
Biceps brachii (cut) —
CORACOBRACHIAL^
LATISSIMUS DORS
Brachialis
Biceps brachii (cut)
Clavicle
PECTORALIS
MAJOR (cut)
Pectoralis minor
- Sternum
Serratus anterior
Anterior deep view (the intact pectoralis major muscle is shown in Figure 8.13a)
* Of the nine muscles that cross the shoulder joint, which two muscles do not originate on the scapula?
206 Chapter 8 The Muscular System
Exhibit 8.8 Muscles That Move the Radius and Ulna (Forearm Bones) (Figure 8.20)
OBJECTIVE * Describe the origin, insertion, and action of the muscles that move the radius and ulna.
Overview: Recall that the elbow joint is a
hfnge joint, capable only of flexion and extension.
The biceps brachii, brachialis, and brachtoradialis
are flexors of the elbow joint; the triceps brachii is
an extensor. Other muscles that move the radius
and ulna are concerned with supination and
pronation. In the limbs, functionally related skeletal
muscles and their associated blood vessels and
nerves are grouped together by deep fascia into
regions called compartments. Thus, in the arm,
the biceps brachii, brachialis, and coracobrachialis
muscles constitute the anterior (flexor)
compartment] the triceps brachii muscle forms
the posterior (extensor) compartment
Relating muscles to movemei
Arrange the muscles in this exh\b\!a££
to the following actions: (1) flexion and
sion of the elbow joint; (2) supination and
pronation of the forearm; and (3) flexion and 1
extension of the humerus. The same muscte
may be mentioned more than once.
■ CHECKPOINT
Which muscles are in the anterior and posl
rior compartments of the arm?
Muscle
Origin
Insertion
Action
Biceps brachii (Bi -ceps
BRA-ke-I; biceps = two heads
of origin; brachi = of the arm)
Brachialis (bra'-ke-A-lis)
Brachioradialis
(bra'-ke-6-ra'-de-A-lis;
radi- - radius) (See Figure 8.21a.)
Triceps brachii (TRi-ceps
BRA-ke-T; triceps = three heads
of origin)
Supinator (SOO-pi-na-tor;
supination = turning palm
forward). (Not illustrated.)
Pronator teres (PRQna-tor
TE-rez; pronation - turning palm
backward) (See Figure 8.21a.)
Scapula.
Humerus.
Humerus,
Scapula and humerus.
Humerus and ulna.
Humerus and ulna.
Radius,
Ulna.
Radius.
Ulna.
Radius.
Radius,
Flexes and supinates forearm at elbow joint; flexes
arm at shoulder joint.
Flexes forearm at elbow joint.
Flexes forearm at elbow joint.
Extends forearm at elbow joint; extends arm at
shoulder joint.
Supinates forearm.
Pronates forearm.
Skeletal Muscles 207
Figure 8.20 Muscles that move the radius and ulna (forearm bones).
The anterior arm muscles flex the forearm, but the posterior arm muscles extend it.
Humerus
Deltoid (cut)
BRACHIALS
Radius
BICEPS BRACHll
Teres major —
TRICEPS
BRACHll:
Long head
Lateral head
Medial head
(a) Anterior view
an 1
(b) Posterior view
What is a compartment?
208 Chapter 8 The Muscular System
Exhibit 8.9 Muscles That Move the Wrist, Hand, and Fingers (Figure 8.21)
OBJECTIVE • Describe the origin, insertion, and action of the m uscles that m ove the wrist, hand, a nd fingers.
Overview: Muscles that move the wrist,
hand, and fingers are located on the forearm
and are many and varied. Their names for the
most part give some indication of their origin,
insertion, or action. On the basis of location
and function, the muscles are divided into two
compartments. The anterior (flexor) com-
partment muscles originate on the humerus
and typically insert on the carpals,
metacarpals, and phalanges. The bellies of
these muscles form the bulk of the proximal
forearm. The posterior (extensor) compart-
ment muscles arise on the humerus and in-
sert on the metacarpals and phalanges.
The tendons of the muscles of the forearm
that attach to the wrist or continue into the
hand, along with blood vessels and nerves,
are held close to bones by fascia, The ten-
dons are also surrounded by tendon sheaths.
At the wrist, the deep fascia is thickened into fi-
brous bands called retinacula (re-ti-NAK-u-la;
retinacul = a holdfast; singular is retinaculum).
The flexor retinaculum is located over the
palmar surface of the carpal bones. Through it
pass the long flexor tendons of the fingers and
wrist and the median nerve. The extensor
retinaculum is located over the dorsal surface
of the carpal bones. Through it pass the exten-
sor tendons of the wrist and fingers.
The carpal tunnel is a narrow passage-
way formed anteriorly by the flexor reti-
naculum and posteriorly by the carpal
bones. Through this tunnel pass the me-
dian nerve, the most superficial structure,
and the long flexor tendons for the digits
(Figure 8,21c). Structures within the
carpal tunnel, especially the median
nerve, are vulnerable to compression, and
the resulting condition is called carpal
tunnel syndrome. Compression of the
median nerve leads to sensory changes
over the lateral side of the hand and
muscle weakness in the thenar eminence.
This results in pain, numbness, and tin-
gling of the fingers. The condition may be
caused by inflammation of the digital
tendon sheaths, fluid retention, excessive
exercise, infection, trauma, and/or repeti-
tive activities that involve flexion of the
wrist, such as keyboarding, cutting hair,
and playing a piano. Treatment may
involve the use of nonsteroidal anti-
inflammatory drugs (such as ibuprofen or
aspirin), wearing a wrist splint, cortico-
steroid injections, or surgery to cut the
flexor retinaculum and release pressure
on the median nerve.
Muscle
Origin
Insertion
Anterior (Flexor) Compartment
Flexor carpi radialis (FLEK-sor
KAR-pe ra'-de-Alis;
flexor - decreases angle at joint;
carpus = wrist; radh = radius)
Flexor carpi ulnaris (ul-NAR-is;
ulnar- - ulna)
Palmaris longus (pal-MA-ris
LON-gus; palma = palm;
longus - long)
Flexor digitorum superf icialis
(soo'-per- fish'-e-A-lis;
digit = finger or toe;
superficial = closer to surface)
Flexor digitorum profundus
(di'-ji-TOR-um pro-FUN-dus
profundus = deep). (Not illustrated.)
Humerus.
Humerus and ulna.
Humerus.
Humerus, ulna,
and radius.
Second and third
metacarpals.
Pisiform, hamate, and
fifth metacarpal.
Flexor retinaculum.
Middle phalanges.
Ulna.
Bases of distal
phalanges.
Posterior (Extensor) Compartment
Extensor carpi radialis longus
(eks-TEN-sor; extensor = increases
angle at joint)
Extensor carpi ulnaris
Extensor digitorum
Humerus.
Humerus and ulna.
Humerus.
Second metacarpal.
Relating muscles to movements:
Arrange the muscles in this exhibit according
to the following actions: (1) flexion, exten-
sion, abduction, and adduction of the wrist
joint and (2) flexion and extension of the
phalanges. The same muscle may be men-
tioned more than once.
■ CHECKPOINT
Which muscles and actions of the wrist.
hand, and digits are used when writing?
Action
Flexes and abducts hand at wrist joint.
Flexes and adducts hand at wrist joint.
Weakly flexes hand at wrist joint.
Flexes hand at wrist joint; flexes phalanges of
finger.
Flexes hand at wrist joint; flexes phalanges of
finger.
Extends and abducts hand at wrist joint.
Fifth metacarpal. Extends and adducts hand at wrist joint.
Second through fifth phalanges. Extends hand at wrist joint; extends phalanges.
Principal Skeletal Muscles 209
lure 8.21 Muscles that move the wrist, hand, and fingers.
The anterior compartment muscles function as flexors, and the posterior compartment muscles function as extensors.
\*s
Biceps brachii
Brachials
Brachial artery
Median nerve
Tendon of biceps brachii
Pronator teres
Brachio radial is
PALMARIS LONGUS
FLEXOR CARPI RADIAUS
FLEXOR CARPI ULNARIS
FLEXOR DIGITORUM
SUPERFICIALIS
Flexor retinaculum
Triceps brachii
Brachioradialis
EXTENSOR CARPI RADIALIS
LONGUS
EXTENSOR CARPI ULNARIS
EXTENSOR DIGITORUM
FLEXOR CARPI ULNARIS
Abductor pollicis longus
Extensor retinaculum
(a) Anterior superficial view
(b) Posterior superficial view
LATERAL
Flexor tendons
MEDIAL
Transverse
plane
Median nerve
Flexor tendon
View
Radial artery
and vein
Wrist bones
Ulnar artery and nerve
Wrist bone
(c) Inferior view of transverse section
Flexor tendons
Wrist bones
Which nerve is associated with the flexor retinaculum?
21 Chapter 8 The Muscular System
Exhibit 8.10 Muscles That Move the Vertebral Column (Backbone) (Figure 8.22)
OBJECTIVE • Describe the origin, insertion, and action of the muscles that move the vertebral column.
Overview: The erector spinae muscles
form the largest muscular mass of the back,
forming a prominent bulge on either side of
the vertebral column (Figure 8.22). It con-
sists of three groups of overlapping muscles:
iliocostalis group (il'-e-d-kos-TA-lis),
longissimus group (ion'-JI-si-mus) f and
spinalis group (spi-NA-lis). Other muscles
that move the vertebral column include
the sternocleidomastoid, quadratus
lumborum, rectus abdominis (see Exhibit
8.4), psoas major (see Exhibit 8.1 1), and
iliacus (see Exhibit 8.1 1).
Full flexion at the waist, as in touching
your toes, overstretches the erector
spinae muscles and muscles that are
overstretched cannot contract effectively.
Straightening up from such a position is
therefore initiated by the hamstring
muscles on the back of the thigh and the
gluteus maximus muscles of the
buttocks.The erector spinae muscles join
in as the degree of flexion decreases.
Improperly lifting a heavy weight,
however, can strain the erector spinae
muscles. The result can be painful muscle
spasms, tearing of tendons and ligaments
of the lower back, and rupturing of inter-
vertebral discs. The lumbar muscles are
adapted for maintaining posture, not for
lifting. This is why it is important to kneel
and use \V\e powertu\ extensor rousdes §\
the thighs and buttocks while lifting a
heavy load.
Relating muscles to movements:
Arrange the muscles in this exhibit acc<
to the following actions on the vertebral
column: (1) flexion and (2) extension.
■ CHECKPOINT
Which groups of muscles make up the
erector spinae?
Muscle
Erector spinae (e-REK-tor
SPI-ne; erector - raise;
spinae = of the spine)
(iliocostalis group, longissimus
group, and spinalis group)
Sternocleidomastoid
(ster'-no-klT-do-MAS-toid;
sternum = breastbone;
cieidO" = clavicle; mastoid^ mastoid
process of temporal bone)
(See Figure 8.13b.)
Quadratus lumborum
(kwod-RA-tus lum-BOR-um;
quadratus = four-sided;
lurnbo= lumbar region).
(See Figure 8.17b.)
Origin
All ribs plus
cervical, thoracic,
and lumbar
vertebrae.
Sternum and
clavicle.
hum
Insertion
Action
Occipital bone,
temporal bone, ribs,
and vertebrae.
Temporal bone.
Twelfth rib and upper
four lumbar vertebrae.
Extends head; extends and laterally flexes verte
column.
Contractions of both muscles flex cervical part oil
vertebral column and flex the head; contraction of
one muscle rotates head toward side opposite
contracting muscle.
Contractions of both muscles extend lumbar parli
the vertebral column; contraction of one muscle I
lumbar part of vertebral column.
Principal Skeletal Muscles 21
Figure 8.22 Major muscles that move the vertebral column (backbone).
, The erector spinae muscles extend the vertebral column.
LONGISSIMUS GROUP
(intermediate)
ILIOCOSTALIS GROUP
(lateral)
SPINALIS GROUP
(media!)
EMASt
Posterior view of erector spinae muscles
Which muscles constitute the erector spinae?
212 Chapter 8 The Muscular System
Exhibit 8.1 1 Muscles That Move the Femur (Thigh Bone) (Figure 8.23)
OBJECTIVE * Describe the origin, insertion, and action of the muscles that move the femur.
Overview: Muscles of the lower limbs are
larger and more powerful than those of the
upper limbs to provide stability, locomotion,
and maintenance of posture. In addition,
muscles of the lower limbs often cross two
joints and act equally on both. The majority
of muscles that act on the femur originate on
the pelvic (hip) girdle and insert on the fe-
mur. The anterior muscles are the psoas ma-
jor and iliacus, together referred to as the
Iliopsoas (il'-e-o-SO-as). The remaining
muscles (except for the pectlneus, adduc-
tors, and tensor fasciae latae) are posterior
muscles. Technically, the pectineus and ad-
ductors are components of the medial com-
partment of the thigh, but they are included
in this exhibit because they act on the thigh,
The tensor fasciae latae is laterally placed.
The fascia lata is a deep fascia of the thigh
that encircles the entire thigh. It is well
developed laterally, where together with the
tendons of the gluteus maximus and tensor
fasciae latae it forms a structure called the
iliotibial tract The tract inserts into the
lateral condyle of the tibia.
The major muscles of the inner thigh func-
tion to move the legs medially. This mus-
cle group is important in activities such as
sprinting, hurdling, and horseback riding.
A rupture or tear of one or more of these
muscles can cause a groin pull. Groin
pulls most often occur during sprinting or
twisting, or from kicking a solid, perhaps
stationary object. Symptoms of a groin
pull may be sudden, or may not surface
until the day after the injury, and include
sharp pain in the inguinal region, swelling,
bruising, or inability to contract the mus-
cles. As with most strain injuries, treat-
ment involves RICE therapy, which stands
for Rest, /ce, Compression, and Elevation.
Ice should be applied immediately, and the
injured part should be elevated and
rested. An elastic bandage should be ap-
plied, if possible, to compress the injured
tissue.
Relating muscles to movements;
Arrange the muscles in this exhibit accor
to the following actions on the thigh at
joint: (1) flexion, (2) extension, (3) abdu<
(4) adduction, (5) medial rotation, and
eral rotation. The same muscle may be
tioned more than once,
■ CHECKPOINT
What forms the iliotibial tract?
Muscle
Psoas major (SO-as;
psoa - a muscle of loin)
Iliacus (il'-e-AK-us;
iliac = ilium)
Gluteus maximus
(GLOO-te-us MAK-si-mus;
glute- = buttock;
maximus = largest)
(See also Figure 8.13b.)
Gluteus rnedius
(ME-de-us; medi- = middle)
(See also Figure 8.13b.)
Tensor fasciae latae
(TEN-sor FA-she-e LA-te;
tensor = makes tense;
fasciae- = of the band;
tat- = wide)
Adductor longus (LONG-us;
adductor = moves part closer
to midline; iongus = long)
Origin
Insertion
Action
Lumbar vertebrae.
Ilium,
Ilium, sacrum, coccyx, and
aponeurosis of sacrospinalis.
lium.
Ilium.
Pubis and pubic symphysis.
Femur.
With psoas major
into femur.
Iliotibial tract of fascia
lata and femur.
Femur.
Tibia by means of the
iliotibial tract,
Femur.
Adductor magnus (MAG-nus;
Pubis and ischium.
Femur.
magnus = large)
Piriformis (pir-i-FOR-mis;
Sacrum.
Femur.
piri- = pear; form- - shape)
Pectineus (pek-TlN-e-us;
Pubis.
Femur.
pectin- = comb-shaped)
Flexes and rotates thigh laterally at the hip joint;
flexes vertebral column.
Flexes and rotates thigh laterally at the hip joint
flexes vertebral column,
Extends and rotates thigh laterally at the hipjoinj
Abducts and rotates thigh medially at the hip joint
Flexes and abducts thigh at the hip joint.
Adducts, medially rotates, and flexes thigh atlhel
joint.
Adducts, flexes, medially rotates and extends
(anterior part flexes, posterior part extends) at tt
hip joint.
Rotates thigh laterally and abducts it at the hip
Flexes and adducts thigh at the hip joint.
Principal Skeletal Muscles 21 3
gure 8.23 Muscles that move the femur (thigh bone).
Most muscies that move the femur originate on the pelvic (hip) girdle and insert on the femur.
ISOR
[FASCIAE
LATAE
[SARTORIUS
ECTUS
'MORIS (cut)
VASTUS
LATERALIS
VASTUS
"MEDIUS
LIS
■LIS
^H tract
"US
FEMORIS (cut)
Ldion of fascia lata
fendon ol quadriceps
pris
-■Patellar ligament
PSOAS
MAJOR
Inguinal
igament
PECTINEUS
ADDUCTOR
LONGUS
GRACILIS
ADDUCTOR
MAGNUS
Patella
(a) Anterior superficial view
Which muscles are part of the quadriceps femoris? The hamstrings?
GLUTEUS
MAXIMUS (cut)
Sciatic nerve
GRACILIS
SARTORIUS
(b) Posterior superficial view
GLUTEUS MEDIUS (cut)
GLUTEUS MINIMUS
PIRIFORMIS
GLUTEUS MAXIMUS (cut)
ADDUCTOR MAGNUS
SEMITENDINOSUS
BICEPS FEMORIS
SEMIMEMBRANOSUS
Vastus lateralis
21 4 Chapter 8 The Muscular System
Exhibit 8.12 Muscles That Move the Femur (Thigh Bone) and Tibia and Fibula (Leg Bones) (See Figure i
OBJECTIVE # Describe the origin, insertion, and action of the muscles that move the femur, tibia, and fibula.
Overview: The muscles that move the fe-
mur, tibia, and fibula originate in the hip and
thigh and are separated into compartments
by deep fascia. The medial (adductor)
compartment is so named because its
muscles adduct the thigh. The adductor
magnus, adductor longus, and pectineus
muscles, components of the medial
compartment, are included in Exhibit 8.1 1
because they act on the femur. The gracilis,
the other muscle in the medial compartment,
not only adducts the thigh but also flexes
the leg. For this reason, it is included in this
exhibit,
The anterior (extensor) compartment is
so designated because its muscles act to ex-
tend the leg at the knee joint, and some also
flex the thigh at the hip joint. It is composed
of the quadriceps femoris and sartortus mus-
cles. The quadriceps femoris muscle is the
largest muscle in the body but has four dis-
tinct parts, usually described as four sepa-
rate muscles (rectus femoris, vastus lateralis,
vastus medialis, and vastus intermedius).
The common tendon for the four muscles is
the quadriceps tendon, which attaches to
the patella. The tendon continues below the
patella as the patellar ligament and
attaches to the tibial tuberosity. The sartorius
muscle is the longest muscle in the body,
extending from the ilium of the hip bone to
the medial side of the tibia. It moves both the
thigh and the leg.
The posterior (flexor) compartment is
so named because its muscles flex the leg
(but also extend the thigh). Included are the
hamstrings (biceps femoris, semitendinosus,
and semimembranosus), so named because
their tendons are long and string-like in the
popliteal area.
A strain or partial tear of the proximal
hamstring muscles is referred to as
"pulled hamstrings" or hamstring
strains. They are common sports injuries
in individuals who run very hard and/or
are required to perform quick starts and
stops. Sometimes the violent muscular ex-
ertion required to perform a feat tears off
part of the tendinous origins of the ham-
strings, especially the biceps femoris,
from the ischial tuberosity. This injury is
usually accompanied by a contusion
(bruising) and tearing of some of the mus-
cle fibers and rupture of blood vessels,
producing a hematoma (collection of
blood) and pain. Adequate training with
good balance between the quadriceps
femoris and hamstrings and stretching ex-
ercises before running or competing are
important in preventing this injury.
Relating muscles to movements
Arrange the muscles in this exhibit acooi
to the following actions on the thigh at the
joint: (1) abduction, (2) adduction, (3)lalai
rotation, (4) flexion, and (5) extension;
according to the following action on the
(1) flexion and (2) extension. The same
muscle may be mentioned more than
■ CHECKPOINT
Which muscle tendons form the medial,
lateral borders of the popliteal fossa?
medial (Adductor) Compartment
Adductor magnus (MAG-nus) ^
Wductorlongus (LONG-us)
Pectineus (pek-TIN-e-us)
Gracilis (GRAS-i-lis;
: = slender)
MS (Extensor) Compartment
Quadriceps femoris
:-ri-seps FEM-or-is;
- four heads of
fegin; femoris - femur)
Rectus femoris (REK-tus
u/'OMs; rectus =
Dht; here, fibers run
parallel to midline)
Vastus lateralis
Muslat'-er-Arlls-
= large;
Blfs = lateral)
Vastus medialis (me -de-A-lis;
Visits = medial)
Vastus intermedi us
ef-ME-de-us;
■'■\odius ~ middle)
Sartorius (sar-TOR-e-us;
tailor; refers to
egged position of tailors)
Longest muscle in the body.
Posterior (Flexor) Compartment
Hamstrings
Biceps femoris
::eps FEM-or-is;
two heads
iginj
Semitendinosus
jBjm'-e-TEN-di-no'-sus;
- = half;
tendon)
Semimembranosus
jsem'-e-MEM-bra-no'-sus;
\hmn- - membrane)
Principal Skeletal Muscles 21 5
Origin
Insertion
Action
See Exhibit 8.11.
Pubic symphysis.
Tibia.
hum.
\
Femur.
Femur.
Femur, j
Ischium and
femur.
Ischium.
Ischium,
Adducts and medially rotates thigh at hip joint; flexes
leg at knee joint.
Patella by means of
quadriceps tendon and
then tibial tuberosity by
means of patellar
ligament.
All four heads extend leg at knee joint; rectus femoris
muscle alone also flexes thigh at hip joint.
Tibia,
Flexes leg at knee joint; flexes, abducts, and laterally
rotates thigh at hip joint, thus crossing leg.
Fibula and tibia.
Flexes leg at knee joint; extends thigh at hip joint.
Tibia.
Flexes leg at knee joint; extends thigh at hip joint.
Tibia.
Flexes leg at knee joint; extends thigh at hip joint.
21 6 Chapter 8 The Muscular System
Exhibit 8.1 3 Muscles That Move the Foot and Toes (Figure 8.24)
OBJECTIVE • Describe the origin, insertion, and action of the muscles that move the foot and toes.
Overview: Muscles that move the foot and
toes are located in the leg. The muscles of
the leg, like those of the thigh, are divided
into three compartments by deep fascia. The
anterior compartment consists of muscles
that dorsiflex the foot. In a situation like that at
the wrist, the tendons of the muscles of the
anterior compartment are held firmly to the
ankle bones by thickenings of deep fascia
called the superior extensor retinaculum
and inferior extensor retinaculum The lat-
eral compartment contains muscles that plan-
tar flex and evert the foot. The posterior com-
partment consists of superficial and deep
muscles. The superficial muscles
(gastrocnemius and soleus) share a common
tendon of insertion, the calcaneal (Achilles) ten-
don, the strongest tendon of the body.
Shinsplint syndroms or simply
shinsplints, refers to pain or soreness
along the medial, distal two-thirds of the
tibia. It may be caused by tendinitis of the
tibialis anterior or toe flexors, inflammation
of the periosteum around the tibia, or
stress fractures of the tibia. The tendinitis
usually occurs when poorly conditioned
runners run on hard or banked surfaces
with poorly supportive running shoes or
walking or running up and down hills. The
condition may also occur as a result of vig-
orous activity of the legs following a period
of relative inactivity. The muscles in the an-
terior compartment (mainly the tibialis an-
terior) can be strengthened to balance the
stronger posterior compartment muscles.
Relating muscles to movements:
Arrange the muscles in this exhibit accorc
to the following actions on the foot: (1) dor
flexion, (2) plantar flexion, (3) inversion,
(4) eversion; and according to the followinj
actions on the toes; (1 ) flexion and (2) e>
sion.The same muscle may be mentioned
more than once.
■ CHECKPOINT
What is the function of the superior and
inferior extensor retinaculum?
Figure 8.24 Muscles that move the foot and toes.
The superficial muscles of the posterior compartment share a common tendon of insertion, the calcaneal
(Achilles) tendon, that inserts into the calcaneal bone of the ankle.
GASTROCNEMIUS (cut)
GASTROCNEMIUS
SOLEUS (cut) — —
TIBIALIS POSTERIOR
SOLEUS
FIBULARIS LGNGUS
FLEXOR DIGITORUM
LONGUS
Calcaneal (Achilles) tendon
Calcaneus
JMWML
[a) Posterior superficial view
(b) Posterior deep view
Principal Skeletal Muscles 21 7
1 !:•:!=.
Origin
Insertion
Action
'Anterior Compartment
lis anterior (tib'-e-A-lis;
; ,; Libia; anterior - front)
jlrtwisor digitorum longus
i- T EN-sordi'"ji-TOR-um LON-gus;
jBnsor= increases angle at joint;
mi finger or toe; longus = long)
Tibia.
Tibia and fibula-
First metatarsal
and first cuneiform.
Middle and distal
phalanges of
four outer toes.
Dorsiflexes and inverts foot.
Dorsiflexes and everts foot; extends toes.
[tiers! Compartment
Flbularis (Peroneus) longus
■VR-is LON-gus)
Fibula and tibia.
First metatarsal and
first cuneiform.
Plantar flexes and everts foot.
^ostmor Compartment
Gastrocnemius (gas'-trok-NE-me-us;
belly; -cnem = leg)
Soleus (SG-le-us;
a type of flatfish)
Hbialis posterior (posterior = back)
tor digitorum longus
lEK-sor; flexor = decreases angle at joint)
Femur.
Fibula and tibia.
Tibia and fibula.
Tibia.
Calcaneus by means
of calcaneal (Achilles) tendon.
Calcaneus by means of
calcaneal (Achilles) tendon.
Second, third, and fourth
metatarsals; navicular; all three
cuneiforms, and cuboid.
Distal phalanges of four
outer toes.
Plantar flexes foot; flexes leg at knee joint.
Plantar flexes foot.
Plantar flexes and inverts foot.
Plantar flexes foot; flexes toes.
TIBIALIS ANTERIOR
GASTROCNEMIUS
FIBULARIS LONGUS
SOLEUS
EXTENSOR
DIGITORUM LONGUS
FLEXOR DIGITORUM
LONGUS
Calcaneal (Achilles)
tendon
Superior extensor
retinaculum
nferior extensor
retinaculum
Jlit/VH—
(c) Anterior superficial view
Which muscle is primarily affected in shinsplint syndrome?
(d) Right lateral superficial view
Body System
The Muscular System
For all body
systems
The muscular system and muscular tissues produce body movements, stabilize body positions,
move substances within the body, and produce heat that helps maintain normal body
temperature.
Integumentary
system
Pull of skeletal muscles on attachments to skin of face causes facial expressions; muscular e*
ercise increases skin blood flow.
Skeletal system
Skeletal muscle causes movement of body parts by pulling on attachments to bones; skeletal
muscle provides stability for bones and joints.
Nervous system
Endocrine
system
Cardiovascular
system
Lymphatic
system and
immunity
Respiratory
system
Digestive
system
Urinary system
§-
Smooth, cardiac, and skeletal muscles carry out commands for the nervous system; shivering-
involuntary contraction of skeletal muscles that is regulated by the brain — generates heat to
raise body temperature.
Regular activity of skeletal muscles (exercise) improves the action of some hormones, such as
insulin; muscles protect some endocrine glands.
Cardiac muscle powers the pumping action of the heart; contraction and relaxation of smooth
muscle in blood vessel walls help adjust the amount of blood flowing through various body
sues; contraction of skeletal muscles in the legs assists return of blood to the heart; regular ei-
ercise causes cardiac hypertrophy (enlargement) and increases the heart's pumping efficiency:
lactic acid produced by active skeletal muscles may be used for ATP production by the heart,
Skeletal muscles protect some lymph nodes and lymphatic vessels and promote the flow of
lymph inside lymphatic vessels; exercise may increase or decrease some immune responses,
Skeletal muscles involved with breathing cause air to flow into and out of the lungs; smooth
muscle fibers adjust the size of airways; vibrations in skeletal muscles of the larynx control air j
flowing past vocal cords, regulating voice production; coughing and sneezing, due to skeletal
muscle contractions, help clear airways; regular exercise improves the efficiency of breathing,
Skeletal muscles protect and support organs in the abdominal cavity; alternating contraction
and relaxation of skeletal muscles power chewing and initiate swallowing; smooth muscle
sphincters control the volume of organs of the gastrointestinal (Gl) tract; smooth muscles in
walls of the Gl tract mix and move its contents through the tract,
Skeletal muscle and smooth muscle sphincters and smooth muscle in the wall of the urinary
bladder control whether urine is stored in the urinary bladder or voided (urination).
Reproductive
systems
218
Skeletal and smooth muscle contractions eject semen; smooth muscle contractions propel
oocytes through uterine tubes, help regulate flow of menstrual blood from the uterus, and force
baby from the uterus during childbirth; during intercourse, skeletal muscle contractions are
sociated with orgasm and pleasurable sensations in both sexes.
Common Disorders 21 9
COMMON
DISORDERS
I muscle function may be abnormal due to disease or damage
nf the components of a motor unit: somatic motor neurons,
iiusi :'iil:ir junctions, or muscle fibers. The term neurommeu-
p disease encompasses problems at all three sites; the term my-
Lriydnl-OP-a-the; -patby = disease) signifies a disease or disor-
;! the skeletal muscle tissue itself
Myasthenia Gravis
heniii gravis (mT-as-THE-ne-a GRAV-is) is an autoimmune
thm causes chronic, progressive damage of die neuromuseu-
- 'i n-iion, In people with myasthenia gravis, the immune system
inappropriately produces antibodies that bind to and block some
tors, thereby decreasing the number of functional ACh
ttptnrs at the motor end plates of skeletal muscles (see figure
Because 75% of patients with myasthenia gravis have hyper-
tumors of the thymus, it is possible that thymic abnormal!-
i cause the disorder, As the disease progresses, more ACh recep-
i lost. Thus, muscles become increasingly weaker, fatigue
ily, and may eventually cease to function.
Iinia gravis occurs in about 1 in 10,000 people and is
iiiin in women, who typically are ages 20 to 40 at onset,
en, who usually are ages 50 to 60 at onset. The muscles of
and neck are most often affected. Initial symptoms include
of the eye muscles, which may produce double vision, and
lilh ulty in swallowing. Later, the person has difficulty chewing
Eventually the muscles of the limbs may become in-
).: I, may result from paralysis of the respiratory muscles,
he disorder does not progress to this stage.
iscular Dystrophy
liiii muscular dystrophy refers to a group of inherited
inning diseases that cause progressive degeneration of
I muscle libers. The most common form of muscular dystro-
W—Duchmne muscular dystrophy (doo-SHAN). Because
nutated gene is on the X chromosome, which males have only
| of, L)\lD strikes boys almost exclusively, (Sex-linked inhcri-
escribed in Chapter 24,) Worldwide, about 1 in every 3500
babies— 21,000 in all— are born with DMD each year. The
I ii i Ily becomes apparent between the ages of 2 and 5,
i parents notice the child falls often and has difficulty running,
;ind hopping. By age 12 most boys with DMD are unable
L Respiratory or cardiac failure usually causes death between
of 20 and 30.
I fa DMD, the gene that codes for the protein dystrophin is mu-
led and little or no dystrophin is present (dystrophin provides
(jural reinforcement for the skeletal muscle filler sarcolemma).
the reinforcing effect of dystrophin, die sarcolemma easily
muscle contraction. Because their plasma membranes
i imscle fibers slowly rupture and die.
Fibromyalgia
Fibromyalgia (night = painful condition) is a painful, nonarticular
rheumatic disorder that usually appears between the ages of 25 and
SO, An estimated 3 million people in the United States suffer from
fibromyalgia, which is 15 times more common in women than in
men. The disorder affects the fibrous connective tissue components
of muscles, tendons, and ligaments. A striking sign is pain that re-
sults from gentle pressure at specific "tender points/' Even without
pressure, there is pain, tenderness, and stiffness of muscles, tendons,
and surrounding soft tissues. Besides muscle pain, those widi fi-
brornyalgia report severe fatigue, poor sleep, headaches, depression,
and inability to cany out their daily activities. Often, a gentle aero-
bic fitness program is beneficial.
Abnormal Contractions of Skeletal Muscle
One kind of abnormal muscular contraction is a spasm, a sudden in-
voluntary contraction of a single muscle in a large group of muscles.
A painful spasmodic contraction is known as a cramp. A tic is a
spasmodic twitching made involuntarily by muscles that are ordi-
narily under voluntary control. Twitching of the eyelid and facial
muscles are examples of tics. A tremor is a rhythmic, involuntary,
purposeless contraction that produces a quivering or shaking move-
ment Afasciailation is an involuntary, brief twitch of an entire mo-
tor unit that is visible under the skin; it occurs irregularly and is not
associated with movement of the affected muscle. Faseiculations
may be seen in multiple sclerosis (see page 237) or in amyotrophic
lateral sclerosis (Lou Gehrig's disease). A. fibrillation is a sponta-
neous contraction of a single muscle fiber that is not visible under
the skin but can be recorded by electromyography. Fibrillations
may signal destruction of motor neurons.
Running Injuries
Nearly 70% of those who jog or run sustain some type of running-
related injury. Most such injuries are minor, but some are quite seri-
ous. In addition, untreated or inappropriately treated minor injuries
may become chronic. Among runners, common sites of injury in-
clude the ankle, knee, calcaneal (Achilles) tendon, hip, groin, foot,
and back. Of these, the knee often is the most severely injured area.
Running injuries are frequently related to faulty training tech-
niques. This may involve improper (or lack of) warm-up routines, run-
ning too much, or running too soon after an injury. Or it might involve
extended running on hard and/or uneven surfaces, Poorly constructed
or worn-out running shoes can also contribute to injury, as can any
biomechanics] problem (such as a fallen arch) aggravated by running.
Most sports injuries should be treated initially with RICE ther-
apy, which stands for Rest, Ice, Compression, and Elevation. Immedi-
ately apply ice, and rest and elevate the injured part. Then apply an
elastic bandage, if possible, to compress the injured tissue. Continue
using RICE for 2 to 3 days, and resist die temptation to apply heat,
which may worsen die swelling. Follow-up treatment may include al-
ternating moist heat and ice massage to enhance blood flow in the in-
jured area. Sometimes ir is helpful to take nonsteroidal anti-inflamma-
tory drugs (NSAIDs) or to have local injections of corticosteroids.
220 Chapter 8 The Muscular System
During the recovery period, it is important to keep active using an al-
ternative fitness program that does not worsen the original injury,
This activity should be determined in consultation with a physician.
Finally, careful exercise is needed to rehabilitate the injured area itself.
-
Effects of Anabolic Streroids
The use of anabolic steroids by athletes has received widespread at-
tention. These steroid hormones, similar to testosterone, are taken
to increase muscle size and strength. The large doses i
produce an effect, however, have damaging, sometimes evendej
taring side effects, including liver cancer, kidney damage, in:.
risk of heart disease, stunted growth, wide mood swings, a 1
creased irritability and aggression. Additionally, females who \
anabolic steroids may experience atrophy of die breasts an
menstrual irregularities, sterility, facial hair growth, and deed
of the voice. Males may experience diminished testosterone ■
i ion, atrophy of the testes, and baldness.
MEDICAL TERMINOLOGY AND CONDITIONS
Electromyography or EMG (e-lek'-tro-rm-OG-ra-fe; electro- =
electricity; myo- = muscle; -graphy — to write) 'I fu: recording
and study of electrical changes that occur in muscular tissue.
Hypertonia (hyper- = above) Increased muscle tone, characterized
by increased muscle stiffness and sometimes associated with a
change in normal reflexes.
Hypotonia (hypo- = below) Decreased or lost muscle tone.
Muscle strain Tearing of a muscle because of forceful impact, ac-
companied by bleeding and severe pain. Also known as a charity
horse or pulled muscle. It often occurs in contact sports and
typically affects the quadriceps femoris muscle on the anterior
surface of the thigh.
Myalgia (mi-AL-je-a; -algia = painful condition) Pain inori
dated with muscles.
Myoma (ml-O-ma; -otmi = tumor) A tumor consisting of
lar tissue.
Myomalacia (mi '-6-ma-LA-she-a; -inalacia = soft) Patholoi
softening of muscle tissue.
Myositis (mi'-o-Sl-tis; -his = inflammation of) Inflammatj
muscle fibers (cells).
Myotonia (mi'-o-TO-ne-a; -tonia = tension) Increased mi
excitability and contractility, with decreased power of
a Lion; tonic spasm of the muscle,
2,
3.
STUDY OUTLINE
Overview of Muscular Tissue (p. 173)
1. The three types of muscular tissue are skeletal muscle, car-
diac muscle, and smooth muscle (summarized in Table 8.1 on
page 1 88).
Skeletal muscle tissue is mostly attached to bones. Tt is striated
and voluntary.
Cardiac muscle tissue forms most of the wall of the heart. It is
striated and involuntary.
4. Smooth muscle tissue is located in viscera. It is nonstriated and
involuntary.
5. Through contraction and relaxation, muscular tissue has live
key functions: producing body movements, stabilizing body po-
sitions, regulating organ volume, moving substances within the
body, and producing beat.
Skeletal Muscle Tissue (p. 173)
1« Connective tissue coverings associated with skeletal muscle in-
clude die epimysium, covering an entire muscle; perimysium,
covering fascicles; and endomysium, covering individual muscle
libers.
2. Tendons are extensions of connective tissue beyond muscle
fibers that attach the muscle to bone.
3. Skeletal muscles are well supplied with nerves and blood 1
sels, which provide nutrients and oxygen for contract]
4. Skeletal muscle consists of muscle fibers (cells) covers
sarcolemma that features tunnel-like extensions, the trans
tubules. The fibers contain sarcoplasm, multiple nuclei,
mitochondria, myoglobin, and sarcoplasmic reticulum.
5. Each fiber also contains myofibrils that contain thin and
filaments. The filaments are arranged in functional units
sarcomeres.
6. Thin filaments are composed of actin, tropomyosin, and
ponin; thick filaments consist of myosin,.
Contraction and Relaxation of Skeletal Muscle (p. 177)
1. Muscle contraction occurs when myosin heads attach &
"walk" along the thin filaments at both ends of a sarc
progressively pulling the thin filaments toward the center i
sarcomere. As the thin filaments slide inward, the Z discs
closer together, and the sarcomere shortens.
2. The neuromuscular junction (NMJ) is the synapse bet
motor neuron and a skeletal muscle fiber. The NMJ inch
the axon terminals and synaptic end bulbs of a motor net
plus the adjacent motor end plate of the muscle fiber
colemma.
Ik motor neuron and all of the muscle fibers it stimulates form a
motor unit. A single motor unit may include as few as 10 or as
[ many as 2000 muscle fibers.
i 'hen a nerve impulse reaches the synaptic end bulbs of a so-
matic motor neuron, it triggers the release of acetylcholine
I (ACh) from synaptic vesicles. ACh diffuses across the synaptic
cleft and binds to ACh receptors, initiating a muscle action po-
tial. Acetylcholinesterase then quickly destroys ACh.
I An increase in the level of Ca 2 in the sarcoplasm, caused by
I the muscle action potential, starts the contraction cycle; as a
decrease in the level of Ca 2+ turns off the contraction cycle.
Tin contraction cycle is die repeating sequence of events that
causes sliding of the filaments: (1) myosin ATPase splits ATP
and becomes energized, (2) the myosin head attaches to actio
forming: a crossbridge, (3) the crossbridge generates force as it
vels or rotates toward the center of the sarcomere (power
stroke), and (4) binding of AFP to myosin detaches myosin from
acrin. The myosin head again splits ATP, returns to its original
position, and binds to a new site on actin as the cycle continues.
active transport pumps continually remove Ca 2 from
arcoplasm into the sarcoplasmic reticulum (SR). When
level of Ca 2 ' in the sarcoplasm decreases, the
troponin- tropomyosin complexes slide back over and cover
lemyosin-binding sites, and the muscle fiber relaxes.
ntinual involuntary activation of a small number of motor units
duces muscle tone, which is essential for maintaining posture.
ihtabolism of Skeletal Muscle Tissue (p. 180)
Muscle libers have three sources for ATP production: creatine
phosphate, anaerobic cellular respiration, and aerobic cellular
respiration,
'The transfer of a high-energy phosphate group from creatine
phosphate Co ADP forms new ATP molecules. 'Together, crea-
phosphate and ATP provide enough energy for muscles to
contract maximally for about 15 seconds.
isc is converted to pyruvic acid in the reactions of glyeoly-
hich yield two ATPs without using oxygen. These anaero-
■. actions can provide enough ATP for about 30 to 40 sec-
onds of maximal muscle activity.
Muscular activity that lasts longer than half a minute depends
on aerobic cellular respiration, mitochondrial reactions that re -
quire oxygen to produce ATP. Aerobic cellular respiration
Lids about 36 molecules of ATP from each glucose molecule.
|h, inability of a muscle to contract forcefully after prolonged
p ',ii. i,, is muscle fatigue.
Elevated oxygen use after exercise is called recovery oxygen up-
Control of Muscle Tension (p. 183)
\ twitch contraction is a brief contraction of all the muscle
fibers in a motor unit in response to a single action potential,
cord of a contraction is called a myogram. It consists of a
latent period, a contraction period, and a relaxation period.
IVave summation is the increased strength of a contraction that
occurs when a second stimulus arrives before the muscle has
iinpletely relaxed after a previous stimulus.
Study Outline 221
4. Repeated stimuli can produce unfused tetanus, a sustained mus-
cle contraction with partial relaxation between stimuli; more
rapidly repeating stimuli will produce fused tetanus, a sustained
contraction without partial relaxation between stimuli.
5. Motor unit recruitment is die process of increasing the number
of active motor units*
6. On the basis of their structure and function, skeletal muscle
libers are classified as slow oxidative (SO), fast oxidative-
glycolytic (FOG), and fast glycolytic (FG) fibers.
7. Most skeletal muscles contain a mixture of all three liber types;
their proportions vary with the typical action of the muscle.
8. The motor units of a muscle are recruited in the following-
order: first SO libers, then FOG fibers, and finally FG fibers.
9. In an isometric contraction, there is no change in the length of
a muscle, but the muscle develops considerable tension. In an
isotonic contraction, there is a change in the length of a mus-
cle, but no change in its tension.
Exercise and Skeletal Muscle Tissue (p. 186)
1 . Various types of exercises can induce changes in die fibers in a
skeletal muscle. Endurance-type (aerobic) exercises cause a
gradual transformation of some fast glycolytic (FG) fibers into
fast oxidative-glycolytic (FOG) libers.
2. Exercises that require great strength for short periods produce
an increase in the size and strength of fast glycolytic (FG)
libers. The increase in size is due to increased synthesis of thick
and diin filaments.
Cardiac Muscle Tissue (p. 186)
1. Cardiac muscle tissue, which is striated and involuntary, is
found only in the heart.
2. Each cardiac muscle fiber usually contains a single centrally
located nucleus and exhibits branching.
3. Cardiac muscle fibers are connected by means of intercalated
discs, which hold the muscle fibers together and allow muscle
action potentials to quickly spread from one cardiac muscle
fiber to another.
4. Cardiac muscle tissue contracts when stimulated by its own au-
torhydimic fibers. Due to its continuous, rhythmic activity,
cardiac muscle depends greatly on aerobic cellular respiration
to generate ATP.
Smooth Muscle Tissue (p. 186)
1. Smooth muscle tissue is nonstriated and involuntary
2. In addition to thin and thick filaments, smooth muscle fibers
contain intermediate filaments and dense bodies.
3. Visceral (single-unit) smooth muscle is found in the walls of
hollow viscera and of small blood vessels. Many visceral fibers
form a network that contracts in unison.
4. Multiunit smooth muscle is found in large blood vessels, large
airways to the lungs, arrector pili muscles, and the eye. The
fibers contract independently rather than in unison.
5. The duration of contraction and relaxation is longer in smooth
muscle than in skeletal muscle.
222 Chapter 8 The Muscular System
6. Smooth muscle fibers can be stretched considerably and still
retain the ability to contract,
7. Smooth muscle fibers contract in response to nerve impulses,
stretching, hormones, and local factors.
Aging and Muscular Tissue (p. 187)
1. Beginning at about 30 years of age, there is a slow, progressive
loss of skeletal muscle, which is replaced by fibrous connective
tissue and fat.
2. Aging' also results in a decrease in muscle strength, slower mus-
cle reflexes, and loss of flexibility.
How Skeletal Muscles Produce Movement (p. 188)
1, Skeletal muscles produce movement by pulling on tendons
attached to bones.
2. The attachment to the stationary bone is the origin. The
attachment to the movable bone is the insertion.
3. The prime mover (agonist) produces the desired action.
antagonist produces an opposite action. The syncrgi
the prime mover by reducing unnecessary movement
fixator stabilizes the origin of the prime mover so that it cam
more efficiently.
Principal Skeletal Muscles (p. 189)
1. The principal skeletal muscles of the body are grouped at
ing to region, as shown in Exhibits 8.1 through 8.13.
2. In studying muscle groups, refer ro Figure 8.13 on
1 92 -193 to see how each group is related to all others
3. The names of most skeletal muscles indicate specific charat
is tics,
4. The major descriptive categories are direction of fibers,
tion, size, number of origins (or heads), shape, origin and ii
turn, and action (see Table 8.2 on page 191).
12
SELF-QUi;
1. The characteristic of muscular tissue that allows it to return to
its original shape after contraction is
a. extensibility 7 b. excitability c. fused tetanus
d. contractility e. elasticity
2. Match the connective tissue coverings with their locations:
a. wraps an entire muscle A. endomysium
_ b. lies immediately tinder the skin **• deep fascia
c. separates muscle into functional C ' penmysium
groups D.epimysmm
. , i ■ l- ■ i i i E, superficial
d. surrounds each individual muscle r ■
,,. fascia
fiber
e. divides muscle fibers into fascicles
3. Which of the following statements about skeletal muscle tissue
is NOT true?
a. Skeletal muscle requires a large blood supply.
b. Skeletal muscle fibers have many mitochondria.
»
c. The arrangement of thick and thin filaments produces the
striatums in skeletal muscle tissue.
d. Skeletal muscle fibers contain gap junctions that help con-
duct action potentials from one fiber to another.
e. A skeletal muscle fiber has many nuclei*
4. Match the following:
a. network of tubules that stores A, thick filaments
calcium B. transverse
b. pigment that stores oxygen tubules
c. composed of myosin C. sarcoplasmic
f if*. ■ reticulum
d. composed or actin, tropomyosin, ^ i x .
. r . r D. mvoglobm
and troponin r , : ?i
L. thin n laments
e. tunnel-like extensions of
sarcolemma
5. The sarcolemma is the equivalent of the
a. cytoplasm b, nucleus c. plasma membrane
d. endoplasmic reticulum c. mitochondria
6, You begin an intensive weightli fling plan because you want to i
ter a weightlifting contest. During the activity of weightlif
your skeletal muscles will obtain en erg) 7 (ATP) primarily til
a. anaerobic cellular respiration h. the complete break-
down of pyruvic acid in the mitochondria c* hyperplasia!
d. hypertrophy e. aerobic cellular respiration
7, Which of the following events of skeletal muscle contrac
does NOT occur during the latent period?
a. Sarcomeres shorten.
b. Action potentials conduct into the T tubules.
t\ The concentration ol calcium ions increases in the sar-
co plasm,
d. Myosin-binding sites on the thin filaments are exposed;
e. Calcium release channels in the sarcoplasmic reticulum
open,
8. For each of the following descriptions, indicate if it reft
skeletal muscle, cardiac muscle, or smooth muscle. Use the
breviations SK for skeletal, CA for cardiac, i\m\ S.V1 for
The same response may be used more than once,
a. involuntary
b* multinucleated
c. striated
d» contain intercalated discs
e. elongated, cylindrical cells
f. voluntary
g. cells that taper at both ends
h. n on stria ted
i. muscle fibers con tr a etindivi dually
j. autorhythmic
i, ATP in the sarcoplasin is exhausted, the muscle must
Bpy tm to quickly produce more ATP from A DP for
.n traction.
fi> acetylcholine b. creatine phosphate c. lactic acid
d. pyruvic acid e. acetylcholinesterase
J), A motor unit consists of
i, i transverse tubule and its associated sarcomeres
! .l motor neuron and all of the muscle fibers it stimulates
, ,i muscle and all of its motor neurons
Id ail of the filaments encased within a sarcomere
I e. the motor end plate and the transverse tubules
■[Thick filaments
la. include aetin, troponin, and tropomyosin
lb. compose the T band
ri.l i i he entire length of a sarcomere
I have binding sites for Ca 2 ""
myosin heads (crossbridges) used for the power stroke
chemical that prevents the continuous stimulation of a
muscle fiber is
I a. ( b. acetylcholinesterase c. ATP
A, acetylcholine e. troponin -tropomyosin
A) of the following is NOT associated with muscle fa-
tigue?
i. depletion of creatine phosphate b* lack of oxygen
c, decrease in Ca 2 + levels in the sarcoplasm
I decrease in lactic acid levels e. lack of glycogen
B, All ol rln.: following may result in an increase in muscle size
ccr.Pi
,i, denervation atrophy b. weight training
c. human growth hormone d. testosterone
tonic contraction
etal muscles are named using several characteristics. Which
cteristic is NOT used to name skeletal muscles?
,i, direction of fibers b. size c. speed of contraction
I location e, shape
II- the following in the correct order for skeletal muscle
i contraction,
I Sarcoplasmic reticulum releases
u .
2, Gi combines widi troponin.
Acetylcholine is released from
the axon terminal.
4, Action potential travels into
transverse tubules.
5, Energized myosin heads
krussbridges) attach to aetin.
6, Thin filaments slide toward the
ter of the sarcomere.
a. 3,4, 1, 2, 5, 6
b. 4, 3, 2, L 5,6
c. 1,2,3,4,5,6
d. 4,1,3,5,2,6
e. 3, 1, 4, 5, 2, 6
Self-Quiz 223
17. Your instructor asks you to pick up a box of books and carry
them to the library in another building. You try to pick up the
box, but the box is too heavy to move. Which of the following
types of muscle contractions would you be utilizing?
a. hypertonic b. isotonic only t\ spastic
d. isometric only e. isometric and isotonic
18. Match the following:
a. extends and laterally
rotates thigh at the hip
joint
b. add nets and medially
rotates thigh at the hip
joint
c« compresses abdomen
and flexes vertebral
column
d. flexes the neck
e* flexes and abducts wrist
joint
f. extends phalanges
g« addncts and rotates arm
medially at shoulder
joint
h. extends lei( at the knee
and flexes thigh at hip
joint
i. plantar flexes foot at
ankle joint and flexes leg
at knee joint
j* dorsi flexes and inverts
foot
k. abducts, flexcs ? extends,
and rotates arm at
shoulder joint
1. elevates clavicle;
depresses or elevates
scapula
m. elevates mandible;
closes mouth
ii- wrinkles skin of fore-
head horizontally as in a
look of surprise
o. extends, adducts, and
rotates arm medially at
shoulder joint
A. trapezius
B. flexor carpi radial is
C. tibialis anterior
D. adductor long us
E. gluteus maximus
E quadriceps group
G. rectus abdominis
H. sternocleidomastoid
I. frontal belly of
occi pi to frontalis
J. gastrocnemius
K. deltoid
L. masse ter
M. extensor digitorum
N. iatissimus dorsi
O. pectoral is major
224 Chapter 8 The Muscular System
19. Match the following:
a, extend from the thick
filaments
b. contain myosin-bi tiding site
c, dense area that separates sarcomeres
d, contain acetylcholine
e. striated zone of the sarcomere com-
posed of thick and thin filaments
_ f, space between axon terminal and the
sarcolemma
g. striated /one of the sarcomere com-
posed of thin filaments only
h. region of sarcolemma near the ad-
joining axon terminal
A. I hand
B. synaptic vesicles
C. myosin heads
D. Z discs
E« motor end plate
K actin molecules
G. A band
H. synaptic cleft
f
CRITICAL THINKING APPLICATIONS
2,
The newspaper reported several cases of botulism poisoning;
following a fund-raiser pothick dinner for the local clinic. The
cause appeared to be three-bean salad "flavored" with the bac-
terium Clostridium Imtulmum. What would be the result of bot-
ulism poisoning on muscle function?
Alis nephew was squealing with laughter. She was entertaining
him by sticking her thumb in her pursed lips, raising her eye-
brows, pumping her arm up and down, and puffing her cheeks in
and out. Name the muscles All was using to maneuver her face.
v
5
ANSWERS TO FIGURE QUESTION
8.1 In order from the inside toward the outside, the connective
tissue layers are endomysium, perimysium, and epimysium.
8.2 The A band is composed of thick filaments in its center and
overlapping thick and thin filaments at each end; the 1 band
is composed of thin filaments.
8.3 A band: myosin, aetin, troponin, and tropomyosin. I band:
actio, troponin, and tropomyosin.
8.4 The 1 bands disappear. The lengths of the thick and thin
filaments do not change.
8.5 The motor end plate is the region of the sarcolemma near
the axon terminal.
8.6 ISimling of AIT to the myosin heads detaches them from actio.
8.7 The power stroke occurs during step 6.
8.8 Glycolysis, exchange of phosphate between creatine phosphate
and ADP, and glycogen breakdown occur in the cytosol. Oxida-
tion of pyruvic acid, amino acids, and fatty acids (aerobic cellu-
lar respiration) occurs in die mitochondria.
8.9 Sarcomeres shorten during the contraction period.
8.10 Fused tetanus occurs when the frequency of stimulation
reaches 80 to 1 00 stimuli per second,
8.11 The walls of hollow organs contain visceral (single-unit)
smooth muscle.
8.12 The prime mover or agonist produces the desired action.
20. Matching the following:
a.
works with prime mover to reduce
un n ece ssa ry m ov em en t
A.
insertion
th
muscle in a group that produces de-
B.
origin
sired movement
C.
synergist
^
stationaty end of a muscle
D.
antagonist
d.
muscle that has an action opposite
to that of another muscle
E.
E
prime mover 1
fixator
e.
helps stabilize the origin of the
prime mover
f.
the end of a muscle attached to the
movable bone
3. When her cast finally came off after six long wedfij
thought she'd be all set to rejoin her volleyball team, but
her left thigh is only half the size of her right. Explain wl
happened to her thigh and what she needs to do to gee ba
the game.
4. The coach of the track team has his athletes erosstrai
They ran 10 miles on Monday, then on Tuesday the) if
weights. How do these types of exercise affect the muscles?
8.13 The following are some possible responses (there arej
correct answers): direction of fibers — external
shape — deltoid; action — extensor digitorum; size — gi
maximus; origin and insertion — sternocleidomastoid;
tion — tibialis anterior; number of origins — biceps bra
8.14 Smiling — zygoinaticus major; pouting — pin
squ i nting — orbicularis oculi .
8. 15 The superior oblique passes through the trochlea.
8.16 The rectus abdominis aids in urination.
8.17 The diaphragm and external intcrcosrals contract tluri
normal quiet inhalation.
8.18 The pectoralis minor and serratus anterior have origins
the ribs; the trapezius, levator scapulae, and rhomboid
have origins on the vertebrae.
8.19 The pectoralis major and latissimus dorsi are muscles
cross the shoulder joint but do not originate on the sen
8.20 A compartment is a group of functionally related ske
muscles in a limb, along with their blood vessels and ne
8.21 The median nerve is associated with the flexor retina
8.22 The iliocostalis, longissimus, and spinalis constitute
erector spinae.
8.23 Quadriceps femoris — rectus fernoris, vastus lateralis,
medialis, and vastus intermedins; hamstxings-J
femoris, semitendinous, semimembranosus.
8.24 Shinsplint syndrome affects the tibialis anterior.
*►
NERVOUS TISSUE
^
*,?■
chapter 9
■ ■'•••
iirfjfoi/ know?
Uepression is characterized by a
mixture of psychological and physical symptoms,
ml is marked by changes in nervous system function.
mmsion is associated with imbalances in some of the
tkmuals that transmit messages between nerve cells.
These chemicals are called neurotransmitters.
Sometimes not enough of a neurotransmitter is
mluceii Other times the nerve cells do not respond to
the neurotransmitter as they should. One of the
neurotransmitters that plays an important role in
impression is serotonin. Psychologists do not yet know
ther the feelings of depression cause or are caused
by neurotransmitter changes.
I Focus on Wellness, page 236
T
www.wiley.com/college/apcentral
Jffe-
ogether, all nervous
tissues in the body comprise
the nervous system. Among the
1 1 body systems, the nervous
system and the endocrine
system play the most important
roles in maintaining homeostasis. The nervous system,
the subject of this and the next three chapters, can re-
spond rapidly to help adjust body processes using nerve
impulses. The endocrine system typically operat
more slowly and exerts its influence on homeostasis by
releasing hormones that the blood delivers to cells
throughout the body. Besides helping maintain
homeostasis, the nervous system is responsible for our
perceptions, behaviors, and memories. It also initiates all
voluntary movements. The branch of medical science
that deals with the normal functioning and disorders ot
the nervous system is called neurology (noo-ROL-6-je;
neuro- = nerve or nervous system; -log} 1 = study of).
looking back to move ahead
« Ion Channels (page 48)
• Sodium-potassium Pump (page 50)
• Nervous Tissue (page 90)
• Sensory Nerve Endings and Sensory Receptors
in the Skin (page 100)
• Release of Acetylcholine at the Neuromuscular
Junction (page 179)
225
226 Chapter 9 Nervous Tissue
OVERVIEW OF THE
NERVOUS SYSTEM
OBJECTIVES • List the structures and basic functions
of the nervous system,
• Describe the organization of the nervous system.
Structures of the Nervous System
The nervous system Is an intricate, highly organized network
of billions of neurons and even more neuroglia. The struc-
tures that make up the nervous system include the brain, cra-
nial nerves and their branches, the spinal cord, spinal nerves
and their branches, ganglia, enteric plexuses, and sensory re-
ceptors (Figure 9.1).
The skull encloses the brain, which contains about 100
billion neurons, Twelve pairs (right and left) of cranial
nerves, numbered I through XII, emerge from the base of
the brain. A nerve is a bundle of hundreds to thousands of
axons plus associated connective tissue and blood vessels that
lie outside the brain and spinal cord. Kach nerve follows a de-
fined path and serves a specific region of the body For exam-
lies
pie, cranial nerve I carries signals for the sense of smell
the nose to the brain.
The spinal cord connects to the brain and is encirch
the bones of the vertebral column. It contains about 100
lion neurons. Thirty-one pairs of spinal nerves emerge
the spinal cord, each serving a specific region on the rig!
left side of the body. Ganglia (GANG-le-a = swelling
knot) are small masses of nervous tissue that are located
side the brain and spinal cord. Ganglia contain cell hot
neurons and are closely associated with cranial and s
nerves. In the walls of organs of the gastrointestinal met
extensive networks of neurons, called enteric plexuses
help regulate the digestive system (Figure 9.1). Sfl
receptors are either the dendrites of sensory neurons (sfl
sensory receptors in the skin) or separate, specialized
that monitor changes in the internal or external environ
(such as photoreceptors in the retina of the eye).
Functions of the Nervous System j
The nervous system carries out a complex array of tasks,
as sensing various smells, producing speech, rememlg
past events, providing signals that control body mi
Figure 9.1 Major structures of the nervous system.
The nervous system includes the brain, cranial nerves, spinal cord, spinal nerves, ganglia, enteric plexuses, and sensory r<
PNS
Cranial
nerves
CMS:
Spinal
cord
5>
What is the total number of cranial and spinal nerves in your body?
PNS;
Enteric
plexuses
in small
intestine
regulating the operation of internal organs. These di-
ie activities can he grouped into three basic functions:
pry, integrative, and motor.
Sensory Junction, The sensory receptors detect many dif-
ferent types of stimuli, both within your body, such as an
increase in blood temperature, and outside your body,
such as a touch on your arm. Sensory or afferent neurons
(AF-er-ent NOOR-onz; af = toward; -ferrent = carried)
carrv this sensory information into the brain and spinal
[cord through cranial and spinal nerves.
Integrative function. The nervous system integrates
processes) sensory information by analyzing and storing
of it and by making decisions for appropriate re-
sponses. An important integrative function is perception,
the conscious awareness of sensory stimuli. Perception
occurs in the brain. Many of the neurons that participate
in integration are interneurons, whose axons extend for
| only a short distance and contact nearby neurons in the
brain or spinal cord. Interneurons comprise the vast ma-
jority of neurons in die body.
Motor function. Once a sensory stimulus is perceived,
the nervous system may elicit an appropriate motor re-
bonse such as muscle contraction or gland secretion.
ih; neurons that serve this function are motor or
efferent neurons (EF-er-ent; ef- = away from). Motor
neurons carry information from the brain toward the
spinal cord or out of the brain and spinal cord to effectors
[muscles and glands) through cranial and spinal nerves.
Stimulation of the effectors by motor neurons causes
muscles to contract and glands to seen
i
Overview of the Nervous System 227
Organization of the Nervous System
The two main subdivisions of die nervous system are the cen-
tral nervous system (CNS), which consists of the brain and
spinal cord, and the peripheral (pe-lUF-er-al) nervous system
(PNS), which includes all nervous tissue outside the CNS,
The CNS integrates and correlates many different kinds of
incoming sensory information. The CNS is also the source
of thoughts, emotions, and memories. Most nerve impulses
that stimulate muscles to contract and glands to secrete origi-
nate in the CNS. Structural components of the PNS are cra-
nial nerves and their branches, spinal nerves and their
branches, ganglia, and sensory receptors. Figure 9.2 shows
the further functional subdivision of the PNS into a somatic
nervous system (SNS) {somtit- — body), an autonomic
nervous system (ANS) (auto- = self; -mmiic = law), and an
enteric nervous system (ENS) (enter- - intestines). The so-
matic nervous system consists of (1) sensory neurons that
convey information from somatic receptors in the head, body
wall, and limbs and from receptors lor the special senses of
vision, hearing, taste, and smell to the CNS and (2) motor
neurons that conduct impulses from the CNS to skeletal mus-
cles only. Because these motor responses can be consciously
controlled, the action of this part of the PNS is voluntary.
The ANS (the focus of Chapter 11) consists of (1) sensory
neurons that convey information from autonomic sensory re-
ceptors, located primarily in visceral organs such as the stom-
ach and lungs, to the CNS, and (2) motor neurons that con-
duct, nerve impulses from the CNS to smooth muscle, cardiac
muscle, and glands* Because its motor responses arc not nor-
mally under conscious control, die action of the ANS is invol-
Figure 9,2 Organization of the nervous system. Subdivisions of the PNS are the somatic nervous system (SNS), the
autonomic nervous system (ANS), and the enteric nervous system (ENS).
The two main subdivisions of the nervous system are (1) the central nervous system (CNS), consisting of the brain and
spinal cord, and (2) the peripheral nervous system (PNS), consisting of all nervous tissue outside the CNS.
SNS
Somatic and special
sensory receptors and
neurons
~N
v
/
ANS
Autonomic sensory
receptors and neurons
->
CNS:
brain and
spinal cord
Somatic motor
neurons (voluntary)
—
S
Autonomic motor
neurons (involuntary):
sympathetic and
parasympathetic
divisions
N
ENS
Sensory receptors and
neurons in Gl tract and
enteric plexuses
Smooth muscle,
cardiac muscle,
and glands
_r
C>
Enteric motor neurons
(involuntary) in enteric
plexuses
3
Smooth muscle,
glands, and endocrine
cells of G I tract
Sensory part of PNS
Motor part of PNS
Effectors
Which types of neurons carry input to the CNS and output from the CNS?
228 Chapter 9 Nervous Tissue
untaiy. The motor part of: the ANS consists oi two divisions,
the sympathetic division and the parasympathetic division. With a
few exceptions, effectors are innervated by both divisions,
and usually the two divisions have opposing actions. For ex-
ample, sympathetic neurons speed the heartbeat, and
parasympathetic neurons slow it down. In general, the sym-
pathetic division helps support exercise or emergency ac-
tions, so-called "ligiit-or-flight" responses, and the parasym-
pathetic division takes care of "rest-and-digest" activities.
The enteric nervous system is the "brain of the gut/ 1 and
its operation is involuntary. Its neurons extend most oi the
length of the gastrointestinal (GI) tract. Sensor) 7 neurons of
the enteric nervous system monitor chemical changes within
the GI tract and the stretching of its walls. Enteric motor
neurons govern contraction of Gl tract smooth muscle, se-
cretions of the GI tract organs, such as acid secretion by the
stomach, and activity of GI tract endocrine cells.
■ CHECKPOINT
1. What are the components of the CNS and PNS?
2. What kinds of problems would result from damage of
sensory neurons, interneurons, and motor neurons?
3. What are the components and functions of the somatic,
autonomic, and enteric nervous systems? Which subdivi-
sions have involuntary actions?
HISTOLOGY OF NERVOUS
TISSUE
OBJECTIVES • Contrast the histological characteris-
tics and the functions of neurons and neuroglia.
• Distinguish between gray matter and white matter.
Nervous tissue consists of two types of cells: neurons and neu-
roglia. Neurons (nerve cells) are the basic information-process-
ing units of the nervous system and are specialized for nei*ve im-
pulse (action potential) conduction. They provide most of the
unique functions of die nervous system, such as sensing, think-
ing, remembering, controlling muscle activity, and regulating
glandular secretions. Neuroglia (noo-ROG-le-a; glia = glue)
support, nourish, and protect the neurons and maintain home-
ostasis in the interstitial fluid that bathes neurons.
Neurons
Neurons usually have three parts: (1) a cell body, (2) den-
drites, and (3) an axon (Figure 9.3). The cell body contains a
nucleus surrounded by cytoplasm that includes typical or-
ganelles such as rough endoplasmic reticulum, lysosomes,
mitochondria, and a Golgi complex. Most cellular molecules
needed for a neuron's operation are synthesized in
body.
Two kinds of processes (extensions) emerge fremiti
body of a neuron: multiple dendrites and a single axon,
cell body and the dendrites {— little trees) are the r
or input parts of a neuron. Usually, dendrites are si
pering, and highly branched, forming a tree-shaped
processes that emerge from the cell body. The second
process, the axon, conducts nerve impulses toward I
neuron, a muscle fiber, or a gland cell. An axon is i
thin, cylindrical projection that often joins the cell IhhIv;
cone-shaped elevation called the axon hillock (= sma
Nerve impulses usually arise at the axon hillock audi
travel along the axon. Some axons have side branches
axon collaterals. The axon and axon collaterals end by difl
into many fine processes called axon terminals.
The site where two neurons or a neuron and an ilia
cell can communicate is termed a synapse. The tips of
a\on terminals swell into synaptic end bulbs. These
shaped structures contain synaptic vesicles^ tiny sacs that st
chemicals ca 1 1 ed neurotransmitters. ' I 'he neurotransml
molecules released from synaptic vesicles are the me
communication at a synapse.
Myelination
The axons of most neurons are surrounded by a myt
sheath, a many-layered covering composed of lipid and
tein (Figure 93). Like insulation covering an electrical
the myelin sheath insulates the axon of a neuron ami
creases the speed of nerve impulse conduction. As von
learn shortly, Schwann cells in the PNS and oligodenj
cytes in the CNS produce myelin sheaths by wrappings
selves around and around axons. Eventually, as man
layers cover the axon, much as multiple layers of paper
the cardboard tube in a roll of toilet paper. Gaps in
myelin sheath, called nodes of Ranvier (RQN-ve-a), aj
at intervals along the axon (Figure 9.3). Axons with a myi
sheath are said to be myelinated, and those without it are;
to be unmyelinated.
The amount of myelin increases from birth to mat
and its presence greatly increases the speed of nerve
conduction. By the time a baby starts to talk, most m)
sheaths are partially formed, but myelination continues intoi
teenage years. An infant's responses to stimuli are neidy
rapid nor as coordinated as those of an older child or in
in part because myelination is still in progress during
Certain diseases, such as multiple sclerosis (see page 23
lay-Sachs disease (see page 56), destroy myelin sheaths.
Gray and White Matter
In a freshly dissected section of the brain or spinal
some regions look white and glistening, and others aj
Histology of Nervous Tissue 229
Figure 9.3 Structure of a typical multipolar neuron. Arrows indicate the direction of information flow:
dendrites -* ceil body -* axon -» axon terminals -* synaptic end bulbs.
■ Th
The basic parts of a neuron are several dendrites, a cell body, and a single axon.
M
CELL BODY
Axon collateral
AXON
•,
Axon hillock
Mitochondrion
Nucleus of
Schwann cell
DENDRITES
Nucleus
Cytoplasm
Rough endoplasmic
reticulum
U*
Schwann cell:
- Cytoplasm
- Myelin sheath
- Plasma membrane
Node of Ranvier
r
i
SS:
V
Axon terminal
'
;
Synaptic end bulb
4
What roles do the axon and axon terminals play in the communication of one neuron with another?
230 Chapter 9 Nervous Tissue
gray. The white matter of nervous tissue consists primarily of
myelinated axons of many neurons. The whitish color of
myelin gives white matter its name. The gray matter of ner-
vous tissue contains neuronal cell bodies, dendrites, unmyeli-
nated axons, axon terminals, and neuroglia. It looks grayish,
rather than white, because the cellular organelles impart a
gray color and there is little or no myelin in these areas.
Blood vessels are present in both white and gray matter.
In the spinal cord, the outer white matter surrounds an
inner core of gray matter shaped like a butterfly or the letter
H (see Figure 10.1 on page 243). In the brain, a thin shell of
gray matter (cortex) covers the surface of the largest parts of
the brain, the cerebrum and cerebellum (see Figures 10.10
and 10.1 I on pages 254 and 256, respectively). When used to
describe nervous tissue, a nucleus is a cluster of neuronal cell
bodies within the CNS. (Recall that the term ganglion refers
to a similar arrangement within the PNS). Many nuclei of
gray matter lie deep within the brain. Much of the CNS
white matter consists of tracts, which are bundles of axons in
the CNS that extend for some distance up or down the spinal
cord or connect parts of the brain with each other and with
the spinal cord. (Recall that the term nerve refers to a bundle
of axons in the PNS).
Human neurons have very limited powers of regenera-
tion, the capability to replicate or repair themselves. In
the PNS, axons and dendrites may undergo repair if the
cell body is intact and if the Schwann cells are functional.
The Schwann cells on either side of an injured site multi-
ply by mitosis, grow toward each other, and may form a
regeneration tube across die injured area. The tube
guides axonal regrowth from the proximal area across the
injured area into the distal area previously occupied by die
original axon. Regrowth is slow, in part, because many
needed materials must be transported from their sites of
synthesis in the cell body several inches or feet down the
axon to the growth region. New axons cannot grow if the
gap becomes filled with scar tissue. In the CNS, even
when the cell body remains intact, a cut axon is usually not
repaired, The presence of CNS myelin is one factor that
actively inhibits regeneration of neurons.
Neuroglia
Neuroglia constitute about half the volume of the CNS.
Their name derives from the idea of early histologists that
they were the "glue" that held nervous tissue together. We
now know that neuroglia are not merely passive bystanders
but rather active participants in the operation of nervous tis-
sue. Generally, neuroglia are smaller than neurons, and they
are 5 to 50 times more numerous. In contrast to neurons, glia
do not generate or conduct nerve impulses, and they can
multiply and divide in the mature nervous system. In cases of
injury or disease, neuroglia multiply to till in the
merly occupied by neurons. Brain tumors derived fromi
called gliomas, often are highly malignant and grow
Of the six types of neuroglia, four- -astrocytes, oligode
cytes, microglia, and ependymal cells — are found on!
CNS. The remaining two types --Schwann cells and i
cells — are present in the PNS. Tabic M.l shows the ap
ance of neuroglia and lists their funcions.
■ CHECKPOINT J
4. What are die functions of die dendrites, cell body,
and synaptic end bulbs of a neuron?
5. Which cells produce myelin in nervous tissue, andj
is the function of a myelin sheath?
6. What are the functions of neuroglia?
ACTION POTENTIALS
OBJECTIVE * Describe how a nerve impulse is
e rated and conducted.
Neurons communicate with one another by means of
action potentials, also called nerve impulses. Recall
Chapter 8 that a muscle fiber contracts in response in ,i hi
cle action potential. The generation of action potentials
both muscle libers and neurons depends on two basic
tures of the plasma membrane: the existence of a
membrane potential and the presence of specific types
channels. Many body cells exhibit a membrane parentis
difference in the amount of electrical charge on the insid|
the plasma membrane as compared to the outside. The
brane potential is like voltage stored in a battery. A cell
has a membrane potential is said to he polarized. When
cle fibers and neurons are "at rest" (not conducting actjj
potentials), the voltage across the plasma membrane
termed the resting membrane potential*
If you connect the positive and negative terminals
battery with a piece of metal (look in the battery coraj
merit of your portable radio), an electrical current can
electrons flows from the battery, allowing you to listen
your favorite music. In living tissues, the flow of ions (rat
than electrons) constitutes electrical currents. The main sit
where ions can flow across the membrane are through
pores of various types of ion channels.
Ion Channels |
When they are open, ion channels allow specific ions to
fuse across the plasma membrane from where the ions
more concentrated to where thev are less concentrated. Sir
larly, positively charged ions will move toward a neptn
Action Potentials 231
of Neuroglial Cell
Central Nervous System
Astrocytes
pHMtz; astro- = star;
cell)
Microglia
iT:i-KROG-le-a;m/cro- - smal
Peripheral Nervous System
Schwann cells
Table 9.1 Neuroglia in the CNS and PNS
Functions
Support neurons; protect neurons from
harmful substances; help maintain proper
chemical environment for generation of
nerve impulses; assist with growth and
migration of neurons during brain
development; play a role in learning and
memory; help form the blood-brain barrier.
Protect CNS cells from disease by
engulfing invading microbes; migrate to
areas of injured nerve tissue where they
clear away debris of dead cells.
Produce and maintain myelin sheath
around a single axon of a PNS neuron;
participate in regeneration of PNS axons.
Type of Neuroglial Cell
Oligodendrocytes
(OL-i-go-den'-dro- sltz; oligo-
few; dendro- = tree)
Ependymal cells
(ep-EN-di-mal; epen- - above;
dym- - garment)
Satellite cells
(SAT-i-ITt)
Functions
Produce and maintain myelin
sheath around several adjacent
axons of CNS neurons.
Line ventricles of the brain
(cavities filled with cerebrospinal
fluid) and central canal of the
spinal cord; form cerebrospinal
fluid and assist in its circulation.
Support neurons in PNS ganglia
and regulate exchange of materials
between neurons and interstitial
fluid.
Oligodendrocyte
Microglial ce
Neuron
Blood capillary
Astrocytes
Microglial cell
Ependymal
cell
Microvillus
Cilia
Inner covering
around brain
Astrocyte
Node of Ranvier
Myelin sheath
Axon
Oligodendrocyte
Neurons
:
-
M
Ventricle of brain
232 Chapter 9 Nervous Tissue
charged urea, and negatively charged ions will move toward a
positively charged area. As ions diffuse across a plasma mem-
brane to equalize differences in charge or concentration, the
result is a How of current that can change the membrane po-
tential.
Two different types of ion channels are leakage channels
and gated channels. Leakage channels allow a small but
steady stream of ions to leak across the membrane. Because
T
plasma membranes typically have many more potassium ion
(lC) leakage channels than sodium ion (Na + ) leakage chan-
nels, die membrane's permeability to K 1 is much higher than
its permeability to Na\ Gated channels, in contrast, open
and close on command (see Figure 3.5 on page 48). Voltage-
gated channels — channels that open in response to a change
in membrane potential — are used to generate and conduct
action potentials.
Resting Membrane Potential
In a resting neuron, the outside surface of the plasma mem-
brane has a positive charge and the inside surface has a nega-
tive charge. The separation of positive and negative electrical
charges is a form of potential energy, which can be measured
in volts. For example, two 1.5-volt batteries can power a
portable radio. Voltages produced by cells typically are much
smaller and are measured in millivolts (1 millivolt — 1 mV =
1/1000 volt). In neurons, the resting membrane potential is
about —70 mV. The minus sign indicates that the inside of
the membrane is negative relative to the outside.
The resting membrane potential arises from die unequal
distributions of various ions in cytosol and interstitial fluid
(Figure 9.4). Interstitial fluid is rich in sodium ions (Na + ) and
chloride ions (CI"). Inside cells, the main positively charged
ions in the cytosol are potassium ions (K 1 ), and the two dom-
inant negatively charged ions are phosphates attached to or-
ganic molecules, such as the three phosphates in ATP
(adenosine triphosphate), and amino acids in proteins. Be-
cause the concentration of K ' is higher in cytosol and be-
cause plasma membranes have many K leakage channels,
potassium ions diffuse down their concentration gradient —
out of cells into the interstitial fluid. As more and more posi-
tive potassium ions exit, the inside of the membrane becomes
increasingly negative, and the outside of the membrane be-
comes increasingly positive. Another factor contributes to the
negativity inside: Most negatively charged ions inside the cell
are not free to leave. They cannot follow the K ' out of the
cell because they are attached either to large proteins or to
other large molecules.
Membrane permeability to Na + is veiy low because there
are only a few sodium leakage channels. Nevertheless,
sodium ions do slowly diffuse inward, down their concentra-
tion gradient. Left unchecked, such inward leakage of Na" 1
would eventually destroy the resting membrane potential.
The small inward Na + leak and outward K ' leak are offset by
Figure 9.4 The distribution of ions that produces the restii
membrane potential.
& ra
The resting membrane potential is due to a small buildup of:
atively charged ions, mainly organic phosphates (PO^J
proteins, in the cytosol just inside the membrane and an
equal buildup of positively charged ions, mainly sodium ions
(Na + ), in the interstitial fluid just outside the membrane.
Interstitial
fluid
- Plasma
memk
Phosphate — £$
ion
Protein
Potassium — aj£
ion
/ What is a typical value for the resting membrane potential of a
neuron?
die sodium-potassium pumps (see figure 3.9 on page S]
These pumps help maintain the resting membrane potentw
by pumping out Na' as fast as it leaks in. At the sank in i
the sodium-potassium pumps bring in K ' ,
Generation of Action Potentials
An action potential (/IP) or impulse is a sequence of rapic
occurring events diat decrease and reverse the membrane
tential and then eventually restore it to the resting state,
ability of muscle fibers and neurons to convert stimuli ii
action potentials is called electrical excitability. A stimnkn
anything in the cell's environment that can change the rest
membrane potential. If a stimulus causes the membrane
depolarize to a critical level, called threshold (typically, il
-55 rnV), then an action potential arises (Figure 9,5).
action potential has two main phases: a depolarizing pha
and a repolarizing phase. During the depolarizing phase,
negative membrane potential becomes less negative, rendu
zero, and then becomes positive. Then, during the repot
ing phase, die membrane polarization is restored to its
ing state of —70 mV (Figure 9.5). In neurons, the depoli
ing and repolarizing phases ot an action potential typicj
last about one millisecond (1/1000 sec).
During an action potential, depolarization to threshold
briefly opens two types of voltage-gated ion channels. In
neurons, these channels are present mainly in the plasma
membrane of die axon and axon terminals. First, a threshold
depolarization opens voltage-gated Na* channels. As these
channels open, about 20,000 sodium ions rush into the cell,
causing die depolarizing phase. The inflow of Na ' causes the
lembrane potential to pass raV and finally reach +30 mV
Lire 9.5). Second, the threshold depolarization also opens
:ge-gated K ! channels. The voltage-gated K ' channels
more slowly, so their opening occurs at about the same
dine the voltage-gated Na + channels are automatically clos-
ing. As the K~ channels open, potassium ions flow out of the
producing the repolarizing phase,
hile the voltage-gated K' f channels are open, outflow
C + may he large enough to cause an after-hyperpolarizing
m of the action potential (Figure 9,5). During hyperpo-
Miioa, the membrane potential becomes even more nega-
wthan the resting level. Finally, as K channels close, the
Lembrane potential returns to the resting level of -70 mV.
Action potentials arise according to the all-or-none prin-
ciple. As long as a stimulus is strong enough to cause depolar-
ization to threshold, the voltage-gated Na* and K + channels
Ken, and an action potential occurs. A much stronger
stimulus cannot cause a larger action potential because the
fee of an action potential is always the same. A weak stimu-
li that fails to cause a threshold-level depolarization does
no t elicit an action potential. For a brief time after an action
Lential begins, a muscle fiber or neuron cannot generate
i action potential This time is called the refractory
Figure 9.5 Action potential (AP). When a stimulus depolarizes
the membrane to threshold, an action potential is generated.
An action potential consists of depolarizing and repolarizing
Hfe. phases.
Depolarizing
- phase
Reversal of
polarization
— Threshold
Resting
membrane
After-hyperpolarizing phase potential
1
Time in milliseconds (msec)
/ Which channels are open during depolarization? During
repolarization?
Action Potentials 233
Conduction of Nerve Impulses
To communicate information from one part of the body to
another, nerve impulses mast travel from where they arise,
usually at the axon hillock, along the axon to the axon termi-
nals (Figure 9.6). This type of impulse movement, which op-
erates by positive feedback, is called conduction or propaga-
tion. Depolarization to threshold at the axon hillock opens
voltage-gated Na~ channels. The resulting inflow of sodium
ions depolarizes the adjacent membrane to threshold, which
opens even more voltage-gated Na ' channels, a positive
feedback effect. Thus, a nerve impulse self-conducts along
the axon plasma membrane. This situation is similar to push-
ing on the first domino in a long row- When the push on the
first domino is strong enough, that domino falls against the
second domino, and eventually the entire row topples.
The type of action potential conduction that occurs in
unmyelinated axons (and in muscle fibers) is called continu-
ous conduction. In this case, each adjacent segment of the
plasma membrane depolarizes to threshold and generates an
action potential that depolarizes the next patch of the mem-
brane (Figure 9.6a). Note that the impulse has traveled only a
relatively short distance after 10 milliseconds (10 msec).
In myelinated axons, conduction is somewhat different.
The voltage-gated Na + and K 1 channels are located primar-
ily at the nodes of Ranvier, the gaps in the myelin sheath.
When a nerve impulse conducts along a myelinated axon,
current carried by Na + and K flows through the interstitial
fluid surrounding the myelin sheath and through die cytosol
from one node to the next (Figure 9.6b). The nerve impulse at
the first node generates ionic currents that open voltage-gated
W channels at the second node and trigger a nerve impulse
diere. Then the nerve impulse from the second node generates
an ionic current that opens voltage-gated Na ' channels at the
third node, and so on. Each node depolarizes and then repolar-
izes. Note the impulse has traveled much farther along die
myelinated axon in Figure 9.6b in the same interval Because
current flows across the membrane only at the nodes, the im-
pulse appears to leap from node to node as each nodal area de-
polarizes to threshold. This type of impulse conduction is
called saltatory conduction (SAL-ta-to-re; saltat- = leaping).
The diameter of the axon and die presence or absence of
a myelin sheath are the most important factors that deter-
mine the speed of nerve impulse conduction. Axons with
large diameters conduct impulses faster than those with small
diameters. xAJso, myelinated axons conduct impulses faster
than do unmyelinated axons. Axons with the largest diame-
ters are all myelinated and therefore capable of saltatory con-
duction. The smallest diameter axons are unmyelinated, so
their conduction is continuous. Axons conduct impulses at
higher speeds when warmed and at lower speeds when
cooled. Pain resulting from tissue injury 7 such as that caused
by a minor burn can be reduced by the application of ice be-
cause cooling slows conduction of nerve impulses along the
axons of pain-sensitive neurons.
234 Chapter 9 Nervous Tissue
Figure 9.6 Conduction of a nerve impulse after it arises at the axon hillock. Dotted lines indicate ionic cur-
rent flow, (a) In continuous conduction along an unmyelinated axon, ionic currents flow across each adjacent portion of
the plasma membrane, (b) In saltatory conduction along a myelinated axon, the nerve impulse at the first node gener-
ates ionic currents in the cytosol and interstitial fluid that open voltage-gated Na 1 channels at the second node, and so
on at each subsequent node.
Unmyelinated axons exhibit continuous conduction, and myelinated axons exhibit saltatory conduction.
Time
1
msec
Current flow due to
opening of Na + channels
Axon hillock
5
msec
-^; Sr *
10
msec
Leading edge of
action potential
(a) Continuous conduction
What factors influence the speed of nerve impulse conduction?
Local anesthetics are drugs that block pain. Examples in-
clude procaine (Novocaine®) and Lidocaine, which may be
used to produce anesthesia in the skin during suturing of a
gash, in the mouth during dental work, or in the lower
body during childbirth. These drugs act by blocking the
opening of voltage-gated Na 4 " channels. Nerve impulses
cannot conduct past die obstructed region, so pain signals
do not reach the CNS.
■ CHECKPOINT
7. What are the meanings of the terms resting membrane
potential, depolarization, repolarization, nerve impulse,
and refractory period?
8. How is saltatory conduction different from continuous
conduction?
SYNAPTIC TRANSMISSION
objective • Explain the events of synaptic transmis-
sion and the types of neurotransmitters used*
Now that you know how action potentials arise and condi
along the axon of an individual neuron, we will explore I
neurons communicate with one another. ±\t synapses, neurot
communicate with other neurons or with effectors by a series
events known as synaptic transmission, hi Chapter 8 we exfl
ined the events occurring at die neuromuscular junction, tfl
synapse between a somatic motor neuron and a skeletal mi
fiber (see Figure 8.5 on page 178), Synapses between newt
operate in a similar way The neuron sending the signal is calk
the presynaptic neuron (pre- - before), and the neuron receiv-]
ing the message is called the postsynaptic neuron {port- — after),
rents at a Synapse
ough the presynaptic and postsynaptic neurons are in
e proximity at a synapse, their plasma membranes do not
, They are separated by the synaptic deft, a tiny space
d with interstitial fluid. Because nerve impulses cannot
t across the synaptic cleft, an alternate, indirect form
communication occurs across this space. A typical synapse
rates as follows (Figure 9.7):
A nerve impulse arrives at a synaptic end bulb of a presy-
naptic axon.
The depolarizing phase of the nerve impulse opens
waltege-gated Ca 2+ channels, which are present in the
nbrane of synaptic end bulbs. Because calcium ions
Synaptic Transmission 235
are more concentrated in the interstitial fluid, Ca 2+ flows
into the synaptic end bulb through the opened channels.
An increase in the concentration ol Ca" inside the
synaptic end bulb triggers exocytosis of some of the
synaptic vesicles, which releases thousands of neurotrans-
mitter molecules into the synaptic cleft.
Q The neurotransmitter molecules diffuse across the synap-
tic cleft and bind to neurotransmitter receptors in the
postsynaptic neuron's plasma membrane.
Q Binding of neurotransmitter molecules opens ion channels,
which allows certain ions to flow across the membrane.
Q As ions flow through the opened channels, the voltage
across the membrane changes. Depending on which ions
Figure 9.7 Synaptic transmission at a chemical synapse. Exocytosis of synaptic vesicles from a
presynaptic neuron releases neurotransmitter molecules, which bind to receptors in the plasma membrane of
the postsynaptic neuron.
At a chemical synapse, a presynaptic electrical signal (nerve impulse) is converted into a chemical signal
(neurotransmitter release). The chemical signal is then converted back into an electrical signal (depolar-
ization or hyperpolarization) In the postsynaptic celJ.
Presynaptic neuron
Voltage-gated Ca 2
channel
Synaptic end bulb
Neurotrans
receptor
Ion channel
closed
on channel open
Postsynaptic neuron
Q Depolarization > "Nerve impulse
«.
What causes the voltage-gated Ca 2 ' channels in synaptic end bulbs to open?
Focus on Wellness
Neurotransmitters
Why Food Affects
Mood
Everyone who has enjoyed the sooth-
ing relaxation of a good meal has expe-
rienced the effect of food on mood.
Neurons manufacture neurotransmit-
ters from chemicals that come from
food, so you could say that die story of
the food-mood link begins with diges-
tion. Many neurotransmitters are made
from amino acids, which are the basic
building blocks of proteins. Amino
acids are made available when your
body digests the protein in the food
you eat. For example, the neurotrans-
mitter serotonin is made from the
amino acid tryptophan, and both
dopamine and norepinephrine are syn-
thesized from the amino acid tyrosine.
Mind-altering Food?
Regulation of neurotransmitter levels
in the brain is quite complicated and
depends not only on the availability of
amino acid (and other) precursors, but
also on competition of these precursors
for entry into the brain. Consider sero-
tonin, one of the neurotransmitters
that appears to have an important ef-
fect on mood. Serotonin leads to feel-
ings of relaxation and sleepiness.
Although serotonin is manufac-
tured from the amino acid tryptophan,
protein foods do not lead to higher lev-
els of tryptophan in the blood or brain.
This is because, after a high-protein
meal, tryptophan must compete with
more than 20 other amino acids for en-
try into the central nervous system, so
► T
its concentration in the brain ra
relatively low. On the other hand
sumption of carbohydrate-rich fa
such as bread, pasta, potatoes
sweets, is associated with an incr
the synthesis and release oi
in the brain. The result: Carbarn
help us feel relaxed and sleepy.
>«
%
- i.« **&±
Why might consuming a high-protein diet for several days lead to r/vn'&H
for carbohydrate-rich foods?
the channels admit, the voltage change may be a depolar-
ization or a hyperpolarization.
If a depolarization occurs in the postsynaptic neuron and
reaches threshold, then it triggers one or more nerve im-
pulses.
At most synapses, only one-way information transfer can
occur- -from a presynaptic neuron to a postsynaptic neuron
or to an effector, such as a muscle fiber or a gland cell. For
example, synaptic transmission at a neuromuscular junction
(NMJ) proceeds from a somatic motor neuron to a skeletal
muscle fiber (but not in the opposite direction). Only synap-
tic end bulbs of presynaptic neurons can release neurotrans-
mitters, and only the postsynaptic neuron's membrane has
the correct receptor proteins to recognize and bind that neu-
rotransmitter. As a result, nerve impulses move along their
pathways in one direction.
When a postsynaptic neuron depolarizes, the effect is ex-
citatory- If threshold is reached, one or more nerve impulses
occur. By contrast, hyperpolarization has an inhibitory effect
on the postsynaptic neuron: As die membrane potential
moves farther away from threshold, nerve impulses are less
likely to arise. A typical neuron in the CNS receives input
from 1000 to 10,000 synapses. Some of this input is excita-
tory and some is inhibitory. The sum of all the excitatoi
Inhibitory effects at any given time determines whether]
or more impulses will occur in the postsynaptic neuron.
A neurotransmitter affects the postsynaptic neun
cle fiber, or gland cell as long as it remains bound in t|
ceptors. Thus, removal of the neurotransmitter is essenj
for normal synaptic function. Neurotransmitter is rei
in three ways. (1) Some of the released neurotriinsmi
molecules diffuse away from the synaptic cleft. Once a n<
transmitter molecule is out of reach of its receptors, ii
longer exert an effect. (2) Some neurotransmitters
stroyed by enzymes. (3) Many neurotransmitters are!
transported back into the neuron that released
(reuptake). Others are transported into neighboring
roglia (uptake).
Several therapeutically important drugs selectively
reuptake of specific neurotransmitters. For exampl
drug fluoxetine (Prozac®) is a selective serotonin
take inhibitor (SSRI). By blocking reuptake of serai
Prozac prolongs the activity of this neurotransmii
synapses in the brain. SSRIs provide relief for those su-
ing from some forms of depression.
236
leurotransmitters
out 100 substances arc either known or suspected neuro-
psmitters. Most neurotransmitters are synthesized and
d into synaptic vesicles in the synaptic end bulbs, close to
fcrsite of release. One of die best-studied neurotransmitters
imtykholme (ACh), which is released by many PNS neu-
rons -and bj some CNS neurons. ACh is an excitatory neuro-
nittcr at some synapses, such as the neuromuscular junc-
II is also known to be an inhibitory 7 neurotransmitter at
synapses. For example, parasympathetic neurons slow
bit rate by releasing ACh at inhibitory synapses.
Several amino acids are neurotransmitters in the CNS.
ikiumite and aspartate have powerful excitatory effects.
ither amino acids, gamma aminohutyric (GAM-ma
no-bu-TIR-ik) acid (GABA) and glycine, are important
ihibitory neurotransmitters. Antianxiety drugs such as
azepam (Valium®) enhance the action of GABA.
me neurotransmitters are modified amino acids. These
include norepinephrine, dopamine, and serotonin. Norepi-
mhrine (NE) plays roles in arousal (awakening from deep
dreaming, and regulating mood. Brain neurons con-
Ling the neurotransmitter dopamine (DA) are active dur-
ational responses, addictive behaviors, and pleasurable
fcriences. In addition, dopamine-releasing neurons help
■ volute skeletal muscle tone and some aspects of movement
o contraction of skeletal muscles. One form of schizo-
id is due to accumulation of excess dopamine.
bwtimin is thought to be involved in sensory perception,
i rature regulation, control of mood, appetite, and the
m» t of sicca
\
fB> COMMON
^ DISORDERS
iltiple Sclerosis
tyh silerom (MS) is a disease that causes progressive destruc-
nyelin sheaths of neurons in the CNS. It afflicts about
million people worldwide and affects females twice as often as
I he condition's name describes die anatomical pathology: In
ions, the myelin sheaths deteriorate to scleroses, which
ed scars or plaques. The destruction of myelin sheaths
md then short-circuits conduction of nerve impulses.
Tin most common form of the condition is relapsing-
VlS, which usually appears in early adulthood. The first
mtoms may include a feeling of heaviness or weakness in the
.Jcs, abnormal sensations, or double vision. An attack is fql-
i period of remission during which the symptoms tem-
prilv disappear. One attack follows another over the years. The
jussive loss of function interspersed with remission
^■during which symptoms abate.
Common Disorders 237
Neurotransmitters consisting of amino acids linked by
peptide bonds are called neuropeptides (noor-6-PRP-tids).
The endorphins (en-DOR-fins) are neuropeptides that are
the body's natural painkillers. Acupuncture may produce
analgesia (loss of pain sensation) by increasing the release of
endorphins. They have also been linked to improved mem-
ory and learning and to feelings of pleasure or euphoria.
An important newcomer to the ranks of recognized neuro-
transmitters is the simple gas nitric oxide (NO), which is differ-
ent from all previously known neurotransmitters because it is
not synthesized in advance and packaged into synaptic vesicles.
Rather, it is formed on demand, diffuses out of cells that pro-
duce it and into neighboring cells, and acts immediately. Some
research suggests that NO plays a role in learning and memory.
Substances naturally present in the body as well as drugs
and toxins can modify the effects of neurotransmitters
in several ways. Cocaine produces euphoria- -intensely
pleasurable feelings — by blocking reuptake of dopamine.
This action allows dopamine to linger longer Ln synaptic
clefts, producing excessive stimulation of certain brain
regions. Isoproterenol (Isuprel®) can be used to dilate
the airways during an asthma attack because it binds to
and activates receptors for norepinephrine. Zyprexa^, a
drug prescribed for schizophrenia, is effective because it
binds to and blocks receptors for serotonin and dopamine.
■ CHECKPOINT
9. How are neurotransmitters removed alter they are re-
leased from synaptic vesicles?
MS is an autoimmune disease— the body's own immune sys-
tem spearheads the attack. Although the trigger of MS is unknown,
both genetic susceptibility and exposure to some environmental fac-
tor (perhaps a herpes virus) appear to contribute. Many patients
with relapsing- remitting MS are treated with injections of beta in-
terferon. This treatment lengthens die time between relapses, de-
creases the severity of relapses, and slows formation of new' lesions
in some cases. Unfortunately not all MS patients can tolerate beta
interferon, and therapy becomes less effective as the disease
progresses.
Epilepsy
Epilepsy is a disorder characterized by short, recurrent, periodic at-
tacks of motor, sensory, or psychological malfunction, although it
almost never affects intelligence. The attacks, called epileptic seizures,
afflict about 1% of the world's population, [hey are initiated by ab-
normal, synchronous electrical discharges from millions of neurons
in the brain. As a result, lights, noise, or smells may be sensed when
the eyes, ears, and nose have not been stimulated. In addition, the
skeletal muscles of a person having a seizure may contract involun-
238 Chapter 9 Nervous Tissue
airily. Partial seizures begin in a small focus on one side of the brain
and produce milder symptoms; generalized seizures involve larger ar-
eas on both sides of the brain and loss of consciousness.
Epilepsy has many causes, including brain damage at birth (the
most common cause); metabolic disturbances such as insufficient
glucose or oxygen in the blood; infections; toxins; loss of blood or
low blood pressure; head injuries; and tumors and abscesses of the
MEDICAL TERMINOLOGY AND CONDITIONS
brain. However, most epileptic seizures have no
cause.
Epileptic seizures often can be eliminated or ullevii
antiepileptic drugs, such as phenytoin, carbanw.epinc, and
ate sodium. An implantable device that stimulates the v,
nerve also has produced dramatic results in redue
some patients whose epilepsy was not well-controlled by di
Demy elinat ion (de-mi-e-li-KA-shun) Loss or destruction of
myelin sheaths around axons in die CNS or PNS.
GiriUain-Barre Syndrome (GBS) (ge-an ba-RA) A demyelinatiiig
disorder in which macrophages remove myelin from PNS ax-
ons. It is a common cause of sudden paralysis and may result
from the immune system's response to a bacterial infection.
Most patients recover completely or partially, hut ;»bc
remain paralyzed.
Neuropathy (aoo-ROP-a-the; neuro- = a nerve; -pat
Any disorder that affects the nervous system, but parti*
disorder of a cranial or spinal nerve,
STUDY OUTLINE
r**'4
1.
2.
3.
4.
5.
6.
7.
8.
Overview of the Nervous System (p. 226)
Components of the nervous system include the brain,
12 pairs of cranial nerves and their branches, the spinal cord,
3 1 pairs of spinal nerves and their branches, sensory receptors,
ganglia, and enteric plexuses.
Three basic functions of the nervous system are detecting stim-
uli (sensor}* function); analyzing, integrating, and storing
sensory information (integrative function); and responding to
integrative decisions (motor function),
Sensory (afferent) neurons provide input to the CNS; motor
(efferent) neurons carry 7 output from the CNS to effectors.
The two main subsystems of the nervous system are (1) the
central nervous system (CNS), the brain and spinal cord, and
(2) the peripheral nervous system (PNS), all nervous tissues
outside the brain and spinal cord.
The PNS also is subdivided into the somatic nervous system
(3NS), autonomic nervous system (ANTS), and enteric nervous
system (ENS).
The SNS consists of (!) sensory neurons that conduct impulses
from somatic and special sense receptors to the CNS, and (2)
motor neurons from the CNS to skeletal muscles.
The ANS contains (1) sensory neurons from visceral organs
and (2) motor neurons in two divisions, sympathetic and
parasympathetic, that convey impulses from the CNS to
smooth muscle tissue, cardiac muscle tissue, and glands.
The ENS consists of neurons in two enteric plexuses that ex-
tend the length of the gastrointestinal (GI) tract; it monitors
sensory changes and controls operation or the GI tract.
Histology of Nervous Tissue (p. 228)
1. Nervous tissue consists of two types of cells: neurons and neu-
roglia. Neurons are specialized for nerve impulse conduction
and provide most of the unique functions of the nerw
tern, such as sensing, thinking, remembering, controllin
cle activity, and regulating glandular secretions, Nei
port,, nourish, and protect the neurons and mail
homeostasis in the interstitial fluid that bathes neurons.
2. Most neurons have three parts, The dendrites are (he \w
ceiving or input region, Integration occurs in the cell
The output part typically is a single axon, which coi
nerve impulses toward another neuron, a muscle
gland cell.
3. Two types of neuroglia produce myelin sheath;
eytes myelinate axons in the CNS, and Schwann cells im
axons in the PNS.
4* White matter primarily contains myelinated axons
ter contains neuronal cell bodies, dendrites, axon I
unmyelinated axons, and neuroglia.
5. In die spinal cord, gray matter forms an U-shaped inner
that is surrounded by white matter In the brain, a thin,
eial shell of gray matter covers the cerebrum and cerebellni
6. Neuroglia include astrocytes, oligodendrocytes, niic
ependymal cells, Schwann cells, and satellite cells
on page 231).
Action Potentials (p. 230)
1. Neurons communicate with one another using nerv«
tentials, also called nerve impulses.
2. Generation of action potentials depends on the existenJ
resting membrane potential and die presence of voltagd
channels for Na + and K + .
3. A typical value for the resting membrane potential (difl
in electrical charge across the plasma membrane) is -
cell thai cvli ' i i > i:rm[>raiu' p< >te.mial is p< larized,
I Ik resting membrane potential arises due to an unequal dis-
tribution of ions on either side of the plasma membrane and a
higher membrane permeability to K ' than to Na + . The level of
K + is higher inside and the level of Na ' is higher outside, a sit-
lion that is maintained by sodium-potassium pumps.
[The ability of muscle libers and neurons to respond to a stimu-
lus and convert it into action potentials is called excitability.
■.During an action potential, voltage-gated Na 1 and K + chan-
nels open in sequence. Opening of voltage-gated Na ' channels
11 depolarization, die loss and then reversal of mem-
Eme polarization (from -70 mV to +30 mV). Then, opening
dtage-gated K 1 channels allows repolarization, recovery of
I the membrane potential to the resting level.
According to the all-or-none principle, if a stimulus is strong
enough to generate an action potential, the impulse generated
is of a constant size,
I During die refractory period, another action potential cannot
generated.
Nerve impulse conduction tliat occurs as a step-by-step process
along an unmyelinated axon is called continuous conduction,
fo saltatory conduction, a nerve impulse "leaps" from one node
of Rainier to the next along a myelinated axon.
Self Quiz 239
10. Axons with larger diameters conduct impulses faster than those
with smaller diameters; myelinated axons conduct impulses
faster than unmyelinated axons.
Synaptic Transmission (p. 234)
1. Neurons communicate with other neurons and with effectors
at synapses in a series of events known as synaptic transmission.
2. At a synapse, a neurotransmitter is released from a presynaptic
neuron into the synaptic cleft and then binds to receptors on
the postsynaptic plasma membrane.
3. An excitatory neurotransmitter depolarizes the postsynaptic
neurons membrane, brings die membrane potential closer to
threshold, and increases the chance that one or more action
potentials will arise. An inhibitory neurotransmitter hyperpo-
I arizes the membrane of the postsynaptic neuron, thereby in-
hibiting action potential generation,
4. Neurotransmitter is removed in mree ways: diffusion, enzy-
matic destruction, and reuptake by neurons or neuroglia.
5. Important neurotransmitters include acetylcholine, glutamate,
aspartate, gamma amino butyric acid (CiABA), glycine, nor-
epinephrine, dopamine, serotonin, neuropeptides, and nitric
oxide.
I
SELF-QU
hich of the following are incorrectly matched?
a. central nervous system: composed of the brain ^nd spinal
<rd
h, somatic nervous system: includes motor neurons to skeletal
muscles
c. sympathetic nervous system: includes motor neurons to
skeletal, smooth, and cardiac muscles
d, peripheral nervous system: includes cranial and spinal
nerves
itonornic nervous system: includes parasympathetic and
mpathetic divisions
[The portion of the nervous system that regulates the gastroin-
testinal (GI) tract is the
a, somatic nervous system b. sympathetic division
,. integrative division d, central nervous system
c. enteric nervous system
I Damage to dendrites would interfere with a neuron's ability to
a, receive input b. make proteins c. conduct nerve im-
pulses to another neuron d. release neurotransmitters
orm myelin
i The type of cell that produces myelin sheaths around axons in
I INS is the
b. myelinocyte c. Schwann cell
d. oligodendrocyte e. microglia
| \ bundle of axons in the CNS is
a, :i tract b. a nucleus c. a mixed nerve
A, a ganglion e. an enteric plexus
6. Which of the following is NOT true concerning the repair of
nervous tissue?
a. If the cell body is not damaged, neurons in the PNS may be
able to repair themselves.
b. In the CNS, myelin inhibits neuronal regeneration.
c. Injury to the CNS is usually permanent.
d. Active Schwann cells contribute to the repair process in the
PNS
e. A regeneration tube forms across the injured area of a CNS
neuron that undergoes repair.
7. In a resting neuron
a, there is a high concentration of K ' outside the cell
b. negatively charged ions move freely through the plasma
membrane
Ci the sodium-potassium pumps help maintain the low concen-
tration of Na + inside the cell
d. die outside surface of the plasma membrane has a negative
charge
e. die plasma membrane is highly permeable to Na '
8. The depolarizing phase of a nerve impulse is caused by a
a. rush of Na into the neuron
fa. rush of Na out of the neuron
c, rush of K ' into the neuron
d. rush of K" out of die neuron
e* pumping of K + into the neuron
>
240 Chapter 9 Nervous Tissue
9. If a stimulus is strong enough to generate an action potential,
the impulse generated is of a constant size. A stronger stimulus
cannot generate a larger impulse. This is known as
a. the principle of polarization-depolarization
b. saltatory conduction
e. the all-or-none principle
d« the principle of reflex action
e. the absolute refractory period
10. Place the following events in the correct order of occurrence:
1. Voltage-gated Na ' channels open and permit Na + to rush
inside the neuron,
2. The Na ' /K ' pump restores the ions to their origitial sites.
3. A stimulus of threshold strength is applied to the neuron,
4. The membrane polarization changes from negative (—55
mV) to positive (4-30 mV).
5. Voltage-gated K ' channels open, and K 4 flows out of the
neurons.
a. 4, 1,2,3,5 b. 4,3, 1,2,5 c. 3,1,4,2,5
d. 5,3,1,4,2 e. 3, 1,4,5,2
11. Saltatory conduction occurs
a* in unmyelinated axons
b* at the nodes of Ranvier
c. in the smallest diameter axons
d. in skeletal muscle fibers
e. in cardiac muscle fibers
12. The speed of nerve impulse conduction is increased by
a. cold b. a very strong stimulus c. small diameter of
the axon d. myelination e. astrocytes
13. For a signal to be transmitted by means of a chemical synapse
from a presynaptic neuron to a postsynaptic neuron,
a. die presynaptic neuron must be touching the postsynaptic
neuron
b. the postsynaptic neuron must contain neurotransmitter re-
ceptors
c« there must be gap junctions present between the two neu-
rons
d. the postsynaptic neuron needs to release neurotransmitters
from its synaptic vesicles
e. the neurons must be myelinated
14. What would happen at the postsynaptic neuron if the total in-
hibitory effects of die neurotransmitters were greater than die
tot a I exci ta to rv effects ?
a. A nerve impulse would be generated.
b. Tt would be easier to generate a nerve impulse when the
next stimulus was received.
c. The nerve impulse would be rerouted to another
neuron.
d. No nerve impulse would be generated.
e. The neurotransmitter would be broken down more quickly.
15. Match the following neurotransmitters with their descrim
a. inhibitor)' amino acid in the A. serotonin
CNS B. acetylcholine
_ b. a gaseous neurotransmitter that q endorphins
is not packaged into _ ,„ . „ ,
" ? . D. GAB A
synaptic vesicles
. , . t E. nitric oxide
c» excitatory amino acid in the
Q^ig F, glutamate
d. body's natural painkillers
e, helps regulate mood
f. neurotransmitter that
activates skeletal muscle fibers
16. Match the following.
a, the portion of a neuron
containing the nucleus
b. rounded structure at the
distal end of an axon terminal
c. highly branched, input part of
a neuron
d. sac in which neurotransmitter is
stored
e. neuron located entirely within
the CNS
f. long, cylindrical process
that conducts impulses
toward another neuron
g. produces myelin sheath
in PNS
h. unmyelinated gap in the
myelin sheath
i. substance diat increases
the speed of nerve impulse
conduction
j. neuron that conveys
information from a receptor
to the CNS
k. neuron that conveys
information from the CNS
to an effector
I. bundle of many axons in
die PNS
m* bundle of many axons in
the CNS
. n. group of cell bodies in
the PNS
o. group of cell bodies in
the CNS
p. substance used for
co m m u n i ca ti o n a t ch em i ea 1
synapses
A, synaptic end
B, motor nunr
C. sensor]
D, dendrite
E. interneuron
F. nucleus
G myelin shefl
H. Schwann cell
I. cell both
J. node o I
K, ganglion
L. nerve
M. n euro trans
N. tract
O. synaptics
P. axon
Answers to Figure Questions 241
I
CRITICAL THINKING APPLICATIONS
The buzzing of the alarm clock awoke Rodrigo. He stretched,
yawned, and started to salivate as he smelted the brewing cof-
fee, List the divisions of the nervous system that are involved in
each of these activities.
'M, : .i .-iiua just figured out that her A & P class actually starts at
10:00 A.M. and not at 10:15, which has been her arrival time
since the beginning of the term. One of the other students re-
marks that Angelina's "gray matter is pretty thin." Should An-
gelina thank him?
4.
Sarah really looks forward to the great feeling she has alter go-
ing for a nice long run on the weekends. By the end of her run,
she doesn't even feel the pain in her sore feet. Sarah read in a
magazine that some kind of natural brain chemical was respon-
sible for the "runners high" that she feels. Are there such
chemicals in Sarah's brain?
The pediatrician was trying to educate die anxious new parents of
a six-month-okl baby: "No, don't worry about him not walking
yet. The myclination of the baby's nervous system is not finished
yet.'* Explain what die pediatrician means by this reassurance.
ANSWERS TO FIGURE QUESTION
M
The total number of cranial and spinal nerves in your body is
(12X2) + (31 X2) = 86.
lory or afferent neurons carry input to the CNS. Motor
or efferent neurons carry output from the CNS.
The axon conducts nerve impulses and transmits die mes-
sage to another neuron or effector cell by releasing a neuro-
transmitter at its axon terminals.
pica! value for the resting membrane potential in a neu-
riih is -70 mV
9.5
9.6
9.7
Vbltage-gated Na ' channels are open during the depolariz-
ing phase, and voltage-gated K" channels are open during
the repolarizing phase of an action potential.
The two main factors that influence conduction speed of a
nerve impulse are the axon diameter (larger axons conduct
impulses more rapidly) and the presence or absence or a
myelin sheath (myelinated axons conduct more rapidly than
unmyelinated axons).
The depolarizing phase of the action potential opens die
voltage-gated Or : channels in synaptic end bulbs.
chapter 10
-
CENTRAL NERVOUS SYSTEM, SPINA
NERVES. AND CRANIAL NERVES
did you know?
xM.tbletes perform exercise train-
ing to stimulate physiological adaptations that lead to
improved sports performance. Researchers now believe
that a similar kind of training effect may occur in one
of the most important organs in your body: the brain.
Just as muscles respond to strength training by
increasing in size and becoming stronger, so does the
brain respond by increasing the number of neural
pathways, the connections between neurons that allow
you to think and to remember. Undergoing years of
"mental exercise" may be one of the reasons that people
with college degrees have a lower
risk of developing Alzheimer disease.
Focus on Wellness, page 257
www.wiley.com/college/apceiTtral
K
'■'"
aw that you understand
how the nervous system functions
on the cellular level, in this chapter we will explo
structure and functions of the central nervous system
(CNS), which consists of the brain and spinal coriLWi
will also examine spinal nerves and cranial nerves,
which are part of the peripheral nervous system (]
(see Figure 9.1 on page 226).
looking back to move ahead
• Skull and Hyoid Bone (page 125)
• Vertebral Column (page 133)
• Structures of the Nervous System (page 226)
• Structure of a Neuron (page 228)
• Gray and White Matter (page 228)
242
kplNAL CORD STRUCTURE
[OBJECTIVES « Describe how the spinal cord is pro-
bed.
Describe the structure of the spinal cord.
Irotection and Coverings: Vertebral Canal
id Meninges
spinal cord is located within the vertebral cavity of the
iral column. Because the wall of the vertebral cavity is
ndally a ring of bone, the cord is well protected. The ver-
ligaments, meninges, and cerebrospinal fluid provide
mal protection.
meninges (me-NIN-jez) are three layers of connec-
jre tissue coverings that extend around the spinal cord and
The meninges that protect the spinal cord, the spinal
how (Figure 10.1), are continuous with those that protect
in, the cranial meninges (see Figure 10.7). The outer-
It of the three layers of the meninges is called the dura
DOO-ra MAter = tough mother). Its tough, dense ir-
tuhr connective tissue helps protect the delicate struc-
ture 10.1 Spinal meninges.
Meninges are connective tissue coverings that surround the
brain and spinal cord.
1NALC0RD:
Gray matter
Wile matter
SPINAL
MENINGES:
Pia mater
(inner)
Arachnoid
mater
(middle)
Dura mater
(outer)
Hal nerve
space
■
Anterior view and transverse section through spinal cord
which meningeal space does cerebrospinal fluid circulate?
Spinal Cord Structure 243
Cures of the CNS. The tube of spinal dura mater extends to
the second sacral vertebra, well beyond the spinal cord,
which ends at about the level of the second lumbar vertebra,
The spinal cord is also protected by a cushion of fat and con-
nective tissue located in the epidural space, a space between
the dura mater and vertebral column.
The middle layer of the meninges is called the arachnoid
mater (a-RAK-noyd; arachn- - spider; -old = similar to)
because the arrangement of its collagen and elastic fibers
resembles a spider's web. The inner layer, the pia mater
(PE-a MA-ter; pia = delicate), is a transparent layer of colla-
gen and elastic fibers that adheres to the surface of die spinal
cord and brain. It contains numerous blood vessels. Between
the arachnoid mater and die pia mater is the subarachnoid
space, where cerebrospinal fluid circulates.
In a spinal tap (lumbar puncture), a local anesthetic is
given, and a long needle is inserted into the subarachnoid
space. In adults, a spinal tap is normally performed be-
tween the third and fourth or fourth and fifth lumbar ver-
tebrae. Because this region is inferior to the lowest portion
of the spinal cord, it provides relatively safe access. The
procedure is used to withdraw cerebrospinal fluid (CSF)
for diagnostic purposes; to introduce antibiotics, contrast
media for myelography, or anesthetics; to administer
chemotherapy; to measure CSF pressure; and/or to evalu-
ate the effects of treatment for diseases such as meningitis.
Gross Anatomy of the Spinal Cord
The length of the adult spinal cord ranges from 42 to 45 cm
(16 to 18 in.). It extends from the lowest part of the brain, the
medulla oblongata, to the upper border of the second lum-
bar vertebra in the vertebral column (Figure 10.2). Because
the spinal cord is shorter than the vertebral column, nerves
that arise from the lumbar, sacral, and coccygeal regions of
the spinal cord do not leave the vertebral column at the
same level they exit the cord. The roots of these spinal
nerves angle down the vertebral cavity like wisps of flowing
hair. They are appropriately named the cauda equina
(KAW-da 6-KWFna), meaning horse's tail. The spinal
cord has two conspicuous enlargements: The cervical en-
largement contains nerves that supply the upper limbs, and
the lumbar enlargement contains nerves supplying the
lower limbs. Each of 31 spinal segments of die spinal cord
gives rise to a pair of spinal nerves (Figure 10.2).
Two grooves, the deep anterior median fissure and die
shallow posterior median sulcus, divide the spinal cord into
right and left halves (see Figure 10.3), In the spinal cord,
white matter surrounds a centrally located H-shaped mass ot
gray matter. In the center of die gray matter is the central
canal, a small space that extends the length of the cord and
contains cerebrospinal fluid.
244 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
Figure 10.2 Spinal cord and spinal nerves. Selected nerves are labeled on the left side of the figure. Together, the
lumbar and sacral plexuses are called the lumbosacral plexus.
:- Th
The spinal cord extends from the base of the skull to the superior border of the second lumbar vertebra.
CERVICAL PLEXUS (C1-C5)
Phrenic nerve
BRACHIAL PLEXUS (C5-T1):
Musculocutaneous nerve
Axillary nerve
Median nerve
Radial nerve
Ulnar nerve
Intercostal
(thoracic) nerves
Pudendal nerve
LUMBAR PLEXUS (L1-L4):
Ilioinguinal nerve
Femoral nerve
Obturator nerve
SACRAL PLEXUS (L4-S4):
Superior gluteal nerve
Inferior gluteal nerve
Sciatic nerve
Medulla oblongata of brain
Atlas (first cervical vertebra)
CERVICAL NERVES (8 pairs)
Cervical enlargement
- First thoracic vertebra
k
THORACIC NERVES (12 pairs)
Lumbar enlargement
Second lumbar vertebra
LUMBAR NERVES (5 pairs)
Cauda equina
Ilium of hip bone
Sacrum
SACRAL NERVES (5 pairs)
I COCCYGEAL NERVES (1 pair)
'-.•
•\
Posterior view of entire spinal cord and portions of
spinal nerves and their branches
Are spinal nerves part of the CNS or the PNS?
ternal Structure of the Spinal Cord
rim
matter of the spinal cord contains neuronal cell
s, dendrites, unmyelinated axons, axon terminals, and
Uroglni. On each side of the spinal cord, the gray matter is
into regions called horns, named relative to their
: anterior, lateral, and posterior (Figure 10.3). The
BtW (ventral) gray horns contain cell bodies oi somatic
tor neurons, which provide the nerve impulses that cause
i ii of skeletal muscles. The posterior (dorsal) gray
contain somatic and autonomic sensory neurons. Be-
i rjk interior and posterior gray horns are the lateral
horns, which are present only in the thoracic, upper lttm-
nJ sacral segments of the cord. The lateral horns contain
Jl bodies of autonomic motor neurons that regulate the
■jvity of smooth muscle, cardiac muscle, and glands.
The white matter of the spinal cord consists primarily of
I axons of neurons and is organized into regions called
H)i; lateral and posterior white columns. Each column con
Spinal Cord Structure 245
tains one or more tracts, which are distinct bundles of axons hav-
ing a common origin or destination and carrying similar infor-
mation. Sensoiy (ascending) tracts consist of axons that conduct
nerve impulses toward the brain. Tracts consisting of axons that
carry nerve impulses down die spinal cord are called motor (de-
scending) tracts. Sensoiy and motor tracts of the spinal cord are
continuous with sensory and motor tracts in die brain. Often, the
name of a tract indicates its position in the white matter, where it
begins and ends, and die direction of nerve impulse conduction.
For example, the anterior spinothalamic tract is located in the
anterior white column; it begins in die spinal cord, and it ends in
the thalamus (a region of the brain) (see Figure 10. 14b).
■ CHECKPOINT
1. How is the spinal cord protected?
2. What body regions are served by nerves from the cervical
and lumbar enlargements?
3. Distinguish between a horn and a column in the spinal cord.
Figure 10.3 Internal structure of the spinal cord. Columns of white matter surround the gray matter.
The spinal cord conducts nerve impulses along tracts and serves as an integrating center for spinal reflexes.
View
Transverse plane
Posterior (dorsal)
root ganglion
Spinal nerve
Lateral white column
Anterior (ventral) root
of spinal nerve
Central canal
Anterior gray horn
Anterior white commissure
Anterior white column
Cell body of motor neuron
Anterior median fissure
Axon of motor neuron
Posterior (dorsal)
root of spinal nerve
Posterior gray horn
Posterior median sulcus
Posterior white column
Axon of sensory neuron
Lateral gray horn
Cell body of
sensory neuron
Superior view of transverse section of thoracic spinal cord
N&rs/e impulses
for sensations
Nerve impulses to
effector tissues
(muscles and glands)
What is trie difference between a horn and a column in the spinal cord?
246 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
SPINAL NERVES
OBJECTIVE • Describe the composition, coverings,
and distribution of spinal nerves.
Spinal nerves are the paths of communication between the
spinal cord and the nerves that serve specific regions of the
body. I wo bundles of axons, called roots, connect each spinal
nerve to a segment of the cord (Figure 1 0.3). The posterior
(dorsal) root contains only sensory axons, which conduct
nerve impulses for sensations from the skin, muscles, and in-
ternal organs into the central nervous system. Each posterior
root also has a swelling, the posterior (dorsal) root ganglion,
that contains die cell bodies of sensory neurons. The other
point of attachment of a spinal nerve to the cord is the ante-
rior (ventral) root. It contains axons of somatic motor neu-
rons, which conduct nerve impulses from the CNS to skeletal
muscles, and autonomic motor neurons, which conduct im-
pulses to smooth muscle, cardiac muscle, and glands. A spinal
nerve thus contains both sensory and motor axons and there-
fore is a mixed nerve.
Spinal nerves and the nerves that branch from them are
part of die peripheral nervous system (PNS). They connect die
CNS to sensory receptors, muscles, and glands in all parts of
the body. The 31 pairs of spinal nerves are named and num-
bered according to the region and level of the vertebral column
from which they emerge (see Figure 10.2), There are 8 pairs of
cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar
nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves.
The first cervical pair emerges above the atlas. All other spinal
nerves leave die vertebral column by passing through the in-
tervertebral foramhw, the holes between vertebrae.
Spinal Nerve Coverings
Each spinal nerve (and cranial nerve) contains layers of pro-
tective connective tissue coverings (Figure 10.4). Individual
axons, whether myelinated or unmyelinated, are wrapped in
endoneurium (en'-do-NOO-re-um; endo- = within or inner).
Groups of axons with their endoneurium are arranged in
bundles, called fascicles, each oi which is wrapped in
perineurium (per'-i-NOO-re-um; peri- = around). The
superficial covering over the entire nerve is the epineurium
(ep'-i-NOO-re-um; epi- = over). The dura mater of the
spinal meninges fuses with the epineurium as a spinal nerve
passes through the intervertebral foramen. Note the presence
of many blood vessels, which nourish nerves, within the per-
ineurium and epineurium.
Distribution of Spinal Nerves
Plexuses
A short distance after passing through its intervertebral fora-
men, a spinal nerve divides into several branches. Many of
die spinal nerve branches do not extend directly to the body
structures they supply. Instead, they form networks on either
side of the body by joining with axons from adjacen (
Such a network is called a plexus (- braid ui
Emerging from the plexuses are nerves bearing nam
are often descriptive of the general regions theysupph
course they take. Each of the nerves, in turn, may hai
era] branches named for the specific structures they stt]
The major plexuses are the cervical plexus, br
plexus, lumbar plexus, and sacral plexus (see I
The cervical plexus supplies the skin and mus
posterior head, neck, upper part of the shoulders, ami
aphragm. The phrenic nerves, which stimulate
aphragm to contract, arise from the cervical plexus, [
to the spinal cord above the origin of the phrenic nei
cause respirator} 7 failure. The brachial plexus cm
nerve supply for the upper limbs and several neck
der muscles. Among die nerves that arise from the
plexus are the musculocutaneous, axillary, median, nidi;
ulnar nerves. The lumbar plexus supplies the :ilu
wall, external genitals, and part of the lower limbs,
from this plexus are the ilioinguinal, femoral, and obt
nerves. The sacral plexus supplies the buttocks.
Figure 10.A Composition and connective tissue coverings*
a spinal nerve.
Three layers of connective tissue wrappings protect axons:
endoneurium surrounds individual axons, perineurium
surrounds bundles of axons, and epineurium surrounds an
entire nerve.
Transverse plane
Spinal nerve
EPINEURIUM around
entire nerve
Blood vessels
Fascicle
PERINEURIUM
around each
ENDONEURIUM around
each axon
Transverse section showing the coverings of a spinal nerve
Why are all spinal nerves classified as mixed nerves'
OI
I 1'
„i lower limbs. Among the nerves that arise from this
«,,: are the gluteal, sciatic, and pudendal nerves. The sci-
jenerve is the longest nerve in die body.
Spinal nerves T2 to Til do not form plexuses. They
uown as intercostal nerves and extend directly to the
■s they supply, including the muscles between ribs,
,[ muscles, and skin of the chest and back (see
i.2).
I CHECKPOINT
do spinal nerves connect to the spinal cord?
Winch regions of the body are supplied by plexuses, and
iich are served by intercostal nerves?
SPINAL CORD FUNCTIONS
rail
(oajECTIVES • Describe the functions of the spinal cord.
, Describe the components of a re flex ar c.
I The spinal cord white matter and gray matter have two ma-
, I, tinns in maintaining homeostasis. (1) The white mat-
I Krofthe spina) cord consists of tracts that serve as highways
r nerve impulse conduction. Along these highways, sensory
I mpulses travel toward the brain and motor impulses travel
I from the brain toward skeletal muscles and other effector tis-
[.The route that nerve impulses follow from a neuron in
,ii nl the body to odier neurons elsewhere in the body
,'i, I i pathway. After describing the functions of various
i, in s ,.1'ilie brain, we will depict some important pathways
[connect the spinal cord and brain (see Figures 10. 14 and
!)The gray matter of the spinal cord receives and in-
incoming and outgoing information and is a site for
■ation of reflexes. A reflex is a fast, involuntary sequence
that occurs in response to a particular stimulus,
tflexes are inborn, such as pulling your hand away
surface before you even feel that it is hot (a wtth-
i reflex). Other reflexes are learned or acquired, such
m an\ reflexes you learn while acquiring driving skills,
-ration takes place in the spinal cord gray matter,
is a spinal reflex. By contrast, if integration occurs
brain stem radier than the spinal cord, the reflex is a
flex. An example is die tracking movements of your
i! read this sentence.
The pathway followed by nerve impulses that produce a
is known as a reflex arc. Using the patellar reflex (knee
; an example, die basic components of a reflex
, follows (Figure 10.5);
A Sensory receptor. The distal end of a sensory neuron
(or sometimes a separate receptor cell) serves as a sensory
Sensory receptors respond to a specific type of
muhis by generating one or more nerve impulses. In
patellar "reflex, sensory receptors known as muscle
Spinal Cord Functions 247
spindles detect slight stretching of the quadriceps femoris
(anterior thigh) muscle when the patellar (knee cap) liga-
ment is tapped with a reflex hammer.
A Sensory neuron. The nerve impulses conduct from the
sensory receptor along the axon of a sensory neuron to
its axon terminals, which are located in the CNS gray
matter. Axon branches of the sensory neuron also relay
nerve impulses to the brain, allowing conscious aware-
ness that the reflex has occurred.
Integrating center. One or more regions of gray matter
in the CNS act as an integrating center. In die simplest
type of reflex, such as the patellar reflex, the integrating
center is a single synapse between a sensory neuron and a
motor neuron. In other types of reflexes, the integrating
center includes one or more interneurons,
Motor neuron. Impulses triggered by the integrating
center pass out of the spinal cord (or brain stem, in the
case of a cranial reflex) along a motor neuron to die part
of the body that will respond. In the patellar reflex, the
axon of the motor neuron extends to the quadriceps
femoris muscle.
Effector. The part of the body that responds to die mo-
tor nerve impulse, such as a muscle or gland, is the effec-
tor. Its action is a reflex. If the effector is skeletal muscle,
the reflex is a somatic reflex. If the effector is smooth
muscle, cardiac muscle, or a gland, the reflex is an auto-
nomic (visceral) reflex. For example, the acts of swallow-
ing, urinating, and defecating all involve autonomic re-
flexes. The patellar reflex is a somatic reflex because its
effector is the quadriceps femoris muscle, which con-
tracts and thereby relieves the stretching diat initiated
the reflex. In sum, die patellar reflex causes extension ot
the knee by contraction of the quadriceps femoris muscle
in response to tapping the patellar ligament.
Damage or disease anywhere along a reflex arc can cause
the reflex to be absent or abnormal. For example, absence
of the patellar reflex could indicate damage of the sen-
sory or motor neurons, or a spinal cord injury, in the lum-
bar region. Somatic reflexes generally can be tested simplj
by tapping or stroking the body surface. Most autonomic
reflexes, by contrast, are not practical diagnostic tools be-
cause it is difficult to stimulate visceral receptors, which
are deep inside the body. Vn exception is the pupillary
light reflex, in which the pupils of both eyes decrease in
diameter when either eye is exposed to light. Because the
reflex arc includes synapses in lower parts of die brain, the
absence of a normal pupillary light reflex may indicate
brain damage or injury.
■ CHECKPOINT
6. What is the significance of the white matter tracts of the
spinal cord?
7. How are somatic and autonomic reflexes similar and dif-
ferent?
248 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
Figure 10.5 Patellar reflex, showing general components of a reflex arc. The arrows show the direction of nerve impulse
A reflex is a fast, involuntary sequence of actions that occurs in response to a particular stimulus.
To brain
Which attachment of a spinal news to the spinal cord contains axons of sensory neurons? Which attachment contains axons of motor
neui
BRAIN
OBJECTIVES • Discuss how the brain is protected
and supplied with blood*
• Name the major parts of the brain and explain the
function of each part.
• Describe three somatic sensory and somatic motor
pathways.
Next, we will consider the major parts of the brain, how the
brain is protected, and how it is related to the spinal cord and
cranial nerves.
Major Parts and Protective Coverings
The brain is one of die largest organs of the bod]
of about 100 billion neurons and 10-50 trillion n
with a mass of about 1300 g (almost 3 lb). The fo
parts are the brain stem, diencephalon, cerebrum, am
bellum (Figure 10.6), The brain stem is continuous \vr
spinal cord and consists of the medulla oblongata, po
midbrain. Above the brain stem is the diencephdim (Ji
SEF-a-lon; di- = through; -encephalov - brain), cti
mostly of the thalamus, hypothalamus, and pined
Supported on the diencephalon and brain stem and
the bulk of the brain is the cerebrum (se-RE-brum -\
ture 10.6 Brain. The pituitary gland is discussed together with the endocrine system in Chapter 13.
The four major parts of the brain are the brain stem, cerebellum, diencephalon, and cerebrum.
Sagittal
plane
DIENCEPHALON:
Thalamus
: m
Hypothalamus
Pineal gland
BRAIN STEM:
Midbrain
Medulla oblongata
Brain 249
CEREBRUM
CFREBELLU
Pituitary gland
Spinal cord
POSTERIOR
ANTERIOR
POSTERIOR
CEREBRUM
CEREBELLUM
Spinal cord
(a) Sagittal section, medial view
ANTERIOR
(b) Sagittal section, medial view
DIENCEPHALON:
Thalamus
Hypothalamus
BRAIN STEM:
Midbrain
Pons
Medulla oblongata
Which part of the brain attaches to the spinal cord?
250 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
The surface of the cerebrum is composed of a thin layer of
gray matter, the cerebral cortex (cortex = rind or bark), be-
neath which lies the cerebral white matter. Posterior to the
brain stem is the cerebellum (ser'-e-BEL-um = little brain).
As you learned earlier in the chapter, the brain is pro-
tected by the cranium and cranial meninges. The cranial
meninges have the same names as the spinal meninges: the
outermost dura mater, middle arachnoid mater, and inner-
most pia mater (Figure 1 0.7).
Brain Blood Supply and
the Blood- Brain Barrier
Although the brain constitutes only about 2% of total body
weight, it requires about 20% of die body's oxygen supply. If
blood flow to the brain stops, even briefly, unconsciousness
may result. Brain neurons that are totally deprived of oxygen
for four or more minutes may be permanently injured. Blood
supplying the brain also contains glucose, the main source of
energy for brain cells. Because virtually no glucose is stored
in the brain, the supply of glucose also must be continuous. If
blood entering the brain has a low level of glucose, mental
confusion, dizziness, convulsions, and loss of consciousness
may occur.
The existence of a blood- brain barrier (BBB) protects
brain cells from harmful substances and pathogens by pre-
venting passage of many substances from blood into brain
tissue. This barrier consists basically of very tightly sealed
blood capillaries (microscopic blood vessels) in the brain.
However, lipid-soluble substances such as oxygen, carbon
dioxide, alcohol, and most anesthetic agents, easily cross the
blood-brain barrier. Trauma, certain toxins, and inflamma-
tion can cause a breakdown of the blood -brain barrier.
Cerebrospinal Fluid
The spinal cord and brain are further protected against
chemical and physical injury by cerebrospinal fluid (CSF).
CSF is a clear, colorless liquid that carries oxygen, glucose,
and other needed chemicals from the blood to neurons and
neuroglia and removes wastes and toxic substances produced
by brain and spinal cord cells. CSF circulates through the
subarachnoid space (between the arachnoid mater and pia
mater), around the brain and spinal cord, and through cavi-
ties in the brain known as ventricles (VEN-tri-kols = little
cavities). There are four ventricles: two lateral ventricles,
one third ventricle, and one fourth ventricle (Figure 10.7).
Openings connect them with one another, with the central
canal of the spinal cord, and with the subarachnoid space.
The sites of CSF production are the choroid plexuses
(KO-royd = membranelike), which are specialized networks
of capillaries in the walls of the ventricles (Figure 10.7).
Covering the choroid plexus capillaries are ependymal cells,
which form cerebrospinal fluid from blood plasma by filtra-
tion and secretion. From the fourth ventricle, CSFftj
the central canal of the spinal cord and into the subai
space around the surface of the brain and spinal cord, (j
gradually reabsorbed into the blood through arad
which are fingerlike extensions of the arachnoid rnv,
CSF drains primarily into a vein called the superior
sinus (Figure 10.7). Normally, the volume of CSF
constant at 80 to 150 mL (3 to 5 oz) because it is absoi
rapidly as it is formed.
Abnormalities in the brain- -tumors, inflammation, j
I velopmental malformation— can interfere with
drainage of CSF from the ventricles into the subarac
space. When excess CSF accumulates in the ventric
CSF pressure rises. Elevated CSF pressure causes a
tion called hydrocephalus (hi'-dro-SEF-a-lu
water; cephal- — head). In a baby in whom the
have not yet closed, the head bulges due to the incn
pressure. If the condition persists, the fluid Ij
compresses and damages the delicate nervous
Hydrocephalus is relieved by draining the exce
neurosurgeon may implant a drain line, calld i
into the lateral ventricle to divert CSF into the su
vena cava or abdominal cavity 7 , where it can be abso
the blood. In adults, hydrocephalus may occur after
injury, meningitis, or subarachnoid hemorrhage, Tin
dition can quickly become life-threatening ami
immediate intervention; since the adult skull be
already fused, nervous tissue damage occurs qui
Brain Stem
The brain stem is the part of the brain between the
cord and the diencephalon. It consists of three regij
the medulla oblongata, (2) pons, and (3) midbrain. h\
through the brain stem is the reticular formatioj
where gray and white matter are intermingled.
Medulla Oblongata
The medulla oblongata (me-DOOL-la ob'-long-(i\-t
simply medulla, is a continuation of the spinal
Figure 10.6). It forms the inferior part of the brain]
(Fi gure 10.8 on page 252). Wi th in th e m edu lla's wh i i
are all sensory (ascending) and motor (descending)
tending between die spinal cord and other parts of theb
The medulla also contains several nuclei, \vhi«
masses of gray matter where neurons form synapsi
another, Two major nuclei are the cardiovascular
which regulates the rate and force of the heartbeat
diameter of blood vessels (see Figure \5. l > on pag<
the medullary rhythmicity area, which adjusts the
rhythm of breathing (see Figure 18.12 on page 4
associated with sensations of touch and vibration an
Brain 251
Figure 10.7 Meninges and ventricles of the brain.
Cerebrospinal fluid (CSF) protects the brain and spinal cord and delivers nutrients from the blood to the brain and spinal cord;
.> CSF also removes wastes from the brain and spinal cord to the blood.
POSTERIOR
ANTERIOR
CHOROID PLEXUS OF
THIRD VENTRICLE
Cerebrum
SUBARACHNOID SPACE
ARACHNOID VILLUS
SUBARACHNOID SPACE
SUPERIOR SAGITTAL
SINUS (contains venous
blood)
LATERAL VENTRICLE
THIRD VENTRICLE
Cranial meninges:
Pia mater
Arachnoid mater
Dura mater
Path of:
> CSF
^ Venous blood
/ .
Where is CSF formed and absorbed?
Sagittal section of brain and spinal cord
252 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
Figure 10.8 Inferior aspect of the brain, showing the brain stem and cranial nerves.
The brain stem consists of the medulla oblongata, pons, and midbrain.
i
t
ANTERIOR
View
Cerebrum
Olfactory bulb
Olfactory tract
Pituitary gland
Optic tract
CEREBRAL PEDUNCLE
OF MIDBRAIN
PONS
Cerebellar
peduncles
MEDULLA
OBLONGATA
Spinal nerve C1
Spinal cord
Cerebellum
POSTERIOR
Inferior aspect of brain
CRANIAL NERVES:
Olfactory (I) nerval
Optic (II) nerve
Oculomotor (III) dot
Trochlear (IV) nerve
Trigeminal (V) nerve
Abducens (VI) mm
Facial (VII) nerve
Vestibulocochlear
(VIII) nerve
Glossopharyngeal
(IX) nerve
Vagus (X) nerve
Accessory (XI) nerve
Hypoglossal (XI I) m
Which part of the brain stem contains the cerebral peduncles?
in the posterior part of the medulla, Many ascending sen-
sory axons form synapses in these nuclei (see Figure
10.14a). Other nuclei in the medulla control reflexes for
swallowing, vomiting, coughing, hiccupping, and sneezing.
Finally, the medulla contains nuclei associated with five
pairs of cranial nerves (Figure 1 0.8): vestibulocochlear
(VTII) nerves., glossopharyngeal (IX) nerves, vagus (X)
nerves, accessory (XI) nerves (cranial portion), and hy-
poglossal (XII) nerves.
Given the many vital activities controlled by the me
V w
it is not surprising that a hard blow to the back of the b
or upper neck can be fatal. Damage to the med
rhythmicity area is particularly serious and can rap
lead to death. Symptoms oi nonfatal injury to the nn
may include paralysis and loss of sensation on the op|
side of the body, and irregularities in breadiing or
rhythm.
his
mpons(= bridge) is above the medulla and anterior to the
Ebellum (Fin-tires 10.6, 10.7, and 10.8). Like the medulla,
Lons consists of both nuclei and tracts. As its name im-
he pons is a bridge that connects parts of the brain
nth one another. These connections are bundles of axons.
L axons of the pons connect the right and left sides of the
Hum. Others are part of ascending sensory tracts and
Wing motor tracts. Several nuclei in the pom are the
here signals for voluntary movements that originate in
.cerebral cortex are relayed into the cerebellum. Other nu-
the pons help control breathing. The pons also contains
associated with the following four pairs of cranial nerves
He 10.8): trigeminal (V) nerves, abdueens (VI) nerves, fa-
\ 11) nerves, and vestibulocochlear (VTII) nerves.
midbrain
midbrain connects the pons to the diencephalon
10.7, and 10.8). The anterior part of the
,ain consists of a pair of large tracts called cerebral
K ks (pe-DUNK-kuls or PE-dung-kuls - little feet;
<)). They contain axons of motor neurons that con-
It nerve impulses from the cerebrum to the spinal cord,
tedulld, and pons and axons of sensory neurons that extend
im the medulla to the thalamus.
Nuclei of the midbrain include the substantia nigra
iTAN-she-a = substance; Nl-gra = black), which is
„u! darkly pigmented. Loss of these neurons is associ-
|.Rgure10.9 Midbrain.
The midbrain connects the pons to the diencephalon.
Brain 253
ated with Parkinson disease (see page 266). Also present are
the right and left red nuclei, which look reddish due to their
rich blood supply and an iron-containing pigment in their
neuronal cell bodies. Axons from the cerebellum and cerebral
cortex form synapses in the red nuclei, which function with
the cerebclhinj to coordinate muscular movements. Other
nuclei in the midbrain are associated with two pairs of cranial
nerves (see Figure 10.8): oculomotor (III) nerves and
trochlear (IV) nerves.
The midbrain also contains nuclei that appear as four
rounded bumps on the posterior surface. The two superior
bumps are the superior colliculi (ko-LIK-u-lT = little hills;
singular is coUimhis) (Figure 10.9). Several reflex arcs pass
through the superior colliculi: tracking and scanning move-
ments of the eyes and reflexes that govern movements of the
eyes, head, and neck in response to visual stimuli. The two
inferior colliculi are part of the auditory pathway, relaying
impulses from the receptors for hearing in the ear to the
thalamus. They also are reflex centers for the startle reflex,
sudden movements of the head and body that occur when
you are surprised by a loud noise.
Reticular Formation
In addition to the well-defined nuclei already described,
much of the brain stem consists of small clusters of neuronal
cell bodies (gray matter) intermingled with small bundles of
myelinated axons (white matter). This region is known as the
reticular formation {ret- = net) due to its netlike arrange-
POSTERIOR
Superior colliculus
Transverse
plane
Reticular formation ■
Medial lemniscus
Cerebral
peduncle
Oculomotor nucleus
Red nucleus
Substantia nigra
Corticospinal, corticopontine,
and corticobulbar axons
Oculomotor (ill) nerve
ANTERIOR
Transverse section of midbrain
functions are carried out by the superior colliculi?
254 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
ment of white matter and gray matter. Neurons within the
reticular formation have both ascending (sensory) and de-
scending (motor) functions,
The ascending part of the reticular formation is called
the reticular activating system (RAS) , which consists of sen-
sory axons that project to the cerebral cortex. When the RAS
is stimulated, many nerve impulses pass upward to wide-
spread areas of die cerebral cortex. The result is a state of
wakefulness called consciousness. The RAS helps maintain
consciousness and is active during awakening from sleep, in-
activation of the RAS produces sleep, a state of partial uncon-
sciousness from which an individual can be aroused. The
reticular formation's main descending function is to help reg-
ulate muscle tone, which is the slight degree of contraction in
normal resting muscles.
■ CHECKPOINT
8. What is the significance of the blood-brain barrier?
9. What structures are the sites of CSF production, and
where are they located?
10. Where are the medulla, pons, and midbrain located
relative to one another?
11 . What functions are governed by nuclei in die brain stem?
12. What are two important functions of the reticular
formation?
Diencephalon
Major regions of the diencephalon include the thahrtj
hypothalamus, and pineal gland (see Figure 1 0.6),
Thalamus
The thalamus (THAL-a-mus = inner chamber) consist,
paired oval masses of gray matter, organized into nuclei, \\
interspersed tracts of white matter (Figure 10,10). Nuclei
the thalamus are important relay stations for sensory impul
that are conducting to the cerebral cortex from die spinal ccj
brain stem, cerebellum, and other parts of the cerebrum
The thalamus contributes to motor functions by
mitring information from the cerebellum and basal gang!
motor areas of die cerebral cortex. It also relays nerve
pulses between different areas of the cerebrum. The th
mus contributes to the regulation of autonomic activitig
the maintenance of consciousness.
Hypothalamus
The hypothalamus (hypo- = under) is the small portion
the diencephalon that lies below die thalamus and ah
pituitary gland (see Figures 10.6 and 10 JO). Although
is small', the hypothalamus controls many important body
tivities, most of them related to homeostasis. The chief
tions of the hypothalamus are as follows:
Figure 10.10 Diencephalon: thalamus and hypothalamus. Also shown are the base! ganglia-the caudate nucleus, puta-
men, and globus pallidus.
^ The thalamus is the principal relay station for sensory impulses that reach the cerebral cortex from other parts of the brain and
the spinal cord.
■'-' " ■ - W
Frontal
plane
View
Longitudinal fissure
Cerebrum
Corpus callosum
Internal capsule
Insula
Thalamus
Hypothalamus
Anterior view of frontal section
Cerebral cortex
Cerebral white matter
Lateral ventricle
— Caudate nucleus
- Putamen
Globus pallidus
Third ventricle
Optic tract
"*) In which major part of the brain are the basal ganglia located, and what kind of tissue composes them?
Control of the ANS. The hypothalamus controls and
integrates activities of the autonomic nervous system,
which regulates contraction of smooth and cardiac mus-
cle and the secretions of many glands. Through the
\\ T S, the hypothalamus helps to regulate activities such
as heart rate, movement of food through the gastroin-
testinal tract, and contraction of the urinary bladder.
| Control of the pituitary gland and production of
hormones. The hypothalamus controls the release of
several hormones from the pituitary gland and thus
serves as a primary connection between the nervous sys-
tem and endocrine system. The hypothalamus also pro-
duces two hormones that are stored in the pituitary gland
prior to their release.
Regulation of emotional and behavioral patterns.
[Together with the limbic system (described shortly), the
Lpothalamus regulates feelings of rage, aggression, pain,
and pleasure, and the behavioral patterns related to sex-
ual arousal.
Regulation of eating and drinking. The hypothalamus
regulates eating behavior and also contains a thirst
cmter, When certain cells in the hypothalamus are stim-
ulated by rising osmotic pressure of the interstitial fluid,
they cause the sensation of thirst. The intake of water by
Banking restores the osmotic pressure to normal, remov-
ing the stimulation and relieving the thirst.
S Control of body temperature. If the temperature of
blood Bowing through the hypothalamus is above nor-
mal, the hypothalamus directs the autonomic nervous
m to stimulate activities that promote heat loss. If,
jiowever, blood temperature is below normal, the hypo-
thalamus generates impulses that promote heat produc-
tion and retention.
Regulation of circadian rhythms and states of con-
sciousness. The hypodialamus establishes patterns of awak-
ening and sleep that occur on a circadian (daily) schedule.
pineal gland (PTN-e-al = pinecone-like) is about the
.1 a small pea and protrudes from the posterior midline
pf the thinl ventricle (see Figure 10.6). Because the pineal
and secretes the hormone melatonin, it is part of the en-
Ji'iiin 1 system. Melatonin promotes sleepiness and con-
■s to the setting of the body's biological clock.
[Cerebellum
fee cerebellum consists of two cerebellar hemispheres,
nrc located posterior to the medulla and pons and be-
eerebrum (see Figure 10.6). The surface of the cere-
,11,1111, called the cerebellar cortex, consists of gray matter.
3th the cortex is white matter that resembles the
dies of a tree (see Figure 10.7). Deep within the white
Brain 255
matter are masses of gray matter, the cerebellar nuclei. The
cerebellum attaches to the brain stem by bundles of axons
called cerebellar peduncles (see Figure 10.8).
The cerebellum compares intended movements pro-
grammed by the cerebral cortex with what is actually hap-
pening. It constantly receives sensory impulses from muscles,
tendons, joints, equilibrium receptors, and visual receptors.
The cerebellum helps to smooth and coordinate complex se-
quences of skeletal muscle contractions. It regulates posture
and balance and is essential for all skilled motor activities,
from catching a baseball to dancing.
Damage to the cerebellum through trauma or disease
disrupts muscle coordination, a condition called ataxia
(a- = without; -taxia = order). Blindfolded people with
| ataxia cannot touch the tip of their nose with a linger be-
cause they cannot coordinate movement with their sense
of where a body part is located. Another sign of ataxia is a
changed speech pattern due to uncoordinated speech mus-
cles. Cerebellar damage may also result in staggering or
abnormal walking movements. People who consume too
much alcohol show signs of ataxia because alcohol inhibits
activity of the cerebellum. Alcohol overdose also sup-
presses the medullary rhythmicity area and may result in
death.
Cerebrum
The cerebrum consists of the cerebral cortex (an outer rim of
gray matter), an internal region of cerebral white matter, and
gray matter nuclei deep within the white matter (Figure
10.10). The cerebrum provides us with the ability to read,
write, and speak; to make calculations and compose music; to
remember the past and plan for the future; and to create.
During embryonic development, when there is a rapid
increase in brain size, the gray mutter of the cerebral cortex
enlarges much faster than the underlying white matter, As a
result, the cerebral cortex rolls and folds upon itself so that it
can fit into the cranial cavity. The folds are called gyri (Jl-rl
circles; singular is gyrus) (Figure 10.11). The deep grooves
between folds are fissures; the shallow grooves are sulci
(SUL-sI = groove; singular is sulcus, SUL-kus). The longitu-
dinal fissure separates the cerebrum into right and left halves
called cerebral hemispheres. The hemispheres are connected
internally by the corpus callosum (kal-LO-sum; corpus z
body; callosum - hard), a broad band of white matter
containing axons that extend between the hemispheres
(see Figure 10.10).
Each cerebral hemisphere has four lobes that arc named
after the bones that cover them; frontal lobe, parietal lobe,
temporal lobe, and occipital lobe (Figure 10. 1 l). The central
sulcus separates the frontal and parietal lobes. A major gyrus,
the precentral gyrus, is located immediately anterior to the
central sulcus. The precentral gyrus contains the primary
256 Chapter 10 Centra! Nervous System, Spinal Nerves, and Cranial Nerves
Figure 10.11 Cerebrum. The inset in (a) indicates the differences among a gyrus, a sulcus, and a fissure.
Because the insula cannot be seen externally, it has been projected to the surface in (b).
The cerebrum provides us with the ability to read, write, and speak; make calculations and compose music;
remember the past and make future plans; and create.
ANTERIOR
Gyrus ■
Sulcus
Cerebral —
cortex
Cerebral —
white matter
Fissure
Details of a gyrus,
sulcus, and fissure
Longitudinal fissure
Precentral gyrus
Central sulcus
Postcentral gyrus
Frontal lobe
Parietal lobe
Left hemisphere
w
Right hemisphere
Occipital lobe
POSTERIOR
(a) Superior view
Postcentral gyrus
Parietal lobe
Parietooccipital
sulcus
Occipital lobe
Transverse fissure
Cerebellum
X
.
1
(b) Right lateral view
What structure separates the right and left cerebral hemispheres?
Central sulcus
Precentral gyrus
Frontal lobe
Insula (projected to surface)
Lateral cerebral sulcus
Temporal lobe
motor iirc.ii of the cerebral cortex. The postcentral f gyrus, lo-
cated immediately posterior to the central sulcus, contains
the primary somatosensory area of the cerebral cortex, which
is discussed shortly. A fifth part of the cerebrum, the insula,
cannot be seen at the surface of the brain because it lies
within the lateral cerebral sulcus, deep to the parietal, frontal,
and temporal lobes (see Figure 1 0.1 0).
The cerebral white matter consists of myelinated and
unmyelinated axons that transmit impulses between gyri in
the same hemisphere, from the gyri in one cerebral hdj
sphere to die corresponding gyri in the opposite cere!
hemisphere via the corpus callosum, and from the cerebi
to other parts of the brain and spinal cord.
Deep within each cerebral hemisphere are three
(masses of gray matter) that are collectively termed the
ganglia (see Figure 10.10). (Recall that "ganglion" usual
means a collection of neuronal cell bodies outside the CM
The name here is the one exception to that general nil]
ocus on Wellness
Brain 257
Coffee
The Health Risks of
Caffeine
paffeint* has been enjoyed by people
ound the world since die beginning
history. Found naturally in over 60
ts, caffeine is the most widely eon-
led drug in North America, priniar-
as a component of coffee, tea, cola,
,| other beverages. It is also found in
i, over-die-counter drugs and in
amounts in chocolate. The aver-
coffee drinker consumes 3 cups a
ith some people (including many
lege students) consuming 10 cups or
a day. How is all of this caffeine
acting our health?
[The Java Jitters
lie's most obvious effect is on the
us system. Caffeine mimics the
{fleets of the sympathetic division of
utonomic nervous system. In gen-
ii, both caffeine and sympathetic
sal tend to wind you up. For exam-
they both make your heart beat
and harden (You will learn more
about the autonomic nervous system in
Chapter 1 1 .)
The immediate effects of caffeine
vary greatly from person to person.
Some people find that any amount of
caffeine causes undesirable symptoms
such as muscle twitches, anxiety, in-
creased blood pressure, an irregular
heartbeat, digestive complaints,
headache, and difficulty sleeping.
Other people get one or more of these
symptoms only if their caffeine con-
sumption exceeds a certain threshold.
How harmful is caffeine overload? If
these symptoms are short-lived, and
caffeine consumption is reduced or
eliminated, no lasting harm seems to
occur in otherwise healthy adults.
How Much Is Too Much?
While caffeine tolerance varies, studies
suggest that long-term consumption of
moderate amounts of caffeine probably
poses little or no risk to long-term
health. A moderate amount of caffeine
is equivalent to that contained in two
cups of coffee per day. This guideline
does not apply to people who experi-
ence negative symptoms with caffeine;
people should avoid caffeine in any
amount that leads to unhealthy symp-
toms. Some animal studies suggest a
link between caffeine and birth defects.
Thus, die U.S. Food and Drug Admin-
istration recommends that women
avoid or greatly reduce caffeine intake
during pregnancy.
Why might your tolerance far caffeine go down during high-stress times,
such as during final exam week? (Hint: Feelings of stress are associated with
overactivation of the sympathetic division of the autonomic nervous system.)
the globus pallidas {globus = hall; paUidits = pale), the
wu (pu-TA-men = shell), and die caudate mtdem {mud-
•ill A major function of the basal ganglia is to help mid-
land terminate movements. They also help regulate the
I [diil required for specific body movements and con-
ubconscious contractions of skeletal muscles, such as au-
ric arm swings while walking.
linage to the basal ganglia results in uncontrollable
ping (tremor), muscular rigidity (stiffness), and invol-
muscle movements. Movement disruptions also are
[hallmark of Parkinson disease (see page 266). In this
iirder, neurons that extend from the substantia nigra to
Bjutarncn and caudate nucleus degenerate, causing the
itions.
Limbic System
Encircling the upper part of the brain stem and the corpus
callosum is a ring of structures on the inner border of the
cerebrum and floor of the diencephalon that constitutes the
limbic system (limbic = border) (Figure 10.12)* The limbic
system is sometimes called the "emotional brain" because it
plays a primary role in a range of emotions, including pain,
pleasure, docility, affection, and anger. Although behavior
is a function of the entire nervous system, the limbic system
controls most of its involuntary aspects related to survival.
Animal experiments suggest that it has a major role in con-
trolling the overall pattern of behavior. Together with parts
of the cerebrum, the limbic system also functions in mem-
ory; damage to the limbic system causes memory impair-
ment.
258 Chapter 10 Central Nervous System, Spinal Nerves, and Crania! Nerves
Figure 10.12 The limbic system. The components of the limbic
system are shaded green.
The limbic system governs emotional aspects of behavior.
Sagittal
plane
View
POSTERIOR .„ .
Sagittal section
Where in the brain is the limbic system located?
ANTERIOR
Functional Areas of the Cerebral Cortex
Specific types of sensory, motor, and integrative signals arc
processed in certain regions of the cerebral cortex (Figure
10.13). Generally, sensory areas receive sensory information
and are involved in perception, the conscious awareness of a
sensation; motor areas initiate movements; and association
areas deal with more complex integrative functions such as
memory, emotions, reasoning, will, judgment, personality
traits, and intelligence.
SENSORY AREAS Sensory input to the cerebral cortex Bows
mainly to the posterior half of the cerebral hemispheres, to
regions behind the central sulci. In the cerebral cortex, pri-
mary sensory areas have the most direct connections with pe-
ripheral sensory receptors.
The primary somatosensory area (so'-mat-6-SEN-s6-re) is
posterior to the central sulcus of each cerebral hemisphere in
the postcentral gyrus of the parietal lobe (Figure 10.13). It
receives nerve impulses for touch, proprioception (joint and
muscle position), pain, itching, tickle, and temperature and is
involved in the perception of these sensations. The primary
somatosensory area allows yon to pinpoint where sensations
originate, so that you know exactly where on your body to
swat that mosquito. The primary visual area, located in the
occipital lobe, receives visual information and is involved in
visual perception. The primary auditory urea, located in
temporal lobe, receives information for sound and is invoS
in auditory perception. The primary gustatory area, located
the base of the postcentral gyrus, receives impulses for
and is involved in gustatory perception. The primary i
(ire a j located on the medial aspect of the temporal lobe (j
thus is not visible in Figure 10,13), receives impulses
smell and is involved in olfactory perception.
MOTOR AREAS Motor output from the cerebral cortex fl(
mainly from the anterior part of each hemisphere. Amt
the most important motor areas are the primary motel
and Broca's speech area (Figure 10.13). The primary m
area is located in the precentral gyrus of the frontal lobe
each hemisphere. Each region in the primary motor
controls voluntary contractions of specific muscles on the
posite side of the body. Broca's speech area (BRO-bz) is
cated in the frontal lobe close to the lateral cerebral suli
Speaking and understanding language are complex aetivii
that involve several sensory, association, and motor areas
die cortex. In 97% of the population, these language r
are localized in the left hemisphere. Neural connections
tween Broca's speech area, the premotor area, and prims
motor area activate muscles needed for speaking and hreat
ing muscles.
ASSOCIATION AREAS The association areas of die cereM
consist of some motor and sensory areas, plus large areas
the lateral surfaces of the occipital, parietal, and temper
lobes and on the frontal lobes anterior to the motor an
Tracts connect association areas to one another* The
matosensoty association area, just posterior to die primary
matosensory area, integrates and interprets somatic sei
dons such as the exact shape and texture of an objt
Another role of the somatosensory association area is
storage of memories of past sensory experiences, enatj
you to compare current sensations with previous experieri
For example, the somatosensory association area allows ij
to recognize objects such as a pencil and a paperclip simpj
by touching them. The visual association area, located in
occipital lobe, relates present and past visual experiences
is essential for recognizing and evaluating what is seen.
auditory association area, located below the primary audit]
area in die temporal cortex, allows you to recognize a par]
ular sound as speech, music, or noise,
Wernicke s area, a broad region in the left temporal
parietal lobes, interprets the meaning of speech by recogniz
ing spoken words. It is active as you translate words ii
thoughts. The regions in the right hemisphere that com
spond to Broca's and Wernicke's areas in the left hemispher
also contribute to verbal communication by adding emc
tional content, for instance, anger or joy, to spoken wore
The common integrative area receives and interprets nerve ii
pulses from the somatosensory, visual, and auditory assoij
tion areas, and from the primary gustatory area, primary
Brain 259
(lire 10.13 Functional areas of the cerebrum. Broca's speech area and Wernicke's area are in the left
jbral hemisphere of most people; they are shown here to indicate their relative locations.
Particular areas of the cerebral cortex process sensory, motor, and integrative signals.
.Central sulcus
PRIMARY SOMATOSENSORY
AREA (postcentral gyrus
SOMATOSENSORY
ASSOCIATION AREA
Parietal lobe
COMMON
INTEGRATIVE
AREA
VISUAL
ASSOCIATION
AREA
PRIMARY
VISUAL
AREA
Occipital lobe
WERNICKE'S AREA
POSTERIOR
PRIMARY MOTOR AREA
(precentral gyrus)
PREMOTOR AREA
FRONTAL EYE FIELD AREA
Frontal lobe
- PRIMARY GUSTATORY AREA
BROCA'S SPEECH AREA
Lateral cerebral sulcus
Temporal lobe
PRIMARY AUDITORY AREA
AUDITORY ASSOCIATION AREA
ANTERIOR
Lateral view of right cerebral hemisphere
Which part of the cerebrum localizes exactly where somatic sensations occur?
Hjrarea, the thalamus, and parts of the brain stem. The
Lfifo/" (irt'it, immediately anterior to the primary motor
crates nerve impulses that cause a specific group of
ii contract in a specific sequence, for example, to
b a word. The frontal eye field area in the frontal cortex
Is voluntary scanning movements of the eyes, such as
lit occur while you are reading this sentence,
to language areas of the cerebral cortex results
Enhasia (a-FA-ze-a; a- = without; -phasia = speech), an
uliilitj to use or comprehend words. Damage to Broca's
area results in nonfluent aphasia, an inability to
j i|i; ii, form words. People with nonfluent aphasia know
J they wish to say but cannot properly speak the
-rds. Damage to Wernicke's area, the common integra-
,ii i'a or auditory association area, results influent apha-
ricterized by faulty understanding of spoken or
tten words, A person experiencing this type of aphasia
produce strings of words that have no meaning
salad"). For example, someone with fluent aphasia
"I rang car porch dinner light river pencil"
Somatic Sensory and Somatic Motor Pathways
Somatic sensory information from the body ascends to die
primary somatosensory area via two main somatic sensory
pathways: (1) the posterior column -medial lemniscus path-
way and (2) the spinothalamic pathways. By contrast, nerve
impulses that cause contraction of skeletal muscles descend
along many pathways that originate mainly in the primary
motor area of the brain and in the brain stem.
Somatic sensory pathways relay information from somatic
sensory receptors to the primary somatosensory area in the
cerebral cortex. The pathways consist of thousands of sets of
three neurons (Figure 10,14).
Nerve impulses for conscious awareness of the position of
muscles and joints (proprioception) and for most touch sensa-
tions ascend to the cortex along the posterior column -medial
lemniscus pathway (Figure 10.14a). The name of the pathway
comes from the names of two white matter tracts that convey
the impulses; the posterior column of the spinal cord and the
medial lemniscus of the brain stem. Impulses conducted along
die posterior column-medial lemniscus pathway give rise to
three main types of sensations:
260 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
Figure 10.14 Somatic sensory pathways. Circles represent cell bodies and dendrites, lines represent axons,
and Y-shaped forks represent axon terminals. Arrows indicate the direction of nerve impulse conduction, (a) In the pos-
terior column- medial lemniscus pathway, the first-order neuron in the pathway ascends to the medulla oblongata via
the posterior column (white matter located on the posterior side of the spinal cord). In the medulla, it synapses with a
second-order neuron, which then extends through the medial lemniscus to the thalamus on the opposite side. The
third-order neuron extends from the thalamus to the cerebral cortex, (b) In the anterolateral pathway, the first-order
neuron synapses with a second-order neuron in the spinal cord gray matter. The second-order neuron extends to the
thalamus on the opposite side, and the third-order neuron extends from the thalamus to the cerebral cortex.
Nerve impulses for somatic sensations conduct to the primary somatosensory area (postcentral gyrus)
of the cerebral cortex.
RIGHT SIDE
OF BODY
Thalamus
Medial
lemniscus
LEFTSIDE
OF BODY
Primary somatosensory
area of cerebral cortex
THIRD
NEURON
RIGHT SIDE
OF BODY
Thalamus
Nuclei of
medulla
FIRST NEURON
Posterior root
ganglaon
Receptors for s#
fine touch,
proprioception,
and vibration
SECOND
NEURON
POSTERIOR
COLUMN
Spinal nerve
Cervica
spinal cord
FIRST NEURON
Posterior root
ganglion
Receptors for pain,
cold, warmth, tickle
and itch
Spinaf cord
(a) Posterior column-medial lemniscus pathway
Which somatic sensations could be lost due to damage of the spinothalamic tracts?
(b) Anterolateral (spinothalamic)
pathways
LEFTSIDE
OF BODY
Primary
somatosens
area of cei
cortex
THIRD
NEURON
SECOND
NEURON
Posterior
gray horn
LATERAL
SPINOTHAt
TRACT
Spinal nerve
ANTERIOR
SPINOTHAU
TRACT
Fine touch is the ability to recognize what point on the
body is touched plus die shape, size, and texture of the
source of stimulation.
Proprioception is the awareness of the precise position of
\mmW parts, axv^YmestVeswiiB ft\e ^waTsmess di fcettAom
of movement.
Vibratmy sensations arise when rapidly fluctuating touch
stimuli are present.
The spinothalamic pathways (spT-no-tha-LAM-ik) bej
in two spinal cord tracts — the anterior spinothalamic
and the lateral spinothalamic tract (Figure 10.141)). The
tracts relay impulses for pain, thermal (hot and cold tempera]
Neurons in the brain and spinal cord coordinate a
untary and involuntary movements. Ultimately, all $mm
motor pathways that control movement converge on nun
wn as fairer motor neurons (Figure 10, 1 5), The axons of
,.i motor neurons extend out of the brain stem to stimu-
skeletal muscles in the head and out of the spinal cord to
filate skeletal muscles in the limbs and trunk.
wer motor neurons receive their instructions from
| other neurons in the brain and spinal cord.
Neart)y local mtcrneurom help coordinate rhythmic activ-
ity in specific muscle groups, such as alternating flexion
and extension of the lower limbs during walking.
Local interneurons and lower motor neurons receive in-
put from upper motor neurons (Figure 10.15). Upper
motor neurons plan, initiate, and direct sequences ol vol-
untary movements. Two major tracts that conduct nerve
Impulses from upper motor neurons in die cerebral cor-
are the lateral corticospinal tract and anterior corti-
cospinal tract. Notice that axons of upper motor neurons
| from one cerebral hemisphere cross over and synapse
I with lower motor neurons in the other side of the spinal
[cord (Figure 10.15).
| The basal ganglia communicate with motor areas of the
cerebral cortex, thalamus, and substantia nigra. These
ections help initiate and terminate movements, sup-
press unwanted movements, and establish a normal level
[of muscle tone.
Neurons connect the cerebellum with motor areas ol the
bra I cortex and the brain stem. The cerebellum coor-
dinates body movements and helps maintain normal pos-
itive and balance.
iage or disease of lower motor neurons produces flac-
paralysis of muscles on the same side of the body: the
, lack voluntary control and reflexes, muscle tone is
led or lost, and the muscle remains flaccid (limp).
jit 1 1, or disease of upper motor neurons causes spastic
jlysis of muscles on the opposite side of the body. In
idition muscle tone is increased, reflexes are exag-
and pathological reflexes appear.
spheric Lateralization
Wi die brain is quite symmetrical, there are subtle
in unreal differences between the two hemispheres. They
functionally different in some ways, with each hemi-
specializing in certain functions. This functional
try is termed hemispheric lateralization.
ou have seen, the left hemisphere receives sensory
from and controls the right side of the body, and die
t hemisphere receives sensory signals from and controls
side of the body. In addition, the left hemisphere is
important for spoken and written language, numerical
mi fie skills, ability to use and understand sign lan-
iii.l reasoning in most people. Patients with damage
Brain 261
Figure 10.15 Somatic motor pathways. Shown here are the
two most direct pathways whereby signals initiated by the primary
motor area in one hemisphere control skeletal muscles on the oppo-
site side of the body Circles represent cell bodies and dendrites,
lines represent axons, and Y-shaped forks represent axon terminals.
Lower motor neurons stimulate skeletal muscles to produce
movements.
•- w
RIGHT SIDE
OF BODY
Primary motor area of cerebral cortex
LEFTSIDE
OF BODY
Internal
capsule
V r I :-:■ r-ri i : l
V
UPPER —
MOTOR
NEURONS
Pons
Cerebral
peduncle
Medulla
Spinal cord
Right anterior
corticospinal
tract
Spinal nerve
Left lateral
corticospinal
tract
LOWER
MOTOR
NEURONS
To skeletal
muscles
■n
Spinal cord
What two spinal cord tracts conduct impulses along axons of up-
per motor neurons?
262 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
in the left hemisphere, for example, often have difficulty
speaking, The right hemisphere is more important for musi-
cal and artistic awareness; spatial and pattern perception;
recognition of faces and emotional content of language; and
for generating mental images of sight, sound, touch, taste,
and smell.
Memory
Without memory, we would repeat mistakes and be unable to
learn. Similarly, we would not be able to repeat our successes
or accomplishments, except by chance. Memory is the
process by which information acquired through learning is
stored and retrieved. For an experience to become part ol
memory, it must produce structural and functional changes in
the brain. The parts of the brain known to be involved with
memory include the association areas of the frontal, parietal,
occipital, and temporal lobes; parts of the limbic system; and
the diencephalon. Memories for motor skills, such as how to
serve a tennis ball, are stored in the basal ganglia and cerebey
lum as well as in the cerebral cortex.
Electroencephalogram (EEG)
At any instant, brain neurons are generating millions of nn,
impulses* Taken together, these electrical signals are called!
brain waves. Brain waves generated by neurons close to the
brain surface, mainly neurons in the cerebral cortex, can bej
detected by metal electrodes placed on the forehead and
scalp. A record of such waves is called an electroencephalo-
gram (e-lek'-tro-en-SEF-a-lo-gram) or EEG, Electn
cephalograms are useful for studying normal brain functions
such as changes that occur during sleep. Neurologists aii
use them to diagnose a variety of brain disorders, such
epilepsy, tumors, metabolic abnormalities^ sites of tram
and degenerative diseases.
fable 1 0.1 summarizes the principal parts of the bi
and their functions.
Table 10.1 Summary of Functions of Principal Parts of the Brain
Part
Function
Part
Function
Brain Stem
k
Medulla
oblongata
Medulla oblongata: Relays motor and
sensory impulses between other parts
of the brain and the spinal cord. Reticu-
lar formation {also in pons, midbrain,
and diencephalon) functions in con-
sciousness and arousal. Vital centers
regulate heartbeat, breathing (together
with pons), and blood vessel diameter.
Other centers coordinate swallowing,
vomiting, coughing, sneezing, and hic-
cupping. Contains nuclei of origin for
cranial nerves VIII, IX, X, XI, and XII.
Pons: Relays impulses from one side of
the cerebellum to the other and between
the medulla and midbrain. Contains nu-
clei of origin for cranial nerves V, VI, VII,
and VIII, Together with the medulla,
helps control breathing.
Pons
Midbrain
Midbrain: Relays motor impulses from
the cerebral cortex to the pons and sen-
sory impulses from the spinal cord to
the thalamus. Most of substantia nigra
and red nucleus contribute to control of
movement. Contains nuclei of origin for
cranial nerves III and IV
Diencephalon
Pineal
gland
Thalamus
Hypothalamus
Cerebellum
Cerebellum
Cerebrum
\
Cerebrum
Thalamus: Relays almost all sensory impuls
to the cerebral cortex. Provides crude percep
tion of touch, pressure, pain, and temperat
Also functions in cognition and awareness,
Hypothalamus: Controls and integrates acta
ties of the autonomic nervous system and pit
itary gland. Regulates emotional and behav-
ioral patterns and circadian rhythms. Controls]
body temperature and regulates eating and
drinking behavior. Helps maintain waking ste
and establishes patterns of sleep.
Pineal gland: Secretes the hormone mela-
tonin.
Compares intended movements with what
actually happening to coordinate complex,
skilled movements. Regulates posture and
ance.
Sensory areas are involved in the perception
of sensory information, motor areas control
muscular movement, and association areas
deal with more complex integrative functions
such as memory, personality traits, and if
gence. Basal ganglia coordinate automatic
muscle movements and help regulate muscle
tone. Limbic system functions in emotional
pects of behavior related to survival.
CHECKPOINT
[Why is the hypothalamus considered part of both the
nervous system and the endocrine system?
I, What are die functions of the cerebellum and basal ganglia?
I Where are the primary somatosensory area and primary
motor area located in the brain? What are their functions?
I What areas of the cerebral cortex are needed for normal
language abilities?
f. Compare and contrast the posterior column -medial
lemniscus pathway and the spinothalamic pathways.
IRANIAL NERVES
)BJECTIVE • Identify the 12 pairs of cranial nerves by
ic and number and give the functions of each,
p 12 pairs of cranial nerves, like spinal nerves, are part of
| peripheral nervous system. The cranial nerves are desig-
ned with roman numerals and with names (see Figure
!, The roman numerals indicate the order (anterior to
Cranial Nerves 263
posterior) in which the nerves emerge from the brain. The
names indicate the distribution or function.
Cranial nerves emerge from the nose (cranial nerve I),
the eyes (cranial nerve IT), the inner ear (cranial nerve VIII),
the brain stem (cranial nerves II1-XII), and the spinal cord
(part of cranial nerve XI). Two cranial nerves (cranial nerves I
and IT) contain only sensory axons and thus arc sensory nerves.
The rest are mixed nerves because they contain axons of both
sensory and motor neurons. Cranial nerves III, IV, VI, XT,
and Xil are mainly motor. A few of their axons are sensory
axons from muscle proprioceptors, but most ot their axons
are motor neurons that innervate skeletal muscles. Cranial
nerves III, VII, DC, and X include both somatic and autonomic
motor axons. The somatic axons stimulate skeletal muscles; the
autonomic axons, which are part of the parasympathetic divi-
sion, go to glands, smooth muscle, and cardiac muscle.
Table 10.2 lists the cranial nerves, along with their com-
ponents (sensory or mixed) and functions.
■ CHECKPOINT
18. What is the difference between a mixed cranial nerve and
a sensory cranial nerve?
Table 10.2 Summary of Cranial Nerves (see Figure 10.8)
Name'
Components
Function
Olfactory nerve (oi-FAK-to-re;
olfact- = to smell)
Sensory: Axons in the lining of the nose.
Smell.
Optic nerve (OP-tik; opth - the
eye, vision)
Sensory: Axons from the retina of the eye.
Vision.
Oculomotor nerve (ok'-u-ld-MCMor;
oculo- = eye; -motor = mover)
Sensory part: Axons from proprioceptors in the
eyeball muscles.
Motor part: Axons of somatic motor neurons
that stimulate muscles of upper eyelid and four
muscles that move the eyeballs plus axons of
parasympathetic neurons that pass to two
smooth muscles— the ciliary muscle of the
eyeball and the sphincter muscle of the iris.
Muscle sense (proprioception).
Movement of eyelid and eyeball;
alters lens for near vision and
constricts pupil.
Trochlear nerve (TROK-le-ar;
trochie- - a pulley)
Sensory part: Axons from proprioceptors in the
superior oblique muscles (muscles that move
the eyeballs).
Motor part: Axons of somatic motor neurons
that stimulate the superior oblique muscles.
Muscle sense (proprioception),
Movement of the eyeball.
Trigeminal nerve (tri-JEM-i-nal
triple, for its three branches)
Sensory part: Consists of three branches: the
ophthalmic nerve contains axons from the scalp
and forehead skin; the maxillary nerve contains
axons from the lower eyelid, nose, upper teeth,
upper lip, and pharynx; and the mandibular nerve
contains axons from the tongue, lower teeth, and
the lower side of the face.
Motor part: Axons of somatic motor neurons that
stimulate muscles used in chewing.
Touch, pain, and temperature
sensations and muscle sense
(proprioception).
Chewing.
(Continues)
264 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
Table 10.2 Summary of Cranial Nerves (Continued)
Number
Name
Components
Function
VI
Abducens nerve (ab-DOO-senz;
ab- = away; -ducens — to lead)
Sensory part: Axons from proprioceptors in
lateral rectus muscles (muscles that move
the eyeballs).
Motor part: Axons of somatic motor neurons
that stimulate the lateral rectus muscles.
Muscle sense (proprioception).
Movement of eyeball.
VII
Facial nerve (FA-shal = face)
Vlll
Vestibulocochlear nerve
( vest-ti b- u - 1 6- KO K- 1 e -a r ; vestibulo-
= small cavity; -cochlear - a spiral,
snail-like)
IX
Glossopharyngeal nerve
(glos'-o-fa-RIN-je-al; gfosso- - tongue;
-pharyngeal = throat)
X
Vagus nerve (VA-gus;
vagus = vagrant or wandering)
Sensory part: Axons from taste buds on tongue
and axons from proprioceptors in muscles of
face and scalp.
Motor part: Axons of somatic motor neurons that
stimulate facial, scalp, and neck muscles plus
parasympathetic axons that stimulate lacrimal
(tear) glands and salivary glands.
Taste and muscle sense
(proprioception).
Facial expressions; secretion of
tears and saliva.
Vestibular branch, sensory part: Axons from
semicircular canals, saccule, and utricle (organs
of equilibrium).
Vestibular branch, motor part: Axons that
synapse with sensory receptors (hair cells)
for equilibrium.
Cochlear branch, sensory part: Axons from
spiral organ (organ of hearing).
Cochlear branch, motor part: Axons that
synapse with sensory receptors (hair cells)
for hearing.
Equilibrium.
Adjusts sensitivity of hair cells.
Hearing.
Modifies responses of hair cells,
Sensory portion: Axons from taste buds and
somatic sensory receptors on part of tongue,
from proprioceptors in some swallowing
muscles, and from stretch receptors in carotid
sinus and chemoreceptors in carotid body.
Motor portion: Axons of somatic motor
neurons that stimulate swallowing muscles of
throat plus parasympathetic axons that
stimulate a salivary gland,
Taste and somatic sensations
(touch, pain, and temperature)
from tongue; muscle sense
(proprioception); monitoring blood
pressure; monitoring oxygen and
carbon dioxide in blood for
regulation of breathing.
Swallowing; secretion of saliva.
Sensory portion: Axons from proprioceptors
in muscles of neck and throat, from stretch
receptors and chemoreceptors in carotid sinus
and carotid body, from chemoreceptors in
aortic body, and from visceral sensory
receptors in most organs of the thoracic and
abdominal cavities.
Motor portion: Axons of somatic motor
neurons that stimulate skeletal muscles of the
throat and neck plus parasympathetic axons
that supply smooth muscle in the airways,
esophagus, stomach, small intestine, most of
the large intestine, and gallbladder; cardiac
muscle in the heart; and glands of the
gastrointestinal tract.
Somatic sensations (touch, pain,
temperature) from throat and
pharynx; monitoring of blood
pressure; monitoring of oxygen and
carbon dioxide in blood for
regulation of breathing; sensations
from visceral organs in thorax and
abdomen.
Swallowing, coughing, and voice
production; smooth muscle
contraction and relaxation in
organs of the gastrointestinal trad;
slowing of the heart rate; secretion
of digestive fluids.
Common Disorders 265
Number
Name
Components
Function
XI
Accessory nerve
(ak-SES-6-re = assisting)
Sensory part: Axons from proprioceptors in
muscles of throat and voice box.
Muscle sense (proprioception).
XII
•Amnemonic device that can be used to remember the names of the nerves is: 'Oh, oh, oh, to touch and feel very green vegetables— AH!" Each boldfaced
corresponds to the first letter of a pair of cranial nerves.
Hypoglossal nerve (hi'-po-GLOS-al;
hypo- = below; -glossal - tongue)
Motor part: Axons of somatic motor neurons
that stimulate muscles of the throat and neck.
Sensory part: Axons from proprioceptors in
tongue muscles.
Motor part: Axons of somatic motor neurons
that stimulate muscles of tongue.
Swallowing and movements of
head and shoulders.
Muscle sense (proprioception).
Movement of tongue during speech
and swallowing.
AGING AND THE
NERVOUS SYSTEM
OBJECTIVE • Describe the effects of aging on the
nervous system,
be brain grows rapidly during the first few years of life.
Growth is due mainly to an increase in the size of neurons al-
present, die proliferation and growth of neuroglia, the
development of dendritic branches and synaptic contacts, and
Ltimiing myelination of axons. From early adulthood on-
ward, brain mass declines. By the time a person reaches age
80, the brain weighs about 7% less than it did in young-
adulthood. Although the number of neurons present does not
decrease very much, the number of synaptic contacts de-
clines. Associated with the decrease in brain mass is a de-
creased capacity for sending nerve impulses to and from the
brain. As a result, processing of information diminishes.
Conduction velocity decreases, voluntary motor movements
slow down, and reflex times increase.
CHECKPOINT
. How is brain mass related to age?
COMMON
DISORDERS
w
■pinal Cord Injury
lost spinal cord injuries are due to trauma as a result of factors
Kchas automobile accidents, falls, contact sports, diving, or acts of
llence, The effects of the injury depend on the extent of direct
uma to the spinal cord or compression of the cord by fractured
ilaccd vertebrae or blood clots. Although any segment of the
cord may be involved, most common sites of injury are in the
Cvical lower thoracic, and upper lumbar regions. Depending on
[location and extent of spinal cord damage, paralysis may occur.
plepa (mono- = one; -plegia = blow or strike) is paralysis of
L limb only. Diplegia (di- = two) is paralysis of both upper limbs
jlboth lower limbs. Paraplegia {para- = beyond) is paralysis of
lower limbs. Hemiplegia (hemi- = half) is paralysis of the up-
\ trunk, and lower limb on one side of the body, and quad-
^Mk(t[tutd- = four) is paralysis of all four limbs.
Shingles
Shingles is an acute infection of the peripheral nervous system caused
by herpes zoster (HER-pez ZOS-ter), the virus that also causes chick-
enpox. After a person recovers from chickenpox, the virus retreats to a
posterior root ganglion. If die virus is reactivated, it may leave the
ganglion and travel down sensory axons to the skin. The result is pain,
discoloration of die skin, and a characteristic line of skin blisters. 1 he
line of blisters marks the distribution of the particular sensory nerve
belonging to the infected posterior root ganglion.
Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis (MS) (a'-mi-6'-TROF-ik; a- = with-
out; myo- = muscle; trophic - nourishment) is a progressive degenera-
tive disease that attacks motor areas of die cerebral cortex, axons of
upper motor neurons, and lower motor neuron cell bodies. ALS is
commonly known as Lou Gehrig** disease after the New York Yankees
baseball player who died of it at age 37 in 1941. ALS causes progres-
sive muscle weakness and atrophy ALS often begins in sections of die
266 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
spinal cord that serve the hands and amis but rapidly spreads to in-
volve the whole body and face, without affecting intellect or sensa-
tions. Death typically occurs in 2 to 5 years. ALS may be caused by
the buildup in the synaptic cleft of the neurotransmitter glutamate re-
leased by motor neurons. The excess glutamate causes motor neurons
to malfunction and eventually die. The drug riluzole, which is used to
treat ALS, reduces damage to motor neurons by decreasing the re-
lease of glutamate. Other factors implicated in the development of
ALS include damage to motor neurons by free radicals, autoimmune
responses, viral infection, deficiency of nerve growth factor, apoptosis
(programmed cell death), environmental toxins, and trauma.
Cerebrovascular Accident
The most common brain disorder is a cerebrovascular accident
(CVA), also called a stroke or brain attack, CVAs affect 500,000
people a year in the United States and represent the third leading
cause of death, behind heart attacks and cancer. A CVA is character-
ized by abrupt onset of persisting symptoms, such as paralysis or
loss of sensation, that arise from destruction of brain tissue. Com-
mon causes of CVAs are hemorrhage from a blood vessel in die pia
mater or brain, blood clots, and formation of cholesterol-containing
atherosclerotic plaques that block brain blood flow. The risk factors
implicated in GVAs are high blood pressure, high blood cholesterol,
heart disease, narrowed carotid arteries, transient ischemic attacks (dis-
cussed next), diabetes, smoking, obesity, and excessive alcohol intake.
Transient Ischemic Attack
A transient ischemic attack (TIA) is an episode of temporary cere-
bral dysfunction caused by impaired blood flow to part of the brain.
Symptoms include dizziness, weakness, numbness, or paralysis in a
limb or in one side of the body; drooping of one side of the face-
headache; slurred speech or difficulty understanding speech; and a
partial loss of vision or double vision. Sometimes nausea or vomit-
ing also occurs. The onset of symptoms is sudden and reaches maxi-
mum intensity almost immediately. A TIA usually persists for 5 to
10 minutes and only rarely lasts as long as 24 hours. Tt leaves no
persistent neurological deficits. The causes of TIAs include blood
clots, atherosclerosis, and certain blood disorders.
Poliomyelitis
Poliomyelitis, or simply poifo, is caused by a virus called poliovirus.
The onset of the disease is marked by fever, severe headache, a stiff
neck and back, deep muscle pain and weakness, and loss of certain
somatic reflexes. In its most serious form, the virus produces paraly-
sis by destroying cell bodies of motor neurons, specifically those in
the anterior "boms of the spinal cord and in the nuclei of the cranial
nerves. Polio can cause death from respiratory or heart failure if the
virus invades neurons in vital centers that control breathing and
heart functions in die brain stem. Even though polio vaccines have
virtually eradicated polio b the United States, outbreaks oi polio
continue throughout the world. Due to international travel, polio
could easily be reintroduced into North America if individuals are
not vaccinated appropriately.
Several decades after suffering a severe attack of polio and fol-
lowing their recovery from it, some individuals develop a condition
called post-polio syndrome. This neurological disorder is charad
ized by progressive muscle weakness, extreme Fatigue, loss off
don, and pain, especially in muscles and joints. Post-polio syndi
seems to involve a slow degeneration of motor neurons that mm mi
muscle fibers. Triggering factors appear to be a fall, a minor n
surgery, or prolonged bed rest. Possible causes include overnsfl
surviving motor neurons over time, smaller motor neurons beat
of the initial infection by the virus, reactivation of dormant pi
viruses, immune-mediated responses, hormone deficiencies, and
vironmental toxins. Treatment consists of muscle-strengthening ejj
rises, administration of drug's to enhance the action of aectykhc
in stimulating muscle contraction, and administration of
growth factors to stimulate both nerve and muscle growth.
Parkinson Disease
Parkinson disease (PD) is a progressive disorder of the ( \^
typically affects its victims around age 60. Neurons that a
Worn the substantia nigra to the putamen and caudate nude
where they release the neurotransmitter dopamine (DA), d
ate in PD, The cause of PD is unknown, but toxic enviromw
chemicals, such as pesticides, herbicides, and carbon monoxide,
suspected contributing agents. Only 5% of PD patients have a
ily history of the disease,
In PD patients, involuntary skeletal muscle contractions ol
interfere with voluntary movement. For instance, the muscles ofi
upper limb may alternately contract and relax, causing the hind I
shake. This shaking, called tremor, is the most common symptfli
PD. Also, muscle tone may increase greatly, causing rigidity ot the
volved body part. Rigidity of die facial muscles gives the face a
like appearance. The expression is characterized by a wide-eyed^
blinking stare and a slightly open mouth with uncontrolled dri
Motor performance is also impaired by bradykinesia {km
slow), slowness of movements. Activities such as shaving, cut
food, and buttoning a shirt take longer and become inc
more difficult as the disease progresses. Muscular movements
exhibit hypokinesia (hypo- = under), decreasing range of mot
For example, words are written smaller, letters are poorly fonffl
and eventually handwriting becomes illegible. Often, walking
impaired; steps become shorter and shuffling, and arm swing
ishes. Even speech may be affected.
Alzheimer Disease
Alzheimer disease (ALTZ-hT-mcr) or AD is a disabling senile
mentia, the loss of reasoning and ability to care for oneself,
flicts about 11% of the population over age 65. In the Vt
States, AD afflicts about 4 million people and claims over
lives a year. The cause of most AD cases is still unknown, bu
dence suggests it is due to a combination ol genetic factors
ronmental or lifestyle factors, and the aging process. Mutatioi
three different genes (coding for presenilin-1, preseniM
amyloid precursor protein) lead to early-onset forms of AD
flicted families but account for less than 1% of all cases. An
ronmental risk factor for developing AD is a history of he;
A similar dementia occurs in boxers, probably caused by rep
blows to the head.
Individuals with AD initially have trouble remembering recent
Lib. They then become confused and forgetful, often repeating
ions or getting lost while traveling to previously familiar places,
Hsoricntation increases; memories of past events disappear; and
Ijsodes of paranoia, hallucination, or violent changes in mood may
leur As their minds continue to deteriorate, AD patients lose dieir
■Utstv to read, write, talk, eat, or walk. At autopsy, brains of \l) vic-
Study Outline 267
tims show three distinct structural abnormal i ties: (1) loss of neurons
that liberate acetylcholine from a brain region called the nucleus
basalis, located below the globus pallidus; (2) beta-amyloid plaques,
clusters of abnormal proteins deposited outside neurons; and (3) neu-
rofibrillary tangles, abnormal bundles of protein filaments inside neu-
rons in affected brain regions. A person with AD usually dies ol some
complication that afflicts bedridden patients, such as pneumonia.
IEDICAL TERMINOLOGY AND CONDITIONS
hdgesm (an'-al-JE-ze-a; an- = without; -algesia = painful con-
dition) Pain relief.
imstbesm (an'-es-THE-ze-a; -esthesia = feeling) Loss of sensation.
tdousness (KON-shus-nes) A state of wakefulness in which an
individual is fully alert, aware, and oriented, partly as a result of
feedback between the cerebral cortex and reticular activating
system.
dementia (de-MKN-shc-a; de- = away from; -mentia = mind)
Permanent or progressive general loss of intellectual abilities,
including impairment of memory, judgment, and abstract
thinking, and changes in personality.
Wmfbalitis (en'-sef-a-Ll-tis) An acute inflammation of the brain
caused by either a direct attack by any of several viruses or an
allergic reaction to any of the many viruses that are normally
t harmless to the central nervous system. If the virus affects the
ml cord as well, the condition is called encephalomyelitis.
mdureil block Injection of an anesthetic drug into the epidural
space, the space between die dura mater and the vertebral column,
to cause a temporary loss of sensation. Such injections in the lower
lumbar region are used to control pain during childbirth.
inptis (men-iivJT-tis) Inflammation of the meninges.
Nerve block Loss of sensation due to injection of a local anes-
thetic; an example is local dental anesthesia.
Neuralgia (noo-RAL-je-a; near- = nerve; -algia = pain) Attacks
of pain along the entire length ur i branch of a peripheral sen-
sory nerve.
Neuritis (near- = nerve; -his = inflammation) Inflammation of
one or several nerves, resulting from irritation caused by bone
fractures, contusions, or penetrating injuries. Additional causes
include infections; vitamin deficiency (usually thiamine); and
poisons such as carbon monoxide, carbon tetrachloride, heavy
metals, and some drugs.
Reye (RI.) syndrome Occurs after a viral infection, particularly
chickenpox or influenza, most often in children or teens who
have taken aspirin; characterized by vomiting and brain dys
function (disorientation, lethargy, and personality changes) that
may progress to coma and death.
Sciatica (si-Al-i-ka) A type of neuritis characterized by severe pain
along the path of the sciatic nerve or its branches; may be caused
by a slipped disc, pelvic injury, osteoarthritis of the backbone, or
pressure from an expanding uterus during pregnane).
DY OUTLINE
I
Spinal Cord Structure (p. 243)
spinal cord is protected by the vertebral column, meninges,
Kid cerebrospinal fluid.
The meninges are diree connective tissue coverings of die spinal
cortland brain: dura mater, arachnoid mater, and pia mater.
Removal of cerebrospinal fluid from die subarachnoid space is
called i spinal tap. The procedure is used to remove CSF and
troduee antibiotics, anesthetics, and chemotherapy.
4. The spinal cord extends from the lowest part of the brain, the
medulla oblongata, to the upper border of the second lumbar
rtebra in die vertebral column.
5, The spinal cord contains cervical and lumbar enlargements that
serve as points of origin for nerves to the limbs,
! The roots of the nerves arising from the lumbar, sacral, and
ac-il regions of the cord are called die eauda equina.
The gray matter in the spinal cord is divided into horns and the
bite matter into columns. Parts of the spinal cord observed in
cross section are the central canal; anterior, posterior, and lat-
eral gray horns; anterior, posterior, and lateral white columns;
and sensory (ascending) and motor (descending) tracts,
Spinal Nerves (p. 246)
1.
2.
The 3 1 pairs of spinal nerves are named and numbered accord-
ing to the region and level of the spinal cord from which tl
emerge.
There are 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of
lumbar, 5 pairs of sacral, and 1 pair of coccygeal nerves.
3. Spinal nerves are attached to the spinal cord by means of a pos-
terior root and an anterior root.
4. All spinal nerves arc mixed nerves containing sensory and mo-
tor axons.
5. Branches of spinal nerves, except for T2 to Tl 1 , form networks
of nerves called plexuses. Nerves T2 to Tl 1 do not form
plexuses and are called intercostal nerves.
268 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
6. The major plexuses arc the cervical, brachial, lumbar, and
sacral plexuses,
Spinal Cord Functions (p. 247)
1. 'The spinal cord white matter and gray matter have two major
functions in maintaining homeostasis. The white matter serves
as highways for nerve impulse conduction. The gray matter re-
ceives and integrates incoming* and outgoing information and. is
a site for integration of reflexes,
2. A reflex is a fast, involuntary sequence of actions that occurs in
response to a particular stimulus. The basic components of a
reflex arc are a receptor, a sensory neuron, an integrating cen-
ter, a motor neuron, and an effector.
Brain (p. 248)
1. The major parts of the brain are the brain stem, dienccphalon,
cerebellum, and cerebrum (see Tabic 10.1 on page 262"). The
brain stem consists of the medulla oblongata, pons, and mid-
brain. The dienccphalon consists of the thalamus, hypothala-
mus, and pineal gland.
2. The brain is well supplied with oxygen and nutrients. Any in-
terruption of the oxygen supply to the brain can weaken, per-
manently damage, or kill brain cells. Glucose deficiency may
produce dizziness, convulsions, and unconsciousness.
3* The blood -brain barrier (BBB) limits the passage of certain
material from the blood into the brain,
4. The brain is protected by cranial bones, meninges, and cere-
brospinal fluid.
5. The cranial meninges are continuous with the spinal meninges
and are named dura mater, arachnoid mater, and pia mater,
6. Cerebrospinal fluid is formed in the choroid plexuses and cir-
culates continually through the subarachnoid space, ventricles,
and central canal.
7. Cerebrospinal fluid protects by serving as a shock absorber. It also
delivers nutritive substances from the blood and removes wastes.
8. The medulla oblongata, or medulla, is continuous with the up-
per part of the spinal cord. It contains regions lor regulating
heart rate, diameter of blood vessels, breathing, swallowing,
coughing, vomiting, sneezing, and hiccupping. Cranial nerves
VIII-XTI originate at the medulla.
9. The pons links parts of the brain with one another; it relays
impulses for voluntary skeletal movements from the cerebral
cortex to the cerebellum, and it contains two regions that con-
trol breathing. Cranial nerves V-VII and part of VIII originate
at the pons,
10. The midbrain is between the pons and diencepfaaloa. It con-
veys motor impulses from the cerebrum to the cerebellum and
spinal cord, sends sensory impulses from the spinal cord to the
thalamus, and mediates auditory and visual reflexes. It also ecu
tains nuclei associated with cranial nerves III and IV
11. The reticular formation is a netlike arrangement of gray and
white matter extending throughout the brain stem that alerts
the cerebral cortex to incoming sensor} 7 signals and helps regu-
late muscle tone.
12. The thalamus contains nuclei that serve as relav stations for
sensory impulses to the cerebral cortex. It also contributes!
motor functions by transmitting information from the cerel
lum and basal ganglia to motor areas of the cerebral coi
13. The hypothalamus is inferior to the thalamus. It controls
autonomic nervous system, secretes hormones, functions]
rage* and aggression, governs body temperature, regulates
and fluid intake, and establishes circadian rhythms,
14. The cerebellum occupies the inferior and posterior aspect]
the cranial cavity. It attaches to the brain stem by cerebellar
duncles. It coordinates movements and helps maintain tiffl
muscle tone, posture, and balance.
15. The cerebrum is the largest part of the brain. Irs cortex A
tains gyri (convolutions), fissures, and sulci. The cerebral lot
are frontal, parietal, temporal, and occipital.
16. The white matter is deep to the cortex and consists ai
nated and unmyelinated axons extending to other CNS reek
17. The basal ganglia are several groups of nuclei in each cere]
hemisphere. They help control automatic movements of si
tal muscles and help regulate muscle tone.
18. The limbic system encircles the upper part of the brail
and die corpus callosum. It functions in emotional aspects]
behavior and memory.
19. The sensory 7 areas of the cerebral cortex receive and pern
sensory information. The motor areas govern muscular m
merit. The association areas are concerned with emotional
intellects 1 proces s e
20. Somatic sensory pathways from receptors to the cerebral coi
involve sets of three neurons. The posterior column -mc(
lemniscus pathway relays nerve impulses for sensations of I
touch, proprioception, and vi bra lions. The lateral and
spinothalamic tracts relay impulses tor pain, thermal, lit
and itch sensations.
21. All somatic motor pathways that control movement coni
on lower motor neurons. Input to lower motor neurons
from local interneurons, upper motor neurons, basal g
neurons, and cerebellar neurons.
22. Subtle anatomical differences exist between the two a
hemispheres, and each has some unique functions.
23. Memory, the ability to store and recall thoughts, involves
sistent changes in the brain,
24. Brain waves generated by the cerebral cortex are recorded as
electroencephalogram (EEG), which may be used to Jul
epilepsy, infections, and tumors.
Cranial Nerves (p. 263)
1. Twelve pairs of cranial nerves emerge from the brain.
2. Like spinal nerves, cranial nerves arc part of the PNS
Table 10.2 on pages 263-265 for the names, components,
functions of each of the cranial nerves.
Aging and the Nervous System (p. 265)
1* The brain grows rapidly during the first few years of life.
2. Age-related effects involve loss of brain mass and decreased
pacity for sending nerve impulses.
Self-Quiz 269
^
SELF-QUIZ
L Which sequence best represents a reflex arc from the stimulus
to the response?
1. effector
2. integrating center
3. motor neuron
4. receptor
5. sensory neuron
a. 3,1,4,5,2 b. 1,5,2,3,4 c. 4,3,2,5,1
dL 5,2, 3,4, 1 c- 4,5,2,3,1
2, Which of the following would carry sensory nerve impulses?
a. interior spinothalamic tract Ik anterior root
c, lateral corticospinal tract <i direct pathways
i\ pyramids
| \n inability to distinguish keys in your pocket by touch could
indicate damage to the
a. gray matter of the cerebellum
b. lateral spinothalamic tract
c. posterior column -medial lemniscus pathway
d. anterior ramus
e. primary motor cortex
[ Carpal tunnel syndrome is due to damage to a nerve in the
a. lumbar plexus b. cervical plexus c. brachial plexus
d, cauda equina e. sacral plexus
eedle used in a spinal tap would penetrate (in order):
I. arachnoid 2. dura mater 3. epidural space
4* subarachnoid space
a. 1,2,3,4 b. 2,3, 1,4 c. 3, 1,4,2 d. 3,2,1,4
e. 4,1,2,3
{,, I'll... Lliencephalon is composed of the
a, medulla, [ions, and hypothalamus
b, midbrain, hypothalamus, and thalamus
c, cerebellum and midbrain
d, medulla, pons, and midbrain
e, hypothalamus and thalamus
'. Which of the following statements about the blood supply to
brain is NOT true?
a. The brain needs a constant supply of glucose delivered by
the blood,
b. The structure of the brain capillaries allows selective pas-
c of certain materials from the blood into the brain.
c. The glucose brought to the brain can be stored for future use
d. Brain neurons that are totally deprived of oxygen for four
minutes or more may be permanently injured.
e. The brain requires about 20% of the body's oxygen supply.
i car accident, joe exhibits severe dizziness, difficulty in
walking, and slurred speech. 1 Ic may have damaged his
I, cerebellum b. pons c. reticular activating system
I fifth cranial nerve e. midbrain
9. Which of the following is NOT a function of cerebrospinal
fluid?
a. protection b. circulation c. conduction of
nerve impulses d* nutrition e. shock absorption
10. Which part of the brain contains the centers that control the
heart rate and breathing rhythm?
a. medulla b. midbrain c* cerebellum
d. thalamus e» pons
11. The part of the brain that serves as a link between the nervous
and endocrine systems is the
a. reticular formation b. hypothalamus c. pons
d. brain stem e. cerebellum
12* Which of the following is NOT a function of the hypothala-
mus?
a. regulates food intake b. controls body temperature
e, regulates feelings of rage and aggression
d. helps establish sleep patterns
e. allows crude interpretation of pain and pressure
13. The part(s) of the brain concerned with memory* reasoning,
judgment, and intelligence is (are) the
a. sensory areas b. limbic system c. motor areas
d, cerebellum e. association areas
14, ( \ broad band of white matter that connects the two cerebral
hemispheres is the
a. corpus callosum b. gyrus c. insula
d. ascending traci e. basal ganglia
15, The ringing of your alarm clock in the morning wakes you up
by stimulating the
a. thalamus b. reticular activating system
t\ Broca'sarea d. basal ganglia e, spinal cord
16. Match the following functions to the primary lobe in which
they are located:
_ a. contains primary visual area A* frontal lobe
that allows interpretation of B. parietal lobe
shape and color c ocdpim l lol)C
D, temporal lobe
b. receives impulses tor smell
c. contains pr 1 1 n a ry 1 1 1 otor a rea
that controls muscle movement
d. receives sensory impulses for
touch, pain, and temperature
17. When entering a restaurant, you arc bombarded with many
different sensory stimuli. The part of the brain that combines
all of those sensory inputs so that you can respond appropri-
ately is the
a . s oi n a u >s c n so r y asso c i a ti o n a r e a
b. common integrative area
c. pre motor area
d. Wernicke's area
e. hypothalamus
270 Chapter 10 Central Nervous System, Spinal Nerves, and Cranial Nerves
18. Which cranial nerves contain only sensory fibers?
a. olfactory, optic, and glossopharyngeal
b. optic and oculomotor
c. optic and trochlear
d. optic and olfactory
e. vagus and facial
19. Which wo of the following cranial nerves are NOT involved
in controlling movement of the eyeball?
a. oculomotor
b. trochlear
c. facial
d. abducens
e. trigeminal
*
CRITICAL THINKING APPLICATIONS
After a few days of using her new crutches, Kate's arms and
hands felt tingly and numb. The physical therapist said Kate
had a case of "crutch palsy" from improper use of her
crutches. Kate had been leaning her armpits on the crutches
while hobbling along. What caused the numbness in her arms
and hands?
Dennis was a little nervous. It was his first visit to the dentist in
10 years. "You won't feel a thing," said the dentist as she in-
jected several doses of "numbing" medication. While having
lunch right after the visit, soup drips down Dennis' chin be-
20. Match the following:
a. organization of white matter
in the spinal cord
. b. absorb cerebrospinal fluid
c. extension of nerves beyond
the end of the spinal cord
_ d, folds of the cerebral cortex
e. contains the sensory fibers
of a spinal nerve
f, contains the motor fibers of
a spinal nerve
. g. separates the cerebrum into
right and left halves
h. divides spinal cord into
right and lefi sides
i. brain cavities where
CSF circulates
j. shallow grooves in the cerebrum
k. contains CSF in the spinal cord
A. longitudinal fissj
B. sulci
C. ventricles
D. anterior median
fissure
E. central canal
F. posterior (dorsal]
root
G. columns
H« arachnoid villi
I. anterior (ven I
root
J- gy ri
K. cauda equina
cause he still doesn't feel a thing in his lower lip and right
per lip. What happened to Dennis?
3. An elderly relative suffered a stroke and now has difficulty
the movement of her right upper limb. She is also worl
with a therapist due to some speech problems. What a
the brain were damaged by the stroke:
4, Lynn flicked on the light when she heard her husband's y
Kyle was bouncing on his left foot while holding his right
in his hand. A pin was sticking out of the bottom of his k
Explain Kyle's response to stepping on the pin.
V
ANSWERS TO FIGURE QUESTION
10.1 CSF circulates in the subarachnoid space.
10.2 Spinal nerves are part of the PNS (peripheral nervous system).
103 A horn is an area of gray matter, and a column is a region o\
white matter in the spinal cord.
10.4 All spinal nerves are mixed (have sensory and motor compo-
nents) because the posterior root containing sensory axons
and the anterior root containing motor axons unite to form
the spinal nerve.
10.5 Axons of sensory neurons are part of the posterior root, and
axons of motor neurons are part of the anterior root.
10.6 The medulla oblongata of the brain attaches to the spinal
cord.
10.7 CSF is formed in the choroid plexuses and is reabsorbed
through arachnoid villi into blood in the superior sagittal sinus.
10.8 The midbrain contains the cerebral peduncles.
10.9 The superior colliculi govern eye movements for tracking
moving images and scanning stationary images and ure re-
sponsible for reflexes that govern movements of the eyes,
head, and neck in response to visual stimuli.
10.10 The basal ganglia arc located in the cerebrum and are conj
posed of gray matter.
10.11 The longitudinal fissure separates the right and left cerebri
hemispheres.
10.12 The limbic system is located on the inner border of the
brum and floor of the diencephalon.
10.13 The primary somatosensory area localizes somatic sensations.
10.14 Damage to the spinothalamic tracts could produce los
pain, thermal, tickle, and itch sensations.
10. 15 In the spinal cord, the lateral and anterior corticospinal
tracts conduct impulses along axons of upper motor neun
AUTONOMIC
NERVOUS SYSTEM
;w
chapter 11
iidyou know?
A he 'fight-or-flight" response of
the sympathetic nervous system is very helpful when
you encounter a snarling dog or need to escape from a
kniiiig building* But when the emergency is over; your
Wff sympathetic nervous system needs time to help your
body relax and recover. What happens when stress
builds up, and no recovery occurs? Winn your days
are filled with negative stress and an overactivated
sympathetic nervous system, stress-related health
problems may develop. Chronic, unrelenting^
overwhelming stress interferes with the body's ability
to maintain homeostasis and health. Learning
relaxation and stress reduction skills can reduce
the harmful effects of stress upon
the body.
Focus on Wellness, page 278
www.wlley.com/college/apcentral
he part of the nervous system
that regulates smooth muscle, cardiac
muscle, and certain glands is the
autonomic nervous system (ANS).
Recall that together the ANS and
somatic nervous system compose the peripheral nervous
system; see Figure 9. 1 on page 226. The ANS was
originally named autonomic (auto- = self; -nomic = law)
because it was thought to function in a self-governing
manner. Although the ANS usually does operate
without conscious control from the cerebral cortex, it
is regulated by other brain regions, mainly the
hypothalamus and brain stem. In this chapter, we
compare the structural and functional features ot the
somatic and autonomic nervous systems. Then we
discuss the anatomy of the motor portion of the ANS
and compare the organization and actions of its two
major branches, the sympathetic and parasympathetic
divisions*
looking back to move ahead
• Structures of the Nervous System (page 226)
• Sensory and Motor Components of the ANS and
ANS Effectors (page 227)
271
272 Chapter 11 Autonomic Nervous System
COMPARISON OF SOMATIC
AND AUTONOMIC NERVOUS
SYSTEMS
OBJECTIVE • Compare the main structural and func-
tional differences between the somatic and autonomic
parts of the nervous system-
As you learned in Chapter 10, the somatic nervous system
includes both sensory and motor neurons. The sensory neu-
rons convey input from receptors for the special senses
(vision, hearing, taste, smell, and equilibrium, described in
Chapter 12) and from receptors for somatic senses (pain,
temperature, touch, and proprioceptive sensations). All these
sensations normally are consciously perceived. In turn, so-
matic motor neurons synapse with skeletal muscle — the ef-
fector tissue of the somatic nervous system— and produce
conscious, voluntary movements. When a somatic motor
neuron stimulates a skeletal muscle, the muscle contracts. If
somatic motor neurons cease to stimulate a muscle, the result
i paralyzed, limp muscle that has no muscle tone. In addi-
tion, even though we are generally not conscious of breath-
ing, the muscles that generate breathing movements arc
skeletal muscles controlled by somatic motor neurons. If the
respiratory motor neurons become inactive, breathing stops.
The main input to the ANS comes from autonomic
sensory neurons. These neurons are associated with sensory
receptors that monitor internal conditions, such as blood CO*
level or the degree of stretching in die walls of internal organs
or blood vessels. When die viscera are functioning properly
diese sensory signals usually are not consciously perceived.
Autonomic motor neurons regulate ongoing activities in
their effector tissues, which are cardiac muscle, smooth mus-
cle, and glands, by both excitation and inhibition. Unlike
skeletal muscle, these tissues often function to some extent
even if their nerve supply is damaged. The heart continues to
beat, for instance, when it is removed for transplantation into
another person. Examples of autonomic responses are
changes in the diameter of the pupil, dilation and constric-
tion of blood vessels, and changes in the rate and force of the
heartbeat. Because most autonomic responses cannot be
sciously altered or suppressed to any great degree, they
the basis for polygraph ("lie detector") tests. However, pn
doners of yoga or other techniques of meditation and til
who employ biofeedback methods may learn how to m
late ANS activities. For example, they may be able to vo.
tarily decrease their heart rate or blood pressure.
Figure 1 1.1 compares somatic and autonomic motor n
rons. The axon of a somatic motor neuron extends all the
from the CNS to the skeletal muscle fibers that it stimula
(Figure 1 1. la). By contrast, autonomic motor pathways co
of sets of two motor neurons (Figure 1 1 .lb). The first ne
called die preganglionic neuron, has its cell body in the C
either in die lateral gray horn of the spinal cord or in a mi
of the brainstem. Its axon extends from the CNS via a
a spinal nerve to an mtttmomk ganglion, where it synapses
the second neuron, (Recall that a ganglion is a collection of tn
ronal cell bodies usually outside die CNS.) The second ne
the postganglionic neuron, lies entirely in the peripheral
vous system. Its cell body is located in an autonomic gangli
and its axon extends from the ganglion to the effector (sin
muscle, cardiac muscle, or a gland). The effect of die post]
glionic neuron on die effector may be either excitation (ca
contraction of smooth or cardiac muscle or increasing
tions of glands) or inhibition (causing relaxation of smc
cardiac muscle or decreasing secretions of glands). In contra
single somatic motor neuron extends from the CNS and ;ilw
excites its effector (causing contraction of skeletal muscle)
urc 1 1.1a). Another difference between autonomic and so
motor neurons is that all somatic motor neurons release i
choline (ACh) as their neurotransmitter. Some autonomic
tor neurons release ACh; others release norepinephrine (M
The output (motor) part of the ANS has two
branches: the sympathetic division and die parasympathetic
vision. Most organs have dual innervation; that is, they re
impulses from both sympathetic and parasympathetic ne
In general, nerve impulses from one division stimulate the o
to increase its activity (excitation), whereas impulses from
other division decrease the organ's activity (inhibition). For
ample, an increased rate of nerve impulses from die sympa
division increases heart rate, and an increased rate of n>
Table 1 1 .1 Comparison of Somatic and Autonomic Nervous Systems
Property
Somatic
Autonomic
Effectors
Type of control
Neural pathway
Neurotransmitter
Action of neurotransmitter
on effector
Skeletal muscles.
Mainly voluntary.
One motor neuron extends from
CNS and synapses directly with
a skeletal muscle fiber.
Acetylcholine.
Always excitatory (causing
contraction of skeletal muscle).
Cardiac muscle, smooth muscle, and glands.
Mainly involuntary.
One motor neuron extends from the CNS and synapses with another motor
neuron in a ganglion; the second motor neuron synapses with an autonomic
effector.
Acetylcholine or norepinephrine,
May be excitatory (causing contraction of smooth muscle, increased heart
increased force of heart contraction, or increased secretions from glands)
inhibitory (causing relaxation of smooth muscle, decreased heart rate, or
decreased secretions from glands).
Structure of the Autonomic Nervous System 273
figure 11.1 Comparison of somatic and autonomic motor neuron pathways to their effector tissues.
Stimulation by the autonomic motor neurons can either excite or inhibit smooth muscle, cardiac muscle,
and glands- Stimulation by somatic motor neurons always causes contraction of skeletal muscle.
/
Somatic
motor neuron
ACh:
Skeletal muscle-
contr action
Spinal cord
Effector
(a) Somatic nervous system
Autonomic
motor neurons
ACh
Spinal cord
sympathetic
neuron
Postga
Autonomic
ganglion
Postganglionic
sympathetic
neuron
Effectors
NEorACh:
Glands-increased or
decreased secretions
Smooth muscle (e.g.
in the urinary bladdery-
contraction or
relaxation
Cardiac muscle (in the
heart)-increased or
decreased rate and
force of contraction
ACh
Spinal cord
Preganglionic
sympathetic
neuron
Adrenal medulla
Epinephrine
and NE
oo
Blood vessel
Spinal cord
Preganglionic
parasympathetic
neuron
ACh
Autonomic
ganglion
Postganglionic
parasympathetic
neuron
Effectors
(b) Autonomic nervous system
What does "dual innervation" mean?
NE or ACh:
Glands-increased or
decreased secretions
Smooth muscle (e.g.
in the urinary bladder-
contraction or
relaxation
Cardiac muscle (in the
heart)-increased or
decreased rate and
force of contraction
Lukes from the parasympathetic division decreases heart rate.
Jble 11.1 on page 272 summarizes the similarities and differ-
ges between the somatic and autonomic nervous systems.
CHECKPOINT
h \ is the autonomic nervous system so named?
[What are the main input and output components or the
autonomic nervous system?
STRUCTURE OF THE AUTONOMIC
NERVOUS SYSTEM
OBJECTIVE • Identify die structural features of the
autonomic nervous system,
We will now examine the structure of preganglionic
neurons, ganglia, and postganglionic neurons and how
274 Chapter 11 Autonomic Nervous System
they rehire to the activities of the autonomic nervous
system.
Organization of the Sympathetic Division
The sympathetic division of the ANS is also called the tho-
racolumbar division (thor'-a-k(>LUM-bar) because the out-
flow of sympathetic nerve impulses comes from the thoracic
and lumbar segments of the spinal cord (Figure I 1. 2). The
sympathetic preganglionic neurons have their cell bodies in
the 12 thoracic and the first two lumbar segments of the
spinal cord. The preganglionic axons emerge from the spinal
cord through the anterior root of a spinal nerve along with
axons of somatic motor neurons. After exiting the cord, the
sympathetic preganglionic axons extend to a sympathetic
ganglion.
In the sympathetic ganglia, sympathetic preganglionic
neurons synapse with postganglionic neurons. Because the
sympathetic trunk ganglia are near the spinal cord, most
sympathetic preganglionic axons are short. Sympathetic
trunk ganglia lie in two vertical rows, one on either side of
the vertebral column (Figure 11.2). Most postganglionic ax-
ons emerging from sympathetic trunk ganglia supply organs
above the diaphragm. Other sympathetic ganglia, the prever-
tebral ganglia, lie anterior to the vertebral column and close
to the large abdominal arteries. These include the celiac gan-
glion (SE-le-ak), the superior mesenteric ganglion, and the infe-
rior mesenteric ganglion. In general, postganglionic axons
emerging from the prevertebral ganglia innervate organs be-
low the diaphragm.
Once the axon of a preganglionic neuron of the sympa-
thetic division enters a sympathetic trunk ganglion, it may
follow one of four paths:
1. It mav synapse with postganglionic neurons in the sym-
pathetic trunk ganglion it first reaches,
2. It may ascend or descend to a higher or lower sympa-
thetic trunk ganglion before synapsing with postgan-
glionic neurons.
3. It may continue, without synapsing, through the sympa-
thetic trunk ganglion to end at a prevertebral ganglion
and synapse with postganglionic neurons there.
4. It may extend to and terminate in the adrenal medulla.
A single sympathetic preganglionic axon has many
branches and may synapse with 20 or more postganglionic
neurons. Thus, nerve impulses that arise in a single pregan-
glionic neuron may activate many different postganglionic
neurons that in turn synapse with several autonomic effec-
tors. This pattern helps explain why sympathetic responses
can affect organs throughout the body almost simultane-
ously.
Most postganglionic axons leaving the cervical sympa-
thetic trunk ganglia serve the head, They are distributed to
sweat glands, smooth muscles of the eye, blood vessels
the face, nasal mucosa, and salivary glands. A few po
glionic axons from the cervical sympathetic trunk gang!
supply the heart. In the thoracic region, postganglioi
axons from the sympathetic trunk serve the heart, lunj
and bronchi. Some axons from thoracic levels also supply
sweat glands, blood vessels, and smooth muscles of hah
follicles in the skin. In the abdomen, axons of pos
glionic neurons leaving the prevertebral ganglia follow the
course of various arteries to abdominal and pelvic aul
nomie effectors.
The sympathetic division of the ANS also includes
of the adrenal glands (Figure 1 1.2). The inner part of
adrenal gland, the adrenal medulla (me-DUL-a), develi
from the same embryonic tissue as the sympathetic g;
and its cells are similar to sympathetic postganglionic m
rons. Rather than extending to another organ, however, the
cells release hormones into the blood. Upon stimulation
sympathetic preganglionic neurons, cells of the adrena
medulla release a mixture of hormones- -about 80%
nephrine and 20% norepinephrine. These hormones circ
late throughout the body and intensify responses elicited
sympathetic postganglionic neurons.
In Horner's syndrome, sympathetic stimulation of one
side of the face is lost due to an inherited mutation, an in-
jury, or a disease that affects sympathetic outflow diroul
the superior cervical ganglion. Symptoms occur in
head on the affected side and include drooping of the up]
per eyelid, constricted pupil, and lack of sweating.
Organization of the Parasympathetic
Division
The parasympathetic division is also called the amim
division (krl'-ne-d-SA-kral) because the outflow of par k
pathetic nerve impulses comes from cranial nerve nuclei
sacral segments of the spinal cord. The cell bodies
parasympathetic preganglionic neurons are located in them
clei of four cranial nerves (III, VII, IX, and X) in the b
stem and in the second through fourth sacral segments of
spinal cord (S2, S3, and S4) (Figure 11.3 on page 2|
Parasympathetic preganglionic axons emerge from the
as part of a cranial nerve or as part of the anterior rontofi
spinal nerve. Axons of the vagus (X) nerve carry near!)' 8C
of the total parasympathetic outflow. In the thorax, a
the vagus nerve extend to ganglia in die heart and the airwj
of die lungs. In the abdomen, axons of die vagus nerve
tend to ganglia in the liver, stomach, pancreas, small int
tine, and part of the large intestine. Parasympathetic prejj
glionic axons exit the sacral spinal cord in the anterior r
figure 11-2 Structure of the sympathetic division of the autonomic nervous system. Although some innervated structures are
Cammed only for one side of the body, the sympathetic division actually innervates tissues and organs on both sides,
Cell bodies of sympathetic preganglionic neurons are located in the gray matter in the 12 thoracic and first two lumbar segments of the
spinal cord.
SYMPATHETIC DIVISION
(thoracolumbar)
Key:
< Preganglionic neurons
— < Postganglionic neurons
W~ Mucous membrane
\ of nose and palate
P* Parotid gland
Sweat gland
Hair follicle
smooth muscle
Adipose tissue
Blood vessels
Stomach
Spleen
Pancreas
Prevertebral
ganglia
Urinary bladder External genitals
Uterus
Which neurons synapse in a sympathetic trunk ganglion?
275
Figure 11.3 Structure of the parasympathetic division of the autonomic nervous system. Although some innervated structures are!
diagrammed on one side of the body, the parasympathetic division actually innervates organs on both sides.
Cell bodies of parasympathetic preganglionic neurons are located in brain stem nuclei and in the gray matter in the second through fourth
pfir*N sacral segments of the spinal cord.
PARASYMPATHETIC DIVISION
(craniosacral)
.
Spina
cord
Urinary bladder External genitals
Which division, sympathetic or parasympathetic, has longer preganglionic axons? (Hint: Compare Figures 11.2 and ,l
[.the second through fourth sacral nerves. The axons then
md to ganglia in the walls of the colon, ureters, urinary
pder, and reproductive organs.
Preganglionic axons of the parasympathetic division
lapse with postganglionic neurons in terminal ganglia,
lich are located close to or actually within the wall of the
lervated organ. Terminal ganglia in the head receive pre-
fglionic axons from the oculomotor (ITT), facia! (VII), or
jossopharyngeal (IX) cranial nerves and supply structures in
| head (Figure 1 1.3). Axons in the vagus (X) nerve extend
many terminal ganglia in the thorax and abdomen.
rose the axons of parasympathetic preganglionic neurons
tend from the brain stem or sacral spinal cord to a terminal
iglion in an innervated organ, they are longer than most of
axons of sympathetic preganglionic neurons (compare
ires 11.2 and 11.3).
In contrast to die preganglionic axons, most parasympa-
ietic postganglionic axons are very short because the terini-
| ganglia lie in die walls of their autonomic effectors. In the
pglion, the preganglionic neuron usually synapses with
aly four or five postganglionic neurons, all of which supply
same effector. Thus, parasympathetic responses are local-
id to a single effector.
A megacolon (mega- = big) is an abnormally large colon.
[n congenital megacolon, parasympathetic nerves to the
listal segment of the colon do not develop properly. Loss
jut 'motor function in the segment causes massive dilation
[of the normal proximal colon. The condition results in ex-
reme constipation, abdominal distension, and occasion-
illy, vomiting. Surgical removal of the affected segment of
ic colon corrects the disorder
CHECKPOINT
Describe the locations of sympathetic trunk ganglia, pre-
vertebral ganglia, and terminal ganglia. Which types of
autonomic neurons synapse in each type of ganglion?
How can the sympathetic division produce simultaneous
effects throughout the body, when parasympathetic
effects typically are localized to specific organs?
NOTIONS OF THE AUTONOMIC
IERV0US SYSTEM
JECTIVE • Describe the functions of the sympa-
tic and parasympathetic divisions of the autonomic
;nous system.
INS Neurotransmitters
htmtianswitters are chemical substances released by neu-
at synapses. Autonomic neurons release neurotransmit-
Functions of the Autonomic Nervous System 277
ters at synapses between neurons (preganglionic to postgan-
glionic) and at synapses with autonomic effectors (smooth
muscle, cardiac muscle, and glands). Some ANS neurons re-
lease acetylcholine; others release norepinephrine.
ANS neurons that release acetylcholine include ( I ) nil sym-
pathetic and parasympathetic preganglionic neurons, (2) all
parasympathetic postganglionic neurons, and (3) a few sym-
pathetic postganglionic neurons. Because acetylcholine is
quickly inactivated by the enzyme acetylcholinesterase (ACbE) t
parasympathetic effects are short-lived and localized.
Most sympathetic postganglionic neurons release die
neurotransmitter norepinephrine (NE), Because norepineph-
rine is inactivated much more slowly than acetylcholine and
because the adrenal medulla also releases epinephrine and
norepinephrine into the bloodstream, the effects of activation
of the sympathetic division are longer lasting and more
widespread than those of the parasympathetic division. For
instance, your heart continues to pound for several minutes
after a near miss at a busy intersection due to the long- la sting
effects of the sympathetic division.
Activities of the ANS
As noted earlier, most body organs receive instructions from
both divisions of the ANS, which typically work in opposi-
tion to one another. The balance between sympathetic and
parasympathetic activity or "tone" is regulated by the hypo-
thalamus. Typically, the hypothalamus turns up sympathetic
tone at the same time it turns down parasympathetic tone,
and vice versa. A few structures receive only sympathetic in-
nervation — sweat glands, arrector pill muscles attached to
hair follicles in the skin, the kidneys, the spleen, most hlood
vessels, and the adrenal medullae (see Figure 11.2). In these
structures there is no opposition from the parasympathetic di-
vision. Still, an increase in sympathetic tone has one effect, and
a decrease in sympathetic tone produces the opposite effect.
Sympathetic Activities
During physical or emotional stress, high sympathetic tone
favors body functions that can support vigorous physical
activity and rapid production of ATP. At the same time, the
sympathetic division reduces body functions that favor die
storage of energy. Besides physical exertion, a variety of
emotions — such as fear, embarrassment, or rage — stimulate
the sympathetic division. Visualizing body changes that occur
during "E situations" (exercise, emergency, excitement,
embarrassment) will help you remember most of the sympa-
thetic responses. Activation of the sympathetic division and
release of hormones by the adrenal medullae result in a
series of physiological responses collectively called thefigbt-
or-jtight response } in which the following occur:
1, The pupils of the eyes dilate.
2. Heart rate, force of heart contraction, and blood pressure
increase.
Wi
'hen we think of exercise, we usu-
ally think of toning up our muscles
and maybe our hearts. But when
some people think of exercise, their
focus is on toning up neural input
from the parasympathetic division of
the autonomic nervous system. As
you learned in this chapter, activation
of the parasympathetic division helps
restore homeostasis in many systems
and is associated with feelings of re-
laxation.
Mind-Body Harmony
Mind-body exercise refers to exercise
systems such as tai ehi, hatha yoga, and
many forms of the martial arts that
couple muscular activity with an inter-
nally directed focus. These exercise
systems exercise the mind as well as the
body. Their internally directed focus
usually includes an awareness oi
breathing, energy, and other physical
sensations.
Practitioners often refer to this in-
ternal awareness as "mindful," meaning
that the exerciser is open to physical
and emotional sensations with an un-
derstanding, non judgmental attitude, A
mindful altitude is typical of many
kinds of meditation and relaxation
practices. For example, when practicing
a yoga pose, you would think some-
thing like "Deep, steady breathing; re-
lax into the pose; shoulders pulling
back, neck lengthening/' rather than
"That girl next to me sure is flexible;
Fm really a failure at this stuff." Of
course, in real life such external
thoughts do sneak in, but we can redi-
rect our attention back to a more neu-
tral, nonjudgmental style,
Mind-Body Benefits
People practicing mind-body activities
reap benefits from both the physical
and mental activity. Hatha yoga, tai chi,
and the martial arts increase muscular
strength and flexibility, posture, bal-
ance, and coordination, and if per-
formed vigorously, they can even ina
prove cardiovascular health and m
durance to some extent. In additio
the stress relief provided by the acthj
extends into both physical and psych
logical realms. Feelings of mental r-
taxation and emotional well-bein
translate into better resting blood p
sure, a healthier immune system, a
more relaxed muscles. Less stress
also mean an improvement in heal
habits. Those who practice mind-fc
exercise often improve their ea
habits and reduce harmful behavw
such as cigarette smoking.
HINK
VER
How could you make walking more of a mind-body activity:
3. The airways dilate, allowing faster movement of air into
and out of the lungs.
4. The blood vessels that supply nonessential organs such
as the kidneys and gastrointestinal tract constrict, which
reduces blood flow through these tissues. The result is a
slowing of urine formation and digestive activities, which
are not essential during exercise.
5. Blood vessels that supply organs involved in exercise or
fighting off danger — skeletal muscles, cardiac muscle,
liver, and adipose tissue — dilate, which allows greater
blood flow through these tissues.
6. liver cells break down glycogen to glucose, and adipose
cells break down triglycerides to fatty acids and glycerol,
providing molecules that can be used by body cells for
ATP production.
7. Release of glucose by the liver increases blood glucose
level.
8. Processes that are not essential for meeting the stress
ful situation are inhibited. For example, musojl
movements of the gastrointestinal tract and digest!
secretions decrease or even stop.
Parasympathetic Activities
In contrast to the "fight-or-flight" activities of the syn»
thetic division, the parasympathetic division en ha
"rest-and-digesf activities. Parasympathetic responses sum
port body functions that conserve and restore body ecfl
during times of rest and recovery. In the quiet intervals ■
tween periods of exercise, parasympathetic impulses to the,
digestive glands and the smooth muscle ot the gastroin
testinal tract predominate over sympathetic impulses, Mi
allows energy-supplying food to be digested and absoi!
At the same time, parasympathetic responses reduce hod
functions that support physical activity.
278
The acronym SLUDD can be helpful in remembering
b parasympathetic responses. It stands for salivation (S),
lamination (L), urination (U), digestion (D), and defecation
Mainly the parasympathetic division stimulates all of
these activities. Besides the increasing SLUDD responses,
Functions of the Autonomic Nervous System 279
other important parasympathetic responses are "three de-
creases": decreased heart rate, decreased diameter of airways,
and decreased diameter (constriction) of the pupils.
Table 11.2 lists the responses of glands, cardiac muscle,
and smooth muscle to stimulation by the sympathetic and
parasympathetic divisions of the ANS.
Table 1 1 .2 Functions of the Autonomic Nervous System
Effector
Effect of Sympathetic Stimulation
Glands
Sweat
Lacrimal (tear)
Adrenal medulla
Pancreas
Posterior pituitary
Liver*
Adipose tissue*
Cardiac Muscle
Heart
Smooth Muscle
Radial muscle of iris of eye
Circular muscle of iris of eye
Ciliary muscle of eye
Gallbladder and ducts
Stomach and intestines
Lungs (smooth muscle
of bronchi)
Urinary bladder
Spleen
Smooth muscle of
hair follicles
Uterus
Sex organs
Salivary glands (arterioles)
Gastric glands and
Intestinal glands
(arterioles)
Kidney (arterioles)
Skeletal muscle
(arterioles)
Heart (coronary arterioles)
Increased sweating.
Slight secretion of tears.
Secretion of epinephrine and norepinephrine.
Inhibition of secretion of digestive enzymes and insulin
(hormone that lowers blood glucose level); secretion of
glucagon (hormone that raises blood glucose level),
Secretion of antidiuretic hormone (ADH).
Breakdown of glycogen into glucose, synthesis of new
glucose, and release of glucose into the blood; decreases
bile secretion.
Breakdown of triglycerides and reJease of fatty adds into
blood.
Increased heart rate and increased force of atrial and
ventricular contraction.
Dilation of the pupil.
No known effect.
Relaxation to adjust shape of lens for distant vision.
Storage of bile in the gallbladder.
Decreased motility (movement); contraction of sphincters.
Widening of the airways (bronchodilation).
Relaxation of muscular wall; contraction of internal
sphincter.
Contraction and discharge of stored blood into general
circulation.
Contraction that results in erection of hairs, producing
"goose bumps."
inhibits contraction in nonpregnant women; stimulates
contraction in pregnant women.
In men, causes ejaculation of semen.
Decreases secretion of saliva.
Inhibits secretion.
Decreases production of urine.
Vasodilation in most, which increases blood flow.
Vasodilation in most, which increases blood flow.
Effect of Parasympathetic Stimulation
No known effect.
Secretion of tears.
No known effect.
Secretion of digestive enzymes and insulin.
No known effect,
Promotes synthesis of glycogen; increases
bile secretion.
No known effect.
Decreased heart rate and decreased force of atrial
contraction.
No known effect.
Constriction of the pupil.
Contraction to adjust shape of lens for close vision.
Release of bile into the small intestine.
Increased motility; relaxation of sphincters.
Narrowing of the airways (bronehoconstriction).
Contraction of muscular wall; relaxation of internal
sphincter.
No known effect.
No known effect.
Minimal effect.
Vasodilation; erection of clitoris (women) and penis
(men).
Stimulates secretion of saliva.
Promotes secretion.
No known effect.
No known effect.
Causes slight constriction, which decreases blood flow.
listed with glands because they release substances into the blood.
280 Chapter 11 Autonomic Nervous System
Dysautonomia (dis-aw-to-NO-me-a; dys- = difficult; au-
tonomia = self-governing) is an inherited disorder in which
the autonomic nervous system functions abnormally.
Symptoms include reduced tear gland secretions, poor va-
somotor control, motor incoordination, skin blotching, ab-
sence of pain sensation, difficulty swallowing, decreased re-
flex responses, excessive vomiting, and emotional instability.
■ CHECKPOINT
5. What are some examples of the opposite effects of the
sympathetic and parasympathetic divisions of the auto-
nomic nervous system?
6, What happens during the fight-or-flight response?
7. Why is the parasympathetic division of the \\S cor
sidcred the rest-and-digest division?
Now that we have discussed the structure and functi<
of the nervous system, we will next consider in Chapter
how sensory information is relayed to the nervous sysfij
and how the nervous system responds to it.
*4L
COMMON
DISORDERS
Autonomic Dysreflexia
Autonomic dysreflexia is an exaggerated response of the sympa-
thetic division of the ANS that occurs in about 85% of individu-
als with spinal cord injury at or above the level of T6. The condi-
tion occurs due to interruption of the control of ANS neurons by
higher centers, When certain sensory impulses, such as those re-
sulting from stretching of a full urinary bladder, are unable to as-
cend the spinal cord, mass stimulation of the sympathetic nerves
below the level of injury occurs. Among the effects of increased
sympathetic activity is severe vasoconstriction, which elevates
blood pressure. In response, die cardiovascular center in the
medulla oblongata (I) increases parasympathetic output via the
vagus nerve, which decreases heart rate, and (2) decreases sympa-
thetic output, which causes dilation of blood vessels above the
level of the injury.
Autonomic dysreflexia is characterized by a pounding headat
severe high blood pressure (hypertension); Hushed, warm skin
profuse sweating above the injury level; pale, cold, and dry
below the injury level; and anxiety. It is an emergency condition
requires immediate intervention. If untreated, autonomic dysreffl
can cause seizures, stroke, or heart attack.
Raynaud Phenomenon
In Raynaud phenomenon (ra-NO), the fingers and toes lu
ischemic (lack blood) after exposure to cold or with emotii
Stress. The condition is due to excessive sympathetic stimulation
smooth muscle in the arterioles of the fingers and toes. When
arterioles constrict in response to sympathetic stimulation, bl
flow is greatly diminished. Symptoms are colorful red, white,
blue. Fingers and toes may look white due to blockage of blc
flow or look blue (cyanotic) due to deoxygenated blood in capil
ies. With rewarming after cold exposure, the arterioles may
causing the fingers and toes to look red. The disorder is ma
in on in young women and occurs more often in cold climates.
TUDY OUTLINE
Comparison of Somatic and Autonomic
Nervous Systems (p, 272)
1. The part of the nervous system that regulates smooth muscle,
cardiac muscle, and certain glands is the autonomic nervous
system (ANS). The ANS usually operates without conscious
control from the cerebral cortex, but other brain regions,
mainly the hypothalamus and brain stem, regulate it
The axons of somatic motor neurons extend from the CNS and
synapse directly with an effector (skeletal muscle). Autonomic
2.
3.
motor pathways consist of two motor neurons. The axontij
first motor neuron extends from the CNS and synapses
ganglion with the second motor neuron; the second m
synapses with an effector (smooth muscle, cardiac musclq
gland).
The output (motor) portion of the ANS has two divisjj
sympathetic and parasympathetic. Most body organs
dual innervation; usually one ANS division causes excitat
and the other causes inhibition.
I Somatic motor neurons release acetylcholine (ACh), and auto-
nomic motor neurons release either acetylcholine or norepi-
nephrine (NE).
I Somatic nervous system effectors are skeletal muscles; ANS
effectors include cardiac muscle, smooth muscle, and glands.
I, Table 11.1 on page 272 compares the somatic and autonomic
nervous systems.
Structure of the Autonomic Nervous System (p. 273)
||, The sympathetic division of the ANS is also called the thora-
columbar division because the outflow of sympathetic nerve
impulses comes from the thoracic and lumbar segments of the
spinal cord. Cell bodies of sympathetic preganglionic neurons
I are in the 1 2 thoracic and the first two lumbar segments of the
spinal cord.
Sympathetic ganglia are classified as sympathetic trunk ganglia
(lateral to the vertebral column) or prevertebral ganglia (ante-
rior to the vertebral column).
J. A single sympathetic preganglionic axon may synapse with 20
I or more postganglionic neurons. Sympathetic responses can af-
fect organs throughout the body almost simultaneously.
The parasympathetic division is also called the craniosacral di-
vision because die outflow of para sympathetic nerve impulses
conies from cranial nerve nuclei and sacral segments of the
spinal cord. The cell bodies of parasympathetic preganglionic
ions are located in the nuclei of cranial nerves III, VII, IX,
and X in the brain stem and in three sacral segments of the
spinal cord (S2, S3, and S4).
Self-Quiz 281
5. Parasympathetic ganglia arc called terminal ganglia and are
located near or within autonomic effectors. Parasympathetic
terminal ganglia are close to or in the walls of their autonomic
effectors, so most parasympathetic postganglionic axons arc
very short. In the ganglion, the preganglionic neuron usually
synapses with only four or five postganglionic neurons, all of
which supply the same effector. Thus, parasympathetic
responses are localized to a single effector.
Functions of the Autonomic Nervous System (p. 277)
L Some ANS neurons release acetylcholine, and others release
norepinephrine; the result is excitation in some cases and inhi-
bition in others.
2, ANS neurons that release acetylcholine include (1) all sympa-
thetic and parasympathetic preganglionic neurons, (2) all
parasympathetic postganglionic neurons, and (3) a few sympa-
thetic postganglionic neurons.
3. Most sympathetic postganglionic neurons release the neuro-
transmitter norepinephrine (NE). The effects of NE are
longer-lasting and more widespread than those of acct\ I
choline.
4. Activation of the sympathetic division causes widespread re-
sponses and is referred to as the fight-or- flight response. Acti-
ve :.i lion of the parasympathetic division produces more restricted
responses that typically are concerned with rest-and-digest
activities.
5, Table 1 I J on page 279 summarizes the main functions of the
sympathetic and parasympathetic divisions of the ANS.
SELF-QUIZ
I, hi comparing the somatic nervous system with the autonomic
nervous system, which of the following statements is true?
a, The autonomic nervous system controls involuntary move-
ments in skeletal muscle.
b.The somatic nervous system controls voluntary activity m
glands and smooth muscle.
, The autonomic nervous system controls involuntary activity
in cardiac muscle, smooth muscle, and glands,
,1 The autonomic nervous system produces voluntary activity
in smooth muscle and glands.
c. The somatic nervous system controls involuntary move-
ments, in smooth muscle, cardiac muscle, and glands.
!. Neurons in the autonomic nervous system include
a. two motor neurons and one ganglion
b. one motor neuron and two ganglia
1 1 motor neurons and two ganglia
I one motor and one sensory neuron, and no ganglia
e. one motor and one sensory neuron, and one ganglion
3. Which statement is NOT true?
a. Most sympathetic postganglionic neurons release
norepinephrine.
b. Parasympathetic preganglionic neurons release acetyl-
choline.
c. Sympathetic effects are more localized and short-lived than
para sym pathetic effects.
d. The effects from norepinephrine tend to be long-lasting.
e. Branches of a single postganglionic neuron in tire sympa-
thetic division extend to many organs.
4. Which of the following pairs is mismatched?
a. acetylcholine, parasympathetic nervous system
b- flght-or-flight, sympathetic nervous system
c. conserves body energy, parasympathetic nervous system
d. rest-and-digest, parasympathetic nervous system
e. norepinephrine, parasympathetic nervous system
282 Chapter 11 Autonomic Nervous System
5. Which of the following statements is NOT true concerning
the autonomic nervous system?
a. Most autonomic responses cannot be consciously cotrolletL
b. In general, if the sympathetic division increases the activity
in a specific organ, then the parasympathetic division de-
creases the activity of that organ,
c. Sensory receptors monitor internal body conditions.
d. Sensory neurons include pre- and postganglionic neurons.
e. Most visceral effectors receive dual innervation.
6. Which part of the central nervous system contains centers that
regulate the autonomic nervous system?
a. hypothalamus b* cerebellum c. spinal cord
d. basal ganglia e. thalamus
7. Place the following structures in the correct order as they re-
late to an autonomic nervous system response from receipt of
the stimulus to response:
1, visceral effector 2. centers in the CNS 3. auto-
nomic ganglion 4. receptor and autonomic sensory neuron
5, preganglionic neuron 6. postganglionic neuron
a. 4, 5, 2, 3, 6, 1 b. 5, 6, 2, 3, 1, 4 c. 1,6, 3, 5, 2, 4
d. 4,2,5,3,6, i e. 2,4,5,6,3, 1
8. Which of the following activities would NOT be monitored by
autonomic sensory 7 neurons?
a. carbon dioxide levels in the blood
b. hearing and equilibrium
c. blood pressure
d. stretching of the walls of visceral organs
e. nausea from damaged viscera
9. The autonomic ganglia associated with the parasympathetic di-
vision are the
a, trunk ganglia b. prevertebral ganglia c. posterior
root ganglia d. terminal ganglia e. basal ganglia
10. Which of diese statements about the parasympathetic division
of the autonomic nervous system is NOT true? The parasym-
pathetic division
a. arises from the cranial nerves in the brain stem and sacral
spinal cord segments
b. is concerned with conserving and restoring energy
c. uses acetylcholine as its neurotransmitter
d. has ganglia near or within visceral effectors
e. initiates responses in preganglionic neurons that synapse
with 20 or more postganglionic neurons
11. Which nerve carries most of the parasympathetic output froi
the brain?
a. spinal b. vagus c* oculomotor d. facial
e. glossopharyngeal
12. Which of the following would NOT be affected by the auto]
nomic nervous system?
a. heart b. intestines c. urinary bladder
d. skeletal muscle e. reproductive organs
13. Which of die following neurons release norepinephrine?
a. somatic motor neurons
b. sympathetic postganglionic neurons
c. sympathetic preganglionic neurons
d. parasympathetic postganglionic neurons
e. parasympathetic preganglionic neurons
14. Match the following:
a. cluster of cell bodies
outside the CNS
b. cell body is in ganglion;
u mn yeli n a ted axon
extends to effector
c. cell bod)' lies inside the
CNS; myelinated axon
extends to ganglion
d. their postganglionic axons
innervate organs below
the diaphragm
e. their postganglionic axons
supply organs above the
diaphragm
f, contain the cell bodies and
dendrites of parasympathetic
postganglionic neurons
15. For each of the following, place a P if it refers to increj
activity of the parasympathetic division or an S if it rei
increased activity of the sympathetic division.
a* dilates pupils
b. decreases heart rate
c. causes bronchoconstriction
d. stimulates breakdown of triglycerides
_ e. inhibits secretion of digestive enzymes and insuli
£ stimulates the gastrointestinal tract
g« occurs tluring exercise
h, causes release of glucose from the liver
i, dilates blood vessels to cardiac muscle
A. sympathetic trunk
ganglia
B. prevertebral ganglia
C. ganglion
D. terminal ganglia
E. preganglionic neuiq
F. postganglionic neui
Answers to Figure Questions 283
^•-
CRITICAL THINKING APPLICATIONS
JL It's Thanksgiving and you've just eaten a huge turkey dinner
with all the trimmings. Now you're going to watch the big
ue on TV, if you can make it to the couch! Which division
the nervous system will be handling your body's post-dinner
activities? Give examples of some organs and the effects on
their functions*
\nthony wanted a toy on the top of the bookcase, so he
climbed up the shelves. His mother ran in when she heard the
crash and lifted the heavy bookcase with one arm while pulling
her son out with die other. Later that day, she could not lift the
bookcase back into position by herself. How do you explain the
temporary "supermom" effect?
3. Taylor was watching a scary late-night horror movie when she
heard a door slam and a cat's yowl The hair rose on her arms
and she was covered with goose bumps. Trace the pathway
taken by the impulses from her CNS to her arms.
4. In the novel The Hitchhikers Guide to the Galaxy, the charac-
ter Zaphod Beehlcborox has two heads and therefore two
brains. Is this what is meant by dual innervation? Explain.
r
V
ANSWERS TO FIGURE QUESTION
LI Dual innervation means that an organ receives impulses from
both the sympathetic and parasympathetic divisions of the
\NS.
11.2 In the sympathetic trunk ganglia, sympathetic preganglionic
axons form synapses with cell bodies and dendrites of sympa-
thetic postganglionic neurons.
11.3 Most parasympathetic preganglionic axons are longer than
most sympathetic preganglionic axons because parasympa-
thetic ganglia are located in die walls of visceral organs,
while most sympathetic ganglia are close to die spinal cord
in the sympathetic trunk.
chapter 1 2
SOMATIC SENSES
AND SPECIAL SENSES
did you know?
\Jwne things improve with age,
but hearing is not one of them. Damage to the hair
cells that convert sound waves into nerve impulses
accumulates over a lifetime, and by the time hearing
loss is discovered, irreversible damage has already
occurred. Exposure to excessive noise is the most
common cause of hair cell damage. Damage increases
with both the intensity and duration of exposure* The
hair cells appear to be less traumatized by short periods
of loud noise, such as afire alarm going off, than by
chronic exposure to moderately loud noise, such as the
noise of vacuum cleaners, power tools, engines, and
loud music
Focus on Wellness, page 289
x.
www.wiley.com/college/apcentral
v^onsider what would
happen if you could not
feel the pain of a hot
pot handle or an in-
flamed appendix, or if you could not see an oncoming
car, hear a baby's cry, smell smoke, taste your favoritd
dessert, or maintain your balance on a flight of stairs,
In short, if you could not "sense" your environment
make the necessary homeostatic adjustments, you conic
not survive very well on your own.
looking back to move ahead
Sensory Nerve Endings and Sensory Receptors in the Skin
(page 1 00)
Somatic Sensory Pathways (page 259)
284
OVERVIEW OF SENSATIONS
OBJECTIVE • Define a sensation and describe the
conditions needed for a sensation to occur.
Host of us nre aware of sensory input to the central nervous
Lem(CNS) from structures associated with smell, taste, vi-
U hearing, and balance. These five senses arc known as
Ac special l senses. The other senses are termed general senses
id include both somatic senses and visceral senses. Somatic
fkses {somM- = of the body) include tactile sensations
Ipuch, pressure, and vibration); thermal sensations (warm
id cold); pain sensations; and proprioceptive sensations
[pnt and muscle position sense and movements of die limbs
Khead), Visceral senses provide information about condi-
wiihin internal organs.
Definition of Sensation
Rutins is the conscious or subconscious awareness of
b in the external or internal environment. For a sensa-
occur, four conditions must be satisfied;
[ \ simndm, or change in die environment, capable of activat-
ing certain sensory neurons, must occur. A stimulus that ac-
tivates a sensory receptor may be in the form of light, heat,
pressure, mechanical energy, or chemical energy.
I A sensory receptor must convert the stimulus to an electri-
cal signal, which ultimately produces one or more nerve
impulses if it is large enough.
J, The nerve impulses must be conducted along a neural
pathway from the sensory receptor to the brain.
-ion of the brain must receive and integrate the nerve
impulses into a sensation.
Overview of Sensations 285
Characteristics of Sensations
As you have learned in Chapter 10, perception is the con-
scious awareness and interpretation of sensations and is pri-
marily a function of the cerebral cortex. Yob seem to see with
your eyes, hear with your ears, and feel pain in an injured
part of your body. This is because sensory nerve impulses
from each part of the body arrive in a specific region of the
cerebral cortex, which interprets the sensation as coming
from the stimulated sensory receptors. A given sensory neu-
ron carries information for one type of sensation only Neu-
rons relaying impulses for touch, for example, do not also
conduct impulses for pain. The specialization of sensory neu-
rons enables nerve impulses from the eyes to be perceived as
sight and diose from the ears to be perceived as sounds.
A characteristic of most sensory receptors is adaptation, a
decrease in the strength of a sensation during a prolonged
stimulus. Adaptation is caused in part by a decrease in the re-
sponsiveness of sensory receptors. As a result of adaptation, the
perception of a sensation may fade or disappear even though
the stimulus persists. For example, when you first step into a
hot sJiOwer s die water may feel very hot, but soon the sensation
decreases to one of comfortable warmth even though the stim-
ulus (the high temperature of the water) does not change. Re-
ceptors vary in how quickly they adapt. Receptors associated
with pressure, touch, and smell adapt rapidly Slowly adapting
receptors monitor stimuli associated with pain, body position,
and die chemical composition of the blood.
Types of Sensory Receptors
Both structural and functional characteristics of sensory re-
ceptors can be used to group them into different classes
(Table 12,1). Structurally, the simplest are free nerve eiMfagr,
Table 12.1 Classification ot Sensory Receptors
Basis of Classification
Structure
Fme nerve endings
Encapsulated nerve endings
Separate cells
Function
ttechanoreceptors
Thermoreceptors
Nociceptors
Photoreceptors
Osmoreceptors
Osmoreceptors
Description
Bare dendrites are associated with pain, thermal, tickle, itch, and some touch sensations.
Dendrites enclosed in a connective tissue capsule, such as a corpuscle of touch.
Receptor cell synapses with first-order neuron; located in the retina of the eye (photoreceptors), inner ear (hair
cells), and taste buds of the tongue (gustatory receptor cells).
Detect mechanical pressure; provide sensations of touch, pressure, vibration, proprioc
equilibrium; also monitor stretching of blood vessels and internal organs,
Detect changes in temperature.
Respond to painful stimuli resulting from physical or chemical damage to tissue.
Detect light that strikes the retina of the eye.
Detect chemicals in mouth (taste), nose (smell), and body fluids.
Sense the osmotic pressure of body fluids.
eption, and hearing and
286 Chapter 12 Somatic Senses and Special Senses
which arc hare dendrites chat lack any structural specializa-
tions at their ends that can be seen under a light microscope
(Figure 12 J)- Receptors for pain, thermal, tickle, itch, and
some touch sensations are free nerve endings. Receptors for
other somatic and visceral sensations, such as touch, pressure,
and vibration, have encapsulated nerve endings. Their dendrites
are enclosed in a connective tissue capsule with a distinctive
mrcrnscopic structure. Still other sensory receptors consist of
specialized, separate cells that synapse with sensory neurons,
for example, hair cells in the inner ear.
Another way to group sensory receptors is functionally —
according to the type of stimulus they detect. Most stimuli
are in the form of mechanical energy, such as sound waves or
pressure changes; electromagnetic energy, such as light or
heat; or chemical energy, such as in a molecule of glucose.
■ Mechanoreceptors are sensitive to mechanical stimuli such
as the deformation, stretching, or bending of cells.
Mechanoreceptors provide sensations of touch, pressure,
vibration, proprioception, and hearing and equilibrium.
They also monitor the stretching of blood vessels and in-
ternal organs.
■ Thermoreceptors detect changes in temperature.
■ Nociceptors respond to painful stimuli resulting fro
physical or chemical damage to tissue.
■ Photoreceptors detect light that strikes the retina of the e
■ Chemorcccptors detect chemicals in the mouth (taste), n
(smell), and body fluids.
■ Owwreceptors detect the osmotic pressure of body flui
■ CHECKPOINT I
1 . Which senses are "special senses"?
2, How is a sensation different from a perception?
SOMATIC SENSES
OBJECTIVES • Describe the location and function
the receptors for tactile, thermal, and pain sensations,
• Identify the receptors for proprioception and descril
their functions.
Somatic sensations arise from stimulation of sensory reqj
tors in the skin, mucous membranes, muscles, tendons,
Figure 12,1 Structure and location of sensory receptors in the skin and subcutaneous layer.
The somatic sensations of touch, pressure, vibration, warmth, cold, and pain arise from sensory re-
ceptors in the skin, subcutaneous layer, and mucous membranes.
Nociceptor
(pain receptor)
Epidermis
Dermis
Subcutaneous layer —
"<
I
/
*
Which receptors are especially abundant in the fingertips, palms, and soles?
Type I cutaneous
mechanoreceptor
Corpuscle of touch
in dermal papilla
Type II cutaneous
mechanoreceptor
Hair root plexus
Lamellated
corpuscle
pints. The sensory receptors for somatic sensations are dis-
puted unevenly. Some parts of the body surface are densely
plated with receptors, and other pans contain only a few.
areas with die largest numbers of sensory receptors are
tip of the tongue, the lips, and the fingertips.
*
|ctile Sensations
fte tactile sensations (TAK-til; tact- = touch) are touch,
Sure, vibration, itch, and tickle. Itch and tickle sensations
detected by free nerve endings. All other tactile sensations
detected by a variety of encapsulated mechanoreceptors
12.1). Tactile receptors in the skin or subcutaneous
include corpuscles of touch, hair root plexuses, type I
nd II cutaneous mechanoreceptors, lamellated corpuscles,
^d free nerve endings (Figure 12,1).
tweh
parions of. touch generally result from stimulation of tac-
) receptors in the skin or subcutaneous layer. There are
types of rapidly adapting touch receptors. Corpuscles of
uh, or Meissner corpuscles (MIS-ner), are located in the
lal papillae of hairless skin. Each corpuscle is an egg-
iped mass of dendrites enclosed by a capsule of connective
Lie. They are abundant in the fingertips, hands, eyelids, tip
the tongue, lips, nipples, soles, clitoris, and tip of the pe-
Hair root plexuses consist of free nerve endings wrapped
Kind hair follicles in hairy skin. Hair root plexuses detect
jvements on the surface of the skin that disturb hairs. For
tuple, an insect landing on a hair causes movement of the
shaft that stimulates the free nerve endings.
There are also two types of slowly adapting touch recep-
Type I cutaneous mechanoreceptors, also known as
$1 discs, are saucer-shaped, flattened free nerve endings
fmake contact with Merkel cells of the stratum hasalc;
are plentiful in the fingertips, hands, lips, and exter-
genkalia. Type II cutaneous mechanoreceptors, or Ruffini
mles, are elongated, encapsulated receptors located deep
fee dermis, and in ligaments and tendons as well. Present
[the hands and abundant on the soles, they are most sensi-
|to stretching that occurs as digits or limbs are moved.
mtre and Vibration
We is a sustained sensation that is felt over a larger area
touch. Receptors that contribute to sensations of
sure include corpuscles of touch, type I mechanoreccp-
and lamellated corpuscles. Lamellated, or pacinian
ve-an), corpuscles are large oval structures composed
a multilayered connective tissue capsule that encloses a
tending (Figure 12.1). Like corpuscles of touch, lamel-
i corpuscles adapt rapidly. They are widely distributed in
body: in the dermis and subcutaneous layer; in tissues
underlie mucous and serous membranes; around joints,
ons, and muscles; in the periosteum; and in die mam-
Somatic Senses 287
maty glands, external genitalia, and certain viscera, such as
the pancreas and urinary bladder.
Sensations of vibration result from rapidly repetitive
sensory signals from tactile receptors. The receptors for
vibration sensations are corpuscles of touch and lamellated
corpuscles. Corpuscles of touch can detect lower-frequency
vi 1 >ra ti ons; lamellated corpuscles tie tect higher-lreq uency
vibrations.
Itch and Tickle
The itch sensation results from stimulation of free nerve end-
ings by certain chemicals, such as bradykinin, often as a result
of a local inflammatory response. Receptors for the tickle
sensation are thought to be free nerve endings and lamellated
corpuscles. This intriguing sensation typically arises only
when someone else touches you, not when you touch your-
self. The explanation of this puzzle seems to lie in the nerve
impulses that conduct to and from the cerebellum when you
are moving your fingers and touching yourself that don't oc-
cur when someone else is tickling you.
Patients who have had a limb amputated may still experi-
ence sensations such as itching, pressure, tingling, or pain
as if the limb were still there. This phenomenon is called
phantom limb sensation* One explanation for phantom
limb sensations is that the cerebral cortex interprets im-
pulses arising in the proximal portions of sensory neurons
that previously carried impulses from the limb as coming
from the nonexistent (phantom) limb. Another explanation
for phantom limb sensations is that neurons in die brain
that previously received sensory impulses from the missing
limb are still active, giving rise to false sensory perceptions.
Thermal Sensations
Thermoreceptors are free nerve endings. Two distinct thermal
sensations — coldness and warmth — are mediated by different
receptors. Temperatures between 10° and 40°C (50-105°F)
activate cold receptors, which are located in the epidermis.
Warm receptors are located in the dermis and are activated by
temperatures between }2° and 48°C (90-1 18°F). Cold and
warm receptors both adapt rapidly at the onset of a stimulus
but continue to generate nerve impulses more slowly
throughout a prolonged stimulus. Temperatures below 1()°C
and above 48°C stimulate mainly nociceptors, rather than
thermoreceptors, producing painful sensations.
Pain Sensations
The sensory receptors for pain, called nociceptors (no'-se-
SEP-tors; noci- = harmful), are free nerve endings (Figure
12.1). Nociceptors are found in practically every tissue of the
body except the brain, and they respond to several types of
stimuli. Excessive stimulation of sensory receptors, excessive
288 Chapter 12 Somatic Senses and Special Senses
stretching of a structure, prolonged muscular contractions,
inadequate blood flow to an organ, or the presence of certain
chemical substances can aJl produce the sensation of pain.
Pain may persist even after a pain-producing stimulus is
removed because pain-causing chemicals linger and because
nociceptors exhibit very little adaptation. The lack of adapta-
tion of nociceptors serves a protective function: If there were
adaptation to painful stimuli, irreparable tissue damage could
result.
There are two types of pain: fast and slow. The percep-
tion of 'fast pain occurs very rapidly, usually within 0.1 sec-
ond after a stimulus is applied. This type of pain is also
known as acute, sharp, or pricking pain. The pain felt from a
needle puncture or knife cut to the skin are examples of fast
pain. Fast pain is not felt in deeper tissues of the body. The
perception of slow pain begins a second or more after a stim-
ulus is applied. It then gradually increases in intensity over a
period of several seconds or minutes. This type of pain,
which may be excruciating, is also referred to as chronic,
burning, aching, or throbbing pain. Slow pain can occur both
in the skin and in deeper tissues or internal organs. An exam-
ple is the pain associated with a toothache.
Fast pain is very precisely localized to the stimulated
area. For example, if someone pricks you with a pin, you
know exactly which part ol your body was stimulated. So-
matic slow pain is well localized but more diffuse (involve
large areas); it usually appears to come from a larger area
the skin. In many instances of visceral pain, the pain is feltii
or just deep to the skin that overlies the stimulated organ,
in a surface area far from the stimulated organ. This pi
nomenonJs called referred pain (figure 12.2). In genei
the visceral organ involved and the area in which the pain
referred are served by the same segment of the spinal cor
For example, sensory neurons from the heart, the skin oi
the heart, and the skin along the medial aspect of the left
enter spinal cord segments Tl to T5. Thus, the pain ofj
heart attack typically is felt in the skin over the heart am]
along the left arm.
Some pain sensations occur out of proportion to minor
damage or persist chronically lor no obvious reason, In
such cases, analgesia {an- = without; -algesia = pain) or
pain relief is needed. Analgesic drugs such as aspirin mi
ibuprofen (for example, Advil®) block formation of some
chemicals that stimulate nociceptors. Local ancstl
such as Novocaine®, provide short-term pain relief bj
blocking conduction of nerve impulses. Morphine and
other opiate drugs alter the quality of pain perception i
the brain; pain is still sensed, but it is no longer percei|
as so unpleasant,
Figure 12.2 Distribution of referred pain. The colored parts of the diagrams indicate skin areas to which
visceral pain is referred.
ft
Nociceptors are present in almost every tissue of the body.
Liver and gallbladder
\
Gallbladder
Small intestine
Ovary
Kidney
Appendix
Ureter
Lung and
diaphragm
Heart
Pancreas
Stomach
Ovary
Colon
Urinary
bladder
Liver and gallbladder
Stomach
Liver and gallbladder
Kidney
(a) Anterior view
) Which visceral organ has the broadest area tor referred pain?
(b) Posterior view
ocus on Wellness
Somatic Senses 289
Pain Manageme
Modulation
fun is a useful sensation when it alerts
ft to an injury that needs attention. We
Bull our finger away from a hot stove,
letake off shoes that are too tight, and
stan ankle that has been sprained.
[e do what we can to help die injury
and meanwhile take over-the-
pter or prescription painkillers until
gain goes away.
Pain that persists for longer than
b or three months despite appropriate
atnient is known as chronic pain. The
,t common forms of chronic pain are
back pain and headache. Cancer,
ids, fibromyalgia, and many other
rders are associated with chronic
, People experiencing chronic pain
experience chronic frustration as
are sent from one specialist to an-
k in search of a diagnosis.
The goal of pain management pro-
s, developed to help people with
nit pain, is to decrease pain as
; possible, and then help pa-
ts learn to cope with whatever pain
ins. Because no single treatment
or everyone, pain management
ams typically offer a wide variety
ments from surgery and nerve
blocks to acupuncture and exercise
therapy. Following are some of the
therapies that complement medical and
surgical treatment for the management
of chronic pain.
Counseling
Pain used to be regarded as a purely
physical response to physical injury.
Psychological factors arc now under-
stood to serve as important mediators
in the perception of pain. Feelings such
as fear and anxiety strengthen the pain
perceptions. Pain may be used to avoid
certain situations, or to gain attention.
Depression and associated symptoms
such as sleep disturbances can con-
tribute to chronic pain. Psychological
counseling techniques can help people
with chronic pain confront issues that
may be worsening their pain.
Relaxation and Meditation
Relaxation and meditation techniques
may reduce pain by decreasing anxiety
and giving people a sense of personal
control. Some of these techniques in-
clude deep breathing, visualization of
positive images, and muscular relax-
ation. Others encourage people to be-
come more aware of thoughts and situ-
ations that increase or decrease pain or
provide a mental distraction from the
sensations of pain.
Exercise
People with chronic pain tend to
avoid movement because it hurts. In-
activity causes muscles and joint
structures to atrophy, which may
eventually cause the pain to worsen.
Regular exercise and improved fitness
help to relieve pain. Why? Exercise
stimulates the production of endor-
phins, chemicals produced by the
body to relieve pain. It also improves
self-confidence, can serve as a distrac-
tion from pain, and improves sleep
quality, which is often a problem for
people with chronic pain.
iprioceptive Sensations
tpn
ioceptive sensations (pro-pre-6-SEP-tive; propria- =
'sown) allow us to know where our head and limbs are
ted and how they are moving even if we are not looking
em, so that we can walk, type, or dress without using our
Kinesthesia (kin'-es-THE-ze-a; kin- = motion; -esthe-
perception) is the perception of body movements. Pro-
jptive sensations arise in receptors termed propriocep-
I Proprioceptors arc located in skeletal muscles (muscle
dies), in tendons (tendon organs), in and around synovial
joints (joint kinesthetic receptors), and in the inner ear (hair
cells). Those proprioceptors embedded in muscles, tendons,
and synovial joints inform us of the degree to which muscles
are contracted, die amount of tension on tendons, and the
positions of joints. Hair cells of the inner ear monitor the
orientation of the head relative to the ground and head posi-
tion during movements. Proprioceptive sensations also allow r
us to estimate the weight of objects and determine die mus-
cular effort necessary to perform a task. For example, as you
pick up a bag you quickly realize whether it contains popcorn
290 Chapter 12 Somatic Senses and Special Senses
or books, and you then exert the correct amount of effort
■d to lift it.
Nerve impulses for conscious proprioception pass along
sensory tracts in the spinal cord and brain stem and are re-
layed to the primary somatosensory area (postcentral gyrus)
in the parietal lobe of the cerebral cortex (see Figure 10.13
on page 259). Proprioceptive impulses also pass to the cere-
bellum, where they contribute to the cerebellum's role in co-
ordinating skilled movements. Because proprioceptors adapt
slowly and only slightly, the brain continually receives nerve
impulses related to the position of different body parts and
makes adjustments to ensure coordination.
■ CHECKPOINT
3. Why is it beneficial to your well-being that nociceptors
and proprioceptors exhibit very little adaptation?
4. Which somatic sensory receptors detect touch sensations?
5. What is referred pain, and how is it useful in diagnosing
internal disorders?
olfactory receptors, supporting cells, and basal stem eel
(Figure 12,3b). Olfactory receptors are the fust-order i
rons of the olfactory pathway. Several cilia called olfact&i)
hairs project from a knob-shaped tip on each olfactory u
ceptor. The olfactory hairs are the parts of the olfactory
ceptor dm respond to inhaled chemicals. Chemicals
have an odor and can therefore stimulate the olfactory haih
are called odor a fits. The axons of olfactory receptors extend
from the olfactory epithelium to the olfactory bulb. Support-
ing cells are columnar epithelial cells of the mucous mem-
brane lining the nose. They provide physical support, nour-
ishment, and electrical insulation for the olfactory receptoi
and they help detoxify chemicals that come in contact wit
the olfactory epithelium. Basal cells are stem cells located be-
tween the bases of the supporting cells and continually
dergo cell division to produce new olfactory receptors, which
live for only a month or so before being replaced. This pro*
ess is remarkable because olfactory receptors are neuroi
and in general, mature neurons are not replaced. Otfat
glands produce mucus that moistens the surface of the oil
tory epithelium and serves as a solvent for inhaled odoraffl
SPECIAL SENSES
Receptors for the special senses— smell, taste, sight, hearing,
and equilibrium — are housed in complex sensory organs
such as the eyes and ears. Like the general senses, the special
senses allow us to detect changes in our environment. Oph-
thalmology (of -thal-MOL-o-je; ophtlmlmo- = eye; -logy =
study of) is the science that deals with the eye and its dis-
orders. The other special senses are, in large part, the con-
cern of otorbinotaryngofogy (o'-to-ri '-no-lar'-in-GOL-o-jjS;
oto- = ear; rhino- = nose; laiyngo- = larynx), the science that
deals with the ears, nose, and throat and their disorders.
Stimulation of Olfactory Receptors
Many attempts have been made to distinguish among
classify "primary" sensations of smell Genetic evidence!
suggests the existence of hundreds of primary odors,
ability to recognize about 10,000 different odors
depends on patterns of activity in the brain that arise
activation of many different combinations of olfactory rece
tors. Olfactory receptors react to odorant molecules by p
doting an electrical signal that triggers one or more n
impulses. Adaptation (decreasing sensitivity) to odors occ
rapidly. Olfactory receptors adapt by about 50% in the li
second or so after stimulation and very slowly thereafter,
lr
OLFACTION: SENSE OF SMELL
OBJECTIVE • Describe the receptors for olfaction and
the olfactory pathway to the brain.
The nose contains 10-100 million receptors for the sense of
smell, or olfaction (ol-FAK-shun; olfact- = smell). Because
some nerve impulses for smell and taste propagate to the lim-
bic system, certain odors and tastes can evoke strong emo-
tional responses or a flood of memories.
Structure of the Olfactory Epithelium
The olfactory epithelium occupies the upper portion of the
nasal cavity (Figure 12.3a) and consists of three types of cells:
The Olfactory Pathway
On each side of die nose, about 40 bundles of the sleuth
unmyelinated axons of olfactory receptors extend thro|
about 20 holes in the cribriform plate of the ethmoid
(Figure 12.31)). These bundles of axons collectively form
right and left olfactory (I) nerves. The olfactory nerves ter<
initiate in die brain in paired masses of gray matter called
olfactmy bulbs, which arc located below die frontal lobes
the cerebrum. Within the olfactory bulbs, the axon termii
of olfactory receptors — the first-order neurons— fl
synapses with the dendrites and cell bodies of second-OK
neurons in the olfactory pathway.
The axons of the neurons extending from the ol
bulb form die olfactofy tract. Some of the axons of the oil
tory tract project to the primary olfactory area in the tempi
lobe of the cerebral cortex (sec figure 10.13 on page 23
Gustation: Sense of Taste 291
Figure 12.3 Olfactory epithelium and olfactory receptors, (a) Location of olfactory epithelium in the nasal cavity,
(b) Anatomy of olfactory receptors, whose axons extend through the cribriform plate to the olfactory bulb.
v-* -^^J^-
The olfactory epithelium consists of olfactory receptors, supporting cells, and basal cells.
[a) Sagittal view
Frontal lobe
of cerebrum
Olfactory tract
Olfactory bulb
Cribriform plate
of ethmoid bone
Olfactory
nerve
Olfactory
epithelium
Superior
nasal
concha
Olfactory
tract
Olfactory -
eptheJium
Mucus
Olfactory bulb
Olfactory bufb
neuron
Paris of olfactory (I) nerve
Cribriform plate
Bundle of axons of
olfactory receptors
Olfactory gland
(produces mucus)
Basal cell
Olfactory receptor
Supporting cell
Olfactory hair
Odorant molecule
What is the function of basal stem cells?
(b) Enlarged aspect of olfactory receptors
Acre conscious awareness of smell begins. Other axons of
ie olfactory tract project to the limbic system and hypothal-
amus; these connections account for emotional and memory-
poked responses to odors, Examples include sexual excite-
ment upon smelling a certain perfume or nausea upon
iling a food that once made you violently ill.
7,
CHECKPOINT
What functions are carried out by the three types of cells
in the olfactory epithelium?
Define the following terms: olfactory nerve, olfactory
bulb, and olfactory tract.
Hyposmia (hf-POZ-me-a; hypo- = below; -omtia = smell,
odor), a reduced ability to smell, affects half of those over
Kge 65 and 75% of those over age 80. With aging the
1 smell deteriorates. Hyposmia also can be caused
[by neurological changes, such as a head injury, Alzheimer
e, or Parkinson disease; certain drugs, such as anti-
histamines, analgesics, or steroids; and the damaging
effects i- »f smoking.
GUSTATION: SENSE OF TASTE
OBJECTIVE • Describe the receptors for gustation
and the gustatory pathway to the brain.
Taste or gustation (gus-TA-shun; gust- = taste) is much sim-
pler than olfaction because only five primary tastes can be
distinguished: sour, sweet, bitter, salty and umami (u-MAM-e).
292 Chapter 12 Somatic Senses and Special Senses
The unraami taste is described as "meaty" or "savory." AJI
other Savors, such as chocolate, pepper, and coffee, are
combinations of the five primary tastes, plus the accompa-
nying olfactory and tactile (touch) sensations. Odors from
food can pass upward from the mouth into the nasal cavity,
where they stimulate olfactory receptors. Because olfaction
is much more sensitive than taste, a given concentration of a
food substance may stimulate the olfactory system thou-
sands of times more strongly than it stimulates the gusta-
tory system. When you have a cold or are suffering from al-
lergies and cannot taste your food, it is actually olfaction
that is blocked, not taste.
Structure of Taste Buds
The receptors for taste sensations are located in the
buds (Figure 12.4). Most of the nearly 10,000 taste hudsofj
young adult are on the tongue, hut some are also found
the root of the mouth, pharynx (throat), and epiglottis (d
lage lid over the voice box). The number of taste buds
dines with age. Taste buds are found in elevations on
tongue called papillae (pa-PIL-e; singular is papilla), \\[
provide a rough texture to the upper surface of the tonf
(Figure 12.4 a,b). Vallate papillae (VAL-at = wall-like)
an inverted V-shaped row at the back of the tongue,]
Fungiform papillae (FUN-ji-form = mushroomlike)
■
Figure 12,4- The relationship of gustatory receptors in taste buds to tongue papillae.
Gustatory (taste) receptor cells are located in taste buds.
Epiglottis
Palatine tonsil
Ungual tonsil
Vallate papilla
Fungiform papilla
Filiform papilla —
Vallate papilla
Filiform papilla
Fungiform papilla
of papillae
V
Dorsum of tongue showing
location of papillae
v
Stratified
squamous
epithelium
Supporting
cell
Connective
tissue
Taste bud
Gustatory hair
Gustatory
receptor cell
Basal cell
First-order
sensory neurons
(c) Structure of a taste bud
y In order, from the tongue to the brain, what structures form the gustatory pathway?
IV
fthroom-shaped elevations scattered over the entire sur-
ce of the tongue. In addition, the entire surface of the
ue has filiform papillae (FIL-i-form = threadlike), which
tain touch receptors but no taste buds.
Each taste bud is an oval body consisting of three types
(epithelial cells: supporting cells, gustatory receptor cells,
Ind basal cells (Figure 12.4c). The supporting cells surround
■bout SO gustatory receptor cells. A single, long gustatory
I kir projects from each gustatory receptor cell to the exter-
M surface through the taste pore, an opening in the taste
Basal celts are stem cells that produce supporting cells,
Much then develop into gustatory receptor cells that have a
fit spun of about 10 days. The gustatory receptor cells arc
separate receptor cells. They do not have an axon (like oltac-
eceptors) but rather synapse with dendrites of the first-
order sensory neurons of the gustatory pathway.
Stimulation of Gustatory Receptors
[Chemicals that stimulate gustatory receptor cells are known
htastants. Once a tastant is dissolved in saliva, it can enter
and make contact with the plasma membrane of
Listatory hairs. The result is an electrical signal that
pnulates release of neurotransmitter molecules from the
gustatory receptor cell. Nerve impulses are triggered when
neurotransmitter molecules bind to their receptors on
endrites of the first-order sensory neuron. The den-
rites branch profusely and contact many gustatory receptors
; . eral taste buds. Individual gustatory receptor cells may
pspimd to more than one of the five primary tastes. Com-
adaptation (loss of sensitivity) to a specific taste can oc-
fcriii 1 to 5 minutes of continuous stimulation.
If all tastants cause release of neurotransmitter from
nan; gustatory receptor cells, why do foods taste different?
The answer to this question is thought to lie in the patterns
f nerve impulses in groups of first-order taste neurons that
e with the gustatory receptor cells. Different tastes
ihi from activation of different groups of taste neurons. In
iddirion, although each individual gustatory receptor cell re-
pels to more than one of the five primary tastes, it may re-
pond more strongly to some tastants than to others.
e Gustatory Pathway
cranial nerves contain axons of first-order gustatory
us that innervate the taste buds. The facial (VII) nerve
lossopharyngeal (IX) nerve serve the tongue; the vagus
\i nerve serves the throat and epiglottis. From taste buds,
Ises propagate along these cranial nerves to the medulla
ftbngata. From the medulla, some axons carrying taste sig-
roject to the limbic system and the hypothalamus, and
project to the thalamus. Taste signals that project from
alamus to the primary gustatory area in the parietal lobe
Vision 293
of the cerebral cortex (see Figure 10.13 on page 259) give
rise to the conscious perception of taste.
Probably because of taste projections to the hypothalamus
I and limbic system, there is a strong link between taste and
pleasant or unpleasant emotions. Sweet foods evoke reac-
tions of pleasure while bitter ones cause expressions of dis-
gust, even in newborn babies. This phenomenon is the ba-
sis for taste aversion, in which people and animals quickly
learn to avoid a food if it upsets the digestive system. Be-
cause the drugs and radiation treatments used to combat
cancer often cause nausea and gastrointestinal upset re-
gardless of what foods are consumed, cancer patients may
lose their appetite because they develop taste aversions for
most foods.
CHECKPOINT
How do olfactory receptors and gustatory receptor cells
9,
differ in structure and function?
Compare the olfactory and gustatory pathwaj s,
VISION
OBJECTIVES • Describe the accessory structures of
the eye, the layers of the eyeball, the lens, the interior of
the eyeball, image formation, and binocular vision.
• Describe the receptors for vision and the visual path-
way to the brain.
More than half the sensory receptors in the human body are
located in the eyes, and a large part of the cerebral cortex is
devoted to processing visual information. In this section of
the chapter, we examine the accessory structures of the eye,
the eyeball itself, the formation of visual images, the physiol-
ogy of vision, and the visual pathway from the eye to the
brain.
Accessory Structures of the Eye
The accessory structures of the eye are the eyebrows, eye-
lashes, eyelids, extrinsic muscles that move the eyeballs, and
lacrimal (tear-producing) apparatus. The eyebrows and eye-
lashes help protect the eyeballs from foreign objects, perspi-
ration, and direct rays of the sun (Figure 12,5). The upper
and lower eyelids shade the eyes during sleep, protect the
eyes from excessive light and foreign objects, and spread
lubricating secretions over the eyeballs (by blinking). Six
extrinsic eye muscles cooperate to move each eyeball right,
left, up, down, and diagonally: the superior rains, inferior rec-
tus, lateral rectus, medial rectus, superior oblique, and inferior
294 Chapter 12 Somatic Senses and Special Senses
Figure 12.5 Accessory structures of the eye.
N.
Accessory structures of the eye are the eyebrows, eyelashes, eyelids, extrinsic eye muscles, and the lacrimal apparatus.
Lacrimal gland
Lacrimal duct
: .' y
< \
f
What are the functions of tears?
Superior lacrimal canal
Lacrimal sac
Inferior lacrimal canal
Nasolacrimal duct
Nasal cavity
FLOW OF TEARS:
Lacrimal gland
\
Excretory
lacrimal ducts
i
Superior or inferior
lacrimal canal
\
Lacrimal sac
\
Nasolacrimal duct
Nasal cavity
oblique. Neurons in the brain stem and cerebellum coordinate
and synchronize the movements of the eyes.
The lacrimal apparatus Qacrifna = tear) is a group of
glands, ducts, canals, and sacs that produce and drain
lacrimal fluid or tears (Figure 1 2. 5). The right and left
lacrimal glands arc each about the size and shape of an al-
mond. They secrete tears through the lacrimal ducts onto
the surface of die upper eyelid. Tears then pass over the sur-
face ot die eyeball toward the nose into two lacrimal canals
and a nasolacrimal duct, which allow the tears to drain into
the nasal cavity.
Tears are a watery solution containing salts, some mucus,
and a bacteria-killing enzyme called lysozyme. Tears clean,
lubricate, and moisten the portion of the eyeball exposed to
the air to prevent it from drying. Normally, tears are cleared
away by evaporation or by passing into the nasal cavity as fast
as they are produced. If, however, an irritating substance
makes contact with the eye, the lacrimal glands are stimu-
lated to oversecrete and tears accumulate. This protective
mechanism dilutes and washes away the irritant. Only hu-
mans express emotions, both happiness and sadness, by cry-
ing. In response to parasympathetic stimulation, the lacrimal
glands produce excessive tears that may spill over the edges
of the eyelids and even fill the nasal cavity with fluid. This is
how crying produces a runny nose.
Layers of the Eyeball
The adult eyeball measures about 2.5 cm (1 inch) in diameter
and is divided into three layers: fibrous tunic, vascular tunic,
and retina (Figure 12.6).
Fibrous Tunic
The fibrous tunic is the outer coat of the eyeball. It consi)
of an anterior cornea and a posterior sclera. The
(KOR-ne-a) is a transparent fibrous coat that covers
ored iris. Because it is curved, die cornea helps focus li
rays onto the retina. The sclera (SKLER-a = hard),
"white" of die eye, is a coat of dense connective tissue
covers all of the entire eyeball except the cornea. The sd]
gives shape to die eyeball, makes it more rigid, and prott
its inner parts. An epithelial layer called the confnm
(kon-junk-TI-va) covers the sclera but not the cornea
lines the inner surface of the eyelids.
Vascular Tunic
The vascular tunic is the middle layer of the eyeball ad
composed of the choroid, ciliary body, and iris. The &
(KO-royd) is a thin membrane that lines most of the int
surface of the sclera. It contains many blood vessels that
nourish the retina. The choroid also contains melano
diat produce the pigment melanin, which causes this la
appear dark brown in colon Melanin in die choroid abso
stray light rays, which prevents reflection and scattering
light within the eyeball. As a result, the image cast on
retina by the cornea and lens remains sharp and clear.
At die front of the eye, die choroid becomes the
body (SlL-e-ar'-e). The ciliary body consists of the da
processes, folds on the inner surface of the ciliary body
capillaries secrete a fluid called aqueous humor, and the
iary muscle, a smooth muscle that alters the shape of
for viewing objects up close or at a distance. The I
transparent structure that focuses light rays onto the i i
Vision 295
(Figure 12.6 Structure of the eyeball.
The wall of the eyeball consists of three layers: the fibrous tunic, the vascular tunic, and the retina.
Transverse
plane
Anterior cavity
(contains aqueous
humor
Light
Scleral venous sinus
Lacrimal sac
Ciliary body:
Ciliary muscle
Ciliary process
Medial rectus
muscle
Vitreous chamber
(contains vitreous body)
MEDIAL
Blood vessels
Cornea
Pupi!
Optic disc Central fovea
Optic (II) nerve {b * nd spot)
Superior view of transverse section of right eyeball
Zonular fibers
lens
Conjunctiva
Retina
Choroid
Sclera
Lateral rectus
muscle
LATERAL
What are the components of the fibrous tunic and vascular tunic?
[tructed of many layers of elastic protein fibers. Zonular
|n attach the lens to die ciliary muscle and hold the lens in
iron.
II iris (= colored circle) is the colored part of the eye-
|, It includes both circular and radial smooth muscle
The hole in the center of the iris, through which light
iters the eyeball, is the pupil (Figure 12.7). The smooth
;le of the iris regulates the amount of light passing
igh the lens. When the eye is stimulated by bright light,
: parasympathetic division of the autonomic nervous sys-
\S) causes contraction of the circular muscles of the
which decreases die size of the pupil (constriction).
When the eye must adjust to dim light, the sympathetic divi-
sion of the ANS causes the radial muscles to contract, which
increases the size oi the pupil (dilation).
Using an ophthalmoscope, (of-THAL-mo-skopj ophtbal-
mas- = eye; -skopeo = to examine), an observer can peer
through the pupil and see a magnified image ol the retina
and the blood vessels that cross it. The surface of the
retina is the only place in the body where blood vessels can
be viewed directly and examined for pathological changes,
such as those that occur with hypertension or diabetes
mellitus.
296 Chapter 12 Somatic Senses and Special Senses
Figure 12.7 Responses of the pupil to light of varying bright-
ness.
: c<
Contraction of the circular muscles causes constriction of the
pupil; contraction of the radial muscles causes dilation of the
pupil.
Pupil constricts as
circular muscles of iris
contract (parasympathetic)
Pupil
,\\\\
m
m
Pupil dilates as
radial muscles of iris
contract (sympathetic)
Bright light
Normal light
Anterior views
Dim light
Which division of the autonomic nervous system causes pupil-
lary constriction? Which causes pupillary dilation?
Retina
The third and inner coat of the eyeball, the retina, lines!
posterior three-quarters of the eyeball and is the beginnij
of the visual pathway (Figure 12.8). Two layers comprise til
retina: the neural layer and the pigmented layer. The
layer of the retina is a multilayered outgrowth of the
Three distinct layers of retinal neurons — the photoreceptor]
layer, the bipolar cell layer, and the ganglion cell layer— \
separated by two zones, the outer and inner synaptic layei
where synaptic contacts are made. Note that light
through the ganglion and bipolar cell layers and both syuj
tic layers before it reaches the photoreceptor layer.
The pigmented layer of the retina is a sheet of met
containing epithelial cells located between the choroid
the neural part of the retina- The melanin in the pigment
layer of the retina, like in the choroid, also helps to aN
stray light rays.
Photoreceptors are specialized cells that begin
process by which light rays are ultimately converted to i
impulses. There are two types oi photoreceptors: rods
cones. Rods allow us to see shades of gray in dim light, sd
as moonlight. Brighter lights stimulate the cones, giving
to highly centre, color vision. Three types of cones are pre;
Figure 12.8 Microscopic structure of the retina. The downward blue arrow at left indicates the
direction of the signals passing through the neural layer of the retina. Eventually, nerve impulses arise
in ganglion cells and propagate along their axons, which make up the optic (II) nerve.
In the retina, visual signals pass from photoreceptors to bipolar cells to ganglion cells.
Choroid
»
Path of
light
through
retina
Direction of
visual data
processing
v
Pigment
layer
Photoreceptor -
layer
Outer
synaptic layer
Bipolar cell
layer
Inner
synaptic layer
Ganglion cell
layer
Optic i
nerve
Retinal blood
vessel
Nerve impulses
*^ propagate along
optic (II) nerve axons
toward optic disk
What are the two types of photoreceptors, and how do their functions differ?
in the retina: (1) blue cones, which are sensitive to blue light,
B) green cones, which are sensitive to green light; and (3) red
which are sensitive to red light. Color vision results
, the stimulation of various combinations of these three
tvpesof cones. Jnst as an artist can obtain almost any color by
Lang them on a palette, the cones can code for different
colors by differential stimulation. There are about 6 million
cones and 120 million rods. Cones are most densely concen-
trated in the central fovea, a small depression in die center of
the macula lutea (MAK-ii-la LQO-te-a), or yellow spot, in
the exact center of die retina. The central fovea is the area of
highest visual acuity or resolution (sharpness of vision) because
of its high concentration of cones. The main reason that you
I move your head and eyes while looking at something, such as
file words of this sentence, is to place images of interest on
r fovea. Rods are absent from the central fovea and mac-
ula lutea and increase in numbers toward the periphery of the
na.
From photoreceptors, information flows through the
outer synaptic layer to the bipolar cells of the bipolar cell layer,
and then from bipolar cells through the inner synaptic layer to
| the ganglion cells of the ganglion cell layer. Between 6 and 600
napse with a single bipolar cell in die outer synaptic
a cone usually synapses with just one bipolar cell. The
Lvergence of many rods onto a single bipolar cell increases
, |: light sensitivity of rod vision but slightly blurs the image
that is perceived/ Cone vision, although less sensitive, has
higher acuity because of die one-to-one synapses between
cones and their bipolar cells. The axons of die ganglion cells
extend posteriorly to a small area of the retina called die optic
ik (blind spot), where they all exit as the optic (II) nerve
(see FWre 12.6)- Because the optic disc contains no rods or
cones, we cannot see an image that strikes the blind spot.
Normally, you are not aware of having a blind spot, but you
can easily demonstrate its presence. Cover your left eye and
oze directly at the cross below. Then increase or decrease the
nance between the book and your eye. At some point, the
square will disappear as its image falls on the blind spot.
+
Interior of the Eyeball
[The lens divides the interior of the eyeball into two cavities,
,e anterior cavity and die vitreous chamber. The anterior
iv jly IIls anterior to the lens and is filled with aqueous
mar (A-kwe-us HU-mor; aqua = water), a watery fluid
.pilar to cerebrospinal fluid. Blood capillaries of the ciliary
sses of the ciliary body secrete aqueous humor into the
ior cavity. It then drains into the scleral vcuom sinus
itfScbknm), an opening where the sclera and cornea
meet (see Figure 12.6), and reenters the blood. The aqueous
or helps maintain the shape of the eye and nourishes the
cornea, neither of which has blood vessels.
Vision 297
Normally, aqueous humor is completely replaced about every
90 minutes.
Behind die lens is the second, and larger, cavity of die
eyeball, the vitreous chamber. It contains a clear, jellylike
substance called the vitreous body, which forms during em-
bryonic life and is not replaced thereafter. This substance
helps prevent die eyeball from collapsing and holds the retina
flush against the choroid.
The pressure in the eye, called intraocular pressure, is
produced mainly by the aqueous humor with a smaller con-
tribution from the vitreous body. Intraocular pressure main-
tains the shape of die eyeball and keeps the retina smoothly
pressed against the choroid so the retina is well nourished
and forms clear images. Normal intraocular pressure (about
16 mm Tig) is maintained by a balance between production
and drainage of the aqueous humor.
Table 12 J summarizes the structures of the eyeball
Image Formation and Binocular Vision
In some ways the eye is like a camera: Its optical elements fo-
cus an image of some object on a light-sensitive "film" -die
retina — while ensuring the correct amount of
tit makes
the proper "exposure. To understand how the eye forms
clear images of objects on the retina, we must examine three
processes: (1) the refraction or bending of light by the lens
and cornea, (2) the change in shape of the lens, and (3) con-
striction or narrowing of the pupil.
Refraction of Light Rays
When light rays traveling through a transparent substance
(such as air) pass into a second transparent substance with a
different density (such as water), they bend at the junction
between the two substances. This bending is called refraction
(Figure 12.9a on page 299). About 75% of the total refrac-
tion of light occurs at the cornea. Then, the lens of the eye
further refracts the light rays so that they come into exact fo-
cus on the retina.
Images focused on the retina are inverted (upside down)
(Figure 12.9b, c). They also undergo right-to-left reversal;
that is, light from the right side of an object strikes the left
side of the retina, and vice versa. The reason the world does
not look inverted and reversed is diat the brain "learns" early
in life to coordinate visual images with the orientations of
objects. The brain stores the inverted and reversed images we
acquire when we first reach for and touch objects and inter-
prets those visual images as being correctly oriented in space.
When an object is more dian 6 meters (20 ft) away from
the viewer, the light rays reflected from the object are nearly
parallel to one another, and die curvatures of die cornea and
lens exactly focus the image on the retina (Figure 12.9b).
However, light rays from objects closer than 6 meters are di-
vergent rather than parallel (Figure I2.9e). The rays must be
refracted more if they are to be focused on the retina. This
298 Chapter 12 Somatic Senses and Special Senses
Table 1 2.2 Summary of the Structures of the Eyeball and Their Functions
Structure
Fibrous tunic
Cornea
Choroid * \ ' : '- '
Retina
Lens
Anterior cavity
Vitreous chamber
Retina
Lens
Anterior
cavity
Vitreous
chamber
Function
Cornea: Admits and refracts (bends) light.
Sclera: Provides shape and protects inner parts.
Iris: Regulates the amount of fight that enters eyeball.
Ciliary body: Secretes aqueous humor and alters the shape of the lens for near
Choroid: Provides blood supply and absorbs scattered light.
Receives light and converts it into nerve impulses. Provides output to brain via axons of ganglion cells,
which form the optic (II) nerve.
Refracts light
Contains aqueous humor that helps maintain the shape of the eyeball and supplies oxygen
and nutrients to the lens and cornea.
Contains the vitreous body, which hefps maintain the shape of eyeball and keeps the retina attached
to the choroid.
figure 12.9 Refraction of light rays and accommodation.
Refraction is the bending of light rays.
m
Light ray before
refraction
Air
Water
Light ray after
refraction
(a) Refraction of light rays
Nearly parallel rays
from distant object
3
Lens
(b) Viewing distant object
Divergent rays
object
< >
(c) Accommodation
What changes occur during accommodation for near vision?
Hjtional refraction is accomplished by changes in the shape
■the lens.
\ttommo(tetion
i surface that curves outward, like the surface of a ball, is
o be convex. The convex surface of a lens refracts incom-
;ht rays toward each other, so that they eventually in-
t The lens of the eye is convex on both its anterior and
Lterior surfaces, and its ability to refract light increases as
rvature becomes greater. When the eye is focusing on a
object, the lens becomes more convex and refracts the
Vision 299
light rays more. This increase in the curvature of the lens for
near vision is called accommodation (Figure 12.9c).
When you are viewing distant objects, the ciliary muscle
of die ciliary body is relaxed and the lens is fairly flat because
it is stretched in all directions by taut zonular fibers. When
you view a dose object, the ciliary muscle contracts, which
pulls the ciliary process and choroid forward toward the lens.
This action releases tension on the lens, allowing it to be-
come rounder (more convex), which increases its focusing
power and causes greater convergence of the light rays.
The normal eye, known as an emmetropic eye (em'-e-
TROP-ik), can sufficiently refract light rays from an object
6 m (20 ft) away so that a clear image is focused on the retina
(Figure 12. 10a). Many people, however, lack this ability
Figure 12.10 Normal and abnormal refraction in the eyeball,
(a) In the normal (emmetropic) eye, light rays from an object are
bent sufficiently by the cornea and lens to focus on the central fovea,
(b) In the nearsighted (myopic) eye, the image is focused in front of
the retina, (c) Correction is by use of a concave lens that diverges
entering light rays so that they have to travel further through the eye-
ball, (d) In the farsighted (hyperopia) eye, the image is focused be-
hind the retina, (e) Correction is by a convex lens that causes enter-
ing light rays to converge.
| In uncorrected myopia, distant objects can't be seen clearly; in
^ uncorrected hyperopia, nearby objects can't be seen clearly.
(a) Normal (emmetropic) eye
Normal plane of focus Concave lens
(b) Nearsighted (myopic) eye, (c) Nearsighted (myopic) eye,
uncorrected corrected
Convex lens
(d) Farsighted (hyperopic!
eye, uncorrected
X)
What is presbyopia?
3
(e) Farsighted (hyperopic)
eye, corrected
300 Chapter 12 Somatic Senses and Special Senses
because of refraction abnormalities. Among these abnormali-
ties are myopia (mi-O-pe-a), or nearsightedness, which
occurs when the eyeball is too long relative to the focusing
power of the cornea and lens. Myopic individuals can see
nearby objects clearly, but not distant objects. In hyperopia
(hi-per-O-pe-a) or farsightedness, also known as hyperme-
tropia (hf'-per-me-TRO-pe-a), the eyeball length is short
relative to the focusing power of the cornea and lens. Hyper-
opia individuals can see distant objects clearly, but not nearby
objects. Figure 12,10b— e illustrates these conditions and
shows how they are corrected. Another retraction abnormal-
ity is astigmatism (a-STIG-ma-tizm), in which either the
cornea or the lens has an irregular curvature.
With aging, the lens loses some of its elasticity so its abil-
ity to accommodate decreases. At about age 40, people
who have not previously worn glasses begin to require
them for close vision, such as reading. This condition is
called presbyopia (prez'-he-O-pe-a; preshy- = old; -opia
= pertaining to the eye or vision).
Constriction of the Pupil
Constriction of the pupil is i narrowing of the diameter of the
hole through which light enters the eye due to contraction of
the circular muscles of the iris. This autonomic reflex occurs
simultaneously with accommodation and prevents light rays
from entering the eye through the periphery of the lens.
Light rays entering at the periphery of the lens would not be
brought to focus on the retina and would result in blurred vi-
sion. The pupil, as noted earlier, also constricts in bright light
to limit the amount of light that strikes the retina.
Convergence
In humans, both eyes focus on only one set of objects, a char-
acteristic called binocular vision. This feature of our visual
system allows the perception of depth and an appreciation of
the three-dimensional nature of objects. When you stare
straight ahead at a distant object, the incoming light rays are
aimed directly at the pupils of both eyes and are refracted to
comparable spots on die two retinas. As you move closer to
the object, your eyes must rotate toward the nose if the light
rays from the object are to strike comparable points on both
retinas. Convergence is the name for this automatic move-
ment of the two eyeballs toward the midline, which is caused
by the coordinated action of die extrinsic eye muscles. The
nearer the object, the greater the convergence needed to
maintain binocular vision.
Stimulation of Photoreceptors
After an image is formed on the retina by refraction, accom-
modation, constriction of die pupil, and convergence, light
rays must be converted into neural signals. The initial step ii
this process is the absorption of light rays by the rods anc
cones of the retina. To understand how absorption occurs, it
is necessary to understand the role of photopigments*
A photopigment is a substance that can absorb light and]
undergo a change in structure. The photopigment in rods i^
called rhodopsin (riodo- = rose; -opsin = related to vision]
and is composed of a protein called opsin and a derivative
vitamin A called retinal. Any amount of light in a darken*
room causes some rhodopsin molecules to split into ops
and retinal and initiate a series of chemical changes in
rods. When the light level is dim, opsin and retinal recoi
bine into rhodopsin as fast as rhodopsin is split apart. Rot
usually are nonfunctional in daylight, however, becai
rhodopsin is split apart faster than it can be reformed. V
going from bright sunlight into a dark room, it takes ab<
40 minutes before the rods function maximally.
Cones function in bright light and provide color visit
xAs in rods, absorption of light rays causes breakdown ofphc
topigment molecules. The photopigments in cones also cor
tain retinal, but there are three different opsin proteins — oi
in each of the three types of cones. The cone photopigment
reform much more quickly than die rod photopigment.
The complete loss of cone vision causes a person to b«
come legally blind. In contrast, a person who loses rod <
sion mainly has difficulty seeing in dim light and thus]
should not, for example, drive at night. Prolonged vitamij
A deficiency and the resulting below-normal amount
rhodopsin may cause night blindness, an inability to
well at low light levels. An individual with an absence
deficiency of one of the three types of cones from
retina cannot distinguish some colors from others and «
said to be colorblind. In the most common type,
red -green color blindness* either red cones or green com
are missing. Thus, the person cannot distinguish between
red and green. The inheritance of color blindness is illus
trated in Figure 24.12 on page 606.
The Visual Pathway
After stimulation by Light, the rods -and cones trigger i
cal signals in bipolar cells. Bipolar cells transmit both
tory and inhibitory signals to ganglion cells. The ganglic
cells become depolarized and generate nerve impulses,
axons of the ganglion cells exit the eyeball as the optic
nerve (Figure 12.1 1) and extend posteriorly to the optic
asm (KT-azm = a crossover, as in the letter X). In tin 1
chiasm, about half of the axons from each eye cross to
opposite side of the brain. After passing the optic chiasm,
axons, now part of the optic tract, terminate in the thala
Here they synapse with neurons whose axons project to
Figure 12.11 Visual pathway.
At the optic chiasm, half of the retinal ganglion cell axons from
each eye cross to the opposite side of the brain.
Primary visual areas
in occipital lobes
of cerebral cortex
) What is the correct order of structures that carry nerve impulses
from the retina to the occipital lobe?
te
i)
ic
ininiirv visual areas in the occipital lobes of the cerebral cor-
e Figure 1 0. 1 3 on page 259). Because of crossing at the
opdc chiasm, the right side of the brain receives signals from
yes for interpretation of visual sensations from die left
,,k of an object, and the left side of the brain receives signals
urn both eyes for interpretation of visual sensations from
ie right side of an object.
I CHECKPOINT
ID, How does the shape of the lens change during accomo-
dation?
Ml, How do photopigments respond to light?
12, By what pathway do nerve impulses triggered by an ob-
r in the left half of die visual field of the left eye reach
primary visual area of the cerebral cortex?
Hearing and Equilibrium 301
HEARING AND EQUILIBRIUM
OBJECTIVES • Describe the structures of the outer,
middle, and inner ear.
• Describe the receptors for hearing and equilibrium
and their pathways to the brain.
The ear is a marvel ously sensitive structure. Its sensory re-
ceptors can convert sound vibrations into electrical signals
1000 times faster than photoreceptors can respond to light.
Beside receptors for sound waves, the ear also contains recep-
tors for equilibrium (balance).
Structure of the Ear
The ear is divided into three main regions: the outer ear,
which collects sound waves and channels diem inward; the
middle ear, which conveys sound vibrations to the oval win-
dow; and the inner ear, which houses the receptors for hear-
ing and equilibrium.
Outer Ear
The outer ear collects sound waves and passes them inward
(Figure 12.12). It consists of an auricle, external auditory
canal, and eardrum. The auricle, the part of the ear that you
can see, is a skin-covered flap of elastic cartilage shaped like
the flared end of a trumpet. It plays a small role in collecting
sound waves and directing them toward the external audi-
tory canal (audit- = hearing), a curved tube that extends
from the auricle and directs sound waves toward the
eardrum. The canal contains a few hairs and ccrumhious
glands (se-ROO-mi-nus; ctr- = wax), which secrete cerumen
(se-ROO-men) (earwax). The hairs and cerumen help
prevent foreign objects from entering the ear. The
eardrum, also called the tympanic membrane (tim-PAN-ik;
tympan- = adrum), is a thin, semitransparent partition be-
tween the external auditory canal and the middle ear. Sound
waves cause the eardrum to vibrate. Tearing of the tympanic
membrane, due to trauma or infection, is called a perforated
eardrum.
Middle Ear
The middle ear is a small, air-filled cavity between the
eardrum and inner ear (Figure 12.12). An opening in the an-
terior wall of the middle ear leads directly into die auditory
tube, commonly known as the eustachian tube, which con-
nects the middle ear with the upper part of the throat. When
the auditory tube is open, air pressure can equalize on both
sides of the eardrum. Otherwise, abrupt changes in air pres-
sure on one side of the eardrum might cause it to rupture.
During swallowing and yawning, the tube opens, which ex-
plains why yawning can help equalize the pressure changes
that occur while flying in an airplane.
302 Chapter 1 2 Somatic Senses and Special Senses
Figure 12.12 Structure of the ear.
The ear has three principal regions: the outer ear, the middle ear, and the inner ear.
Semicircular cana!
Frontal — \" ^^
plane
Temporal bone
Vestibulocochlear
(VIII) nerve:
Vestibular branch]
Auricle
CocNa
Elastic
cartilage
To nasopharynx
□ Outer ear
■ Middle ear
II Inner ear
External auditory canal
Eardrum
Auditory tube
Frontal section through the right side of the skull
showing the three principal regions of the ear
Where are the receptors for hearing and equilibrium located?
Extending across the middle ear and attached to it by
means of ligaments are three liny bones called auditory ossi-
cles (OS-si-kuls) that are named for their shapes: the malleus
(MAL-e-us), incus (ING-kus), and stapes (STA-pez), com-
monly called the hammer, anvil, and stirrup (Figure 12.12).
Equally tiny skeletal muscles control the amount of move-
ment of these bones to prevent damage by excessively loud
noises. The stapes fits into a small opening in the thin bony
partition between the middle and inner car called the oval
window, where the inner ear begins.
Inner Ear
The inner ear is divided into the outer bony labyrinth and
inner membranous labyrinth (Figure 12.13). The bony
labyrinth (LAB-i-rinth) is a series of cavities in the temporal
bone, including the cochlea, vestibule, and semicircular
canals. The cochlea is the sense organ for hearing, and the
vestibule and semicircular canals are the sense organs for
equilibrium and balance. The bony labyrinth contains a
called perilymph. This fluid surrounds the inner memhraim
labyrinth, a series of sacs and tubes with the same gene
shape as the bony labyrinth. The membranous labyrinth d
tains a fluid called emiolymph.
The vestibule (VES-ti-biil) is the oval-shaped mid
part of the bony labyrinth. The membranous labyrinth
vestibule consists of two sacs called the utricle (U-tri-kl z
tie bag) and saccule (SAK-ul = little sac). Behind
vestibule are the three bony semicircular canals. The an
rior and posterior semicircular canals are both vertical,
the lateral canal is horizontal One end of each canal enlar
into a swelling called die ampulla (am-POOL-la - little j
The portions of the membranous labyrinth that lie inside
bony semicricular canals are called the semicircular h
which connect with the utricle of the vestibule,
A transverse section through the cochlea (KQK-le-a
snail's shell), a bony spiral canal that resembles a snail's sh
Hearing and Equilibrium 303
Figure 12.13 Details of the right inner ear. (a) Relationship of the scala tympani, cochlear duct, and scala
vestibuli. The arrows indicate the transmission of sound waves, (b) Details of the spiral organ (organ of Corti).
\ The three channels in the cochlea are the scala vestibuli, scala tympani, and cochlear duct.
Membranous labyrinth
(contains endolymph)
Bony labyrinth
(contains perilymph)
LATERAL
□ Outer ear
9 Middle ear
I I Inner ear
Ampulla of semicircular canal
Utricle
Stapes in oval window
Semicircular canals
(contain membranous
semicircular ducts):
Anterior
Posterior
Latera
Cochlea
Ampulla of
semicircular duct
MEDIAL
Scala tympani
Spiral organ
(organ of Corti)
Cochlear duct
Scala vestibuli
Vestibular membrane
Cochlear duct
Basilar membrane
Round window
Scala
tympan
(a) Sections through the cochlea
Tectorial membrane
Hairs
/*
Hair cell —
Supporting cells
Cells lining
Basilar membrane scala tympani
(b) Enlargement of spiral organ (organ of Corti)
) What structures separate the outer ear from the middle ear? The middle ear from the inner
Hair cell
Sensory and motor neurons
in cochlear branch of
vestibulocochlear nerve
304 Chapter 12 Somatic Senses and Special Senses
shows that it is divided into three channels: cochlear duct,
scala vestibuli, and scala tympani. Hie cochlear duct is a con-
tinuation of the membranous labyrinth into the cochlea; it is
filled with endolymph. The channel above the cochlear duct
is the scala vestibuli, which ends at the oval window. The
channel below the cochlear duct is the scala tympani, which
ends at the round window (a membrane-covered opening
directly below the oval window). Both the scala vestibnli
and scala tympani are part of the bony labyrinth of the
cochlea and are filled with perilymph. The scala vestibnli
and scala tympani are completely separated, except for an
opening at the apex of the cochlea. Between the cochlear
duct and the scala vestibuli is the vestibular membrane. Be-
tween the cochlear duct and scala tympani is the basilar
membrane.
Resting on the basilar membrane is the spiral organ
(organ ofCorti), the organ of hearing (Figure 12,13b). The
spiral organ consists of supporting cells and hair cells, The
hair cells, the receptors for auditory sensations, have long
processes at their free ends that extend into the endolymph
of the cochlear duct. The hair cells form synapses with sen-
sory and motor neurons in the cochlear branch of the
vestibulocochlear (VIII) nerve. The tectorial membrane, a fl«
ible gelatinous membrane, covers the hair cells.
Physiology of Hearing
The events involved in stimulation of hair cells by :
waves are as follows (Figure 12.14):
^ The auricle directs sound waves into the externa
tory canal.
Q Sound waves striking the eardrum cause it to vihra
The distance and speed of its movement depend on
intensity and frequency of the sound waves. More inte
(louder) sounds produce larger vibrations. The card
vibrates slowly in response to low-frequency (1
pitched) sounds and rapidly in response to hi
frequency (high-pitched) sounds.
Q The central area of the eardrum connects to the mall*
which also starts to vibrate. The vibration is transmit
from the malleus to the incus and then to the stapes,
Q As the stapes moves back and forth, it pushes the c
window in and out.
Figure 12.14 Physiology of hearing shown in the right ear. The numbers correspond to the events listed in
the text. The cochlea has been uncoiled in order to more easily visualize the transmission of sound waves and their
subsequent distortion of the vestibular and basilar membranes of the cochlear duct.
^ Sound waves originate from vibrating objects.
Malleus Incus
Stapes vtbrating
in oval window
Helicotrema
Cochlea
Sound waves
Scala
tympani
Scala
vestibuli
Basilar
membrane
Spiral organ
(organ of Corti)
Tectorial membrane
Vestibular membrane
Eardrum
Cochlear duct
(contains endolymph)
Round window
membrane vibrating
f
Middle ear
Auditory tube
What is the function of hair cells?
ft The movement of the oval window sets up fluid pressure
ives in the perilymph of the cochlea. As the oval win-
dow bulges inward, it pushes on the perilymph of the
scala vestibulL
A The fluid pressure waves are transmitted from the scala
yestibuli to the scala tympani and eventually to the mem-
brane covering the round window, causing it to bulge
outward into the middle ear. (See ©in the figure.)
A As the pressure waves deform the walls of the scala
vestibuli and scala tympani, they also push the vestibular
membrane back and forth, creating pressure waves in the
endolymph inside the cochlear duct.
The pressure waves in the endolymph cause the basilar
membrane to vibrate, which moves the hair cells of the
spiral organ against the tectorial membrane. Bending of
their hairs stimulates the hair cells to release neurotrans-
mitter molecules at synapses with sensory neurons that
are part of the vestibulocochlear (VIII) nerve, (see Figure
12.13b). Then, the sensory neurons generate nerve im-
pulses that conduct along the vestibulocochlear (VIII)
nerve.
Sound waves of various frequencies cause certain regions
of the basilar membrane to vibrate more intensely than other
regions. Each segment of the basilar membrane is "tuned"
[fora particular pitch. Because the membrane is narrower and
stilfcr at the base of the cochlea (closer to the oval window),
high-frequency (high-pitched) sounds induce maximal vibra-
tjons in this region. Toward the apex of the cochlea, the basi-
lar membrane is wider and more flexible; low-frequency
few-pitched) sounds cause maximal vibration of the basilar
feembmne ihere. Loudness is determined by the intensity of
sound waves. High-intensity sound waves cause larger vibra-
:iis of the basilar membrane, which leads to a higher fre-
luency of nerve impulses reaching the brain. Louder sounds
nay stimulate a larger number of hair cells.
Besides its role in detecting sounds, the cochlea has die
surprising ability to produce sounds, which are called
otoacoustic emissions. These sounds arise from vibra-
tions of the hair cells themselves, caused in part by sig-
nals from motor neurons that synapse with the hair cells- A
itive microphone placed next to the eardrum can pick
up these very-low-volume sounds. Detection of otoa-
jc emissions is a fast, inexpensive, and noninvasive
to screen newborns for hearing defects. In deaf babies,
otoacoustic emissions are not produced or are greatly re-
duced in size.
Auditory Pathway
Lsorv neurons in the cochlear branch of each vestibulo-
Ichlear (VIII) nerve terminate in the medulla oblongata on
Hearing and Equilibrium 305
die same side of the brain. From the medulla, axons ascend
to the midbrain, then to die thalamus, and finally to the pri-
mary auditory area in the temporal lobe (see Figure 1013 on
page 259). Because many auditoiy axons cross to die opposite
side, the right and left primary auditory areas receive nerve
impulses from both ears.
Physiology of Equilibrium
You learned about the anatomy of the inner ear structures for
equilibrium in the previous section. In this section we will
cover the physiology of balance, or how you are able to stay
on your feet after tripping over your roommate's shoes.
There are two types of equilibrium (balance). One kind,
called static equilibrium, refers to the maintenance of the
position of the body (mainly the head) relative to the force of
gravity. The second kind, dynamic equilibrium, is the main-
tenance of body position (mainly the head) in response to
sudden movements such as rotation, acceleration, and decel-
eration. Collectively, the receptor organs for equilibrium,
which include the saccule, utricle, and membranous semicircu-
lar ducts, are called the vestibular apparatus (ves-TIB-u-lar).
Static Equilibrium
The walls of both the utricle and die saccule contain a small,
thickened region called a macula (MAK-u-la; macula = spot).
The two maculae (plural), which are perpendicular to one an-
other, are the receptors for static equilibrium. The maculae
provide sensory information on the position of die head in
space and help maintain appropriate posture and balance.
The maculae also contribute to some aspects of dynamic
equilibrium by detecting linear acceleration and deceleration,
such as the sensations you feel while in an elevator or a car
that is speeding up or slowing down.
The two maculae consist of two kinds of cells: hair
cells, which are the sensory receptors, and supporting cells
(Figure 12.15). The hairs of the hair cells protrude into a
thick, jellylike substance called the otolithic membrane. A layer
of dense calcium carbonate crystals, called otoliths (ofo- : = ear;
-liths = stones), extends over the entire surface of the
otolithic membrane. If you tilt your head forward, gravity
pulls the membrane (and die otoliths) so it slides over the
hair cells in the direction of the tilt. This stimulates the hair
cells and triggers nerve impulses diat conduct along the
vestibular branch of the vestibulocochlear (VIII) nerve (see
Figure 1.2.12).
Dynamic Equilibrium
The three membranous semicircular ducts lie at right angles
to one another in three planes (see Figure 12.13a). The posi-
tioning permits detection of rotational acceleration or decel-
eration. The dilated portion of each duct, the ampulla, con-
tains a small elevation called the crista (KRIS-ta = crest;
306 Chapter 12 Somatic Senses and Special Senses
Figure 12.15 Location and structure of receptors in the maculae of the right ear, Both sensory neu-
rons (blue) and motor neurons (red) synapse with the hair cells.
Movements of the otolithic membrane stimulate the hair ceils.
Otoliths
Otolithic
membrane
Hairs
Hair cell
Utricle
Supporting cell
Location of utricle and saccule
(contain maculae
Vestibular branches of vestibulocochlear (VIII) nerve
(a) Overall structure of a section of the macula
Head upright
v
Otolithic Otoliths Hair cell
membrane
■HE !
Force of
gravity
.,
Head tilted forward
(b) Position of macula with head upright (left) and tilted forward (right)
What is the function of the maculae?
plural is cristae) (Figure 12.16). Each crista contains a group
of hair cells and supporting cells. Covering the crista is a
mass of gelatinous material called the cupula (KU-pu-la).
When the head moves, the attached membranous semicircu-
lar ducts and hair cells move with it. However, die endolymph
within the membranous semicircular ducts is not attached and
lags behind due to its inertia. As the moving hair cells dray
along the stationary 7 endolymph, the hairs bend. Bending of
the hairs causes electrical signals in the hair cells. In turn,
diese signals trigger nerve impulses in sensory neurons that
are part of the vestibular branch of the vestibulocochlear
(VI II) nerve.
Equilibrium Pathways
Most of the vestibular branch axons of the vestibulocochfi
(VIII) nerve enter the brain stem and then extend to
medulla or the cerebellum, where they synapse with the nt
neurons in the equilibrium pathways. From the medulla
some axons conduct nerve impulses along the cranial nervj
that control eye movements and head and neck movements,
Other axons form a spinal cord tract that conveys imp
for regulation of muscle tone in response to head movi
ments. Various padiways among the medulla, cerebellar
and cerebrum enable the cerebellum to play a key role
maintaining equilibrium. The cerebellum continuously
Hearing and Equilibrium 307
figure 12,16 Location and structure of the membranous semicircular ducts of the right ear. Both
sensory neurons (blue) and motor neurons (red) synapse with the hair cells. The ampullary nerves are
Bches of the vestibular division of the vestibulocochlear (VIII) nerve.
The positions of the membranous semicircular ducts permit detection of rotational movements.
Semicircular duct
Ampulla
Location of ampullae
of semicircular ducts
(contain cristae)
Cupula
Supporting eel
(
h Crista
Ampullary nerve
(a) Details of a crista
Cupula sensing movement
and direction of flow of endolymph
Head rotating
■ With which type of equilibrium are the membranous semicircular ducts associated?
308 Chapter 12 Somatic Senses and Special Senses
ceives sensory information from the utricle and saccule. In
response, the cerebellum makes adjustments to the signals
going from the motor cortex to specific skeletal muscles to
maintain equilibrium.
Table 12 J summarizes the structures of the ear related to
hearing and equilibrium.
■ CHECKPOINT
13. What is the pathway for auditory impulses from the
cochlea to the cerebral cortex?
14. Compare the function of the maculae in maintaining stal
tic equilibrium with the role of the cristae in maintaining
dynamic equilibrium.
• • •
Now that our exploration of the nervous system and sel
sations is completed, you can appreciate the many ways
the nervous system contributes to homeostasis of other bod]
systems by examining Focus on Homeostasis: The Nervous
System on page 309. Next, in Chapter 13, we will sec !
the hormones released by the endocrine system also help
maintain homeostasis of many body processus.
Table 12.3 Summary of Structures of the Ear Related to Hearing and Equilibrium
Regions of the Ear and Key Structures
Outer Ear
External auditory
canal
Auricle
Middle Ear
Auditory
Auditory
tube
Inner Ear
Semicircular
ducts
Functions
(
Auricle: Collects sound waves.
External auditory canal: Directs sound waves to the eardrum.
Eardrum (tympanic membrane): Sound waves cause it to vibrate, which, in turn, causes the
malleus to vibrate.
Auditory ossicles: Transmit and amplify vibrations from tympanic membrane to oval window.
Auditory (eustachian) tube: Equalizes air pressure on both sides of the tympanic membrane.
Cochlea: Contains a series of fluids, channels, and membranes that transmit vibrations to the
spiral organ (organ of Corti), the organ of hearing; hair cells in the spiral organ trigger nerve im-
pulses in the cochlear branch of the vestibulocochlear (VIII) nerve.
Vestibular apparatus: Includes semicircular ducts, utricle, and saccule, which generate nerve
impulses that propagate along the vestibular branch of the vestibulocochlear (VIII) nerve,
Semicircular ducts: Contain cristae, sites of hair cells for dynamic equilibrium.
Utricle: Contains macula, site of hair cells for static and dynamic equilibrium.
Saccule: Contains macula, site of hair cells for static and dynamic equilibrium.
Cochlea
Saccule
ocus
IONIEQSTASIS
Body System
•or all body
^sterns
i\
Integumentary
jystem
The Nervous System
Contribution of the Nervous System
Together with hormones from the endocrine system, nerve impulses provide communication and
regulation of most body tissues.
Sympathetic nerves of the autonomic nervous system (ANS) control contraction of smooth mus-
cles attached to hair follicles and secretion of perspiration from sweat glands.
ikeletal system ^ Nociceptors {pain receptors) in bone tissue warn of bone trauma or damage.
Muscular system
Somatic motor neurons receive instructions from motor areas of the bra.n and stimulate con-
traction of skeletal muscles to bring about body movements.The basal ganglia and reticular ft
mation set the level of muscle tone.The cerebellum coordinates skilled movements.
I Endocrine
[system
Cardiovascular
system
lymphatic
system and
immunity
Inspiratory
/stem
Digestive system
Urinary system
*
The hypothalamus regulates secretion of hormones from the anterior and posterior pituitary. The
ANS regulates secretion of hormones from the adrenal medulla and pancreas.
The cardiovascular center in the medulla oblongata provides nerve impulses to the ANS that
govern heart rate and the forcefulness of the heartbeat. Nerve impulses from the ANS also regu-
late blood pressure and blood flow through blood vessels.
Certain neurotransmitters help regulate immune responses. Activity in the nervous system may
increase or decrease immune responses.
Respiratory areas in the brain stem control breathing rate and depth.The ANS helps regulate the
diameter of airways.
The ANS and enteric nervous system (ENS) help regulate digestion.The parasympathetic divi-
sion of the ANS stimulates many digestive processes.
The ANS helps regulate blood flow to kidneys, thereby influencing the rate of urine formation;
brain and spinal cord centers govern emptying of urinary bladder.
Reproductive
(systems
The hypothalamus and limbic system govern a variety of sexual behaviors; the ANS brings
about erection of the penis in males and the clitoris in females and ejaculation of semen in
males The hypothalamus regulates release of anterior pituitary hormones that control the go-
nads (ovaries and testes). Nerve impulses elicited by touch stimuli from suckling infant cause re-
lease of oxytocin and milk ejection in nursing mothers.
309
31 Chapter 12 Somatic Senses and Special Senses
COMMON
DISORDERS
Cataracts
A common cause of blindness is a loss of transparency of the lens
known as a cataract (CAT-a-rakt). The lens becomes cloudy (less
transparent) due to changes in the structure of die lens proteins.
Cataracts often occur with aging hut may also be caused by injury,
excessive exposure to ultraviolet rays, certain medications (such as
long-term use of steroids), or complications of other diseases (for
example, diabetes). People who smoke also have increased risk of de-
veloping cataracts. Fortunately, sight can usually be restored by surgi-
cal removal of the old lens and implantation of an artificial one.
Glaucoma
In glaucoma (glaw-KO-ma), the most common cause of- blindness
in the United States, a buildup of aqueous humor within the ante-
rior cavity causes an abnormally high intraocular pressure. Persis-
tent pressure results in a progression from mild visual impairment
to irreversible destruction of the retina, damage to the optic nerve,
and blindness. Because glaucoma is painless, and because the other
eve initially compensates to a large extent for the loss of vision, a
person may experience considerable retinal damage and loss of vi-
sion before the condition is diagnosed.
Deafness
Deafitess is significant or total hearing loss. Sensorineural duafhexs is
caused by either impairment of hair ceils in the cochlea or damage
MEDICAL TERMINOLOGY AND CONDITIONS
Age-related macular disease (AMD) Degeneration of the macula
lutea of the retina in persons 50 years of age and older.
Anosmia (an-OZ-me-a; a~ = without; -osmi = smell, odor) Total
lack of the sense of smell.
Cochlear impkmt A device that translates sounds into electrical signals
that can be interpreted by the brain. It is especially useful for peo-
ple with deafness caused by damage to hair cells in the cochlea.
Conjunctivitis (pinkeye) An inflammation of the conjunctiva; when
caused by bacteria such as pneumoeocci, staphylococci, or He-
mophilus mflumzae, it is very contagious and more common in
children. May also be caused by irritants, such as dust, smoke,
or pollutants in the air, in which case it is not contagious.
Detached retina Detachment of the neural portion of die retina
from the pigment epithelium due to trauma, disease, or age-re-
lated degeneration. The result is distorted vision and blindness.
; LAS1K Surgery with a laser to correct the curvature of the cornea
for conditions such as nearsightedness, farsightedness, and
astigmatism.
Nystagmus (nis-TAG-mus; nystagm- = nodding or drowsy) A rapid
involuntary movement of the eyeballs, possibly caused by a dis-
ease of the central nervous system. It is associated with condi-
tions that cause vertigo.
of the cochlear branch of the vestibulocochlear nerve. IT
deafness may be caused by atherosclerosis, which reuV.
supply to the ears; repeated exposure to loud noise, which d
hair cells "of the spiral organ; or certain drugs such as aspit|
streptomycin, Conduction deafness is caused by impairment
outer and middle car mechanisms for transmitting sounds
cochlea. It may be caused by otosclerosis, the deposition of]
bone around the oval window; impacted cerumen; injur) to
eardrum; or aging, which often results in thickening of the^j
and stiffening of the joints of the auditory ossicles,
Meniere's Disease
Meniere's disease (mcn'-e-ARZ) results from an increased a
of endolymph that enlarges the membranous labyrinth. Among!
symptoms are fluctuating hearing loss (caused by distortion
basilar membrane of the cochlea) and roaring tinnitus
Vertigo (a sensation of spinning or whirling) is character]
Meniere's disease. Almost total destruction of hearing may
over a period of years.
Otitis Media
Otitis media is an acute infection of the middle ear caused prim/nk l
bacteria and associated with infections of die nose and throat Syi
tpms include pain; malaise (discomfort or uneasiness); lever; anil I
dening and outward bulging of the eardrum, which may rupture
prompt treatment is received (this may involve draining pus from
middle ear). Bacteria from the nasopharynx passing into the adit
tube is the primary cause of all middle ear infections. Children are
susceptible than adults to middle ear infections because their ,m,
tubes are almost horizontal, which decreases drainage.
Otalgia (6-TAL-je-a; at- = ear; -a/gia = pain) Earache,
Retinoblastoma (ret-i-no-blas-T( )-ma; -oma = tumor) A
arising from immature retinal cells; it accounts lor 2% ol |
hood cancers.
Scotoma (sko-TO-ma = darkness) An area of reduced or li
in die visual field.
Strabismus (stra-BIZ-mus) An imbalance in the extrinsic eye:
cles that causes a misalignment ol one eye so that its lin
sion is not parallel with that of the other eye (cross-eyes)
both eyes are not pointed at the same object at die same m
the condition produces a squint.
Tinnitus (ti-NT-tus) A ringing, roaring, or clicking in the ears,
Trachoma (tra-KO-ma) A serious form of conjunctivitis and
greatest single cause of blindness in the world. It is caused
the bacterium Chlamydia trachomatis. The disease pi
excessive growth of subconjunctival tissue and invasion
blood vessels into the cornea, which progresses until the ent
cornea is opaque, causing blindness.
Vertigo (VER-ti-go = dizziness) A sensation of spinning or mc
ment in which the world seems to revolve or the person
to revolve in space.
.-->•-.,.
Study Outline 311
?v
STUDY OUTLINE
Overview of Sensations (p. 285)
I. Sensation is the conscious or subconscious awareness of exter-
nal and interna] stimuli.
[v,o general classes of senses arc (1) general senses, which include
somatic senses and visceral senses, and (2) special senses, which
include smell, taste, vision, hearing, and equilibrium (balance).
The conditions for a sensation to occur are reception of a stim-
ulus by a sensory receptor, conversion of the stimulus into one
or inure nerve impulses, conduction of the impulses to the
brain, and integration of the impulses by a region of the brain.
Sensory impulses from each part of the hotly arrive in specific
regions of the cerebral cortex.
Adaptation is a decrease in sensation during a prolonged stimu-
lus. Some receptors are rapidly adapting; others are slowly
adapting.
Receptors can be classified structurally by their microscopic fea-
tures as free nerve endings, encapsulated nerve endings, or sepa-
rate cells. Functionally, receptors arc classified by the type of
stimulus they detect as mechanoreceptors, thermoreceptors, no-
ciceptors, photoreceptors, osmoreceptors, and chemoreceptors.
[somatic Senses (p. 286)
1. Somatic sensations include tactile sensations (touch, pressure,
,il niion, itch, and tickle), thermal sensations (heat and cold),
in sensations, and proprioceptive sensations (joint and
muscle position sense and movements of the limbs). Receptors
for these sensations are located in the skin, mucous mem-
lies, muscles, tendons, and joints.
Ixceptors for touch include corpuscles of touch (Meissner
corpuscks), hair root plexuses, type I cutaneous mechanore-
ceptors (Merkel discs), and type II cutaneous mechanorecep-
tors (Ruffini corpuscles). Receptors for pressure and vibration
are lamellatcd (pacinian) corpuscles. Tickle and itch sensations
result from stimulation of free nerve endings.
Thermoreceptors, free nerve endings in the epidermis and der-
mis, adapt to continuous stimulation.
Nociceptors are free nerve endings that are located in nearly
every body tissue; they provide pain sensations.
Proprioceptors inform us of the degree to which muscles are
contracted, the amount of tension present in tendons, the posi-
iis of joints, and the orientation of the head.
[Olfaction: Sense of Smell (p. 290)
olfactory epithelium in the upper portion of the nasal eav-
-ntains olfactory receptors, supporting cells, and basal
n cells.
Individual olfactory receptors respond to hundreds of different
brant molecules by producing an electrical signal that trig-
gers one or more nerve impulses. Adaptation (decreasing sensi-
n liv) to odors occurs rapidly
of olfactory receptors form die olfactory nerves, which
•mm jv nerve impulses to the olfactory bulbs. From there,
en
impulses conduct via the olfactory tracts to the limbic system,
hypothalamus, and cerebral cortex (temporal lobe).
Gustation: Sense of Taste (p. 291)
1. The receptors for gustation, the gustatory receptor cells, are
located in taste buds.
2. To be tasted, substances must be dissolved in saliva.
3. The five primary tastes are salty, sweet, sour, bitter, and umamL
4. Gustatory receptor cells trigger impulses in cranial nerves VII
(facial), IX (glossopharyngeal), and X (vagus). Impulses for taste
conduct to the medulla oblongata, limbic system, hypothala-
mus, thalamus, and the primary gustatory area in the parietal
lobe of the cerebral cortex.
Vision (p. 293)
L Accessory structures of the eyes include the eyebrows, eyelids,
eyelashes, the lacrimal apparatus (which produces and drains
tears), and extrinsic eye muscles (which move the eyes).
2. The eyeball has three layers: (a) fibrous tunic (sclera and
cornea), (b) vascular tunic (choroid, ciliary body, and iris), and
(c) retina.
3. The retina consists of a neural layer (photo receptor layer, bipo-
lar cell layer, and ganglion cell layer) and a pigmented layer (a
sheet of melanin -containing epithelial cells).
4. The anterior cavity contains aqueous humor; the vitreous
chamber contains the vitreous body.
5. Image formation on the retina involves refraction of light rays
by the cornea and lens, which focus an inverted image on the
central fovea of the retina.
6. For viewing close objects, the lens increases its curvature (ac-
commodation), and the pupil constricts to prevent light rays
from entering the eye through the periphery oi the lens.
7. Improper refraction may result from myopia (nearsightedness),
hypermetropic (farsightedness), or astigmatism (irregular cur-
vature of the cornea or lens).
8* Movement of the eyeballs toward the nose to view an object is
called convergence.
9. The first step in vision is the absorption of light rays by pho-
topigments in rods and cones (photoreceptors). Stimulation of
the rods and cones then activates bipolar cells, which in turn
activate the ganglion cells.
10. Nerve impulses arise in ganglion cells and conduct along the
optic nerve, through the optic chiasm and optic tract to the
thalamus. From the thalamus, die optic radiations extend to the
primary visual area in the occipital lobe of the cerebral cortex.
Hearing and Equilibrium (p. 301)
1. The outer ear consists of the auricle, external auditory canal,
and eardrum.
2. The middle ear consists of the auditory (eustachian) tube, audi-
tory ossicles, oval window; and round window,
Chapter 12 Somatic Senses and Special Senses
3. The inner ear consists of the bony labyrinth and membranous
labyrinth. The inner ear contains the spiral organ (organ of
Cord), the organ of hearing.
4. Sound waves enter the external auditory canal, strike the
eardrum, pass through the ossicles, strike die oval window, set
up pressure waves in the perilymph, strike the vestibular mem-
brane and sea I a tynipani, increase pressure in the endolymph,
vibrate the basilar membrane, and stimulate hair cells in the
spiral organ,
5. Hair cells release neurotransmitter molecules that can initiate
nerve impulses in sensory neurons.
6* Sensory neurons in the cochlear branch of the vestibulo-
cochlear nerve terminate in the medulla oblongata. Auditory
signals then pass to the midbrain, thalamus, and tempor
lobes.
7. Static equilibrium is the orientation of the body relative to
pull of gravity. The maculae of the utricle and saccule are
sense organs of static equilibrium*
8. Dynamic equilibrium is the maintenance of body position
response to rotation, acceleration, and deceleration,
maculae of the utricle and saccule and the cristae in the n
branous semicircular ducts are the sense organs of dynai
equilibrium,
9. Most vestibular branch axons of the vestibulocochlear
enter the brain stem and terminate in the medulla and
other axons extend to the cerebellum.
12
SELF-QUIZ
1. You enter a sauna and it feels awfully hot, but soon the
temperature feels comfortably warm. What have you have
experienced?
a. damage to your thermoreceptors
b. sensory adaptation
c. a change in the temperature of the sauna
d. in activation of your thermoreceptors
e. damage to the parietal lobe
2. The lacrimal glands produce _ , which drain(s) into the
a. tears; anterior cavity
b. tears; nasal cavity
c. aqueous humor; anterior chamber
d. aqueous humor; anterior cavity
e. aqueous humor; sclera! venous sinus
3. The spiral organ (organ of Corti)
a. contains hair cells
b. is responsible for equilibrium
c« is filled with perilymph
d. is another name for the auditory (eustachian) tube
e, transmits auditory nerve impulses to the brain
4. Equilibrium and the activities of muscles and joints are moni-
tored by
a, olfactory receptors b. nociceptors
c. tactile receptors d. proprioceptors
e. thermoreceptors
5. In the retina, cone photoreceptors
a. are more numerous than rods
b. contain the photopigment rhodopsin
c. are more sensitive to low light level than are rods
d. reform their photopigments more slowly than do rods
e. provide higher acuity vision than do rods
6. Which of the following is NOT required for a sensation
occur?
a. the presence of a stimulus
b. a receptor specialized to detect a stimulus
c. the presence of slowly adapting receptors
d. a sensory neuron to conduct impulses
e« a region of the brain for integration of the nerve impulse
7. Match each receptor with its function.
_a, color vision A, tamellated (pacinian) corpusde
_b. taste B. type I cutaneous mec Hanoi
_c. smell C. rod photoreceptor
— d. dynamic D. nociceptor
equilibrium E> gustatory receptor cel |
E olfactory receptor
G. muscle spindle
f- stretch in TT .
,i H. maculae
a muscle
1. cristae
g. static
equilibrium J' cone photoreceptors
h, pressure
i. touch
— j . detection of pa i n
8* For taste to occur
a. the mouth must be dry
b. die chemical must be in contact with the basal cells
c. filiform papillae must be stimulated
d. the limbic system needs to be activated
c. the gustatory hair must be stimulated by the dissolved
chemical
9* Which of the following characteristics of taste is NOT true?
a. Olfaction can affect taste.
b. Three crania] nerves conduct the impulses for taste to dig
brain.
e« vision in
dim light
n
c. Taste adaptation occurs quickly.
d. Humans can recognize about 10 primary tastes.
e. Taste receptors arc located in taste buds on the tongue, on
the roof of the mouth, in the throat, and in the epiglottis.
10. You are seated at your desk and drop your pencil As you lea
over to retrieve it, what is occurring in your inner ear?
a. The hair cells on the macula are responding to changes in
static equilibrium.
b. The hair cells in the cochlea arc responding to changes in
dynamic equilibrium,
c. The cristae of each semicircular duct arc responding to
changes in dynamic equilibrium.
d. The cochlear branch of the vestibulocochlear (VIII) nerve
begins to transmit nerve impulses to the brain.
e. The auditory (eustachian) tube makes adjustments for vary-
ing air pressures,
11, Kinesthesia is the
a. perception of body movements
b. ability to identify an object by feeling it
c. sensation of weightlessness that occurs in outer space
d. decrease in sensitivity of receptors to a prolonged stimulus
e. movement of body parts in a rhythmic manner
12, Which of the following is NOT true about nociceptors?
a. They respond to stimuli that may cause tissue damage,
b. Thev consist of free nerve endings.
c. They can be activated by excessive stimuli from other sensa-
tions,
d. They arc found in virtually every body tissue except the
brain.
e. They adapt very rapidly.
[J. Which of the following is NOT a function of tears?
a, moisten the eye b. wash away eye irritants
c destroy certain bacteria d- lubricate the eye
i>, provide nutrients to the cornea
14, Transmission of vibrations (sound waves) from the tympanic
membrane to the oval window is accomplished by
a. neurons b. the tectorial membrane
c. the auditory ossicles d. the endolymph
e. the auditory (Eustachian) tube
itch the following:
_ a. focuses light rays onto
the retina
_b, regulates the amount of
light entering the eye
_c. contains aqueous humor
_d. contains blood vessels that
help nourish the retina
__e. produce tears
_f dense connective tissue diat
provides shape to die eye
_g, contains photoreceptors
A. sclera
B. choroid
C. lacrimal glands
D. lens
E. retina
F. iris
G. anterior cavity
Self-Quiz 313
16. Which of the following structures refracts light rays entering
die eye?
a. cornea b. sclera c, pupil d. retina
e. conjunctiva
17. Your 45-year-old neighbor has recently begun to have difficulty
reading die morning newspaper. You explain that diis condition
is known as and is due to .
a. myopia, inability of his eyes to properly focus light on his
retinas
b. night blindness, a vitamin A deficiency
c. binocular vision, the eyes focusing on two different objects
d. astigmatism, an irregularity in the curvature of the lens
e. presbyopia, the loss of elasticity in the lens
18. Damage to cells in die central fovea would interfere with
a. dynamic equilibrium b. accommodation
c. visual acuity d. ability to sec in dim light
e . in tra ocu I a r pressu re
19. Place the following events concerning the visual pathway in the
correct order:
1. Nerve impulses exit the eye via the optic nerve,
2. Optic tract axons terminate in the thalamus,
3. Light reaches the retina.
4. Rods and cones are stimulated,
5. Synapses occur in the thalamus and continue to die primary
visual area in the occipital lobe.
6. Ganglion cells generate nerve impulses.
a, 4, 1, 2, 5, 6, 3 b. 5, 4, 1, 3, 2, 6 c. 3, 4, 6, I, 5, 2
d. 3,4,6,1,2,5 e. 3,4,5,6, 1,2
20. Place the following events of the auditory pathway in the cor-
rect order:
1. I lair cells in the spiral organ bend as they rub against the
tectorial membrane.
2. Movement in die oval window begins movement in the per-
ilymph,
3. Nerve impulses exit the ear via the vestibulocochlear (VTTT)
nerve.
4. The eardrum and auditory ossicles transmit vibrations from
sound waves.
5. Pressure waves from the perilymph cause bulging of die
round window and formation of pressure waves in the en-
dolymph.
a. 4,2,5, 1,3 b, 4,5,2,3, 1 c. 5,3,2,4,1
d. 3,4,5, 1,2 e. 2,4,1,5,3
31 4 Chapter 12 Somatic Senses and Special Senses
CRITICAL THINKING APPLICATIONS
When vcm first enter a coffee shop, the aroma of fresh Java is
wonderfully strong and full-bodied. After several minutes wait-
ing in line, the odor is barely noticeable. Has something hap-
pened to the coffee or has something happened to yon?
Cliff works the night shift and sometimes falls asleep in A&P
class, What is the effect on the structures in his internal ear
when his head falls backward as he slumps in his scat?
3. A medical procedure used to improve visual acuity invoh
shaving of a thin layer off the cornea, I low could this pre
dure improve vision?
4* The optometrist put drops in Latasha s eyes during her eye 1
When Latasha looked in the mirror after the exam, her puf
were very large and her eyes were sensitive to the bright 1
I low did die eye drops produce this effect on Latasha s eyes?
v
ANSWERS TO FIGURE QUESTIONS
n
12.1 Corpuscles of touch (Meissner corpuscles) are abundant i
the fingertips, palms, and soles.
12.2 The kidneys have the broadest area for referred pain.
123 Basal stem cells undergo cell division to produce new olfac-
tory receptors,
12.4 The gustatory pathway: gustatory receptor cells — » cranial
nerves Vll, IX, and X — > medulla oblongata — > thalamus — *
primary gustatory area in the parietal lobe ol the cerebral
cortex.
12.5 Tears clean, lubricate, and moisten the eyeball.
12.6 The fibrous ainic consists of the cornea and sclera; the vas-
cular tunic consists of the choroid, ciliary body, and iris.
12.7 The parasympathetic division of the autonomic nervous sys-
tem causes pupillary constriction; die sympathetic division
causes pupillary dilation.
12.8 The two types of photoreceptors are rods and cones. Rods
provide black-and-white vision in dim light; cones provide
high visual acuity and color vision in bright light.
12.9 During accommodation, the ciliary muscle contracts, zonu-
lar fibers slacken, and the lens becomes more rounded (con-
vex) and refracts light more.
r
12.10 Presbyopia is the loss of elasticity in the lens that occur?;
aging. j
12.11 Structures carrying visual impulses from the retina: m
ganglion cells — * optic (II) nerve — * optic chiasm Hs
tract — * thalamus — » primary visual area in occipital lol
the cerebral cortex.
12.12 The receptors for hearing and equilibrium are located in
inner ear: cochlea (bearing) and semicircular ducts (eqi
Hum),
12*13 The eardrum (tympanic membrane) separates the outer i
from the middle ear. The oval and round windows seg
the middle car from the inner ear.
12.14 Hair cells convert a mechanical force (stimulus) into ;m
trical signal (depolarization and repolarization of the
cell membrane).
12.15 The maculae are the receptors for static equilibrium and
contribute to dynamic equilibrium.
12.16 The membranous semicircular ducts function in dyn
equilibrium.
THE ENDOCRINE SYSTEM
chapter 13
HA you know?
J. he high blood sugar levels seen
in Type 2 diabetes occur because the body's ability to
respond to the important hormone insulin is im-
paired. Researchers do not know exactly why cells be-
come sluggish in their response to insulin, but they do
know that obesity and a sedentary lifestyle increase a
person's risk for developing this disorder. The number
of young people diagnosed with Type 2 diabetes has in-
creased almost tenfold since the 1980s, probably be-
cause of increasing rates of childhood obesity. Before
that time, Type 2 diabetes was so rarely seen in
children and adolescents that it was called
"adult-onset diabetes. "
>,
Focus on Wellness, page 332
wvtfw.wiley.com/college/apcentral
jTxs they mature, boys
and girls develop
striking differences in
physical appearance and
behavior. In girls, estrogens
(female sex hormones) promote accumulation of adi-
pose tissue in the breasts and hips, sculpting a feminine
shape. In boys, testosterone (a male sex hormone)
enlarges the vocal cords, producing a lower-pitched
voice, and begins to help build muscle mass. These
changes are examples of the powerful influence of
hormones (hormon = excite or get moving), secretions
of the endocrine system. Less dramatically, but just as
importantly, hormones help maintain homeostasis on a
daily basis. They regulate the activity of smooth muscle,
cardiac muscle, and some glands; alter metabolism; spur
growth and development; influence reproductive
processes; and participate in circadian (daily) rhythms
established by the hypothalamus.
looking back to move ahead
• Steroids (page 35)
• The Plasma Membrane (page 46)
• Neurons (page 228)
• Negative and Positive Feedback Systems (page 8)
315
31 6 Chapter 13 The Endocrine System
INTRODUCTION
OBJECTIVE •
system.
List the components of the endocrine
The endocrine system consists of several endocrine glands
plus many hormone-secreting cells in organs that have func-
tions besides secreting hormones. In contrast to the nervous
system, which controls body activities through the release of
neurotransmitters at synapses, the endocrine system releases
hormones into interstitial fluid and then into the blood-
stream, The circulating blood then delivers hormones to vir-
tually all cells throughout die body and cells that recognize a
particular hormone will respond. The nervous system and
endocrine system often work together. For example, certain
parts of the nervous system stimulate or inhibit the release oi
hormones by the endocrine system. Typically, the endocrine
system acts more slowly than the nervous system, which of-
ten produces an effect within a fraction of a second. More-
over, the effects of hormones linger until they are cleard
from the blood. The liver inactivates some hormones, anc
the kidneys excrete others in the urine.
As you learned in Chapter 4, two types of glands j
present in the body: exocrine glands and endocrine glands.}
Exocrine glands secrete their products into ducts that earn the
secretions into a body cavity, into the lumen of an organ, or
onto the outer surface of the body. Sweat glands are one ex-
ample of exocrine glands. The cells of endocrine glands, b]
contrast, secrete their products (hormones) into intent
fluid, the fluid that surrounds tissue cells. Then, die hor-
mones diffuse into blood capillaries, and blood carries t
throughout the body
The endocrine glands include the pituitary, thyrok
parathyroid, adrenal, and pineal glands (Kigure I 3. 1). In ad-j
ditiom several organs and tissues are not exclusively classifiei
as endocrine Hands but contain cells that secrete hormonal
These include the hypothalamus, thymus, pancreas, ova
testes, kidneys, stomach, liver, small intestine, skin, he
"'
Figure 13.1 Location of endocrine glands and other organs that contain endocrine cells. Some nearby structures are
shown for orientation (trachea, lungs, scrotum, and uterus).
Endocrine glands secrete hormones, which circulating blood delivers to target tissues.
V En
HYPOTHALAMUS
PINEAL GLAND
*
PITUITARY
GLAND
PARATHYROID
GLANDS
(behind thyroid
glands)
THYROID GLAND
Trachea
THYMUS
STOMACH
ADRENAL
GLANDS
PANCREAS
SMALL
INTESTINE
OVARY
Scrotum
TESTES
What is the basic difference between endocrine glands and exocrine glands?
Functions of Hormones
1 . Help regulate:
• Chemical composition and volume
of interstitial fluid
• Metabolism and energy balance
• Contraction of smooth and cardiac
muscle fibers
• Glandular secretions
• Some immune system activities
2. Control growth and development.
3. Regulate operation of reproductive
systems.
4. Help establish circadian rhythms.
e tissue, and placenta. Endocrinology (en'-do-kri-
KOL-6-je; endo- = within; -crino — to secrete; -logy ' '■ study
Wis the scientific and medical specialty concerned with hor-
monal secretions and the diagnosis and treatment of disor-
if the endocrine system.
CHECKPOINT
L Why are organs such as the kidneys, stomach, heart, and
skin considered part of the endocrine system?
HORMONE ACTION
OBJECTIVES • Define target cells and describe the
|ole of hormone receptors.
■Describe the two general mechanisms of action of
hormones.
farget Cells and Hormone Receptors
Although ;i given hormone travels throughout die body in
lie blood, it affects only specific target cells. Hormones, like
protransmitters, influence their target cells by chemically
hiding to specific protein receptors. Only the target cells for
i) hormone have receptors that bind and recognize that
me, For example, thyroid-stimulating hormone (TSH)
Us to receptors on cells of the thyroid gland, but it does
in: hind to cells of the ovaries because ovarian cells do not
TSH receptors. Generally, a target cell has 2000 to
receptors for a particular hormone.
be drug RU486 (mifepristone) can be used to induce
i abortion, ft binds to the receptors for progesterone (a
nil: sex hormone) and prevents progesterone from
i iiii! its normal effects. When RU486 is given to a
nit woman, the conditions needed for embryonic
irelopment are lost, and the embryo is sloughed off
iiiu with the lining of the uterus. This example illus-
an important principle: If a hormone is prevented
:m interacting with its receptors, the hormone cannot
m its normal functions.
biemistry of Hormones
^Bb/Iy, some hormones are soluble in lipids (fats) ami
arc soluble in water. The lipid-soluble hormones ta-
ils steroid hormones, thyroid hormones, and nitric oxide.
moid hormones are made from cholesterol. The two thy-
M hormones (T 3 and T 4 ) are made by attaching iodine
to the amino acid tyrosine. The gas nitric oxide (NO)
,>ns as both a hormone and a neurotransmitter,
■lost of the water-soluble hormones are made trom
Lino acids. For instance, the amino acid tyrosine is modi-
Hormone Action 317
fied to form the hormones epinephrine and norepinephrine
(which are also neurotransmitters). Other water-soluble hor-
mones consist of short chains of amino acids (peptide hor-
mones), such as antidiuretic hormone (ADl I) and oxytocin,
or longer chains of amino acids (protein hormones), tor in-
stance, insulin and human growth hormone.
Mechanisms of Hormone Action
The response to a hormone depends on both the hormone
and the target cell. Various target cells respond differently to
die same hormone. Insulin, for example, stimulates the synthesis
of glycogen in liver cells but die synthesis of triglycerides in adi-
pose cells. To exert an effect, a hormone first must "announce
its arrival" to a target cell by binding to its receptors. The re-
ceptors for lipid-soluble hormones are located inside target
cells, and the receptors for water-soluble hormones are part
of the plasma membrane of target cells.
Action of Lipid- Soluble Hormones
Lipid-soluble hormones diffuse through the lipid bilayer of
the plasma membrane and bind to their receptors within
target cells, They exert their effects in the following way
(Figure I3.2):
Figure 13.2 Mechanism of action of lipid-soluble hormones.
Lipid-soluble hormones bind to their receptors inside target
^*
cells.
Free hormone
Blood capillary
Transport
protein
Activated
receptor-hormone
complex alters —
gene expression
O i| O Lipid-soluble
Q — hormone
it
diffuses into cell
O
Cytosol -
Newly formed
mRNA directs
synthesis of
specific proteins
on ribosomes
ffico
< 1
3£ Ribosome
Nucleus
Receptor
DNA
mRNA
^*^^ New
protein
Q New proteins alter
cell's activity
Target cell
What types of molecules are synthesized after lipid-soluble
hormones bind to their receptors?
31 8 Chapter 13 The Endocrine System
A lipid-soluble hormone detaches from its transport pro-
tein in the bloodstream . Then, the free hormone diffuses
from blood into interstitial fluid, and through the plasma
membrane into a cell.
The hormone binds to and activates receptors within the
cell The activated receptor- hormone complex then al-
ters gene expression: It aims specific genes on or off.
As the DNA is transcribed, new messenger RNA
(mRNA) forms, leaves the nucleus, and enters the cy-
-tosol. There it directs synthesis of a new protein, often
an enzyme, on the ribosomes.
The new proteins alter the cell's activity and cause the re-
sponses typical of that specific hormone.
Action of Water-soluble Hormones
Because most amino acid-based hormones are not lipid-soluble,
they cannot diffuse through the lipid bilayer of die plasma
membrane. Instead, water-soluble hormones bind to receptors
that protrude from the target cell surface. When a water-soluble
hormone binds to its receptor at the outer surface of the plasma
membrane, it acts as the first messenger. The first messenger
(the hormone) then causes production of a second messefiger
inside the cell, where specific hormone-stimulated responses
take place. One common second messenger is cyclic AMP
(cAMP), which is synthesized from ATE
Water-soluble hormones exert their effects as follows
(Figure 13.3):
A water-soluble hormone (the first messenger) diffuses
from die blood and binds to its receptor in a target cell's
plasma membrane.
As a result of die binding, a reaction starts inside the cell
that converts ATP into cyclic AMP.
Cyclic AMP (die second messenger) causes the activation
of several proteins (such as enzymes),
Activated proteins cause reactions that produce physio-
logical responses.
After a brief time, cyclic AMP is inactivated. Thus, the
cell's response is turned off unless new hormone mole-
cules continue to bind to their receptors in the plasma
membrane.
Control of Hormone Secretions
The release of most hormones occurs in short bursts, with
little or no secretion between bursts. When stimulated, an
endocrine gland releases its hormone in more frequent
bursts, increasing the concentration of the hormone in the
blood. In the absence of stimulation, the blood level of the
hormone decreases as the hormone is inactivated or excreted.
Regulation of secretion normally prevents overproduction or
underproduction of any given hormone.
Figure 13.3 Mechanism of action of water-soluble hormones,
Water-soluble hormones bind to receptors embedded in the
plasma membrane of target cells.
Blood capillary
Water-soluble
hormone
Receptor
Binding of hormone (first
messenger) to its receptor
Second messenger
oamp y © ATP i s converted
to CAMP
Proteins
QcAMP is inactivated
J cAMP serves as a Activated
second messenger proteins
to activate certain
proteins
Q Activated proteins cause reactions
that produce physiological responses
Target cell
/ Why is cAMP called a "second messenger"?
Hormone secretion is regulated by (1) signals from
nervous system, (2) chemical changes in the blood, aj
other hormones. For example, nerve impulses to the adn
medullae regulate the release of epinephrine and norq
nephrine; blood Ca 2+ level regulates the secretion of para?
roid hormone; and a hormone from the anterior pitim
(ACTH) stimulates the release of Cortisol by the adrenal
tex. Most systems that regulate secretion of hormones wi
by negative feedback, but a few operate by positive fen I'
For example, during childbirth, the hormone oxytocin stii
lates contractions of the uterus, and uterine contractions,!
turn, stimulate more oxytocin release, a positive feedl
effect.
■ CHECKPOINT
2, Chemically, what types of molecules are hormones!
3. What are the general ways in which blood hoi
levels are regulated?
Hypothalamus and Pituitary Gland 31 9
\ '%
HYPOTHALAMUS AND
PITUITARY GLAND
OBJECTIVES • Describe the locations of and relation-
ship between the hypothalamus and the pituitary gland,
i Describe the functions of each hormone secreted by
the pituitary gland.
For many years, the pituitary gland (pi-TOO-i-tar-e) or
physis (hl-POF-i-sis) was considered the "master" endocrine
I And because it secretes several hormones diat control odier
endocrine glands. We now know that the pituitary gland itself
has a master — the hypothalamus. This small region of the brain
is the major link between the nervous and endocrine systems.
Cells in the hypothalamus synthesize at least nine hormones,
and die pituitary gland secretes seven. Together, these hormones
play important roles in die regulation of virtually all aspects of
growth, development, metabolism, and homeostasis.
The pituitary gland is about die size of a small grape and
has two lobes: a larger anterior pituitary or mrterior lobe and a
smaller posterior pituitmy or posterior lobe (Figure 1 3.4). Both
lobes of the pituitary gland rest in the hypophyseal jvm 9 a cup-
shaped depression in the sphenoid bone. A stalklike structure,
Figure 13.4 The pituitary gland and its blood supply. As shown in the inset, to the right, releasing and inhibiting hormones synthesized by hy-
pothalamic neurosecretory cells diffuse into capillaries of the hypothalamus and are carried by the hypophyseal portal veins to the anterior pituitary
Hypothalamic releasing and inhibiting hormones are an important link between the nervous and endocrine systems.
Hypothalamus
Pituitary gland
Hypothalamic
neurosecretory
ce
HYPOTHALAMUS
Capillaries of hypothalamus
tnfundibulum
V(; IK-
POSTERIOR PITUITARY
Capillaries of posterior
pituitary
Hypophysea
fossa
POSTERIOR
ANTERIOR
Capillaries of
hypothalamus
V s
Hypophyseal
portal veins
r
Capillaries of
anterior pituitary
Artery
Hypophyseal portal
veins
Sphenoid bone
ANTERIOR PITUITARY
Capillaries of anterior
pituitary
Veins
APtery
Which
lobe of the pituitary gland does not synthesize the hormones it releases? Where are its hormones produced?
320 Chapter 13 The Endocrine System
the infimdilmlum, attaches the pituitary gland to die hypothala-
mus. Within the infundibulum, blood vessels termed hypophyseal
portal veins (hi' -pd-FIZ-e-al) connect capillaries in the hypothal-
amus to capillaries in the anterior pituitary. Axons of hypothala-
mic neurons called neurosecretory cells end near the capillaries
of the hypothalamus (inset on right in Figure l 3.4), where they
release several hormones into the blood.
Anterior Pituitary Hormones
The interior pituitary synthesizes and secretes hormones that
regulate a wide range of bodily activities, from growth to
reproduction. Secretion of anterior pituitary hormones is
stimulated by releasing hormones and suppressed by inhibiting
hormones, both produced by neurosecretory cells of the
hypothalamus. The hypophyseal portal veins deliver the
hypothalamic releasing and inhibiting hormones from the hy-
pothalamus to the anterior pituitary (Figure 13.4). This direct
route allows the releasing and inhibiting hormones to act
quickly on cells of the anterior pituitary before the hormones
are diluted or destroyed in the general circulation. Those an-
terior pituitary hormones that act on other endocrine glands
are called tropic hormones (TRO-pik) or tropins.
Human Growth Hormone and Insulinlike
Growth Factors
Human growth hormone (hGH) is the most abundant ante-
rior pituitary hormone. The main function of hGII is to pro-
mote synthesis and secretion of small protein hormones
called insulinlike growth factors (IGFs) or somatomedins.
IGFs are so named because some of their actions are similar
to those of insulin. In response to hGH, cells in die liver,
skeletal muscles, cartilage, bones, and other tissues secrete
IGFs, which may either enter the bloodstream or act locally.
IGFs stimulate protein synthesis, help maintain muscle and
hone mass, and promote healing of injuries and tissue repair.
They also enhance breakdown of triglycerides (fats), which
releases fatty acids into the blood, and breakdown of liver
glycogen, which releases glucose into the blood. Cells
throughout the body can use the released fatty acids and glu-
cose for the production of ATE.
The anterior pituitary releases hGH in bursts that occur
every few hours, especially during sleep. Two hypothalamic
hormones control secretion of hGH: Growth hormone-releas-
ing hormone (GHRH) promotes secretion of human growth
hormone, and growth hormone-inhibiting hormone (GHIH)
suppresses it. Blood glucose level is a major regulator of
GHRH and GHIH secretion. Low blood glucose level (hy-
poglycemia) stimulates the hypothalamus to secrete GHRH.
By means of negative feedback, an increase in blood glucose
concentration above die normal level (hyperglycemia) in-
hibits release of GHRH. By contrast, hyperglycemia stimu-
lates the hypothalamus to secrete GHIH and hypoglycemia
inhibits release of GHIH.
Thyroid-Stimulating Hormone
Thyroid-stimulating hormone (TSH) stimulates the synt
sis and secretion of thyroid hormones by the thyroid gfc
Thyrotropm-rekming hormone (TRH) from die hypothalai
controls TSH secretion. Release of TRH, in turn, d<
on blood levels of thyroid hormones, which inhibit sacred
of TRH via negative feedback. There is no thyrotroa
inhibiting hormone.
Follicle-Stimulating Hormone
and Luteinizing Hormone
In females, the ovaries are the targets for follicle -stimuli
hormone (FSH) and luteinizing hormone (LH). Each
FSH initiates the development of several ovarian follicles ai
LH triggers ovulation (described in Chapter 23). After ovi
tion, LH stimulates formation of the corpus luteum in
ovary and the secretion of progesterone (another female
hormone) by the corpus luteum. FSH and LH also stimul
follicular cells to secrete estrogens. In males, FSFI stimulaj
sperm production in the testes, and LFI stimulates the testesi
secrete testosterone. G&mdotropin-rekasing hormone (Gri
from the hypothalamus stimulates release of FSH
LH. The release of GnRII, FSH, and LH is suppressed
estrogens in females and by testosterone in males throuj
negative feedback systems. There is no gonadotroph
inhibiting hormone.
Prolactin
Prolactin (PRL), together with other hormones, initiates
maintains milk production by the mammary glands. Ejectj
of milk from the mammary glands depends on the horiiu
oxytocin, which is released from the posterior pituitary,
function of prolactin is unknown in males, but prolactin
persecution causes erectile dysfunction (impotence, the
ability to have an erection of the penis). In females,/?
inhibiting hormone (Pill) suppresses release of prolactin mc
of the time. Each month, just before menstruation bej
die secretion of PIH diminishes and the blood level of pr
lactin rises, but not enough to stimulate milk production,
the menstrual cycle begins anew, PIH is again secreted
the prolactin level drops. During pregnancy, very high levc
of estrogens promote secretion of prolactin-releasing buna
(PRH), which in turn stimulates release of prolactin.
Adrenocorticotropic Hormone
Adrenocorticotropic hormone (ACTH) or corticotropin com
the production and secretion of hormones called glucocor
coids by the cortex (outer portion) of the adrenal glands,
ticotropin-releasing hormone (CRH) from the hypothalami
stimulates secretion of ACTH. Stress-related stimuli, sucl
low blood glucose or physical trauma, and interleukin-l,
substance produced by macrophages, also stimulate release
ACTH. Glucocorticoids cause negative feedback inhibition!
both CRH and ACTH release.
feknocyte-Stimulating Hormone
There is little circulating melanocyte-stimulating hormone
MSH) in humans. Although an excessive amount of MSH
cs darkening of the skin, the function of normal levels
nl MSH is unknown. The presence of MSH receptors in
Hie brain suggests it may influence brain activity. Excessive
[corticotropin -releasing hormone (CRH) can stimulate
[SH release, and dopamine inhibits MSII release.
Hypothalamus and Pituitary Gland 321
Posterior Pituitary Hormones
The posterior pituitary contains the axons and axon termi-
nals of more than 10,000 neurosecretory cells whose cell
bodies are in the hypothalamus (Figure 13.5). Although the
posterior pituitary does not synthesize hormones, it does store
and release two hormones, in the hypothalamus, the hor*
mones oxytocin (ok'-se-TO-sin; axytoc- = quick birth) and
antidiuretic hormone (ADH) are synthesized and packaged
Figure 13.5 Hypothalamic neurosecretory cells synthesize oxytocin and antidiuretic hormone. Their
axons extend from the hypothalamus to the posterior pituitary. Nerve impulses trigger release of the hormones
from vesicles in the axon terminals in the posterior pituitary
Oxytocin and antidiuretic hormone are synthesized in the hypothalamus and released into capillaries of the
— posterior pituitary.
Hypothalamus
Pituitary gland
Capillaries
of posterior
pituitary
Axons of neurosecretory cells
Axon terminal
POSTERIOR PITUITARY
Cell bodies of
neurosecretory cells
Sphenoid bone
ANTERIOR PITUITARY
Where are the target cells of oxytocin located?
322 Chapter 13 The Endocrine System
into secretory vesicles within the cell bodies of different neu-
rosecretory cells. The vesicles then move down the axons to
the axon terminals in the posterior pituitary. Nerve impulses
that arrive at the axon terminals trigger release of these hor-
mones into the capillaries of the posterior pituitary.
Oxytocin
During and after delivery of a baby, oxytocin has two target
tissues: the mother's uterus and breasts. During delivery, oxy-
tocin enhances contraction of smooth muscle cells in die wall
of the uterus; after delivery, it stimulates milk ejection ("let-
down") from the mammary glands in response to die mechan-
ical stimulus provided by a suckling infant. Together, milk
production and ejection constitute lactation. The function of
oxytocin in males and in nonpregnant females is not clear. Ex-
periments with animals have suggested actions within the
brain that foster parental caretaking behavior toward young
offspring. Oxytocin also may be partly responsible for the
feelings of sexual pleasure during and after intercourse.
Years before oxytocin was discovered, midwives commonly
let a first-born twin nurse at the mother's breast to speed
the birth of the second child. Now we know why this prac-
tice is helpful — it stimulates release of oxytocin. Even
after a single birth, nursing promotes expulsion of the pla-
centa (afterbirth) and helps the uterus regain its smaller
size. Synthetic oxytocin (Pitocin®) often is given to in-
duce labor or to increase uterine tone and control hemor-
rhage just after giving birth.
Antidiuretic Hormone
An antidiuretic {anti- = against; diuretic = urine-producing
agent) is a substance that decreases urine production. Antidi-
uretic hormone (ADH) causes the kidneys to retain more wa-
ter, thus decreasing urine volume. In the absence of ADH,
urine output increases more than tenfold, from the normal
1-2 liters to about 20 liters a day ADH also decreases the
water lost through sweating and causes constriction of arteri-
oles. This hormone's other name, vasopressin (vaso- = vessel;
pressin- = pressing or constricting), reflects its effect on in-
creasing blood pressure.
The amount of ADH secreted varies with blood osmotic
pressure and blood volume. Blood osmotic pressure is pro-
portional to the concentration of solutes in the blood plasma.
When bodv water is lost faster than it is taken in, a condition
termed dehydration, the blood volume falls and blood osmotic
pressure rises. Figure 13.6 shows regulation of ADH secre-
tion and the actions of ADH on its target tissues.
High blood osmotic pressure- -due to dehydration or a
drop in blood volume because of hemorrhage, diarrhea, or
excessive sweating — stimulates osmoreceptors, neurons in
the hypothalamus that monitor blood osmotic pressure.
Figure 13.6 Regulation of secretion and actions of antidi-
uretic hormone (ADH).
ADH acts to retain body water and increase blood pressure.
High blood osmotic
pressure stimulates
hypothalamic
osmoreceptors
Q Osmoreceptors
activate the
neurosecretory cells
that synthesize and
release ADH
@ Low blood osmotic
., pressure inhibits
N / hypothalamic
^| 4r osmoreceptors
Osmoreceptors
I
I
I
I
I
^y Inhibition of osmo-
receptors reduces or
stops ADH secretion
^f Nerve impulse
liberate ADH from
axon terminals in
the posterior
pituitary into
the bloodstream
Hypothalamus.
3S J A
O
Kidneys retain
more water,
which decreases
urine output
Sweat glands Arterioles constrict,
decrease water which increases
loss by perspiration blood pressure
from the skin
What effect would drinking a large glass of water have on the
t osmotic pressure of your blood, and how would the level of ADH
J change tn your blood?
Osmoreceptors activate the hypothalamic neurosecrett
cells that synthesize and release ADM.
When neurosecretory cells receive excitatory input frc
the osmoreceptors, they generate nerve impulses
cause the release of ADH in the posterior pituitary.
ADII then diffuses into blood capillaries of the post*
pituitary,
The blood carries ADH to three target tissues: the
neys, sweat glands, and smooth muscle in blood vc
walls. The kidneys respond by retaining more vat
which decreases urine output. Secretory activity of s\
glands decreases, which lowers the rate of water loss
Thyroid Gland 323
perspiration from the skin. Smooth muscle in the walk of
arterioles (small arteries) contracts in response to high
levels of ADH, which constricts (narrows) the lumen of
these blood vessels and increases blood pressure,
Low blood osmotic pressure or increased blood volume
inhibits die osmoreceptors.
Inhibition of osmoreceptors reduces or stops ADH se-
cretion. The kidneys then retain less water by forming
a larger volume of urine, secretory activity of sweat
glands increases,* and arterioles dilate. The blood vol-
ume and osmotic pressure of body fluids return to
normal.
Secretion of ADIT can also be altered in other ways.
Pain, stress, trauma, anxiety, acetylcholine, nicotine, and
drugs such as morphine, tranquilizers, and some anesthetics
stimulate ADH secretion. Alcohol inhibits ADH secretion,
thereby increasing urine output. The resulting dehydration
may cause both the thirst and the headache typical of a
[hangover.
de 15.1 lists the pituitary gland hormones and sum-
marizes their actions.
I CHECKPOINT
4. In what respect is the pituitary gland actually two glands?
■ 5. How do hypothalamic releasing and inhibiting hormones
influence secretions of anterior pituitary hormones?
THYROID GLAND
objective • Describe the location, hormones, and
functions of the thyroid gland.
The butterfly-shaped thyroid gland is located just below the
larynx (voice box). It is composed of right and left lobes, one
on either side of the trachea {Figure 13.7a).
Microscopic spherical sacs called thyroid follicles (Fit
1 3.7b) make up most of the thyroid gland. The wall ol each
thyroid follicle consists primarily of cells called follicular
cells, which produce two hormones: thyroxine (thi-ROK-
sen), also called T 4 because it containsfour atoms of iodine,
and triiodothyronine (trl-T'-o-do-THi-ro-nen) (!»> which
contains three atoms of iodine. M\ and T 4 are also known as
thyroid hormones. The central cavity of each thyroid follicle
contains stored thyroid hormones. As T 4 circulates in the
blood and enters cells throughout the body, most of it is con-
verted to Tj by removal of one iodine aspm.
A smaller number of cells called parafollicular cells lie
between the follicles (Figure 13.7b). They produce the hor-
mone calcitonin.
Actions of Thyroid Hormones
Because most body cells have receptors for thyroid hor-
mones, T 3 and T 4 exert their effects throughout the body.
Table 1 3.1 Summary of Pituitary Gland Hormones and Their Actions
Hormone
Anterior Pituitary Hormones
Human growth hormone (hGH)
Thyroid-stimulating hormone (TSH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin (PRL)
Adrenocorticotropic hormone (ACTH),
also known as corticotropin
Melanocyte-stimulating hormone (MSH)
Posterior Pituitary Hormones
Oxytocin
Antidiuretic hormone (ADH), also
own as vasopressin
Actions
Stimulates liver, muscle, cartilage, bone, and other tissues to synthesize and secrete insulinlike growth
factors (IGFs). IGFs promote growth of body cells, protein synthesis, tissue repair, breakdown of triglyc-
erides, and elevation of blood glucose level.
Stimulates synthesis and secretion of thyroid hormones by the thyroid gland,
in females, initiates development of oocytes and induces secretion of estrogens by the ovaries. In
males, stimulates testes to produce sperm.
tn females, stimulates secretion of estrogens and progesterone, ovulation, and formation of corpus
luteum. In males, stimulates testes to produce testosterone.
In females, stimulates milk production by the mammary glands.
Stimulates secretion of glucocorticoids (mainly Cortisol) by the adrenal cortex.
Exact role in humans is unknown but may influence brain activity. When present in excess, can cause
darkening of skin.
Stimulates contraction of smooth muscle cells of uterus during childbirth. Stimulates milk ejection from
the mammary glands.
Conserves body water by decreasing urine output. Decreases water loss through sweating. Raises
blood pressure by constricting (narrowing) arterioles.
324 Chapter 13 The Endocrine System
Figure 13.7 Location and histology of the thyroid gland.
Thyroid hormones regulate (1) oxygen use and basal metabolic rate, (2) cellular metabolism, and (3)
^ growth and development.
Trachea
Hyoid bone
RIGHT LOBE OF
THYROID GLAND
Common carotid artery
v
Parafollicular cell
Follicular cell
Thyroid follicle
Stored thyroid
hormones
Trachea
Sternum
(a) Anterior view of thyroid gland
Which cells secrete T 3 andT 4 ? Which cells secrete calcitonin?
(b) Thyroid follicles
Thyroid hormones increase basal metabolic rate (BMR), the
ice of oxygen consumption under standard or basal condi-
I&s (awake, at rest, and fasting). The BMR rises due to in-
Led synthesis and use of ATP. As cells use more oxygen to
loduce the ATP, more heat is given off, and body tempera-
re rises. Tn this way, thyroid hormones play an important
)le in die maintenance of normal body temperature. The
fcyroid hormones also stimulate protein synthesis, increase
|he use of glucose and fatty acids for ATP production, in-
to the breakdown of triglycerides, and enhance choles-
|ol excretion, thus reducing blood cholesterol level. To-
with human growth hormone and insulin, thyroid
tones stimulate body growti^ particularly the growth of
IneiYOtxs and skeletal systems.
ess secretion of thyroid hormones is known as Iiyper-
yroidism. Symptoms of hyperthyroidism include in-
eased heart rate and more forceful heartbeats, increased
pressure, and increased nervousness,
mtrol of Thyroid Hormone Secretion
i ptropin-rel easing hormone (TRH) from the hypothala-
ancl thyroid-stimulating hormone (TSH) from the ante-
r pituitary stimulate synthesis and release of thyroid hor-
des, as shown in Figure 13.8:
Low blood level of thyroid hormones or low metabolic
rate stimulate the hypothalamus to secrete TRH.
TRH is carried to the anterior pituitary; where it stimu-
lates secretion of thyroid-stimulating hormone (TSH).
TSH stimulates thyroid follicular cell activity, including
thyroid hormone synthesis and secretion, and growth of
the follicular cells.
The thyroid follicular cells release thyroid hormones into
the blood until the metabolic rate returns to normal.
i elevated level of thyroid hormones inhibits release of
TRH and TSH (negative feedback).
Conditions that increase ATP demand — a cold environ-
low blood glucose, high altitude, and pregnancy — also
icrease secretion of the thyroid hormones.
ilcitonin
ie hormone produced by the parafollicular cells of the thy-
H gland is calcitonin (CT) (kal-si-TO-nin). Calcitonin can
-crease the level of calcium in the blood by inhibiting the
ion of osteoclasts, the cells that break down bone. The se-
ction of calcitonin is controlled by a negative feedback sys-
(see Figure 13.10). Calcitonin's importance in normal
nolofrv is unclear because it can be present in excess or
jnipletdy absent without causing clinical symptoms.
Parathyroid Glands 325
Figure 13.8 Regulation of secretion of thyroid hormones.
| TSH promotes release of thyroid hormones.
Low blood levels of thyroid
hormones or low metabolic
rate stimulate release of
©
TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
O
Thyroid
follicle
Hypothalamus
■ © Elevated level of
thyroid hormones
inhibits release of
TRH and TSH
(negative feedback)
TSH released into
blood stimulates
thyroid follicular cells
Thyroid hormones
released into blood
by follicular cells
J
What is the effect of thyroid hormones on metabolic rate?
Miacalcin®, a calcitonin extract from salmon, is an effec-
tive treatment for osteoporosis, a disorder in which the
pace of bone breakdown exceeds the pace of bone rebuild-
ing. It inhibits breakdown of bone and accelerates uptake
of calcium and phosphates into bone.
■ CHECKPOINT
6. How is the secretion of T 3 and T 4 regulated?
7, What are the actions of the thyroid hormones and calci-
tonin?
PARATHYROID GLANDS
OBJECTIVE • Describe the location, hormones, and
functions of the parathyroid glands.
The parathyroid glands (para- = beside) are small, round
masses of glandular tissue that are partially embedded in the
326 Chapter 13 The Endocrine System
posterior surface of the thyroid gland (Figure 13.9). Usually,
one superior and one inferior parathyroid gland are attached
to each thyroid lobe. Within the parathyroid glands are
secretory cells called chief cells that release parathyroid hor-
mone (PTH).
PTTT is the major regulator of the levels of calcium
(Ca 2+ ) s magnesium (Alg 24 ), and phosphate (HP0 4 2_ ) ions in
the blood. PTII increases the number and activity of osteo-
clasts, which break down bone extracellular matrix and re-
lease Ca 2+ and HPO4 2 " into the blood. PTII also produces
three changes in the kidneys. First, it slows the rate at which
Ca 2 ' and Mg 2+ are lost from blood into the urine. Second, it
increases loss of HPO4 2 from blood in urine. Because more
is lost in the urine than is gained from the bones, PTII de-
creases blood IIPO4 2 " level and increases blood Ca 2 " and
Mg 2 ^ levels. Third, PTH promotes formation of the hor-
mone calcitriol, rbe active form of vitamin D. Calcitriol acts
on the gastrointestinal tract to increase die rate of Ca 2+ ,
Mg 2 ' , and HPO4 2 *" absorption from foods into the blood.
The blood calcium level directly controls the secretion of
calcitonin and parathyroid hormone via negative feedback,
and the two hormones have opposite effects on blood (>
level (Figure 13 JO).
Q A higher-than-normal level of calcium ions (Ca 2+ ) in
blood stimulates parafollicular cells of the thyroid glaJK
to release more calcitonin.
m
Q CT inhibits the activity of osteoclasts, thereby deereasii
blood Ca 24 level.
© A lower-than -normal level of Ca 2 ** in the blood stimuJ
kites chief cells of the parathyroid gland to release mq
PTII.
PTH increases the number and activity of osteocld
which break down bone and release Ca 2 ' into the blool
PTH also slows loss of Ca in the urine. Both actions
PTH raise the blood level of Ca 2 + .
© PTH also stimulates the kidneys to release calcitriol.
active form of vitamin D.
Q Calcitriol stimulates increased absorption of ( "1 fro*
foods in the gastrointestinal tract, which helps in
the blood level of Cfc 2+ .
Figure 13.9 Location of the parathyroid glands.
The four parathyroid glands are attached to the posterior surface of the thyroid gland.
Parathyroid
glands (behind
thyroid gland)
LEFT SUPERIOR
PARATHYROID GLAND
Esophagus
LEFT INFERIOR
PARATHYROID GLAND
Thyroid gland
RIGHT SUPERIOR
PARATHYROID GLAND
RIGHT INFERIOR
PARATHYROID GLAND
Trachea
S What effect does parathyroid hormone have on osteoclasts?
Posterior view
Pancreatic Islets 327
Figure 13.10 The roles of calcitonin (green arrows), parathyroid hormone (purple arrows), and cai
citriol (orange arrows) in homeostasis of blood calcium level
PTH and calcitonin have opposite effects on the level of calcium ions (Ca 2+ ) in the blood.
O
CALCITRIOL stimulates
increased absorption of
Ca a+ from foods, which
increases blood Ca i+ level.
PTH also stimulates
the kidneys to release
CALCITRIOL
► O H '9 h level of Ca ^ in blood
stimulates thyroid gland
parafollicular cells to release
more CT.
Q Low level of Ca^ + in blood
stimulates parathyroid gland
chief cells to release more PT!
PARATHYROID HORMONE (PTH)
promotes release of Ca**" from
bone extracellular matrix info
blood and slows loss of Ca +
in urine, thus increasing blood
Ca 2+ level.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca 2 " level.
r\
What are the primary target tissues for PTH, calcitonin, and calcitriol?
| CHECKPOINT
J. How is secretion of PTH regulated?
t In what ways are the actions of PTH and calcitriol simi-
lar and different?
PANCREATIC ISLETS
ECT1VE • Describe the location, hormones, and
functions of the pancreatic islets,
Qk pancreas (pan- = all; -areas = flesh) is a flattened organ
kated in the curve of the duodenum, the first part of the
intestine (Figure 13.1 la). It has both endocrine fane-
discussed in this chapter, and exocrine functions, dis-
ced in Chapter 19. The endocrine part of the pancreas
Mists of clusters of cells called pancreatic islets or islets of
Langerhans (LAHNG-er-hanz), Some of die islet cells, the
alpha cells, secrete die hormone glucagon (GLQO-ka-gon),
and other islet cells, the beta cells, secrete insulin (IN-soo-
lin). The islets also contain abundant blood capillaries and
are surrounded by cells that form the exocrine part of the
pancreas (Figure 1 3.1 lb, c).
Actions of Glucagon and Insulin
The main action of glucagon is to increase blood glucose level
when it tails below normal, which provides neurons with glucose
for AIT production. Insulin, by contrast, helps glucose move
into cells, especially muscle fibers, which lowers blood glucose
level when it is too high. The level of blood glucose controls se
cretion of both glucagon and insulin via negative feedback.
Figure 1 3.12 on page 329 shows die conditions that stimulate die
pancreatic islets to secrete their hormones, die ways in which
glucagon and insulin produce their effects on blood glucose level,
and the negative feedback control of hormone secretion.
328 Chapter 13 The Endocrine System
Figure 13.11 Location and histology of the pancreas.
Hormones released by pancreatic islets regulate blood glucose level
Pancreas
Kidney
Abdominal aorta
PANCREAS
Duodenum of
small intestine
Spleen
(elevated)
(a) Anterior view
Blood capillary
Exocrine celts
Endocrine cells:
Alpha cell
(secretes glucagon)
Beta cell
(secretes insulin)
Blood capillary
-V- Pancreatic
7 p, % islet
- Alpha cell
300x
(b) Pancreatic islet and surrounding acini
* Is the pancreas an exocrine gland or an endocrine gland?
7
(c) Pancreatic islet and surrounding acini
iRqure 13.12 Regulation of blood glucose level by negative
(feedback systems involving glucagon (blue arrows) and insulin
(orange arrows).
I Low blood glucose stimulates secretion of glucagon, and high
fe^ blood glucose stimulates secretion of insulin.
A Low blood glucose
(hypoglycemia)
stimulates alpha
cells to secrete
U High blood glucose
(hyperglycemia)
stimulates beta cells
to secrete
<
GLUCAGON
Glucagon acts on
liver cells to:
• break down
glycogen into
glucose
• form glucose from
lactic acid and
certain amino acids
I
INSULIN
Insulin acts on various
body celts to:
promote facilitated
diffusion of glucose
into cells
speed synthesis of
glycogen from glucose
increase uptake of
amino acids and increase
protein synthesis
A Glucose released
by liver cells raises
blood glucose
level to normal
A Blood glucose level falls
I I
A If blood glucose If blood glucose continues
\ continues to rise, to fall, hypoglycemia
* hyperglycemia inhibits inhibits release of insulin
release of glucagon
Why is glucagon sometimes called an "anti-insulin" hormone?
Low blood glucose level (hypoglycemia) stimulates secre-
tion of glucagon.
A Glucagon acts on liver cells to promote breakdown of
glycogen into glucose and formation of glucose from lactic
[ -and certain amino acids.
ft Ma result, the liver releases glucose into the blood more
rapidly, and blood glucose level rises.
L if blood glucose continues to rise, high blood glucose
level (hyperglycemia) inhibits release of glucagon by al-
ia cells (negative feedback).
Adrenal Glands 329
—
At the same time, high blood glucose level stimulates se-
cretion of insulin.
© Insulin acts on various cells in the body to promote facili-
tated diffusion of glucose into cells, especially skeletal
muscle fibers; to speed synthesis of glycogen from glu-
cose; to increase uptake of amino acids by cells; and to
increase protein synthesis.
As a result, blood glucose level falls,
G If blood glucose level drops below normal, low blood
glucose inhibits release of insulin by beta cells (negative
feedback).
hi addition to affecting glucose metabolism, insulin pro-
motes the uptake of amino acids into body cells and increases
the synthesis of proteins and fatty acids within cells. There-
lure, 'insulin is an important hormone when tissues are devel-
oping, growing, or being repaired. '
Release of insulin and glucagon is also regulated by the
autonomic nervous system (ANS). The parasympathetic divi-
sion of the ANS stimulates secretion of insulin, for instance,
during digestion and absorption of a meal. The sympathetic
division of the ANS, by contrast, stimulates secretion ot
glucagon, as happens during exercise.
■ CHECKPOINT
10. What are rite functions of insulin?
11. How are blood levels of glucagon and insulin controlled?
ADRENAL GLANDS
OBJECTIVE • Describe the location, hormones, and
functions of the adrena l glands.
There are two adrenal glands, one lying atop each kidney
(Figure 1 3. 13). Each adrenal gland has regions that produce
different hormones: the outer adrenal cortex, which makes
up 85% of the gland, and the inner adrenal medulla.
Adrenal Cortex Hormones
The adrenal cortex consists of three zones, each of which
synthesizes and secretes different steroid hormones. I In
outer zone releases hormones called mineralocortiooids
because they affect mineral homeostasis. The middle zone
releases hormones called glucocorticoids because they affect
glucose homeostasis. The inner zone releases androgens
(steroid hormones that have masculinizing effects).
Figure 13.13 Location and histology of the adrenal glands.
The adrenal cortex secretes steroid hormones, and the adrenal medulla secretes epinephrine and norepinephrine.
Adrenal
glands
Kidney
RIGHT ADRENAL
GLAND
Right renal artery
Right rena! vein
Inferior vena cava
Abdominal aorta
LEFT ADRENAL
GLAND
Left renal artery
Left renal vein
(a) Anterior view
Capsule
Adrenal
cortex
Adrenal
medulla
Section through left adrenal gland
c ^
Capsule
Adrenal cortex:
Middle zone
secretes
glucocorticoids,
mainly Cortisol
CUB 50x
(b) Subdivisions of the adrenal gland
inner zone
secretes androgens
Adrenal medulla
secretes
epinephrine and
norepinephrine
330
J What hormones are secreted by the three zones of the adrenal cortex?
Adrenal Glands 331
i/linemlocorticoids
Aldosterone (al-DO-ster-6ii) is the major mmeralocortkoid
(min'-er-al-o-KOR-ti-koyd). It regulates homeostasis of two
mineral ions, namely, sodium ions (Na 1 ) and potassium ions
K + ). Aldosterone increases reabsorption of Na" from the
prine into the blood, and it stimulates excretion of K into
Re urine. It also helps adjust blood pressure and blood vol-
lume, and promotes excretion of H + in the urine. Such re-
moval of acids from the body can help prevent acidosis
■flood pH below 7.35).
Secretion of aldosterone occurs as part of the renin-
gmotensin -aldosterone pathway (RE-nin an'-je-o-TEN-sin)
lure 13.14). Conditions diat initiate this pathway include
iLiun, Nil deficiency, or hemorrhage, which decrease
Wood volume and blood pressure. Lowered blood pressure
Stimulates the kidneys to secrete the enzyme renin, which
LOtes a reaction in the blood that forms angiotensin I. As
flows through the lungs, another enzyme called
itensin convening enzyme (ACE) converts inactive an-
giotensin I into the active hormone angiotensin II. An-
Wotensin II stimulates the adrenal cortex to secrete aklos-
:.. Udosterone, in turn, acts on the kidneys to promote
;|il return of Na + and water to the blood. As more water re-
turns to die blood (and less is lost in the urine), blood volume
:ases. As blood volume increases, blood pressure in-
es to normal.
UucMonicoids
tost abundant glucocorticoid (gloo'-ko-KOR-ti-koyd;
= sugar; conk- = the bark, shell) is Cortisol Cortisol
>ther glucocorticoids have the following actions:
Protein breakdown. Glucocorticoids increase the rate
of protein breakdown, mainly in muscle fibers, and dius
increase the liberation of amino acids into die blood-
earn, The amino acids may be used by body cells for
tithesis of new proteins or for ATP production.
I Glucose formation. Upon stimulation by glucocorti-
coids, liver cells may convert certain amino acids or lactic
acid to glucose, which neurons and other cells can use for
ATP production.
Breakdown of triglycerides. Glucocorticoids stimulate
the breakdown of triglycerides in adipose tissue. The
fatty acids thus released into the blood can be used for
ATP production by many body cells.
Anti-inflammatory effects. Glucocorticoids inhibit white
id cells that participate in inflammatory responses.
v are often used in the treatment of chronic inflam-
matory disorders such as rheumatoid arthritis. Unfortu-
nately, glucocorticoids also retard tissue repair, which
slows wound healing.
I Depression of immune responses. High doses of glu-
cocorticoids depress immune responses. For this reason,
Figure 13.14 The renin-angiotensin-aldosterone pathway.
■•._-•-'•. p p
Aldosterone helps regulate blood volume, blood pressure, and
levels of Na+ and K + in the blood.
Dehydration, Na 4 " deficiency,
or hemorrhage
i
Decrease in blood volume
and blood pressure
Kidney
Adrenal
cortex
Aldosterone
In kidneys, more Na + and
water return to blood and
more K + eliminated in urine
Increase in blood volume
and blood pressure
Could a drug that blocks the action of the enzyme ACE be used
t to rah
:
ise or to lower blood pressure?
glucocorticoids are prescribed for organ transplant recip-
ients to decrease the risk of tissue rejection by die im-
mune system.
The control of secretion of Cortisol (and other glucocor-
ticoids) occurs by negative feedback. A low blood level of
Cortisol stimulates neurosecretory cells in the hypothalamus
to secrete conicotropm-rekasmg hormone (CRH). The hy-
pophyseal portal veins cany CRH to the anterior pituitary,
where it stimulates release of ACTH {adrenocorticotropic
hormone). ACTH, in turn, stimulates cells of the adrenal
cortex to secrete Cortisol As the level of Cortisol rises, it ex-
Insulin Resistanc
A Metabolic
Medley
line of the most common endocrine
disorders, type 2 diabetes, is charac-
terized by high levels of insulin in the
blood. Insulin levels are high due to
insulin resistance, a condition in
which insulin receptors do not re-
spond properly to insulin. Despite
plentiful insulin, blood glucose level
remains high, because the receptors
are not letting insulin help the glu-
cose across the membrane and into
the cells.
A Little Riddle About Fat in the
Middle
Many people who develop type 2 dia-
betes also develop hypertension (high
blood pressure) and high blood choles-
terol. They also tend to be overweight
and sedentary. This cluster of disor-
ders — termed metabolic syndrome —
may be related to excess adipose tissue
around the abdominal viscera.
Why is abdominal fat riskier than
other adipose tissue? Adipocytes (fat
cells) in the abdominal region are
metabolically "more active" than
lower-body fat cells, and they are more
responsive to hormones such as epi-
nephrine. This means they release fatty
acids into the bloodstream more read-
ily, which, in the abdominal area, flows
to the liver. The liver takes up the tatty
acids and produces triglycerides that
are packaged into very-low-density
lipoprotein (VLDL) particles. Later,
the VLDLs are converted into low-
density lipoprotein (LDL) particles.
Higher levels of LDLs are associated
with the formation of artery- clogging
atherosclerotic plaques.
The elevation in triglycerides may
disrupt blood sugar regulation and trig-
ger a rise in insulin. Elevated insulin
levels in turn stimulate the sympathetic
nervous system, which increases blood
pressure. And there you have it, all in
one package: high blood sugar, high
blood lipids, hypertension, and abdom-
inal obesity, a package that significant
increases artery disease risk.
Smoking, alcohol consumpti
poor diet, and a sedentary lifestyle pj
dispose a person to the development
type 2 diabetes. Both exercise
weight loss (in people who are ov«
weight) increase the sensitivity of
sulin receptors and improve tm
of glucose into body ceils.
► Th
Why do you think extra fat tends to be lost more easily in the abdominal
region than in the hips and thighs? Are you at risk for metabolic syndrom
Use a tape measure to take the circumferences of your hips and waist. 1 1
waist-hips ratio greater than 1.0 for men or 0.8 for women is considered
risky.
332
Jrts negative feedback inhibition both on the anterior pitu-
[tar\ ? toreduce release of ACTH and on the hypothalamus to
reduce release of CRH.
Androgens
h both males and females, the adrenal cortex secretes small
amounts of weak androgens. After puberty in males, andro-
is are also released in much greater quantity by the testes.
he amount of androgens secreted by the adrenal gland
in males is usually so low that their effects are insignificant.
In females, however, adrenal androgens play important roles:
■They contribute to libido (sex drive) and are converted into
fcxogens (feminizing sex steroids) by other body tissues. Af-
ter menopause, when ovarian secretion of estrogens ceases,
■ female estrogens come from conversion of adrenal andro-
gens. Adrenal androgens also stimulate growth of axillary
flarmpit) and pubic hair in boys and girls and contribute to
Je growth spurt before puberty. Although control of adrenal
idrogen secretion is not fully understood, the main hoi-
lonc that stimulates its secretion is ACTH.
Congenital adrenal hyperplasia (CAH) is a genetic dis-
:r in which one or more enzymes needed for the pro-
duction of Cortisol are absent. Because the Cortisol level is
secretion of ACTH by die anterior pituitary is high due
to lick of negative feedback inhibition. ACTH, in turn,
■ dates growth and secretory activity of die adrenal cor-
Vs a result, both adrenal glands are enlarged However,
| certain steps leading to synthesis of Cortisol are blocked.
Thus, precursor molecules build up, and some of these are
weak androgens that can he converted to testosterone. The
result is virilism, or masculinization. In a female, virile char-
acteristics include growth of a beard, development of a much
deeper voice and a masculine distribution of body hair,
ili of the clitoris so it may resemble a penis, atrophy of
ilic breasts, and increased muscularity that produces a mas-
culine physique. In males, virilism causes the same charac-
teristics as in females, plus rapid development of the male
ii organs and emergence of male sexual desires.
■Adrenal Medulla Hormones
innermost region of each adrenal gland, the adrenal
Ledulla, consists of sympathetic postganglionic cells of the
Autonomic nervous system (ANS) that are specialized to se-
te hormones. The two main hormones of the adrenal
rfullac are epinephrine and norepinephrine (Ms), also
Bed adrenaline and noradrenaline.
In stressful situations and during exercise, impulses from
L hypothalamus stimulate sympathetic preganglionic neu-
ps, which in turn stimulate the cells of the adrenal medul-
secrete epinephrine and norepinephrine. These two
Ovaries and Testes 333
hormones greatly augment the fight-or-flight response (see
page 335). By increasing heart rate and force of contraction,
epinephrine and norepinephrine increase the pumping out-
put of the heart, which increases blood pressure. They also
increase blood flow to the heart, liver, skeletal muscles, and
adipose tissue; dilate airways to the lungs; and increase blood
levels of glucose and fatty acids. Like the glucocorticoids of
the adrenal cortex, epinephrine and norepinephrine also help
the body resist stress.
■ CHECKPOINT
12. How do the adrenal cortex and adrenal medulla compare
with regard to their location and histology?
13. How is secretion of adrenal cortex hormones regulated?
OVARIES AND TESTES
OBJECTIVE • Describe the location, hormones, and
functions of the ovaries and testes.
Gonads are the organs that produce gametes- -sperm in
males and oocytes in females, The female gonads, the
ovaries, are paired oval bodies located in the pelvic cavity.
They produce the female sex hormones estrogens and pro-
gesterone. Along with FSH and LI I from the anterior pitu-
itary, the female sex hormones regulate the menstrual cycle,
maintain pregnancy, and prepare die mammary glands for
lactation. They also help establish and maintain the feminine
body shape.
The ovaries also produce inhihin, a protein hormone
that inhibits secretion of follicle-stimulating hormone (FSH).
During pregnancy, the ovaries and placenta produce a pep-
tide hormone called relaxin, which increases the flexibility of
the pubic symphysis during pregnancy and helps dilate the
uterine cervix during labor and delivery. These actions en-
large the birth canal, which helps ease the baby's passage.
The male gonads, the testes, are oval glands that lie in
the scrotum. They produce testosterone, die primary andro-
gen or male sex hormone. Testosterone regulates production
of sperm and stimulates the development and maintenance of
masculine characteristics such as beard growth and deepen-
ing of the voice. The testes also produce inhibin, which in-
hibits secretion of FSH. The detailed structure of the ovaries
and testes and the specific roles of sex hormones will be dis-
cussed in Chapter 23.
Seasonal affective disorder (SAD) is a type of depression
that afflicts some people during the winter months, when
day length is short. It is thought to be due, in part, to
overproduction of melatonin. Bright light therapy —
repeated exposure to artificial light- -can provide relief.
334 Chapter 13 The Endocrine System
■ CHECKPOINT
14, Why are the ovaries and testes included among the en-
docrine glands?
PINEAL GLAND
OBJECTIVE • Describe the location, hormone,
functions of the pineal gland.
The pineal I gland (PIN-e-al - pinecone shape) is a small en-
docrine gland attached to the roof of the third ventricle of
the brain at the midline (see Figures I 3. 1 and 10.6 on pages
316 and 249, respectively). One hormone secreted by the
pineal gland is melatonin, which contributes to setting the
body's biological clock. More melatonin is released in dark-
ness and during sleep; less melatonin is liberated in strong
sunlight. In animals that breed during specific seasons, mela-
tonin inhibits reproductive functions. Whether melatonin
influences human reproductive function, however, is still
unclear. Melatonin levels are higher in children and decline
with age into adulthood, but there is no evidence that
changes in melatonin secretion correlate with the onset oj
puberty and sexual maturation.
■ CHECKPOINT
15. What is the relationship between melatonin secretion
and sleep?
OTHER HORMONES
objective • List the hormones secreted by cells ii
tissues and organs other than endocrine glands, and de-
scribe their functions.
Hormones from Other Endocrine Cells I
Some tissues and organs other than those already deseri
contain endocrine cells that secrete hormones. Table I.v
summarizes these hormones and their actions.
Table 13,2 Summary of Hormones Produced by Endocrine Cells
Source and Hormone
Thymus
Thymosin
Gastrointestinal Tract
Gastrin
G I ucose-dependent
insulinotropic peptide (GiP)
Secretin
Cholecystokinin (CCK)
Kidney
Erythropoietin (EPO)
Heart
Atrial natriuretic peptide (ANP)
Adipose Tissue
Leptin
Placenta
Human chorionic gonadotropin (hCG)
Actions
Promotes the maturation of T cells (a type of white blood ceil that destroys microbes and foreign
substances) and may retard the aging process (discussed in Chapter 17).
Promotes secretion of gastric juice and increases movements of the stomach (discussed in Chapter 19),
Stimulates release of insulin by pancreatic beta cells (discussed in Chapter 19).
Stimulates secretion of pancreatic juice and bile (discussed in Chapter 19).
Stimulates secretion of pancreatic juice, regulates release of bile from the gallbladder, and brings aboul
a feeling of fullness after eating (discussed in Chapter 19),
Increases rate of red blood cell production (discussed in Chapter 14).
Decreases blood pressure (discussed in Chapter 16).
Suppresses appetite and may increase the activity of FSH and LH (discussed in Chapter 20).
Stimulates the ovary to continue production of estrogens and progesterone during pregnancy (dis-
cussed in Chapter 24),
prostaglandins and Leukotrienes
families of molecules derived from fatty acids, the
wstagtemMm (pros'-ta-GLAN-dins), or PGs, and the
ikotrimes (loo-ko-TRI-ens), or LTs, act locally as hormones in
[lost tissues of the body. Virtually all body cells except red blood
Is release these local hormones in response to chemical and
lechanical stimuli. Because the PGs and LTs act close to their
>f release, diey appear in only tiny quantities in the blood,
Leukotrienes stimulate movement of white blood cells
id mediate inflammation. The prostaglandins alter smooth
jiuscle contraction, glandular secretions, blood flow, rcpro-
nctive processes, platelet function, respiration, nerve im-
|e transmission, fat metabolism, and immune responses.
also have roles in inflammation, promoting lever, and
falsifying pain.
[Aspirin and related nonsteroidal anti-inflammatory
[drugs (NSAIDs), such as ibuprofen (Motrin®), inhibit a
k? enzyme in prostaglandin synthesis without affecting
ithesis of leukotrienes. They are used to treat a wide va-
riety of inflammatory disorders, from rheumatoid arthritis
tennis elbow.
CHECKPOINT
i. What hormones are secreted by the gastrointestinal tract,
placenta, kidneys, skin, adipose tissue, and heart?
[What are some functions of prostaglandins and leuko-
trienes?
HE STRESS RESPONSE
ECT1VE • Describe how the body responds to
impossible to remove all stress from our everyday lives.
L stimulus that produces a stress response is called a stres-
j A stressor may be almost any disturbance — heat or cold,
. nninental poisons, toxins given off by bacteria, heavy
[ding from a wound or surgery, or a strong emotional re-
tail Stressors may be pleasant or unpleasant, and they vary
kmis people and even within the same person at different
ies. When homeostatic mechanisms are successful in
Lteracting stress, the internal environment remains
^chin normal physiological limits. If stress is extreme, un-
lal, or long lasting, it elicits the stress response, a sequence
[bodily changes that can progress through three stages: (1)
(initial fight-or-flight response, (2) a slower resistance reae-
jiund eventually (3) exhaustion.
The fight-or-flight response, initiated by nerve impulses
M the hypothalamus to the sympathetic division of the au-
The Stress Response 335
tonomic nervous system (ANS), including the adrenal medul-
lae, quickly mobilizes the body's resources for immediate
physical activity. It brings huge amounts of glucose and oxy-
gen to the organs that are most active in warding off danger:
the brain, which must become highly alert; the skeletal mus-
cles, which mayhave to fight off an attacker or flee; and the
heart, which must work vigorously to pump enough blood to
the brain and muscles. Reduction of blood flow to the kid-
neys, however, promotes the release of renin, which sets into
motion the renin-angiotensin -aldosterone pathway (see
Figure I 3.14). Aldosterone causes the kidneys to retain Na f ,
which leads to water retention and elevated blood pressure.
Water retention also helps preserve body fluid volume in the
case of severe bleeding.
The second stage in the stress response is die resistance
reaction. Unlike the short-lived fight-or-flight response, which
is initiated by nerve impulses from the hypothalamus, the
resistance reaction is initiated in large part by hypothalamic
releasing hormones and is a longer-lasting response. The
hormones involved are corticotropin- releasi n ;j hormone
(CRH), growth hormone-releasing hormone (GHRJ1), and
thyrotropin-releasing hormone (TRH)«
CRH stimulates the anterior pituitary to secrete
ACTH, which in turn stimulates the adrenal cortex to re-
lease more Cortisol. Cortisol then stimulates release of glu-
cose by liver cells, breakdown of triglycerides into tatty
acids, and catabolism of proteins into amino acids. Tissues
throughout the body can use the resulting glucose, fatty
acids, and amino acids to produce ATP or to repair dam-
aged cells. Cortisol also reduces inflammation. A second hy-
pothalamic releasing hormone, GHRH, causes the anterior
pituitary to secrete human growth hormone (hGH). Acting
via insulinlike growth factors, hGH stimulates breakdown
of triglycerides and glycogen. A third hypothalamic releas-
ing hormone, TRH, stimulates the anterior pituitary to se-
crete thyroid-stimulating hormone (TSH). TSH promotes
secretion of thyroid hormones, which stimulate the in-
creased use of glucose for ATP production. The combined
actions of hGH and TSH thereby supply additional ATP
for metabolically active cells.
The resistance stage helps the body continue fighting a
stressor long after the fight-or-flight response dissipates.
Generally, it is successful in seeing us through a stressful
episode, and our bodies then return to normal Occasionally,
however, the resistance stage fails to combat the stressor: The
resources of the body may eventually become so depleted
that they cannot sustain the resistance stage, and exhaustion
ensues. Prolonged exposure to high levels of Cortisol and
other hormones involved in the resistance reaction causes
wasting of muscles, suppression of the immune system, ulcer-
ation of the gastrointestinal tract, and failure of pancreatic
beta cells. In addition, pathological changes may occur be-
cause resistance reactions persist after the stressor has been
removed.
336 Chapter 13 The Endocrine System
Although the exact role of stress in human diseases is not
known, it is clear that stress can temporarily inhibit certain
components of the immune system. Stress-related disorders
include gastritis, ulcerative colitis, irritable bowel syndrome,
hypertension, asthma, rheumatoid arthritis, migraine
headaches, anxiety, and depression. People under stress also
are at a greater risk of developing a chronic disease or dying
prematurely.
Posttraumatic stress disorder (PTSD) may develop in
someone who has experienced, witnessed, or learned about
a physically or psychologically distressing event, The im-
mediate cause of PTSD appears to be the specific stressors
associated with the events. Among the stressors are terror-
ism, hostage taking, imprisonment, serious accidents, tor-
ture, sexual or physical abuse, violent crimes, and natural
disasters. In the United States, PTSD affects 10% of
females and 5% of males. Symptoms of PTSD include re-
living the event through nightmares or flashbacks; loss
of interest and lack of motivation; poor concentration;
irritability; and insomnia,
■ CHECKPOINT
18. What is the role of the hypothalamus during stress?
19. How are stress and immunity related?
AGING AND THE
ENDOCRINE SYSTEM
OBJECTIVE • Describe the effects of aging on the en-
docrine system.
Although some endocrine glands shrink as we get older, their
performance may or may not be compromised. Production of
human growth hormone by the anterior pituitary decreases,
which is one cause of muscle atrophy as aging proceeds. The
thyroid gland often decreases its output of thyroid hormones
with age, causing a decrease in metabolic rate, an increase in
body fat, and hypothyroidism, which is seen more often in
older people. Because there is less negative feedback (lower
levels of thyroid hormones), the level of thyroid-stimulating
hormone increases with age.
With aging, the blood level of PHI rises, perhaps due
inadequate dietary intake of calcium. In a study of olfl
women who took 2,400 mg/day of supplemental calciur
blood levels of PTH were as low as those in younger worn!
Both calcitriol and calcitonin levels are lower in older pefl
sons. Together, the rise in PTH md the fall in calcitoi
heighten the age-related decrease in bone mass that leads
osteoporosis and increased risk of fractures.
The adrenal glands contain increasingly more fibrous
sue and produce less Cortisol and aldosterone with advanj
age. However, production of epinephrine and norepinq
rine remains normal. The pancreas releases insulin
slowly with age, and receptor sensitivity to glucose decline
As a result, blood glucose levels in older people inert
faster and return to normal more slowly than in younger ii
divi duals.
The thymus is largest in infancy. After puberty, its si]
begins to decrease, and thymic tissue is replaced by adi|
and areolar connective tissue. In older adults, the thvinusil
atrophied significantly. However, it still produces new T cell
for immune responses.
The ovaries decrease in size with age 3 and they no lorn
respond to gonadotropins* The resultant decreased output i
estrogens leads to conditions such as osteoporosis, hif
blood cholesterol, and atherosclerosis. FSH and LH k\
are high due to less negative feedback inhibition of estrogei
Although testosterone production by the testes de<
with age, the effects are not usually apparent until ven
age, and many elderly males can still produce ,n n i | i
normal numbers,
■ CHECKPOINT
20. Which hormone is related to the muscle atrophy that
curs with aging?
To appreciate the many ways the endocrine system
tributes to homeostasis of other body systems, examine F(
on Homeostasis: The Endocrine System on page 339. Nes
in Chapter 14, we will begin to explore the cardiovasc
system, starting with a description of the composition
functions of the blood.
Common W\swAm
COMMON
DISORDERS
Lders of the endocrine system often involve cither byposeere-
£a (hypo- = too little or under), inadequate release of a hormone,
.hypersecretion (hyper- = too much or above), excessive release or
Swrmonc, In other cases, the problem is faulty hormone receptors
i,i inadequate number of receptors.
[pituitary Gland Disorders
ton! disorders of the anterior pituitary involve human growth
jjnone (hGH). Underseeretion of hGH during die growth years
m bone growth, and the epiphyseal plates close before normal
Kt is reached. This condition is called pituitmy dwarfism,
L organs of the body also fail to grow, and the body propor-
js are childlike. . . , ,
ersecretion of hGH during childhood results in giantism
ngmitismh an abnormal increase in the length of long bones. The
Ion grows to be very tall, but body proportions are about nor-
1 Figure 13.15a shows identical twins; one brother developed
giantism due to a pituitary tumor. Oversecretion of hGH during
adulthood is called acromegaly (ak'-ro-MFXi-a-le). Although
hGH cannot produce further lengthening of the long bones
because the epiphyseal plates are already closed, the hones of the
hands, feet, cheeks, and jaws thicken and other tissues enlarge
(Figure. 13.15 b).
L The most common abnormality of the posterior pituitary is
diabetes insipidus (di-a-BE-tes in-SIP-i-dus; diabetes « overflow;
insipidus = tasteless). This disorder is due to defects in antidiuretic
hormone (ADII) receptors or an inability to secrete \D\ [. Usually
the disorder is caused by a brain tumor, head trauma, or brain
surgery that damages the posterior pituitary or the hypothalamus. A
common symptom is excretion of large volumes of urine, with
resulting dehydration and thirst. Because so much water is lost in
die urine, a person with diabetes insipidus may die of dehydration if
deprived of water for only a day or so.
Thyroid Gland Disorders r
Thyroid gland disorders affect all major body systems and arc
among the most common endocrine disorders. Congenital hypothy-
roidism, hyposecretion of thyroid hormones that is present at birth,
Figure 13.15 Photographs of people with various endocrine disorders.
£ Disorders of the endocrine system often involve hyposecretion or hypersecretion of
various hormones.
50
(b) Acromegaly (excess hGH
during adulthood)
(c) Goiter (enlargement
of thyroid gland)
(a) A 22-year old man with pituitary giantism
shown beside his identical twin
(d) Exophthalmos (excess
thyroid hormones, as
in Graves disease)
(e) Cushing's syndrome
(excess glucocorticoids)
l Which of the disorders shown here is due to antibodies that mimic the action of TSH?
f
338 Chapter 13 The Endocrine System
has devastating consequences if not treated promptly* Previously
termed cretinism, this condition causes severe mental retardation. At
birth, the baby typically is normal because lipid-soluble maternal
thyroid hormones crossed the placenta during pregnancy and
allowed normal development. Most states require testing of all
newborns to ensure adequate thyroid function, tf congenital
hypothyroidism exists, oral thyroid hormone treatment must he
started soon after birth and continued for life.
Hypothyroidism during the adult years produces myxedema
(mix-e-DE-ma), which occurs about five times more often in females
than in males, A hallmark of this disorder is edema (accumulation of
interstitial fluid) that causes the facial tissues to swell and look puffy.
A person with myxedema has a slow heart rate, low body tempera-
ture, sensitivity to cold, dry hair arid skin, muscular weakness, gen-
eral lethargy, and a tendency to gain weight easily.
The most common form of hyperthyroidism is Graves disease.
which also occurs much more often in females than in males, usu-
ally before age 40. Graves disease is an autoimmune disorder in
which the person produces antibodies that mimic the action of thy-
roid-stimulating hormone (TSI I). The antibodies continually stim-
ulate the thyroid gland to grow and produce thyroid hormones.
Thus, the thyroid gland may enlarge to two to three times its nor-
mal size, a condition called goiter (GOY-ter; gutter = throat)
(Figure I > 1 5c). Goiter also occurs in other thyroid diseases and if
dietary intake of iodine is inadequate. Graves patients often have
a peculiar edema behind the eyes, called exophthalmos (ek'-sof-
Ti lAL-mos), which causes die eyes to protrude (Figure 13 J 5d).
Parathyroid Gland Disorders
Hypoparathyroidism — too little parathyroid hormone — leads to a
deficiency of Ca 2+ , which causes neurons and muscle fibers to depo-
larize arid produce action potentials spontaneously. This leads to
twitches, spasms, and tetany (maintained contraction) of skeletal
muscle. The leading cause of hypoparathyroidism is accidental
damage to the parathyroid glands or to their blood supply during
surgery to remove the thyroid gland.
Adrenal Gland Disorders
Hypersecretion of Cortisol by the adrenal cortex produces Cushing's
syndrome. The condition is characterized by the breakdown of mus-
cle proteins and redistribution of body fat, resulting in spindly arms
and legs accompanied by a rounded "moon face" (Figure 1 3.15e),
"bufjfalo hump" on the back, and pendulous (hanging-) abdomen.
The elevated level ot Cortisol causes hyperglycemia, osteoporosis,
weakness, hypertension, increased susceptibility to infection, de-
creased resistance to stress, and mood swings.
I lyposccretion of glucocorticoids and aldosterone causes Addi-
son's disease. Symptoms include mental lethargy, anorexia, nausea
and vomiting; weight loss, hypoglycemia, and muscular weakness.
Loss of aldosterone leads to elevated potassium and decreased
sodium in the blood; low blood pressure; dehydration; and de-
creased cardiac output, cardiac arrhythmias, and even cardiac arrest
The skin may have a "bronzed" appearance that often is mistaken
■ a suntan. Such was true in the case of President John
Kennedy, whose Addison's disease was known to only a few while
was alive.
Usually benign tumors of the adrenal medulla, called pheocb
mocytomas (fe'-o-kro'-mo-si-TO-mas; pbeb- = dusky; chromo-
eolor; cyta- = cell), cause oversecretion of epinephrine and note;
nephrine. The result is a prolonged version of the fight-or-flffl
response: rapid heart rate, headache, high blood pressure, his
levels of glucose in blood and urine, an elevated basal metabolic rat
(BMR), flushed face, nervousness, sweating, and decreased gastroiq]
testinal motility.
Pancreatic Islet Disorders
The most common endocrine disorder is diabetes mellitus (Ml
tus; melli- : : honey sweetened), caused by an inability either to pi
duce or to use insulin. Diabetes mellitus is the fourth leading cadi
of death by disease in the United States, primarily because of it
damage to the cardiovascular system. Because insulin is unavailal
to aid the movement of glucose into body cells, blood glucose IctJ
is high and glucose "spills" into the urine (glueosuria). Hallmarks
diabetes mellitus are the three "polys"; polyuria, excessive urine
duction due to an inability of the kidneys to reabsorb water; /w/dj
siti, excessive thirst; and polyphagia, excessive eating.
Both genetic and environmental factors contribute to oi
the two types of diabetes mellitus — Type 1 and Type 2 — but d
exact mechanisms are still unknown. In Type 1 diabetes insulin Id
is low because the person's immune system destroys the pimcreaffl
beta cells. Most commonly, Type 1 diabetes develops in pcuji
younger than age 20, though it persists throughout life. By the time
symptoms arise, 80-90% of the islet beta cells have been des
Because insulin is not present to aid the entry of glucose up
body cells, most cells use fatty acids to produce ATP, Stores
triglycerides in adipose tissue are broken down to fatty acids
glycerol. The byproducts of fatty acid breakdown — organic m
called ketones or ketone bodies — accumulate. Buildup of kctoi
causes blood pH to fall, a condition known as ketoacidosis. Unl<
treated quickly, ketoacidosis can cause death.
Type 2 diabetes is much more common than Type L It
often occurs in people who are over 35 and overweight. The
glucose levels in the blood often can be controlled by diet, exei
and weight loss. Sometimes, an antidiabetic drug such as
(Diabeta^) is used to stimulate secretion of insulin by pain
beta cells. Although some Type 2 diabetics need insulin, mar
a sufficient amount (or even a surplus) of insulin in the blood. !-
these people, diabetes arises not from a shortage of insulin but
cause target cells become less sensitive, to it.
Hyperimiilinism most often results when a diabetic injects
much insulin. The main symptom is hypoglycemia, decreased
glucose level, which occurs because the excess insulin stimulates
much uptake of glucose by body cells. When blood glue,
neurons are deprived of the steady supply of glucose they m
function effectively. Severe hypoglycemia leads to mental disoijj
tation, convulsions, unconsciousness, and shock and is termd
sulin shock. Death can occur quickly unless blood glucose is
I FOCUS
Ion
■homeostasis
Body System
?or all body
systems
[Integumentary
[system
Skeletal system
Muscular system
s?
Nervous system
Cardiovascular
[system
Lymphatic
system and
Immunity
Respiratory
system
Digestive system
binary system
reductive
systems
The Endocrine System
Contribution of the Endocrine System
«, e t«,m hnrmones of the endocrine system regulate the activity and
^^zzxzzs~~ m re9ulate me,abo " sn " up,ake *
Jjlucose, and molecules used for ATP production by body colls.
Androgens stimulate the growth o, ax,„.ry end pubic heir and activation „« sebaceous glands.
Snocyte-stlmulatmg hormone <MSH) can osus. darttening o. the stun.
„„„ran growth hormone (hOH, and MM*** ^SSSSSSSZ ^^
.rogens cause closure o, *»££~^«W * "» £, a „ P d other mlne ra,s horn
and growth of the skeleton.
epinephrine end norepinephrine *^^^ZZ£££2 7<ZZZ"*
the proper level o, %£%£Z^£^VZ£. — -* ■»- -
mo U nTaXsrl^P^" syndesis and thereby help maintain muscle mass.
Several hormones, especially thyroid hormones, insulin, and IGFs, influence grown, and dove,-
opment of the nervous system.
Erythropoietin ( EPO, promotee .he production o, red bio* >££££££!£?
other stresses.
?:— m rm=^^
responses.
red blood cells.
cium, Leptin suppresses appetite.
ADH aidosterone, and atria, natriuretic peptide (ANP) adjust the rate of ioss of water and ions
J^^SS^ reguiating biood vo.ume and ion ieveis in the b.ood.
Hypothalamic releasing and •^rT^tSSS^SS
from the mammary glands. 339
340 Chapter 13 The Endocrine System
MEDICAL TERMINOLOGY AND CONDITIONS
Gynecomastia (gi-ne'-ko-iWAS-te-a; gyneco- = woman; mast- =
breast) Excessive development of mammary glands in a male.
Sometimes a tumor of the adrenal gland may secrete sufficient
amounts of estrogen to cause the condition.
Hirmtimt (HFR-soo-tizm; birsut- = shaggy) Presence of excessive
bodily and facial hair in a male pattern, especially in women;
may be due to excess androgen production caused by tumors or
drugs.
Thyroid crisis (storm) A severe state of hyperthyroidism that can be
life-threatening. It is characterized by high body temperature,
rapid heart rate, high blood pressure, gastrointestinal sj
toms (abdominal pain, vomiting, diarrhea), agitation, trem<
confusion, seizures, and possibly coma.
Virilizing adenoma {aden- — gland; -own — tumor) Tumor of
adrenal gland that liberates excessive androgens, causing vj
ism (maseulinization) in females. Occasionally, adrenal mi
cells liberate estrogens to the extent that a male patient
ops gynecomastia. Such a tumor is called a feminizing at
noma.
STUDY OUTLINE
Introduction (p. 316)
1. The nervous system controls homeostasis through the release
of neurotransmitters; the endocrine system uses hormones.
2. The nervous system causes muscles to contract and glands to
secrete; the endocrine system affects virtually all body tissues*
3. Exocrine glands (sweat, oil, mucous, digestive) secrete their prod-
ucts through ducts into body cavities or onto body surfaces,
4. The endocrine system consists of endocrine glands and several
organs that contain endocrine tissue.
Hormone Action (p. 317)
1. Endocrine glands secrete hormones into interstitial fluid.
Then, the hormones diffuse into the blood.
2 . II o r m on e s a fleet o n I y s pec i fi c ta rge t cells th a t h a vc t f l c p ro p er
receptors to bind a given hormone.
3. Chemically, hormones are either lipid-soluble (steroids, thyroid
hormones, and nitric oxide) or water-soluble (modified amino
acids, peptides, and proteins).
4. Lipid-soluble hormones affect cell function by altering gene
expression.
5. Water-soluble hormones alter cell function by activating
plasma membrane receptors, which elicit production of a sec-
ond messenger that activates various proteins inside the cell.
6. Hormone secretion is controlled by signals from the nervous
system, chemical changes in the blood, and other hormones.
Hypothalamus and Pituitary Gland (p, 319)
1. The pituitary gland is attached to the hypothalamus and con-
sists of two lobes: the anterior pituitary and the posterior
pituitary.
2. Hormones of the pituitary gland are controlled by inhibiting and
releasing hormones produced by die hypothalamus. The hy-
pophyseal portal veins cany hypothalamic releasing and inhibit
hormones from die hypothalamus to the anterior pituitary
3. The anterior pituitary consists of cells that produce hi
growth hormone (hGH), prolactin (PRL), thyroid-stimulat
hormone (TSI I), follicle-stimulating hormone (FS1 1), luteii
ing hormone (LH) f adrenocorticotropic hormone (AC
and melanoeyte-stiinulating hormone (MSTT),
4. Human growth hormone (hGH) stimulates body gro^
through insulinlike growth factors (IGFs) and is controlled
growth hormone-releasing hormone (GHR1I) and ^ro\
hormone-inhibiting hormone (GHIH).
5. TSH regulates thyroid gland activities and is controlled hy
rotropin-releasing hormone (TRH).
6. FSH and LH regulate activities of the gonads— ovaries
testes — and arc controlled by gonadotropin-releasing borrtu
(GnRTI),
7. PRL helps stimulate milk production. Prolactin-inhibituig
monc (PITT) suppresses release of prolactin. Prolactin-releaJ
hormone (PRH) stimulates a rise in prolactin level Jnm
pregnancy.
8. ACTH regulates activities of the adrenal cortex and is
trolled by cortieotropin-releasmg hormone (CRH).
9. The posterior pituitary contains axon terminals of tieurosj
tory cells whose cell bodies are in the hypothalamus,
10, Hormones made in die hypothalamus and released in the
terior pituitary include oxytocin, which stimulates comma
ol the uterus and ejection of milk from the breasts, and
uretic hormone (ADH), which stimulates water rcabsor
by the kidneys and constriction of arterioles,
11. Oxytocin secretion is stimulated by uterine stretching ami
suckling during nursing; ADH secretion is controlled bv
osmotic pressure of the blood and blood volume.
12, [able I U on page 323 summarizes the hormones of the ante-
rior and posterior pituitary.
Thyroid Gland (p- 323)
1, The thyroid gland is located below the larynx.
1 2 It consists of thyroid follicles composed of follicular cells, which
secrete the thyroid hormones thyroxine (T 4 ) and triiodothyro-
nine (TV), and parafollicular cells, which secrete calcitonin.
I Thyroid hormones regulate oxygen use and metabolic rate, cel-
lular metabolism, and growth and development. Secretion is
trolled byTRH from the hypothalamus and thyroid-stimu-
lating hormone (TSTI) from the anterior pituitary.
I Calcitonin (CT) can lower the blood level of calcium; its secre-
tion is controlled by the level of calcium in the blood.
Parathyroid Glands (p. 325)
I, The parathyroid glands are embedded on the posterior surfaces
of the thyroid.
I Parathyroid hormone (PTH) regulates the homeostasis of cal-
cium, magnesium, and phosphate by increasing blood calcium
and magnesium levels and decreasing blood phosphate level,
H secretion is controlled by the level of calcium in the
blood,
mcreatlc Islets (p. 327)
The pancreas lies in the curve of the duodenum. It has both
endocrine and exocrine functions.
I The endocrine portion consists of pancreatic islets or islets of
Langerhans, which are made up of alpha and beta cells.
I, Alpha cells secrete glucagon and beta cells secrete insulin,
! ueagon increases blood glucose level and insulin decreases
blood glucose level. Secretion of both hormones is controlled
by die level of glucose in the blood.
jrenal Glands (p. 329)
[ The adrenal glands are located above die kidneys. They consist
in outer cortex and inner medulla.
The adrenal cortex is divided into three zones: The outer zone
is mineralocorticoids; the middle zone secretes glucocor-
ticoids; and the inner zone secretes androgens.
Mineralocorticoids (mainly aldosterone) increase sodium and
water reabsorption and decrease potassium reabsorption. Se-
cretion is controlled by the renin -angiotensin-aldosterone
pathway
\ t Glucocorticoids (mainly Cortisol) promote normal metabolism,
help resist stress, and decrease inflammation. Secretion is con-
trolled by ACTH.
; Androgens secreted by the adrenal cortex stimulate growth of
axillary and pubic hair, aid the prepubertal growth spurt, and
on tribute to libido.
I I he adrenal medullae secrete epinephrine and norepinephrine
(NE), which are released under stress.
Self-Quiz 341
Ovaries and Testes (p. 333)
1. The ovaries are located in the pelvic cavity and produce estro-
gens, progesterone, and inhibin. These sex hormones regulate
the menstrual cycle, maintain pregnancy, and prepare the
mammary glands for lactation. They also help establish and
maintain the feminine body shape.
2. The testes lie inside the scrotum and produce testosterone and
inhibin. Testosterone regulates production of sperm and stimu-
lates the development and maintenance of masculine character-
istics such as beard growth and deepening of the voice,
Pineal Gland (p. 334)
1. Hie pineal gland, attached to the roof of the third ventricle in
die brain, secretes melatonin, which contributes to setting the
body's biological clock.
Other Hormones (p. 334)
L Body tissues other than those normally classified as endocrine
glands contain endocrine tissue and secrete hormones. These
include the gastrointestinal tract, placenta, kidneys, skin, and
heart. (See Table 13.2 on page 334.)
2, Prostaglandins and leukotrieiies act locally in most body
tissues.
The Stress Response (p. 335)
1. Stressors include surgical operations, poisons, infections, fever,
and strong emotional responses,
2. If stress is extreme, it triggers the stress response, which occurs
in three stages: the (ight-or- flight response, resistance reaction,
and exhaustion.
3. The fight-or-fiight response is initiated by nerve impulses from
the hypothalamus to the sympathetic division of the autonomic
nervous system and the adrenal medullae. This response
rapidly increases circulation and promotes ATP production.
4. The resistance reaction is initiated by releasing hormones se-
creted by the hypothalamus. Resistance reactions are longer
lasting and accelerate breakdown reactions to provide ATP for
counteracting stress.
5. Exhaustion results from depletion of body resources during the
resistance stage.
6. Stress may trigger certain diseases by inhibiting die immune
system.
Aging and the Endocrine System (p, 336)
1. Although some endocrine glands shrink as we get older, their
performance may or may not be compromised.
2. Production of human growth hormone, thyroid hormones, cord-
sol, aldosterone, and estrogens decrease with advancing age.
3. With aging, the blood levels of TH I, LI 1, FSH, and PTH rise,
4. The pancreas releases insulin more slowly with age, and recep-
tor sensitivity to glucose declines.
5. After puberty, thymus size begins to decrease, and thymic tis-
sue is replaced by adipose and areolar comuv i tissue.
342 Chapter 1 3 The Endocrine System
v
SELF-QUIZ
1. Which of the following is NOT true concerning hormones?
a. Responses to hormones are generally slower and longer
lasting than the responses stimulated by the nervous system.
b. Hormones are generally controlled by negative feedback
systems.
c. The hypothalamus inhibits the release of some hormones,
d. Most hormones are released steadily throughout the day.
e. Hormone secretion is determined by the body's need to
maintain homeostasis.
2. Which of the following statements concerning hormone action
is NOT true?
a. Hormones bring about changes in metabolic activities of cells
b. Target cells must have receptors for a hormone.
c. Lipid-soluble hormones may directly enter target cells and
activate the genes.
d. A hormone that attaches to a membrane receptor is termed
the first messenger,
e. ATP is a common second messenger in target cells.
3. Which of the following statements is NOT true?
a. The secretion of hormones by the anterior pituitary is
controlled by hypothalamic releasing hormones.
b. The pituitary is attached to the hypothalamus by the
infundibulum,
c. Hypophyseal portal veins connect die posterior pituitary to
the hypothalamus.
d* The anterior pituitary constitutes the majority of the pitu-
itary gland,
e. The posterior pituitary releases hormones produced by ncu-
rosecre tory ce 1 1 s o f th e h ypoth a 1 a in us.
4. The hormone that promotes milk release from the mammary
glands and that stimulates the uterus to contract is
a, oxytocin b. prolactin c, rclaxin
d. calcitonin e, follicle-stimulating hormone
5. The gland that prepares die body to react to stress by releasing
> pinephrine is the
a. posterior pituitary b. anterior pituitary c. pineal
d. adrenal e. pancreas
6. To help prevent rejection, organ transplant patients could be
given
a. gl ti COCO rti cc > i d s
b. calcitonin
c. m i n era] ocorticoi ds
d« thymopoietin
e. melanocyte-stimulating hormone
7* A female who is sluggish, gaining weight, and has a low bo|
temperature may be having problems with her
a. pancreas b. parathyroid glands c adrenal mcdullac
d. ovaries e. thyroid gland
8. Destruction of the alpha cells of the pancreas might result in
a. hypoglycemia b. seasonal affective disorder
c. acromegaly d. hyperglycemia
e. decreased urine output
9. Which of the following is NOT true concerning humd
growth hormone (hGH) and insulinlike growth factors?
a. They stimulate protein synthesis.
b. They have one primary target tissue in the body.
c. They stimulate skeletal muscle growth,
d. Hyposecretion in childhood results in dwarfism.
e. Hypoglycemia can stimulate the release of hGH from die
pituitary gland.
10. Follicle-stimulating hormone (FS11) acts on —
luteinizing hormone (LI I) acts on .
a. the ovaries, the testes b. the testes, die ovaries
c. the ovaries and testes, the ovaries and testes
d. the ovaries, the mammary glands
e. the ovaries and uterus, the testes
11. An injection of adrenocorticotropic hormone (ACTH) wot
a. stimulate the ovaries
b. influence thyroid gland activity
c stimulate die release of Cortisol
d. cause uterine contractions
e. decrease urine output
12. Which of the following is NOT true concerning glucocorn
coids?
a. They help to control electrolyte balance,
b. They help provide resistance to stress.
c. They help promote normal metabolism.
d. They are anti-inflammatory hormones.
e. They provide the body with energy,
1 3 . M i n era 1 o c or t i coi d s
a. help prevent die loss of potassium from the body
b. are secreted based on the renin -angiotensin -aldosterone
pathway
c. increase die rate of sodium loss in the urine
d. are involved in lowering die body's blood pressure
e. increase water loss from the body by increasing urine pro-
duction
14. A lack of iodine in the diet affects the production of which hor-
mone?
a. calcitonin
b. parathyroid hormone
c. aldosterone
d. thyroxin'.'
e. glucagon
15, Which of the following hormones with opposite effects are
correctly paired?
a. parathyroid hormone, thyroid hormones
b. parathyroid hormone, calcitonin
c. oxytocin, glucocorticoids
d. aldosterone, oxytocin
e. thyroid hormones, thymosin
L. The hormone that normally functions as part of a positive
feedback cycle is
a. Cortisol
b. testosterone
c. oxytocin
d. insulin
e. thyroxine
1 17, Match the following:
a. produce thyroid hormones
b. secrete insulin
c. release hormones into
capillaries of the posterior
pituitary
_d. store oxytocin
_e. secrete glucagon
_ f. produce calcitonin
_g. secrete steroid hormones
A. posterior pituitary
R, adrenal cortex
C. follicular cells
D. alpha cells
E. parafollicular cells
E beta cells
G. neurosecretory cells
Critical Thinking Applications 343
18. In a dehydrated person, you would expect to sec an increased
release of
a. parathyroid hormone
b. aldosterone
e. insulin
d- melatonin
e. inhihin
19. Match the following:
_a, diabetes insipidus A. hypersecretion of glucocorticoids
b. diabetes mellitus B. hyposecretion of antidiuretic
_C myxedema hormone
_ _d. Gushing* C - hyposecretion of insulin
syndrome D. hyposecretion of parathyroid
_e. Addison's disease hormone
f tetany ^* hyposecretion of thyroid hormone
E hyposecretion of glucocorticoids
20. For each of the following, indicate at which stage they would
occur as part of the stress response. Use F to indicate fight-or-
ilight response, R to indicate resistance reaction, and E to indi-
cate exhaustion.
_ a. initiated by hypothalamic releasing hormones
_ b. initiated by the sympathetic division of the autonomic
nervous system
c. immediately prepares die body for action
_ d. increases Cortisol release
e. short-lived response
_ £ bodv resources become depleted
. g. increased release of many hormones that ensure a contin-
ued ATP supply
. h. failure of pancreatic beta cells
i. nonessential bodv functions inhibited
CRITICAL THINKING APPLICATIONS
Patrick was diagnosed with diabetes mellitus on his 8th birth-
fly His 65-year-old aunt was just diagnosed with diabetes also.
Patrick is having a hard time understanding why he needs in-
jections, while his aunt controls her blood sugar with diet and
oral medication. Why is his aunt's treatment different from his?
Eddie, the tallest man in the world, suffered from an oversecre-
i of a pituitary hormone his entire life. Eddie died in early
adulthood due to the effects of his condition. Name Eddie's
condition and explain its cause.
Melatonin has been suggested as a possible aid for sleeping
problems due to jet lag and rotating work schedules (shift
work). It may also be involved in seasonal affective disorder
(SAD), Explain how melatonin may affect sleeping.
Brian is in a 50-mile bike-a-thon on a hot summer day. He's
breathing dust at the back of the pack, lies sweating profusely,
and now he's lost his water bottle. Brian is not having a good
time. How will his hormones respond to decreased intake of
water and the stress of die situation?
344 Chapter 13 The Endocrine System
ANSWERS TO FIGURE QUESTIONS
13.1 Secretions of endocrine glands diffuse into interstitial fluid
and then into the blood; exocrine secretions flow into ducts
that lead into body cavities or to the body surface.
13.2 RNA molecules are synthesized when genes are expressed
(transcribed), and then mRNA codes for the synthesis of
protein molecules.
13.3 It brings the message of the first messenger, the water-soluble
hormone, into the cell.
13.4 The posterior pituitary releases hormones synthesized in the
hypothalamus.
13.5 Oxytocin's target cells are in the uterus and mammary
glands.
13.6 Absorption of a large glass of water in the intestines would
decrease the osmotic pressure (concentration of solutes) of
your blood plasma, turning off secretion of ADH and de-
creasing the ADH level in your blood.
13.7 Follicular cells secrete T 3 and T 4 ; parafollicular cells secrete
calcitonin.
13.8 Thyroid hormones increase metabolic rate.
13.9 PTII increases the number and activity of osteoclasts.
13.10 larger tissues for PTII are hone and kidneys; the target cis* I
sue for calcitonin is bone; the target tissue for calcitriol is the)
gastrointestinal (GI) tract.
13.11 The pancreas is both an endocrine and an exocrine gland.
13.12 Glucagon is considered an "anti-insulin" hormone bean
has several effects that are opposite to those of insulin.
13.13 The outer zone of the adrenal cortex secretes mineralocoid
coids, the middle zone secretes glucocorticoids, and their
ner zone secretes adrenal androgens.
13.14 Because drugs that block ACM 7 , lower blood pressure, th(
are used to treat high blood pressure (hypertension),
13.15 In Graves disease, antibodies are produced that mimic j
action of 1 SIT.
THE CARDIOVASCULAR
SYSTEM: BLOOD
chapter 14
ill you know?
X he American Red Cross calls
blood donation "The Gift of Life. n But many people
waving a blood donation, or transfusion, worry about
the safety of the blood they will receive. Many viruses
can be transmitted easily from donor to patient
through a transfusion* Because the blood supply is
carefully screened for the presence of viruses such as
HIV (the virus that causes AIDS) and the viruses
that cause Hepatitis B and Hepatitis C 7 the risk of
receiving unsafe blood is extremely low. For example,
the risk of receiving a unit of HIV-positive blood is
I in 1.5 million.
Focus on Wellness, page 359
www.wiley.com/college/apcentral
71
he cardiovascular
system (cardio- = heart; 1
-vascular = blood or
blood vessels) consists
of three interrelated
components: blood, the heart, and blood vessels. The
focus of this chapter is blood; the next two chapters will
cover the heart and blood vessels, respectively.
Functionally, the cardiovascular system transports
substances to and from body cells. To perform its func-
tions, blood must circulate throughout the body. The
heart serves as the pump for circulation, and blood ves-
sels carry blood from the heart to body cells and from
bodv cells back to the heart.
The branch of science concerned with the study
of blood, blood-forming tissues, and the disorders
associated with them is hematology (hem-a-TOL-6-je;
hemo- or hemato- — blood; -logy = study of).
looking back to move ahead
» Blood Tissue (page 90)
* Positive Feedback System (page 8)
• Phagocytosis (page 51)
345
346 Chapter 14 The Cardiovascular System: Blood
FUNCTIONS OF BLOOD
objective • List and describe the functions of blood*
Blood, a liquid connective tissue, has three general functions:
transportation, regulation, and protection.
1. Transportation. Blood transports oxygen from the lungs
to cells throughout the body and carbon dioxide (a waste
product of cellular respiration; see Chapter 20) from the
cells to the lungs. It also carries nutrients from the gas-
trointestinal tract to body cells, heat and waste products
away from cells, and hormones from endocrine glands to
other body cells.
2. Regulation, Blood helps regulate the pH of body fluids.
The heat-absorbing and coolant properties of the water
in blood plasma (see page 30) and its variable rate of flow
through the skin help adjust body temperature. Blood
osmotic pressure also influences the water content of
1.
2.
Protection. Blood clots (becomes gel-like) in response to
an injury, which protects against its excessive loss from
the cardiovascular system. In addition, white blood cells
protect against disease by carrying on phagocytosis and
producing proteins called antibodies. Blood contains ad-
ditional proteins, called interferons and complement,
that also help protect against disease.
CHECKPOINT
Name several substances transported by blood.
I low is blood protective?
COMPONENTS OF
WHOLE BLOOD
objective • Discuss the formation, components,
and functions of whole blood.
Blood is denser and more viscous (thicker) than water. The
temperature of blood is about 38°C (100.4°F). Its pH is
slightly alkaline, ranging from 7.35 to 7.45. Blood constitutes
about 8% of the total body weight. The blood volume is 5 to
6 liters (1,5 gal) in an average-sized adult male and 4 to 5
liters (1.2 gal) in an average-sized adult female. The differ-
ence in volume is due to differences in body size.
Whole blood is composed of two portions: (1) blood
plasma^ a liquid that contains dissolved substances, and (2)
formed elements, which are cells and cell fragments. If a sam-
ple of blood is centrifuged (spun at high speed) in a small
glass tube, the cells sink to the bottom of the tube and the
lighter-weight blood plasma forms a layer on top (Fig
14.1a). Blood is about 45% formed elements and V) {
plasma. Normally, more than 99% of the formed element
are red blood cells (RBCs). The percentage of total bloc
volume occupied by red blood cells is termed the hematoi
(he-ALAT-6-krit). Pale, colorless white blood cells (WBQ
and platelets occupy less than 1% of total blood volurm
They form a very thin layer, called the huffy coat, between
packed RBCs and blood plasma in centrifuged blood. Pig;
14.11) shows the composition of blood plasma and the num-
bers of the various types of formed elements in blood.
Blood Plasma
When the formed elements are removed from blood, a straw]
colored liquid called blood plasma (or simply phis
remains. Plasma is about 91,5% water, 7%> proteins, ai
1.5% solutes other than proteins. Proteins in the blood,
plasma proteins, are synthesized mainly by the liver. The m<
plentiful plasma proteins are the albumins, which account
for about 54% of all plasma proteins. Among other functi
albumins help maintain proper blood osmotic pressure,
which is an important factor in the exchange of fluids at
capillary walls. Globulins, which compose 38% of plasm
proteins, include antibodies, defensive proteins produce
during certain immune responses. Fibrinogen makes
about 7% of plasma proteins and is a key protein in forJ
tion of blood clots. Other solutes in plasma include e|
trolytes, nutrients, gases, regulatory substances such
enzymes and hormones, vitamins, and waste products.
Formed Elements j
The firmed elements oi Fthe blood are the following (see
14.2 on page 348):
I. Red blood cells
IL White blood cells
A. Granular leukocytes (contain conspicuous grari
that are visible tinder a light microscope after sumiii
1. Neutrophils
2* Eosinophils
3, Basophils
B. Agranular leukocytes (no granules are visible under
light microscope after staining)
1. T and B lymphocytes and natural killer cells
2. Monocytes
m. Platelets
Formation of Blood Cells
The process by which the formed elements of blood ■
is called hemopoiesis (he-mo-poy-E-sis; -poiesis = md
Components of Whole Blood 347
Fig urt'
14.1 Components of blood in a normal adult.
Blood is a connective tissue that consists of blood plasma (liquid) plus formed elements:
^ red blood cells, white blood cells, and platelets.
Plasma (55%) -
Red blood cells -
(45%)
;
Buffy coat,
composed of
white blood cells
and platelets
(a) Appearance of centrifuged blood
Whole blood
8%
Other fluids
and tissues
92%
r r/
Blood plasma
55%
i-/
Formed elements
BODY WEIGHT
VOLUME
-
Functions of Blood
1. Transport of oxygen, carbon dioxide, nutrients,
hormones, heat, and wastes,
2. Regulation of pH, body temperature, and water
content of cells.
3. Protection against blood loss through clotting
4. Protection against disease through platelets;
phagocytic white blood cells; and proteins such
as antibodies, complement, and interferons.
Proteins
7%
Water
91,5%
Other solutes
1.5*
PLASMA (weight)
Platelets
150,000-400,000
^
White blood cells
5,000-1 0,000
Red blood cells
4.8-5.4 million
m
<&
FORMED ELEMENTS
(number per uL)
(b) Components of blood
Which formed elements of blood are most numerous?
r'
Albumins 54%
Globulins 38%
Fibrinogen 7%
All others 1%
Electrolytes
Nutrients
Gases
Regulatory
substances
Waste products
SOLUTES
Neutrophils
60-70%
e e cc c
eeee
Lymphocytes^!
20-25%
Basophils
0.5-1.0%
WHITE BLOOD CELLS
348 Chapter 14 The Cardiovascular System; Blood
Figure 14,2 Origin, development, and structure of blood cells. Some of the generations of some cell lines have been omitted
& bi
Blood cell production, called hemopoiesis, occurs in red bone marrow after birth.
Key:
Formed elements of circulating blood
Tissue cells
Pluripotent stem ce
Myeloid stem eel
Reticulocyte
Red blood eel!
(erythrocyte)
Megakaryocyte
p&r
Lymphoid stem eel
Platelets
(thrombocytes)
Eosinophil
ft
Basophil
— White blood cells
(granular leukocytes;
Neutrophil ( Monocyte T lymphocyte B lymphocyte
(T cell) (B cell)
White blood cells
(agranular leukocytes)
Macrophage
4
Plasma
(a) Origin of bfood celts from pluripotent stem cells
Before birth, hemopoiesis first occurs in the yolk sac of an
embryo and later in die liver, spleen, thymus, and lymph
nodes of a fetus. In the last three months before birth, red
bone marrow becomes the primary site of hemopoiesis and
continues as the source of blood cells after birth and
throughout life.
lied bone marrow is a highly vascularized connective
tissue located in the microscopic spaces between trabeculae
of spongy bone tissue. It is present chiefly in bones of the
axial skeleton, pectoral and pelvic girdles, and the proximal
epiphyses of the humerus and femur. About 0.05 — 0. 1 % of
red bone marrow cells are cells called pluripotent stem cells
(ploo-RIP-6-tent; pluri- — several). Pluripotent stem cells
arc cells that have the capacity to develop into many differa
types of cells (Figure 14.2a).
In response to stimulation by specific hormones, plurij
tent stem cells generate two other types of stem cells .Ji,
have the capacity to develop into fewer types of cells: wye/oil
stem cells and lymphoid stem cells (Figure 14.2a), Myeloid sti
cells begin their development in red bone marrow and tlif
entiate into several types of cells from which red blood a
platelets, eosinophils, basophils, neutrophils, and nion
develop. Lymphoid stem cells begin their development in
bone marrow but complete it in lymphatic tissues.
differentiate into cells from which the T and B lymphi
develop.
ft
.:
nan
ttaj
Components of Whole Blood 349
142QX
Basophil
Neutrophil
Platelet
White blood eel
Red blood cell
Blood Smear
Platelet
all1600x
Monocyte Lymphocyte
(b) Photomicrographs
What percentage of body weight is made up of blood?
Red blood ceil
•■ •ii
ti Blood Cells
Structure Red blood cells (RBCs) or erythrocytes
-MTH-rd-sits; erytbro- = red; -cyte = cell) contain the
en-carrying protein hemoglobin, which is a pigment
lives whole blood its red color. Hemoglobin also
jnsports about 23% of the carbon dioxide in die blood. A
by adult male has about 5.4 million red blood cells per
liter (jjlL) of blood, and a healthy adult female has
Lteut 4.8 million. (One drop of blood is about 50/x,L.)
this difference reflects differences in body size. To
ain normal numbers of RBCs, new mature cells must
die circulation at the astonishing rate of at least 2
million per second, a pace that balances the equally high
rate of RBC destruction. RBCs are biconcave (concave on
both sides) discs averaging about Bfim* in diameter. Mature
RBCs lack a nucleus and other organelles and can neither
reproduce nor carry on extensive metabolic activities.
However, all of their internal space is available for oxv;
and carbon dioxide transport. Essentially, RBCs consist of
•a selectively permeable plasma membrane, cytosol, and
hemoglobin.
*l/i.m = 1/25,000 of an inch or 1/10,000 of a centimeter (cm), which is
3/1 000 of a millimeter (mm).
350 Chapter 14 The Cardiovascular System: Blood
Since a biconcave disc has a much greater surface area for
its volume (compared to a sphere or a cube), this shape pro-
vides a large surface area for the diffusion of gas molecules
into and out of a RBC.
Delivery of oxygen to muscles is a limiting factor in mus-
cular feats. As a result, increasing the oxygen- carrying
capacity of the blood enhances athletic performance,
especially in endurance events. Because RBCs are the
main transport vehicle for oxygen, athletes have tried
several means of increasing their RBC count, causing
induced polycythemia, to gain a competitive edge. Ath-
letes have enhanced their RBC production by injecting
Epoetin alfa (Procrit® or Epogen®), a drug that is used to
treat anemia by stimulating the production of RBCs by red
bone marrow. Practices that increase the number of RBCs
are dangerous because they raise the viscosity of the blood,
which increases the resistance to blood flow and makes the
blood more difficult for the heart to pump. Increased vis-
cosity also contributes to high blood pressure and in-
creased risk of stroke. During the 1980s, at least IS com-
petitive cyclists died from heart attacks or strokes linked to
suspected use of Epoetin alia. Although the International
Olympics Committee bans Epoetin alfa use, enforcement
is difficult because the drug is identical to naturally occur-
ring EPO,
RBC Like Cycle Red blood cells live only about 120 dl
because of wear and tear on their plasma membranes asm
squeeze through blood capillaries. Worn-out red blood celt
are removed from circulation as follows (Figure 14.3).
O Macrophages in the spleen, liver, and red bone inarroj
phagocytize ruptured and worn-out red blood cells, spl.ii
ing apart the heme and globin portions of hemoglobin,
Q The protein globin is broken down into amino ack
which can be reused by body cells to synthesize oi
proteins.
Q Iron removed from die heme portion associates with
plasma protein transferrin (trans-FER-in; trt
across;/r/T" = iron), which acts as a transporter
Q The iron-transferrin complex is then carried to
bone marrow, where RBC precursor cells use it in he
moglobin synthesis. Iron is needed for the heme p(
tion of the hemoglobin molecule, and amino acids
needed for the globin portion. Vitamin B ]2 is
needed for synthesis of hemoglobin. (The lining; oft
stomach must produce a protein called intrinsic facm
absorption of dietary vitamin Bi 2 from the GI tract ii
the blood.)
^ Erythropoiesis in red bone marrow results in the
tion of red blood cells, which enter the circulation.
Figure 14.3 Formation and destruction of red blood cells, and the recycling of hemoglobin components.
The rate of RBC formation by red bone marrow equals the rate of RBC destruction by macrophages.
:■> Th
Q Red blood cell
death and
phagocytosis
Macrophage in
spleen, liver, or
red bone marrow
Urine
^ Bilirubin
Ox
irobflinogen
, r
Stercobilin
lM Large
& intestine
Feces
n bile
?
What substance is responsible for the brown color of feces?
When iron is removed from heme, the non-iron portion
of heme is converted to hiliverdin (bil'-i-VER-din), a
green pigment, and then into bilirubin (bU'-i-ROO~bin),
a yellow-orange pigment. Bilirubin enters the blood and
is" transported to the liver. Within the liver, bilirubin is
secreted by liver cells into bile, which passes into the
small intestine and then into the large intestine,
A In the large intestine, bacteria convert bilirubin into uro-
bilinogen (ur-6-bI-LIN-6-jen). Some urobilinogen is ab-
sorbed back into the blood, converted to a yellow pig-
ment called urobilin (ur-6-BI-lin), and excreted in urine.
Most urobilinogen is eliminated in feces in the form of a
brown pigment called stercobilim (ster'-ko-BI-Iin), which
gives feces its characteristic color.
Because free iron ions bind to and damage molecules in
or in the blood, transferrin acts as a protective "protein
tort" during transport of iron ions. As a result, plasma con-
tinually no free iron.
i:|!C Production The formation of blood cells in general
h called hemopoiesis; the formation of just RBCs is termed
\mthmpoksis (e-rith'-ro-poy-E-sis). Near the end of ery-
Lopoiesis, an RBC precursor ejects its nucleus and becomes
thnlocyte (re-TIK-ii-lo-sIt; see Figure 14.2a). Loss of the
Lbs causes the center of the cell to indent, producing the
(RBCs distinctive biconcave shape. Reticulocytes, which are
[about 34% hemoglobin and retain some mitochondria, ribo-
soitics, and endoplasmic reticulum, pass from red bone mar-
taw into the bloodstream. Reticulocytes usually develop into
BCs within 1 to 2 days after their release from bone
Normally, erythropoiesis and destruction of RBCs
cd at die same pace. If the oxygen-carrying capacity of
! blood falls because erythropoiesis is not keeping up with
tC destruction, RBC production increases (Figure 14.4).
ontrolled condition in this particular negative feed-
loop is the amount of oxygen delivered to the kid-
(and thus to body tissues in general). Hypoxia
POKS-e-a), a deficiency of oxygen, stimulates increased
, of erythropoietin (e-rith'-ro-POY-e-tin), or EPO, a
one made by the kidneys. EPO circulates through the
ro the red bone marrow, where it stimulates erythro-
,. The larger the number of RBCs in die blood, the
the oxygen delivery to the tissues (Figure 14.4). A per-
mli prolonged hypoxia may develop a life-threatening
Udirion called cyanosis (si'-a-NOsis), characterized by a
purple skin coloration most easily seen in the nails and
Lcous membranes. Oxygen delivery may fall due to anemia
er-than-normal number of RBCs or reduced quantity
of hemoglobin) or circulatory problems that reduce blood
to tissues.
A test that measures the rate of erythropoiesis is called a
Oocyte count. This and several other tests related to red
cells are explained in Table 14.1.
Components of Whole Blood 351
Figure 14.4 Negative feedback regulation of erythropoiesis (red
blood cell formation).
V The main stimulus for erythropoiesis is hypoxia, a decrease in
the oxygen-carrying capacity of the blood.
Some stimulus disrupts
homeostasis by
Decreasing
Oxygen delivery to kid-
neys (and other tissues)
Kidney celts that secrete
erythropoietin
detect low
oxygen level
screie
Input
\
i
Increased erythropoietin
secreted into blood
/*
Control center
V
Proerythroblasts in
red bone marrow
mature more quickly
into reticulocytes
Output
Return to homeostasis
when oxygen delivery
to kidneys increases to
normal
More reticulocytes
enter circulating blood
2
Larger number
of RBCs in
circulation
Increased oxygen
delivery to tissues
S What is the term for cellular oxygen deficiency?
J
Premature newborns often exhibit anemia, due in part
to inadequate production of erythropoietin. During the
first weeks after birth, the liver, not the kidneys, produces
most EPO. Because die liver is less sensitive than the kid-
neys to hypoxia, newborns have a smaller IPC ) response to
anemia than do adults. In addition, in infants, fetal hemo-
globin is converted into adult hemoglobin; since fetal he*
moglobin carries up to 30% more oxygen, the loss of fetal
hemoglobin makes die anemia worse.
352 Chapter 14 The Cardiovascular System: Blood
Table 14.1 Obtaining Blood Samples and Common Medical Tests Involving Blood
Obtaining Blood Samples
A. Venipuncture. This most frequently used procedure involves
withdrawal of blood from a vein using a sterile needle and
syringe. (Veins are used instead of arteries because they are
closer to the skin, more readily accessible, and contain blood
at a much lower pressure.) A commonfy used vein is the
median cubital vein in front of the elbow (see Figure 16.14 on
page 407). A tourniquet is wrapped around the arm, which
stops blood flow through the veins and makes the veins below
the tourniquet stand out.
B. Fingerstick. Using a sterile needle or lancet, a drop or two of
capillary blood is taken from a finger, earlobe, or heel.
C. Arterial stick. Sample is most often taken from radial artery
in the wrist or femoral artery in the thigh (see Figure 16.9 on
page 397).
Testing Blood Samples
A. Reticulocyte count (indicates the rate of erythropoiesis)
Normal value: 0,5% to 1.5%.
Abnormal values; A high reticulocyte count might indicate
the presence of bleeding or hemolysis (rupture of
erythrocytes), or it may be the response of someone who is
iron deficient. Low reticulocyte count in the presence of
anemia might indicate a malfunction of the red bone marrow,
owing to a nutritional deficiency, pernicious anemia, or
leukemia.
B, Hematocrit (the percentage of red blood cells in blood). A
hematocrit of 40 means that 40% of the volume of blood is
composed of RBCs.
Normal values:
Females: 38 to 46 (average 42)
Males: 40 to 54 (average 47)
Abnormal values: The test is used to diagnose anemia,
polycythemia (an increased percentage of red blood cells),
and abnormal states of hydration. Anemia may vary from mild
(hematocrit of 35) to severe (hematocrit of less than 15).
Athletes often have a higher-than-average hematocrit, and
the average hematocrit of persons living at high altitude is
greater than that of persons living at sea level.
C. Differential white blood cell count (the percentage of each type of
white blood cells in a sample of 100 WBCs)
Normal values:
Type of WBC Percentage
neutrophils 60-70
eosinophils 2-4
basophils 0.5-1
lymphocytes 20-25
monocytes 3-8
Abnormal values: A high neutrophil count might result from bacterial
infections, burns, stress, or inflammation; a low neutrophil count might be
caused by radiation, certain drugs, vitamin B 12 deficiency, or systemic
lupus erythematosus (SLE) (see page 93). A high eosinophil count could
indicate allergic reactions, parasitic infections, autoimmune disease, or
adrenal insufficiency; a low eosinophil count could be caused by certain
drugs, stress, or Cushing's syndrome. Basophils could be elevated in some
types of allergic responses, leukemias, cancers, and hyperthyroidism;
decreases in basophils couid occur during pregnancy, ovulation, stress,
and hyperthyroidism. High lymphocyte counts couid indicate viral
infections, immune diseases, and some leukemias; low lymphocyte counls
might occur as a result of prolonged severe illness, high steroid levels, and
immunosuppression. A high monocyte count could result from certain viral
or fungal infections, tuberculosis (TB) S some leukemias, and chronic
diseases; low monocyte levels rarely occur.
D. Complete blood count (CBC) (provides information about the formed
elements in blood)*
Normal values:
RBC count
Hemoglobin
Hematocrit
WBC count
Differential white
blood count
Platelet count 1 50,000-400,000 pi
Abnormal values: Increased RBC count, hemoglobin, and hematocrit
occur in polycythemia, congenital heart disease, and hypoxia; decreas
RBC count, hemoglobin, and hematocrit occur in hemorrhage and
certain types of anemia. Increased WBC counts may indicate acute or
chronic infections, trauma, leukemia, or stress (see also above under
differential white blood cell count). Decreased WBC counts could
indicate anemia and viral infections (see also above under differential
white blood cell count). High platelet counts may indicate cancer,
trauma, or cirrhosis. Low platelet counts could indicate anemia, allergic.]
conditions, or hemorrhage.
About 5.4 million per /A. in males
About 4.8 million per iiL in females
14-18 g/dl in adult males
12-16 g/dl in adult females
See B
5,000- 10,000 per fil
SeeC
'Not all components of a CBC have been included.
Ute Blood Cells
mC Structure and Types Unlike red blood cells,
Mte blood cells (WBCs) or leukocytes (LOO-ko-sJts;
- = white) have nuclei and do not contain hemoglobin.
ICs arc classified as either granular or agranular, depend-
|?on whether diey contain chemical-filled cytoplasmic gran-
le (vesicles) that are made visible by staining when viewed
i^h a light microscope. The gramdar leukocytes include
itlrophils (NOO-tro-fils), eosinophils (S -6-SIN-o-fils),
I basophils (BA-so-fils), The agranular leukocytes include
nphoijtes and monocytes (MON-6-sits). (See Tabic 14 2
jrthe sizes and microscopic characteristics of WBCs,)
1C FUNCTIONS The skin and mucous membranes of the
ky are continuously exposed to microbes (microscopic or-
Ksms), such as bacteria, some of which are capable of
/ading deeper tissues and causing disease. Once microbes
Iter the body, some WBCs combat them by phagocytosis,
I others produce antibodies. Neutrophils respond first to
|teria1 invasion, carrying on phagocytosis and releasing en-
ics such as lysozyme that destroy certain bacteria. Mono-
tes take longer to reach the site of infection than neu-
ils, but they eventually arrive in larger numbers.
Monocytes that migrate into infected tissues develop into
[Is called wandering macrophages (macro- = large; -phages
titers), which can phagocytic many more microbes than
itrophils. They also clean up cellular debris following an
fiction.
Eosinophils leave the capillaries and enter interstitial
id, They release enzymes that combat inflammation in
lergic reactions. Eosinophils also phagocytize antigen-anti-
ly complexes and are effective against certain parasitic
ps. A high eosinophil count often indicates an allergic
idition or a parasitic infection.
Basophils are also involved in inflammatory and allergic
actions. They leave capillaries, enter tissues, and can liber-
heparin, histamine, and serotonin. These substances in-
iify the inflammatory reaction and are involved in allergic
urns.
Three types of lymphocytes — B cells, T cells, and nat-
I killer (NK) cells — are the major combatants in immune
ises, which are described in detail in Chapter 17. B
levelop into plasma cells, which produce antibodies that
ielp destroy bacteria and inactivate their toxins. T cells at-
iruses, fungi, transplanted cells, cancer cells, and some
Lteria. Natural killer cells attack a wide variety of infectious
lies and certain spontaneously arising tumor cells.
White blood cells and other nucleated body cells have
:ins, called major histocompatibility (MHC) antigens,
, riding from their plasma membrane into the extracellu-
[r fluid. These "cell identity markers" are unique for each
(except identical twins). Although RBCs (which do
Components of Whole Blood 353
not possess nuclei) possess blood group antigens, they lack
the MHC antigens. An incompatible tissue transplant is
rejected by the recipient due, in part, to differences in donor
and recipient MHC" antigens. The MHC antigens are used to
type tissues to identify compatible donors and recipients and
thus reduce the*chance of tissue rejection.
WBC LIFE Span Red blood cells outnumber white blood
cells about 700 to 1. There arc normally about 5000 to 10,000
WBCs per fih of blood. Bacteria have continuous access to
the body through the mouth, nose, and pores of die skin. Fur-
thermore, many cells, especially diose of epithelial tissue, age
and die daily, and their remains must be removed. However, a
WBC can phagocytic only a certain amount of material be-
fore it interferes with the WBCs own metabolic activities.
Thus, the life span of most WBCs is only a few days. During
a period of infection, many WBCs live only a few hours.
However, some B and T cells remain in die body for years.
Leukocytosis (loo'-ko-si- TO-sis), an increase in the num-
ber of WBCs, is a normal, protective response to stresses
such as invading microbes, strenuous exercise, anesthesia,
and surgery. Leukocytosis usually indicates an inflammation
or infection. Because each type of white blood eell plays a
different role, determining the percentage of each type in the
blood assists in diagnosing die condition. This test, called a
differential white blood cell count, measures the number of
each kind of white cell in a sample of 100 white blood cells
(see Table 14.1). An abnormally low level of white blood cells
(below 5000 cells//xL), called leukopenia (loo'-ko-PE-ne-a),
is never beneficial; it may be caused by exposure to radiation,
shock, and certain chemotherapeutic agents,
WBC Production Leukocytes develop in red bone mar-
row. As shown in Figure 14.2a, monocytes and granular
leukocytes develop from a myeloid stem cell. T and B cells
develop from a lymphoid stem cell
Platelets
Pluripotent stem cells also differentiate into cells that pro-
duce platelets (see Figure 14.2a). Some myeloid stem cells
develop into cells called megak an obi lists, which in turn trans-
form into megakaryocytes, huge cells diat splinter into
2000-3000 fragments in the red bone marrow and then en-
ter the bloodstream. Each fragment, enclosed by a piece ol
the megakaryocyte cell membrane, is a platelet. Between
150,000 and 400,000 platelets are present in each /iL of
blood. Platelets are disc-shaped, have a diameter of 2-4 /xm,
and exhibit many vesicles hut no nucleus. When blood ves-
sels are damaged, platelets help stop blood loss by forming a
platelet plug. Their vesicles also contain chemicals that pro-
mote blood clotting (both processes are described shortly).
After their short life span of 5-9 days, platelets are removed
by macrophages in the spleen and liver.
354 Chapter 14 The Cardiovascular System: Blood
A bone marrow transplant is the replacement of cancer-
ous or abnormal red bone marrow with healthy red bone
marrow in order to establish normal blood cell counts.
The defective red bone marrow is destroyed by high doses
of chemotherapy and whole body radiation just before the
transplant takes place* These treatments kill the cancer
cells and destroy the patient's immune system in order to
decrease the chance of transplant rejection. The red bone
marrow from a donor is usually removed from the hip
bone under general anesthesia with a syringe and is then
Injected into the recipient's vein, much like a blood trans-
fusion. The injected marrow migrates to the recipient's red
bone marrow cavities, and the stem cells in the marrow
multiply. If all goes well, the recipient's red bone marrow
is replaced entirely by healthy, noncancerous cells.
Bone marrow transplants have been used to treat aplas-
tic anemia, certain types of leukemia, severe combined im-
munodeficiency disease (SCID), Hodgkin's disease, non-
Hodgkin's lymphoma, multiple myeloma, thalassemia,
sickle-cell disease, breast cancer, ovarian cancer, testicular
cancer, and hemolytic anemia. However, there are some
drawbacks. Since the recipient's white blood cells have been
completely destroyed by chemotherapy and radiation, the
patient is extremely vulnerable to infection. (It takes about
2-3 weeks for transplanted bone marrow to produce
enough white blood cells to protect against infection.) In
addition, transplanted red bone marrow may produce T
lymphocytes that attack the recipient's tissues. Another
drawback is that patients must take immunosuppressive
drugs for life. Because these drugs reduce the level of im-
mune system activity, they increase die risk of infection,
Table 14.2 presents a summary of the formed elements in
blood.
■ CHECKPOINT
3. Briefly outline the process of hemopoiesis.
4. What is erythropoiesis? How does erythropoiesis affect
hematocrit? What factors speed up and slow down
erythropoiesis?
5. What functions do neutrophils, eosinophils, basophils,
monocytes, 1$ cells, T cells, and natural killer cells perform?
6. How are leukocytosis and leukopenia different? What is
a differential white blood cell count?
HEMOSTASIS
OBJECTIVE • Describe the various mechanisms that
prevent blood loss.
Hemostasis (he'-rno-STA-sis; stasis = standing still) is a se-
quence of responses that stops bleeding when blood vessels
are injured, (Be sure not to confuse the two words hemo
and homeostasis.) The hemostatic response must be quick,
calized to the region of damage, and carefully controlled
Three mechanisms can reduce loss of blood from bloodves-
sels: (1) vascular spasm, (2) platelet plug formation, and (3j
blood ciptting (coagulation). When successful, hemostasis
prevents hemorrhage (JIEM-or-ij; -rhage = burst forth), die
loss of a large amount of blood from the vessels. Hemostasis
can prevent hemorrhage from smaller blood vessels, but era
tensive hemorrhage from larger vessels usually requires m
ical intervention.
Vascular Spasm
When a blood vessel is damaged, the smooth muscle in
wall contracts immediately, a response called a vascm
spasm. Vascular spasm reduces blood loss for several minute
to several hours, during which time the other hemostat
mechanisms begin to operate. The spasm is probably cai
by damage to the smooth muscle and by reflexes initiated
pain receptors. As platelets accumulate at the damaged sit
they release chemicals that enhance vasoconstriction (narrcn
ingofa blood vessel), thus maintaining the vascular spasm.
Platelet Plug Formation
When platelets come into contact with parts of a damai
blood vessel, their characteristics change drastically and th«
quickly come together to form a platelet plug that helps
the gap in the injured blood vessel wall. Platelet plug fori
tion occurs as follows.
Initially, platelets contact and stick to parts of a damage
blood vessel, such as collagen fibers. Then, they interact ijj
one another and begin to liberate the chemicals. The chei
cals activate nearby platelets and sustain the vascular spaj
which decreases blood flow through the injured vessel.
release of platelet chemicals makes other platelets in the
sticky, and the stickiness of the newly recruited and activat
platelets causes them to stick to the originally acuva:
platelets. Eventually, a large number of platelets forms a
called a platelet plug. A platelet plug can slop blood It
completely if the hole in a blood vessel is small enough.
Blood Clotting
Normally, blood remains in its liquid form as long as it sta
within its vessels. If it is withdrawn from the body, howev
it thickens and forms a gel. Eventually, the gel separates fcjj
the liquid. The straw-colored liquid, called serum, is sim
plasma minus the clotting proteins. The gel is called a d
and consists of a network of insoluble protein fibers !
fibrin in which the formed elements of blood are trap
(see figure 14.5).
Hemostasia 355
Table 14.2 Summary of Formed Elements in Blood
Name and Appearance
Number
Characteristics*
fled Blood Cells (RBCs) or 4.8 million//iL in females; 7- 8 ^m diameter, biconcave discs,
Erythrocytes 5.4 million//iL in males. without a nucleus; live for about
%
mite Blood Cells (WBCs)
or Leukocytes
Granular Leukocytes
Neutrophils
e
Eosinophils
Basophils
Agranular Leukocytes
Lymphocytes (T cells,
B cells, and natural
killer cells)
5000-10,000//iL
60-70% of all WBCs.
2-4% of all WBCs.
0.5-1% of all WBCs.
20-25% of all WBCs.
Monocytes
3-8% of all WBCs,
1 50,000 -400,000//*!-.
120 days.
Most live for a few hours to a few
days. 1
10-12 ^m diameter; nucleus has
2-5 lobes connected by thin strands
of chromatin; cytoplasm has very fine,
pale lilac granules.
10-12 jLtm diameter; nucleus has 2
or 3 lobes; large, red-orange granules
fill the cytoplasm.
8-10 M m diameter; nucleus has
2 lobes; large cytoplasmic granules
appear deep blue-purple.
Small lymphocytes are 6-9 /xm in
diameter; large lymphocytes are
10-14 p.m in diameter; nucleus is round
or slightly indented; cytoplasm forms a rim
around the nucleus that looks sky blue; the
larger the cell, the more cytoplasm is visible.
12-20 /xm diameter; nucleus is kidney
shaped or horseshoe shaped; cytoplasm
is blue-gray and has foamy appearance.
2-4 ^m diameter cell fragments that live
for 5-9 days; contain many vesicles but
no nucleus.
'Colors are those seen when using Wright's stain.
fSome lymphocytes, called T and B memory cells, can live for many years once they are established
Functions
Hemoglobin within RBCs
transports most of the oxygen
and part of the carbon dixoide in
the blood.
Combat pathogens and
other foreign substances that
enter the body.
Phagocytosis, Destruction of bacteria
with lysozyme, defensins, and strong
oxidants, such as superoxide anion,
hydrogen peroxide, and hypochlorite
anion.
Combat the effects of histamine in
allergic reactions, phagocytize
antigen - antibody complexes,
and destroy certain parasitic worms.
Liberate heparin, histamine, and
serotonin in allergic reactions that
intensify the overall inflammatory
response.
Mediate immune responses,
including antigen -antibody
reactions. B cells develop into
plasma cells, which secrete
antibodies. T cells attack invading
viruses, cancer cells, and
transplanted tissue cells. Natural
killer cells attack a wide variety of
infectious microbes and certain
spontaneously arising tumor cells.
Phagocytosis (after transforming into
fixed or wandering macrophages).
Form platelet plug in hemostasis;
release chemicals that promote
vascular spasm and blood clotting.
I he process of clot formation, called clotting (cmgula-
is a series of chemical reactions that culminates in the
formation of fibrin threads. If blood clots too easily, the re-
i can be thrombosis, clotting in an unbroken blood vessel
Frie blood takes too long to clot, hemorrhage can result.
Clotting is a complex process in which various chemicals
hown as clotting factors activate each other. Clotting (coag-
ulation) factors include calcium ions (Ca 2+ ), several enzymes
that are made by liver cells and released into the blood, and
various molecules associated with platelets or released by
damaged tissues. Many clotting factors are identified by
Roman numerals. Clotting occurs in three stages (Figure
14.5):
356 Chapter 14 The Cardiovascular System: Blood
Figure 14.5 Blood clotting.
During blood clotting, the clotting factors activate each other, re-
- suiting in a cascade of reactions that includes positive feed-
back cycles.
(a) Extrinsic pathway
Tissue trauma
(b) Intrinsic pathway
Blood trauma
Damaged
endothelial cells
expose collagen
fibers
Damaged— -JljcQ
platelets
Clotting factors
and Ca 2 *
Activated
platelets
o
PROTHROMBIN
PROTHROMBINASE
[c) Common
pathway
THROMBIN
FIBRINOGEN
Loose fibrin
threads
STRENGTHENED
FIBRIN THREADS
Red blood cell
\- Fibrin threads
s What is the outcome of stage 1 of clotting?
Prothrombinase is formed.
Prothrombinase converts prothrombin (a plasma proteii
formed by the liver with the help of vitamin K) into th|
enzyme thrombin.
Thrombin converts soluble fibrinogen (another plasi
protein formed by the liver) into insoluble fibrin. Fibril
forms the threads of the clot. (Cigarette smoke contati
substances that interfere with fibrin formation.)
Prothrombinase can be formed in two ways, bv either tht
extrinsic or the intrinsic pathway of blood clotting (Fij
14.5). The extrinsic pathway of blood clotting occurs rapilj
within seconds. It is so-named because damaged tissue eel
release a tissue protein called tissue factor (TF) into
blood from outside (extrinsic to) blood vessels (figure 14Jjj
Following several additional reactions that require eal
ions (Ca 2+ ) and several clotting factors, tissue factor is even-
tually converted into prothrombinase. This completes the . .
trinsic pathway.
The intrinsic pathway of blood clotting (Figure 14,
more complex than the extrinsic pathway, and it occurs mof
slowly, usually requiring several minutes. The intrinsic pa
way is so-named because its activators are either in di
contact with blood or contained within (intrinsic to)
blood. If endothelial cells lining the blood vessels 1<
roughened or damaged, blood can come in contact with cof]
lagen fibers in the adjacent connective tissue. Such ami;
activates clotting factors. In addition, trauma to endothelffl
cells activates platelets, causing them to release phospholipids
that can also activate certain clotting factors. After several
additional reactions that require C a and several clot™
factors, prothrombinase is formed. Once formed, thrombin
activates more platelets, resulting in the release of more 'I
platelet phospholipids, an example of a positive feeclb
cycle.
Clot formation occurs locally; it does not extend beyoi
the wound site into the general circulation. One reason
this is that fibrin has the ability to absorb and inactivate up
nearly 90% of the thrombin formed from prothrombin
helps stop the spread of thrombin into the blood and thus in-]
hibits clotting except at the wound.
Clot Refraction and Blood Vessel Repair
Once a clot is formed, it plugs die ruptured area of the
vessel and thus stops blood loss. Clot retraction is the conj
idation or tightening of the fibrin clot. The fibrin threads
tached to the damaged surfaces of the blood vessel gnu
contract as platelets pull on them. As the clot retracts, it pnl
the edges of the damaged vessel closer together, deereas
the risk of further damage. Permanent repair of the bli
vessel can then take place. In time, fibroblasts form co
tive tissue in the ruptured area, and new endothelial cells i
pair the vessel lining'.
Hemostatic Control Mechanisms
iv times a day little clots start to form, often at a site of
[minor roughness inside a blood vessel, Usually, small,
inappropriate clots dissolve in a process called fibrinolysis
ilV-bri-NIOL-i-sis). When a clot is formed, an inactive
i m enzyme called plasminogen is incorporated into the
Both body tissues and blood contain substances that can
ate plasminogen to plasmin, an active plasma enzyme.
Once plasmin is formed, it can dissolve the clot by digesting
[brin threads. Plasmin also dissolves clots at sites of damage
the damage is repaired.
nts who are at increased risk of forming blood clots
-,i!v receive an anticoagulant drug, a substance that
uliiys, suppresses, or prevents blood clotting. Examples
■e heparin or warfarin. Heparin, an anticoagulant that is
,1 by mast cells and basophils, inhibits the conver-
sion of prothrombin to thrombin, thereby preventing
I clot formation. Heparin extracted from animal tis-
is often used to prevent clotting during hemodialysis
after open heart surgery. Coumadin® (warfarin sodium)
is an antagonist to vitamin K and thus blocks synthe-
four clotting factors. To prevent clotting in donated
blood, blood hanks and laboratories often add a substance
at removes Ca 2 ", for example, CPD (citrate phosphate
•ose).
Clotting in Bloodvessels
fespite fibrinolysis and the action of anticoagulants, blood
lots sometimes form within blood vessels. The endothelial
Eta of a blood vessel may be roughened as a result of
m?rosderosis (accumulation of tatty substances on arterial
Ms), trauma, or infection. These conditions also make the
jclets that are attracted to the rough spots more sticky.
Dots may also form in blood vessels when blood flows too
Jmvly. allowing clotting factors to accumulate in high
plough concentrations to initiate a clot.
lotting in an unbroken blood vessel is called thrombosis
L^,- = clot; -osis = a condition of). The clot itself, called
i thrombus, may dissolve spontaneously. If it remains intact,
Lever, the thrombus may become dislodged and be swept
n\ in the blood, A blood clot, bubble of air, tat from bro-
th tones, or a piece of debris transported by the blood-
.;n;mi is called an embolus (em- = in; -bolus - a mass; plural
tflwW). Because emboli often form in veins, where blood
lower, the most common site for the embolus to he-
me lodged is in the lungs, a condition called pulmonary
I mbolism. Massive emboli in the lungs may result in right
trtculnr failure and death in a few minutes or hours. An
embolus that breaks away from an arterial wall may lodge in
■mailer-diameter arterv downstream. If it blocks blood flow
Blood Groups and Blood Types 357
to the brain, kidney, or heart, the embolus can cause a stroke,
kidney failure, or heart attack, respectively.
In patients widi heart and blood vessel disease, the events
of hemostasis may occur even without external injury to a
blood vessel. At low doses, aspirin inhibits vasoconstric-
tion and platelet aggregation. It also reduces the chance of
thrombus formation, Due to these effects, aspirin reduces
the risk of" transient ischemic attacks (TIA), strokes, my-
ocardial infarction, and blockage of peripheral arteries.
Thrombolytic agents are chemical substances that are
injected into the body to dissolve blood clots that have al-
ready formed to restore circulation. They either directly
or indirectly activate plasminogen. The first thrombolytic
agent, approved in 1982 for dissolving clots in the coro-
nary arteries of the heart, was streptokinase, which is
produced by streptococcal bacteria. A genetically engi-
neered version of human tissue plasminogen activator
(tPA) is now used to treat both heart attacks and brain at-
tacks (strokes) that are caused by blood clots.
■ CHECKPOINT
7. What is hemostasis?
8. How do vascular spasm and platelet plug formation occur?
9. What is fibrinolysis? Why does blood rarely remain clot-
ted inside blood vessels?
BLOOD GROUPS AND
BLOOD TYPES
OBJECTIVE • Describe the ABO and Rh blood groups.
The surfaces of red blood cells contain a genetically deter-
mined assortment of antigens composed of glycolipids and
glycoproteins called agglutinogens (ag'-loo-TIN-o-jen/).
Based on the presence or absence of various antigens, blood
is categorized into different blood groups. Within a given
blood group there may be two or more different blood types.
There are at least 24 blood groups and more than 100 anti-
gens that can be detected on the surface of red blood cells.
Here we discuss two major blood groups; ABO and Rh.
ABO Blood Group
The ABO blood group is based on two antigens called A and
B (Figure 14.6). People whose RBCs display only antigen A
have type A blood. Those who have only antigen B are type
B. Individuals who have both A and B antigens are type AB,
and those who have neither antigen A nor B are type (). In
about 80% of the population, soluble antigens of the ABO
type appear in saliva and other body fluids, in which case
blood type can be identified from a sample of saliva. The in-
cidence of ABO blood types varies among different popula-
tion groups, as indicated in Table 14.3.
358 Chapter 14 The Cardiovascular System: Blood
Figure 14.6 Antigens and antibodies involved in the ABO blood grouping system.
~\ Your plasma does not contain antibodies that could react with the antigens on your red blood cells.
BLOOD TYPE
Red blood cells
TYPE AB
Both A and B antigens
TYPEO
Neither
A nor B antigen
Plasma
Anti-B Anti-A
antibody antibody
Which antibodies are found in type O blood?
Neither
antibody
Both anti-A and
anti-B antibodies
In addition to antigens on RBCs, blood plasma usually
contains antibodies or agglutinins (a-GLOO-ti-nins) that re-
act with the A or B antigens if the two arc mixed. These are
the anti-A antibody, which reacts with antigen A, and die
anti-B antibody, which reacts with antigen B. The antibodies
present in each of the four ABO blood types are also shown
in Figure 14.6. You do not have antibodies that react with
your ow r n antigens, but you do have antibodies for any anti-
gens that your RBCs lack. For example, if you have type A
blood, it means that you have A antigens on the surfaces of
your RBCs, but anti-B antibodies in your blood plasma. If
you had anti-A antibodies in your blood plasma, they would
attack your RBCs.
Rh Blood Group
The Rh blood group is so named because the Rh antigen was
first found in the blood of the rhesus monkey People whose
Table 1 4.3 Blood Types in the United States
Blood
Type (percentage)
Population Group
A
B
AB
Rh +
European American
45
40
11
4
85
African American
49
27
20
4
95
Korean
32
28
30
10
100
Japanese
31
38
21
10
100
Chinese
42
27
25
6
100
Native American
79
16
4
1
100
RBCs have die Rh antigen are designated Rh + (Rh positive);
those who lack the Rh antigen are designated Rh (Rh
tive). The percentages of Rh + and Rh" individuals in vari|
populations are shown in Table 14 3. Under normal cm
stances, plasma does not contain anti-Rh antibodies, If
Rh person receives an Rli + blood transfusion, howevi
immune system starts to make anti-Rh antibodies that
remain in the blood.
Transfusions |
Despite the differences in RBC antigens, blood is the m
easily shared of human tissues, saving many thousands
lives every year through transfusions. A transfusion (tnu
FU-zhun) is the transfer of whole blood or blood com]
nents (red blood cells only or plasma only) into the hlooc
stream. Most often a transfusion is given to alleviate anemia
or when blood volume is low, for example, after a severe heitij
orrhage.
In an incompatible blood transfusion, antibodies in
recipient's plasma bind to the antigens on the donated RB(
When these antigen-antibody complexes form, they m
hemolysis and release hemoglobin into the plasma. Co
what happens if a person with type A blood receives ;i trans*
fusion of type B blood. In this situation, two things ar
happen. First, the anti-B antibodies in the recipient's plasnuu
can bind to the B antigens on the donors RBCs, causing he-
molysis. Second, the anti-A antibodies in the donors plasir.-
can bind to the A antigens on the recipient s RIK o
ond reaction is usually not serious because the donor's anti-A
OCUS ON Wellnes
Blood Groups and Blood Types 359
rtiTt
Lifesty
Blood Circulation
It Flow
lany people fear cholesterol, an evil
Ltance that silently accumulates
tithin artery walls, year after year, un-
it eventually kills its victim by shut-
las off blood How to an important or-
nch as the heart or brain. But
sterol is not die only villain in this
bosclerosis melodrama. Cholesterol
^tributes to the formation of arterial
|i.ies, but the antagonist delivering
final blow is often a blood clot that
, in a blood vessel and subse-
jptly blocks a narrowed artery, cut-
ilf circulation to the tissues down-
Beam. Fortunately, many of the things
an do to keep your arteries healthy
i reduce your risk of blood clots.
Smoking
■ you need yet another reason to quit
ing, here it is: Smoking increases
fibrinogen levels. Increased
t)gen levels arc associated with
ased clotting risk. High fibrinogen
,i Is increase platelet aggregation and
n deposition, contributing to both
igand plaque deposition.
Exercise Regularly
Regular physical activity increases
plasma volume. An increase in plasma
volume means that the blood is more
dilute, or "thinner," with a lower per-
centage of red blood cells and less
fibrinogen, and consequently a reduced
risk of blood clotting. Several studies
have shown that vigorous exercise also
reduces platelet stickiness and enhances
fibrinolytic activity. These effects may
help to explain why active people are at
lower risk for heart disease and stroke. A
sedentary lifestyle, by contrast, leads to
increased clotting risk: Blood thickens as
plasma volume decreases. Sedentary
people have stickier platelets, which to-
gether with higher levels of fibrinogen
are more likely to form blood clots.
Cope Effectively with Stress
Prolonged mental stress impairs fibri-
nolysis by decreasing the activity of tis-
sue plasminogen activator (tPA), which
helps break down fibrinogen.
Eat a Heart-healthy Diet
People with high blood cholesterol lev-
els exhibit disturbances in coagulation,
fibrinolysis, and platelet behavior. Low-
ering blood lipid levels by diet or drug
therapy seems to reverse these distur-
bances and may be one way that a heart-
healthy lifestyle reduces heart disease
risk. An interesting study from Den-
mark found that volunteers who stuck to
a low-fat, high-fiber diet showed in-
creased fibrinolytic activity and thus a
reduced risk of blood clot formation.
A moderate alcohol intake (one to
two drinks per day) has been associated
with a reduced heart disease risk. This
risk reduction may he due in part to the
increase in tPA level observed in mod-
erate drinkers.
Why are people at risk for clot formation told to avoid sitting for extended
periods of time, such as on long airplane flights or ear rides?
nuijics become so diluted in die recipient's plasma that they
inot cause any significant hemolysis of die recipient's RBCs.
Beople with type AB blood do not have any anti-A or
iri-B antibodies in their plasma. They are sometimes called
recipients" because theoretically they can receive
,| from donors of all four ABO blood types. People with
e blood have neither A nor B antigens on their RBCs
are sometimes called "universal donors." Theoretically,
pse there are no antigens on their RBCs for antibodies to
E they can donate blood to all four ABO blood types.
1 persons requiring blood may receive only type O
as they have antibodies to both A and B antigens in
tenia. In practice, use of the terms universal recipient
niversal donor is misleading and dangerous. Blood
contains antigens and antibodies other than those associated
with the ABO system, and they can cause transfusion
problems. Thus, blood should always be carefully matched
before transfusion.
■ CHECKPOINT
10. What is the basis for distinguishing the various blood
groups?
11. What precautions must be taken before giving a blood
transfusion?
• • •
We will next direct our attention to die heart, die second ma-
jor component of the cardiovascular system.
360 Chapter 14 The Cardiovascular System: Blood
COMMON
DISORDERS
Anemia
Anemia is a condition in which the oxygen -carrying capacity of
blood is reduced, Many types of anemia exist; all are characterized
by reduced numbers of RBCs or a decreased amount of hemoglobin
in the blood. The person feels fatigued and is intolerant ot cold,
both of which are related to lack of oxygen needed for ATP and
heat production, Also, the skin appears pale, due to the low content
of red-colored hemoglobin circulating in skin blood vessels. Among
the most important types of anemia are the following:
• Iron-deficiency anemia, the most prevalent kind of anemia, is
caused by inadequate absorption of iron, excessive loss of iron,
or insufficient intake of iron. Women are at greater risk for
iron-deficiency anemia due to monthly menstrual blood loss.
• Pernicious anemia is caused by insufficient hemopoiesis resulting
from an inability of the stomach to produce intrinsic factor
(needed for absorption of dietary vitamin B I2 ).
• Hemorrhagic anemia is due to an excessive loss of RBCs through
bleeding resulting from large wounds, stomach ulcers, or espe-
c i a 1 1 y h ea vy mens tru a t i o n .
• In hemolytic anemia, RBC plasma membranes rupture prema-
turely. The condition may result from inherited defects or from
outside agents such as parasites, toxins, or antibodies from
incompatible transfused blood.
• Thalassemia (thal'-a-SE-me-a) is a group of hereditary
hemolytic anemias hi which there is an abnormality in one or
more of die four polypeptide chains of the hemoglobin mole-
cule. Thalassemia occurs primarily in populations from coun-
tries bordering the Mediterranean Sea,
• Aplastic anemia results from destruction of the red bone marrow
caused by toxins, gamma radiation, and certain medications
that inhibit enzymes needed for hemopoiesis.
Sickle Cell Disease
The RBCs of a person with sickle cell disease (SCD) contain Ilb-S,
an abnormal kind of hemoglobin. When T Tb-S gives up oxygen to
the interstitial fluid, it forms long, stiff, rodlike structures that bend
the erythrocyte into a sickle shape. The sickled cells rapture easily.
Even though die loss of RBCs stimulates erythropoiesis, it cannot
keep pace with hemolysis; hemolytic anemia is the result. Prolonged
oxygen reduction may eventually cause extensive tissue damage.
Hemophilia
Hemophilia (he-mo-FlL-e-a; -philia = loving) is an inherited defi-
ciency of clotting in which bleeding may occur spontaneously or
after only minor trauma* Different types of hemophilia are due
deficiencies of different blood clotting factors and exhibit
degrees of severity. Hemophilia is characterized by spontaneous
traumatic subcutaneous and intramuscular hemorrhaging, iu
bleeds, blood in the urine, and hemorrhages in joints that prodi
pain and tissue damage. Treatment involves transfusions of
plasma or concentrates of the deficient clotting factor to relieve
tendency to bleed.
Hemolytic Disease of the Newborn
Hemolytic disease of the newborn (HDN) is a problem that
suits from Rh incompatibility between a mother and her M
Normally, no direct contact occurs between maternal and fet
blood while a woman is pregnant. However, if a small aim mm
RfT blood leaks from the fetus through the placenta into
bloodstream of an Rh mother, her body starts to make antil
antibodies. Because the greatest possibility of fetal blood tnmi
occurs at delivery, the first-born baby typically is not affected
the mother becomes pregnant again, however, her anti-Rh ant
bodies, made after delivery of the first baby, can cross the |
centa and enter the bloodstream of the fetus. If the fetus is
there is no problem, because Rh blood does not have the
antigen. If, however, the fetus is Rh\ life-threatening/
(rupture of RBCs) is likely to occur in the fetal blood. By
trast, ABO incompatibility between a mother and her fetus rai
causes problems because the anti-A and anti-B antibodies do
cross the placenta,
HDN is prevented by giving all Rh women an injection of;
Rh antibodies called anti-Rh gamma globulin (RhoGAM) soon
every delivery, miscarriage, or abortion. These antibodies des
Rh antigens that are present so die mother doesn't produce her
antibodies ro rhcin, hi the case ol mi Rh mother, there arc in :
plications, because she cannot make anti-Rh antibodies.
Leukemia
The term leukemia (loo-KE-me-a; leuko- = white) refers!
group of red bone marrow cancers in which abnormal white I
cells multiply uncontrollably. The accumulation of the cane
white blood cells in red bone marrow interferes with the produc
of red blood cells, white blood cells, and platelets. As a i
oxygen-carrying capacity of the blood is reduced, an indivi
more susceptible to infection, and blood clotting is abnormal,
most leukemias, the cancerous white blood cells spread Co
lymph nodes, liver, and spleen, causing them to enlarge,
leukemias produce the usual symptoms of anemia (fatigue, mi
erance to cold, and pale skin). In addition, weight loss, km
night sweats, excessive bleeding, and recurrent infections maj
also occur.
Study Outline 361
MEDICAL TERMINOLOGY AND CONDITIONS
Autologous preoperative transfusion (aw-TOL-o-gus trans-FU-
zhun; auto- = self) Donating one's own blood in preparation
tfor surgery; can be done up to six weeks before elective surgery.
i > called predonation,
Hood hank A facility that collects and stores a supply of blood for
future use by the donor or others. Because blood banks have
now assumed additional and diverse functions (iinmunohema-
tology reference work, continuing medical education, bone and
tissue storage, and clinical consultation), they arc more appro-
priately referred to as centers of trans fusion medicine,
gnosis (si-a-NO-sis; cyano- = blue) Slightly bhiish/dark-purple
skin discoloration, most easily seen in the nail beds and mucous
membranes, due to an increased quantity of reduced hemoglo-
bin (hemoglobin not combined with oxygen) in systemic blood.
mhromatosis (he'-mo-kro'-ma-TO-sis; chroma = = color)
Disorder of iron metabolism characterized by excess deposits
of iron in tissues (especially the liver, heart, pituitary gland, go-
nads, and pancreas) that result in discoloration (bronzing) of
the skin, cirrhosis, diabetes meilitus, and bone and joint abnor-
malities.
Jaundice (jaund- = yellow) An abnormal yellowish discoloration
of the scferae of the eyes, skin, and mucous membranes due to
excess bilirubin (yellow-orange pigment) in the blood that is
produced when the heme pigment in aged red blood cells is
broken down.
Phlehotomisl (fle-ROT-6-inist; phleho- = vein; -tarn - z cut) A
technician who specializes in withdrawing blood.
Polycythemia (pol'-e-sI-THE-me-a) An abnormal increase in die
number of red blood cells in which hematocrit is above 55%,
the upper limit of normal.
Septicemia (sep'-ti-SE-me-a; septic- = decay; -emia = condition
of blood) An accumulation of toxins or disease-causing bacteria
in the blood. Also called blood poisoning.
Thrombocytopenia (tlirom' -bo-si '-to-PE-ne-a; -fienia == poverty)
Very low platelet count that results in a tendency to bleed from
capillaries.
fl| STUI
STUDY OUTLINE
Functions of Blood (p. 346)
Blood transports oxygen, carbon dioxide, nutrients, wastes, and
hormones.
It helps to regulate pi I, body temperature, and water content
of cells,
It prevents blood loss through clotting and combats microbes
and toxins through the action of certain phagocytic white blood
cells or specialized plasma proteins.
[ Components of Whole Blood (p. 346)
I, Physical characteristics of whole blood include a viscosity
greater than that of water, a temperature of 38°C (100.4 I c
and a pH range between 7.35 and 7.45.
[ Blood constitutes about 8% of body weight in an adult.
B. Blood consists of 55% plasma and 45% formed elements.
4, The formed elements in blood include red blood cells (erythro-
cytes), white blood cells (leukocytes), and platelets. Hematocrit
is the percentage of red blood cells in whole blood.
I Plasma contains 91.5% water, 7% proteins, and 1.5% solutes
other than proteins.
6, Principal solutes include proteins (albumins, globulins, fibrino-
gen), nutrients, hormones, respiratory gases, electrolytes, and
waste products.
■ Hemopoiesis, the formation of blood cells from pluripotent
stem cells, occurs in red bone marrow.
I Red blood cells (RliCs) are biconcave discs without nuclei that
I contain hemoglobin.
19, The (unction of the hemoglobin in red blood cells is to trans-
port oxygen.
11.
12.
10, Red blood cells live about 120 days. A healthy male has about
5.4 million RBCs/juL of blood and a healthy female has about
4.8 million RBCs/^L.
\Ftcr phagocytosis of aged red blood cells by macrophages, he-
moglobin is recycled.
RBC formation, called eiythropoiesis, occurs in adult red bone
marrow. It is stimulated by hypoxia, which stimulates release of
erythropoietin by the kidneys.
13. A reticulocyte count is a diagnostic test that indicates the rate
of erythropoicsis.
14. White blood cells (WBCs) arc nucleated cells. The two principal
types are granular leukocytes (neutrophils, eosinophils, basophils)
and agranular leukocytes (lymphocytes and monocytes).
15. The general function of WBCs is to combat inflammation and
infection. Neutrophils and macrophages (which develop from
monocytes) do so through phagocytosis.
16. Eosinophils combat inflammation in allergic reactions, phago-
cytize antigen -antibody complexes, and combat parasitic
worms; basophils liberate heparin, histamine, and serotonin in
allergic reactions that intensify the in 11 a mm a to ry response.
17. B cells (lymphocytes) are effective against bacteria and other tox-
ins. T cells (lymphocytes) are effective against viruses, fungi, and
cancer cells. Natural killer cells attack microbes and tumor cells.
18. White blood cells usually live for only a lew hours or a few
days. Normal blood contains 5000 to 10,000 WBCs/juh.
19. Platelets are disc-shaped cell fragments without nuclei.
20. Platelets are formed from megakaryocytes and take part in
hemostasia by forming a platelet plug.
21. Normal blood contains 150,000 to 400,000 platelets/juL.
362 Chapter 14 The Cardiovascular System: Blood
Hemostasia (p. 354)
1. Heniostasis, the stoppage of bleeding, involves vascular spasm,
platelet plug formation, and blood clotting.
2. In vascular spasm, the smooth muscle of a blood vessel wall
contracts,
3. Platelet plug formation is the aggregation of platelets to stop
hi ee ding,
4. A clot is a network of insoluble protein fibers (fibrin) in which
Formed elements of blood are trapped. The chemicals involved
in clotting are known as clotting - factors,
5. Blood clotting involves a series of reactions diat may be divided
into three stages: formation of prothrombinase by either the ex-
trinsic or intrinsic pathway, conversion of prothrombin into throm-
bin, and conversion of soluble fibrinogen into insoluble fibrin,
6. Normal coagulation involves clot retraction (tightening of
clot) and fibrinolysis (dissolution ol the clot),
7. Anticoagulants (for example, heparin) prevent clotting,
8. ("lotting; in an unbroken blood vessel is called thrombosis,
thrombus that moves from its site of origin is called an ei
bolus.
Blood Groups and Blood Types (p. 357)
1, In the ABO system, the antigens on RBCs, called A and B, &
termine blood type. Plasma contains antibodies termed and]
and and- 13 antibodies.
2. In the Rh system, individuals whose erythrocytes have
antigens are classified as Rh ' . Those who lack the nntigc
are
SELF-QUIZ
A. albumin
B. fibrinogen
C. intrinsic factor
D. immunoglobulins
E. plasma
K serum
G. reticulocytes
1. A hematocrit is
a. used to measure the quantity ot the five types of white blood
cells
b. essential for determining a person's blood type
c. the percentage of red blood cells in whole blood
d. also known as a platelet count
e. involved in blood clotting
2. Match the I oil owing:
a. involved in certain immune
responses
b. develop into mature red blood
cells
c. required for vitamin B l2
absorption
. d. most abundant plasma protein
e« blood after formed elements
are removed
f. plasma without clotting proteins
g. needed for blood clotting
3. In adults, erythropoiesis takes place in
a. the liver b. yellow bone marrow
d, lymphatic tissue e. the kidneys
4. Which of the following pigments contributes to the yellow
color in urine?
a. hemoglobin b. stcrcobilin c. biliverdin
d. urobilin c. bilirubin
5. Which of the following statements is NOT true about red
blood cells?
a. The production of red blood cells is known as erythropoiesis.
b. Red blood cells originate from pluripotent stem cells.
c. Hypoxia increases the production of red blood cells,
d. The liver takes part in the destruction and recycling of red
blood cell components.
e. Red blood cells have a lobed nucleus and granular cyto-
plasm.
red bone marrow
6. A primary function of red blood cells is to
a. maintain blood volume
b. help blood clot
e* provide immunity against some diseases
d. clean up debris following infection
e. deliver oxygen to the cells of die body
7. If a differential white blood cell count indicated higher
normal numbers of basophils, what may be occurring in
body?
a. chronic infection b. allergic reaction c, leukopenia
d* initial response to invading bacteria e, hcmostasis
8. In a person with blood type A, the antibodies that would nc
m ally be present in the plasma is (are)
a. and -A antibody
b« anti-B antibody
c. bodi anti-Aand anti-B antibodies
d. neither anti-A nor anti-B
e. anti-O antibodies
9. Hemolytic disease of the newborn (IIDN) may occur in the
tus of a second pregnancy if
a. the mother is Rh' 1 and the baby is Rh"
b. the mother is Rh 1 and the baby is Rh '
c. the mother is Rh " and the baby is Rh
d. the mother is Rh and the baby is Rh '
e. the hither is Rh" and the mother is Rh
10. Place the following steps of hemostasis in the correct order.
1. clot retraction 2. prothrombinase formed
3. fibrinolysis by plasmin 4. vascular spasm
5. conversion of prothrombin into thrombin
6, platelet plug formation
7* conversion ol fibrinogen into fibrin
a. 4,6,2,5,7, 1,3 b. 5,4,7,6,2,3, I j
c. 2,5,6,7, 1,4,3 d. 4,6,5,2,7, 1,3
e, 4,2,6,5,3,7,1
[1. Which of the following is NOT a normal component of blood
plasma?
a. albumins b. fibrinogen c. hemoglobin
d. immunoglobulins e. water
12. How does aspirin prevent thrombosis?
a. It inhibits platelet aggregation.
b. It interferes with Ca 24 absorption.
c. It inhibits the conversion of prothrombin to thrombin.
d. It acts as an enzyme to dissolve the thrombus.
e. It prevents the accumulation of fatty substances on blood
vessel walls.
I B, Match the following:
_ a. become wandering macrophages
b. produce antibodies
. c. are involved in allergic reactions
cl. first to respond to bacterial invasion
I e, destroy antigen -antibody
complexes; combat inflammation
A. neutrophils
B. eosinophils
C. basophils
D. lymphocytes
E. monocytes
li Hemostasia is
a. maintenance of a steady state in die body
b. an abnormal increase in leukocytes
c. a hereditary condition in which spontaneous hemorrhaging
occurs
i an anticoagulant produced by some leukocytes
e. a scries of events that stop bleeding
IS. Which of the following are mismatched?
a. white blood cell count below 5000 cells//xL, leukopenia
h. red blood cell count of 250,000 cdk/jt*L, normal adult male
t. white blood cell count above 10,000 cells/juL, leukocytosis
,|. platelet count of 300,000 cells/juL, normal adult
e, pH 7.4, normal blood
Answers to Figure Questions 363
16. An individual with type A blood has in die plasma
membranes of red blood cells,
a. antigen A b. antigen B c, major histocompatibility
antigen A d. antigen A and antigen Rh
e. antigen B and antigen Rh
17. Mrs. Smith arrives at a health clinic with her ill daughter Beth.
It is suspected that Beth has recently developed a bacterial in-
fection. It is likely that Betlvs leukocyte count will be
cells/ /uL of blood, a condition known as .
A differential white blood cell count shows an abnormally high
percentage of _•
a. 20,000, leukopenia, neutrophils
b. 5000, Leukocytosis, monocytes
c. 7000, leukocytosis, basophils
d. 2000, leukopenia, platelets
e. 20,000, leukocytosis, neutrophils
18. Clot retraction
a. draws torn edges of the damaged vessel closer together
b. dissolves clots c. is also known as the intrinsic pathway
d. involves the formation of fibrin from fibrinogen
e. helps prevent the formation of an embolus
19. Persons with blood type AB are sometimes referred to as uni-
versal recipients because their blood
a. lacks A and B antigens b. lacks ami -A and anti-B anti-
bodies c. possesses type O antigens and anti-O antibodies
d. has natural immunity to disease
c. contains A and B antigens
20. A thrombus that is being transported by die bloodstream is called
a. a plasma protein b. a platelet c. an embolus
d. a wandering macrophage e. a reticulocyte
I
CRITICAL THINKING APPLICATION
Biliary atresia is a condition in which the duets that transport
bile out of the liver do not function properly The whites of the
eyes in a baby with this condition have a yellow color. What is
die name of the yellow color and what is its cause?
A woman with blood type Rh 4 is married to a man with blood
Rh and is pregnant with their second child. What is the
chance the baby will have hemolytic disease of the newborn
(HDN)?
The school nurse sighed, "I just can't get used to the blue nail
polish the kids are wearing. 1 keep thinking there s a medical
problem." What type of problem might result in blue finger-
nails?
Very small numbers of pluripotent stem cells occur normally in
blood. If these cells could be isolated and grown in sufficient
numbers, what medically useful products could they producer
■\NSWERS TO FIGURE QUESTIONS
L 14,| Red blood cells are the most numerous formed element in
blood.
14,) Blood makes up 8% of body weight.
Stercobilin is responsible for the brown color of feces.
14-4 Hypoxia means cellular oxygen deficiency.
14.5 Prothrombinase is formed during stage 1 of clotting,
14*6 lype O blood has anti-A and anti-B antibodies.
chapter 1 5
THE CARDIOVASCULAR
SYSTEM: HEART
did you know?
W hat is a ^'heart-healthy diet"
and how does it help your heart? A heart-healthy
diet is one that is low in saturated fats, high in fruits
and vegetables, and contains plenty of fiber. A heart-
healthy diet encourages the consumption offish hut
warns against too much sugar and salt. A heart-
healthy diet is actually an a artefy- healthy diet"
because it is associated with health improvements that
reduce the risk of artery disease: better blood cholesterol
levels, better blood pressure, and less obesity. Coronary
artery disease is the leading cause of death from heart
disease, so by keeping the heart's arteries healthy, the
heart stays healthy as well.
Focus on Wellness, page 376
www.wiley.com/college/apcentral
f
In the last chapter we examined
the composition and functions of
blood. For blood to reach body cells
and exchange materials with them, it must be
constantly pumped by the heart through the body's blood
vessels, The heart beats about 100,000 times everyday,
which adds up to about 35 million beats in a year. The left
side of the heart pumps blood through an estimated 100,
km (60,000 mi) of blood vessels. The right side of the heart
pumps blood through the lungs, enabling blood to pidfe
oxygen and unload carbon dioxide. Even while you are
sleeping, your heart pumps 30 times its own weight each
minute, which amounts to about 5 liters (5.3 qt) to the I
and the same volume to die rest of the body. At diis rate, the
heart pumps more than 14,000 liters (3,600 gal) ofblooi
day, or 10 million liters (2.6 million gal) in a year. You don't
spend all your time sleeping, however, and your heart pum
more vigorously when you are active. Thus, the actual bl
volume die heart pumps in a single day is much larger,
The scientific study of the normal heart and the disc
associated with it is cardiology (kar'-de-OL-o-je;
uinlio- — heart; -fogy = study of). This chapter explores
design of the heart and the unique properties that permi
to pump for a lifetime without a moment of rest.
looking back to move ahead . . .
* Functions of Bfood (page 346)
* Membranes (page 90)
* MuscularTissue (page 90)
* Cardiac Muscle Tissue (page 186)
* Free Radicals (page 25)
* ANS Neurotransmitters (page 277)
364
Structure and Organization of the Heart 365
STRUCTURE AND ORGANIZATION
OF THE HEART
OBJECTIVES • Describe the location of the heart and
the structure and functions of the pericardium.
i Describe the layers of the heart wall and the chambers
of the heart.
1 1 Identify the major blood vessels that enter and exit the
heart.
i Describe the structure and functions of the valves of
the heart.
Location and Coverings of the Heart
The heart is situated between the two lungs in the thoracic
cavity, with about two-thirds of its mass lying to the left of
ie body's midline (Figure 15.1). Your heart is about the size
mr closed fist. The pointed end, the apex, is formed by
the tip of the left ventricle, a lower chamber of the heart, and
rest* on the diaphragm. The base of the heart is its posterior
ice. It is formed by the atria (upper chambers of the
heart), mostly the left atrium, into which the four pulmonary
veins open, and a portion of the right atrium that receives the
superior and inferior vena cavae (see Figure 15.3b), The base
lies opposite the apex*
The membrane that surrounds and protects the heart and
holds it in place is the pericardium (peri- = around). It con-
sists of two parts: the fibrous pericardium and the serous
pericardium (Figure 15.2). The outer fibrous pericardium is
a tough, inelastic, dense irregular connective tissue. It pre-
vents overstretching of the heart, provides protection, and
anchors the heart in place.
The inner serous pericardium is a thinner, more delicate
membrane that forms a double layer around the heart, The
outer parietal layer of die serous pericardium is fused to the
fibrous pericardium, and the inner visceral layer ot die
serous pericardium, also called the epicardium (epi- -- on top
of), adheres tightly to the surface of the heart Between the
parietal and visceral layers of the serous pericardium is a thin
film of fluid. This fluid, known as pericardial fluid, reduces
friction between the membranes as the heart moves. The
pericardial cavity is the space that contains the pericardial
fluid.
Figure 15.1 Position of the heart and associated blood vessels in the thoracic cavity. In this and
subsequent illustrations, vessels that carry oxygenated blood are colored red; vessels that carry deoxygenated
blood are colored blue.
The heart is located between the lungs, with about two-thirds of its mass to the left of the midline.
Superior vena cava
Right lung
Pleura (cut to
reveal lung inside)
Arch of aorta
Pulmonary trunk
Left lung
Apex of heart
Diaphragm
Anterior view of the heart in the thoracic cavity
5 )
What forms the base of the heart?
366 Chapter 15 The Cardiovascular System: Heart
Figure 15.2 Pericardium and heart wall.
| The pericardium is a sac that surrounds and protects the heart.
Pericardium
Epicardium
Myocardium
Endocardium
Pericardium
Heart wall
Intercalated*
discs
Opening of
transverse
tubule
Mitochondrion
Cardiac muscle fiber
Nucleus
Sarcolemma
Fibrous
pericardium
Parietal
layer of
serous
pericardium
Pericardia
cavity
Visceral layer
of serous pericardium
(epicardium)
(b) Cardiac muscle fibers
Endocardium
Coronary blood
vessels
Myocardium
(cardiac muscle)
Intercale
discs
Nucleus
Cardiac
muscle fib
(cell)
Striations
eonx
(a) Portion of pericardium and right ventricular heart wail
showing the divisions of the pericardium and layers of
the heart wall
(c) Longitudinal section of cardiac muscle tissue
Which layer is both a part of the pericardium and a part of the heart wall?
Inflammation of the pericardium is called pericarditis
(per'-i-kar-DI-tis). In one form of this condition, there is a
buildup of pericardial fluid. If a great deal of fluid accumu-
lates, this is a life-threatening condition because the fluid
compresses the heart, a condition called cardiac tmupojiade
(tam'-pon- AD). As a result of the compression, ventricu-
lar filling is decreased, cardiac output is reduced, venous
return to the heart is diminished, blood presure falls, and
breathing is difficult.
Heart Wall
The wall of the heart (Figure 15.2a) is composed of three lay-
ers: epicardium (external layer), myocardium (middle layer),
and endocardium (inner layer). The epicardium, which is
also known as the visceral layer of serous pericardium, is the
thin, transparent outer layer of the walk It is composed
mesothelium and connective tissue.
The myocardium (myo- — muscle) consists of cardial
muscle tissue, which constitutes the bulk of the heart. Tl
tissue is found only in the heart and is specialized in stmctd
and function. The myocardium is responsible for the p
ing action of the heart. Cardiac muscle fibers (cells) are im
untary, striated, and branched, and the tissue is arranged i
interlacing bundles of fibers (Figure 15.2b).
Cardiac muscle fibers form two separate networks— oi
atrial and one ventricular. Each cardiac muscle fiber cornier,
with other fibers in the networks by thickenings of the a
oolemma (plasma membrane) called intercalated Mst
Within the discs are gap junctions that allow action pore
rials to conduct from one cardiac muscle fiber to the in
The intercalated discs also link cardiac muscle fibers to
mother so they do not pull apart. Each network contracts as
Ifcnctional unit, so the atria contract separately from the
ventricles. In response to a single action potential, cardiac
muscle fibers develop a prolonged contraction, 10-15 times
er than the contraction observed in skeletal muscle
fibers. Also, the refractor)' period of a cardiac fiber lasts
longer than the contraction itself. Thus, another contraction
cardiac muscle cannot begin until relaxation is well under-
y, For this reason, tetanus (maintained contraction) cannot
ir in cardiac muscle tissue.
The endocardium (endo- = within) is a thin layer of sim-
k squamous epithelium that lines the inside of the my-
irdium and covers the valves of the heart and the tendons
rached to the valves. It is continuous with the epithelial liiv
ig of the large blood vessels.
The heart of a heart attack survivor often has regions of in-
n led (dead) cardiac muscle tissue that typically are re-
laced with noncontractile fibrous scar tissue over time.
[Our inability to repair damage from a heart attack has been
attributed to a lack of stem cells in cardiac muscle and to
the absence of mitosis in mature cardiac muscle fibers, A
it study of heart transplant recipients by American and
Italian scientists, however, provides evidence for significant
replacement of heart cells. The researchers studied men
Structure and Organization of the Heart 367
who had received a heart from a female, and then looked for
the presence of a Y chromosome in heart cells. (All female
cells except gametes have two X chromosomes and lack
the Y chromosome.) Several years after the transplant
surgery, between 7% and 16% of the heart cells in the
transplanted tissue, including cardiac muscle libers and en-
dothelial cells in coronary arterioles and capillaries, had
been replaced by the recipient's own cells, as evidenced by
the presence of a Y chromosome. The study also revealed
cells with some of the characteristics of stem cells in both
transplanted hearts and control hearts. Evidently, stem
cells can migrate from the blood into the heart and differ
entiate into functional muscle and endothelial cells. The
hope is that researchers can learn how to "turn on" such
regeneration of heart cells to treat people with heart fail-
ure or cardiomyopathy (diseased heart).
Chambers of the Heart
The heart contains four chambers (Figure 1 5.3). The two up-
per chambers are the atria ( = entry halls or chambers), and
the two lower chambers are the ventricles ( = little bellies).
Between the right atrium and left atrium is a thin partition
called the interatrial septum (inter- = between; septum = a
Figure 15.3 Structure of the heart.
The four chambers of the heart are the two upper atria and two lower ventricles.
Superior vena cava
Ascending aorta
Parietal pericardium (cut)
Right pulmonary artery
Right pulmonary veins
Right auricle of right atrium
Right coronary artery
Right atrium
Right ventricle
Inferior vena cava
Arch of aorta
Ligamentum arteriosum
Left pulmonary artery
Pulmonary trunk
Left pulmonary veins
Left auricle of left atrium
Branch of left coronary artery
Left ventricle
Descending aorta
(a) Anterior external view showing surface features
(Continues)
368 Chapter 15 The Cardiovascular System: Heart
Figure 15.3 (Continued)
Arch of aorta
Descending aorta —
Left pulmonary artery
Auricle of left atrium
Left pulmonary veins
Left atrium
Coronary sinus
Left ventricle
Superior vena cava
Ascending aorta
Right pulmonary artery
Right pulmonary veins
Right atrium
Right coronary artery
Inferior vena cava
Right ventricle
(b) Posterior external view showing surface features
Superior vena cava
Right pulmonary artery
Pulmonary valve
Right pulmonary veins
Frontal
plane
/
Opening of superior vena cava
Fossa ovalis
Right atrium
Opening of coronary sinus
Opening of inferior vena cava
Tricuspid vaive
Right ventricle
Interior vena cava
(c) Anterior view of frontal section showing internal anatomy
Through which type of vessel does blood flow away from the heart?
Arch of aorta
Ligamentum arteriosum
Left pulmonary artery
Pulmonary trunk
Left pulmonary veins
Left atrium
Aortic valve
Bicuspid (mitral) valve
Chordae tendineae
■ Interventricular septum
Papillary muscle
Left ventricle
Descending aorta
Structure and Organization of the Heart 369
dividing wall or partition); a prominent feature of this septum
[is an oval depression called the fossa ovalis. It is the remnant
If the foramen ovale, an opening in die fetal heart that di-
rects blood from the right to left atrium in order to bypass
[the nonfunctioning fetal lungs. The foramen ovale normally
closes soon after birth. An interventricular septum separates
lie right ventricle from the left ventricle (Figure 15.3c). On
[the anterior surface of each atrium is a wrinkled pouchlike
Lucture called an auricle (OR-i-kul; auri- = ear), so named
[because of its resemblance to a dogs ear. Each auricle slightly
increases the capacity of an atrium so that it can hold a
greater volume of blood.
The thickness of the myocardium of the chambers varies
■ xling to the amount of work each chamber has to per-
form. The walls of the atria are thin compared to those of the
ltricles because the atria need only enough cardiac muscle
sue to deliver blood into the ventricles (Figure 1 5,3c). The
rht ventricle pumps blood only to the lungs (pulmonary?
Dilation); the left ventricle pumps blood to all other parts
the body (systemic circulation). The left ventricle must
ni harder than the right ventricle to maintain the same
te of blood flow, so the muscular wall of die left ventricle is
tsiderably thicker than the wall of the right ventricle to
rercome the greater pressure.
Ireat Vessels of the Heart
jk right atrium receives deoxygenated blood (oxygen-poor
that has given up some of its oxygen to cells) through
ree veins ^ blood vessels that return blood to the heart. The
wior vena cava (VE-na CA-va; vena = vein; cava = hol-
I, a cave) brings blood mainly from parts of the body above
heart; the inferior vena cava brings blood mostly from
ts of the body below the heart; and the coronary sinus
lins blood from most of the vessels supplying the wall of
I heart (Figure 15.3b, c). The right atrium then delivers
| deoxygenated blood into the right ventricle, which
ips it into the pulmonary trunk. The pulmonary trunk
ides into a right and left pulmonary artery, each of which
blood to the corresponding lung. Arteries are blood
jels that carry blood away from the heart. In the lungs, the
nwgenated blood unloads carbon dioxide and picks up
fgen. This oxygenated Hood (oxygen-rich blood that has
up oxygen as it flow r s through the lungs) then enters
^e left atrium via four pulmonary veins. The blood then
into the left ventricle, which pumps the blood into the
jding aona. From here the oxygenated blood is carried
jjl parts of the body.
Between the pulmonary trunk and arch of the aorta is a
jctnrc called the ligamentum arteriosum, Tt is the rem-
the ductus arteriosus, a blood vessel in fetal circula-
that allows most blood to bypass the nonfunctional fetal
ee page 412).
Valves of the Heart
As each chamber of the heart contracts, it pushes a volume of
blood into a ventricle or out of the heart into an artery. To
prevent the blood from flowing backward, the heart has four
valves composed^of dense connective tissue covered by en-
dothelium. These valves open and close in response to pres-
sure changes as the heart contracts and relaxes.
As their names imply, atrioventricular (AV) valves lie
between the atria and ventricles (Figure 1 5.>c)~ The atrioven-
tricular valve between the right atrium and right ventricle is
called the tricuspid valve because it consists of three cusps
(leaflets). The pointed ends of the cusps project into the ven-
tricle. Tendonlike cords, called chordae tendineae (KOR-de
ten-DIN-e-e; chord- = cord; tend- = tendon), connect die
pointed ends to papillaty muscles (papiU- = nipple), cardiac
muscle projections located on the inner surface of the ventri-
cles. The chordae tendineae prevent the valve cusps from
pushing up into the atria when the ventricles contract.
The atrioventricular valve between the left atrium and
left ventricle is called the bicuspid (fuitral) valve. It has two
cusps that work in the same way as die cusps of die tricuspid
valve. For blood to pass from an atrium to a ventricle, an atri-
oventricular valve must open.
The opening and closing of the valves are due to pressure
differences across the valves. When blood moves from an
atrium to a ventricle, the valve is pushed open, the papillary
muscles relax, and the chordae tendineae slacken (Figure
15.4a). When a ventricle contracts, the pressure of the ven-
tricular blood drives the cusps upward until their edges meet
and close the opening (Figure 1 5.4b). At the same time, con-
traction of the papillaty muscles and tightening of the chor-
dae tendineae help prevent the cusps from swinging upward
into the atrium.
Near the origin of the pulmonary trunk and aorta are
semilunar valves called the pulmonary valve and the aortic
valve that prevent blood from flowing back into the heart
(see Figure 15.3c). The pulmonary valve lies in die opening
where the pulmonary trunk leaves the right ventricle. The
aortic valve is situated at the opening between die left ventri-
cle and the aorta. Each valve consists of three semilunar
(half-moon-shaped) cusps that attach to the artery wall. Like
the atrioventricular valves, the semilunar valves permit blood
to flow in one direction only — in this case, from die ventri-
cles into the arteries.
When the ventricles contract, pressure builds up within
them. The semilunar valves open when pressure in the ven-
tricles exceeds the pressure in the arteries, permitting ejec-
tion of blood from the ventricles into the pulmonary trunk
and aorta (see Figure I5.4d). As the ventricles relax, blood
starts to flow back toward the heart This back-Mowing blood
fills the valve cusps, which tightly closes die semilunar valves
(see Figure 15.4c).
Figure 15.4 Atrioventricular (AV) valves. The bicuspid and tricuspid valves operate in a similar manner.
Heart valves open and close in response to pressure changes as the heart contracts and relaxes.
... He
BICUSPID VALVE CUSPS
Open Closed
CHORDAE TENDINEAE
Slack Taut
PAPILLARY
MUSCLE
Relaxed Contracted
[a) Bicuspid valve open
(b) Bicuspid valve closed
ANTERIOR
ANTERIOR
Pulmonary
vafve (closed)
Left coronary
artery
Bicuspid
valve
(open)
Tricuspid
valve
(open)
Aortic valve
(closed)
Pulmonary
valve (open)
POSTERIOR
(c) Superior view with atria removed;
pulmonary and aortic valves closed,
bicuspid and tricuspid valves open
What is the function of heart valves?
Right coronary
artery
Bicuspid
valve
(closed)
POSTERIOR
(d) Superior view with atria removed:
pulmonary and aortic valves open,
bicuspid and tricuspid valves closed
Aortic valve
(open)
Tricuspid
valve
(closed)
When heart valves operate normally, they open fully and
close completely at the proper times. A narrowing of a
heart valve opening that restricts blood flow is known as
stenosis (ste-NO-sis = a narrowing); failure of a valve to
close completely is termed insufficiency or incompe-
tence- In mitral stenosis, scar formation or a congenital
detect causes narrowing of the mitral valve. One cause of
mitral insufficiency, in which there is backflow of blood
from the left ventricle into the left atrium, is mitral valve
prolapse (MVP). In MVP, one or both cusps of the mitral
valve protrude into the left atrium during ventricular con-
traction. Mitral valve prolapse is one of the most common
valvular disorders, affecting as much as 30% of the popu-
lation. It is more prevalent in women than in men, and
does not always pose a serious threat. In aortic stenosis, the
aortic valve is narrowed, and in aortic insufficiency, there is
backflow of blood from the aorta into the left ventricle.
370
If a heart valve cannot be repaired surgically, dien
valve must be replaced. Tissue (biologic) valves may
provided by human donors or pigs; sometimes mechanlj
(artificial) valves made of plastic or metal are used. TI
aortic valve is the most commonly replaced heart valve,
■ CHECKPOINT
1. Identify the location of the heart,
2. Describe the various layers of the pericardium and
heart walk
3. How do atria and ventricles differ in structure and functii
4. Which blood vessels that enter and exit the heart
oxygenated blood? Which carry deoxygenated blood?
5. In correct sequence, which heart chambers, heart valves* ;
blood vessels would a drop or blood encounter from die
it flows out of die right atrium until it reaches die aorta?
ILOOD FLOWANO BLOOD
lllPPLY OF THE HEART
UECTIVES • Explain how blood flows through the
scribe the clinical importance of the blood supply
the heart.
>d Flow Through the Heart
\i [lows through the heart from areas of higher blood
mm to areas of lower blood pressure. As the walls of the
Blood Flow and Blood Supply of the Heart 371
atria contract, the pressure of the blood within them in-
creases. This increased blood pressure forces the AV valves
open, allowing atrial blood to flow through the AV valves
into the ventricles.
After the atria are finished contracting, the walls of
the ventricles contract, increasing ventricular blood pres-
sure and pushing blood through the semilunar valves into
the pulmonary trunk and aorta. At the same time, the
shape of the AV valve cusps causes them to be pushed
shut, preventing backflow of ventricular blood into the
atria. Figure I 5.5 summarizes the flow of blood through
the heart.
ire 15.5 Blood flow through the heart
The right and left coronary arteries deliver blood to the heart; the coronary veins drain blood from
the heart into the coronary sinus.
4. In pulmonary capillaries, blood
loses CO.> and gains 2
3.
9. Capillaries of head
and upper limbs
A \ Pulmonary trunk and
pulmonary arteries
S.
I
'ulmonary veins
[oxygenated blood)
t
lary
ies
il lung
Pulmonary valve
4. Pulmonary
capillaries
of left lung
6.
Lei
i
Left atrium
1.
Tricuspid valve
Right atrium
(deoxygenated blood)
.
Bicuspid valve
Left ventricle
10. | Superior
vena
I
L
cava
fnferior
vena
cava
i
oronary
sinui
9. Capillaries of trunk
and lower limbs
fa) Path of blood flow through heart
Aortic valve
8. i^TOfflffiWo*
Aorta ana
systemic
veins deliver deoxygenated blood into the right atrium?
9. In systemic capillaries, blood
loses 2 and gains CO ,
(b) Diagram of blood flow
<
372 Chapter 15 The Cardiovascular System: Heart
Blood Supply of the Heart
The wall of the heart, like any other tissue, has its own blood
vessels. The flow of blood through the numerous vessels in
the myocardium is called coronary (cardiac) circulation. The
principal corollary vessels are the left and right coronary
arteries, which originate as branches of the ascending aorta
(see Figure I 5.3a), Each artery branches and then branches
again to deliver oxygen and nutrients throughout the heart
muscle. Most of the deoxygenated blood, which carries car-
bon dioxide and wastes, is collected by a large vein on the
posterior surface of the heart, the coronary sinus (see
Figure 15,3b), which empties into die right atrium.
Most parts of the body receive blood from branches of
more than one artery and where two or more arteries supply
the same region, they usually connect. These connections,
called anastomoses (a-nas'-to-MO-ses), provide alternate
routes for blood to reach a particular organ or tissue. The
myocardium contains many anastomoses that connect
branches of a given coronary artery or extend between
branches of different coronary 7 arteries. They provide detours
for arterial blood if a main route becomes obstructed. Thus,
heart muscle may receive sufficient oxygen even if one of its
coronary arteries is partially blocked.
When blockage of a coronary artery deprives the heart mus-
cle of oxygen, reperfusion, the reestablish ment of blood
flow, may damage the tissue further. This surprising effect is
due to die formation of oxygen free radicals from the rein-
troduced oxygen. Free radicals are electrically charged mole-
cules that have an unpaired electron. Such molecules are un-
stable and highly reactive. They cause chain reactions that
lead to cellular damage and death. To counter the effects of
oxygen free radicals, body cells produce enzymes that con-
vert free radicals to less reactive substances. In addition,
some nutrients, such as vitamin E, vitamin C, beta-carotene,
zinc, and selenium, are antioxidants, which remove oxygen
free radicals. Drugs diat lessen reperfusion damage after a
heart attack or stroke are currently under development.
■ CHECKPOINT
6. Describe the main force that causes blood to flow
through the heart.
7. Why is it that blood flowing through the chambers
within the heart cannot supply sufficient oxygen or re-
move enough carbon dioxide from the myocardium?
CONDUCTION SYSTEM
OF THE HEART
objective # Explain how each heartbeat is initiated
and maintained.
About 1% of the cardiac muscle fibers are different from all
others because they can generate action potentials over
over and do so in a rhythmical pattern. These cells have til
important functions: They act as a pacemaker, setting the
rhythm for the entire heart, and they form the conduction
system, the route for action potentials throughout the Ik hi
muscle. The conduction system ensures that cardiac chain-]
bers are stimulated to contract in a coordinated ma
which makes the heart an effective pump. Cardiac
potentials pass through the following components o
conduction system (Figure 15.6):
O Normally, cardiac excitation begins in the sinoatrial (Sm
node, located in the right atrial wall just inferior to re-
opening of the superior vena cava. An action pot<
spontaneously arises in the SA node and then condw
throughout both atria via gap junctions in the
ealated discs of atrial fibers (see Figure 15.2b). Fiilivr
the action potential, the atria contract.
© By conducting along atrial muscle fibers, the actioi
tential also reaches the atrioventricular (AV) node, Lo-J
cated in the interatrial septum, just anterior to the open-
ing of the coronary sinus. At the AV node, the action
potential slows considerably; providing time for the;
to empty their blood into the ventricles.
© From the AV node, the action potential enters i!
atrioventricular (AV) bundle (also known as the bmulk
of His), in the interventricular septum. The AV bun
the only site where action potentials can conduct from
the atria to the ventricles,
^ After conducting along the AV bundle, the action jmu
rial then enters both the right and left bundle brand
that course through the interventricular septum toi
the apex of the heart. ^
^ Finally large-diameter Purkinje fibers (pur-KIN-j
rapidly conduct the action potential, first to the apex
the ventricles and then upward to the remainder of
ventricular myocardium. Then, a fraction of a second
ter the atria contract, the ventricles contract.
Conduction System of the Heart 373
Figure 15.6 Conduction system of the heart. The SA node, located in the right atrial wall, is
the heart's pacemaker, initiating cardiac action potentials that cause contraction of the heart's cham-
bers. The arrows indicate the flow of action potentials through the atria. The route of action potentials
through the numbered components of the conduction system is described in the text.
$ n
The conduction system ensures that cardiac chambers contract in a coordinated manner.
Frontal plane
Right atrium
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR
(AV) NODE
ATRIOVENTRICULAR (AV)
BUNDLE (BUNDLE OF HIS)
Q RIGHT AND LEFT
BUNDLE BRANCHES
Right ventricle
PURKINJE FIBERS
Anterior view of frontal section
Left atrium
Left ventricle
Which component of the conduction system provides the only route for action potentials to conduct be-
tween the atria and the ventricles?
The SA node initiates action potentials about 100 times
ir minute, faster than any other region of the conducting
i. Thus, the SA node sets the rhythm for contraction of
|e heart— it is the pacemaker of the heart. Various hormones
neurotransmitters can speed or slow pacing of the heart
SA node fibers. In a person at rest, for example, acetyl-
choline released by the parasympathetic division of the ANS
Ucally slows SA node pacing to about 75 action potentials
|r minute, causing 75 heartbeats per minute. If the SA node
les diseased or damaged, the slower AV node fibers can
Lome the pacemaker. With pacing by the AV node, how-
t heart rate is slower, only 40 to 60 beats/min. If the ac-
of both nodes is suppressed, the heartbeat may still be
Lintained by the AV bundle, a bundle branch, or Purkinje
These fibers generate action potentials very slowly,
20 to 35 times per minute. At such a low heart rate,
j flow to the brain is inadequate.
When die heart rate is too low, normal heart rhythm can
be restored and maintained by surgically implanting an ar-
tificial pacemaker, a device that sends out small electrical
currents to stimulate the heart to contract, A pacemaker
consists of a battery and impulse generator and is usually
implanted beneath the skin just inferior to theL clavicle.
The pacemaker is connected to one or two flexible wires
(leads) that are threaded through the superior vena cava
and then passed into the right atrium and right ventricle.
Many of the newer pacemakers, called activity-adjusted
pacemakers, automatically speed up the heartbeat during
exercise.
■ CHECKPOINT
8. Describe the path of an action potential through the con-
duction system.
374 Chapter 15 The Cardiovascular System: Heart
ELECTROCARDIOGRAM
OBJECTIVE • Describe the meaning and diagnostic
value of an electrocardiogram.
Conduction of action potentials through the heart generates
electrical currents that can be picked up by electrodes placed on
the skin. A recording of the electrical changes that accompany
the heartbeat is called an electrocardiogram (e-lek'-tro-KAR-
de-6-gram), which is abbreviated as cither ECG or EKG.
Three clearly recognizable waves accompany each heart-
beat. The first, called the P wave, is a small upward deflec-
tion on the ECG (Figure I 5.7); it represents atrial depolar-
ization, the depolarizing- phase of the cardiac action potential
as it spreads from the SA node throughout both atria. Depo-
larization causes contraction. Thus, a fraction of a second af-
ter the P wave begins, the atria contract. The second wave,
called the QRS complex, begins as a downward deflection
(Q); continues as a large, upright, triangular wave (R); and
ends as a downward wave (S). The QRS complex represents
the onset of ventricular depolarization, as the cardiac action
potential spreads through the ventricles. Shortly after the
QRS complex begins, the ventricles start to contract. The
Figure 15.7 Normal electrocardiogram (ECG) of a single
heartbeat. P wave - atrial depolarization; QRS complex = onset of
ventricular depolarization; T wave = ventricular repolarization.
An electrocardiogram is a recording of the electrical activity that
initiates each heartbeat.
1.0
0,5
>
E
1 o
-0,5
i
=i
i
rt
T
p
^PK
qI/
s
\
0.2
0,6
0,8
Seconds
Key:
Atrial contraction
Ventricular contraction
J )
/
J
What event occurs in response to atrial depolarization?
third wave is the T wave, a dome-shaped upward deflect]
that indicates ventricular repolarization and occurs jui
fore the ventricles start to relax. Repolarization of the atria;
not usually evident in an ECG because it is masked by
larger QRS complex.
Variations in the size and duration of the waves of
ECG are useful in diagnosing abnormal cardiac rhythms a
conduction patterns and in following the course of recover
from a heart attack An ECG can also reveal the presence oi
living fetus.
■ CHECKPOINT
9, What is the significance of the P wave, QRS compi
and T wave?
THE CARDIAC CYCLE
objective • Describe the phases of the cardiac cyt
A single cardiac cycle includes all die events associated wit
one heartbeat. In a normal cardiac cycle, the two atria
tract while the two ventricles relax; then, while the tv,
tricles contract, the two atria relax. The teTM systole (SJS-t
le = contraction) refers to the phase of contraction; dun
(di-AS-to-le = dilation or expansion) refers to the phase
relaxation. A cardiac cycle consists of systole and diastole
both atria plus systole and diastole of both ventricles.
For the purposes of our discussion, we will divide
cardiac cycle into three phases (Figure 1 5.S):
Q Relaxation period. The relaxation period begins it
end of a cardiac cycle when the ventricles start to rci;
and all four chambers are in diastole. Repolarization
the ventricular muscle fibers (T wave in the ECG) inii
ates relaxation. As the ventricles relax, pressure wit
them drops. When ventricular pressure drops
atrial pressure, the AV valves open and ventricular fillii
begins. About 75% of the ventricular filling occurs a
the AV valves open and before the atria contract.
Q Atrial systole (contraction). An action potential from
SA node causes atrial depolarization, noted as the P wa
in the ECG* Atrial systole follows the P wave, whic
marks the end of the relaxation period. As the atria coi
tract, they force the last 25% of the blood into then
tricles. At the end of atrial systole, each ventricle com
about 130 niL of blood. The AV valves arc still open
the semilunar valves are still closed,
Q Ventricular systole (contraction). The QRS complex |
the ECG indicates ventricular depolarization, vh
leads to contraction of the ventricles. Ventricular
traction pushes blood against the AV 7 valves, forcing fl
shut. As ventricular contraction continues, press
side the chambers quickly rises. When left ventriol
ire 15.8 Cardiac cycle.
A cardiac cycle is composed of all the events associated with
fe~- one heartbeat.
\ if ▼..
Q Relaxation
period
A Ventricular
systole
Atrial
systole
/ What is the term used for the contraction phase of the cardiac
■ } cycle? The relaxation phase?
pressure surpasses aortic pressure and right ventricular
pressure rises above the pressure in the pulmonary trunk,
both semilunar valves open, and ejection of blood from
[ the heart begins. Ejection continues until the ventricles
I start to relax. At rest, die volume of blood ejected from
each ventricle during ventricular systole is about 70 mL
I (a little more than 2 oz.). When the ventricles begin to
relax, ventricular pressure drops, the semilunar valves
fclose, and another relaxation period begins.
: rest, each cardiac cycle lasts about 0.8 sec. In one
Lplete cycle, the first 0.4 sec of the cycle is the relaxation
period, when all four chambers are in diastole. Then, the
ire in systole for 0J sec and in diastole for the next 07
Iter atrial systole, the ventricles are in systole for 0.3 sec
Id in diastole for 0.5 sec. When the heart heats faster, for
mice during exercise, the relaxation period is shorter.
■Heart Sounds
Resound of the heartbeat comes primarily from turbulence
L blood Bow created by the closure of flic valves, not Irom
Cardiac Output 375
the contraction of the heart muscle. The first sound, hibh, is
a long, booming sound from the AV valves closing after ven-
tricular systole begins. The second sound, a short, sharp
sound, dupp, is from the semilunar valves closing at the end
of ventricular systole. There is a pause during the relaxation
period. Thus, the cardiac cycle is heard as: lubb, dupp, pause;
lubb, dupp, pause; lubb, dupp, pause.
Heart sounds provide valuable information about the me-
chanical operation of the heart. A heart murmur is an ab-
normal sound consisting of a clicking, rushing, or gurgling
noise that is heard before, between, or after the normal
heart sounds, or that may mask the normal heart sounds.
Heart murmurs in children are extremely common and
usually do not represent a health condition. These types of
heart murmurs often subside or disappear with growth.
Although some heart murmurs in adults are innocent,
most often a murmur indicates a valve disorder.
■ CHECKPOINT
10. Explain the events that occur during each of the three
phases of the cardiac cycle.
11 . What causes the heart sounds?
CARDIAC OUTPUT
OBJECTIVE • Define cardiac output, explain how it is
calculated, and describe how it i s regulated.
The volume of blood ejected per minute from the left ventri-
cle into the aorta is called the cardiac output (CO). (Note
that the same amount of blood is also ejected from the right
ventricle into the pulmonary trunk.) Cardiac output is deter-
mined by (1) the stroke volume (SI 7 )* the amount of blood
ejected by the left ventricle during each heat (contraction),
and (2) heart rate (HR), the number of heartbeats per
minute. In a resting adult, stroke volume averages 70 mL,
and heart rate is about 75 beats per minute. Thus the average
cardiac output in a resting adult is
Cardiac output = stroke volume X heart rate
= 70 mL/beat X 75 beats/min
= 5250 mL/min or 5.25 liters/min
Factors that increase stroke volume or heart rate, such as ex-
ercise, increase cardiac output.
Regulation of Stroke Volume
Although some blood is always left in the ventricles at the
end of their contraction, a healthy heart pumps out the blood
that has entered its chambers during the previous diastole.
Focus on Well
Sudden Cardiac Death
During Exercise —
What's the Risk?
Regular physical activity helps keep
hearts and arteries healthy. But very
rarely, strenuous activity can precipitate
a heart attack. In adults of middle age
and older, a heart attack, or myocardial
infarction, typically occurs because a
blood clot lodges in an artery of die
heart already narrowed by atheroscle-
rotic plaque. During exercise, heart
rate and blood pressure increase. Un-
der this stress, an unstable plaque may
rupture, stimulating the clotting
process as the body tries to repair the
damaged artery,
How Risky Is Exercise?
Many studies have been conducted in
an attempt to quantify the risk imposed
by strenuous exercise. Researchers have
concluded that, in general, risk of heart
attack is about two to six times higher
during strenuous exercise than during
light physical activity or rest. The sta-
tistical risk of heart attack varies con-
siderably depending on a person's exer-
cise history. Risk is lowest for those
who exercise regularly and highest for
people unaccustomed to exercise. Risk
during exercise also rises with the num-
ber and severity of other cardiovascular
risk factors* For example, people al-
ready diagnosed with heart disease are
10 times as likely to have a heart attack
during exercise as apparently healthy
individuals. Though this may sound
discouraging, the risk can be seen from
another point of view. Overall, the inci-
dence of death during physical activity
is very low, about 6 deaths per 100,000
middle-aged men per yean
Exercise is also safe for most peo-
ple recovering from heart attacks. In
167 supervised cardiac rehabilitation
exercise programs, the incidence of
heart attack in 51,000 patients was 1 in
294,000 person-hours (number of peo-
ple multiplied by number of hours each
exercised). Incidence of death was only
1 in 784,000 person -hours.
Who Is at Risk?
Although these figures illustrate that
risk of heart attack and death are quite
low, if the death occurs to someoii
love, it happens 100% and is stdJ
tragic loss. People with diagnosed or]
suspected artery disease are most at J
and should check with their physiciai
before starting an exercise prograj
Risk can be reduced by exercising regu-j
larly (several times per week) at a loj
to moderate intensity, and by h ceding]
any warning signs of cardiovascular
ease, such as chest pain or pressure, abj
normal heart rhythms, or dizziness.
i
>
► Think It Over
Why do you think exercise stress tests are used to help diagnose coronary
artery disease?
The more blood that returns to the heart during diastole, the
more blood that is ejected during the next systole. Three fac-
tors regulate stroke volume and ensure that the left and right
ventricles pump equal volumes of blood:
1. The degree of stretch in the heart before it con-
tracts* Within limits, the more the heart is stretched as it
fills during diastole, the greater die force of contrac-
tion during systole, a relationship known as the Frank -
Starling law of the heart. The situation is somewhat like
stretching a rubber band: The more you stretch the
heart, the more forcefully it contracts. In other words,
within physiological limits, the heart pumps all the blood
it receives. If die left side of the heart pumps a little more
blood than the right side, a larger volume of blood returns to
die right ventricle. On the next beat the right ventricle con-
tracts more forcefully, and the two sides are again in balance.
376
3.
The forcefulness of contraction of individual ventrk
ular muscle fibers. Even at a constant degree of si
the heart can contract more or less forcefully when
tain substances are present. Stimulation of the symi
thetie division of the autonomic nervous system (A
hormones such as epinephrine and norepinephrine, ii
li cased Ca 2 level in the interstitial fluid, and the d]
digitalis all increase the force of contraction of can
muscle libers. In contrast, inhibition of the sym]
division of the ANS, anoxia, acidosis, some anestherii
and increased K + level in die extracellular fluid decrc
contraction force.
The pressure required to eject blood from the vt
tricles. The semilunar valves open and ejection of bit
from the heart begins when pressure in the right vent
cle exceeds the pressure in the pulmonary trunk ai
when the pressure in the left ventricle exceeds the pres-
sure in the aorta. When the required pressure is higher
than normal, the valves open later than normal, stroke
volume decreases, and more blood remains in the ventri-
cles at the end of systole.
congestive heart failure (CHF), the heart is a failing
Imp. Tt pumps blood less and less effectively, leaving
lore blood in the ventricles at the end of each cycle, The
suit is a positive feedback cycle: Less-effective pumping
i I to even lower pumping capability. Often, one side of
le heart starts to fail before the other. If the left ventricle
lis first, it can't pnrnp out all the blood it receives, and
ill ml backs up in the lungs. The result is pulmonary edema,
id accumulation in the lungs that can lead to suffoca-
)n. If the right ventricle fails first, blood backs up in the
Stemic blood vessels. In this case, the resulting peripheral
is usually most noticeable as swelling in the feet and
[es. Common causes of CHF are coronary artery dis-
(see page 379), long-term high blood pressure, my-
irdial infarctions, and valve disorders.
igulation of Heart Rate
mismients to the heart rate are important in die short-term
jntrol of cardiac output and blood pressure. If left to itself,
Igure 15.9 Autonomic nervous system regulation of heart rate.
Cardiac Output 377
the sinoatrial node would set a constant heart rate of about
100 beats/min. However, tissues require different volumes of
blood How under different conditions. During exercise, for
example, cardiac output rises to supply working tissues with
increased amounts of oxygen and nutrients. The most impor-
tant factors in the regulation of heart rate are the autonomic
nervous system and the hormones epinephrine and norepi-
nephrine, released by die adrenal glands.
Autonomic Regulation of Heart Rate
The nervous system regulation of the heart originates in the
cardiovascular (CV) center in the medulla oblongata. This
region of the brain stem receives input from a variety of
sensory receptors and from higher brain centers, such as the
limbic system and cerebral cortex. The cardiovascular center
then directs appropriate output by increasing or decreasing the
frequency of nerve impulses sent out to both the sympathetic
and parasympathetic branches of the ANS (Figure 1 5,9).
Arising from the CV center are sympathetic neurons that
reach the heart via cardiac accelerator nerves. They inner-
vate the conduction system, atria, and ventricles. The norepi-
nephrine released by cardiac accelerator nerves increases the
heart rate. Also arising from die CV center are parasympa-
thetic neurons that reach the heart via the vagus (X) nerves.
These parasympathetic neurons extend to the conduction
system and atria. The neurotransmitter thev release — acetyl -
The cardiovascular center in the medulla oblongata controls both sympathetic and parasympathetic
nerves that innervate the heart.
0*
Cardiovascular
(CV) center
Key:
Sensory neurons
Motor neurons
Baro receptors
in carotid sinus
Baroreceptors
in arch of aorta
AV node
Ventricular
myocardium
Cardiac accelerator
nerves (sympathetic)
Sympathetic trunk
ganglion
What effect does acetylcholine, released by parasympathetic nerves, have on heart rate?
378 Chapter 15 The Cardiovascular System: Heart
choline (ACh) — decreases the heart rate by slowing the
pacemaking activity of the SA node.
Several types of sensory receptors provide input to the
cardiovascular center. For example, baroreceptors (haro- =
pressure), neurons sensitive to blood pressure changes, are
strategically located in the arch of the aorta and carotid arter-
ies (arteries in the neck that supply blood to die brain). If
diere is an increase in blood pressure, the baroreceptors send
nerve impulses along sensory neurons that are part of the
glossopharyngeal (IX) and vagus (X) nerves to the CV center
(Figure 15.9). The cardiovascular center responds by putting
out more nerve impulses along the piu\i sympathetic (motor)
neurons that are also part of the vagus (X) nerves. The resulting
decrease in heart rate lowers cardiac output and thus lowers
blood pressure. If blood pressure foils, baroreceptors do not
stimulate the cardiovascular center. As a result of this lack of
stimulation, heart rate increases, cardiac output increases,
and blood pressure increases to die normal level Chemore-
ceptors, neurons sensitive to chemical changes in the blood,
detect changes in blood levels of chemicals such as O2, CO?,
and H + , Their relationship to the cardiovascular center is
considered in Chapter 16 with regard to blood pressure.
Chemical Regulation of Heart Rate
Certain chemicals influence both die basic physiology of car-
diac muscle and its rate of contraction. Chemicals with major
effects on the heart fall into one of two categories:
1. Hormones. Epinephrine and norepinephrine (from the
adrenal medullae) enhance the heart's pumping effectiveness
by increasing bodi heart rate and contraction force. Exercise,
stress, and excitement cause the adrenal medullae to release
more hormones. Thyroid hormones also increase heart rate.
One sign of hyperthyroidism (excessive levels of thyroid hor-
mone) is tachycardia (elevated resting heart rate).
2. Ions, Elevated blood levels of K~ or Na" 1 decrease heart
rate and contraction force, A moderate increase in extra-
cellular and intracellular Ca 2 level increases heart rate
and contraction force.
Other Factors in Heart Rate Regulation
Age, gender, physical fitness, and body temperature also in-
fluence resting heart rate- A newborn baby is likely to have a
resting heart rate over 120 beats per minute; the rate then
declines throughout childhood to the adult level of 75 beats
per minute. Adult females generally have slightly higher rest-
ing heart rates than adult males, although regular exercise
tends to bring resting heart rate down in both sexes. As
adults age, their heart rates may increase.
Increased body temperature, such as occurs during fever
or strenuous exercise, increases heart rate by causing die SA
node to discharge more rapidly. Decreased body temperature
decreases heart rate and force of contraction. During surgical
repair of certain heart abnormalities, it is helpful to slow
patient's heart rate by deliberately cooling die body.
■ CHECKPOINT J
12. Describe how stroke volume is regulated.
. How tloes the autonomic nervous system help regulaw
heart rate?
EXERCISE AND THE HEART
objective • Explain the relationship between exei
cise and the heart.
Regardless of the current level, a person's cardiovascular fit-
ness can be improved at any age with regular exercise. Si
types of exercise are more effective than others for improvi
the health of the cardiovascular system. Aerobics, any activit
diat works large body muscles for at least ^20 minutes, eljj
vates cardiac output and accelerates metabolic rate. Three
five such sessions a week are usuallv recommended for ii
proving the health of the cardiovascular system. Brisk wall
ing, running, bicycling, cross-country skiing, and swimming!
are examples of aerobic activities.
Sustained exercise increases the oxygen demand of
muscles. Whether the demand is met depends mainly on
adequacy of cardiac output and proper functioning of there!
piratory system. After several weeks of training, a healffl
person increases maximal cardiac output, thereby increase
die maximal rate of oxygen delivery to the tissues*
delivery also rises because skeletal muscles develop more cap
illary networks in response to long-term training.
During strenuous activity, a well-trained athlete
achieve a cardiac output double that of a sedentary person,
part because training causes hypertrophy (enlargement)
the heart. Even though the heart of a well-trained athlete
larger, resting cardiac output is about the same as in a heal
untrained person, because stroke volume is increased w\
heart rate is decreased. The resting heart rate of a train
athlete often is only 40-60 beats per minute {resting
did). Regular exercise also helps to reduce blood pr;
anxiety, and depression; control weight; and increase
body's ability to dissolve blood clots by increasing fibrino|
activity.
■ CHECKPOINT
14. What is aerobic exercise? Why are aerobic exercises
eficial?
• • •
The heart is the blood pump for the cardiovascular 1
but it is the blood vessels that distribute blood to all pai
the body and collect blood from them. In the next chapter]
will see how blood vessels accomplish this.
:;<'■= ■
— ■
COMMON
DISORDERS
ironary Artery Disease
wary artery disease (CAD) affects about 7 million people and
ses nearly 750,000 deaths in the United States each year, CAD is
led as the effects of the accumulation of atherosclerotic plaques
scribed shortly) in coronary arteries that lead to a reduction in
)d flow to die myocardium. Some individuals have no signs or
iptuins, others experience angina pectoris (chest pain), and still
|s suffer a heart attack.
People who possess combinations of certain risk factors are
re likely to develop CAD. Risk factors (characteristics, syrnp-
or signs that are statistically associated with a greater chance
developing a disease) include smoking, high blood pressure,
ies, high cholesterol levels, obesity, "type A" personality,
itary lifestyle, and a family history of CAD. Most of these
In modified by changing diet and other habits or can be con-
lid by taking medications. However, other risk factors are
Modifiable — that is, beyond our control — including genetic
Imposition (family history of CAD at an early age), age, and
Icr. For example, adult males are more likely than adult females
I lop CAD; after age 70 the risks are roughly equal,
lokirtg is undoubtedly the number-one risk factor in all CAD-
feted diseases, roughly doubling the risk of morbidity and
ity.
In recent years, a number of new risk factors (all modifiable)
^ve been identified as significant predictors of CAD. C-reavtive
(CRPs) are proteins produced by the liver or present in
i in ;ni inactive form that are convened to an active form dur-
Common Disorders 379
ing inflammation, CRPs may play a direct role in die development
of atherosclerosis by promoting the uptake of LDLs by
macrophages. Lipoprotein (a) is an LDL-like particle that binds to
endothelial cells, macrophages, and blood platelets, may promote
the proliferation of smooth muscle fibers, and inhibits the break-
down of blood clots. Fibrinogen is a glycoprotein involved in blood
clotting that may help regulate cellular proliferation, vasoconstric-
tion, and platelet aggregation. Homocysteine is an amino acid that
may induce blood vessel damage by promoting platelet aggregation
and smooth muscle fiber proliferation.
Atherosclerosis (ath'-er-o-skler-o-sis) is a progressive disease
characterized by the formation in the walls of large- and medium-
sized arteries of lesions called atherosclerotic plaques (Figure
15.10).
To understand how atherosclerotic plaques develop, you will
need to know about molecules produced by the liver and small in-
testine called lipoproteins. These spherical particles consist of an in-
ner core of triglycerides and other lipids and an outer shell of pro-
teins, phospholipids, and cholesterol. Two major lipoproteins are
low-density lipoproteins or LDLs and high-density lipoproteins or
HDLs. LDLs transport cholesterol from the liver to body cells for
use in cell membrane repair and the production of steroid hor-
mones and bile salts. 1 low ever, excessive amounts of LDLs pro-
mote atherosclerosis, so the cholesterol in these particles is known
as "bad cholesterol" HDLs, on the other hand, remove excess cho-
lesterol from body cells and transport it to the liver for elimination.
Because HDLs decrease blood cholesterol level, the cholesterol in
HDLs is laiown as "good cholesterol." Basically, you want your
LDL to be low and your HDL to be high.
It has recently been learned that inflammation, a defensive re-
sponse of the body to tissue damage, plays a key role in the develop-
ment of atherosclerotic plaques. As a result of die damage, blood
Figure 15. 10 Photomicrographs of a transverse section of (a) a normal artery and (b)
one partially obstructed by an atherosclerotic plaque.
At
Atherosclerosis is a progressive disease caused by the formation of atherosclerotic plaques.
Partially
obstructed
space through
which blood
flows
Atherosclerotic
plaque
(a) Normal artery (b) Obstructed artery
What substances are part of an atherosclerotic plaque?
380 Chapter 15 The Cardiovascular System: Heart
vessels dilate and increase their permeability. The formation of
atherosclerotic plaques begins when excess LDLs from the blood
accumulate in the artery wall and undergo oxidation. Tn response,
endothelial and smooth muscle cells of the artery secrete sub-
stances that attract monocytes from the blood and convert them
into macrophages. The macrophages then ingest and become so
filled with the oxidized LDL particles that they have a foamy ap-
pearance when viewed microscopically (foam celts). Together with
T cells (lymphocytes), foam cells form a fatty Streak, the begin-
ning of an atherosclerotic plaque. Following tatty streak forma-
tion, smooth muscle cells ot the artery migrate to the top of the
atherosclerotic plaque, forming a cap over it and thus walling it
off from the blood.
Because most atherosclerotic plaques expand away from the
bloodstream rather than into it, blood can flow through an artery
with relative ease, often for decades. Most heart attacks occur when
the cap over the plaque breaks open in response to chemicals pro-
duced by foam cells, causing a clot to form. If the clot in a coronary
artery is large enough, it can significantly decrease or stop the How
of blood and result in a heart attack.
Treatment options for CAD include drugs (antihypertensive
drugs, nitroglycerin, beta-blockers, and cholesterol-lowering and
clot-dissolving agents) and various surgical and nonsurgical proce-
dures designed to increase the blood supply to the heart.
Myocardial Ischemia and Infarction
Partial obstruction of blood flow in the coronary arteries may cause
myocardial ischemia (is-KE-ine-a; tsche- = to obstruct; -emia - in
the blood), a condition of reduced blood flow to die myocardium.
Usually, ischemia causes hypoxia (reduced oxygen supply), which
may weaken cells without killing them. Angina pectoris (an-Jl-na or
AN-ji-na PEK-to-ris), which literally means "strangled chest," is a
severe pain that usually accompanies myocardial ischemia. Typi-
cally, sufferers describe it as a tightness or squeezing sensation, as
though the chest were in a vise. The pain associated with angina
pectoris is often referred to the neck, chin, or down the left arm to
the elbow. Silent myocardial ischemia, ischemic episodes without
pain, is particulary dangerous because the person has no forewarn-
ing of an impending heart attack.
A complete obstruction to blood flow in a coronary artery may
result in a myocardial infarction (in-FARK-shun), or Ml, com-
monly called a heart attack. Infarction means die death of an area of
tissue because of interrupted blood supply. Because the heart tissue
distal to the obstruction dies and is replaced by noncontractile scar
tissue, the heart muscle loses some of its strength. Depending on
the size and location of rhc infarcted (dead) area, an infarction may
disrupt the conduction system of the heart and cause sudden death
by triggering ventricular fibrillation. Treatment for a myocardial in-
farction may involve injection of a thrombolytic (clot-dissolving)
agent such as streptokinase or tPA, plus heparin (an anticoagulant),
or performing coronary angioplasty or coronary artery bypass graft-
ing. Fortunately, heart muscle can remain alive in a resting person if
it receives as little as 10-15% of its normal blood supply.
Congenital Defects
A defect that exists at birth (and usually before) is a coiigcmtd
defect. Among die several congenital defects that affect the heart aj
the following:
• In patent ductus arteriosus, the ducnis arteriosus (ten
blood vessel) between the aorta and die pulmonary trunk, which
normally closes shortly after birdi, remains open (see Yvm
16.17 on page 413). Closure of the ductus arteriosus leaves a rem
nant called the ligamentum arteriosum (see Figure 1 5.3a),
• Atrial septal defect (ASD) is caused by incomplete closure
the interatrial septum. The most common type involves d*
foramen ovale, which normally closes shortly after birth (set
figure 16.17 on page 413).
• Ventricular septal defect (VSD) is caused by an incomplete
sure of the interventricular septum.
• Valvular stenosis is a narrowing of one of the valves associafl
with blood flow through the heart.
• Tetralogy of Fallot (te-TRAL-O-jc of fa-LO) is a combination
of four defects: an interventricular septal detect, an aorta
emerges from both ventricles instead of from the left ventrical
only, a narrowed pulmonary semilunar valve, and an enlarge
right ventricle.
Some congenital heart defects are being surgicallv corrects
prior to birth in order to prevent complications at the time of bi
and following the birth of an infant.
Arrhythmias
The usual rhythm of heartbeats, established by the SA mode, is <
normal sinus rhythm. The term arrhythmia (a-RITH-me-ajl
widiout) or dysrhythmia refers to an abnormal rhythm as a resuffl
defect in the conduction system of die heart. The heart may beat!
ularly, too fast, or too slowly. Symptoms include chest pain, shop
of breath, lightheadedness, dizziness, and fainting. Arrhythmias ma
caused by factors that stimulate the heart, such as stress, caffeine^
hoi, nicotine, cocaine, and certain drug's diat contain caffeine on
stimulants. Arrhythmias may also be caused by a congenital deft
coronary arteiy disease, myocardial infarction, hypertension, deli
heart valves, rheumatic heart disease, hyperthyroidism, and pot
deficiency.
One serious arrhythmia is called a heart block. The most con
heart block occurs in the atrioventricular node, which conducts!
pulses from die atria to the ventricles. This disturbance is called i
oventiicular (AV) block.
Tn atrial flutter, the atrial rhythm averages between _'4();
360 beats per minute. The condition is essentiallv rapid atrial
tractions accompanied by AV block. Atrial fibrillation is an
ordinated contraction of the atrial muscles. When the muscle I
latcs, the muscle fibers of the atrium quiver individually insttt
contracting together, canceling out the pumping of die atriij
Ventricular fibrillation (VF) is characterized by uncoordij
haphazard ventricular muscle contractions. Ventricular ejee
ceases, and circulatory failure and death occur.
lEDICAL TERMINOLOGY AND CONDITIONS
Study Outline 381
Imoeardwgrapby (an r -je-o-kar'-de-OG-ra-fe; angio- - vessel;
mrdio- = heart) X-ray examination of the heart and great blood
vessels after injection of a radiopaque dye into the bloodstream.
prdiac arrest (KAR-dc-ak a-REST) A clinical term meaning ces-
sation of an effective heartbeat. The heart may be completely
I stopped or in ventricular fibrillation.
prdiac catheterization (kath'-e-tcr-i-ZA-shun) Procedure that is
1 used to visualize the heart's coronary arteries, chambers, valves,
and great vessels, k may also be used to measure pressure in
I the heart and blood vessels; to assess cardiac output; and to
I measure the flow of blood through the heart and blood vessels,
the oxygen content of blood, and the status of the heart valves
.nil conduction system. The basic procedure involves inserting
n catheter into a peripheral vein (for right heart catheteriza-
tion) or artery (for left heart catheterization) and guiding it un-
der fluoroscopy (x-ray observation).
hmlitic rehabilitation (re-ha-bil-i-TA-shun) A supervised program
of progressive exercise, psychological support, education, and
training to enable a patient to resume normal activities follow-
ing a myocardial infarction.
fydionugaly (kar'-de-o-MEG-a-le; mega- = large) Heart enlarge-
ment.
• pulmonale (CP) (kor pul-mon-ALE; cor- = heart; pubwii-
lung) Right ventricular hypertrophy caused by hypertension
(high blood pressure) in the pulmonary circulation.
Cardiopulmonary resuscitation (kar'-de-6-PUL-md -ner-e re-sus-
i-TA-shun) (CPR) The artificial establishment of normal or
near-normal respiration and circulation. The ABCs of car-
diopulmonary resuscitation are Airway, Breathing, and Circu-
lation, meaning the rescuer must establish an airway, provide
artificial ventilation if breathing has stopped, and reestablish
circulation if there is inadequate cardiac action.
Palpitation (pal'-pi-'i A-shuti) A fluttering of the heart or abnormal
rate or rhythm of the heart.
Paroxysmal tachycardia (par'-ok-SIZ-mal tak-e-KAR-de~a) A pe-
riod of rapid heartbeats that begins and ends suddenly.
Rheumatic fever (roo-MAT-ik) An acute systemic inflammatory dis-
ease that usually occurs after a streptococcal infection of the
throat. The bacteria trigger an immune response in which anti-
bodies that are produced to destroy the bacteria attack and in-
flame the connective tissues in joints, heart valves, and other or-
gans. Even though rheumatic fever may weaken the entire heart
wall, most often it damages die bicuspid (mitral) and aortic valves.
Sudden cardiac death The unexpected cessation of circulation and
breathing due to an underlying heart disease such as ischemia,
myocardial infarction, or a disturbance in cardiac rhythm.
STUDY OUTLINE
tore and Organization of the Heart (p. 365}
[, The heart is situated between die lungs, with about two-thirds
[of its mass to the left of the midline.
| The pericardium consists of an outer fibrous layer and an inner
ppous pericardium.
3, The serous pericardium is composed of a parietal layer and a
[viscera! layer.
W, Between the parietal and visceral layers of the serous peri-
cardium is the pericardial cavity, a space filled with pericardial
Slid that reduces friction between the two membranes.
|The wall of the heart has three layers: epicardium, myo-
Irdium, and endocardium.
The chambers include two upper atria and two lower ventricles.
i The blood flows through the heart from the superior and infe-
,-enac cavac and the coronary sinus to the right atrium,
tough the tricuspid valve to the right ventricle, and through
ilmonary trunk to die lungs.
(rom the lungs, blood flows through the pulmonary veins into
left atrium, through the bicuspid valve to the left ventricle,
nd out through the aorta.
9. Four valves prevent the backflow of blood in the heart.
10. Atrioventricular (AV) valves, between the atria and their ventri-
cles, are the tricuspid valve on the right side of the heart and
the bicuspid (mitral) valve on die left.
11. The atrioventricular valves, chordae tendineae, and their papil-
lary muscles stop blood from Rowing back into the atria.
12. Each of the two arteries that leave the heart has a semilunar
valve.
Blood Flow and Blood Supply of the Heart (p. 371)
1. Blood flows through the heart from areas of higher pressure to
areas of lower pressure.
2. The pressure is related to the size and volume ol a chamber.
3. The movement of blood through the heart is controlled by the
opening and closing of the valves and the contraction and re-
laxation of die myocardium.
4. Coronary circulation delivers oxygenated blood to the my-
ocardium and removes carbon dioxide from it.
5. Deoxygenated blood returns to the right atrium via the coro-
nary sinus.
382 Chapter 15 The Cardiovascular System: Heart
6. Malfunctions of this system can result in angina pectoris or
myocardial infarction (MI).
Conduction System of the Heart (p. 372)
1. The conduction system consists of specialized cardiac muscle
tissue that generates and distributes action potentials.
2. Components of this system arc the sinoatrial (SA) node (pace-
maker), atrioventricular (AV) node, atrioventricular (AV) bun-
dle (bundle of His), bundle branches, and Purkinje fibers.
Electrocardiogram (p. 374)
1. The record of electrical changes during each cardiac cycle is
referred to as an electrocardiogram (ECG),
2. A normal ECG consists of a P wave (depolarization of atria),
QRS complex (onset of ventricular depolarization), and T wave
(ventricular repolarization}.
3. The ECG is used to diagnose abnormal cardiac rhythms and
conduction patterns.
The Cardiac Cycle (p. 374)
1. A cardiac cycle consists of systole (contraction) and diastole (re-
laxation) of the chambers of the heart.
2. The phases of the cardiac cycle are (a) the relaxation period, (b)
atrial systole, and (c) ventricular systole.
3. A complete cardiac cycle takes 0.8 sec at an average heartbeat
of 75 beats per minute.
4. The first heart sound (lubb) represents the closing of the ntri
ovcntricular valves. The second sound (dupp) represents di
closing or semilunar valves.
Cardiac Output (p. 375)
1. Cardiac .output (CO) is the amount of blood ejected by the led
ventricle into the aorta each minute: CO = stroke volume X
beats per minute.
2. Stroke volume (SV) is the amount of blood ejected by ;i ventri-
cle during ventricular systole. It is related to stretch on th«
heart before it contracts, force fulness of contraction, and the
amount of pressure required to eject blood from the venfrieta
3. Nervous control of the cardiovascular system originates in the
cardiovascular center in the medulla oblongata.
4. Sympathetic impulses increase heart rate and force of contrac-
tion; parasympathetic impulses decrease heart rate.
5. Heart rate is affected by hormones (epinephrine, norepinm
rine, thyroid hormones), ions (Na 1 , K , Ca 2 ' ), age, genfl
physical fitness, and body temperature.
Exercise and the Heart (p. 378)
1. Sustained exercise increases oxygen demand on muscles,
2. Among the benefits of aerobic exercise are increased maximal
cardiac output, decreased blood pressure, weight control, and
increased ability to dissolve clots.
2.
A. aortic valve
B. right atrium
C. left atrium
D. bicuspid (mitral) valve
E. pulmonary valve
F. right ventricle
G. left ventricle
H. tricuspid valve
Match the following:
a. valve between the left
atrium and
left ventricle
b. valve between the
right atrium and right
ventricle
c. chamber that pumps
blood to the lungs
d. chamber that pumps
blood into aorta
e. chamber that receives
oxygenated blood from lungs
f. chamber that receives dcoxygenated blood from
body
g. valve between the left ventricle and aorta
h. valve between right ventricle and pulmonary trunk
Which of the following statements describes the pericardium
a. It is a layer of nervous tissue.
b. It lines the inside of the myocardium.
c. It is continuous with the epithelial lining of the large blood
\ essels.
d. It is responsible for the contraction of the heart,
e. It is a membrane that surrounds and protects the heart.
3. Which blood vessel delivers deoxygcuated blood from
and neck to the heart?
a. pulmonary vein b. thoracic aorta
c, pulmonary artery d. inferior vena cava
e. superior vena cava
4. An embolus originating in the coronary sinus would first entertld
a. right atrium b. pulmonary veins c. left atrium
d. right ventricle e. aorta
5. The chordae tendineae and papillary muscles of die heart
a. are responsible for connecting cardiac muscle libers tor the
spread of action potentials
b. can develop self-excitability and stimulate contraction
c. help prevent the atrioventricular valves from protruding
into the atria when the ventricles contract
d. help anchor and protect the heart
e. form the cusps (flaps) of the heart valves
6. Which chamber of die heart has the thickest layer
cardium?
a. right ventricle b. right atrium c. left: ventricH
d. left atrium e. coronary sinus
7. The normal "pacemaker" of the heart is the
a. sinoatrial (SA) node b. atrioventricular (AV) node
c. Purkinje fibers d. atrioventricular (AV) bundle
e. right bundle branch
In normal he -art action,
a. the right atrium and ventricle contract, followed by the con-
traction of the left atrium and ventricle
b. the order of eon traction is right atrium, then right ventricle,
then left atrium, then left ventricle
c. the two atria contract together, and then die two ventricles
contract together
d. the right atrium and left ventricle contract, followed by the
contraction of the left atrium and right ventricle
c, ill four chambers of the heart contract and then relax simul-
taneously
Heart sounds are produced by
a, contraction of the myocardium
b. closure of the heart valves
It die flow of blood in the coronary arteries
d, the flow of blood in the ventricles
I «, the transmission of action potentials through the conduc-
tion system
\, Heart rate and strength of contraction are controlled by the
I cardiovascular center, which is located in the
I a. cerebrum b. pons c. right atrium d. medulla
e, atrioventricular node
■The portion of the ECG that corresponds to atrial depolariza-
gra is the
L R peak b. space between the T wave and P wave
c. Twave d. P wave e. QRS complex
[The opening of the semilunar valves is due to the pressure in the
[t ventricles exceeding the pressure in the aorta and pul-
monary trunk
b. ventricles exceeding the pressure in the atria
c. atria exceeding the pressure in the ventricles
d. atria exceeding the pressure in the aorta and pulmonary trunk
| e, aorta and pulmonary trunk exceeding the pressure in the
ventricles
\, On the anterior surface of each atrium is a wrinkled pouchlike
structure called a(n)
a. anterior interventricular sulcus b. coronary sulcus
L auricle d. interatrial septum
icrior interventricular sulcus
■The Frank- Starling law of the heart
I. is important in maintaining equal blood output from both
I ventricles
Is. is used in reference to the force of contraction of the atria
c. results in a decreased heart rate
d causes blood to accumulate in the lungs
e, is related to the stretching of the cardiac muscle cells in die atria
i Which of the following sequences best represents the pathway
fan action potential through the hearts conduction^system?
, sinoatrial (SA) node 2. Purkinje fibers
I atrioventricular (AV) bundle
atrioventricular (AV) node
right and left bundle branches
a, 1,4,3,2.5 b. 4,1,3,5,2 c 3,4,1,2,5
(1,1,4,3,5,2 e, 2,5,3,4,1
Sell-Quiz 383
16. Which of the following is NOT true concerning ventricular
filling during the cardiac cycler
a.. The atrioventricular (AV) valves are open.
b. The ventricles fill to 75% of their capacity before the atria
contract.
c. The remaining 25% of the ventricular blood is forced into
the ventricles when the atria contract.
d. The semilunar valves are open.
e. Ventricular filling begins when the ventricular pressure drops
below the atrial pressure, causing the AV valves to open.
17. Cardiac output
a. equals stroke volume (SV) X blood pressure (BP)
b. equals stroke volume (SV) X heart rate (HR)
c. is calculated using the formula for the Frank- Starling law of
the heart
d. is about 70 mL in the average adult male
e. equals blood pressure (BP) X heart rate (1 IR)
18. Most heart problems are due to
a, old age b. leakages at the valves
c. problems in the coronary circulation
d. the failure of the conduction system
e. infections in the heart coverings
19. Using die situations that follow, indicate if the heart rate would
speed up (A) or slow down (B).
a. sympathetic stimulation of die sinoatrial (SA) node
b. decrease in blood pressure
c, fever
_ d. parasympathetic stimulation of the heart's conduction
system
e. release of epinephrine
f. elevated K + level
g. release of acetylcholine
h. strenuous exercise
_ i. stimulation by the vagus (X) nerve
j. fear, anger, stress
k. cooling the body
I. hypoxia
_ m. excessive thyroid hormones
20. Match the following:
a, may cause a heart
murmur
b, heart compression
c. inflammation ot
heart covering
d, heart chamber
contraction
e. chest pain from
ischemia
f. heart attack
g. heart chamber
relaxation
A. pericarditis
B. mitral valve prolapse
C. myocardial infarction
1). angina pectoris
E. diastole
E systole
G. cardiac tamponade
384 Chapter 15 The Cardiovascular System: Heart
*
CRITICAL T
HINKING APPLICATIONS
1. Your uncle had an artificial pacemaker inserted after his last
bout with heart trouble. What is the function of a pacemaker?
For which heart structure does the pacemaker substitute?
2. Nikos was strolling across a four-lane highway when a car sud-
denly appeared out of nowhere. As he finished sprinting across
the road, he felt his heart racing. Trace the route of the signal
from his brain to his heart.
3. Jean-Claude, a member of the college's cross-country ski team,
volunteered to have his heart function evaluated by the exercise
physiology class. His resting pulse rate was 40 beats per
■I.
minute. Assuming that he has an average cardiac output iQV.
determine Jean-Claude's stroke volume (SV). Next, ]m
Claude rode an exercise bike until his heart rate had risen to (■
beats per minute. Assuming that his SV stayed constant, oil
late Jean-Claude's CO during this moderate exercise.
Rosa's great Aunt. Frieda likes to say that she has complain
feet and a mumbling heart. Aunt Frieda's physician uses mt
terms "edema" and "murmur." Explain Aunt Frieda's medicJ
condition.
ANSWERS TO FIGURE QUESTIONS
15.1 The base of the heart consists mainly of the left atrium.
15.2 The visceral layer of the serous pericardium is also part of
the heart wall (cpicardium).
15.3 Blood flows away from the heart in arteries.
15.4 Fleart valves prevent the backflow of blood.
15.5 The superior vena cava, inferior vena cava, and coronary si-
nus deliver deoxygenated blood into the right atrium.
15.6 The only electrical connection between the atria ami the I
ventricles is the atrioventricular (AV) bundle.
15.7 Atrial depolarization causes contraction of the atria.
15.8 The contraction phase is called systole; the relaxation phase i
is called diastole.
15.9 Acetylcholine decreases heart rate.
15.10 Fatty substances, cholesterol, and smooth muscle libers
make up atherosclerotic plaques.
THE CARDIOVASCULAR SYSTEM:
BLOOD VESSELS AND CIRCULATION
-
chapter 16
jjidyou know?
physical activity helps to protect
the cardiovascular system in many ways. It
improves blood cholesterol levels and blood sugar
emulation. Regular exercise leads to increased output
» the parasympathetic nervous system (not during
mrcise, but during the rest of the day), which leads to
vwer resting heart rate and lower resting blood pres-
sure. Physical activity burns calories, thus helping to
prevent obesity. People who exercise regularly have
lower rates of inflammation markers, such as
tC-reactive protein. Less inflammation suggests lower
risk of artery disease. To maximize cardiovascular
health, researchers recommend about an hour a day of
brisk activity.
Focus on Wellness, page 410
www.wiley.com/college/apcen1ral
J. he cardiovascular system con-
tributes to the homeostasis of other body
systems by transporting- and distributing
blood throughout the body to deliver
materials such as oxygen, nutrients,
and hormones and to carry away wastes. This transport
is accomplished by blood vessels, which form closed
circulatory routes for blood to travel from the heart to
body organs and back again. In Chapters 14 and 15 we
discussed the composition and functions of blood and
the structure and function of the heart. In this chapter,
we examine the structure and functions of the different
types of blood vessels that carry the blood to and from
the heart, as well as factors that contribute to blood
flow and regulation of blood pressure.
looking back to move ahead
Diffusion {page 47)
Medulla Oblongata (page 250)
Antidiuretic Hormone (page 322)
Mineralocorticoids (page 331)
Great Vessels of the Heart (page 369)
385
386 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
BLOOD VESSEL STRUCTURE
AND FUNCTION
OBJECTIVES • Compare the structure and function of
the different types of blood vessels.
• Describe how substances enter and leave the blood
in capillaries.
• Explain how venous blood returns to the heart.
There are five types of blood vessels: arteries, arterioles, cap-
illaries, venules, and veins. Arteries (AR-ter-ez) carry blood
away from the heart to body tissues. Two large arteries — the
aorta and the pulmonary trunk— emerge from the heart and
branch out into medium-sized arteries that serve various re-
gions of the body. These medium-sized arteries then divide
into small arteries, which, in turn, divide into still smaller ar-
teries called arterioles (ar-TER-e-dls). Arterioles within a tis-
sue or organ branch into numerous microscopic vessels called
capillaries (EAP-i-lar'-ez), Groups of capillaries within a tis-
sue reunite to form small veins called venules (VEN-uls).
These, in turn, merge to form progressively larger vessels
called veins. Veins (VANZ) are the blood vessels that convey
blood from die tissues back to the heart.
At any one time, systemic veins and venules contain
about 64% of the total volume of blood in the system, sys-
temic arteries and arterioles about 13%, systemic capillaries
about 7%, pulmonary blood vessels about 9%, and the heart
chambers about 7%. Because veins contain so much of the
blood, certain veins function as blood reservoirs. The main
blood reservoirs, are the veins of the abdominal organs (espe-
cially die liver and spleen) and the skin. Blood can be di-
verted quickly from its reservoirs to other parts of the body,
for example, to skeletal muscles to support increased muscu-
lar activity.
Arteries and Arterioles
The walls of arteries have three layers of tissue surrounding a
hollow space, the lumen, through which the blood flows
(Figure 16.1a). The inner layer is composed of endothelium,
a type of simple squamous epithelium; a basement mem-
brane; and an elastic tissue called the internal elastic lamina.
The middle layer consists of smooth muscle and elastic tis-
sue. The outer layer is composed mainly of elastic and colla-
gen fibers.
Sympathetic fibers of the autonomic nervous system in-
nervate vascular smooth muscle. An increase in sympathetic
stimulation typically causes the smooth muscle to contract,
squeezing the vessel wall and narrowing the lumen. Such a
decrease in the diameter of the lumen of a blood vessel is
called vasoconstriction. In contrast, when sympathetic stimu-
lation decreases, or in the presence of certain chemicals
(such as nitric oxide or lactic acid), smooth muscle libers re-
lax. The resulting increase in lumen diameter is called
vasodilation. Additionally, when an artery or arteriole
damaged, its smooth muscle contracts, producing vascula
spasm of the vessel. Such a vasospasm limits blood llnu
through the damaged vessel and helps reduce blood loss i
the vessel is small.
The largest-diameter arteries contain a high proportion
of elastic fibers in their middle layer, and their walls are
tively thin in proportion to their overall diameter. Such arte
ies are called elastic arteries. These arteries help prope
blood onward while the ventricles are relaxing. As blood
ejected from the heart, into elastic arteries, their highly ela
walls stretch, accommodating the surge of blood. Th
while the ventricles are relaxing, the elastic fibers in
artery walls recoil, which forces blood onward towa
smaller arteries. Examples include the aorta and the brads
cephalic, common carotid, subclavian, vertebral, pulmnr
and common iliac arteries. Medium-sized arteries, on
other hand, contain more smooth muscle and fewer ela
fibers than elastic arteries. Such arteries are called muse
arteries and are capable of greater vasoconstriction and
sodilation to adjust the rate of blood flow. Examples inclu
the brachial artery (arm) and radial artery (forearm).
An arteriole ( = small artery) is a very small, aim
croscopic, artery that delivers blood to capillaries. The small]
est arterioles consist of little more than a layer of endothe
Hum covered by a few smooth muscle fibers (see Figuri
16.2a). Arterioles play a key role in regulating blood flw
from arteries into capillaries. During vasoconstriction, blooc
flow from the arterioles to the capillaries is restricted: dunr
vasodilation, the flow' is significantly increased. A change i
diameter of arterioles can also significantly alter blood pres-1
sure; vasodilation decreases blood pressure and vasoconstricj
tion increases blood pressure.
Capillaries
Capillaries (capillar- = hairlike) are microscopic vessels thi|
connect arterioles to venules (Figure 16.1c). Capillaries
are present near almost every body cell, and they are knowd
as exchange vessels because they permit the exchange ofiuitn-j
ents and wastes between the body's cells and the blood. Ik
number of capillaries varies with the metabolic activity of fl
tissue they serve. Body tissues with high metabolic require!
ments, such as muscles, the liver, the kidneys, and die nen
vous system, have extensive capillary networks. Tissues™
lower metabolic requirements, such as tendons and ligal
ments, contain fewer capillaries, A few tissues — all covetB
and lining epithelial, the cornea and lens of the eye, and carti-
lage — lack capillaries completely.
Blood Vessel Structure and Function 387
igure 16.1 Comparative structure of blood vessels. The relative size of the capillary in (c) is enlarged
emphasis. Note the valve in the vein.
Arteries carry blood away from the heart to tissues. Veins carry blood from tissues back to the heart.
Lumen
fa) Artery
.mi
Endothelium
INNER LAYER:
Endothelium -
Basement membrane
Internal elastic lamina
MIDDLE LAYER:
Smooth muscle
OUTER LAYER
Valve
Lumen
(b) Vein
Lumen
Basement membrane
(c) Capillary
Functions of Bloodvessels
1 . Blood vessels form a closed
system of tubes thai carries blood
away from the hear? (in arteries),
transports it through the tissues of
the body (in arterioles, capillaries,
and venules), and then returns it
to the heart (in veins),
2. Exchange of substances between
the blood and body tissue cells
occurs as blood flows through the
capillaries.
3. Nutrients and oxygen diffuse from
the blood through interstitial fluid
into tissue cells. Waste products,
including carbon dioxide, diffuse
from tissue cells through interstitial
fluid into the blood.
W Would you expect a femoral artery or a femoral vein to have the thicker wall? A wider lumen?
\tOure of Capillaries
papillary consists of a layer of endothelium that is sur-
ded by basement membrane (Figure 16.1c). Because
llary walls are very thin, many substances easily pass
trough them to reach tissue cells from the blood or to enter
ilood from interstitial fluid. The walls of all other blood
re too thick to permit the exchange of substances be-
ieen blood and interstitial fluid. Depending on how tightly
Ir endothelial cells are joined, different types of capillaries
ying degrees of permeability.
In some regions, capillaries link arterioles to venules di-
in other places, they form extensive branching net-
nrc 16.2). Blood flows through only a small part of
a tissue's capillary network when metabolic needs are low.
But when a tissue becomes active, the entire capillary net-
work fills with blood. The flow of blood in capillaries is regu-
lated by smooth muscle fibers in arteriole walls and by pre-
capillary sphincters, rings of smooth muscle at the point
where capillaries branch from arterioles (Figure 16.2a).
When precapillary sphincters relax, more blood flows into
the connected capillaries; when precapillary sphincters con-
tract, less blood flows through their capillaries.
Capillary Exchange
Because of the small diameter of capillaries, blood flows more
slowly through them than through larger blood vessels. The
388 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Figure 16.2 Capillaries. Because red blood cells and capillaries are nearly the same size, red blood
cells squeeze through capillaries in single file.
.Y
Arterioles regulate blood flow into capillaries, where nutrients, gases, and wastes are exchanged
between blood and interstitial fluid.
Smooth muscle fiber (cell)
Endothelium
Precapillary
sphincters
Capillary
Venule
Endothelium
- To heart
Blood
capillary
Red blood
cell
(a) Details of a capillary network
Why do metabolically active tissues have extensive capillary networks?
CJJgoox
(b) Photomicrograph showing red blood cells
squeezing through a blood capillary
slow How aids the prime mission of the entire cardiovascular
system: to keep blood flowing through capillaries so that
capillary exchange the movement of substances into and
our of capillaries — can occur.
Capillary blood pressure, the pressure of blood against the
walls of capillaries, "pushes" fluid out of capillaries into inter-
stitial fluid, An opposing pressure, termed blood colloid os-motic
pressure, "pulls" fluid into capillaries. (Recall that osmotic
pressure is the pressure of a fluid due to its solute concentra-
tion. The higher the solute concentration, the greater the os-
motic pressure.) Most solutes are present in nearly equal cod
centrations in blood and interstitial fluid. But the presence J
proteins in plasma and their virtual absence in interstitial flu
gives blood the higher osmotic pressure. Blood colloid osmo
pressure is osmotic pressure due mainly to plasma proteins
Capillary blood pressure is higher than blood rj
osmotic pressure for about die first half of die length of a
capillary. Thus, water and solutes flow out of the blood ca|
lary into the surrounding interstitial fluid, a movement
filtration (Figure 16. 3). Because capillary blood pressure
Blood Vessel Structure and Function 389
Figure 16.3 Capillary exchange.
Capillary blood pressure pushes fluid out of capillaries (filtration); blood colloid osmotic pressure pulls
fluid into capillaries (reabsorption).
Blood flow Irom blood
arteriole into capillary
Blood flow from blood
capillary into venule
Filtration Reabsorption
What happens to excess filtered fluid and proteins that are not reabsorbed?
ases progressively as blood flows along a capillary, at. about
jpillary's midpoint, blood pressure drops below blood
osmotic pressure. Then, water and solutes move from
itial fluid into the blood capillary, a process termed
ion. Normally, about 85% of the filtered fluid is reab-
J, The excess Altered fluid and the few plasma proteins
lo escape enter lymphatic capillaries and eventually are re-
d by the lymphatic system to die cardiovascular system.
call zed changes in each capillary network can regulate
ation and vasoconstriction. When vasodilators are re-
by tissue cells, they cause dilation of nearby arterioles
fixation of precapillary sphincters. Then, blood flow
e capillary networks increases, and Q 2 delivery to the
es. Vasoconstrictors have the opposite effect. The
a tissue to automatically adjust its blood flow to
pits metabolic demands is called autoregulation.
enules and Veins
everal capillaries unite, they form venules. Venules
five blood from capillaries and empty blood into veins,
bch return blood to the heart.
Structure of Venules and Veins
Venules ( = little veins) are similar in structure to arterioles;
their walls are thinner near the capillary end and thicker as
they progress tow r ard the heart. Veins are structurally similar
to arteries, but their middle and inner layers are thinner (see
Figure 16.1b). The outer layer of veins is the thickest layer.
The lumen of a vein is w r ider than that of a corresponding
artery.
In some veins, the inner layer folds inward to form valves
that prevent the backflow of blood. h\ people with weak ve-
nous valves, gravity forces blood backward through the valve.
This increases venous blood pressure, which pushes the vein's
wall outward. After repeated overloading", the walls lose their
elasticity and become stretched and flabby, a condition called
varicose veins.
By the time blood leaves the capillaries and moves into
veins, it has lost a great deal of pressure. This can be ob-
served in the blood leaving a cut vessel: Blood flows from a
cut vein slowly and evenly, whereas it gushes out of a cut
artery in rapid spurts. When a blood sample is needed, it is
usually collected from a vein because pressure is low in veins
ami manv of them are close to the skin surface.
390 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Venous Return-
Venous return, the volume of blood flowing back to the
heart through systemic veins, occurs due to pressure gener-
ated in three ways: (1) contractions of the heart, (2) the
skeletal muscle pump, and (3) the respiratory pump. Blood
pressure is generated by contraction of the hearts ventricles
and is measured in millimeters of mercury, abbreviated mm
Hg, The pressure difference from venules (averaging about
16 mm Hg) to the right atrium (0 mm Hg), although small,
normally is sufficient to cause venous return to the heart.
When you stand, the pressure pushing blood up the veins in
your lower limbs is barely enough to overcome the force of
gravity pushing it back down.
The skeletal muscle pump operates as follows (Fig-
ure 16.4):
While you are standing at rest, both the venous valve
closer to the heart and the one farther from the heart in
this part of the leg are open, and blood flows upward to-
ward the heart.
Contraction of leg muscles, such as when you stand on
tiptoes or take a step, compresses the vein. The compres-
sion pushes blood through the valve closer to the heart,
an action called milk/tig. At the same time, the valve far-
ther from the heart in the uncompressed segment of the
Figure 16. -4 Action of the skeletal muscle pump in returning
blood to the heart. Steps are described in the text.
: , Mi
Milking refers to skeletal muscle contractions that drive venous
blood toward the heart.
Distal
valve
e
vein closes as some blood is pushed against it. Peopl
who are immobilized through injury or disease hick thest
contractions of leg muscles. As a result, their venous J
turn is slower and they may develop circulation problem*
© Just after muscle relaxation, pressure falls in the previ-
ously compressed section of vein, which causes tin
closer to the heart to close. The valve farther from
heart now opens because blood pressure in the foot]
higher than in the leg, and the vein fills with blood
the foot.
The respiratory pump is also based on alternating cq
pression and decompression of veins. During inhalat
(breathing in) the diaphragm moves downward, which cl
a decrease in pressure in the thoracic cavity and an inci
in pressure in the abdominal cavity. As a result, abdonl
veins are compressed, and a greater volume of blood movefl
from the compressed abdominal veins into the dccomprJ
thoracic veins and then into the right atrium. When the [
sures reverse during exhalation (breathing out), the valves ii
the veins prevent backflow of blood from the thoracic vj
to the abdominal veins.
■ CHECKPOINT
1 . How do arteries, capillaries, and veins differ in function?;
2. Distinguish between filtration and reabsorption.
3. What factors contribute to blood flow back to i
BLOOD FLOW THROUGH
BLOOD VESSELS
objectives • Define blood pressure and de
how it varies throughout the systemic circulation.
• Identify the factors that affect blood pressure
vascular resistance.
• Describe how blood pressure and blood flow are i
ulated.
n
What mechanisms, besides cardiac contractions, act as pumps
i to boost venous return?
We saw in Chapter IS that cardiac output (CO) depewj
stroke volume and heart rate. Two other factors infhj
cardiac output and the proportion of blood that
through specific circulatory routes are blood pressure
vascular resistance.
Blood Pressure
As you have just learned, blood flows from regions oflj
pressure to regions of lower pressure; the greater the
sure difference, the greater the blood flow. Contractu]
the ventricles generates blood pressure (BP), the pressure,
ertcd by blood on the walls of a blood vessel. BP is highe
h
Blood Flow Through Blood Vessels 391
aorta and large systemic arteries, where in a resting,
D adult, it rises to about IK) mm Hg during systole
[contraction) and drops to about 70 mm Hg during diastole
fixation). Blood pressure falls progressively as the distance
im the left ventricle increases (Figure 16,5), to about
nm Hg as blood passes into systemic capillaries. At the
nous end of capillaries, blood pressure drops to about
mm Hg. Blood pressure continues to drop as blood enters
lie venules and then veins, and it reaches mm Hg as
ood returns to the right atrium.
Blood pressure depends in part on the total volume or
ood in the cardiovascular system. The normal volume of
,il in ;in adult is about 5 liters (5.3 qt). Any decrease in
lis volume, as from hemorrhage, decreases the amount of
! dun is circulated through the arteries. A modest de-
Lse can be compensated by homeostatic mechanisms thai
, maintain blood pressure, but if the decrease in blood
Jume is greater than 10% of total blood volume, blood
[sure drops, with potentially life-threatening results. Con-
versely, anything that increases blood volume, such as water
etenrion in the body, tends to increase blood pressure.
figure 16.5 Blood pressure changes as blood flows through
systemic circulation. The dashed line is the mean (average)
issure in the aorta, arteries, and arterioles.
Blood pressure tails progressively as blood flows from sys-
;•. temic arteries through capillaries and back to the right
atrium. The greatest drop in blood pressure occurs in the
arterioles.
I/hat is the relationship between blood pressure and blood flow?
Resistance
Vascular resistance is the opposition to blood flow due to
friction between blood and the walls of blood vessels. An in-
crease in vascular resistance increases blood pressure; a de-
crease in vascular resistance has the opposite effect. Vascular
resistance depends on (1) size of the blood vessel lumen, (2)
blood viscosity, and (3) total blood vessel length.
1. Size of the lumen. The smaller the lumen of a blood
vessel, the greater its resistance to blood flow. Vasocon-
striction narrows the lumen, and vasodilation widens it.
Normally, moment-to-moment fluctuations in blood
flow through a given tissue are due to vasoconstriction and
vasodilation of the tissues arterioles. As arterioles dilate,
resistance decreases, and blood pressure falls. As arterioles
constrict, resistance increases, and blood pressure rises.
2. Blood viscosity. The viscosity (thickness) of blood de-
pends mostly on the ratio of red blood cells to plasma
(fluid) volume, and to a smaller extent on the concentra-
tion of proteins in plasma. The higher the blood's viscos-
ity, the higher the resistance. Any condition that in-
creases the viscosity of blood, such as dehydration or
polycythemia (an unusually high number of red blood
cells), thus increases blood pressure. A depiction of
plasma proteins or red blood cells, as a result of anemia
or hemorrhage, decreases viscosity and thus decreases
blood pressure.
3. Total blood vessel length. Resistance to blood flow in-
creases when the total length of all blood vessels in the
body increases. The longer the blood vessel, die greater
the contact between the vessel wall and the blood. The
greater the contact between the vessel wall and the
blood, the greater the friction. An estimated 400 miles of
additional blood vessels develop for each extra pound of
rat, one reason why overweight individuals may have
higher blood pressure.
Regulation of Blood Pressure
and Blood Flow
Several interconnected negative feedback systems control
blood pressure and blood flow by adjusting heart rate, stroke
volume, vascular resistance, and blood volume. Some systems
allow rapid adjustments to cope with sudden changes, such as
the drop in blood pressure in the brain that occurs when you
stand up; others provide long-term regulation. The body
may also require adjustments to the distribution of blood
flow. During exercise, for example, a greater percentage of
blood flow is diverted to skeletal muscles.
Role of the Cardiovascular Center
In Chapter 1 5 we noted how the cardiovascular (CV) center
in the medulla oblongata helps regulate heart rate and stroke
392 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
volume. The CV center also controls the neural and hor-
monal negative feedback systems that regulate blood pressure
and blood flow to specific tissues.
INPUT The cardiovascular center receives input from
higher brain regions: the cerebral cortex, limbic system, and
hypothalamus (Figure 16.6). For example, even before you
start to run a race, your heart rate may increase due to nerve
impulses conveyed from the limbic system to the CV center.
If your body temperature rises during a race, the hypothala-
mus sends nerve impulses to the CV center. The resulting
vasodilation of skin blood vessels allows heat to dissipate
more rapidly from the surface of the skin.
The CV center also receives input from three main types
of sensory receptors: proprioceptors, baroreceptors, and
chemoreceptors. Proprioceptors, which monitor movements of
joints and muscles, provide input to the cardiovascular center
during physical activity, such as playing tennis, and cause the
rapid increase in heart rate at the beginning of exercise.
Baroreceptors (pressure receptors) are located in the aorta,
internal carotid arteries (arteries in the neck that supply
blood to the brain), and other large arteries in the neck and
chest. They send impulses continuously to the cardiovascu-
lar center to help regulate blood pressure. If blood pressure
falls, the baroreceptors are stretched less, and they send
nerve impulses at a slower rate to the cardiovascular center
(Figure 16.7). In response, the cardiovascular center fl
creases parasympathetic stimulation of the heart and ia
creases sympathetic stimulation of the heart. As the heaiq
beats faster and more forcefully, and as vascular resistance ij
creases, blood pressure increases to the normal level.
By contrast, when an increase in pressure is detected, ihc
baroreceptors send impulses at a faster rate. The cardiovascuj
lar center responds by increasing parasympathetic stimuhq
and decreasing sympathetic stimulation. The resulting 4
creases in heart rate and force of contraction lower andiac
output, and vasodilation lowers vascular resistance, Eli
creased cardiac output and decreased vascular resistance boa
lower blood pressure.
Moving from a prone (lying down) to an erect position dJ
i creases blood pressure and blood flow in the head and J
per part of the body. The drop in pressure, hov,
quickly counteracted by the baroreceptor reflexes.
Sometimes these reflexes operate more slowly than nor-
mal, especially in older people. As a result, a person caft)
faint due to reduced brain blood flow upon standing m
| too quickly.
Chemoreceptor Reflexes Chemoreceptors (chemical
ceptors) that monitor blood levels of 0>, CCK and II
located in the two carotid bodies in the common c;
Figure 16.6 The cardiovascular (CV) center. Located in the medulla oblongata, the CV center re-
ceives input from higher brain centers, proprioceptors, baroreceptors, and chemoreceptors. It provides
output to both the sympathetic and parasympathetic divisions of the autonomic nervous system.
w
The cardiovascular center is the main region for the nervous system regulation of heart rate, force of
heart contractions, and vasodilation or vasoconstriction of blood vessels.
Vagus nerves
INPUT TO CARDIOVASCULAR
CENTER (nerve impulses)
CFrom higher brain centers: cerebral cortex.
limbic system, and hypothalamus
From proprioceptors: monitor joint movements
From baroreceptors: monitor blood pressure
(parasympathetic)
Cardiac accelerator
Cardiovascular
(CV) center
nerves (sympathetic)
Vasomotor nerves
(sympathetic)
From chemoreceptors: monitor blood acidity
(H + ), C0 2 , and 2
OUTPUT TO EFFECTORS
(increased frequency of nerve impulses)
Heart: decreased rate
Heart: increased rate and contractility
Blood vessels: vasoconstriction
V
How does vasoconstriction affect vascular resistance and blood flow?
figure 16.7 Negative feedback regulation of blood pressure
ila baroreceptor reflexes.
Ik The baroreceptor reflex is a neural mechanism for rapid
B^-- regulation of blood pressure.
Some stimulus disrupts V
homeostasis by
Decreasing
Baroreceptors in
arch o< aorta and
carotid sinus are
stretched less
Input
\
/
Decreased rate of
nerve impulses
Control center
CVcenter in
medulla oblongata
\and adrenal medulla
Output
Return to homeostasis
when increased
cardiac output and
increased vascular
resistance bring
; blood pressure
! back to normal
Increased sympathetic,
decreased parasympathetic
stimulation
Increased secretion of
epinephrine and
norepinephrine from
adrenal medulla
ectors
ft
Increased
Constrictio
stroke
of blood
volume and
vessels
heart rate
increases
lead to
vascular
increased
resistance
cardiac
output
I
I
Increased blood pressure
Does this negative feedback cycle happen when you lie down or
I when you stand up?
Blood Flow Through Blood Vessels 393
teries and in the aortic body in the arch of the aorta. Hypoxia
(lowered 2 availability), acidosis (an increase in H + concen-
tration), or hypercapnia (excess CO?) stimulates the chemore-
ceptors to send impulses to the cardiovascular center. In re-
sponse, the CV center increases sympathetic stimulation of
arterioles and veins, producing vasoconstriction and an in-
crease in blood pressure.
OUTPUT Output from the cardiovascular center flows along
sympathetic and parasympathetic fibers of the ANS (see Fig-
ure 16.6). An increase in sympathetic stimulation increases
heart rate and the forccfulness of contraction, whereas a de-
crease in sympathetic stimulation decreases heart rate and
contraction force. The vasomotor region of the cardiovascu-
lar center also sends impulses to arterioles throughout the
body. The result is a moderate state of vasoconstriction,
called vasomotor tone, that sets the resting level of vascular
resistance. Sympathetic stimulation of most veins results in
movement of blood out of venous blood reservoirs, which in-
creases blood pressure.
Hormonal Regulation of Blood Pressure and Blood Flow
Several hormones help regulate blood pressure and blood
flow by altering cardiac output, changing vascular resistance,
or adjusting the total blood volume.
1. Renin -angiotensin -aldosterone (RAA) system. When
blood volume falls or blood flow to the kidneys de-
creases, certain cells in the kidneys secrete the enzyme
renin into the bloodstream (see Figure 13.14 on page
331). Together, renin and angiotensin converting enzyme
(ACE) produce the active hormone angiotensin II, which
raises blood pressure by causing vasoconstriction. An-
giotensin 11 also stimulates secretion of aldosterone, which
increases reabsorption of sodium ions (Na + ) and water by
the kidneys. The water reabsorption increases total blood
volume, which increases blood pressure.
2. Epinephrine and norepinephrine. In response to sym-
pathetic stimulation, the adrenal medulla releases epi-
nephrine and norepinephrine. These hormones increase
cardiac output by increasing the rate and force of heart
contractions; they also cause vasoconstriction of arteri-
oles and veins in the skin and abdominal organs.
3. Antidiuretic hormone (ADH). ADFI is produced by
the hypothalamus and released from the posterior pitu-
itary in response to dehydration or decreased blood vol-
ume. Among other actions, ADH causes vasoconstric-
tion, which increases blood pressure. For this reason
ADH is also called vasopressin.
4. Atrial natriuretic peptide (ANP). Released by cells in
the atria of the heart, ANP lowers blood pressure by
causing vasodilation and by promoting die loss of salt
and water in the urine, which reduces blood volume.
394 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
■ CHECKPOINT
4. What two factors influence cardiac output?
5. Describe how blood pressure decreases as distance from
the left ventricle increases.
6. What factors determine vascular resistance?
7. Explain the role of the cardiovascular center, reflexes,
and hormones in regulating blood pressure.
CHECKING CIRCULATION
objective • Explain how pulse and blood pressure
are measured.
Pulse
The alternate expansion and elastic recoil of an artery after
each contraction and relaxation of the left ventricle is called a
pulse. The pulse is strongest in the arteries closest to the
heart. It becomes weaker as it passes through the arterioles,
and it disappears altogether in the capillaries. The radial
artery at the wrist is most commonly used to feel the pulse.
Other sices where the pulse may be felt include the brachial
artery along the medial side of the biceps brachii muscle; the
common carotid artery, next to the voice box, which is usu-
ally monitored during cardiopulmonary resuscitation; the
.popliteal artery behind the knee; and the dorsal artery of the
foot above the instep of the foot.
The pulse rate normally is the same as the heart rare,
about 75 beats per minute at rest. Tachycardia (tak'-i-KAR-
de-a; tachy- = fast) is a rapid resting heart or pulse rate over
100 beats/min. Bradycardia (brad'-i-KAR-de-a; brady- =
slow) indicates a slow resting heart or pulse rate under 50
beats/min.
Measurement of Blood Pressure
In clinical use, the term blood pressure usually refers to the
pressure in arteries generated by the left ventricle during sys-
tole and the pressure remaining in the arteries when the ven-
tricle is in diastole. Blood pressure is usually measured in the
brachial artery in the left arm (see Figure 16.10a). The device
used to measure blood pressure is a sphygmomanometer
(sfig-mo-ma-NOM-e-ter; sphygmo- = pulse; manometer =
instrument used to measure pressure). When the pressure
cuff is inflated above the blood pressure attained during sys-
tole, the artery is compressed so that blood Bow stops. The
technician places a stethoscope below the cuff over the
brachial artery and then slowly deflates the cuff. When the
cuff is deflated enough to allow the artery to open, a spurt of
blood passes through, resulting in the first sound
through the stethoscope. This sound corresponds to sys
blood pressure (SBP) — the force with which blood is pushii]
against arterial walls during ventricular contraction. As
cuff is deflated further, the sounds suddenly become fain
This*level, called the diastolic blood pressure (DBP), rep
sents the force exerted by the blood remaining in arts
during ventricular relaxation.
The normal blood pressure of a young' adult male is ltd
than 120 mm Tig systolic and less than 80 mm Hg diastolic
reported, for example, as "1 10 over 70" and written as 1
In young adult females, the pressures are 8 to 10 mm HglesB
People who exercise regularly and are in good physical coj
dition may have even lower blood pressures.
■ CHECKPOINT
8. What causes pulse?
9. Distinguish between systolic and diastolic blooa i
sure.
CIRCULATORY ROUTES
OBJECTIVE • Compare the major routes that
takes through various regions of the body.
Blood vessels are organized into circulatory routes that ca|
blood throughout the body (Figure 16.8). As noted earlij
the two main circulatory routes are the systemic circulffl
and the pulmonary circulation.
Systemic Circulation
The systemic circulation includes the arteries and arterij
that carry blood containing oxygen and nutrients from
left ventricle to systemic capillaries throughout the body.pl]
the veins and venules that carry blood containing card
dioxide and wastes to the right atrium. Blood leaving
aorta and traveling through the systemic arteries is a brig
red color. As it moves through the capillaries, it loses some]
its oxygen and takes on carbon dioxide, so that the blood
the systemic veins is a dark red color.
All systemic arteries branch from the aorta, which ail
from the left ventricle of the heart (see Figure 16.9). Den
genated blood returns to the heart through the sysi
veins. All the veins of the systemic circulation empty into
superior vena cava, inferior vena cava, or the corona
sinus, which, in turn, empty into the right atrium. Theprij
cipal blood vessels of the systemic circulation are describ
and illustrated in Exhibits 16.1 through 16.7 and Figures
through 16.15 starting on page 396.
Circulatory Routes 395
Figure 16.8 Circulatory routes. Red arrows indicate hepatic portal circulation. The details of the
pulmonary circulation are shown here, and the details of the hepatic portal circulation are shown in
Figure 16.16.
\ Blood vessels are organized into routes that deliver blood to various tissues of the body.
= Oxygenated blood
= Deoxygenated blood
<*»
Systemic capillaries of
head, neck, and upper limbs
Aorta
Pulmonary trunk
Superior
vena cava
Right atrium
Right ventricle
Inferior vena cava
Hepatic vein
Sinusoids of liver
Hepatic portal vein
Common iliac vein
Systemic
capillaries of
gastrointestinal tract
Internal iliac vein
External iliac vein
Systemic
capillaries
of pelvis
Venules
Pulmonary capillaries of
left lung
Left pulmonary veins
Left atrium
Left ventricle
Celiac trunk
Common hepatic artery
Splenic artery
Left gastric artery
Capillaries of spleen
Capillaries of stomach
Superior mesenteric artery
Inferior mesenteric artery
Common iliac artery
internal iliac artery
External iliac artery
Arterioles
Systemic capillaries of
lower limbs
What are the two principal circulatory routes?
396 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Exhibit 16.1 The Aorta and Its Branches (Figure 16.9)
i
OBJECTIVE • Identify the four principal divisions of the aorta and locate the major arterial branches arising from each.
• The aorta {aortae - to lift up), the largest
artery of the body, is 2 to 3 cm (about 1 in.)
in diameter. Its four principal divisions are the
ascending aorta, arch ot the aorta, thoracic
aorta, and abdominal aorta. The ascending
aorta emerges from the left ventricle poste-
rior to the pulmonary trunk. It gives off two
coronary artery branches that supply the my-
ocardium of the heart. Then it turns to the
left, forming the arch of the aorta. Branches
of the arch of the aorta are described in Ex-
hibit 1 6.2, The part of the aorta between the
arch of the aorta and the diaphragm, the
thoracic aorta, is about 20 cm (8 in.) long.
The part of the aorta between the diaphragm
and the common iliac arteries is the abdom-
inal aorta (ab-DOM-i-nal). The main
branches of the abdominal aorta are the
celiac trunk, the superior mesenteric
artery, and the inferior mesenteric artery,
The abdominal aorta divides at the level of Iti
fourth lumbar vertebra into two common ilia
arteries, which carry blood to the lower limbs
■ CHECKPOINT
What general regions do each of the four
principal divisions of the aorta supply?
Division and Branches
Region Supplied
Ascending Aorta
Right and left coronary arteries
Heart.
Arch of the Aorta (see Exhibit 16.2)
Brachiocephalic trunk (bra'-ke-c-se-FAL-ik)
Right common carotid artery (ka-ROT-id)
Right subclavian artery (sub-KLA-ve-an)
Left common carotid artery
Left subclavian artery
Right side of head and neck.
Right upper limb.
Left side of head and neck.
Left upper limb.
Thoracic Aorta {thorac- = chest)
Bronchial arteries (BRONG-ke-al)
Esophageal arteries (e-sof'-a-JE-al)
Posterior intercostal arteries (in'-ter-KOS-tal)
Superior phrenic arteries (FREN-ik)
Abdominal Aorta
Inferior phrenic arteries (FREN-ik)
Celiac trunk (SE-le-ak)
Common hepatic artery (he-PAT-ik)
Left gastric artery (GAS-trik)
Splenic artery (SPLEN-ik)
Superior mesenteric artery (MES-en-ter'-ik)
Suprarenal arteries (soo'-pra-RE-nal)
Renal arteries (RE-nal)
Gonadal arteries (go-NAD-al)
Testicular arteries (tes-TIK-u-lar)
Ovarian arteries (o-VAR-e-an)
Inferior mesenteric artery
Common iliac arteries (IL-e-ak)
External iliac arteries
Internal iliac arteries
Bronchi of lungs.
Esophagus.
Intercostal and chest muscles.
Superior and posterior surfaces of diaphragm.
Inferior surface of diaphragm.
Liver.
Stomach and esophagus.
Spleen, pancreas, and stomach.
Small intestine, cecum, ascending and transverse colons, and pancreas.
Adrenal (suprarenal) glands.
Kidneys.
Testes (male).
Ovaries (female).
Transverse, descending, and sigmoid colons; rectum.
Lower limbs.
Uterus (female), prostate (male), muscles of buttocks, and urinary bladder.
I
Circulatory Routes 397
5\^
[figure 16.9 Aorta and its principal branches
All systemic arteries branch from the aorta.
Right subclavian
Brachiocephalic trunk
ASCENDING AORTA
Right external carotid
Left common carotid
Left subclavian
ARCH OF AORTA
Left axillary
THORACIC AORTA
Diaphragm
Left gastric
Splenic
— Left renal
Superior mesenteric
Left gonadal
(testicular or ovarian)
Inferior mesenteric
Left common iliac
Ideep
•arch
uperficial
■arch
After blood is ejected from
Ihe heart, what are the names
ol the four divisions of the
aorta that it passes through?
Overall anterior view of the principal branches of the aorta
398 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Exhibit 1 6.2 The Arch of the Aorta (Figure 16.W)
J
objective • Identify the three arteries that branch from the arch of the aorta.
• The arch of the aorta, the continuation of
the ascending aorta, is 4 to 5 cm (almost 2 in.
in length, ft has three branches. In order, as
they emerge from the arch of the aorta, the
three branches are the brachiocephalic trunk,
the left common carotid artery, and»the left
subclavian artery.
■ CHECKPOINT
What general regions do the arteries that
arise from the arch of the aorta supply?
Artery
Description and Region Supplied
Brachiocephalic Trunk
(bra'-ke-6-se-FAL-ik;
brachio- = arm; -cephalic = head)
Right subclavian artery
(sub-KLA-ve-an)
Axillary artery
(AK-si-ler-e = armpit)
Brachial artery
(BRA-ke-al - arm)
Radial artery
(RA-de-al = radius)
Ulnar artery
(UL-nar - ulna)
Superficial palmar arch
{palma - palm)
Deep palmar arch
Vertebral artery
<VER-te-bral)
Right common carotid artery
(ka-ROT-id)
External carotid artery
Internal carotid artery
The brachiocephalic trunk divides to form the right subclavian artery and right common
carotid artery (Figure 16.10a).
The right subclavian artery extends from the brachiocephalic trunk and then passes into the armpit (axilla).
The general distribution of the artery is to the brain and spinal cord, neck, shoulder, and chest.
The continuation of the right subclavian artery into the axilla is called the axillary artery Its general
distribution is to the shoulder.
The brachial artery, which provides the main bfood supply to the arm, is the continuation of the axillary
artery into the arm. It is commonly used to measure blood pressure. Just below the bend in the elbow, the J
brachial artery divides into the radial artery and ulnar artery.
The radial artery is a direct continuation of the brachial artery. It passes along the lateral (radial) aspect ol
the forearm and then through the wrist and hand; it is a common site for measuring radial pulse.
The ulnar artery passes along the medial (ulnar) aspect of the forearm and then into the wrist and hand, J
The superficial palmar arch is formed mainly by the ulnar artery and extends across the palm. It gives rissj
to blood vessels that supply the palm and the fingers.
The deep palmar arch is formed mainly by the radial artery. The arch extends across the palm and gives I
rise to blood vessels that supply the palm.
Before passing into the axilla, the right subclavian artery gives off a major branch to the brain called the
right vertebral artery (Figure 16. 10b). The right vertebral artery passes through the foramina of the
transverse processes of the cervical vertebrae and enters the skull through the foramen magnum to reach I
the inferior surface of the brain. Here it unites with the left vertebral artery to form the basilar artery
(BAS-i-lar). The vertebral artery supplies the posterior portion of the brain with blood. The basilar artery I
supplies the cerebellum and pons of the brain and the internal ear.
The right common carotid artery begins at the branching of the brachiocephalic trunk and supplies
structures in the head (Figure 1 6.1 Ob). Near the larynx (voice box), it divides into the right external and nghll
internal carotid arteries.
The external carotid artery supplies structures external to the skull.
The internal carotid artery supplies structures internal lo the skull such as the eyeball, ear, most of the I
cerebrum of the brain, and pituitary gland. Inside the cranium, the internal carotid arteries along with the |
basilar artery form an arrangement of blood vessels at the base of the brain near the hypophyseal fossa
called the cerebral arterial circle (circle of Willis). From this circle (Figure 16.1 0c) arise arteries supply™
most of the brain. The cerebral arterial circle is formed by the union of the anterior cerebral arteries
(branches of internal carotids) and posterior cerebral arteries (branches of basilar artery). The posterior I
cerebral arteries are connected with the internal carotid arteries by the posterior communicating arteihm
(ko-MU-ni-ka'-ting). The anterior cerebral arteries are connected by the anterior communicating artery.
The internal carotid arteries are also considered part of the cerebral arterial circle. The functions of the
cerebral arterial circle are to equalize blood pressure to the brain and provide alternate routes for blood I
to the brain, should the arteries become damaged.
Left Common Carotid Artery
Divides into basically the same branches with the same names as the right common carotid artery.
Left Subclavian Artery
Divides into basically the same branches with the same names as the right subclavian artery.
Circulatory Routes 399
Figure 16.10 Arch of the aorta and its branches,
v The arch of the aorta is the continuation of the ascending aorta.
0- -
Brachiocephalic
trunk
Lett common
carotid
Right common carotid
Right vertebral
Right subclavian
Right posterior
cerebral
Basilar
Right deep palmar arch
Right superficial
palmar arch
Left . Right internal
subclavian carotjd
. . , Right subclavian
Arch of
aorta Right axillary
First rib
Right middle
cerebral
Right
external carotid
Right common carotid
Right vertebral
Clavicle
Brachiocephalic trunk
(b) Right lateral view of branches of
brachiocephalic trunk in neck and head
ANTERIOR
Cerebral arterial
circle (circle of Willis):
Anterior
cerebral
Anterior
communicating
Internal
carotid
Posterior
communicating
Posterior
cerebral
■
1/
C,., " "
%
■^v.
Frontal lobe
of cerebrum
Middle cerebral
Temporal lobe
of cerebrum
Pons
Basilar
Medulla
oblongata
- Vertebral
Cerebellum
(a) Anterior view of branches of
brachiocephalic trunk in upper limb
POSTERIOR
(C) Inferior view of base of brain showing cerebral arterial circle
What are the three major branches of the arch of the aorta, in order of their origination?
400 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Exhibit 16.3 Arteries of the Pelvis and Lower Limbs (Figure 16.11)
OBJECTIVE • Identify the two major branches of the common ilfac arteries.
• The abdominal aorta ends by dividing into
the right and left common iliac arteries.
These, in turn, divide into the internal and
external iliac arteries. In sequence, the ex-
ternal iliacs become the femoral arteries in
the thighs, the popliteal arteries posterior to
the knee, and the anterior and posterior
tibial arteries in the legs.
■ CHECKPOINT
What general regions do the internal and ex-
ternal iliac arteries supply?
Artery
Description and Region Supplied
Common iliac arteries
(IL-e-ak = ilium)
Internal iliac arteries
External iliac arteries
Femoral arteries
(FEM-o-ral - thigh)
Popliteal arteries
(pop'-li-TE-al = posterior
surface of the knee)
Anterior tibial arteries
(TIB-e-al = shin bone)
Posterior tibial arteries
At about the level of the fourth lumbar vertebra, the abdominal aorta divides into the right and left common iliac
arteries. Each gives rise to two branches: internal iliac and external iliac arteries. The general distribution of the
common iliac arteries is to the pelvis, external genitals, and lower limbs.
The internal iliac arteries are the primary arteries of the pelvis. They supply the pelvis, buttocks, external genitais.
and thigh.
The external iliac arteries supply the lower limbs.
The femoral arteries, continuations of the external iliacs, supply the lower abdominal wall, groin, external genitals,
and muscles of the thigh.
The popliteal arteries, continuations of the femoral arteries, supply muscles and the skin on the posterior of the
legs; muscles of the calf; knee joint; femur; patella; and fibula.
The anterior tibial arteries, which branch from the popliteal arteries, supply the knee joints, anterior muscles offlie
legs, skin on the anterior of the legs, and ankle joints. At the ankles, the anterior tibial arteries become the dorsal
arteries of the foot (dorsalis pedis arteries), which supply the muscles, skin, and joints on the dorsal aspects of
the feet. The dorsal arteries of the foot give off branches that supply the feet and toes.
The posterior tibial arteries, the direct continuations of the popliteal arteries, distribute to the muscles, bones, and
joints of the leg and foot. Major branches of the posterior tibial arteries are the fibular (peroneal) arteries, which
supply the leg and ankle. Branching of the posterior tibial arteries gives rise to the medial and lateral plantar arteries.
The medial plantar arteries (PLAN-tar = sole) supply the muscles and skin ol the feet and toes. The lateral plan-
tar arteries supply the feet and toes.
Circulatory Routes 401
Figure 16.11 Arteries of the pelvis and right lower limb.
The internal iliac arteries carry most of the blood supply to the pelvis, buttocks, external genitals,
and thigh.
Abdominal
aorta
Right common iliac
Right internal iliac
Right external iliac
Left
common iliac
Right femora
Right popliteal
■ Right anterior tibial
Right posterior tibial
Right fibular (peroneal)
Right dorsal Right lateral
artery of foot plantar
(dorsalis pedis)
Right medi
plantar
5
? At what point does the abdominal aorta divide into the common iliac arteries?
402 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Exhibit 16.4 Veins of the Systemic Circulation (Figurt I6.12)
objective • Identify the three systemic veins that return deoxygenated blood to the heart.
• Arteries distribute blood to various parts of
the body, and veins drain blood away from
them. For the most part, arteries are deep.
Veins may be superficial (located just be-
neath the skin) or deep. Deep veins gener-
ally travel alongside arteries and usually
bear the same name. Because there are no
large superficial arteries, the names of su-
perficial veins do not correspond to those of
arteries. Superficial veins are clinically impor-
tant as sites for withdrawing blood or giving
injections. Arteries usually follow definite
pathways. Veins are more difficult to follow
because they connect in irregular networks
in which many smaller veins merge to form a
larger vein. Although only one systemic
artery, the aorta, takes oxygenated blood
away from the heart (left ventricle), three
systemic veins, the coronary sinus, supe-
rior vena cava, and inferior vena cava, de-
liver deoxygenated blood to the right atrium
of the heart. The coronary sinus receives
blood from the cardiac veins; the superior
vena cava receives blood from other veins
superior to the diaphragm, except the air
sacs (alveoli) of the lungs; the inferior vena
cava receives blood from veins inferior to the
diaphragm.
■ CHECKPOINT
What are the basic differences between sys-
temic arteries and veins?
Vein
Description and Region Drained
Coronary sinus
(KOR-d-nar-e; corona -■ crown)
Superior vena cava (SVC)
(VE-na CA-va; vena vein;
cava = cavelike
Inferior vena cava (IVC)
The coronary sinus is the main vein of the heart; it receives almost all venous blood from the myocardium. It opens
into the right atrium between the opening of the inferior vena cava and the tricuspid valve.
The SVC empties its bfood into the superior part of the right atrium. It begins by the union of the right and left
brachiocephalic veins and enters the right atrium. The SVC drains the head, neck, chest, and upper limbs.
The IVCis the largest vein in the body. It begins by the union of the common iliac veins, passes through the dia-
phragm, and enters the inferior part of the right atrium, The IVC drains the abdomen, pelvis, and lower limbs. The ifc |
ferior vena cava is commonly compressed during the later stages of pregnancy by the enlarging uterus, producing
edema of the ankles and feet and temporary varicose veins.
Circulatory Routes 403
L
ure 16.12 Principal veins.
Deoxygenated blood returns
|S to the heart via the
superior and inferior
venae cavae and the
coronary sinus.
Right internal jugular
Right external jugular
Right subclavian
Right brachiocephalic
Superior vena cava
Right axillary
Right cephalic
Right hepatic
Right brachia
Right median cubita
Right basilic
Right radia
Right ulnar
Superior sagittal sinus
Inferior sagittal sinus
Straight sinus
Right transverse sinus
Sigmoid sinus
Right palmar
venous plexus
Left small saphenous
Left anterior tibial
Left posterior tibial
Left dorsal venous arch
P Which general regions of the body are
■j drained by the superior vena cava and the
inferior vena cava?
Pulmonary trunk
Coronary sinus
Great cardiac
Hepatic portal
Splenic
Superior mesenteric
Left renal
nferior mesenteric
Inferior vena cava
Left common iliac
Left internal iliac
Left external iliac
Overall anterior view of the principal veins
404 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Exhibit 16.5 Veins of the Head and Neck (Figure 16.13}
OBJECTIVE • Identify the three major veins that drain blood from the head.
• Most blood draining from the head passes
into three pairs of veins: the internal jugular
veins, external jugular veins, and verte-
bral veins. Within the brain, all veins drain
into dura! venous sinuses and then into the
internal jugular veins. Oural venous sinuses
are endothelium-lined venous channels be-
tween layers of the cranial dura mater.
■ CHECKPOINT
Which general areas are drained by the In- .
ternal jugular, external jugular, and vertebral
veins?
vein
Description and Region Drained
Internal jugular veins
(JUG-u-lar; jugular ■ throal)
External jugular veins
Vertebral veins
(VER-te-bral; vertebra - vertebrae)
The dural venous sinuses (the light blue vessels in Figure 16.13) dram blood irom the cranial bones, meninges, ahd
brain. The right and lefl internal jugular veins pass interiorly on either side of the neck lateral to the internal caroffl
and common carotid arteries. They then unite with the subclavian veins to lorm Ihe right and lelt brachiocephalic
veins (bra'-ke-o-se-FAL-ik: brachio- = arm; -cephalic = head). From here blood Hows into the superior vena cava
The general structures drained by Ihe internal jugular veins are the brain (through the dural venous sinuses), lace,
and neck.
The right and lefl external jugular veins empty Into the subclavian veins The general structures drained by Ihe ex-
ternal jugular veins are external to the cranium, such as the scalp and superficial and deep regions ol the lace.
The right and left vertebral veins empty into the brachiocephalic veins in the neck. They drain deep structures in H»'
neck such as the cervical vertebrae, cervical spinal cord, and some neck muscles.
Circulatory Routes 405
Figure 16.13 Principal veins of the head and neck.
Blood draining from the head passes fnto the internal jugular, external jugular, and
vertebral veins.
Right vertebral
Right external jugular
Right subclavian
Righi axillary —
Right internal jugular
Right brachiocephalic
Right lateral view
Into which veins in the neck does all venous blood from the brain drain?
406 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Exhibit 16.6 Veins of the Upper Limbs (Figure 16.14)
i
objective • Identify the principal veins that drain the upper limbs.
• Blood from the upper limbs is returned to
the heart by both superficial and deep veins.
Both sets of veins have valves, which are
more numerous in the deep veins.
• Superficial veins are larger than deep veins
and return most of the blood from the upper
limbs.
■ CHECKPOINT
Where do the cephalic, basilic, median ante-
brachial, radial, and ulnar veins originate?
Vein
Description and Region Drained
Superficial Veins
Cephalic veins
(se-FAL-ik = head)
Basilic veins
(ba-SIL-lk royal)
Median antebrachial veins
(an'-te-BRA-ke-al; ante-
before, in ironi ot; brachh = arm)
The principal superficial veins that drain the upper limbs originate In the hand and convey blood from the smaller
superficial veins into the axillary veins. The cephalic veins begin on the lateral aspect o( the dorsal venous
networks of the hands (dorsal venous arches), networks of veins on the dorsum of the hands (Figure 16.1 la]
that drain the fingers. The cephalic veins drain blood from (he lateral aspect of the upper limbs.
The basilic veins begin on the medial aspects of the dorsal venous networks of the hands (Figure 1 6. 1 4b) and
drain blood from the medial aspects of the upper limbs. Anterior to the elbow, the basilic veins are connected lo the
cephalic veins by the median cubital veins [cubitus - elbow), which drain the forearm. It a vein must be punctured I
for an injection, transfusion, or removal of a blood sample, the median cubital vein is preferred. The basilic veins
continue ascending until they pin the brachial veins. As the basilic and brachial veins merge in the axillary area,
they form the axillary veins.
The median antebrachial veins (median veins of the forearm) begin in the palmar venous plexuses, nalworta
of veins on the palms. The plexuses drain the fingers. The median antebrachial veins ascend in the forearms lo w
the basilic or median cubital veins, sometimes boih.They drain the palms and forearms.
Deep Veins
Radial veins
(RA-de-al = pertaining lo the radius)
Ulnar veins
(UL-nar = pertaining to the ulna)
Brachial veins
(BRA-ke-al)
Axillary veins
(AK-si-ler'-e; axilla = armpit)
Subclavian veins
(sub-KLA-ve-an: sub- - under;
•clavian - pertaining to the clavicle)
The paired radial veins begin at the deep palmar venous arches (Figure 16.1 4c), These arches drain the palms
The radial veins drain the lateral aspects of the forearms and pass alongside each radial artery. Just below the
elbow joint, the radial veins unite with the ulnar veins to form Ihe brachial veins.
The paired ulnar veins begin at the superficial palmar venous arches, which drain ihe palms and the fingers. lm
ulnar veins drain the medial aspect of the forearms, pass alongside each ulnar artery, and join with the radial vgiru
to form the brachial veins,
The paired brachial veins accompany the brachial arteries. They drain the forearms, elbow joints, and arm
join with the basilic veins to form the axillary veins.
The axillary veins ascend to become the subclavian veins. They drain the arms, axillae, and upper part of thechMjJ
wall,
The subclavian veins are continuations of Ihe axillary veins that unite with the internal jugular veins to form trie
brachiocephalic veins. The brachiocephalic veins unite to form the superior vena cava. The subclavian veins drain
the arms, neck, and thoracic wall.
Jjgure 16.14 Principal veins of the right upper limb
Deep veins usually accompany arteries that
have similar names.
Circulatory Routes 407
Right cephalic
Right dorsal venous network of the hand
< dorsal venous arch)
(a) Posterior view ol superficial veins of the hand
Right external |ugular
Right subclavian
Right
brachiocephalic
Right axillary
Right basilic
Right cephalic
Right
cephalic
Right interna!
jugular
Superior I
vena cava
Sternum -
Right median cubital
Right basilic
Right median antebrachial
Right palmar venous plexus
Right externa
jugular
Right
subclaviar
Right
brachiocephalic
Right
axillary
Right
brachial
Right Internal
jugular
Right
ra dials
(b) Anterior view ol superficial veins
From which vein in the upper limb is a blood sample often taken?
Right deep palmar
venous arch
Right superficial palmar
venous arch
{c) Anterior view of deep veins
408 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
Exhibit 16.7 Veins of the Lower Limbs (Figure 16.15)
OBJECTIVE • Identify the principal veins that drain the lower limbs.
• As with the upper limbs, blood from the
lower limbs is drained by both superficial and
deep veins. The superficial veins often
branch with each other and with deep veins
along their length. All veins of the lower limbs
have valves, which are more numerous than
in veins of the upper limbs.
■ CHECKPOINT
Why are the great saphenous veins clinically
important?
Vein
Description and Region Drained
Superficial Veins
Great saphenous veins
(sa-FE-nus = clearly visible)
Small saphenous veins
Deep Veins
Posterior tibial veins
(TIB-e-al)
Anterior tibial veins
Popliteal veins
(pop'-li-TE-al; popliteus
.hollow behind knee)
Femoral veins
(FEM-o-ral)
The great saphenous veins, the longest veins in the body, begin at the medial side of the dorsal venous arches
(VE-nus) of the foot, networks of veins on the top of the foot that collect blood from the toes. The great saphenous
veins empty into the femoral veins, and they mainly drain the leg and thigh, the groin, external genitals, and
abdominal wall. Along their length, the great saphenous veins have from 10 to 20 valves, with more located in the
leg than the thigh. The great saphenous veins are often used for prolonged administration of intravenous fluids.
This is particularly important in very young children and in patients of any age who are in shock and whose veins
are collapsed. The great saphenous veins are also often used as a source of vascular grafts, especially for coronary
bypass surgery. In the procedure, the vein is removed and then reversed so that the valves do not obstruct the flow
of blood.
The small saphenous veins begin at the lateral side of the dorsal venous arches of the foot. They empty into the
popliteal veins behind the knee. Along their length, the small saphenous veins have from 9 to 12 valves. The small
saphenous veins drain the foot and leg.
The deep plantar venous arches on the soles drain the toes and ultimately give rise to the paired posterior tibial
veins. They accompany the posterior tibial arteries through the leg and drain the foot and posterior leg muscles.
About two-thirds the way up the leg, the posterior tibial veins drain blood from the fibular (peroneal) veins, which
serve the lateral and posterior leg muscles.
The paired anterior tibial veins arise in the dorsal venous arch and accompany each anterior tibial artery. They
unite with the posterior tibial veins to form the popliteal vein. The anterior tibial veins drain the ankle joint, kni
tibiofibular joint, and anterior portion of the leg.
The popliteal veins are formed by the union of the anterior and posterior tibial veins. They drain the skin, muscles,
and bones of the knee joint.
The femoral veins accompany each femoral artery and are the continuations of the popliteal veins. They drain tf
muscles of the thighs, femurs, external genitals, and superficial lymph nodes. The femoral veins enter the pelvic
cavity, where they are known as the external iliac veins. The external and internal iliac veins unite to form the
common iliac veins, which unite to form the inferior vena cava.
Circulatory Routes 409
Figure 16.15 Principal veins of the pelvis and lower limbs.
All veins of the lower limbs have valves.
£ fl "
Inferior vena cava
Right common iliac
Right internal iliac
Right external iliac
Right anterior tibial
Right small saphenous
Left common
iac
Right femoral
Right great saphenous
Right popliteal
Right great saphenous
Right posterior tibial
Right dorsal
venous arch
(a) Anterior view
Which veins of the lower limb are superficial?
Right deep plantar
venous arch
Right small saphenous
Right fibular
(peroneal)
(b) Posterior view
Focus on Well
Artena.
Undoing the Damage
of Atherosclerosis
lllot so long ago scientists believed that
once plaque formed in an artery, it
never went away. Medical researchers
thought that lifestyle changes and
drugs could slow the process of athero-
sclerosis, but they could not undo dam-
age already done. In recent years, how-
ever, researchers have discovered that
the body's own healing processes can
reverse arterial plaque buildup.
Lifestyle changes and drug treatments
appear to stabilize the most dangerous
atherosclerotic plaques and may even
eliminate the need for surgical inter-
ventions, such as bypass surgery, in
some people-
Stabilizing Dangerous Plaque
The health risk imposed by plaque that
accumulates within the artery lining
depends upon several factors. Some
plaque is fairly stable: It has a low r lipid
content, is not growing much in size,
and has a strong fibrous cap that keeps
it from rupturing when blood pressure
rises. Unstable plaque is characterized
by a large accumulation of lipid in its
core and only a thin fibrous cap. In ad-
dition, unstable plaques contain a large
number of macrophages. In a mis-
guided attempt to heal endothelial
damage, macrophages ingest plaque
lipids; the net result is increased arter-
ial injury and lipid accumulation. An
unstable plaque is apt to rupture, trig-
gering formation of a life-threatening
blood clot at the plaque site.
Aggressive Prevention
The first step in preventing, slowing,
and possibly reversing artery disease is
to control the risk factors associated
with its progression. Recommenda-
tions for a heart-healthy and artery-
healthy lifestyle include no smoking,
regular exercise (at least 30 minutes of
moderate-intensity exercise per day),
stress management, and a heart-healthy
diet. Diet recommendations include
limiting fat intake and dramatically in-
creasing consumption of plant foods,
such as grains, fruits, and vegetables,
These recommendations help prevent
arterial disease by reducing obesiB
blood lipids, platelet stickiness, and,
blood pressure, and by improving blood
glucose control in people at risl
type 2 diabetes.
Studies have found that only diets extremely low in fat (10% or fewer ca
ties from fat) lead to plaque regression. Why do you think public health of
rials generally recommend a diet that supplies up to 30% of its calories
fat? Do you think this recommendation should he lower? Remember, this
guideline is supposed to apply to all North Americans, not just those at in
for artery disease.
Pulmonary Circulation
When deoxygenated blood returns to the heart from die sys-
temic route, it is pumped out of the right ventricle into the
Lungs. In the lungs, it loses carbon dioxide and picks up oxy-
gen. Now bright red again, the blood returns to the left
atrium of the heart and is pumped again into the systemic
circulation. The flow of deoxygenated blood from the right
ventricle to the air sacs of the lungs and the return of oxy-
genated blood from the air sacs to the left atrium is called the
pulmonary circulation (see Figure 16.8). The pulmonary
trunk emerges from the right ventricle and then divides into
two branches. The right pulmonary artery runs to the right
lung; the left pulmonary artery goes to the left lung. After
birth, the pulmonary arteries are the only arteries that carry
deoxygenated blood. On entering the lungs, the branches di-
vide and subdivide until ultimately they form capillaries
around the air sacs in the lungs. Carbon dioxide passes horn
410
the blood into the air sacs and is exhaled, while inhaled]
gen passes from the air sacs into the blood. The capilla
unite, venules and veins are formed, and, eventually, two]
monary veins from each lung transport the oxygenated
to the left atrium. (After birth, the pulmonary veins are;
only veins that carry oxygenated blood.) Contractions on
left ventricle then send the blood into die system le ciivulat
Hepatic Portal Circulation
A vein that carries blood from one capillary network to ara
called a portal vein. The hepatic portal vein, formed
union of the splenic and superior mesenteric veins
16.16), receives blood from capillaries of digestive organsi
livers it to capillary-like structures in the liver called sinusoid
the hepatic portal circulation (hepat- = liver), venous blood J
the gastrointestinal organs and spleen, rich with substan
sorbed from the gastrointestinal tract, is delivered to the 1
411
Figure 16.16 Hepatic portal circulation.
\ The hepatic portal circulation delivers venous blood from the gastrointestinal organs and
spleen to the liver-
Inferior vena cava Sto mach
Cecum
Appendix
Hepatic vein
Liver
HEPATIC
PORTAL VEIN
Gallbladder
Small intestine
SUPERIOR
MESENTERIC
VEIN
Large intestine
Spleen
Pancreas (behind
stomach)
SPLENIC VEIN
Large intestine
(a) Anterior view of veins draining into the hepatic portal vein
^^J^T^
Inferior vena
cava
r
Hepatic
veins
Abdominal
aorta
Proper hepatic
artery
Splenic
Superior
mesenteric
vein
Tributaries from spleen,
stomach, pancreas, and
portions of large intestine
Tributaries from
small intestine and
portions of large intestine,
stomach, and pancreas
(b) Scheme of principal blood vessels of hepatic portal circulation and arterial
supply and venous drainage of liver
Which veins carry blood away from the liver?
41 2 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
portal vein and enters the liver. The liver processes these sub-
stances before they pass into the general circulation. At the same
time, the liver receives oxygenated blood from the systemic cir-
culation via the hepatic artery. The oxygenated blood mixes with
the dcoxygenated blood in sinusoids. Ultimately, all blood leaves
the sinusoids of the liver through the hepatic veins, which drain
into die inferior vena cava.
Fetal Circulation
The circulatory system of a fetus, called fetal circulation, ex-
ists only in the fetus and contains special structures that allow
the developing fetus to exchange materials with its mother
(Figure 16.17). It differs from the postnatal (after birth) cir-
culation because the lungs, kidneys, and gastrointestinal or-
gans do not begin to function until birth. The fetus obtains
2 and nutrients from and eliminates CO? and other wastes
into the maternal blood.
The exchange of materials between fetal and maternal
circulations occurs through the placenta (pla-SF.N-ta), which
forms inside the mother's uterus and attaches to the umbili-
cus (navel) of the fetus by the umbilical cord (uni-BlL-i-kal).
Blood passes from the fetus to die placenta via two umbilical
arteries (Figure 16.17a). These branches of the internal iliac
arteries are within the umbilical cord. At the placenta, fetal
blood picks up Q 2 and nutrients and eliminates CO? and
wastes. The oxygenated blood returns from the placenta via a
single umbilical vein. This vein ascends to the liver of the fe-
tus, where it divides into two branches. Some blood flows
through the branch that joins the hepatic portal vein and en-
ters the liver, but most of the blood flows into the second
branch, the ductus venoms (DUK-tus ve-NO-sus), which
drains into the inferior vena cava.
Deoxygenated blood returning from lower body regions
of the fetus mingles witli oxygenated blood from the ductus
venosus in the interior vena cava. This mixed blood then en-
ters the right atrium. Deoxygenated blood returning from
upper body regions of the fetus enters the superior vena cava
and passes into the right atrium.
Most of the fetal blood does not pass from the right ven-
tricle to the lungs, as it does in postnatal circulation, because
an opening called the foramen ovale (fo-RA-men 6-VAL-e)
exists in the septum between the right and left atria. About
one-third of the blood that enters the right atrium passes
through the foramen ovale into the left atrium and joins the
systemic circulation. The blood that does pass into the right
ventricle is pumped into the pulmonary trunk, but little of
this blood reaches the nonfunctioning fetal lungs. Instead,
most is sent through the ductus arteriosus (ar-te-rc-O-sus), a
vessel that connects the pulmonary trunk with the aorta, so
that most hi nod bypasses the fetal lungs. The blood in the
aorta is carried to all fetal tissues through the systemic circu-
lation. When the common iliac arteries branch into the ex-
ternal and internal iliacs, part of the blood flows into the in-
ternal iliacs, into the umbilical arteries, and back to the
placenta for another exchange of materials.
After birth, when pulmonary (lung), renal, and digestivi
functions begin, the following vascular changes occur (Fig
ure 16,17b):
1. When the umbilical cord is tied off, blood no longei
flows through the umbilical arteries, they fill with con-
nective tissue, and the distal portions of the umbilical
arteries become fibrous cords called medial ■umbilical
ligaments,
2. The umbilical vein collapses but remains as the ligamm
turn teres (round ligament), a structure that attache^
the umbilicus to the liver.
3. The ductus venosus collapses but remains as the liga-
mention venomm, a fibrous cord on the inferior surfaoa
of the liver.
4. The placenta is expelled as the "afterbirth."
5. The foramen ovale normally closes shortly after birth toj
become the fossa ovalis, a depression in the interatrial
septum. When an infant takes its first breath, the lung
expand and blood flow to the lungs increases. Blood ra
turning from the lungs to the heart increases pressurej]
the left atrium. This closes the foramen ovale by pus
ing the valve that guards it against the interatrial se
turn. Permanent closure occurs in about a year.
6. The ductus arteriosus closes by vasoconstriction aimed
immediately after birth and becomes the ligameiitunt
arteriosimt.
■ CHECKPOINT
10. What are the main functions of the systemic, puJ
monary, hepatic portal, and fetal circulations?
AGING AND THE
CARDIOVASCULAR SYSTEM
OBJECTIVE • Describe the effects of aging on the]
cardiovascular system.
General changes in the cardiovascular system associated
with aging include increased stiffness of the aorta. reductiJ
in cardiac muscle fiber size, progressive loss of cardiac mil
cular strength, reduced cardiac output, a decline in mam
mum heart rate, and an increase in systolic blood press™
Coronary artery disease (CAD) is the major cause of heJ
disease and death in older Americans. Congestive In
ure (CHF), a set of symptoms associated with impaij
pumping of the heart, is also prevalent in older indivic
Changes in blood vessels that serve brain tissue— fores!
pie, atherosclerosis — reduce nourishment to the brain
result in the mall-unction or death of brain cells. By age
blood flow to the brain is 20% less, and blood How to 1
kidneys is 50% less, than it was in the same person at age;
CHECKPOINT
: What are some of the signs that the cardiovascular sys-
tem is aging?
To appreciate the many ways the cardiovascular system
tributes to homeostasis of other body systems, examine
Aging and the Cardiovascular System 41 3
Focus on Homeostasis: The Cardiovascular System on page
414. Next, in Chapter 17, we will examine the structure and
function of the lymphatic system, seeing how it returns ex-
cess fluid filtered from capillaries to the cardiovascular sys-
tem. We will also take a more detailed look at how some
white blood cells function as defenders of the body by carry-
ing out immune responses.
lure 16.17 Fetal circulation and changes at birth. The boxes between parts (a) and (b) describe the fate of certain fetal structures
[dice postnatal circulation is established.
The lungs and gastrointestinal organs do not begin to function until birth.
Right
atrium
Right
ventricle
(a) Fetal circulation
Heart
Arch of aorta
Superior vena cava
DUCTUS ARTERIOSUS
becomes
Ligamentum arteriosum
Lung
Pulmonary artery
Pulmonary veins
FORAMEN
OVALE becomes
Fossa ovalis
Liver
DUCTUS VENOSUS
becomes
Ligamentum venosum
Hepatic portal vein
UMBILICAL VEIN
becomes
Ligamentum teres
Umbilicus
Inferior vena cava
Abdominal aorta
Common iliac artery
UMBILICAL ARTERIES
become
Medial umbilical ligaments
Urinary bladder
Urethra
UMBILICAL CORD
placenta
Left
atrium
'Which
structure provides for exchange of materials between mother and fetus?
(b) Circulation at birth
Oxygenated blood
Mixed oxygenated and
deoxygenated blood
Deoxygenated blood
FOCUS
ON
HOMEOSTASIS
Body System
For all body
systems
Integumentary
system
Skeletal system
Jl
The Cardiovascular System
Contribution of the Cardiovascular System
The heart pumps blood through blood vessels to body tissues, delivering oxygen and nutrients
and removing wastes by means of capillary exchange. Circulating blood keeps body tissues ata
proper temperature.
Blood delivers clotting factors and white blood cells that aid in hemostasis when skin Is dam-
aged and contribute to repair of injured skin. Changes in skin blood flow contribute to body tow
perature regulation by adjusting the amount of heat loss via the skin. Blood flowing in skin may
give skin a pink hue.
Blood delivers calcium and phosphate ions that are needed for building bone extracellular ma*
trix, hormones that govern building and breakdown of bone extracellular matrix, and erythropoi*
etin that stimulates production of red blood cells by red bone marrow.
Muscular system
Blood circulating through exercising muscles remove heat and lactic acid-
Nervous system
Endothelial cells lining choroid plexuses in brain ventricles help produce cerebrospinal lluid
(CSF) and contribute to the blood-brain barrier.
Endocrine
system
Circulating blood delivers most hormones to their target tissues. Atrial cells of the heart secret*
atrial natriuretic peptide.
Lymphatic
system and
immunity
Circulating blood distributes lymphocytes, antibodies, and macrophages that carry out immune
functions. Lymph forms from excess interstitial fluid, which filters from blood plasma duo to
blood pressure generated by the heart.
Respiratory
system
Circulating blood transports oxygen from the lungs to body tissues and carbon dioxide to the
lungs for exhalation.
Digestive system
Blood carries newly absorbed nutrients and water to the liver. Blood distributes hormones thai
aid digestion.
Urinary system
f
The heart and blood vessels deliver 20% of the resting cardiac output to the kidneys, where
blood is filtered, needed substances are reabsorbed, and unneeded substances are eliminated
as part of urine, which is excreted.
Reproductive
systems
414
Vasodilation of arterioles in the penis and clitoris causes erection during sexual intercourse,
Blood distributes hormones that regulate reproductive functions.
Common Disorders 415
W COMMON
DISORDERS
Hypertension
JO million Americans have hypertension, or persistently high
pressure. It is the mosi common disorder affecting the bean
Sblnod vessels and is the major cause of heart failure, kidney dfe-
md stroke. In Ma\ 2003, the Joint National Comnutteje on
nun. Detection, Evaluation, and Treatment ol High Blood
published new guidelines lor hypertension because clinical
: ,. linked what were ..nee considered hurl) low pressure
flings to an increased risk of cardiovascular disease. The new
„ :. ■ , ;!• I ..lion-:
Systolic (mm Hg) Diastolic (mm Hg)
| N „ rrni i Less than 1 20 «td Less than 80
EhviKrtension m-WW 8M»
[hypertension MO- IS*'" 9®
hypertension Greater than 1 60 or C heater than 1 00
Using the new guidelines, the manna I classification was previ-
fc considered optimal; prchypertensiofl now ineludes many more
Uvuhials previousl) classified as normal or high-normal; stage I
jenensiun is the same as in previous guidelines; and stag* 2 liy-
jBnsion now combines the previous stage 2 and stage J categories
, „ nl options are ihe same for the former stages - 1 an* *>
Although several categories of drugs can reduce elevated bfoed
sure, iiu following lifestyle changes are also effective in manaj-
JflJiyuerterision: .
I hue Pcijiht. This is the best treatment lor high blood pressure
usine drugs. I a.ss of even a few pounds helps reduce
blood pressure in overweight hypertensive individuals.
putt nkobol make, Drinking in moderation may tower die risk
nl'coronan Heart disease, mainly among males over 45 ami Ic-
(jafes over 55. Moderation is defined as so more than one 12
Lbeer per da) For females and no more lhan two L2-02 beers
for males.
, Becoming more physically (it by engaging in moderate
.. 1 5l ,ch as brisk walking) sei cral times a week tor ffl to 45
Scutes can lower systolic blood pressure by about 10 mm Hg.
JMut inmke af sodium (Sffit). Roughly half the people with hy-
i sion are "salt sensitive." For them, a high-sail did > P
S0ICAL TFRMINQLOGY AND CONDITIONS
Wio^csi, (an ie-o-JEN-e-sis) Formation of new blood vessels:
ggftpfty (u'-or 1 1 KJ-ra-fi) X-ray examination ol the aorta and
ilsmain branches after injection ol a dye.
xuiutinn lime The time required for a drop c*J Wood m pass
ifrum the right atrium, through the pulmonary circulation, hack
. ,, ,. ft icrium, through the systemic circulation, down to
00 t, and back again to the rfgm atrium-, normally about 1
,-niimtc in a resting person.
pears Bo promote hypertension and a low-salt diet can lowei
their blood pressure.
• Xhimiaiii mwmnenM dictttr) &pfa of patassitim, aikwm, mm
mammim. Higher levels of potassium, calcium, and magne-
sium in the diet are associated with a bwei risk of hypertension.
• Dm/t mtoMe, Smokmg has devastatJ ffi CIS on the heart, and
can augment the damaging effects of high blood pressure U
promoting VBSQP.OnStJ action.
• Mmsm tt&fc Various meditation and biofeedback techniques
help some people redtice high blood pressure. I hese methods
may work by decreasing the dail\ release of epinephrine and
norepinephrine hy the adrenal meilulla.
Shock
Shock is fl failure of the cardiovascular system to deliver enough < >
m d mum in-, to meet cellular metabolic needs, fhi i Fshocfe
are many and varied, but all are I baraeteri/.ed bj mudci|ii.itc blood
flow to body tissues, Common causes of shock include loss Oi bode
fluids, as occurs W hemorchagei dehydraiion, burns, excessive vom-
umu, diarrhea, OT sweating. IT shock persists, cells and orgUBS be
eo.ue damaged, ami cells may die unless proper treatment begins
ipiicklv. .
Although the symptoms of shock vary with the severe ol me
condition, the Following arc commonly observed: systolic bfood
pressure lower iban % mm 1 lg; rapid resting hen I rate due lo van-
pathetic stimulation and increased blo.nl levels ol epinephrine and
norepinephrine, weak, rapid pulse ^ ro reduced cardiac output
and hist heart rale; cool, pale skin due to vasoconstriction ol SI n
blood vessels; sweating due to sympathc-nc stimulation reduced
urine formation and ouiput due to increased levels ol aldoMerone
and lun.ditirei.c hormone- (AlJll): altered mental state due to re-
duced osygen M.pplv to the brain; cfeirst mic m loss ol eMia.ellular
llnid: aiid i.ausea due to impviired cireulatton to digestive Organs.
Aneurysm
\n aneurysm (ANnVriyan) is a thin, weakened section of the wall ol
an ;uterv'<.r a vein thai bulges outward, forming a balloonlike sac.
Common causes are atihe*osclerOsis, svphibs, congenital bbod ves-
sel defects, and trauma. Lf untreated, ihe aneurysm enlarges and the
blood vessel wall becomes so thin that it hursts. The result is mas-
sive hemorrhage along with shock, severe pain, stroke, or death.
Claudication [Uaw'-dhlvVshun) Pain and lameness or limping
caused by defective circulation of the blood in the vesseM the
limbs.
Deep vein thrombosis (BIT) 'Hie presence of a thrombus (Nood
riot) in a deep vein of the lower limbs.
Hypotension (hi-po-'l hX'-shun) Low blood pressure: mosi 01 I
nionh used lo describe an acute drop in blood pressure. 85 Q.«
curs during excessive blood loss.
41 6 Chapter 16 The Cardiovascular Syslem: Blood Vessels and Circulation
Occlusion (6-KLOO-ahun,) The closure or obstruction of the lu-
men of n structure such as a blood vessel. An example is an ath-
erosd erotic plaque in an Srtery.
Orthostatic hypotension (or'-tho-S "!'AT-ik; oriho- — straight; -i*itj8
= causing bo stand) \n c\e< ssive towering i »f systemic blood
. ssiuv when a person stands up; usually a sign of disease.
May be caused by excessive fluid loss, certain drugs, and car-
diovascular or neurogenic factors. Also called post urn I hypoten-
sion.
"Phlebitis (fle-BI-tis; phkb- — vein) Inflammation of a vein, often in
.i [eg, rin- o.iulnn.n i-, often accompanied by pain and redness
of the sjdfi over the inflamed vein. It is frequently caused ■
trauma or bacterial infection.
Syncope (SINI-kn-pe) A temporary cessation of cousciousnesv i
faint. C )ne cause is insufficient blood supply to die brain.
Thrombophlebitis iihr '-li.~p-lh.--rd u-o Inflammation of a vi in
voicing clot formation. Superficial thrombophlebitis oci
Veins under rhe skin, especially in the calf.
White coat (office) hypertension A stress-induced symlrniru
in patients who have elevated blood pressure when being i-oi
ined by health-care personnel, but otherwise have norrj
blood pfessuue.
in
STUDY OUTLINE
" ■ Blood vessel Structure and Function (p. 386)
1. Arteries carry blood .may from the heart. Their walls consist ol
three layers.
2. The structure ol die middle layer gives arteries their two major
properties, elasticity and contractility.
3. Arterioles are small arteries that deliver blood to capillaries.
4. Through constriction and dilation, arterioles play a key role in
regulating blood flow from arteries into capillaries;
5. Capillaries aw microscopic blood vessels through which mate-
rials are exchanged between blood and interstitial lluid.
6. Precapillary sphincters regulate blood llow through capillaries.
7. Capillary blood pressure "poshes" Ihud out oj 'capillaries into
interstitial fluid (filtration).
8. Bipod colloid osmotic pressure "pulls"' fluid into capillaries
from interstitial fluid (reabsorpm an
9. A mo regulation refers to local adjustments of blood flow in re-
sponse co physical arid chemical changes m a tissue.
10. Venules arc small vessels that emerge from capillaries and
merge to form veins. 1 hey drain blood from capillaries into
veins.
11. Vein- consist "I the same three layers as arteries but have less
elastic tissue and smooth muscle. They contain valves that pre-
vent baekilow o| blood.
12. Weak venous valves can lead to varicose veins.
13. Venous return., the volume of blood flowing back to the heart
through systemic veins; occurs due to the pumping action ol
the heart, aided by skeletal muscle contractions (the skeletal
muscle pump), and breathing {the respiratory pump).
Blood Flow Through Blood Vessels (p. 390)
1. Blood flow is determined by blood pressure and vascular resis-
tance.
2. Bli" >d lh m s hi an regions of higher pressure 10 regions of lower
ptifiESUft ■
3. Blood pressure is highest in the aorta and large sysreink
ies: it drops progressively as distance from the left vcium
creases. Blood pressure in the right atrium is close to f) nun I
4. An increase m blood volume increases blood pressure ,inih
decrease in blood volume decreases it,
5. Vascular resistance is the opposition to blood flow inainlrq
result of friction between blood and the walls of bloCHJ
6. Vascular resistance depends on size ol the hi I
blood viscosity, and total blood vessel length.
7. Blood pressure and blood (low art regulated by neural, afldlj
monal negative lecdbacl systems and by ivutuieguladoi
8. The cardiovascular center in the medulla oblongata hcl[*
late heart rate, stroke volume, and size of blood vessel 1
9. Vasomotor nerves (sympathetic) control vasoconstriei
vasodilation.
It). Baroreceptors (pressure-sensitive receptors) send
the cardiovascular center to regulate blood pressure.
11. Chcinorcceptors (receptors sensitive- to concentration.".
gerii carbon dioxide, and hydrogen ions) also send rinpuls
the cardiovascular center to regulate blood pressure.
12. I lormoiies such as angiotensin II, aldosterone, cpinepJ
epinephrine, and antidiuretic hormone raise blood pre,
natriuretic peptide lowers it.
Checking Circulation (p. 394)
1. Pulse is the alternate expansion and elastic recoil p$j
with each heartbeat. It may he felt in any artery thai
the surface or over a hard tissue.
2. A normal pulse rate is about 7ii-S(i heats per minute,
3. Blood pressure is the pressure exerted l>\ hlnod on if
an artery when the left ventricle undergoes systole anil i
astole. It is measured by a sphygmomanometer
4. Systolic blood pressure (SB1 1 ) is die force ol blood recort
i.n» ventricular conn ■action. Diastolic blood pressure
1 1 'ivr of blood recorded during ventricular relaxation,
blood pressure of a young adult male is less than I2(
Circulatory Routes (p. 394)
he two mniur circulatory routes arc the systemic circulation
and the pulmonary circulation.
, systemic circulation lakes oxygenated blood Broai the left
1 wmtride through the aorta to all pans of the body and returns
;ceov\gcnated blood to the right atrium.
The pints of the aorta include the aseendmg aorta, the an
the aorta, the thoracic aona, and the abdominal wf*. E*c&
pan piv.es off arteries that branch to supply the whole body.
. ;cnated blond is returned K> the heart Trough the ays-
jemieteins. All the veins of systemic circulation flow into ci-
ther the superior or inferior vena cava or the coftMftty S»us,
which empty into die right atrium.
,ulmon;vn circulation takes deoxygenated blood from the
right ventricle to the air sacs of the tengS and returns oxy-
! Wood from the air sacs to the left atrium. Il allows
; sygenntcd for systemic circulation.
Sell-Quiz 417
6. I he hepatic portal circulation collects deoxygenated blood
from the veins of the gastroimesiinal trad and spleen and di-
et ( D it into the hepatic portal vein of the liver. This routing al-
lows the livei to extract and uiodily nutrients and deioxib
harmful substances in the blood. The liver also receives oxy-
genated blood from the hepatic 9W ttf,
7. Fetal circulation exists only 111 the fetus, h involves the ex-
change of materials between fetus and mother via the placenta.
The Veins derives : and nutrients from am! eliminates CG 2
ami wastes into maternal blnod. \t built, when pulmonary
(king), digestive, and liver functions begin, the special struc-
tures of tetal circulation are no longer needed.
Aging and the Cardiovascular System (p. 412)
1. General changes associated with aging include reduced ekstic-
iry of blood vessels, reduction in eardiae muscle si/.e. reduced
cardiac output, and increased systolic blnod pressure.
2. The incidence of coronary arlen disease n M^ congestive
bean laihuv <( 3 ITT and atherosclerosis increases with
JELF-QUI
Sensory receptors that monitor changes in the blood pressure
j to the brain are
i i , morei cptors in the aorta
|i. iMrorcccpmrs in the carotid arteries
aortic bodies
I precapillary sphincters in the arterioles
proprioceptors in die muscles
|p fa] I vessels that allow the exchange of nutrients, wastes,
mi | C ; ir bon dioxide between the blood and tissues are
irie.s h. arteries c. venules d. arterioles
Lances undergo capillary exchange hj nic nisei
pmple diffusion and hulk fiou
t. uuloatosis. exoeytosis, and active transport
[ ft simple diffusion and facilitated diffusion
,l . , ,J Jil'tiision and active transport
[»e. filtration, re-absorption, an. I secretion
: IWs through the blood vessels because "I the
shment of a concentration gr
recoil of the veins
191 J llshmentof-J pressure gradient
k mess i of the blood
. tliimuss of the walls of capillaries
...ik-li of the following represents pulmonan circulation as the
Imvs from the righi ventricle;
icnary trunk — pulmonary veins -> pulmonary cnpil-
-* pulmonan arteries
pulmonary arteries -» pulmonary capillaries — pulmonary
i . ,.| * pulmonary '.ems
c. indmonary capillaries — pulmonary trunk -" pulmonary ar-
i cries — > pulmonan veins
d. pulmonary crunk — pulmonan aru i les - • pulmonan i ap
Maries — pulmonary veins
e. pulmonary wins -* pulmonarj capillaries -* pu'liuon®
arteries — * pulmonary trunk
6. 1 be 1 issue thai allows arteries to stretch 13
a. endothelium b. collagen C. basement membrane
d. cardiac muscle c. elastic lamina
7. .Yltuh ihe following descriptions to the appropriate I
vessel:
a. composed of a single !.u
endothelial ceBsanda A "
li.jsc-nis.-m ineinbraiie B< arterioles
b. formed In ■reuniting' capillaries ' cms
c. carry blood away from heart D. venules
d. regul.ue blood (low loeapilhu us E. capillaries
e. may contain valves
8. nUrahon of substances out ofcajriMaries bei ors when the eapij-
|;ii-«, blood pressure
a. is less than the blood colloid osmotic pressure
b. and the blood colloid osmotic pressure are equal
c. is high and the blood colloid osmotic pressure is high
d. is higher than the blood colloid osmotic pressure
c. is low and ihe blood colloid osmotic pressure is low
9. Weakened leg muscles would slow 1 Ik-
a., blood Bow "iii ol the heart
b. respirator} pump
c. venous return
d. ability ol arteries to vasodilate
e. pulse
41 8 Chapter 16 The Cardiovascular System: Blood Vessels and Circulation
in. Which of the following statements about Wood vessels is truer
a. Capillaries contain valves.
b. V5fells.ofart«cteS;are general]) thicket rand cantata mom
clastic tissue than mAii of veins.
c. Veins carry blood awa) front the heart.
d. Blood Sows most rapidh through veins.
e. Blood pressure, in arteries is always lover than in veins.
11. Wh is ii important th.it blood Sows slowly through the c.ipil-
lanes?
a. Ii allows tune for the materials in the blood to puss through
i lit- chklc capillary waits.
h. It prevents damage to the capillaries.
« . h pennies the efficient exchange of nutrients and wastes be-
tween the blood and body ■ clK.
d. It allows the heart time to rest.
0. It allows the blood pressure hi capillaries EO me alwne die
blood pressure in the veins.
12. Match the rblJowjagl
a. source of all systemic
arteries
b. supplies a lower ttmfo
c. bean s blood system
d. returns blood to heart
frnni lover limbs
. . e. carries blood CO liver
f, lends to lungs
A. hepatic- purral vein
B. pulmonary trunk
C. pulmonary vein
D. common iliac arterj
F. coronary circulation
F. inferior vena cava
(;. siiperuir vena cava
H- aorta
_ g. returns blood from lungs , a , rd ,, lhl| . k , u | cird ,
in lieai i
h. supplies blood to brain
i. returns blood to heart from head an. I upper body
13. For each of the following ftciorv indicate if it increases (A) or
decreases (ii) blood pressure:
a;, an increase in cardiac output
b. hemorrhage
c. vasodilation
d. vasoconstriction
e, stimulation of the heart h\ tlie sympathetic nervous
system
f. hypoxia
g. epinephrine
h. increase in blood volume
i. bradycardia
14. Aldosterone affects blood pressure by
a. increasing heart rate
b. increasing vasoconstriction of arterioles
c. reducing Mood volume
d. stimulating release oi atrial natriuretic peptide by the hear
e. increasing reabsorprion of Sodium ions ami water hy the
i idiievs
15. In a blood pressure reading of 1 1 0/70.
a. I in repr, sents ihe diastolic pressure
b. 70 represents the pressure of the blond against the arteria
during ventricular relaxation
C; I 10 represents the blood pressure ami 70 represents the
heart rate
(I. 70 is the reading taken when the first sound is beard
e. the patient has a severe problem unit hypertension
16. Which of the following statements is NOT true?
a. Regulation of blood vessel diameter originates from :
somoror region of the cerebral Cortex.
b. The cerebral cortex m;n provide input to the CX center.
e. Raro receptors maj stimulate the cardiovascular center
d* Activation ol proprioceptors increases heart rate at iIil- be-
ginning o I exercise.
c. Vasomotor tone is due to a moderate lev?] of vasoomstripj
tlOII.
17. Venous return to the heart is enhanced by all of the foil
FXC.FPT
a. skeletal muscle "milking* 1
F. waives in veins
c. the pressure difference from venules to the riglu
d. vasodilation
e* inhalation during breathing
I
i CRITICALTHINKING APPLICATIONS
J. The l<.c-.i1 anesthetic injected by a dentisi often contains a small
amount of epinephrine. What effect would epinephrine have
un the blood vessels in the viciiuty of E&fl dental work? Win
I might this effect be desired?
EL In this chapter, you've read about varicose veins. Why didn't
read about varicose arteries?
5, Jalif was all flustered when she run m late to her anatomy and
i fogy lab- She had spilled a cup of coffee on herself n bile
she was weaving in and out of traffic white tr> mg to get around
i traffic jam. Then she missed her exit while she was changing
Answers to Figure Questions 419
the station on the radii), couldn't rind a place to park, and
missed the lab qui/.. The life today is learning to rake blood
pressures, and Julie's is highl (Us normally I LQ over "<).) vVtiill
is i Ik- physiological expknatiOB for Julie's elevated BE?
4. Peter spent 10 minutes snarpning his faw.nre knife before
carving the roast. Unfortunately, he sliced Ins linger along with
i lie roast Hi-- wife slapped a towel over tine spurting cm and
drove him ro the emergency room. What type ol vessel did IV-
tcrcut. .ind how do voti know?
ANSWERS TO FIGURE QUESTIONS
The femoral artery has the thicker wall; the femoral vein has
I'cr lumen.
AK-uil»olieally active tissues haw more capillaries because
ihcy list- oxygen and product wastes more rapid!) than inac-
tive tissues,
i | X.CCS5 filtered Hu-id and proteins that escape from plasma
drain into lymphatic capillaries and are returned by the l\ m-
prinuc system to die cn'diov ascuhir system.
The skeletal muscle pump and the respiratory pump help
boost venous return.
RlftiS Vs blood pressure increases, blood flow increases.
| Vasoconstriction increases vascular resistance, which de-
ist's blood Row through the vasoconstricfed Mood vessels.
ii happens when you stand up because gravity causes pooling
ol blood in leg veins as you stand Upright, decreasing the
ibod pressure in your upper body
TIk principal cm ulatory mutes are the systemic and the
ijulmonarv circulations.
16.9 The four parts ol " i hi- at trta are the ascending aorta, arch of
the aorta, thoracic aorta, and abdominal aona.
16.10 Branches, "h he arch of die aorta are the hraeluoecpli alu
trunk, left common carotid artery, and left subclavian artery
16.11 The abdominal aorta di\ulcs into die amnion iliac art* ;i. -
at about the level oldie fourth lumbar vertebra.
16.12 The superior vena cava drains regions above the diaphragm
(except the cardiac veins and the alveoli of the ItiligM. and
the inferior vena cava drains regions below the diaphragm,
16.13 Ml venous blood in the brain drains into the internal jugular
veins.
16.14 The median cubital vein is often used For withdrawing
blond.
16.1 5 Superficial veins of the lower limbs include the dorsal %■ i
arch and the great saphenous and small saphenous \
16.16 The hepatic veins carry blood aw a j. From the liver.
16.17 The exchange ol materials bcrvveen mother and fetus ik i
across the placenta.
chapter 1
THE LYMPHATIC SYSTEM
AND IMMUNITY
/\
did you know?
good laugh not
only feels great, it is good mediant' as well.
Researchers exploring the health benefits of
humor suggest that a good seme of humor
enhances your health, partly because it
helps to protect the immune system.
Laughter increases blood levels of impor-
tant immune components, such as im-
munoglobulin /!, which helps fight infec-
tions in the upper respiratory and
gastrointestinal tracts. Some research has
shown that laughter may also increase lev-
els of disease -fight lag T cells and natural
killer cells. Laughter may exert its effects
by decreasing feelings of stress, and short-
circuiting the stress response and the int-
m unoyuppressiie effects of stress.
Focus on Wellness, page 431
www, wiley.com/college/apcentral
M
j H'ntaint'n g homeostasis in the body requires
continual combat against harmful agents in our
environment. Despite constant exposure Co a
variety n\ pathogens (P:\YH-o-\ens), disease -
producing microbes such as bacteria and viruses.
rJOOSt people remain healthy. The hodv surface also
endures cuts and bumps, exposure to ultraviolet rays in
sunlight, chemical toxins, and minor burns with an array of defenses. In this
chapter, we will explore the mechanisms that provide defenses against intrud-
ers and promote the repair of damaged body tissues.
Immunity or resistance is the ability to use our body's defenses to ward i
damage or disease. The two types nl immunity are ( I ) innate and (2)adaptfil
Innate (nonspecific) bmnnnity relers to defenses that an present at hinh
arc always present and available to provide rapid responses to protect lisagMB
disease. Innate immunity does not involve- specific recognition of a microbe.
acts against all microbes in the same way. However, innate immunity ducsaot
have a menu >rv component, that is, it cannot recall a pre\ bus contact w iili i
foreign molecule. Among the components (if innate immunity arc the first line
of defense (skin and mucous membranes) and the second line of defen-
ural killer cells and phagocytes, inflammation, lever, and antimicrobial sub-
stances). Innate immune responses represent immunity's early-warning
system -,m<\ are designed it? prevent microbes from gaining access into
die body and to help i-limnv.uc those dial do gam ac<
Adaptive (specific) intmumty refers io defenses that involve specific
recognition of a microbe once it has breached the innate immunity ileluiistSL-J
Adaptive immunity is based on a specific response to a specific micron
that is, it adapts or adjusts to handle a specific microbe. Unlike innate im-
munity, adaptive immunit y is slower to respond but it does have a m
component. Adaptive immunity involves fymphocj tes (a type of white
blood cell) called T lymphocytes (T cells) and B lymphocytes (B i
looki
move ahead
■ Veins (page 389)
• Cancer (page 66)
■ Epidermis of Skin (page 99)
• Mucous Membranes (page 90)
• Phagocytosis (page 51)
420
Lymphatic System
421
LYMPHATIC SYSTEM
OBJECTIVES • Describe die components and major
(unctions of the lymphatic system.
L Describe the organization of lymphatic vessels and
the circulation of lymph.
t Compare the structure and functions of the primary
and secondary lymp hatic organs and tissues.
, system responsible fur adaptive immunity (and
fc aspects of innate immunity) is the lymphatic (lim-FAT-
, system, which consists of lymph, lymphatic vessels, a
I i ,j structures and organs confining lymplv.uic i issue,
red hone marrow I e 17.1). Lymphatic tissue is a
, d form of reticular connective tissue (sir Fable 4JC
;vi that contains large numbers of lymphocytes.
Y|,,si components of blood plasma filter our ot blood
walls to form mterstilhil fluid, die fluid mat sur-
feme cells of bod) tissues. After intcrsi-iti-.il fluid passes
,„ 'lymphatic vessels, it is called lymph (LLML -clear
jd).' Both fluids nre chemically similar to blood plasma,
riiiin difference is that interstitial fluid and lymph eon-
i protein than blood plasma because most plasma pro-
jectiles are too large to filter through the capillary
i ch day, about 28 titers of ttoi'd filter frqm blood into
This fluid must be returned tG the eardiosaseu-
•,vmliii to maintain normal blood volume; About 17 liters
fluid filtered daily from the arterial end of blood capil-
ics return to the blood directly by reabsorprion at the \e-
jjjeml »f the capillaries. The remaining 3 liters per day
si into lymphatic vessels and arc then returned CO the
, lymphatic system has three primary fund ions:
Draining excess interstitial fluid. Lymphatic vessels
excess interstitial fluid and leaked proteins from tis-
L spaces and return them to the blood. This activity
WpS maintain fluid balance in the body and prevents de-
af vital plasma proteins.
Transporting dietary lipids. Lymphatic vessels trans-
rtthe Lipids and lipid-soluble vitamins (A. D. V. and K)
rorhed by die gastrointestinal tract into the blood.
Buying out immune responses. Lymphatic tissue im-
, highly specific responses directed against particular
.r abnormal cells.
iptiatic Vessels and Lymph Circulation
■ssels begin as lymphatic capillaries. These liny
re dosed ai one end and located in the spaces be-
i \'.l on page 423). Lymphatic capillaries
• cr than blood capillaries and have a unique
Lhat permits interstitial fluid to flow into them, but
! ht endothelial cells that make up the wall ol a
lymphatic capillary are not attached end to <:m\. but rather,
the ends overlap (Figure 1.7.2b). When pressure is greater in
interstitial lltud than in lymph, the cells separate slightly, like
a one-wav swinging door, and interstitial fluid enters the
lymphatic capillary. V\ 'ben pressure is greater inside the lym-
phatic capillary, the cells adhere more closely and !\ mph can-
not escape back into interstitial tltud.
Unlike blood capillaries, which link two larger blood ves-
sels that form pan of a circuit, lymphatic capillaries begin in
the tissues and carry the lymph that forms there toward a
larger lymphatic vessel.. lust as blood capillaries unite CO Form
venules and veins, lymphatic capillaries unite CO form larger
and larger lymphatic vessels (see figure 17.1). Lymphatic
vessels resemble veins in structure but have thinner walls and
more valves. Located at intervals along lymphatic vessels are
lymph nodes, masses of B cells and I cells that are sur-
rounded by a capsule. Lymph flows through lymph nodes.
From the Lymphatic vessels, lymph eventually passes into
one of two main channels: the thoracic duel or the right lym-
phatic duct. The thoracic duct, the main lymph ••collet'tinti
duct, receives lymph from the leii side of the head. neck, and
chest; the left upper limbi and the enlire bod\ below I he ribs.
The right lymphatic duct drains lymph from the upper Qgtht
side of the body (see FtgUTl 17.1 ).
Ultimately; the thoracic duct empties its lymph into the
jtmeiion of the left internal jugular and left subclavian veins,
and the right lymphatic dud empties Its lymph into the [unc-
tion of the right internal jugular and right subclavian veins.
Thus, lymph drains back into the blood (FigUl el OB page
423).
The same two pumps that aid return of venous blood to
ih. heart maintain the flow of lymph:
1 , Skeletal muscle pump. 1 be "milking action" of skeletal
muscle contractions (see Figure 16*4 on page J9.0) com-
presses lymphatic vessels (as well as veins | and forces
lymph toward the subclavian veins.
2. Respiratory pump. Lymph flow is also maintained by
pressure changes that occur during inhalation (breathing
in). Lymph flows from the abdominal region, where the
pressure is higher, toward the thoracic region, where it is
lower. When the pressures reverse during evhahuiou
(breathing out), the valves prevent backflow ol lymph.
Edema (e-Dli- ma) is an exces.sne accumulation df mleisii-
tial fluid in tissue spaces. It may be caused by ■* lymphatic
tern obstruction, such as an infected lymph node or a
blocked lymphatic vessel. Ldema may also result from in-
creased capillary blood pressure, which c.m^- eXfcfiSS in;
siii.i.il fluid to form faster than it can pass into tymphfttH
vessels or be ceabsorbed Imck into fihe eapiflapes. Another
cause is lack of skeletal muscle com raci ions, as to individu-
als who are paralyzed,
Figure 17.1 Components of the lymphatic system.
The lymphatic system consists of lymph, lymphatic vessels, lymphatic tissues, and red bone marrow.
Palatine lonsil
Submandibular node
Cervical node
Right internal jugular vein
Right lymphatic duct
Right subclavian vein
Thymus
Lymphatic vessel
Thoracic duct
Cisterna chyli
intestinal node
Large intestine
Appendix
Left internal Jugular vein
Thoracic duct
Left subclavian vein
Axillary node
Spleen
Small intestine
Aggregated lymphatic
nodule (Peyer's patch)
iac node
Inguinal node
(bl Areas drained by
right lymphatic and
thoracic ducts
Area drained by
right lymphatic duct
Area drained by
thoracic duct
Functions of the Lymphatic System
1. Draining excess interstitial lluld.
2. Transporting dietary lipids and lipid-solubie vitamins to the blood
3. Carrying out immune responses.
422
(a) Anterior view or principal components oi lymphatic system
What is lymphatic tissue?
Lymphatic System 423
Figure 17.2 Lymphatic capillaries.
Lymphatic capillaries arc found throughout the body except In the centra, nervous syatem. portions o. the spleen, reo bone marrow, end tls-
- sues that lack blood capillaries.
Venule
Interstitial fluid
Lymph
(a) Relationship ol lymphatic capillaries
io tissue cells and blood capillaries
Blood
capillary
Arteriole
Lymphatic
capillary
Why is lymph more similar to inlerstitial fluid than it is to blood plasma?
(b) Details ol a lymphatic capillary
- interstitial fluid
Opening
Tissue cell
Endothelium
of lymphatic
capillary
Lymph
, 17.3 Relationship of lymphatic vessels and lymph nodes to .he cardiovascular syatem. Arrows show the direction ol flow of
land blood.
The secuence of fluid flow is: blood capillaries (blood plasma) - > interstitial spaces (interstitial fluid) - lymphatic capillaries (lymph) - lym-
ph" lymph nodes (lymph) - lymphatic ducts (lymph) . junction of jugular and subclavian veins (bfood plasma).
SYSTEMIC CIRCULATION PULMONARY CIRCULATION
\ Lymph node
Lymphalic
duct
Subclavian
vein
Valve
Lymphatic
vesse
Lymph
node
Lymphatic
capillaries
Pulmonary
blood
capillanes
Systemic
blood
capillaries
Lymphalic
capillaries
Which vessels
of the cardiovascular system (arteries, veins, or capillaries) produce lymph?
424 Chapter 17 The Lymphatic System and Immunity
Lymphatic Organs and Tissues
Lymphatic organs and tissues, which are widely distributed
throughaui the body, are classified into two groups based on
their functions. Primary lymphatic organs and tissues, the
sites where Mem ceils divide and develop into mature B cells
and T cells, include the red hone marrow (in ilui bones and
the ends of the long hemes of adults) and the thymus. The
secondary lymphatic organs and tissues, the sites where most
immune responses occur, include lymph nodes, the spleen,
and lymphatic nodules.
Thymus
1 lie thymus fs ,i two-lobed organ located posterior to die
sternum and media! to the lung's and Superior to the heart
(see Figure 17.1). Jt contains large numbers of T cells and
scattered dendritic cells (so named for their long, brnnchltke
projections), epithelial cells, and macrophages. Immature T
cells migrate from led hone marrow to the thymus, when
iliev multiply niul begin to mature. Only about 2% of dieim-
mature T cells that arrive in the thymus achieve the propej
-education" t-b "padnace* into mature T cells. The remain
ing cells die via npoprosis (programmed cell death), Thymic
macrophages help clear out the debris of dead and dying
cells. Mature T cells leave the thymus via the Mood and ma
carried to lymph nodes, the spleen, and other lymphatic w
sues where they populate parts of these organs and tissues.
Lymph Nodes
Located along lymphatic vessels are about 600 bean-shapd
lymph nodes. They are scattered throughout the body, .batfi
superficially and deep, and usually occur in groups (sec
ure 17.1). I.ymph nodes are heavily concentrated near the]
mammary glands and in the axillae and yroin. I:ieh node id
covered by a capsule of dense connective tissue (lie,ui
Internally* different regions of a lymph node inav conram 1!
cells that develop into plasma cells, as well as IT
dritic cells, and macrophages.
Figure 17. A Structure of a lymph node (partially sectioned). Green arrows indicate
direction of lymph flow into and out of the lymph node.
h£
Lymph nodes are present throughout the body, usually clustered in groups.
m <u 4
B cells Plasma T cells
cells
A
Dendritic
cells
X
Macrophages
Types of cells In a lymph node
Afferent lymphatic
vessels
Valve
T> Efferent lymphatic
vessels
Reticular fiber
Afferent
lymphatic vessel
What happens to foreign substances that enter a lymph node in lymph?
Lvmph nodes liter \ympk which enters a node through
^of several afferent hmphu 'tic: vessels uf- = coward; -fitment
po carry). to lymph Hows through the node, foreign sub-
are trapped by rmcukr fibers within the spaces be-
in cells. Macrophages destroy some foreign substances by
Locytosis. and lymphocytes destroy others by a variety oj
IIII1C responses. Filtered lymph leaves the other end of
node through one or two #nwi ivtuphnric vessels (cj-
m) Plasma culls and T cells thai have divided many times
Jthin a lymph node can also leave the node and circulate to
Let parts of the body Valves direct the flow ol lymph m-
Lrd through the afferent lymphatic vessels and outward
,h iheei'lercni lymphatic vessels (Figure 17-4).
Metastasis (me-TAS-ta-sis; tmta- = beyond; stash - 60
the spread of a disease from one part ol the body 63
-,. can occur via lymphatic vessels. All malignant tu-
eventuaHv metastasize. Cancer cells may travel in the
„ lymph and establish new tumors where they lodge.
Mien metastasis occurs via lymphatic vessels, secondary tu-
- can be predicted according to the directum of
ow from die prunarj tumor site. Cancerous lymph
Jes fed enlarged, firm, nontender, and feed to underly-
LGtU res. By contrast, most lymph nodes that are en-
id due to an infection are softer, tender, and movable.
ms
spleen is the largest single mass ol" lymphatic tissue in
see Figure 17.1). It lies between the stomach and
inuim and is covered by a capsule of dense connective
\ The spleen contains wo types of tissue called white
m ,| r,-d pulp. White pulp is lymphatic tissue, consisting
of lymphocytes and macrophages. Red pulp consists ol
01ed venom sinuses and cords ofspknk tissue consisting
btood cells, macrophages, lymphocytes, plasma cells.
gaiaular leukocytes.
|ood flowing into the spleen through the splenic artery
white pulp. Within the white pulp. B cells and I
i ; ,. immune responses, while macrophages destroy
en- bv phagocytosis. Within the red pulp, the spleen
us three functions related to blood cells: (1) removal
phages ol worn out or defective blood cells and
I , (2) storage of platelets, perhaps up to one-third ol
snpply;"and (3) production ol blood cells gfanto-
m during fetal life.
Jkspleen is the organ most often damaged in cases qA
"nmuval trauma. \ i spleen causes severe internal
, „ and shock. Prompt splenectomy, removal ol
, is needed to prevem bleeding to death. After a
, im . other structures, particularly red bone mar-
he lam can take over functions normally carried
tin die spleen.
Innate Immunity 425
Lymphatic Nodules
Lymphatic nodules *k egg-shaped masses otlymphatic tissue
that are not surrounded by a capsule. "I beg are plenTSfW in
the connective tissue of mucous membranes lining the gas-
trointestinal, urinary and reprodticuve tracts ami the resp.ra-
,,,n .nrw.tvs- Although many lymplvam nodules are small and
.oln.n-v. some occur as large aggregations in specific parts oi
the body- Among these are the tonsils in the pharyngeal re-
u 1( ,n and the aggregated lymphatic follicles (Peyer's patches)
m the ileum ofthe small intestine (see I i I >. ^ggrega-
lions of lymphatic nodules also occur m the appendix. I he
five tonsils, which form a ring at the jttiwii.m of the oral ca\
ity. nasal c.n ity, and throat, are strategically positioned to
participate m i'mmune responses against inhaled or ingested
foreign substances. The ,m$U pharyngeal tonsil (\x-\UX-\e-
al) or adenoid is embedded in the posterior wall ol the upper
part of the throat (see Figure 18.2 on par. I he two
palatine tonsils (PAL-a-un) lie at the back of the rm •
on either side: these are the tonsils commonK removed in a
tonsillectomy. The paired lineal tonsils (UN-Ltw.il), located
at the base of the tongue, may also require removal during a
tonsillectomy.
■ CHECKPOINT
1. How are interstitial fluid and lymph similar, and bow do
they differ?
2. What are the roles of die thymus and the lymph nodes in
immunii\ :
3. Describe the functions of the spleen and tonsils,
INNATE IMMUNITY
OBJECTIVE • Describe the various components ol in-
nate immunity.
|„,v.ue mimunih includes barriers provide.! by the skin and
mucous membranes. It also include various nmrn-.d de-
feases, such as internal ;iimmicrolnal proteins, natural killer
cells. phagocytes, inflammation, anil lever,
First Line of Defense: Skin and Mucous
Membranes
Both physical barriers and chemical barriers to pat ho ecus
and foreign substances are found in the skin thai covers the
body and m mucous membranes that Inn to b i openings such
8S the mouth :md breathing airways. With us mam layers oi
closely packed, keratinized cells, the epidermis (the outer ep-
ithelial layer of the skin) pnmdes a formidable physical hai-
rier to the entrance of microbes (see Rjj vl on page
98). In addition, continual shedding of the rap epidermal
426 Chapter 17 The Lymphatic System and Immunity
Cells lu-lps remove microbes at the skin's surface. Bacteria
r.ircls penetrate an intact am! healthy epidermis.
The epithelial layer of muanis membranes seerei.es a fluid
called mucus dun lubricates and moistens die surface ul a
bods unity. Because mucus is sticky, it traps many microbes
and I'li'i-ii-n substances. 'The muCOUb membrane nl the nose
has mucus-coated hairs that trap and filter microbes, dust,
and pollutants from inhaled air. The mucous membrane of
die upper airways contains «/////, microscopic hairlike projec-
tions on die surface of the epithelial cells, which propel in-
haled dust arid microbes thai have become trapped in mucus
toward the throat.
Other fluids produced In various organs also help protect
epithelial surfaces nl the skin and mucous membranes. The
lacrimal apparatus (LAJC-ri-mal) of the eyes (see I : tre 12.5
on page 294) produces and drains away tears in response to
irritants, diluting microbes and keeping them from settling
on die surface of the eves. Saliva, produced by the salivary
glands, washes microbes from die surfaces of die leedi and
from the mucous membrane of the mouth, much like tears
wash the eyes. The cleansing of the nrathra by die ffow of
urine retards microbial colonization of the urinary system.
lamina! secretions, likewise, move microbes out of the bod) in
females. Defecation and vomiting also expel microbes.
Certain chemicals also contribute to the resistance of die
skin and mucous membranes to microbial invasion. Seba-
ceous (oil) glands of die skin secrete an oily substance called
sebum that forms a protective Him over the surface of the
skin. Pvrsfnrtititni helps flush microbes Irom the surface ol the
skin and contains lyseyzyme, an enzyme capable of breaking
down the cell walls of certain bacteria. (I.yso/.yme is also
found in tears, nasal secretions, and tissue fluids). Gastrii
fitice, a mixture of hydrochloric acid, en/.yines. and mucus in
the stomach, destroys many bacteria anil most bacterial tox-
ins. Vaginai xeeretiows also are slightly acidic, which discour-
.,1 growth.
Second Line of Defense: Internal Defenses
Although the skin ami mucous membranes are very elf
barriers in preventing invasion by pathogens, they may
be broken by injuries or everyday activities such as brushing
the teeth or shaving. Any pathogens that get past rhe surface
harriers encounter a second line of defense consisting ol in-
ternal antimicrobial proteins, phagocytes, natural killer cells,
inflammation, and fiver,
Internal Antimicrobial Proteins
Parlous bod] fluids contain four main types of antimicrobial
protein* .'thai discourage microbial growth:
L Lymphocytes, macrophages, and fibroblasts infected with
viruses produce proteins called interferons (in'-rer-IT k-
ioi.s), or IFNs. After their release by virus-infected cells,
LFNs diffuse to uninfected neighboring cells, where they
stimulate synthesis of proteins thai interfere with mil
replication. Viruses can cause disease only il the
replicate within body cells.
2. A group of normally inactive proteins in blood plasma
and on plasma membranes makes up rhe complement n'v-
tern. When activated, diese proteins "complemeti
enhance certain immune, allergic, and inllumman i
actions. One effect of complement proteins is to i
holes in the plasma membrane of the microbe. As ;i
curacellular Fluid moves into the holes, causing dn
crobc to burst, a process called cytufyaY. Another die,.: r
complement is to cause chemotaxis (kc'-mo-'I \k~-sis
chemical attraction of phagocytes to a site. Some colM
plenient proteins cause opsonization lop'-son-r-ZA-shiim.
a process in which complement proteins bind to th
face of a microbe and promote phagocytosis.
3. Transferrins are proteins that bind to iron in hi
milk, saliva, and tears. The) inhibit microbial growth U
reducing the amount of available iron, a substance]
needed for bacterial metabolism.
4. Antimicrobial I peptides are newly discovered short-i
proteins dial are produced by phagocytes ^w<\ mtlCOUl
membrane epitheiiaJ cells. They cause lysis ol microbfl
Phagocytes and Natural Killer Cells
When microbes penetrate the skin and mucous mciuhi
or bypass the antimicrobial proteins in blood, the next «■
specific defense consists of phagocytes and natural killer cot
Phagocytes (pbaga- = eat; -cytes ~ cells) are specialise
cells that perform phagocytosis i-os/s = process), die mgcw
tion of microbes nr other particles such as cellular debffl
The two main types ol phagocytes are neutrophil*
macrophages. When an infection occurs, neutrophil-
monocytes migrate to the infected area. During this mi^>
tion. the monocytes enlarge and develop into activi
cytic eel Is called macrophages t \ 1 A K - ro - ta -je/.) (see I ujira
14.2a on page 348). Some are wandering macrophages, w|
migrate to infected areas. ( Hhcrs are fixed tiHhrophagcs A uh
remain in certain locations, including the skin and sub
neous layer, liver, lungs, brain, spleen, lymph nodes, and
bone marrow.
About 5-10% of lymphocytes in die blood are na
killer (NK) cells; which have the ability to kill a wide
of microbes and certain tumor cells. NK cells also are pnj
in the spleen, lymph nodes, and red bone marrow. Some (a
cer and AIDS patients have defective or decreased
of NK cells. They cause cellular dcstructii in by releasing |
iciiiN that destroy the target cell's membrane.
InfJainmat io n
Inflammation is a defensive response ol the body to
damage. Because inflammation is one of the body's mnaiiil
lenses, the response ol a [issue to a cut is similar to the |
,,, damage caused by bums, radiation, or invasion of
a or viruses. The events of inflammation dispose o!
aerobes, t« , :-, or foreign material at the site of injury, pre-
hi clieir spread to other tissues, and prepare the site for tis-
i repair, Thus, inflammation helps restore tissue home-
_8Sis, The four signs and symptoms of inflammation are
fcss.pain, heat, and swelling. Inflammation can ska .cause
[•loss of function in the injured area, depending on the site
jjuextem of the injury.
The stages of inflammation are as follows:
| a region of tissue injury; mast ceils in connective tissue
ami basophils and platelets in blood release ftiswrrmte. In re-
£onse to histamine, WO immediate changes occur in the
ltl. mi I vessels: mortised permeability and vasodilation, an is-
ps&e. in tlie diameter of the blood vessels Q igure 17,5).
Increased permeability means that substances normally
, ned in blood ore permitted to pa$S (Hit of the bbod
vessels. Vasodilation is an increase in tive dtaaetH of the
Blood vessels and allows more blood to How to the
damaged area and helps remove microbial toxins and dead
Increased permeability permits defensive substances
iire 17.5 Inflammation. Several substances stimulate vasodi-
ji, increased permeability of blood vessels, chemotaxis, emigra-
L and phagocytosis. Phagocytes migrate from blood to the site of
(injury.
Inflammation Is an Innate immune response of the body to tissue
damage.
.Tissue injury
i
"'•""'
\L\
Chemotaxis ;•.**•* i-\. .
Microbe
\
Phagocytes A
Emigration/
Innate Immunity 427
such as antibodies and clot-forming chemicals to enter the
injured area from the blood.
I mm the events thai occur during inflammation, itis
B3Sy to understand the signs and syinptoiiiv I I eat ami
redness result from the large amount of blood that accu-
mulates in the damaged area. The area swells due to .m
increased amount of interstitial fluid that has leaked out
of the capillaries (edema). Pain results frorfl injury to
neurons, from toxic chemicals released by microbes, and
from the increased pressure ol edema.
2, The increased permeability of capillaries c.uises leakage
of dotting- proteins into tissues. Fibrinogeln is converted
to an insoluble, thick network of fibrin threads, which
traps the invading organisms and prevents their spread.
I he resulting clot isolates the invading microbes and
their toxins.
3. Shortly alter the inflammatory process starts, pfagi n
•are attracted to the sue of miury by chemotaxis Q
If. Near the damaged area, neutrophils hetjin to
squeeze through the wall of the blood vessel, a process
called emigration. Neutrophils predominate in the early
stages of infection, but the) die off captdly together with
the microbes they have eaten. Within a few hours, mono-
cytes arrive in the infected area. Once in the tissue, tkej
turn into wandering macrophages that engulf damaged tis-
sue, worn-out neutrophils, and invading mien -lies.
4. Eventual!}, macrophages also die. Within a few days, a
pocket of dead phagOl '• and damaged tissue forms;
this collection of dead cells and llmd is called ptts. \t
tunes, pus reaches the surface of the hodi or drains into
an internal cavity and is dispersed? on other occasions the
pus remains even alter die infection is terminated. In this
case, the pus is gradually destroyed oxer a period of days
and is absorbed.
If pus cannot drain out of an inflamed region, the result is
an abscess — an excessive accumulation ol pus m a con-
fined space. Common examples are pimples and bolls.
When superficial blamed tissue sloughs oil the surface of
an organ or tissue, the resulting' open sore is called an ul-
cer. People with poor circulation — for Instance, diabetics
with advanced atherosclerosis — ;ire particulate suscep
hie to ulcers in the tissues of their legs.
31
Vasodilation -^
and increased
permeability
Phagocytes migrate from blood to site of tissue injury
f What causes redness at a site of Inflammation?
Fever
Fever is -an abnormally high hodv icmperature that occurs
because the hypothalamic thermostai is reset. It commonij
occurs during infection and inflammation. Mam bacterial
toxins elevate hody temperature, sometimes bj triggering re-
lease of fever-causing substances such as interleukin-l from
macrophages. Elevated bod) temperature intensifies the ef-
fects of interferons, inhibits rlie growth of some microbes,
and speeds up hotly reactions that aid repair.
428 Chapter 17 The Lymphatic System and Immunity
Table 17.1 summarizes the component- gj innate defenses.
■ CHECKPOINT
4. What physical attd chemical factors provide protection
from disease in the likffl and dlUCOUS ineinbninesr
5. \\li;n internal defenses provide protection against mi-
crobes that penetrate the skin and mucous Ettticbtwaxwesl
6. What are the main sigBS and symptoms of inflammation?
ADAPTIVE IMMUNITY
lartvpe of invader, Adapiixc (specific) immunity invt.lv.--
production of specific types of cells or specific aiuii>nilit
destroy a particular antigen. An antigen is any substeuM
such as microbes, foods, drugs, pollen, or tissue ih.n
Immune system recognizes as foreign (nonself). I he Um
Of science that deals with the responses of the hotly o
gens is called immunology (im'-u-NC >L-6-je). The hnmua
system includes die cells and tissues that carry out in
responses. Normally, a persons adaptive immune
cells recognize .\m\ do not attack their own tissues m
chemicals. Such lack of reaction against self-tissues is calij
\elf-tol trance.
OBJECTIVES • Define adative immunity and compare
it with innate immunity,
• Explain the relationship between an antigen and an
antibody.
• Compare the functions of cell-mediated immunity
and antibody-mediated immunity.
The \arious aspects of innate immunity have one thing in
common: The} arc not specifically directed againsi a parricu-
;,i
H
At times, sell-tolerance breaks down, which leads to
autoimmune disease. Sometimes (issues und
changes thar cause the adaptive immune system to rcco
in/ ,.: tliem as Foreign antigens and attack them. Amor
human autoimmune diseases are systemic lupus en tin
matosus (SLE), Addison's disease, Graves disease. typjj
diabetes mellitus. myasthenia gravis, multiple scle£|
(MS), and ulcerative colitis.
Table 17.1 Summary of Innate Defenses
Component
Functions
First Line of Defense: Skin and
Physical Factors
Epidermis of skin
Mucous membranes
Mucus
Hairs
Cilia
Lacrimal apparatus
Saliva
Flow of urine
Defecation and vomiting
Chemical Factors
Sebum
Perspiration
Lysozyme
Gastric juice
Vaginal secretions
Mucous Membranes
Forms a physical barrier lo the enlrance ol microbes.
Inhibit the entrance of many microbes, but not as effective as intact skin.
Traps microbes in respiratory and gastrointestinal tracts.
Filter out microbes and dust in nose.
Together with mucus, trap and remove microbes and dust from upper respiratory Iract.
Tears dilute and wash away irritating substances and microbes.
Washes microbes from surfaces ol teeth and mucous membranes of moulh.
Washes microbes from urethra,
Expel microbes from body.
Forms a protective acidic film over the skin suiiace that inhibits growth of many microbes-
Flushes microbes from skin surface.
Antimicrobial subsiance in perspiration, tears, saliva, nasal secretions, and [issue fluids.
Destroys most bacteria and toxins in stomach.
Slight acidily discourages bacterial grow!h; flush microbes out of vagina
Second Line of Defense: Internal Defenses
Internal Antimicrobial Proteins
Interferons (IFNs)
Complement system
Transferrins
Antimicrobial peptides
Natural killer (NK) cells
Phagocytes
Inflammation
Fever
Protect uninfected host cells from viral Infection.
Causes cylolysis of microbes, promotes phagocytosis, and contributes lo Inflammation.
Inhibit growth of certain bacteria by reducing the amount of available iron.
Cause lysis of microbes.
Kill infected large! cells by releasing proteins that destroy target cell's membranes.
Ingest microbes and other particles.
Confines and destroys microbes and Initiates tissue repair.
Intensifies the effects of Interferons. Inhibits growth of some microbes, and speeds up body reactions that aidngl
Adaptive Immunity 429
Maturation of T Cells and B Cells
lie cells that carry out adaptive immune- responses arc hmpho-
b called B cells and T cells. Both develop from stem cells
. uri'iinm- in red bone marrow (see Figure I4J 00 page
| B cells complete cheir development in red bone marrow;
.ature T cells migrate from r^\ bone marrow to the fcb) mU5,
.re thej mature. Before T cells leave the thymus or B cells
I red bone marrow, they begin to make several distinctive
Jus ihar are inserted into dteir plasma membranes. Some ol
isi: pr^eins function as antigen receptors— molecules capable
^.cognizing and binding to specific antigens.
js of Adaptive Immune Responses
iptivc immunity consists of two types of closely allied
_JMises, both triggered bj antigens. In eel I -media ted
Jmimnw responses. « nu I cells are like an army of sol
Ersthat direct!) attack the invading antigen. In antibody-
mtiated immune responses, B cells change into plasma
ills, winch synthesize and secrete antibodies. A given anti-
ftvean bind to and inactivate a specific antigen. Other
j cells aid both cell-mediated and antibody-mediated
immune responses. Although each type of re-
ins.' is specialized to combat different aspects of an inva-
i, ,i given pathogen can provoke both typos of adaptive
Hliunc responses.
[Antigens and Antibodies
n (meaning tfW//bod) Moveraror) causes ihe bod}' to
pecrftc antibodies and/or specific I cells thai react
.., Entire microbes or parts of microbes may act as anti-
Ghemical components of bacterial structures such as
Ik capsules, and cell walls arc antigenic, as are bacterial
jand viral proteins. Other examples of antigens include
„.nir.il components of pollen, egg white, incompatible
Is, and transplanted tissues and organs. The huge
n antigens in the environment provider myriad op-
for provoking immune responses.
:il at the plasma membrane surface of most body cells
[^antigens" known as major histwmtpatiblltjty mnpkx
Djimteiiis. Unless you have an identical twin, your MllC
ms arc unique. Thousands to several hundred thousand
^molecules mark the surface of each of your body cells ex-
blood cells. MHC proteins are the reason lhat tissues
jected when they arc transplanted from one person to
in. their normal function is to help T cells recognize
rjgen is foreign, not self. This recognition is an nnpor
lirsi ste[) in any adaptive immune response.
^utocess of an organ or tissue transplant depends on
_impatibility (his'-to-kom-pat-i-BTL-i-re), the ris-
patibitity between the donor and the recipient.
.Similar the Ml EC antigens, die greater the his-
tocompatibility, and thus the greater the chance thai tjfce
transplant will not be rejected. In the United Slates, a na-
tionwide computerized registry helps physickns select the
most histocompatible and neediest organ n.insplam recipi
ems whenever donor organs become available.
Antigens induce plasma cells CO secrete proteins known as
antibodies. .Most antibodies contain four polypeptide chains
(Figure I 7.6a). At two tips of the chains are variable regions.
Figure 17.6 Structure of an antibody and relationship ot an
antigen to an antibody.
y An antigen stimulates plasma cells to secrete specific antibod-
ies lhal combine with the antigen
Variable
Polypeptide
chains
(a) Diagram ol an antibody molecule
Antigen
on surface
of microbe
Y-shaped antibody
(b) Antibody molecules binding to antigens
What is the function of the variable regions of an antibody?
430 Chapter 17 The Lymphatic System and Immunity
so mimed because the sequence of amino acids there varies
for each different antibody. The variable regions are the
antigen-binding silts, the parts of an antibody thai "lit" and
bind 10 a particular antigen, much like your house key his
into its lock. Because the amilunh 'arms" can move some-
what, an antibody can assume either a T shape or a V shape.
Tin's fk-xibiliu enhances the ability of the antibody to hind to
two identical antigens at die same rime — for example, on die
surface of microbes (Fi run 1 7.6b).
Antibodies belong to a group of plasma proteins called
globulins, and lor this reason they are also known as im-
munogiobulins (im'-u-ub-tiLOB-u-lins). Immunoglobulins
are grouped in live different classes, designated EgG, IgA,
[gM, JgD. .md igE. Each class has a distinct chemical struc-
ture and different functions I Pabh I .2). Because they appear
lu'si and are relatively. short-Iked, IgM antibodies indicate!
recent invasion. In a sick patient, a high level of IgM against
a particular pathogen helps identify the cause of the illncsl
Resistance of the fetus and newborn to infection .stem
mainly from maternal IgCJ antibodies that cross the placenta
before birth and IgA antibodies in breast milk alter birth,
Processing and Presenting Antigens
FOE an adaptive immune response to occur, B cells ami
cells must recognize that a foreign antigen is pros
cells can recognize and bunt to antigens in lymph, in: ■■
rial fluid, or blood plasma, but T cells only recognize
ments of antigens that are processed and presented in
certain way.
Table 17.2 Classes of Immunoglobulins
Name and Structure
Characteristics and Functions
About 80% ol all antibodies in the blood. Also found in lymph and the intestines. Protects against bacteria and viruses by en-
hancing phagocytosis, neutralizing toxins, and triggering the complement system. Only class of antibody to cross the placental
from mother to fetus, thereby conferring considerable immune protection in newborns.
IgA
i
c
About 10% to 15% of ail antibodies in the Wood. Found mainly in sweat, tears, saliva, mucus, breasl milk, and gastrointestalh
secretions, Levels decrease during stress, lowering resistance lo infection. Provides localized protection against bacteria ana
viruses on mucous membranes.
IgM
About 5% to 10% of all antibodies in the blood. Also found in lymph First antibody class lo be secreted by plasma cells afin
initial exposure lo any antigen. Activates complement and causes agglutination and lysis of microbes. In blood plasm a
A and anti-B antibodies of the ABO blood group, which bind to A and B antigens during incompatible blood transfusions, ate
also IgM antibodies <see Figure 14.8 on page 35B).
igD
About 0,2% of all antibodies in the blood. Also found in lymph and on the surfaces of B cells as antigen receptors Irwi
activation ol B cells.
igE
Less than 0.1% of all antibodies in the blood. Also locked on mast cells and basophils. Involved In allergic and hypersans
reactions and provides protection against parasitic worms.
Adaptive Immunity 431
immune Function, and
Resistance to Disease
I you warn co observe the relationship
between lifestyle and immune function,
m x college campus. As the semester
fesses and the workload aceumu-
,. an increasing number of students
i n U round in the waiting rooms of
kuddU health services.
jStrcss the Culprit?
pas been implicated as hazardous
monmune function. Researchers in the
I psychmu'immnnnmnivgy (PN1)
Re found man} communication path-
Ik thai link the nervous, endocrine,
'] immune systems. Chronic stress
necb the immune system in several
i example, Cortisol, a hormone
freted by the adrenal cortex in asso
Rno with the stress response, in-
[unune system activity, perhaps
i its energy conservation effects.
earch supports what many pco-
Qjkve observed since the beginning
rime: Your thoughts, feelings,
and beliefs influence your level
d ': course of disease
cialk toxic to the immune system are
if helplessness, hopelessness,
Ififlml social isolation.
People resistant to the negative
health effects of stress ;ire more likely
to experience a sense of control over
the nature, a commitment to their
work, expectations of generally pasijyve
outcomes for themselves, and feelings
of social support, lb increase your
si ress resistance, cultivate an optimistic
outlook, get involved in your work, mid
build good relationships with others.
Oris Lifestyle srt Fanlt?
When work and stress pile tip, health
habits can change. Many people smoke
Of consume more alcohol when
stressed. CWO habits detrimental to op-
timal immune function. Under stress,
people are less likely ro eat well or ex-
ercise regularly, two habits that en-
hance immunity.
Adequate sleep and relaxation are
especially important for a healthy im-
mune system. But when there aren't
enough hours in the day. you may be
tempted to steal some from the night,
While skipping sleep may give you .1
few more hours of productive time in
1 he short run. in the long run you end
up even farther behind, especially if
► Think
getting sick keeps you out of commis-
sion for several days, blurs your con-
centration, mm\ blocks your crcali\it\.
Even if you make nine to get eight
hours of sleep, stress can cause insom-
nia. If you find yourself tossing and
turning at night, it's ume 10 improve
your stress management and relaxation
skills! Be sure to unwind from tin dfl5
before going to bed.
hi antigen processing, antigenic proteins are broken
Lit into fragments and then combine with A'THC mole-
• I the antigen-MHC complex is inserted into the
u,i membrane of a bod) Bell The insertion of the eom-
jfcx into die plasma membrane is called antigen
'titiHioii. When an antigenic fragment comes from a sr!j-
wi. I cells ignore the antigen-MHC complex. I lowever,
Rk bametu canes from a Ionian pn/tei/h T cells recognize
:ii-MHC as an intruder, and an adaptive immune
place.
\ special class of cells called antigen-presenting cells
(/IPCs) process and present antigens. VPCs include dendritic
cells, macrophages and B cell>. They are strategical!} located
in places where antigens are likely 10 penetrate innate de-
fenses and enter the body, such as the is and dermis
of the skin (l.angcrhans cells are a type of dendi itic cell); mu-
cous membranes thai line the respiratory, gastrointestinal,
urinary, and reproductive tracts; and lymph nodes; VfteT pro-
cessing and presenting an antigen, APGs migrate from issues
via lymphatic vessels to lymph nodes.
432 Chapter 17 The Lymphatic System and Immunity
The steps in the processing and presenting of an antigen
by an APC occur as follows I ! .7):
Ingestion of the antigen. Antigen-presenting cells ingest
antigens by phagocytosis. Ingestion could occur almost
anywhere in the body that invaders, such as microbes,
have penetrated the nonspecific defenses.
Digestion of antigen into fragments. Within the A PC],
protein-digesting enzymes split large antigens into short
peptide fragments.
Synthesis of MHC molecules. At the same lime, the \P(
synthesizes MHC molecules and packages them into
vesicles.
Fusion of vesicles. The vesicles containing antigen frag-
ments and A 1 1 1 C I molecules merge and fuse.
Binding of fragments la MilC molecules. Alter fusion of
die two vesicles, antigen fragments bind to MHC mole-
cules.
Insertion of antigen -MHC complex into the plasma
membrane The combined vesicle that contains amigen-
MI K complexes splits open and die antiu.en-.Mi it. com-
plexes are inserted into the plasma membrane,
After processing an antigen, the A PC migrates to lun-
phatic tissue to present the antigen to T cells. Within lym-
phatic tissue, a small number of T cells that have the correa
antigen receptors recognize and hind to the antigen frag*
mem — MHC complex, triggering either a cell-mediated a
an antiboilv iiu JiatL-d immune response.
T Cells and Cell-Mediated Immunity
The presentation of an antigen together with .MIK
cules by APCs informs T cells that intruders are present!
the body and that combative action should begin. Bui
cell becomes activated only if its antigen receptor himku
the foreign antigen (antigen recognition) \\\m\ m the sain
time it receives a second stimulating signal, a process !
as coslimidalion (Figure I 7.8). A common costi inula tor is w
terleakin-2 {11.-2), The need for two signals is a little lit
starting and driving a car. When you inserl the correct M
(antigen) in the ignition ("I" cell receptor) and turn it, the qj
starts (recognition of specific antigen), but it cannoi move!
Forward until yon move the gear shift into drive (eustiirwlj-j
i ion i. The need for costimuliltion probably helps pre\cm im-
mune, responses from occurring accidentally,
Figure 17.7 Processing and presenting of antigen by an antigen-presenting cell (APC).
, A,
An APC migrates to a lymphatic tissue where it "presents'" a processed antigen toT cells having
receptors that fit that particular antigen fragment.
Antigen
fragments
Anligen-
presenting
cell (APC)
APCs present exogenous antigens In association with MHC- II molecules
Which types of cells can function as APCs?
Adaptive Immunity 433
[figure 17.8 Activation and division of T cells in cell-medi-
ated immunity.
It Two signals are needed for activation o1 a T cell: (1) recognition
*--. of a processed antigen presented by an APC and (2)
costimulation.
Coslimulation
by IL-2
Processed
antigen
Clones of cytotoxic T cells
attack infected body cells
Memory cytotoxic
T cells (long-lived)
What is a clone?
cc a T cell is activated, it enlarges and divides many
s. The resulting population of identical cells, termed a
ii| recognize the same antigen. Before the first expo-
n antigen, only a few T cells are able to recog-
Ince an adaptive immune response has begun, thou-
,;• I cells can respond. Activation and division of T
.. i in rhe secondary lymphatic organs and tissues, II
JVC ever noticed swollen tonsils or lymph nodes in your
k continuous division of lymphocytes participating in
Immune response was likely the cause.
The three major types of T cells are helper T cells, cyto-
toxic T cells, and memon I edits. Helper T cells help i.ikr
cells of the adaptive immune system combat intruders. For
Instance, helper T cells release the coslimularor protein
interleukm-2, which enhances the activation and division ol
T cells. Other proteins released by helper T cells attract
phagocytes and enhance the phagocytic ability off macrophages.
Helper T cells also stimulate "he development of B cells into
antibody-producing plasma cell>and the development of nat-
ural killer cells.
To reduce the risk of rejection. recipients of organ trans-
plants receive imiiairaosnppressive drugs. Out- m.k.1i drug
is cytivsporme, derived from a fungus, which inhibits secre-
tion of mterleukin-2 by helper T cells hut has only a mini-
mal effect on B cells. Thus, the risk of rejection is dimin-
ished while resistance to some diseases is maintained.
Cytotoxic T cells are the soldiers that march forth to do
battle with foreign invaders in cell-mediated adaptive im-
mune responses. The name "cytotoxic" reflects their func-
tion— killing cells. Cytotoxic T cells are especially effective
against hri.lv cells infected by microbes, some tumor evils,
and cells of a transplant. After they divide, cyrmoxic V cells
leave secondary lymphatic organs and tissues and mimaie to
sites of invasion, infection, and tumor formation. Cytotoxic
T cells recognize and attach to cells beanuy. the BJitigeil that
stimulated their activation and division, operating ut the lul-
1 1 1 w 1 1 ig wa y ( 1 igu r e 17. 9 ) :
1. Cytotoxic T cells, using receptors OjH their surfaces, rec-
ognize and hind to infected target ceils that have micro-
bial antigens displayed on their surface. The cytotoxic I
cell then releases gratizymcs. protein-digesting enzymes
that trigger apoptosis, the fragmentation ol cellular con-
tents. (1 9a). Once the infected; cell is destroyed,
the released microbes are killed by phagocytes.
2, Cytotoxic T cells can also bind to infected body cells md
release two proteins: perforin and gramilysin. Perform
insert-- into the plasma membrane ol the target cell and
creates channels in the membrane (Figure I "-"!>). As a
result, extracellular fluid Hows mm the target: cell and cy-
nJ.'.is (cell bursting) occurs. Grtimilysui enters through
line channels and destroys the microbes by creating holes
in their plasma membranes. Cytotoxic T cells ma\ also
destroy target cells In releasing a toxic molecule called
fympbotoxm, which activates enzymes in the target cell.
These en /.sines cau.se the target cell's UNA to fragment
and the cell dies. In addition. e\im«>xic T cells secrete
gamma-inr.erferon, which attracts and actuates phago-
cytic cells, and macrophage migration inhibition factor,
which prevents migration of pliagocytes troiu the infec-
tion site. After detaching from a target cell, a cyton i
cell can seek OUT and destroy another target cell.
434 Chapter 17 The Lymphatic System and Immunity
Figure 17.9 Action of a cytotoxic T cell. After delivering a "lethal hit," a cytotoxic T cell
can delach and attack another target cell displaying the same antigen.
Cytotoxic T cells kill their targets directly by secreting granzymes that trigger apoptosis and
perforin that triggers cytolysis of infected target ceils.
Activate
cytotoxic
Tcel"
Recognition
of processed
antigen
Miciobe
Infected
body cell
/ated
Gran-zymes
Activatad
cytotoxic
T cell
Recognition
of processed oAf) • "
antigen -&
Infe'd
"ly cell
Granulysin
Perforin
Channel
Infected body cell
undergoing apoptosis
j
Infected body cell ,
undergoing cytolysis
(b) Cytotoxic T cell destruction of Infected cell by
release of perforins I hat cause cyro lysis- microbes
are destroyed by granulysin.
Phagocyte
Key:
fa) Cytotoxic T cell destruction of infected cell by
release of granzymes that cause apoptosis;
released microbes are destroyed by phagocyte
I T cell antigen
' receptor
Antigen-MHC
complex
Besides cells infected by microbes, what other types of cells do cytotoxic T cells attack?
Memory T cells remain in lymphatic tissue bng after the
original infection and are able to recognize the original in-
vading iintiiien. Should the same antigen invade the body at a
Later dme, the memory. T cells initiate a fester reaction than
Qceturefj dtuiiiig the first invasion. The second response is so
rapid that the pathogens are usually destroyed before any
sigos or symptoms of die disease occur. Memory T cells may
provide immunity to a particular antigen for years. For in-
stance. ;i person usually lias lite ehickeupo.v only once he-
cause of memory T cells.
■ CHECKPOINT
7. What is the normal function of major hjstocatnnj
complex proteins (self-antigens)?
8. How do antigens arrive at lymphatic tissues?
9. I Tow do antigen-presenting cells process antigcod
10. What are the Junctions of" helper, cytotoxic, and
I" cells?
11. I low do cytotoxic T cells kill their targets:
J Cells and Antibody-Mediated Immunity
n, body contains not only millions of different T cells but
i dllions of different B cells, each capable ol responding
C spcC ifi t antigen. Cytotoxic T cells leave lymphatic tissues
. .•uii and destroj a foreign antigen, but B cells stay put
presence of a foreign antigen, specific B cells m lymph
, , the spleen, or lymphatic nodules become activated.
tin n divide wd develop into plasma cells chat secrete
„ ai uihndies, which in turn circulate in the lymph and
I Lad io reach die situs of invasion.
I' DurinK activation of a B cell, antigen receptors on the
| a jl surface of a B cell bind to an antigen (Figure ! UO). B-
fflgure 17.10 Activation, division, and differentiation of B
ells in antibody-mediated immunity.
B cells develop into antibody-secreting plasma cells.
B-cell antigen
receptor
\V^ Processed antigen-
7 MHC protein complex
Activated helper
C^ Helper 1
CJ Tcall
Bcsll
recognizing
unprocessed
antigen
K
Costimulation
by interleukin-2
and olher proteins
B cell displaying processed
antigen is recognized
Cell division and t>y helper T cell, which
differentiation ie i eaS es costlmulators
Plasma cells
6 . i*
Memory B cells
Antibodies
Clones of plasma cells secrete
antibodies.
Long-lived memory
B cells remain to
respond to same antigen
when It appears again.
1 What types of cells respond to a second or subsequent invasion
[by an antigen?
Adaptive Immunity 435
cell antigen receptors are chemically sum!... KJ the antibodies
thai eventually aw secreted by the plasma cells, Mlhough B
cells can respond to an unprocessed antigen present in lymph
or interstitial fluid, their response is much more intense
when fhev process die antigen. Antigen processing in a B cell
occurs in the lolloping way: The antigen is taken into l he B
cell, broken down inm fragments and comhined with MHC
protein, and moved to the B cell surface. I lelper T cells rec-
ognize the processed antigen-MHC protein eomplev an<J de-
liver the eoMiinulaimn needed for B cell division and .Idler
filiation. The helper T cell releases inierlcukin-2 and other
proteins that function as co&timtklators to activate B cells.
Some of the activated B cells enlarge, divide* and diiier-
entuite into a clone of antibody-secreting plasm* wife \ I
days or weeks alter exposure to an antigen, a plasma cell se-
cretes hundreds of millions of antibodies daily, and secretion
occurs for about lour or rive days, until the plasma cell dies.
Most antibodies travel in Lymph and blood to the invasion
sites. Some activated B cells do not differentiate into plasma
cells I 'iu rather remain as memory B cells that are read) to
respond more rapidly and forcefully should the same antigen
reappear at a future time.
Although the functions of the five classes oi antiUod.es
differ somewhat, all attack antigens in several W,
L Neutralizing antigen. The binding of an antibody to its
antigen neutralizes some bacterial toxins and prevents at-
tachment of some viruses to body cells.
2. Immobilizing bacteria. Some antibodies cause bacteria
to lose their motility, which limits bacterial spread into
nearby, tissues.
3. Agglutinating antigen. Binding of antibodies m ami
gens may connect pathogens to one another, causing tg
vhtmuttw, rhe dumping together of particles. Phago-
eytte cells ingest agglutinated microbes more readily.
4. Activating complement. Intigen-anttbady complexes
.unvote complement proteins, which then work to re-
move microbes through opsonization and cytotysis-
5. Enhancing phagocytosis. Once antigens have bound to
an antibody s variable region, the antibody acts as a "flag"
that attracts phagocytes. Antibodies enhance the aetivitv
of phagocytes by causing aggktination, by activating
complement, and by coating microbes so that they are
more susceptible to phagocytosis (opsonization).
hl.le 17J summarizes the functions of cells that pariici-
pate in adaptive immune responses.
An antibody -mediated response typically produces many
different antibodies that recognize different parts 0,1 an
antigen or different antigens dfa foreign ceil. Bj contrast,
a monoclonal antibody (MAb) is a pure antibody pro
duced from a single clone of identical cells grown ... the
laboratory. Clinical uses ofMAbs Wude the diagnosis oi
436 Chapter 17 The Lymphatic System and Immunity
Table 1 7.3 Summary of Cell Functions in Adaptive Immune Responses
Cell
Functions
Antigen-presenting Cell (APC) Processes and presents foreign antigens to T cells. APCs include macrophages. B cells, and dendritic cells.
Helper T Ceil
Cytotoxic T Cell
Memory T Cell
BCell
Plasma Cell
Memory B Cell
Helps other cells ol the immune system combat intruders by releasing the costimulator protein tnleHeukin-5
which enhances the activation and division of T cells v Other proteins attract phagocytes and enhance the phagocyte
ability ot macrophages. Helper T cells also stimulate the development ot B cells into antlbooy-prodticins plasma col
and the development ol natural killer cells.
Kills host target cells by releasing granzymes that induce apoptosis, perforin that forms channels to cause cytolysiS,'
granulysin that destroys microbes, lymphotoxin that destroys target cell DMA. gamma-lnterteran that attracts
macrophages and increases their phagocytic activity, and macrophage inhibition lactor that prevents macrophage it
gration from site of infection.
Remains in lymphatic tissue and recognizes original Invading antigen, even years alter the first encounter.
Differentiates Into antibody-producing plasma cell.
Descendant ol B cell that produces and secretes antibodies.
Remains ready to produce a more rapid and forceful secondary response should the same antigen enter the twdy
the future.
pregnancy, allergies, and diseases such as strep throat, he-
patitis, rabies, and some sexually transmitted diseases.
\1 \Us have also been used to detect cancer at an early
stage and to determine the extent of metastasis. 'I 'hey may
also he useful in preparing vaccines to COtinteract &e re-
jection associated witfa transplants, to treat autoimmune
diseases, and perhaps to treat AIDS.
antigen, no anybodies arc present for a lew days. I In i
levels of antibodies slowly rise, first IyM and then IgG.1
lowed by a gradual decline (heme l~-l i )• This is
mtiry response. Memory cells may live for decades, ftj
new encounter with the same antigen causes a rapid 1 dH
of memory cells. The antibody level alter subsequent]
counters is far greater than during a priinan
consists mainly of IgCi antibodies. This accelerated, mur
Immunological Memory
A hallmark of adaptive immune responses js memory for spe-
ll miigins that have triggered immune responses in the
i ,:!■-. i. hum analogical memory is due to the presence ol long-
htsrm- antibodies and very long-lived lymphocytes chat arise
during division and differentiation el antigen-stimulated 15
cells and T cells.
Primary and Secondary Response
Adaptive immune responses, whether cell-mediated or and -
hod\ -mediated, are much quicker and more intense alter a
second W subsequent exposure to an antigen than alter the
first exposure. Initially, onlj a lew celts have the correct: anti-
yen receptors ro respond, ami the immune response may rake
several days to build to maximum intensity. Because thou-
sands of memoir cells exist after an initial encounter with an
antigen, they can divide and differentiate into plasma cells or
cytotoxic T 'cells within hours die next time the same am
appears.
One measure of immunological memory is die amount of
antibody in blood plasma. Alter an initial contact with an
Figure 17.11 Secretion of antibodies. The primary respa
(after first exposure) is milder than the secondary response
second or subsequent exposure) to a given antigen.
Immunological memory Is the basis for successful Immunti
by vaccination.
■
■
1000- Primary response Secondary response
_ 100
0.1
>
>
c
10 -
1
./KW\
M
First exposure
28
Second exposure
42
Days
n
Which type of antibody responds most strongly during thai
ondary response?
II
inlci'i
l eespouse is called the ftwndary response, Antibody
| . i during -.1 secondary response m W> more cftec-
,!,,,„ those produced during .1 primary response. Tiros,
pre more successful in disposing ofthe invaders. _
Primary and secondary responses occur during iwcrefasS
crjon. When vou recover from an infect. on uithout fcafe-
inmim -,nbial'drugs, it is usually because of the prunun
,unse. If rhc Same microbe infects you later, the secundan
£ e could fae so swift thai the niicirobes are destroyed
. IU exhibit am sfensor symptoms of in lection.
tonally Acquired and Artificially Acquired Immunity
linunological memory provides ihe basis for immunization
„ ccination against certain diseases, lor instance, polio.
\ ..,, ,, receive the vaccine, which may contain weakened
killed whole microbes of parts of microbes, your 13 cells
-ilT cells are activated. Should you subsequent]} encounter
ing pathogen as an infecting microbe, your body mm-
.nd.irv response. However, booster doses o1 some
rtiuniang agents must he given periodically ro maintain
, protection against the pathogeu. Bible 17.4 sum-
he various types of antigen encounters 1h.1i provide
■pity and artificial!-) acquired immunity.
Table 17.4 Types of Adaptive Immunity
How Acquired
salty acquired
: immunity
Following exposure to a microbe, antigen
recognition by B cells and T cells and cos-
Umulalion lead to antibody-secreting
plasma cells, cytotoxic T cells, and B andT
memory cells.
acquired
live Immunity
Transler ol IgG antibodies from mother
to leius across the placenta, or ol igA
antibodies irom mother to baby in milk
during breastfeeding.
dally acquired
(immunity
Antigens introduced during a vaccination
stimulate cell-mediated and anllbody-
medialed Immune responses, leading to
production of memory cells, The antigens
are pretreated to be immunogenic but not
pathogenic; that is, they will irigger an im-
mune response but not cause significant
illness.
ClaHy acquired
■saWe immunity
Intravenous injection of immunoglobulins
(antibodies),
Aging and the Immune System 437
■ CHECKPOINT
12. Hem are cell-mediated mm\ anuUdv ■ mediated immune
responses similar and different?
13. How is the secondary response td Bin antigen different
Bom the primary response-
AGING AND THE IMMUNE
SYSTEM
OBJECTIVE
mime system.
Describe die effects of aging on the im
With advancing age^ most people become more susceptible
to all types of infections and malignancies. Their response to
vaccines is decreased. ;md the\ tend to produce more autoan-
tibodies (antibodies againsi their body's own molecules). In
addition, the immune system exhibits lowered levels ol func-
tiun. For example, T cells become less responsive to antigens,
and fewer T evils respond to infections. This m;ty result from
age-related atrophy ofthe thymus or decreased production o\
thymic hormones.' Because the T cell population deCreas
with age, B cells are also less responsive. ( Consequently* ;mti-
body levels do not increase as rapidly m response to a chal-
lenge by an antigen, resulting in increased susceptibility to
various infections, It is for this kej reason that elder!) indi-
viduals are encouraged to get influenza (flu) vaccinations each
year.
■ CHECKPOINT
14. What are the consequejices of decreases m the number ol
T cells and B cells with fcdvancliig »ge?
• • •
To appreciate the many ways that the Iwnplvatic system
vu\ immunity coninhuie to homeostasis of other body ty*
turns, examine Focus on Homeostasis; I lie LymphnrU •
tern and Immunity on page 43 H. Next, in Chapter 18, »ve will
explore the structure and function of the respiratory s\sicin
and see how its operation is regulated by the nervous system.
Most importantly, the respiratory system provides for gas
exchange— taking in oxvuen and blowing ofl carbon
dioxide. The cardiovascular systep aids gas exchange bj
transporting blood containing the- gases between the lungs
;mil tissue cells.
FOCUS
ON
HOMEOSTASIS
Body System
The Lymphatic System and Immunity
Contribution of the Lymphatic System and Immunity
For all body
systems
Integumentary
system
Skeletal system
B cells, T celts, and antibodies protect all body systems from attack by harmful foreign mlcrobw
(pathogens), foreign cells, and cancer cells.
Lymphatic vessels drain excess interstitial fluid and leaked plasma proteins from the dermis of
the skin. Immune system cells (Langerhans cells) In the skin help protect the skin. Lymphatic
tissue provides IgA antibodies in sweat.
Lymphatic vessels drain excess Interstitial fluid and leaked plasma proteins from connective lis- 1
sue around bones.
Muscular system
Lymphatic vessels drain excess interstitial fluid and leaked plasma proteins from muscles.
Nervous system
Endocrine
system
Cardiovascular
system
Respiratory
system
Digestive system
i
Urinary system
*
Reproductive
systems k ,
438
Lymphatic vessels drain excess interstitial fluid and leaked plasma proteins from the peripheral
nervous system.
Flow of lymph distributes some hormones. Lymphatic vessels drain excess interstitial fluid and
leaked plasma proteins from endocrine glands.
Lymph returns excess fluid filtered from blood capillaries and leaked plasma proteins to venoi« |
blood. Macrophages in spleen destroy aged red blood cells and remove debris in blood.
Tonsils, lymphatic nodules in the mucosa, and alveolar macrophages in the lungs help protect
airways and lungs trom pathogens. Lymphatic vessels drain excess interstitial fluid from the
lungs.
Tonsils and lymphatic nodules In the mucosa help detend against toxins and pathogens that i
penetrate the body from the gastrointestinal tract. Digestive system provides IgA antibodies in
saliva and gastrointestinal secretions. Lymphatic vessels pick up absorbed dietary lipids ana
fat-soluble vitamins from the small intestine and transport them to the blood. Lymphatic ve
drain excess interstitial fluid and leaked plasma proteins from organs of the digestive system.
Lymphatic vessels drain excess interstitial fluid and leaked plasma proteins from organs of I
urinary system. Lymphatic nodules in the mucosa help defend against toxins and pathogerw
that penetrate the body via the urethra.
Lymphatic vessels drain excess interstitial fluid and leaked plasma proteins from organs oil
reproductive systems. Lymphatic nodules in the mucosa help defend against toxins and
pathogens that penetrate the body via the vagina and penis. In females, sperm deposited Inl
vagina are not attacked as foreign invaders due to components in seminal fluid that inhibit im-
mune responses. IgG antibodies can cross the placenta to provide protection to a developing!
tus. Lymphatic tissue provides IgA antibodies in the milk of the nursing mother.
Common Disorders 439
COMMON
DISORDERS
AIDS: Acquired Immunodeficiency Syndrome
,' immunodeficiency syndrome (AIDS) is a condition in
person experiences a telltale assortment of infections due to
» progressive destruction or" immune system evils In the human
mnodeficieticy vims Q&V) UBS represents the end stage or
i bj HIV. A parson Who is fefected witfi I Hv mg be synip-
to-!itc for mam vears, even while the virus is actively attacking
mm, system. In the two decades after the first five cases
|eft:ported in 1981,22 million people died of UDS. Worldwide,
, llm ri people are currently infected with ECIVi
'Transmission
I IIV is preseni in the lilood and some body fluids,, il is
, i, , i, ii. mined (sprend from one person to another. U
n involve the exchange of blood or body fluids. Hl\ is
[.,! in semen or vaginal fluid during unprotected (without a
«lomr;m.il. vaginal or oral sex. HIV also is transmitted h> cured
onract, such vis occurs in intravenous drug users
I shore hypodermic needles or hcalth-eare professionals
lW aj he accidentally stuck by HlV-contaminated hypodermic
j . in addition., H TV can be transmitted From an HIV-infected
„„■ tu her baby al birth or during breasi-ieeding.
The chances of transmitting or of being infected by I IIV dur-
or anal intercourse can he greatl) reduced— although
tcliminatcd by the use of latex eondorttt. Public health pro-
, :! nt encouraging drug users not to share needles have
feeficctive ..i checking the increase in new HIV infections in
gpjjulation. AKo. giving certain drugs to pregnant IllV-in-
'., nen greatly reduces the risk of transmission of the virus
1 abicSl • i •!
a very fragile vims; is cannot survive for long otnstqe
The vims is mat transmitted by inseel bins. \ pcr-
not become infected bj casual physical contact with an
isetcd person, such as by hugging or sharing household
virus can be eliminated from personal care items and
J iiipmem by exposing them to heat (13S°F for 10 min-
t-leaning them with common disinfectants such as hy-
,. nx'kle. rubbing alcohol, household bleach, or germicidal
such as ['.eiadme' 1 or I libiclcns '■- Standard dishwashing
I nhhlg 'Is" loll 1 IIV
ftructttre and Infection
, i >f an inner core of riln .nucleic acid I k\ A I covered by
.com. tcapsid) surrounded hv ah outer layer, ihe envelope,
ftrfi lipid hilayer penetrated bj proteins. Outside a living
.. rims is unable to replicate. However, when the vims in-
jenters a host cell, its RNA uses the host cell's resources to
feusands of copies of the virus. New viruses eventually leave
fflfect other cells.
IIIY maiidv damages helper T cells. (Her IU biibun viral
copies mac be made each da\. The viruses bud so rapullv from an
Infected cell's plasma membrane ih.n the cell repmivs and dies. In
h„,si HIV-infected people, helper I celjs are initiall.v replaced as
fast as they arte destroyed. After several years, however, ihe body's
ability to replace helper T cells is slowly evha usied. ami the number
of helper i cells m circulation gradually declines.
Signs, Symptoms, and Diagnosis ofHIl Infection
Soon after being infected with H'V mosl peoplfi esperienee a briel
llu-like illness. Common signs and symptoms are fever. Jaugiie,
rash, headache, joint pain, sore throat, and swollen lymph nodes.
About 50% of infected people have night sweats. As early as three
to four weeks alter 1 II V infection, plasma cells begin secreting anti-
bodies auainsi I1IV, These antibodies are delectable in blodfcl
plasma and form the basis fbl some ofthc screening tests For 1 IIV.
When people test "HIV-positive," u usually means they have anti-
bodies to I II V antigens in their bloodstream.
Progression to AIDS
Alter a period of 2 to ID years, the virus destroys enough helper I"
cells that most infected people begin to experience SJ inptoms "I im-
munodeficiency. HIV-infected people common!) have enlar; -,. ■,!
lymph nodes and experience persistent fatigue, involnni arj « ligftl
loss, night sweats, skin rashes, diarrhea, and various lesions ol th»
mouth ami gums. In addition, die virus may begin to iuicet neurons
in the brain, affecting die person's ntcniorv mil producing «S»aJ
disturhan
As tin immune system slowly collapses, ait I IIY-infected per-
son becomes susceptible to a host of uppurtnimu. . >nps«
are diseases caused by microorganisms that are normally held in
check but now proliferate because of the defective immune system,
UDS is diagnosed when the helper I cell count drops below 200
cells per microliter ( = cubic uutlimeuri al blood or when oppor-
tunistic infections arise, whichever occurs first. In mm. opportujlis
tie infections usually arc the cause of death.
Treatment ofHW Infection
At present, infection with I ITV cannot be cured. Vaccines designed
co block new I IIV Infections and to reduce the viral load (the nutn-
|„r ofcopjes ot I IIV RNA m a microliter offolood pl^ma) in those
Vtka :.re already infected are in elumal trials, Meanwhile, two cate-
gories el drugs have proved successful in extending the life "I manv
] U\ '-infected people:
1. Reverse transcriptase inhibitors interfere mm die anion ol re-
verse txunscripiase. the en/.yme that the nnn uses to convert its
RNA into fl PN A copy. Among the drugs in this category are
zidovudine (ZDV, previously called \/ I '•. didanosiiii (dell),
and stavudiiu; C44TT). IH/ivir®, approved in 20QQ for trcaLiiiem
of I IIV infection, combines three icversfi I fa»S< r.pt.ise in-
hibitors in one jiill.
2. Protease inhibitors interlere with the action of protease, a viral
en/yinc that cuts proteins into pieces in as>etnble the coat ot
440 Chapter 17 The Lymphatic System and Immunity
newly produced HIV particles. Drags in this category include
nelfinavir. .saquinavir, ritonavir, and indinavir.
In L996, physici.ins treating i I IV- infected patients widely
adopted highly active mtirztrtiuifaL therapy (HAAin) — a combina-
tion of two differently acting reverse eran'scriptase inhibitors and
one protease inhibitor. Most HIV-infected individuals receiving
1 1 A \R'I experience a drastic reduction in viral load and an increase
in the number of helper T cells in their blood. Not only does
HAART delay the progression ol I IIV infection to AIDS, but many
people with AIDS have seen the remission or disappearance of'op-
porrunisric infections and an apparent return to health. Unforru-
narclv. I IAART is very costly (exceeding- .S 10,000 per year), the dos-
ing schedule is grueling, and nm all people can tolerate the toxic
side effects of these drugs. Although I1IV may virtually disappear
I ii mi die blood with drug treatment (and thus a blood test may be
'negative" for I IIV), the virus typically still lurks in various lym-
phatic tissues. In such eases, the infected person can still transmit
die virus to another person.
Allergic Reactions
A person who is overly reactive to ,i substance linn is tolerated by
most other people is said CO be allergic. Whenever an allergk iv-ac-
tion takes place, some tissue injury occurs. The antigens that induce
:iu allergic reaction are termed allergens. Common allergens in-
clude certain foods (milk, peanuts, shellfish, eggs), antibiotics (peni-
cillin, tetracycline), vaccines (pertussis, typhoid), venoms (honey-
bee, wasp, snake), cosmetics, chemicals in plains such as poison ivy,
fjollenSj dust, molds, iodme-coutaming dyes used in certain x-raj
sdures, and even microti
Type I (anaphylactic) reactions are the most common and typi-
cally occur within a few minutes after person W N.0 Was previously
sensil.iv.ed to an allerecu is tteexpOSCd to it. In response to certain al-
lergens, some people produce JgF antibodies dial bind to the sur-
face of mast cells and basophils. I he next time the same allergen
enters the body, it attaches to the IgF antibodies already present. In
response, both the mast cells and basophils release histamine.
prostaglandins, and other chemicals. Collectively, these chemicals
cause vasodilation, increased blood capillary permeability, increased
smooth muscle contraction in the airways of the lungs, ,m{\ in-
creased mucus secretion. \s a result, a person may experience in-
flammatory responses, difficulty m breathing through the narrowed
airways, and a runny nose trom excess mucus secretion. In anaphy-
lactic shock, which may occur in a susceptible individual who has
jusi ni lived a triggering drug or been stung by a wasp,, wheezing
and shortness of breath as airways constrict are usually accompanied
bock due to vasodilation and fluid loss from blood. Injecting ep-
inephrine to dilate the airways and strengthen the heartbeat usually
iv effective in this life-lhreatening emergency.
Type II (cytotoxic) reactions are caused toy antibodies directed
against jnugeiis on a persons blood cells or tissue cells. Type II re-
actions, which may occur m incompatible blood tr.msftision reac-
tions, damage cells by causing 1\ Sis,
Type III (immune -complex) reactions involve antigen
bodies, ami complement. Glomerulonephritis and rheumaio
arthritis (RA) arise in this wav.
Type IV (cell -media ted) reactions or delayed hypttsiinithity
reaction* usually appear 12-72 hours after exposure to an alii
Type IV reactions occur when allergens are taken up by antra
presenting cells (such as Langerhans cells m the skin) thai inigrajj
CO lymph nodes and present the allergen to T cells, which d i
vide. Some of the new T cells return to the site of allergen on
into the body, where they produce gauima-interferon, which H
vaics macrophages, and minor necrosis factor, which stimukttg
inflammatory response. Intracellular bacteria such aS V/l
in/rradom trigger this type of cell-mediated immune u
do certain haptens, such as poison \\\ to\in. I he skin test foj I
beruclosis also is a delayed hyperscnsiij\ ity reaction,
infectious Mononucleosis
Infectious mononucleosis or "mono" is a contagious disease
by the Epsteiil-Barr virus i/'JH J. h occurs mainly in children
yoting adults, and more often In females than in males, I
commonly enters the hod\ through intimate oral contact Midi
lining, which accounts h»r lis heme called the "kissing dis
I. BY then multiplies in lymphatic tissues and spreads it
blood, where n infects and multiplies in Ii cells, the prim.;
cells. Because of this infection, the B cells become enlarged m\A
normal in appearance so thai they resemble monocytes, t.he primifl
reason for the term mmumucleash. Besides an elevated w i
cell count; with an abnormally high percentage of lymphod
signs and symptoms include- fiiigm, headache, dizziness^
throat, enlarged and tender lymph nodes, and fever. Their |
CUT' tor infectious mononucleosis, hut the disease usually runi
course in a few weeks.
Lymphomas
Lymphomas (lim-IA )-mas; lymph- - clear water; -wnus =
are cancers of the lymphatic organs, especially die Ivmph.
Most have no known cause. The two main types ofiymphan
I lodgkin disease and non-1 lodgkin lymphoma.
I lodgkin disease (I ID) is characterized by painless, iHing
enlargement of one or move lymph nodes, most communlt
neck, chest, and axillae (armpits). If the disease has in
from these sites, levers, night sweats, weighl loss, .mj
also occur I II) primarily affects individuals between ages |j
and those over 60; it is more common in nudes. I] diagnosed ■<
HDlvjsa ( HM>5% cure rate.
Nou-lhdgkin lymphoma (NHL), which is more eumjlwflj
Ml), occurs in all age groups. Nl II. may start the sami
but may also include an enlarged spleen, anemia, anil general i
Up to half of all individuals with Mill, are cured or survive I
lengthy period. Treatment options for both III) ami Ml!
diatton liunpy, chemotherapy, and red bone marrow ti
fstemic Lupus Erythematosus
■Hemic lupus erythematosus (er-e-them-a- TO-sus), SLE, oi ht-
■\ln]tm = wolf) is <i chronic autoimmune disease thai effects mol-
, .;, \. ■■;.. ... stums. Viost cases of SLE occur in women between tile
wf 15 and 25, more often in blacks than in whites. \khough the
i S 1 .1 is not known, both a genetic predisposition id the dis-
use mid environ mental factors contribute. Females ate rune times
lire likely than males to suiter from SIX The disorder often oc~
bu Females who exhibit extremely low levels of androgen (male
ffi.lloriii.ones').
iffllCAL TERMINOLOGY AND CONDITIONS
raft (Al.-o-L'.Taft: alh- - orherl \ transplant between geneti-
cally different indh idnals of tin same species. Skin transplants
from other people and blood transfusions are allografts.
\utugrafi i :A\\ to-g.rali; atiin- = self) A transplant in which Otte's
own fissne is grafted to another part of the body (auefa iv skin
;-. for burn treatment or plastic surgery).
jbwY fatigue syndrome (CFS) \ disorder, tasu&Ua occurring bi
voiJiiLi- female adults, characterized by (1) extreme tatigue that
impairs normal activities fbr at least si.\ months and 1.2} the ab-
ftnee of other known diseases (cancer, infections, drag abuse,
KNBcicy, or psychiatric disorders) thai mighi produce similar
syiiipuniis.
Bwrnw globulin (GL0Il-ti4fn) Suspension of immunoglobulins
from blood consisting ol antibodies that react with a specific
;i n, I' is prepared by injecting the pathogen into animals.
Study Outline 441
Signs and symptoms of SIT include joint pain, slight fever, fa-
tigue, oral ulcers, weight loss, enlarged lymph nodes and spleen,
photosensitivity, rapid loss of large amounts of scalp ban n-l
sometimes .w\ eruption across the bridge of the nose and cheeks
Called a "luuiei -\\\ rash." The erosive nature of some ol the SLE
skin lesions WffS thought to resemble the damage inflicted by the
bite of a wolf — thus, the term lupus. Kidney damage occurs as
antigen anubodv complexes become trapped in kidney capillaries,
thereby obstructing blood filtering; Renal failure is the most com
mon cause of death.
removing blood from the animals after antibodies have been
produced, isolating the antibodies, and injecting them into •
human to provide short-term immunity.
Graft Any tissue or organ used for Transplantation or a transplant "1
such structures.
Lympbadenopatby (lim-tad'-c-NOP-a-the; lymph- - clear fluid;
-pathy = disease) Enlarged, sornei.iuies tender hmph "lands as
a response to infection, also called sv.nlien glands.
Splenomegaly (sple'-n6-.\lK( .-a-le; mcyi- ~ large) Enlarged splea n
Tonsillectomy (ton'-si-LKk-ro-me: -atomy = excision) kcuiouil of
a tonsil.
Xenograft i/FX-o-gtaii.; vaw - strange or foreign) A transplant
between animals of different species. Xenografts Irom porcine
(pig) of bovine (cow) tissue may lie used in people as a physio-
logical dressing for severe bums.
^
STUDY OUTLINE
ductlon (p. 420)
bespite constant exposure to a variety of pathogens (disease-
ttxhidna microbes such as bacteria and viruses), most peopfe
remain healthy,
Immunity or resistance is the ability to ward off damage or dis-
[.nnate immunity refers to defenses ih.u are present at
birth, they are always present ami provide immediate but gcu-
oiection against invasion In a wide vm\^ of pathogens.
irivc immunity refers to defenses that respond to a parrieu-
hr invader; n involves activation of specific lymphocytes thai
,,i:i com I kh a specific invader.
atlc System (p. 421)
he bod) system responsible for adaptive immunity (and some
_ ecu. of innate immunity) is die lymphatic system, which
[consists of lymph, lymphatic vessels, structures and organs that
Rfentain lymphatic tissue, .\\\A ivd bone marrow.
pnncius of blood plasma filler through blood capillary
,, toon interstitial fluid, the fluid that bathes die cells or
s. Alter interstitial fluid passes into lymphatic ves-
5.
1.
5.
6.
sets, it is called lymph. Interstitial fluid and lymph are chemi
Call) similar to blond plasma.
The lymphatic system drains tissue spaces of excess fluid and
returns proteins that have escaped from blood to the cardiovftS-
cul.ir system. It also transports lipids and lipid-sohible vitamins
from tiie gastrointestinal tract to the blood, and it protects the
body against invasion.
Lymphatic vessels begin as lymphatic capillaries m tissue spaces
b W n pells. The lympharic capillaries merge to form larger
Ivjupbatic vessels, which ultimately drain into the thoracic •hid
or right lymphatic duct. Located at intervals along lymphatic
vessels are lymph nodes, masses of B cells and I cells sur-
rounded by a capsule.
The passage of hmph is from interstitial flunk BO lymphatii
capillaries, m lymphatic vessels and hmph nodes, to the tho-
racic duct or right lymphatic duct, to the junction ol the inter-
nal jugular and subclavian veins.
Lymph Hows due to the "milking action" of skeletal muscle
contractions and pressure changes that, occur flitting inhalation.
Valves u» die lymphatic vessels prevent back 11 ov ol h mph.
442 Chapter 17 The Lymphatic System anil Immunity
I, Primary lymphatic organs and tissues are the af^ 8 tvhefe stem
cells divide and develop into mature IJ cells and I cells. They
include the red boric marrow (in flat hones and the ends .1 the
long hones uf adults) .mul the thymus. Stem evils in red hone
I i.nr^ l'iv. rise to mature 13 ccllsand in miniature (' tells- th;ir
migrate to the thymus, where cjtey inquire into liincnt>iml T
cells.
K. The secondary lymphatic organs and tissues arc the sites where
most immune responses eeetm They include lymph nodes, die
Spleen, 8|ld lymphatic nodules.
o. Lymph nodes contain B cells chat develop into plasma cells, T
Cells, dendritic cells, and macrophages. Lymph enters nudes
through afferent lymphatic vessels and exits through efferent
lymphatic vessels.
10, The spleen is the single largest mass of hiuphudc tissue in the
body. It is a sire where IJ cells divide into plasma cells and
macrophages phagocytic worn-out red blood cells and
I bis,
II. Lymphatic nodules jre oval-shaped concentrations of lym-
phatic tissue that are not surrounded by a capsule. They are
scattered throughout the mucosa of rhe gastrointestinal respi-
raion, nnn.in. and reproductive tracts;
Innate Immunity (p. 425)
1. Innate immunity defenses include harriers provided liy the skin
and mucous membranes {first hue oj defense). They also in-
clude various internal defenses (second line of defense): inter-
na] aptiiniiTuliial proteins (interferons, complement, transfer-
rin. Slid annum .Tiihttfl peptides), phagocytes (neutrophils arid
macrophages), natural Idler cells (winch have the ahilin to kill
a wide variety of ink-cm lUs uiutoU-s and certain tumor cells),
irillammation, and fever.
2. [able 17.1 on page 42s summarises the c&mpeneaiaE of innate
immunity.
Adaptive Immunity (p. 428)
L Adaptive immunity involves the production 61 specific types ol
cells or specific antihodies to destroy fl particular antigen.
2. An antincn is art) substance thai the adaptive Immune system
recognizes as foreign tuonscif). Normally, a person's immune
system cells exhibit self- tolerance; Thev. recognize and do 1101
■arrack rheir own tissues -.md chemicals.
3. H tells complete their development in \x<\ hone marrow, but
mature T cells develop in die i hymns from immature T cells
that migrate from hone marrow.
4. The major histocompatibility complex (.V111C!) protein
unique to each person's body cells. All cells except red l«i..,»l (
celU display Ml IC . molecules.
5. Antigens induce plasma cells to secrete antihodies, protunl
dun typically contain four polv, peptide chains. "1 he van
gitWS ol an antibody are the amiLU R-hindrng sues, ulaic tfcl
antibody can hind to a particular antigen,
6. Based on chemistry and structure, antibodies, also low
immunoglobulins (IGs), arc grouped in five classes, ca
rpearlc bmctions: [gG, IgA, IgM, fgD, and IgE (see I
on page 430); Functionally, antihodies neutralize antigen*, tua
mobilize bacteria, agglutinate antigens, activate comphnajH
and enhance phagocytosis.
7. AiUigen-presentniL; cells (\P(.si process and presenr anlmrcJ
to activate I cells, and they secrete snhsiances lluu: sumitfcB
division of T cells and li cells.
8. There are three main kinds of T cells-, helper "I cell
stimulate growth and division of cytotoxic T cells, ,\urxm
phagocytes, and stimulate development o\ II cells into him
body-prod ucing plasma cells; cytotoxic I cells, which eliimrian
invaders hy (I] releasing gnmzyines that cause target cell d
rosis (phagocytes rhen kill die microbes) and (2) releasingiffl
forin, which causes cytolysis, and grantilysm that destroys?
ntiej'ohes: and memory I cells, which recognize pre
countered antigens at a later date.
9. Antibody-mediated immunity relets to destruction <
bj antihodies. which are produced by descendants of B cti
called plasma cells.
It). 15 cells develop into antibody-producing plasma cell* m di j
influence of chemicals secreted bj antigen-presemirij
helper T ceils.
11. fable 17J "ii page 436" summarizes die functions uf^
participate in adaptive immune responses.
12. Immunization against certain microbes is possible h
memory \\ cells and memory T cells remain after a printing
sponsc to an anrigi n, I hv secondary response pmviil
tion should the same microbe enter the body again. | fl
on page 4.> 7 summarizes the various types ol Tung
ters that provide naturally and artificial!) acquired immunity]
Aging and the Immune System (p. 437)
1. With advancing age, individuals become more siuctptiWu
infections and malignancies, respond less well to vai
produce more autoantibodies.
2. I" cell responses also diminish with age.
Self-Quiz 443
#A
1 Which of the following is H( FT true concerning the lymphatic
. ie i ti-
ll. Lymphatic vessels transport fcipids Crom tjhc gastroincesriwaJ
craci H) the blood.
I). I ymph is more •iimil.ir to interatirial fluid than to blood,
c. Lymphatic tissue is present in only a tew isolated organs m
the body.
3, The unique structure oflymphatic capillaries allows fluid to
low into them but CIO! GUI of them.
B, ! unplvatie vessels resemble veins in Rtnietttf&
\\ I,,. h ol' the following are produced 1 >> virus- in leered cells to
protect unitlfcieteid cells from viral invasion?
a. .complement molecules b. prostaglandins c. fibrins
- d. interferons e. histaminc-
5. \ blockage in the right lymphatic duel would interfere with
lymph drainage from the
ii. left arm h. nt-hi leg c. lower abdomen
I left leg e. right arm
L Which nl" the following hesi represents lymph flow from the
interstitial spaces back to the blood?
u. lymphatic capillaries -» lymphatic duets — lympli:i' "
isels -» junction of internal jugular and subclavian veins
b. junction of internal jugular and subclavian veins -* lymphatic
llories -* lymphatic vessels -* lymphatic ducts
,-, lymphatic capillaries -* lymphatic vessels — lymphatic
,L • — junction of internal jugular and subclavian veins
tmhatic ducts — lymphatic vessels — lymphatic capillar-
ies • junction of internal jugular and subclavian veins
P , lj inphatic capillaries -+ lymphatic vessels — junction of in-
, nn! jugular and subclavian veins -* lymphatic ducts
jrmph mules
i lymph b. are another name for tonsils
produce lymph d, are a primary Storage site lor blood
produce :i protective mucus
•h of the following is NOT true about the role of skin in
^specific immunity?
n inhibits the grov th of certain bacteria,
rmal cells produce interferons to destroy virusesy
idding of epidermal cells helps remove microbes.
l.vsu/v me in sweat destroys some bacteria.
The skin forms a physical hairier to prevent entry of
microbes.
nil of the follow ing statements about B cells is true?
H,.,v become functional while in the thymus
,, vm", develop into pksma cells that secrete antibodies.
We B cells become natural killer cells.
,! , I, B cells travel in lymph and blond to react with
foreign antigens.
r . i b< J kill virus-infected cells by secreting perforin.
8, The cells that release gnm/.ymes, perforin, granulysin, and
Ivmphoco.vin are
a. cytotoxic T cells h. plasma cells c. B veil-.
d. natural Toller cells e. helper I colls
9. The secondary response m antibody-mediated immunity
a. is characterized In a slow rise m antibody levels and then a
gradual decline
b. occurs when you fust receive a vaccination against some
disease
c. produces fewer hot more responsive antibodies than OCCffl
during the primary respon-
d. is an intense response bj memory cells CO ptoduce amibod-
ics when an antigen is contacted again
e. is rarely seen except in autoimmune disorders
10. The ubilii\ of the body's immune system CO recognize its own
tissues is known as
a. immunological escape b, autoimmunity c. non-
specific resistance A. hypersensitivity e. sdl-tolerancc
11. A disease that causes destruction of helper 1 cells would result
in all of the following effects EXCEPT
a. inability" to produce e>toio-oc- 1 Cells
b. alteration of lymph flow
c. lack of dcvelopmenl of plasma cells
d. decreased production of antibodies
e. increased risk of developing infectious
12. In which lymphatic organ do I' cells mature?
a. thyroid gland b. spleen c. thymus
cl. red bone marrow e. lymph node
L-3. I'lace the follow ing Steps involved in the process oJ iiillanimu-
tion in the correct order.
1. arrival of large numbers of neutrophils
2. vasodilation and increased permeability of blood vessels
3. formation of pus
4. increased migration of monocytes
5. formation of fibrin network m Ebittn a clot
6. release of histamine
a. 6.14, 1,5,3 l». 3,6, 1,4,2* 5 c. 5. 1. ! 6,3
d. 6,2,5,1,-4,3 e. 4,6, I, .3, 2,5
14. Match the following:
a. destroy antigens b\ A. natural killer cells
■:\ n .lysis B. helper I cells
b. stimulate other cells of (J. 15 cells
the adaptive immune D . ,n c ,noiv I ■ ■ II
response E . cytotoxic T cells
c. arc programmed to
ret i.gni/.e the original
inv;iilin;; antigen; allow
immunity lo last lor ye U
d. function in innate immunity
c. develop into plasma cclK
444 Chapter 17 The Lymphatic System and Immunity
15. What happens durinj opsonization?
a. engulfment ©fa microbe bj :i phagocyte
b. chemical attraction oi a phagocyte
c. binding of complement to a microbe
d. iiiuitliiiK-iii of a phagocyte to ;i microbe
e. breakdown of a microbe by enzymes
16. Ml of the following contribute to nonspecific imiii.tuii.iA IX
a w\
-.]. complement b- immunoglobulltiis
C. nai.und killer cells d. lysu/yuu- c. interferons
17. Inflammation produces
a. redness due to bleeding
b. heat due to fever-causing toxins
c. swelling due to increased peraieabilttj «ifcupiilaries
d. pain clue to histamine release
c. mucus due to £hagOCyt<)«Js
18. Place i he phases ol phagocytosis in the correct order.
1. ndHeretice to foreign material
2. chcuiotaxis ol phagocytes
3. c\'.i.)'i'isi> of indigestible material?
4. ingestion "i' foreign material
a! 1.2, \4 b. 2. 1.4. J c. 1,4.3,2 cf. I
ft. 2,1., J, I
19. Antibodies attack anrigens In all of the following methods. EXj
I if I
a. agglutination of antigens
b. activation of complement
c. opsonization to enhance phagocytosis
d. preventing attachment to bod) cells
e. producing ucid secretions
20. What is the importance of tonsils m the bodys tlctcnsc
a. Thc\ help destroy microbes thai arc inhaled.
b. They contain ciliated cells that move trapped puihog n-
froui the breathing passages.
c. They .iiv needed for T cell maturation,
d. I hey are needed for li fell matur.it.ion.
c. They filter U mph.
m
CRITICAL THINKING APPLICATIONS
1. Ylarcia found a lamp in her light breast daring her monthly
sc I l'-cv.mii notion. The lump was found to be cancerous. The
surgeon removed the breast lump, the surrounding tissue, and
some lymph nodes. Which nodes were prohabh removed ami
why?
2. Years ago, 8 tonsillectomy was almost considered a "rite oi pas*
.!:.:. for children m elemental} school, li seemed like nil chil-
dren were getting their tonsils removed] Why are tonsils fre-
tpienth infected in young children?
3. B.J. Stepped on a rtJSty fishhook while walking along the bi
The emergency room nurse removed ihc liTliuul, 1
B.J. a tetanus booster. Why?
4. V«it,i learned in Chapter 16 thai the cornea and lens til
are completely lacking in capillaries, I low is this fact ti-Lw
the high success of comeal transplants?
?
ANSWERS TO FIGURE QUESTIONS
17.1 Lvrnpharic tissue, is reticular connective tissue chat contains
large rrombers of lymphocytes.
17.2 Lymph is more simitar to interstitial lluid because its protein
content is low.
17.3 Capillaries produce lymph,
17.4 Foreign substances m lymph may be phagocytized by
macrophages Ot destroyed by I" cells «»r antibodies produced
In plasma cells.
17.5 Redness is caused by inn-eased blood Bow due to vasodila-
tion.
17-6 The \ ariable regions of an antibody can bind spcrificiill) i
the antigen that triggered its production.
17.7 APt Is Include macrophages, 15 culls, and dendritic eel
1 7.8 \ clone is a population of identical cells.
17.9 Cytotoxic I cells can also attack some tumor cells JttOl
planted tissue cells,
17.10 Memory 4" ami B cells respond to a second im
same antigen.
17.1 1 li;( ! is die and bod J secreted, in greatest amount during
secondary response,
THE RESPIRATORY SYSTEM
Mpu know?
C-> igarette smoking is the single
lit preventable cause of death and disabiUt)' world-
zule. Smoking disrupts the body's ability to maintain
homeostasis and health became it introduces many
\rmftd substances into the body, and wreaks havoc on
I ffagjle tissues of the respiratory system. For exam-
, footing causes emphysema by progressively destroy-
ing the alveoli and bronchioles. The irritation produced
by cigarette smoke often leads to chronic bronchitis.
Smoking causes many types of earners, including cancers
, mouth, throat, lungs, esophagus, stomach, kidneys,
( pumnus, colon, and urinary bladder. The chemicals in
rigantte smoke also raise blood pressure and accelerate
the process of atherosclerosis.
Focus on Wellness, page 463
www.wiley.com/colleoe/apcen1ral
jDody cells continually use
oxygen (C) ? ) for the metabolic
reactions that release energy from
nutrient molecules and produce ATP.
These same reactions produce carbon
dioxide (CO : ). Because an excessive amount i .1 « ' )
produces acidity tlv.it can be toxic to cells, excess CO>
must be eliminated ipiiekly and efficiently. The respira-
tory system, which includes the nose. pharynx (tfotoat),
larynx (voice box), trachea (windpipe), bronchi, and
lungs (Figure 1 B. I ), provides Tor gas exchange, the in-
take oft ),, and the removal of CO, "1 "he ivspiraioi -\
system also helps regulate blood p] I: contains receptors
for the sense of smell; filters, warms, and moisl
inspired air; produces sounds; and rids die body ol some
water and heat in exhaled air.
looking back to move ahead . . .
- Cartilage (page 89}
• Pseudostratifled Ciliated Columnar Epithelium (page 75)
• Simple Squamous Epithelium (page 75)
• Muscles Used in Breathing (page 200)
■ Diffusion (page 47)
» tons (page 25)
■ Medulla and Pons (pages 250-253)
445
446 Chapter 18 The Respiratory System
Figure 18.1 Organs of the respiratory system.
W
The upper respiratory system includes the nose, pharynx, and associated structures. The lower respiratory
system includes the larynx, trachea, bronchi, and lungs.
Pharynx
Right primary
bronchus
Lungs
Nose
Nasal cavity
Oral cavity
Larynx
Trachea
Functions of the Respiratory System
1. Provides for gas exchange — intake of ; . for delivery
to body cells and removal of CO :J produced by body
cells.
2. Helps regulate blood pH.
3. Contains receplors for the sense of smell-, filters,
Warms, and moistens inspired air; produces sounds;
and excretes some water and heat.
Anterior view
Which structures comprise the conducting zone of the respiratory system?
I he branch of medicine chat deals with the diagnosis and
treatment of diseases of the ears, nose, and throat (F.NT) is
i ;i lied otorhinolaryngology ( o' -to-ii" -no-lar' -in-CiOL-6-je:
olo- = ear; rhino- — nose; laryngo- = voice box: -fo0 = Study
of). A [m/wn/wloght {ptdnittn- = lung) is a specialist in the
diagnosis and treatment o$ diseases of the lungs.
The entire process of gas exchange in the hotly, called
respiration, occurs in three baste steps:
1. Pulmonary ventilation, or breathing, is the How of m
IttO » and oui of the lungs.
2. External respiration i^ the exchange of gases between
the air spaces (alveoli) ol die lungs and the blood in pul-
monary capillaries. In this process, pulmonary capillary
blood gains : and loses CO..
3. Internal respiration is the exchange of gases between
blood in systemic capillaries and tissue cells. The blood
loses Oj and gains CO* Within cells, the metabolic reac-
tions that consume (). and give off CO.- during the pro-
duction of VI j? are termed ccllulur respfcativn (discussed
m Chapter 20).
■\s you i an ^e< . ru.i simvius nre i ooperaring to supply i ) m
eliminate CO? — the cardiovascular and respirator) svstql
The first wo steps are the responsibility of the resjiinuiifi
system, while the third step is :i function ol the cardiuvusofl
system.
ORGANS OF THE
RESPIRATORY SYSTEM
OBJECTIVE « Describe the structure and fiinctic
the nose, pharynx, larynx, trachea, bronchi, hnuuhioii
and lungs.
Structurally, the respiratory system Consists ol tWO !
upper respiratory system includes die nose ph iryn
soeiated structures: the lower respiratory system ctirwha
the larynx, trachea, bronchi, and lungs. The respirai
lein can also be divided into two parts based on funis
The cnudtuting zone consists of .1 series of interconnecting
Lies and tubes— nose, pharynx, larynx, trachea, bronchi,
Lclnnlcs, and terminal bronchioles— thai conduct air nun
t lungs. The respiratory zone consists of tissues within the
fe where gas exchange occurs— the respiratory hronclu-
jolar ducts, alveolar sacs, and alveoli
hose
\u nose has .1 \isihle eMernal portion and an internal por-
Einside the skull I . L8.2). The external nose consists
..,(;„„„ , m .| cartilage covered with skin and lined with mu-
membrane. It has two openings called the external
IWft'j-iN V ix y; singular is naris) or nostrils.
rnal nose connects to the throat through two
Inning called the internal nares. Four paranasal sinuses
pmtai, sphenoidal, maxillary, and ethmoidal) and the naso-
Organs ol the Respiratory System 447
lacrimal duels -also connect to the internal nose. The space
inside the mierual nose, called the nasal cavity, lies bfefov dtt
cranium and above the mouth. \ verlieal partition, the miscd
scpnmt. divides the nasal cavity into right and left sides, The
septum consists of rhe perpendicular plate of the ethmoid
bone, vomer, and cartilage (see l-'igiiiv 6, "a on page I26>.
Rhinoplasty (KI-n6-plas'-tei -pk<rx to mold or 10
shape), mmmonly called a "nose job," is a surgical proce-
dure to alter the shape ol the external nose. Mihough
rhinoplasty is often done lor cosmetic nsj ij tS some-
times pt-rlJ Miiir.l tO repair a fractured ROSe or a deviated
nasal septum. With anesthesia, instruments [inserted
through the nostrils are used to reshape the nasal canil
and fracture and reposition the nasal hones, to achieve the
desired shape. An internal packing and splint keep da-
nose in the desired position while ! i tb
%
jure 18.2 Respiratory organs in the head and neck.
As air passes through The nose, it is warmed, filtered, and moistened.
Sagittal plane
Sphenoid bone
Internal naris
Pharyngeal tonsil
Nasopharynx
Orifice of auditory
(eustachian) tube
Uvula — ■
Palatine tonsil
Oropharynx
Epiglottis
Lai yngopharynx
Esophagus
Trachea —
- True vocal eord
Larynx
Thyroid cartilage
Thyroid gland
Frontal hone
Olfactory epithelium
Superior
Middle
Inferior J
Nasal
conehae
External naris
Maxilla
Oral cavity
Palatine Pone
Soil palate
Lingual tonsil
Hyoid bono
Sagittal section ol the left side oi the head and neck
^ what is the path taken by air molecules into and through the nose?
448 Chapter 18 The Respiratory System
The interior structures of the nose are specialized for
three basic functions (h filtering, wanning, tod moistening'
incoming air; (2) detecting olfactory (smell) stimuli; jml
(>) modifying the vibrations of speech sounds. When air
enters the nostrils, ii passes coarse hairs dial trap large dust
particles. The air then Rows over three shelves called the su-
perior, middle, and inferior nasal conchae (KUNd-Le) that
extend out of the wall or the cavity. Mucous membrane lines
the OasaJ cavity anil the three conchae. As umpired ait whirls
around the conchae, it is warmed by blood circulating m
abundant capillaries. The olfactory receptors lie- in the mem-
brane lining - the superior nasal conchae .\n\\ adjacent septum.
This region is called the Qljatftoty ("pithclni//;.
Pseudostraiified ciliated columnar epithelial cells and
goblet cells line the nasal cavity. Mucus secreted by gohlcr
cells moistens the air and traps dust particles, (alia move the
dust-laden mucus toward the pharynx, at which point it can
be swallowed or spit out, thus removing panicles from the
respiratory tract.
Substances in cigarette smoke inhibit movement of cilia.
If the cilia are paralyzed, only coughing can remove
mucus-dust packages from the airways. This is why smok-
ers cough SO much and are more prone to respirator)
'MIS.
Pharynx
The pharynx (FAlk-inks), or throat, is a tunnel-shaped tube
that Starts .it the internal nares and extends partway down the
neck (Figure IK.-). It lies just posterior to the nasal and oral
cavities and just anterior to the cervical (neck) vertebrae. Its
wall is composed of skeletal muscle and lined with mucous
membrane, The pharynx functions as a passageway for air
and food, provides a resonating chamber for speech sounds,
and houses the tonsils, which participate in immunological
responses to foreign menders.
The upper part of die pharynx, called the nasopharynx.
connects with the two internal nares and has two openings
that lead into the auditory (eustachian) tabes. The posterior
wall contains the pharyngeffl wnsiL The nasopharynx ex-
changes air with the nasal Cavities and receives mucus dust
packages. The cilia of its pseudnstratihed ciliated columnar
epithelium move the mucus-dust packages toward the
mouth. The nasopharynx also exchanges small amounts of air
with the auditory tubes to equalize air pressure between the
pharynx and middle ear. The middle portion ol the pharynx.
die oropharynx, opens into the mouth and nasopharynx. Two
pairs of n >nsils, the palatini wisifc and lingual tonsil*,, are found
in the oropharynx. The lowest portion ol the pharynx, the
laryngopharynx i .la-rin'-go-KAlU-inks), connects with both
the esophagus (food tube) and the larynx (voice box). Thus.
the oropharynx and laryngopharynx both serve as passage-
ways for air as well as for food and drink.
Larynx
The larynx (LAIR-inks), or voice box, is a short tube of OR
tilage lined by mucous membrane that connects the phriryni
with the trachea (Figure 18.3). It lies in the midline ol tlu
neck anterior to the fourth, fifth, and sixth cervical verrebnj
(C4to C6).
The thyroid cartilage, which consists of hyaline can ibi.'c
forms the anterior wall ol the larynx. Its common iiume
(Adam s apple) reflects the I act that it is often larger in maid
than in females due to the influence of male se.\ honmiiMj
ill i ring puberty.
The epiglottis (cpi- = over; .glottis - tongue) is a larg
kiii-shaped piece ol elastic cartilage, that is covered with i
ithelium (see also Figure IS. 2). The "stem" of the cpi™
is attached to the anterior rim ol the thyroid cartiiaffl
hynid bone, The broad superior "leal" portion ol rite epigll
tag is unattached and is free to move up ami down i I. .
door. During swallowing, the pharynx and larynx rise. EJqsj
tion ol the pharynx widens it to receive food or drink; iTn
lion of the larynx causes the epiglottis to move down am)
form a lid over the larynx, el.. sing it off. The closing fifr.be
larynx in this way during swallowing routes liquids and foot
into the esophagus and keeps them out ol the ainvaVslwdfl
When anything but air passes into the larynx, a cough reft
attempts to expel the material.
The cricoid cartilage (KRI-koyd) is a ring of'hjaffl
cartilage that forms the inferior wall of the larynx nndisa
tached to the fust tracheal cartilage. The paired arytcna^
cartilages (ar'-i-TE-noyd), consisting mostly of UyaJlhi
cartilage, are located -above the cricoid cartilage. They i
t.icli in the true vocal cords and pharyngeal tiULselesfl
function in voice production. The cricoid cartilage is n
landmark for making an emergency airway (a iracheoum
see page 451).
The Structures of Voice Production
The mucous membrane of the larynx forms two \\wrsi
folds; an upper pair called thcfilse vocal cords ami .i Us
pair called the true vocal cords (see l-'igure I:- i
vocal cords hold the breath against pressure in the ilmre
cavity when you strain to lift a heavy object, such i .
puck filled with textbooks. The} do not produce sound
The true vocal cords produce sou mis during •.)
and singing. They contain elastic ligaments Stretdn
tween pieces of rigid cartilage like the strings on a,
Muscles attach both to die cartilage and to die true i
cords. When the muscles contract, they pull the eltisri)}
ments tight, which moves the true vocal cords out intent
passageway. The air pushed against the true vot
causes them to vibrate and sets up sound waves in die
the pharynx, nose, and mouth. The greater the air [»
the louder the sound.
Organs of the Respiratory System 449
Figure 18.3 Larynx.
The larynx is composed ol cartilage.
Larynx
Thyroid
gland
i
i
Eplgiotlis
Hyoid bone
Gornlculate cartilage
Thyroid cartilage
(Adams apple)
Arytenoid cartilage
Cricoid cartilage
Thyroid gland
Parathyroid
glands (4)
Tracheal cartilage
(a) Anterior view
How does the epiglottis prevent loods and liquids from entering the larynx?
lb) Posterior view
Pitch is controlled by the tension of the croe vocal cords.
phey are pulled taut, they vibrate more rapidly and a higher
Iresults. Lower sounds arc produced by decreasing the
,„.il,u tension. Due to the influence of male sex hor-
.ords are usually thicker and longer in males
malts. They therefore vibrate more slowly, giving
n lower range of pitch than women.
„#tis is an inflammation of the larynx that is most
i grtised by a respiratory infection or irritants such as
^ette smoke. Inflammation of the vocal folds causes
. S s or loss of \ oice H\ interfering with the contrac-
i i. L ' folds or by causing them to swell to the point
„-ibey cannot vibrate freely. Many long-term smokers
i permanent hoarseness from the damage done by
| chronic inflammation. Cancer of the larynx is Found aj-
moM exclusively in individuals who smoke. The condition
is characterized by hoarseness, pain on swallowing, or pap
radiating to an ear. Treatment consists of radiation therspj
and/or surgery.
■ CHECKPOINT
1. Wham, functions do the respiratory and cardiovascular
systems have in common?
2. Compare the structure and functions of the external and
internal nose.
3. Hou does the larynx function in respiration and voice
production?
450 Chapter 18 The Respiratory System
Trachea
The trachea (TlvX-U-a), or windpipe, js a tubular passage-
way for air that is located anterior to tke esonhagus. It ex-
iliu\s from vVic larynx to tfee upper pun. oS ihe filKb lihoradc
vertebra (TS), where it divides into fight and left primary
bronchi (Figur* I >'.
The \v:)ll of the trachea is lined with raucous mcmlu-nne
and ts supported by cartilage. The raucous membrane is
composed of pseadosrrarirled ciliated columnar epithelium,
consisting of ciliated columnar cells, goblet cells, -nul basal
cells (see ialilc 4.ti- (in page 78), and provides the same pre*-
teetion against dnst as the membrane lining the nasal cavity
and larynx. The cilia in the upper respirator) tract mim
mucus and trapped particles thorn toward the pharyrui, I*
the alia in the lower respiratory tract move mi
v :-.\y\>mi\ \Yit\ic\«is \\\\ uw -.vcvV vW ^faftE^nat. TVvc cariil
consists of 16 to 20 C-shaped rings ol hyaline
stacked one on top of another. The open pun uf|
C-shaped cartilage ring laces the esophagus and pcrtnitSij
expand slight I \ inin the trachea during swallowing. TW
parts ol die C-shaped cartilage rings provide a
90 ihe trachea! wall does not collapse inward and
air passageway The rings of cartilage may be fell uiu!
skin hclow the larvnx.
Figure 18.4 Branching of airways from the trachea and lobes of the lungs.
i The bronchial tree consists of airways that begin at the trachea and end at the terminal bronchioles.
■'-
Pleural membrane:
Parietal pleura —
Visceral pleura -
Pleural cavity
flight primary bronchu
Right superior lobe
Horizontal fissure
Right middle lobe
Right oblique fissure
Right inferior lobe
Diaphragm
Larynx
Trachea
- Apex ol lung
Anterior view
How many lobes and secondary bronchi are present in each lung?
BRANCHING OF
BRONCHIAL TRI
EE
Trachea
\
Primary bronchi
\
Secondary bronchi
1
Terliary bi'Oflclll
I
ichfc-les
L
Bronchioles
Terminal bronchioles
Left primary i'
Left superior lobe
Secondary bronchus
Terrlary bronchus
Bronchiole
Teiminal bronchiole
Left oblique lissure
Left interior Jobe
Base ol lung
il conditions may block airflow by obstructing the
mohcfl. 'Ilir rings of cartilage chat support the trachea
j be accidental!) crushed, the mucous membrane may
jpme inflamed and swell so much thai it. closes off the
vcess mucus secreted by inflamed membranes
,:; the lower respirator)' passages, or .1 large object
aspirated (breathed in). Lf the obstruction is above
I of the larynx, a tracheotomy (tra-ke-O-to-me)
rncd. In this procedure, also called a trn-
mstwiy an incision is made in the trachea below the
Ecnid cartilage and a tracheal tube is inserted to create an
passageway.
Michi and Bronchioles
hen divides into a right primary bronchus {I5RON-
= windpipe), which goes to the right lung, and a left pri-
brnrrchus, which goes to the left lung (Figure 18.4).
j 1 trachea, the primary bronchi (BRONCi-ke) contain
Uptatc rings of cartilage and arc lined by pseudosrrati-
hi m nar epithelium, Pulmonaiy blood vessels,
sets, and nerves enter and exit the lungs with
hi
tin entering the lungs, the primary bronchi divide to
pj the secondary bronchi, one for each lobe of the lung.
right lung has three lobes; the left lung has iwo.) The
uliin bronchi continue to branch, forming still smaller
ichi, called tertiary bronchi, that divide several rimes, ill—
pely giving rise to smaller bronchioles: Bronchioles, in
hranch into even smaller tubes called terminal bron-
t(. Because the airways resemble an upside-down tree
branches, their arrangement is known as the
mhinl tree.
As die branching becomes more extensive in the
pi'hial tret, structural changes occur, hirst, plates of card*
Ewadiiiilly replace the incomplete rings of cartilage in
§ dicbi and finally disappear in the distal bronchi-
as the amount of cartilage decreases, the
fct.yf smooth muscle increases. Smooth muscle encircles
il bunds. During exercise, activity in the
pjtht n of the autonomic nervous system (ANS)
I causes the adrenal medullae to release die bor-
I'lnephrine and norepinephrine. Both chemicals
m of smooth muscle in the bronchioles, which
ms) the airways. The resulr is improved airflow,
?ehes the alveoli more quickly.
in asthma attack, bronchiolar smooth muscle
asm. Because there is no supporting cartilage,
can close off the air passageway s. Mo\ entcnt of
ted bronchioles causes breathing to be
Organs 0! the Respiratory System 451
more labored. The parasympathetic division of the ANS
and mediators ol allergic reactions such as histamine also
I cause narrowing of bronchioles (bronchoconstriction) due
to contraction of bronchiolar smooth muscle.
Lungs
The tangs (= lightweights, because the) float) are tun
spongy, cone-shaped organs in die thoracic cavity. They are
separated from each other by the heart and other structures
in the mediastinum (see Figure I5.l on page 365). The
pleural membrane is a double-layered serous membrane that
encloses and protects each lung (Figure 18«4)« 'he outer
layer is attached to the wait of the thoracic cavity and di-
aphragm and is called the parietal pleura. The inner layer,
the visceral pleura, is attached to the lungs. Between the \ is-
ceral and parietal pleurae is a narrow space, the pleural
cavity, which contains a lubricating fluid secreted 03 the
membranes. This fluid reduces friction between the mem-
branes, allowing them to shde eadij over one another during
Urea tiling.
The lung$ extend irom the diaphragm to slightly above
the clavicles and lie against the ribs. The broad bottom por-
tion of each lung - is its base; the narrow top portion is the
apex (Figure i 8.4)- The left lung has an indentation, the ctw-
diac notch, in which the limn lies. Due to the space occupied
by the heart, the left lung- is about 10% smaller than the right
lung.
Deep grooves called fissures divide each lung into lobes.
The oblique fissure divides the left lung into siijh-nnr and infi-
rior lobes. The nhUtjiic and horizontal fissures divide the right
lung into superior, middle, and inferior lobes (I ■ igure 18.4); bach
lobe receives its own secondary bronchus.
Each lung lobe is divided into smaller segments thai
are supplied by a ternary bronchus, Fhe segments, in
turn, are subdivided into many small compartments called
lobules (Figure 18.5), Each lobule contains a lymphatic ves-
sel, an arteriole, a venule, and a branch from a terminal
bronchiole wrapped in elastic connective tissue. Terminal
bronchioles subdivide into microscopic branches called
•respiratory bronchioles, which are lined bv nonciliated sim-
ple cuboidal epithelium, Respiratory bronchioles, in turn,
subdivide into Several alveolar ducts. I he two or more alve-
oli that share a common opening to the alveolar duet are
called alveolar sacs.
Alveoli
An alveolus (al-VT-6-lus; plural is alveoli) is a cup-shaped
outpouching of an alveolar sac. Many alveoli and alveolar
sacs siUTbund each alveolar duct. The walls <A alveoli consist
mainly of thin alveolar cells, which are simple squamous ep«
452 Chapter 18 The Respiratory System
Figure 18.5 Lobule ot the lung.
Alveolar sacs are two or more alveoli thai share a common opening into an alveolar duel.
Visceral
pleura
Alvso
(a) Diagram of a portion of a lobule of the lung
What are the major parts ot 8 lobule of a lung?
Visceral
pleura
ytpyn
(b) Lung lobul©
irhelial cells ( I 6). They are die main sites of
gas exchange. Scattered atoong fcherta are wrfactmfa
Wcretmg cdk that secrete alvealw ftniti which keeps the sur-
face between the cells and the air moist. Included in the alve-
olar fluid \s surfactant (sur-t Ak-Unu), a mixture of phospho-
lipid and lipoproteins that reduces the tendency of alveoli to
collapse, \Uo present are ahwiar miia-ophn^i, wandering
phagocytes thai remove line dust particles and other debris in
the alveolar spaces. Underlying the layer of alveolar cells is
an elastic basement membrane and a thin layer of connective
containing plentiful elastic and reticular fibers (de-
scribed shortly). Around the alveoli, the pulmonary arteri-
ole and venule form lush networks of blood capillaries (see
I '■
" The exchange of 2 and C( ) 3 between the air spaces m
die lungs and the blood takes place by diffusion across the
alveolar and capillary walls, which together form the respi-
ratory membrme. It consists of the following layers (I Lg-
V.f.h):
1 . The alveolar, cells that U una the wall of a n a I vc< ih is.
2, An epithelial basement membrane underlying die alveolar
cells.
3. A alpiliiiiy base-incut membrane that is often fused mi
epithelial basement membrane.
4. The aiduthclml ce&of a capillary.
Despite having' several layers, die respiratory membra
is only 0.5 pint wide. This thin width, far less lb
ness of a sheet of tissue paper, permits (>■ and C0 2 In (liffitj
efficiently between the blood and alveolar air spaces; Mure
over, the lungs contain roughly 300 million alvcn
provide a huge surface area for the euh.ui'M i|
QQ 2 — a b oU t JO to 40 times greater than the surface arq
your skin or half die si/e of a tennis court!
■ CHECKPOINT
4. W h.u is the bronchial tree? Describe its structure.
5. Where are the lungs located? Distinguish thi
pleura from the visceral pleura.
6. Where in the lungs does the exchange ol u. and ^
take place?
'1 /in. (micrometer) = 1/1,000,000 of a meter or 1/25,000 of an iod
Pulmonary Ventilation 453
Figure 18.6 Structure of an alveolus.
The exchange of respiratory gases occurs by diffusion across the respiratory membrane.
respiratory
[lerobrane
Uveolar ca
llveolar
macrophage
led blood cell
V pulmonary
apillary
Diffusion of O fi
Diffusion pi CO : ,
Capillary endothelial
cell
Capillary -basemen I
membrane
Connective tissue
Epithelial basement
membrane
Alveolar cell
(a) Section through an alveolus
showing its cellular components
Alveolar fluid
with surfactant
(b) Details ot respiratory membrane
Which cells secrete alveolar fluid?
10NARY VENTILATION
IVES • Explain how inhalation and exhalation
B.
the various lung volumes and capacities.
y ventilation, the low ui air between the armo-
I the lungs, occurs due eg differences in air pres-
inhnlc or breatite in when the pressure inside the
}S rlv.ni the atmospheric air pressure, YVc c.vhak <>r
breathe out when the pressure inside the lungs is greater than
die atmospheric sir pressure. Contraction and relaxation of
skeletal muscles create the air pressure changes thai power
hrcathinii.
Muscles of Inhalation and Exhalation
Breathing m is tailed inhalation or htspimtivn, The muscles
nj ipiiei (unforced) inhalation are the diaphragm, the dome-
shaped skeletal muscle thai fibrins ihe floor <>i" the cborncic
454 Chapter 18 The Respiratory System
cavity, and the externa] intercostals. which extend between
the ribs (Figure 18." J. The diaphragna contracts when ii re-
ceives nerve impulses from the phrenic nerves. As the di-
aphragm contracts, it descends and becomes Batter, which
causes the volume of the attached lungs to expand. As the ex-
ternal intercostals contract, they pull the fibs upuird and
outward; the attached lungs Follow, further increasing lung
volume. Contraction pf die diaphragm is responsible lor
about 75% of die ait that enters the lungs during quiet
breathing; Advanced pregnancy, obesity; confining clothing,
or increased size of die stomach after eating a large meal can
impede descent of the •li.mhrngm and m:iy cause shortness of
breath.
During deep, labored inhalations, the sternocleidomas-
toid muscles elevate the sternum, the scalene muscles elevate
the two uppermost ribs, .uid the pectoralis minor muscles el-
evate the third through filth ribs. As the ribs and sternum are
elevated, the size of the lungs increases (I i
Movements of the pleural membrane aid expai :
lungs. The parietal and visceral pleurae normally adlffl
tightly because ol the surface tension created by the
-adjoining surfaces. Whenever the thoracic cavity expands*!
parietal pleura lining the cavity follows, and the viaj
pleura and lungs are pulled along with ir.
Breathing out. called exhalation or expiration*
when the diaphragm and external intercostals relax.
tion occurs due to dbttit remil of the chest wall and
both of which have a natural tendency to spring back am
they have been sri etched. Although the alveoli ami aind
recoil, tbe\ don't completely collapse. Because sin:.
alveolar Fluid reduces elastic recoil, a lack of surf'actui
causes breathing difficulty by increasing the chance of jq
olar collapse.
Figure 18.7 Muscles of inhalation and exhalation and their actions. The pectoralis minor muscle (not shown
here) is illustrated in Figures 8. 1 7 and 8 1 8 on pages 201 and 203.
During quiet inhalation, the diaphragm and externa] intercostals contract, the lungs expand, and air moves into the
lungs. During exhalation, the diaphragm relaxes and the lungs recoil inward, forcing air out of the lungs.
MUSCLES OF INHALATION
MUSCLES OF EXHALATION
Sternocleidomastoid
Scalenes
External
intercostals
Diaphragm
Internal
intercostals
External
oblique
Internal
oblique
Transversus
abdominis
Rectus
abdominis
Sternum:
Exhalation
Inhalation
Diaphragm:
Exhalation
Inhalation
(a) Anterior view o1 the muscles of inhalation and their actions (left)
and the muscles of exhalation and Iheir actions (right)
What are the main muscles that power your breathing?
(b) Lateral view ol the changes in size ol the thoracic
cavity during Inhalation and exhalation
Because no muscular contractions arc involved) qudetJex-
lalation, unlike quier Inhalation, is ;i passive pm&. Exhale
ion becomes udivc only during forceful breathing, such as in
iiying a wind instrument or during exercise. During these
nuts, muscles of exhalation — the internal intercostals. exrer-
Ktl oblique, internal oblique, iransvcrsus abdominis, and rec-
loniinis — contract in move the lower ribs downward
ind compress the abdominal viscera, thus forcing the di-
Eiragm upward (Figure 18.
pressure Changes During Ventilation
kthe lungs expand, the air molecules inside OCCUp) a larger
mm. which causes the air premm inside to decrease.
lU'hi.r. gas molecules are put into a larger container, they ex-
tra smaller pressure on the walls of the container, in this
Lethe airways and alveoli of the lungs.) Because the atmo-
Pulmonary Ventilation 455
Spheric air pressure is now higher than the alveolar pressuff,
the air pressure inside the lungs, air moves into the Lttngt. B)
contrast, when lung volume decreases, the alveolar pressure
increases, (When gas molecules arc squeezed into a smaller
container, the) e\evt a larger pressure on the walls of the
container.) Air then Hows from the area of higher pressure ill
the alveoli ro the area of lower pressure in the atmosphere.
Figure 18.8 shows the sequence of pressure changes during
quiet breathing;.
At resi jusi before an inhalation, the air pressure inside
the lungs is the same as the pressure of the atmosphere,
which is about 760 nun II:. '.' 1 1 1 1 1 1 i 1 1 1 ■ lers of mercury) at
sea level.
As the diaphragm and external nucrcostals contract and
the overall size ol the thoracic cavit} increases, the vol-
ume of the lungs increases and alveolar pressure- de-
jre 18.8 Pressure changes during pulmonary ventilation.
Air moves into the tungs when alveolar pressure is less than atmospheric pressure, and out of the lungs
when alveolar pressure Is greater than atmospheric pressure.
Atmospheric pressure = 760 mm Hg
Atmospheric pressure = 760 mm Hg
Alveolar
pressure =
760 mm Hg
Alveolar
pressure =
758 mm Hg
At rest (diaphragm relaxed)
Ql During inhalation (diaphragm contracting}
Atmospheric pressure = 760 mm Hg
Alveolar
pressure =
762 mm Hg
© During exhalation (diaphragm relaxing)
/ How does the alveolar pressure change during a normal, quiet breath?
456 Chapter 18 The Respiratory System
creases from 760 to 75$ mm Ilg. Now there is a pressure
difference between the atmosphere and the alveoli, ami
air (lows from the atmosphere (higher prcssmv.) imu tin
lungs (lower pressure),
© When the diaphragm and external intercostals relax, lung
elastic recoil causes the lung volume go decrease, and
alveolar pressure rises from 760 to 762 mm I Ig. Air then
flows from the area ol higher pressure in the alveoli ro
the area ©flower pressure in the atmosphere.
Lung Volumes and Capacities
While at rest, a healthy adult breathes about 12 times a
minute, with each inhalation and exhalation moving about
500 ml. of air into and out ol the lungs. The volume of one
breath is called the tidal volume. The minute ventilation
(MV) — the total volume of air inhaled and exhaled each
minuie — is equal ro breathing rare multiplied by tidal
volume:
MV = 12 breaths/min X 500 ml. /breath
= 6000 ml, /min or n lirers/inin
Tidal volume varies considerably from one person
Other and in the same person at different times. Ah.uu "pm
of the tidal volume (350 ml.) actually reaches the n-spn.iin
bronchioles and alveolar sacs and thus participates in gas til
change. The oilier 30% I I s " ml.) does not participate mild
exchange because ir remains in the conducting airways o£fl
nose, pharynx, larynx, trachea, bronchi, bronchioles andtfl
minal bronchioles. Collectively, these conducting airways' m
know u as the anatomic dead spate.
The apparatus commonly used to measure respn
rate and the amount of air inhaled and exhaled durin
breathing is a spirometer (spiro- = breathe; meter iue:i<.ura
ing device). The record produced by a spirometer is called 4
spirogram. Inhalation is recorded as an upward dctlcctifHi, anj
exhalation is recorded as a downward deflection (
By taking a very deep breath, you can inhale a gnu
more than 500 ml.. This additional inhaled air, called i
inspiratory reserve volume, is about MOO ml., in an aval
adult male and 1'MiO ml. in an average adult female
18.9), l-vcii more air can be inhaled if inhalation tulle
forced exhalation. If you inhale normally anil then exbfl
forcibly as possible, yon should be able to push out conslij
Figure 18.9 Spirogram showing lung volumes and capacities in milliliters (mL). The average
values tor a healthy adult male and female are Indicated, with the values for a female in parentheses.
Note that the spirogram is read from right (start of record) to left (end of record).
Lung capacities are combinations of various lung volumes.
6,000 ml
5.000 mL
4,000 rnl_
3.000 mL
2,000 mL
1 ,000 mL
LUNG VOLUMES
LUNG CAPACITIES
Breathe In as deeply as possible and then exhale as much air as you can. Which lung capacity have you
demonstrated?
458 Chapter 18 The Respiratory System
External Respiration: Pulmonary
Gas Exchange
External respiration, also termed pulmonary gas exchange,
is the diffusion of (). from air in the alveoli of the lungs to
blood in pulmonary capillaries and the diffusion of CQj a
the opposite direction (Figure I K.I On). External respr
in the lungs converts deoxygenated (low-oxygon) blood i\\4
comes from the right side of the heart to oxygenated (him
Figure 18. 10 Changes in partial pressures of oxygen (0 2 ) and carbon dioxide (C0 2 ) in mm Hg
during external and internal respiration.
Each gas in a mixture ot gases diffuses from an area of higher partial pressure of that gas to an area of
lower partial pressure of that gas.
^
Atmospheric air:
P/ = 1 59 mm Hg
p n.-03rtimHg
Alveoli
CO. exhaled
/
O, inhaled
c ? 2 o.
Alveolar air:
P. = lO&mmHg
i L = 40 mm Hg
Deoxygenated blood: -
P a 40 mm Hg
= 45 mm Hg
To lungs
What causes 2 to enter pulmonary cap-
illaries from alveolar air and to enter tissue
cells from systemic capillaries?
?u\Tc\wrar>i ca$NTOta&,
(a) External respiration:
pulmonary gas
exchange
(b) internal respiration:
systemic gas
exchange
To tissue cells
/
Systemic tissue cells:
P = 40 mm Hg
P co =45minHg
Oxygenated tnooa
- i
J Ga-
len) blood that returns CO the let! side of the heart. As
flows through die pulmonary capillaries, it picks up Q 3
[i tlveohir air ;md unloads CO. into alveolar air. Although
his process is commonly called an "exchange" of gases, each
indi-fwutiemiy from an urea where its partial pres-
X is higher to Lin area where its partial pressure is lower,
import-am factor that affects the rate of external rcspira-
in. is the total surface area available For gas exchange- \ny
©nary disorder that decreases the functional surface area
c respiratory membrane, for example, emphysema (see
467), decreases the rate of gas exchange.
Q : diffuses from alveolar air, where its partial pressure
§h 105 mm I Ig, into the bloo<1 in pulmonary capillaries,
\'\,, is about 40 mm rig in a resting person. During
rise, the P Q , of blood entering the pulmonary capillaries
jpren lower Because contracting muscle libers are using
b Oi. Diffusion continues until the P 0l of pulmonary
Bar) blood increases to 105 mm rig. matching the Pq 2 of
Bkrair, Blood leaving pulmonary capillaries near alveolar
spaces mixes with a small volume of Mood that has flowed
Jjrough conducting portions of the respiratory system.
WJtK pb exchange does not occtir. Thus, the P n , of blood in
pulmonary veins is about 100 mm Hg. slightly less than
in pulmonary capillaries.
'While ( ) is diffusing from alveolar air into deoxj uenated
ikilI. ("O. is diffusing in the opposite direction. The 1\ ,,,
jgenated blood is 45 mm Hg in a resting person*
i the P ( j), of alveolar air, which is 40 mm Hg.
of this difference in P C o 2 i carbon dioxide diffuses
tdcowgenated blood into the alveoli until the Pcos nl
decreases to 40 mm Hg. Exhalation keeps alveolar
s-lt'40 mm I Ig. Oxygenated blood returning to the left
of the heart in the pulmoitary veins thus has a P t;n , ot
Ipi'i I Ig.
arson ascends in altitude, the total atmospheric pres-
ses, with a parallel decrease in the partial pres-
lofoxygen. P Q , decreases from 1 59 nun Hgatsea level
i i Hi; u 6000 meters (about 20,000 ft). Alveolar
reases correspondingly, and less oxygen diffuses
blood. The common symptoniis of high altitude
i — shortness of breath, nausea, and dizziness —
toa lower level of oxygen in the blood.
§emai Respiration: Systemic
Exchange
dull ventricle pumps oxygenated blood into the aorta and
„<li die systemic arteries to systemic capillaries. 'The ex-
, m , p< ) -,irul ( X V between systemic capillaries and tissue
led internal respiration or systemic gas exchange
Transport of Respiratory "Gases 459
respiration, which occurs only in the Jungs, internal respira-
tion occurs m tissues throughout die body.
The P (l> of blood pumped ini" systemic capillaries is
higher (100 mm Hg) than die P, ,, in tissue cells (about
40 mm Hg at rest) because cells constantly use up O re pro
duce VI'P Due to this pressure difference, oxygen diffuses
out of die capillaries into tissue cells, and blood P n , de-
creases. While (>• diffuses from the systemic capillaries into
tissue cells, CO2 diffuses in the opposite direction. Because
tissue cells are constantly producing ^-^h- lnL ' Pt n> of cells
(45 mm Hg at rest) is higher than that of 'systemic capillary
blood (40 mm Hg). As a result. GOj diffuses from tissue cells
through interstitial fluid into systemic capillaries until the
P C o, in the blood increases. The deovygenated blood then
returns to the heart and is pumped to the limes lor another
cycle of external respiration.
■ CHECKPOINT
9. What are the basic differences among pulmonary \emil.i
lion, external respiration, and internal respiration?
10. In a person at resi, v. bat is the partial pressure difference
that drives diffusion of oxygen into the blood in pul-
monary capillaries?
TRANSPORT OF
RESPIRATORY GASES
OBJECTIVE • Describe how the blood transports
oxygen and carbon dioxide.
The blood transports gases between the lungs and body tis-
sues. VVhen Oj and CO enter the blood, certain physical
and chemical changes occur that aid m gas transport ami
exchange.
Oxygen Transport
Oxygen does not dissolve easily in water, and therefore only
about 1.5% of the Q a in Mood IS dissolved in blood plasma,
winch is mostb water. About 98.5% of Wood 0> is bound 10
hemoglobin in red blood celts (Figure LB.1 1).
The heme part of hemoglobin contains four atoms of
iron, each capable of binding to a molecule ol (.).. Oxygen
and deaxy hemoglobin (Hb) bind in an easily reversible reac-
tion to rorru oxyhemoglobin (I lb ( \ );
Mb
+ o m
1
K ■ lO
D\ ■ licmttglobin Oxygen
Hb
Qxyhcmugli ibin
460 Chapter 18 The Respiratory System
Figure 18.11 Transport of oxygen and carbon dioxide in the blood.
W
Most O, is transported by hemoglobin as oxyhemoglobin within red blood cells; most CO.
~. is transported in blood plasma as bicarbonate ions.
Transport of C0 2
dissolved in plasma
23% as Hb-CO
70% as HCO,"
/
Transport of ;i
1 .5% -dissolved In plasma
93.5% as Hb-
A ■:■ ".I
CO,
(dissolved)
To lungs
co 2
1.5% 98-6%
\
(dissolved)
(a) External respiration:
pulmonary gas
exchange
(b) Internal respiration:
systemic gas
<* exchange
23% f )
70% 15%
'"ferstlllal fluid
Pulmonary
capillaries
Red blood cell
Plasma
To left atrium
To tissue ceils
Systemic
capillaries
Systemic
tissue cells
What percentage of oxygen is transported in blood by hemoglobin?
mil has combined with a molecule <>l 2 . When blood
P. is Low, hemoglobin releases O,. Therefore, m Mstermc
;;,iil,n,s, where the Pn, <s lower, hemoglobin releases Q*
£cb dien on diffuse from blood plasma into isntiuaJ
feaiid into tissue cells (Figure 18.1 lb')i
Besides I 5 ,.,,, several other factors influence the amount ol
0- release! U\ hemoglobin:
i C .irbon dioxide. As the P ( ,„ rises in any tissue, liernog& -
' bin releases O, more readily. Thus, hemoglobin releases
more O, as blood flows dwragh active tissues thai are pro-
ducing more CO., such as muscular tissue during exercise,
j Acidity. In an acidic environment, hemoglobin releases
* 0, more readily. During exereise, muscles produce lacac
idd, whieh promotes release ofO, from hemoglobin.
Temperature. Within limns, as temperature increases,
i so does the amount of Oj released from hemoglebni. Ac-
| tive tissues produce more heat, which elevates the local
temperature and promotes release oj ( )-.
,n monoxide (CO) is a colorless and odorless gas
n tobacco smoke and in exhaust lumes irom atito-
muhiles, gas furnaces, and space heaters. CO binds to die
km F oup of hemoglobin, jusi as : does, except that
rtiuls over 200 rimes more strongly, V« a concentra-
toa as small as 0.1%, CO combines with half die available
,,!„bm molecules and reduces die oxygen -carrying
,i the blood bv 50%. Elevated blood levels ol U >
cose carbon monoxide poisoning, which can cause the
|L ,n,l oral mucosa to appear bright, cherry-red (the
Bor of hemoglobin with carbon monoxide hound to it).
Administering pure oxygen, which speeds pp the separa-
:ar bon monoxide from hemoglobin, may rescue
. | rson.
[Carbon Dioxide Transport
m dioxide is transport! m the blood m three main
,:,,.,! I S.I I):
1 Dissolved C0 2 . The smallest percentage— aboul 7%-
' | s dissolved in blood plasma. Upon reaching die lungs, u
diffuses into alveolar air and is exhaled.
Bound to amino adds. A somewhat higher percentage,
" about ^%, combines with Hie amino groups «»t ammo
lends and proteins In blood. Because the most pr^atet
Motrin in blood is hemoglobin (inside red blood cells),
Lst of the C0 2 transported in this maimer is bound to
hemoglobin. Kemogfobki that has bound CO, Is termed
uirhaminobevwglabin (Hh - CO&
Hh + CO, =^^ Hb-<<>
Ikinodnbm < wbflMtax**! G«rf«iii»nobeBMgTbbSn
I tissue capillaries I',,, is relariveh high, which pro-
Ltes formation of carbaminohemoglobin. But in pul-
Contro! a! Respin.. )n 4b l
monarv up&rfe* P«fc ls wttwdj tew, and the QO
readily splits apart Irom hemoglobin and enters the alve-
oli by diffusion.
5, Bicarbonate ions. The greatest percentage of COj
aboul 70^ —is transported in blood plasma zsbkarkon-
ate wnsfHCOi )■ As CO, diffuses into tissue capillaries
and enters the red blood cells, it combines with water to
form carbonic acd (H,CO>), T|*e enssyme iasirifl red
blood cells that drives this reaction is cmUuk mk ! '
(CX). The carbonic add then breaks dm n into hydrogen
lunsdl land HCOj \
co ? + h : o =^
Carbon Watei
dioxide
< ■■•
II ,co 3 =?
Carbonic
If
HCO,
Hydrogen fficBri&ttaaw
i, mi inn
Thus, as Wood picks up ( -O, I ICOj accumulates in-
side RBCs. Some I ICO, moves out into the blood
plasma, down its concentration gradient. In exchange,
chloride tons i.Ci | mtitt Irom plasma into the 8BCs.
j his exchange of negative ions, which maintains m
electrical balance between blood plasma and KB« cy-
DOSOI is known as the &Mlk sftjfr Xs ;1 rcslllt ° J ™ *
chemical reactions. CO, is removed from t.ssiie celts and
transported in blood plasma as MCO, ,
As blood passes through pulmonarv capillaries in fe
lungs, all these reactions reverse. The CO- that was dissolved
in plasma diffuses into alveolar air. The CO, that was com-
bined with hemoglobin splits and diffuses ffltO the alveoli. I he
bicarbonate ions PCQ 3 ) reenter the red blood cells Ivom the
blood plasma and recombine with 1 1 to form HjjGO* wtafl
sphts into CO and I I ..O. This CO, leaves the red blood cells,
diffuses into alveolar air, and is exhaled (ligure I K.P I,
■ CHECKPOINT
ft. What is the relationship between hemoglobin and r\,. :
12. What factors cause hemoglobin to unload more oxygen
as blood Hows through capillaries of metaholically active
tissues, such lis skeletal muscle during exercise?
CONTROL OF RESPIRATION
OBJECTIVE • Explain how the nervous system con-
trols breathing and list the factors that can alter the rate
and depth of breat hing. ___
\t rest, about 200 ml. of O. are used, each mfcme k
cells. During strenuous exercise, however, O, use tsp.caih
increases L> to HJ-&W in normal healthy adulfe, and ftS
much as J0-fold in elite endtantf named athletes. Several
meclmnisnis help match respiraiorv efl.-.i ;■ metabolic
iml.
462 Chapter 18 The Respiratory System
Respiratory Center
The basic rhythm of respiration is controlled by groups of
neurons in die brain stem. The area from which nerve im-
pulses are sent to respiratory Enuscles is called the respiratory
center and consists of groups- of neurons in both the medulla
oblongata and the pons.
The medullary rhyibirtic'rly area (nth-AIIS-i-te) in the
medulla oblongata controls the basic rhythm of respiration.
W chin the medullary rhythmiciry area arc both inspiratory
and expiratorj areas. Ffgun 18.1 2 shows the relationships of
the inspiratory ami expiratory areas during normal quiet
breathing and Forceful breathing.
During quiet breathing', inhalation lasts for about 2 sec-
onds and exhalation lasts lor about 3 seconds. Nerve impulses
. i rated in the inspiratory area establish the basic rhythm
of breathing. While the inspiratory area is active, ii generates
nerve impulses for about 2 seconds (Figure 1 8.12a). The im-
pulses propagate to the external intercostal muscles via inter-
costal nerves and to the diaphragn] via the phrenic nerves.
When the nerve impulses reach ihe diaphragm ami external
intercostal muscles, the muscles contract and inhalation oc-
curs. Even when all incoming nerve connections to the inspi-
ratory area are cut or blocked, neurons in this area still
rhythmical!} discharge impulses that cause inhalation. At the
end of 2 seconds, the inspirator)-' area becomes inactive and
nerve impulses cease. With no impulses arriving, the di-
aphragm and external intercostal muscles relax for about 3
seconds, allowing passive elastic recoil ol the lungs and tho-
racic wall. Then, the cycle repeats.
The neurons of 'the expiratory area remain inactive dur-
ing quiet: breathing. However, (luring forceful breathilffl
nerve impulses Irnm the inspirator) area activate the expi.ru*
tory area (Figure I S.I 2b). Impulses from the expiratory area
then cause contraption of die internal intercostal and abdomj
inal muscles, which decreases die size of the thoracic
and causes forceful exhalation.
The pneumotaxic area (noo-mo-T \k-sik; fmrwmo- =
air or breath; -toxic = arrangement) In the upper pons held
turn off the inspiratory arm to shorten die duration al n;-
halalions and to increase breathing rate. The uprrenstic am
(ap-NOO-stik) in the lower pons sends excitatory impulsa
to the inspiratory area that activate it and prolong inhnliitioi
The result is a lung, deep inhalation.
Regulation of the Respiratory Center
Although the basic rhythm of respiration is set and eucirdk
nated by the inspiratory area, the rhythm can be moiliti
response to inputs from other brain regions, receptors in tin
peripheral nervous system, ami other factors,
Cortical Influences on Respiration
Because the cerebral cortex has connections with the respirj
tory center, we can voluntarily alter our pattern of bi
'We can even refuse to breathe at all for a short time. Un
tary control is protective because it enables us to pn
u irritating gases from entering the lungs. The ability
not breathe, however, is limited by the buildup ol CO ^
H 1 in body lluids. When the P\ Ah and I' concennurio
Figure 18.12 Rotes of the medullary rhythmieity area in controlling (a) the basic
rhythm of quiet respiration and (b) forceful breathing.
•, • - ^ . b
During normal, quiet breathing, the expiratory area Is inactive. During forceful breath-
ing, the Inspiratory area activates the expiratory area.
INSPIRATORY AREA
ACTIVE INACTIVE
2 seconds
aphragm and external
intorcoslats contract
formal quiet inhalation
I
3 seconds
Diaphragm and external
Intercostals relax,
followed by ets: i'
recoil of lungs
I
Normal quiet exhalation
(a) During normal quiel breathing
Activates
INSPIRATORY AREA 8 >
ACTIVE
1
Diaphragm.
sternocleidomastoid,
and scalene muscles
contract
EXPIRATORY AREA
Internal intercostal
and abdominal
muscles contracl
— T~
Forceful Inhalation Forceful exhalation j
(b) During forceful breathing
Which nerves convey impulses from the respiratory center to the diaphragm?
Focus ON Wellne
Smok
Control ot Respiration 463
A Breathtaking
Experience
■pigarettc smoking is the single mosi
breven table ciiu.se of deatfe and disabilr
. irldwide. Ml forms of tobacco use
tlisriipi The body's ability to maintain
homeostasis and health. Here arc a f&b
u kings most deadly effects on the
respiratory system.
Micro ' here's Smoke . . .
. there is injury. The delicate struc-
Unreuf the alveoli aIk>WS fOU to extract
fife-giving oxygen and cleanse > ii 1 1 r
(uhIv of metabolic wastes. Chronic e\-
pss co smoke gradually destroys
g elasticity. The result is empby-
Rtf, ;i progressive destruction oi ihe
iilvtnli and collapse of respirator)
'(mi'hinlcs. As a result, oxygen uptake
increasingly more difficult.
Bronchitis is an inflammation of
fc upper respiratory tract. In smokers.
Sonic bronchitis may result from the
Ration of cigarette smoke. "Smokers
Mjh" is a symptom oi bronchitis. II
Untreated, bronchitis increases the
| i more serious infections and per-
i : airway damage.
in the short term, several fac-
E> decrease respiratory efficient} tn
jokers. (I) Nicotine constricts teroii-
,i bronchioles, which decreases air-
flow into am] oiii of the lungs. (2) ( lar-
bon monoxide in smoke binds to he-
moglobin and reduces its oxygen-cany
tag capability. (3) Irritants in smoke
cause increased mucus secretion by the
mucosa of the bronchia] tree and
swelling of the mucosal lining, both of
which impede airSov. into and ont of
the lungs, (4) Irritants in smoke also in-
hibit the cilia and destroy cilia in the
lining of the airways. Thus, excess mu-
cus and foreign debris are not easily re-
moved, which turther ailds to die diffi-
cult] in breathing.
Calling for Cancel 1
Lung cancer was a rare disease in die
earl) 1900$. Mow i« is the leading can-
cer killer for both men and women,
thanks primarily to smoking. Cigarette
smoke contains a number of known
carcinogens, including hen/o[//jpyrene,
.Y-nitrosoa mines, and radioactive parti-
cles such as radon and polonium, which
may initiate and promote the cellular
changes leading to lung cancer
Smoking increases the risk of can-
cers at other sites as well. Cancel's of
the oral cavity (iuoni.li, tongue, lip,
cheek, and throat) and larynx occur m
pipe and cigar smokers as well as ciga-
rette smokers, ami in people win. use
smokeless tobacco. When .smoke is in-
haled, carcinogens are absorbed from
the airways into the bloodstream and
can thus contribute to cancers at sites
outside the lungs. Cancers of the
esophagus, stomach, kidney, pancreas,
colon, and urinary bladder are more
common in smokers than in nonsmok-
ere. Women who smoke have higher
rates of cervical and breast cancer-
Spioking reduces the amount of oxygen reaching hotly tissues, which inter-
b the hotly \ ability to make collagen. How does thh help explain ivhy
smokers beat more slowly from ulcers, surgery, mtdfrnctur
—
m\ a certain level, the inspirator) area is strongly stimu-
brea thing resumes, whether the person wants ii or
|i k impossible for people to kill themselves by voluntar-
:ling their breath. Keen if breath is held long enough
feinting, breathing resumes when consciousness is
.. impulses from the hypothalamus and limbic system
il.ite the respiratory center, allowing emotional stimuli
•respirations as, for example, in laughing and crying.
receptor Regulation of Respiration
sin chemical stimuli determine how quickly and how
breathe. The respiratory system functions to main-
tain proper levels of CO? and (). and is v$f) responsive to
changes in the levels of either m body fluids. Snisory neu-
rons that arc responsive to chemicals are termed chc/nnivtcft-
tors. Central cheinoreceptorS, located within the medulla oblon-
gata, respond to changes in IT level or P, n , or both, in
cerebrospinal fluid. Pai()hmd chanonxxploiy. located within
the arch of the aorta and common carotid arteries, are espe-
cially sensitive co changes m P,,., 11. mu\ P m , ta the blood.
because CO, is lipid-solublc, it easil\ dill uses through
the plasma membrane into cells, where it combines with w i
ter (IPO) to form carbonic acid | .1 I < . !t ) ■ >. Carbonic acid
quickly breaks down into II and I It ".O- . \m increase in
464 Chapter 18 The Respiratory System
CO. m the blood thus causes an increase in II inside cells,
mil :im decrease in COj causes a decrease in H \
Normally, the P^qj Ui arterial blood is 40 mm 1%. II" even
a slight increase in Pa> 2 occurs — a condition called liy-
perenpnia — rhe centra] ehemoreceptors are stimulated
and respond vigorously to the resulting increase in H~
fevei The peripheral chemoreceptors also are stimulated
by liotli die high P<,o 2 and die rise in H 4 . In addition, the
peripheral chemoreceptors respond to severe hypoxia, a
deficiency of Oj. If FVi. in arterial blood falls from a nor-
mal level ot 100 mm Hg to about 50 mm Hg, the periph-
eral chemoreceptors nrc strongly stimulated.
The chemoreceptors participate in a negative feedback
SysCem that regulates the levels of CO.. : , and II' in the
blood (Figure 1 S. I >). As a result of increased Pgxb, decreased
pi I (increased IT), or decreased P 0> . input from the central
and peripheral chemoreceptors causes die inspiratory urea to
become highly active. Then, rhe rate and depth of breathing
increase. Rapid and deep breathing, called bypervi'ntilalhn.
allows the exhalation of more (X)> until Pro, and IT arc
lowered to normal.
If the partial pressure of CQj in arterial blood is lower
than 40 mm Hg — a condition called hypucapnia — the
central and peripheral chemoreceptors are not stimulated.
and stimulatory impulses are not sent to the inspiratory
area. Then, the area sets its own moderate pace until GO*
accumulates ami the P( X \. rises to 40 mm Hg. People who
hyperventilate voluntarily and cause hypoeapnia can hold
their breath for an unusually long period of time. Swim-
mers were once encouraged to hyperventilate just before a
competition. However, this practice is risky because the O,
level may fall dangerously low and cause fainting before
the IV, , HfefiS hiiih enough to stimulate inhalation. A per-
son who hunts on land may suffer bumps ;md bruises, but
one who faints in the water may drown.
Severe deficiency of () depresses activity of the central
chemoreceptors and inspiratory area, which then do not re-
spond well to any inputs anil send fewer impulses to rhe mus-
cles of respi ration. As the breathing rate decreases car breath-
ing ceases altogether. P<» GiJIs tower and lower, thereby
L'.i;ili|ishmg a positive feedback cycle with a possil.ily fatal
result;
Other Influences on Respiration
Oilier factors that contribute to regulation of respiration in-
clude die following:
■ Limbic system stimulation. Anticipation of "activity or
emotional anxiety ma\. stimulate the limbic system,
which then sends excitatory input to the inspiratory area,
increasing the race and depth of ventilation.
Figure 18.13 Negative feedback control of breathing in re-
sponse to changes m blood P C o 2 . pH (H + level), and P .
v An increase in blood P co? stimulates the inspiratory center
Some stimulus disrupts
homeostasis by
Increasing
Arterial blood R
«fe
(or decreasing pH or P^) ,
Central
Penpi
chemo-
chemo- > */
receptors receptors
in
medulla
in aortic V
and
carotid
•
bodies
Input
Nerve
impulses
Control center
Inspiratory area in
medulla oblongata
Output
Eftecto
Muscles of
inhalation and
exhalation
contract more
forcefully and
more frequently
(hyperventilation)
Nerve
impulses
Decrease. in arterial
blood Poftj increase in
pH, and increase In P^
I
I
I
Return to homeoai
when response brings
arterial Wood I
and p^ back ro normal
D-
I
I
I
9
What is the normal arterial blood P C o a ?
Aging and Ihe Respiratory System
-
65
Proprioceptor stimulation of respiration. As soon as
,n. exercising, your rate and depth of bjceathi.Bg in-
|ease, even before changes m l\,,. V, , , or 1 1 level oc-
cur. The main stimulus for these quick changes in venti-
lation is input from proprioceptors, which monitor
movement of joints and muscles. Nerve impulses from
,lu- proprioceptors stimulate the inspirator) area ot the
bedulla oblongata,
jfemperature. An increase in body temperature, as oc-
uir- during a fever or vigorous muscular exercise, in-
• the rate of respiration; a decrease m body temper-
| . decreases respiratory rate. A sudden cold stimulus
as plunging into cold water) causes temporary
hm (AP-ne-a; a- = without; -prOu = breath), an absence
of breathing-
Pain. A sudden, severe pain brings about brief apnea, bill
I prolonged somatic pain increases respiratory rate. \ is*
ccral pain maj sli >v he respiratory rate.
1 Irritation of airways. Physical or chemical irritation of
liarynx or larynx brings about an immediate cessa-
tion of breathing followed by coughing or sneezing.
| The inlTation reflex. Located in the walls of bronchi
m \ bronchioles are pressure-sensitive stretch receptors.
When these receptors become stretched during' overinfla-
fonofthe lungs, die inspiratory area is inhibited, tea re-
sult, exhalation begins. I Ins reflex is mainly a protective
inism for preventing excessive inflation of the lungs.
I CHECKPOINT
Iocs the medullary rhythmicity area function in
■ iting respiration?"
rhe cerebral cortex, levels of C0 2 and 2 , pro-
ceptors, inflation reflex, temperature changes, pain,
h I irritation of the airwaj s modify respiration?
IRCISE AND THE
IPIRATORY SYSTEM
TIVE • Describe the effects of exercise on die
Btorj syste m. __ _
L exercise, the respiratory and cardiovascular systems
Listments in response to both the intensity and dtira-
rfthe exercise. The effects of exercise on the heart were
ii Chapter 15; here we focus on how exercise ai-
ipiratory system.
tall rlv.it the heart pumps the same amount or blood to
rsas to all the rest of the body. Thus, as cardiac out*
S f the rate of blood flow through the lungs also in-
,. i blood Bows rhrough the lungs twice as fast as at
, ./picks up twice as much oxygen per minute. In addi-
Lthe rate at which 2 diffuses from alveolar air into the
bkod increases during maximal exercise because blood Hows
ilirmiuh a larger percentage of the pulmonary capillaries, pro-
viding* greatef surface area for diffusion of O. into the Mood.
When muscles contract during exercise, they consume
large amounts of Oj and produce large amounts f CO.,
forcing the respiratory system to work harder to maintain
normal blood gas levels. During vigorous exercise, <) ; con-
sumption and ventilation increase drama tically. \i the onset
f ,i exercise, ^m abrupt increase in ventilation, due to actiya
tion of proprioceptors, is followed by a more jradual in-
crease. Willi moderate exercise, die depth of ventilation
rather than breathing rate is increased. When exercise is
more strenuous, breathing rate also increases.
At the end of an exercise session, an abrupt decrease in
ventilation rale is followed by a more gradual decline to the
resting level. The initial decrease is due mainly t<» decreased
stimulation 0$ proprioceptors when movement Stops 01
slows. The more gradual decrease reflects the slower return
of blood chemistry and blood temperalure to resting levels.
<»^
AGING AND THE
RESPIRATORY SYSTEM
OBJECTIVE • Describe the effects of aging on the res-
pirator) 7 system. ^
With advancing afS. lhc airways and tissues of the respira-
tor) tract, including the alveoli, become less elastic and more
rigid; the chest wall becomes more rigid as well. The result is
a decrease m lung capacity. In fact, vital capacity (the maxi-
mum amount ol 'air thai can be expired after maximal inhala-
tion) can decrease as much as iS% by age 70. A decrease in
blood level of Oi, decreased activity af alveolar maen.pl-
and diminished ciliary action of the epithelium lining die res
pnatorv tract occur. Owing to all these age -related factors,
elderly people are more susceptible to i>neumonia, hmncht-
lis, emphysema, and other pulmonary disorders- \gc-related
changes in the structure and functions of the lung can also
contribute to an older person's reduced ability to perform
vigorous exercises, such as running.
■ CHECKPOINT
15. How does exercise affect the inspiratory area?
16. What accounts for the decrease m vital capacity with
aging?
To appreciate the many ways that the respiratory system
contributes to homeostasis of other body systems, examine
FOCUS on Homeostasis: The Respiratory System on page 46o.
Next, in Chapter IV. we will see how the digestive svstem
makes nutrients available to body cells SO that oxygen provided
by the respiratory system can he used for ATP production.
FOCUS
ON
HOMEOSTASIS
Body System
For all body
systems
Muscular system
The Respiratory System
Contribution of the Respiratory System
i
*
Provides oxygen and removes carbon dioxide. Helps adjust the pH of body fluids through exhfr
lation of carbon dioxide.
Increased rate and depth of breathing support increased activity of skeletal muscles during
exercise.
Nervous system
Nose contains receptors for the sense of smell (olfaction). Vibrations of air flowing across the
vocal cords produce sounds for speech.
Endocrine
system
Cardiovascular
system
a
Angiotensin converting enzyme (ACE) in the lungs promotes formation of the hormone an-
giotensin II, which in turn stimulates the adrenal gland to release the hormone aldosterone.
During inhalations, the respiratory pump aids the return of venous blood to the heart.
Lymphatic
system and
immunity
Hairs in the nose, cilia and mucus in the trachea, bronchi and smaller airways, and alveolar
macrophages contribute to nonspecific immunity to disease. The pharynx (throat) contains lyifc
phatic tissue (tonsils). During inhalation, the respiratory pump promotes the flow of lymph.
Digestive system
Urinary system
Reproductive
systems
*
\ , '
t
Forceful contraction of the respiratory muscles can assist in defecation.
Together, the respiratory and urinary systems regulate the pH of body fluids.
Increased rate and depth of breathing support activity during sexual intercourse. Internal respK
ration provides oxygen to the developing fetus.
466
Common Disorders 467
COMMON
DISORDERS
ima
hmi, i \/-ma panting) is a disorder characterized by chronic airway
fnmation, airway hypersensitivity to a variety of stimuli, and airwaj
„,,;,,, m„ airuav obstruenon may be due to smooth ifcusck
, -,1k- walls of smaller bronchi tod bronchioles, belling d the
l&ofthe airways, increased munis secretion, or dpiagera the c-|>-
uiin of the airway. Asthma is at least partiaUj reversible, either spon-
gLorwith rreauneut. h aB»Cts J-5% of the I & population and
r> increasingly common in children.
hmatics tvpicallj read to low concentrations of stimuli thai
ttot normally 'cause symptoms in people without asthma. Some-
™» its the trigger is an allergen such as pollen, dust mites, molds, 01 a
, ,nl. Other common triggers include emotional upset. as>
Ulrinsi agents (used in wine and liter and to keep greens fresh
kabuil barsl exercise, and breathing cold air or cigarette smoke.
H! include difficult, breathing, coughing, wheeang, chest
ichvcardia, fatigue, moisi skm. and anviny.
fcironic Obstructive Pulmonary Disease
mic obstructive pulmonary disease (COPD) is a respiratory dis-
Eiaracterized bj chronic obstrtacripn of airflow. I be principal
nEf COPD are "emphysema and chronic bronchitis, In must
I COPD 1- preventable because its most common cause is cign-
:,ig or breathing secondhand smoke. Other causes meh.de
pulmonary infection, occupational exposure Co dusts
■ and genetic factors.
fobysenw
mLma (em'-fi-SE-raa - blown up or lull ofM is a. disorder char-
■ | iy destruction of the walls of the alveoli, which produces W>
1 spaces that remain filled with air during rioMatL
(surface area for gas excliatlge, ( > diflusion across the rcspira-
j i, L is reduced. Blond Q : level is somewhat lowered, and
,iu exercise that raises the ( >■ requirements of the cells leaves rhe
ithless. As increasing numbers of alveolar walls are damaged,
recoil decreases due to lass of clastic fibers, and an mcrcas-
faii becomes trapped m the lungs at the end ol ^lulauon.
' ivcral years, added respiratory exertion increases the si«e ol the
iiimtg in a "'barrel chest." Kmphysema is a common pre-
. Lc\ elopment of lung cancer.
nk Bronchitis
bronchitis is a disorder characterized In ewtinfrg secretion of
,ial mucus accompanied by a cough. Inhaled irritants lead to
nutation with an increase in the size anil number of mucous
oblet cells ui the ainv.n epithelium. The thickened and ex-
Lucas produced narrows the airwaj and impairs the action ol aba
inhaled pathogens become embedded in airway seeretkna and
rapidly. Besides a cough. symptoms of chrome bmnduns are
,,.h. u freezing, cyanosis, auA pulmonary hypertensii >n.
I Cancer
■ United States, lanir earner is the leading cause of cancer death
males uul females. \i the time of diagnosis, lung cancer is
usually well advannd. Vlovt people With lung cancer die vuhiii n year
Of the diagnosis, and rhe overall survival rate is only 10- 1 5%, Vboja
• ; •■■■,, of lung cancer cases are due to smoking, and the disease is 1 1
30 limes inure common in smokers than nonsmokcrs. l\-posure to
secondhand smoke also cause-. IttBg cancer and heart disease. Other
causes of lung cancer are ionizing radiation, such as y-ravs, ami inhaled
irritants, such as asbestos and radon gas.
Snnpioms of lung cancer may include a chrome coueh, spitting
bloodlTom the n-spiratory tract, wheezing, shoreless ol breath, chest
pam. hoarseness diflicnlly swallowing, weight loss, iinoivvia. B
bone pain, confusion, problems with balance, head.! h . Ufemfe low
|jj I platelet, count, and jaundice.
Pneumonia
Pneumonia or pneumonitis is an acute infection or nillammim-ii of the
alveoli. It is the CtlflSI common infectious cause of death in the Unii
Slates, where an estimated 4 million cases occur annually. U lien certain
microbes enter rhe lungs of susceptible individuals, tbej release damag
ing tofldnSi stimulating iutlainuiaiion and immune responses that KaMC
damaging side effeciv The towns and immune response damage alveoli
and bronchial mucous membranes; inflammation ,m..\ edema cause the
alveoli CO till with debris and llmd. interfering villi ventilation .\nd gas
exchange. The most common cause is the Imeieiium Spt#ttnwcn
Mttnm'jnn otner bactcna. \ iruses. or fungi may als.i cause pnjSJBk
Tuberculosis
The bacterium Mycobiicteriwn tubermktis produces an infectious, com-
municable disease called tuberculosis (7'B) that most oftfiXI aflfe* CS the
lungs and the pleurae but may involve other parts of I lie body. Once
me bacteria arc inside die lungs, they muliiply and cause inllaiuma-
mm. which stimulates neutrophils and macrophages kg migrate "
aw,\ and engulf the bacteria CO prevent their spread, il the immune
system is QOI impaired, the bacteria may remain dormant im-lilc. Im-
paired imnumitv m:n enable the hacicna CO CSCap« into blood and
lymph to infect' other organs, tn mam people, symptoms- latum,
unulu loss, lethargy, anorexia., a low-grade lever, night sweats, cough,
dyspnea, chest pahi. and Spitcmg blood (hemoptysis) -do not de-
velop until rhe disease is advanced,
Coryza and Influenza
Hundreds of viruses, especially the rbfnovimsct ('/'"■'- ''- nose), can
cause coryza <ko-Ki-/.a) or the (xmnmm coitl. lypical symptoms io
elude sneezing, excessive nasal secretion, dry cough, and congestion,
The uncomplicated common cold is not usually accompanied by fl
fever. (.om|mcations include stmisuis. asthuia, bronchitis, ear mtee-
linns, and laryngitis.
Influenza (flu) is also caused by a urns. Its symp'oms include
chills, lever (.u-ualU higher than 10PF, or JPCJ, headache, and tuus
cular aches. C .uidhkc symptoms appear as the lever subsides.
Pulmonary Edema
Pulmonary edema is an abnormal accumulation ol "inu-rsviii-.il fluid in the
uuersritiaf spaces and alveoli of the lungs. 'I he edema may arise from m-
creased pulmonary capillary permeability (pulmonary origin) or increased
pulmiMiarv capuforj pressure due to congestive hcarl failure (cardiac «»n-
.. .., I be most common symptom is painful or labored breathing. ( Ulier
symptom include wheezing, rapid breaching rate, fesdesshess; a fcefingof
snabcarion. cyanosis, paleness, am! excessive pei-spiratiou.
Respiratory System
OLOGY AND CONDITIONS
iiuvcr Kim-aid procedure- to clear the air-
» objects. Tl is performed \sf applying .1 quick
ween the navel and rower ribs that causes
it" the- diaphragm and forceful, rapid expul-
lungs, Forcing air our of i:he trachea to eject
jeer. Also used to expel water from the lungs
victims before resuscitation is began. Also
tilth nti<tiiitviT{\ li.YI-lik ma-NOO-ver).
via - pulse) Oxygen starvation due to
a/gen or interference with ventilation, excer-
iiicrual rcspii.uii mi.
shun) Inhalation into the brnncliinl tree of a
t air, lor instance, uater, food, or a foreign body.
.ual c.xaiiimanon of the bronchi through a
Eliminated, tubular instrument that is passed
Upr nose), larynx, and irachen inio the bronchi.
11 inherited disease of secretory epirhelia thai
. liver, pancreas, srna.ll intestine, and sweat
nil infection of the airways leads to difficulty'
entttftl destruction of brig tissue.
dyt- ~ painful, difficult) Painful OJ? labored
I-sis) Loss of blood from the nose due K)
i' iligfl nil growths, or bleeding dis-
'■ :, 6 b) '■anterv with Silver nitrate, clcciro-
king. Also called nosrh/eed.
■■■■ = below or under) A deficiency of
■I thai may be caused by 9 low I 1 ,,, in arterial
altitudes; too little functioning hemoglobin
niemia; inability of die blood to carry : to
tu sustain their needs, as in heart failure; or
10 use 0_. properly, as in cyanide poisoning.
Mechanical ventilation The use of an automatically c; r. 1
(ventilator pf respirator) to assist breathing. A piustii tui 1
seried into the nose <>r moiiib ami the lube is attached t.
vice ihai Forces air into the' lungs. Exhalation occur-
due to the elastic recoil of the lungs.
Pleurisy Inflammation of the pleural membranes, which causa
tion during breathing diat can be quite painful when 1 1 1 m
membranes rub against each other. Msu know u as plenritis.
Rales (KM.Sj Sounds sometimes heard in the lungs that 11
bubbling or rattling. Different types are due to the prea tl
abnormal type or amount of tluid or mucus within the hroiuhn
alveoli, or to fn'onchoconsmerion that causes turbulent airfla
Respiratory distress syndrome (RDS) \ breathing disorder otpn
inatiire newborns in which the alveoli do not remain i>|icrida
to a tack of surfactant. Surfactant reduces surface: tension amp
necessary to prevent the collapse of alveoli durin
Respiratoty failure A condition in which the respirai
eidier cannot supply enough »>■ to maintain uietaliolisiaj
cannot eliminate enough CO, to prevent respiratory ,\
higher-than-normal 1 1 ' level in interstitial fluid).
Rhinitis (ji-N 1-iis; rhm- - nose) Chronic or acute inflammattl
the mucous membrane of the nose.
Sudden iufaii! death syndrome (Slt)S) Death of in film h
the ages of I week and \2 months thought to he vine to
thai occurs while sleeping \n a prone position (on the scon
and re-breathing exhaled air propped in a depression of thm
tress, ft is now recommended thai normal newborns In
on their backs for sleeping (remember: "back to sleep" -
tachypnea Uak'-ip-NF -a; tttchy- = rapid) Rapid hrcathi
Wheeze UIUIZ) A whistling, squeaking, or musical
pitched sound during breathing resulting from a p.irtudlv 1
struc led airway,
ITLINE
? Respiratory System (p. 446)
mchidc the nose, pharynx, laniiv. trachea.
.\\m\ they aei with 'he cardiovascular system
(1 remove carbon dioxide from the blood,
»n of the nose is made of cartilage and skin
UCOUS membrane. Openings to the exterior
-■s.
in ol the nose, divided from the external
turn, communicates with the paranasal sa-
il nx through the internal nares.
I for wanning. moistening, and filtering air;
ing as a rcsonanng cliamber for special
1.1, .1 muscular tube lined by a mucous mein-
to the nasopharynx, oropharynx, and laryri-
.'.< 1 io ns in respiration. The oropharynx -\<\.\
ciion both iii digestion and in respiration.
7. The larynx connects the pharynx and the trachea.
the thyroid cartilage (Adam's apple), the epiglottis, the
cartilage, arytenoid cartilages, false vocal cords, ami a
cords, laut true vocal cords produce high pitches; rcf:
produce low pitches.
8. The trachea (windpipe) extends from die larynx iodic,
bronchi. It is composed of smooth muscle and ( -di.ijn:
of cartilage arid is lined wiih pscndosiraiificd cili.nd
epithelium.
9. The bronchial tree consists of die trachea, priti
secondary bronchi, tertian bronchi, bronchioles, and ■■><
bronchioles.
10. Lungs are paired organs in the thoracic cavuy eneloflfl
pleural membrane. The parietal pleura is die outer
viscenil pleura is die inner lau r.
11. I he right lmig h.is three tabes separated bj two
left lung has two kibes separated by one fissure pi
sioil. llic cardiac notch.
'. i ... h lobe consists oJ lobules, which contain lymphatic vessels,
arterioles, venules, terminal bronchioles, rasprratorj bronchi-
oles, alveolar ducts, alveolar sacs, and alveoli.
: hangc of gases (oxygen and carbon dioxide) m Che lungs de-
curs across the respiratory membrane. -.1 thin "sandwich'" con-
sisring of alveolar cells, basement membrane, and ciul«ahe1i.il
colls of a capillary.
Pulmonary Ventilation (p. 453)
1. Puimonan ventilation ('breathing) consists ol iiih.ilatioii ;in<l
exhalation, the movement of air into and oui of the Iwngs, Mr
ftows from higher to lower pressure.
;-2, inhalation occurs when alveolar pressure falls below atmo-
spheric pressure. Contraction of the diaphragm and external
intercostal* expands the volume of the lUiigS, Increased volume
I of the hums decreases alveolar pressure, and air moves trora
he,- a, lower pressure, From the atmosphere into die tangs.
(haiaiiou oc< u rs when alveolar pressure is higher than atrno-
^..|,|,._l^ pressure. Relaxation of die diaphragm and external in-
tercosrals decreases lung volume, and alveolar pressure in-
nses so thai air moves from the lungs to die.armosphese,
'Flic sternocleidomastoids, seaknes, and pectoralls minora con-
tribute to forced ml-ulation. Farced escalation Involves con-
;r,!ciitiii ol the internal inrercostak external oblique, internal
oblique, transversas abdominis, and rectus abdominis.
The iniimir ventilation is the total air taken in during 1 minute
(breathing rote per minute multiplied by tidal volume).
The lung volumes are tidal volume, inspiratory reserve volume,
expiratory reserve volume, and residual volume.
Lung capacities, the sum of two or more lung volumes, include
inspiratory, functional residual, vita], and total'.
Exchange of Oxygen and Carbon Dioxide (p. 457)
i Kc partial pressure of a gas (P) is die pressure exerted bj that
1 a mixture of gases.
It bach gas in a mixture of gases exerts its own pressure and bc-
hiivcs ,is if no other gases are present,
f, fa external and internal respiration, 2 and C.O. move Irom ar-
GK (if higher partial pressure to areas of lower partial pressure.
Sell-Quiz 469
4. External respiration is the exchange of gases between alveolar ah*
ami pulmonary blood capillaries. It is aided by a thin respi«(nry
membrane. .1 large alveolar surface area, and a rich blood si -ly
5. Internal respiration is the exchange of gases between systCTfiic
I issue capillaries ami systemic tissue cells.
Transport of Respiratory Gases (p. 459)
1. Most oxygen, 98.5%, is earned by the iron atoms of the Rent*
in hemoglobin; L.5% is dissolved in plasma.
2. The association ol Qj ami hemoglobin Is affected bj l' ( , . pi 1.
temperature, ami I', ,,..
3. Hypoxia refers to O3 deficiency at the tissue level.
4. Carbon dioxide is transported in three ways, \hout 7";. is dis-
solved in plasma. 23% combines with the globin df hemoglo-
bin, -.ml 70% is converted to bicarbonate ions d K ;i I
Control of Respiration (p. 461}
1. The respiratory center consists of a medullary rhyrhmirity area
(inspirators ami expiratory areas) in the medulla oblongata and
groups nl neurons in the pons.
2. The inspiratory are:, sets rite basic rhythm ol respiration.
3. Kespiraiioiis may he modified by several (actors, includim
tioil influences; chemical stimuli, sueh as levels ofOj, COj, and
II ; limine system stimulation; proprioceptor input; tempera
itirc; pain; the inflation reflex; and irritation to the airways,
Exercise and the Respiratory System (p. 465)
1. The rate and depth of ventilation chftBge m response to both
the intensity ami duration of exercise.
2. The abrupt increase in ventilation ft the star* of exercise is dm
to neural changes thai send excitatory impulses to the inspira-
tory area in the medulla oblongata. The more gradual increase
in ventilation during moderate exerds* is due do chemical and
physical changes in the bloodstream.
Aging and the Respiratory System (p. 465)
1. Aging results in decreased vital capacity, decreased biood tBVJel
ofOj, and diminished alveolar macrophage activity.
2. Elderly people arc more susceptible to pneumonia, emphy-
sema, bronchitis, and other p1.1l1110iv.11y disorders.
|i Winch of the following is NOT true concerning the pharynx?
nl, drink, and air pass through the oropharynx and Ian. n
go 1 larynx.
b, 1 hi: auditory (eustachian) tubes have openings in the
uphtuynx.
c. The pseudostratilied ciliated epithelium of the nasopharynx
|ps move dust-laden mucus toward the mouth.
jj, [Tie palatine and lingual tonsils are located in the laryn-
ghplwrynx.
fei The wall of the pharynx is composed of skeletal muscle
luted with mucous membranes.
2. During speaking, you raise your voices pitch. This j,& possible
because
a. the epiglottis vibrates rapidly
b. .mi have increased the air pressure push: M the
vocal cords
c. you have increased the tension On the true vocal eonls
d. your true vocal cords have become thicker and longer
e. the true vocal cords begin to v ihraie more slowly
3. Johnnv is having an asthma attack and feels ,is if he cannot
breathe. Why?
a. I lis diaphragm is not contracting.
470 Chapter 18 The Respiratory System
li. Spasms in liu: bronchiole smooth musde have blocked
airflow to the alveoli.
. ExbCSS mucus production i.s interfering with airflow into
the lungs.
d. The epiglottis has closed and air is not entering rhe lungs.
e. Insufficient surfactant is beting produced.
4. Which sequence ofei eats best describes inhalation?
a. connection of diaphragm — increase in shse of thoracic
ry—* decrease in alveolar pressure h. relaxation of
diaphragm — > decrease in state "I thoracic cavity — * increase
in alveolar pressure c. conirae i of diaphragm ~*
decrease in siae oi thoracic cavity —* decrease in alveolar
pressure d. relaxation oj diaphragm-^ increase m sfae
0# thoracic cavity—* increase in alveolar pressure e.
contraction of diaphragm — * decrease in size of thoracic
can itv — * increase in alveolar pressure
5. Which of the following does NOT help keep air passages
clean?
;i, nostril hairs b. alveolar macrophages
c. capillaries in the nasal cavities
d. cilia in the upper and lower respiratory traces e, mucus
6. If the total pressure of a mixture of gases is 760 men I lg and
gas 7. makes up 20% of the total mixture, then the partial
press re of gas / would be:
a. t'52 mm \\^ l>. 175 mm Tig c. 225 nun I [g
d. <SS8 mm Hg c. T6® mm %
7- How does hypercapiua affect respi ration?
a. h increases the rate o| respiration.
b. Ii decreases the rate of respiration.
c. It causes hypoventilation.
d. It does not change the rate ofrespiration.
c. 1 1 iiet.ivaiL", si ivtch receptors in die lungs,
S. \ir would flow inro the lungs along the following rantte:
1. bronchioles 2. primary bronchi
3. Secondary bronchi 4. terminal bronchioles
6. trachea
b. 6, $,.2,4,2, I c, 6, _'. 3; 5.4. I
e. 6, 1.4,5.5,2
5. tertiary bronchi
a. 6, 1,2,3,5,4
d. 6.2. *,-5, 1,4
9. Match the Following:
a. normally inactive; when
act bated, causes coni-r.icrinin
ot internal tnteriostals and
abdominal nm-di sand
forced exhalation
b. located in ponsrj stimulates
mspiraton area to prolong
inli.ilaiion
c. sets basic rhythm of respira-
tion; located in medulla
d. transmits inhibitor-, im-
pulses in inspiratory area;
located in pons
__ e. allows voluntary alteration
of breathing patterns
A. inspiratory area
B. expiratorj area
(.'. pneumoraxie area
D. apnetistic area
E. cerebral cortex
10. Under normal body conditions:, hemoglobin rcl
more readily when
a. body tcmpcraiiiiv increases
b. blood acidity decreases v_
c. blood plT increases
d. -blood oxygen partial pressure is high
e. blood ( ;Oj is low
11.. Match the following:
a. decreased carbon dioxide A, external n
'evels |J. .ipnea
b. normal, quiet brcaihin.u ( . hypereapnja
c. rapid breaching rj. L . upnt . a
_ d. exchange of gases between L\, uuernnl ivsjuoi J
the blood and lungs p t hypocapnia
c. inhalation and exhalation q^ pnhncmarv
F. increased carbon dioxide ventilation
' CVc '' s H. hypenenubrion 1
g. exchange oi gases between
blood and tissue cells
h. absence < >f breathing
12. Which of the following statements is NOT true miicc
the lungs?
a. The lungs contain about 300 million alveoli.
b. The left lung is thicker and broader because the IhtrU
lie low it.
c. 'I he right lung is composed oi three lobes.
d. The top portion of the lung is rhe apex.
e. The lungs are surrounded by 3 serous membrane.
13. Exhalation
a. occurs when alveolar pressure reaches 758 mm I U
b. is normally considered an active process requiring d
coiuraciion
C occurs when alveolar pressure is greater than niJimstiliBflj
pressure
d. involves rhe expansion of the pleural membranes
e. occurs when the atmospheric pressure is equal to tl
sure in the IttUgS
14. h\ which structures would you find simple squainmis
lllimr
a. secondary bronchi b. larynx and pharynx
c. tertiary bronchi d. primary bronchi
e; alveoli
I 5. ( Herinilation of the lungs is prevented by
a. 1 1n- inflation reflex b. pain in the pleural iiicml)tnjjj
c. nerve impulses from proprioceptors <I. control limud
cerebral cortex e. controlling blood pressure
16. The liincnou o| gohlel cells in the nasal cavities is to
a. warm the air entering the nose
b. produce mucus to rrap inhaled dust
c. increase the surface area inside die nose
d. help produce speech
q. exchange < > and ( X ' h nhiri the nasal cavities
Answers lo Figure Questions 471
IT.
IH.
I".
Decreasing the Mirface area of the respiratory membrane would
affect
a. internal respiration b. inhalation c. speech
d. external respiration c. mucus production
In which form is eafbosi dioxide NOT carried in the blood?
.1. bicarbonate um
b. bound to globiH
c. oxyhemoglobin
■ noheniogtobin
e. dissolved in plasma
Pill in the blanks in the foil owing entemica] reactions;
< ■•():- + ==*= ii : c:(>; =^= ir +
a. HCOi p O, b. IICO, . IbO c. II, H,0
io : ,HGO c. JUUJCO,
20. Of the following, which would have the highest partial pressure
of oxygen?
a. alveolar air at the end of exhalation
b. fapidlj contracting skeletal muscle libers
C alveolar air immediateh, after inhalation
d. i'li >od*fiovi ing into the lungs from die right side of the heart
e. blood returning EQ rlie heart nroitn the tissue cells
21. Match die following:
a. Jorce/uJ exbffilfltjon of air
1>. inspii:it(ir-_\ reserve \olurue -
tidal volume — expiratory
reserve volume
c. volume "fair moved during
rj< 'i i'l.il «jiiiei breatbitig
d. air remaining alter forced
exhalarmn
e- forceful inhalation of air
A. vita) (■.)/>:/ c -in
B. inspiratory
reserve volume
C residuaj voltaic
I), expiratory reserve
volume
F.. 1 1. 1.i ! volume
I
CRITICAL THINKING APPLICATIONS
l.hree-year-otd nephew Levi likes to get his own waj .ill
iIk time! Right now. Levi wants to eat 20 chocolate kisses
i| for bath linger and toe), but you'll only give him one for
twh yearol his age. I le is at this moment "holding my breath
Until I turn blue ami won't you be sorry!" Is he in dagger of
\ |!|
was diagnosed with esercise-indnced asthma after she
r.-jH'iieil trouble catching her breath during a swim inert.
| erqse-induced asthma is a particularly annoying condition
Bran athlete because the bodys response to exercise is the
Bract opposite of the .b.ody% need. Explain this >.uteiiiL-m.
3. Briruma has a flare for being dramatic, i can't come EQ work
today." she whispered, '*TVe goi laryngitis and a horrible case of
eory/.a." What is wrong with Ib'taimar
4. The entire tour group was in fine heahh when they Kit (hi
eoasi oJ < lima for ' ht ir mvi stop — lihet! \fter touring the
mountainous aivi !m j Jay, many of the group felt dizzy,
nauseous ami exhausted. The) wejre hyperventilating and could
not Catch then breath. The local -physician had seen this condi-
tion many time-; before in people thai did not take the liute to
acclimate to the mountains. Who caused the tour groups
symptom*^
ISWERSTO FIGURE QUESTIONS
The conducting wme of the respiratory system inelmli-s the
,1.1m . pharynx, larynx, trachea, bronchi, and bronchioles (tat-
tept the respiratory bronchioles).
Air molecules flow through the external uares, the nasal v.w-
ityand then the internal nares.
\ During swallowing, the epiglottis closes over thi laryn* to
block luoil and liquids from entering.
There are two lobes and two secondary bronchi in rhe left
lung and three lobes and three secondary bronchi in the
n e h 1 lung,
A lane lobule includes a lymphatic vessel, arteriole, venule.
and branch of a terminal bronchiole wrapped in elastic con-
nective tissue.
lam secreting cells secrete alveolar fluid, which in-
clude* surfactant
18.7 The main muscles that cause quiet breathing are the di-
aphragm and external intsrcostals.
18.8 Alveolar pressure is 758 mm rig during inhalation; alveolar
pressure during exhalation is 762 mm I Eg.
18.9 You demonstrate vital capacity when v. hi hreathe in as
deeply as possible and then exhale as much air as you can.
18.10 Oxygen enters pulmonary capillaries from alveolar air ami
enters rissue cells from systemic capillaries due Co differences
in l\>,
18.11 Hemoglobin transports about 98.$% of the o.yvgcn carried
in blond.
18.12 The phrenic nerves stimulate the diaphragm to contract.
18.13 Normal arterial blood I'. n , is 40 mm I ly.
I THE DIGESTIVE SYSTEM
v
did you know?
W bile a fink' alcohol may reduce
the risk of heart disease, the overconsiimption of
alcohol leads to many health problems. The organ that
sustains the most damage from, alcohol abase is the
liver. The liver converts alcohol into acetaldehyde,
which is even more toxic to the body than alcohol, This
process is associated with the deposition of fatly com-
pounds in the liver. If drinking continues, this condition
progresses to an inflammatory condition called alcohol
hepatitis, and then to cirrhosis, a condition in which
scar tissue replaces junctional liver tissue. Risk of cancer
of the liver is 30% higher in people with cirrhosis.
Focus on Wellness, page 494
www. wiley.com/college/apcentral
472
j| he food we eat contains a
variety ol nutrients, which are
used lor building new body tissues
and repairing damaged tissues.
I [owever, most of the lot id we eat consists of molecules
that are too large to be used by body cells. Therefore,
loud must be broken down into molecules dim art
enough to enter body cells. a process known <\s diges-
tion. CollecLJvely, the organs that perform these liinc- J
rions are known as the digestive system.
The medical specialty that, deals with the structure, I
function, diagnosis, and treatment of diseases of the
stomach and intestines is gastroenterology (gas'-tro-t 1
ter-OL-o-ie; gastro- = stomach; mien- = intestines;
= study of). The medical specialty that deals wiili
diagnosis and treatment of disorders of the rectum and
anus is proctology (prok-TOL-6-je; prod- - rectum},
looking back to move ahead .
• Mucous Membranes (page 90}
• Serous Membranes (page 91)
• Smooth Muscle Tissue (page 186)
■ Muscles that Move the Mandible (page 195)
• Negalive Feedback System (page 8)
• Simple Columnar Epithelium (page 75)
• Carbohydrates, Lipids, Proteins (pages 31-37)
• Enzymes (page 37)
Overview ol the Digestive System 473
OVERVIEW OF THE
DIGESTIVE SYSTEM
OBJECTIVE • Identify the organs of the digestive
system and their hasic functions.
ps O'J organs compose die digestive system (Figure
i i lu- gastrointestinal tract and die accessor) digestive
m, 11^. The gastrointestinal (GI) tract is :i continuous tithe
jtlui extends from the mouth to the anus. The GI tract con-
i rod i'rom die time it is eaten until ii is digested and ab-
H .'. or eliminated from the body. Organs ol the gastro-
pnestinal tract include the mouth, pharynx, esophagus,
ich, small intestine, and large intestine. The teeth,
Boe, salivary gJ&nds, ti'ver, gallbladder, and pancreas serve
as accessory digestive organs. Teeth aid in the physical break-
down ol UkhI. and the tongue assists in chewing and swallow-
ing. The other accessory dii»esi.hc organs never come into d^
PI :■. r contact with food. 1 he secretions that the}' proline if*
store flow into the Q] craci dirough ducts and aid m the
chemical breakdown of food.
Overall, the digestive system performs si\ basic processes:
1. Ingestion. Tin's process involves taking food:-, and Liquids
into the mouth (eating).
2. Secretion. Each day. cells within die walls of the (il tract
and accessory organs secrete a total <>i about 7 liters of
water, acid, buffers, and eiv\nies into the lumen of the
tract.
3. Mixing and propulsion. Alternating contraction anil re-
laxation of smooth muscle in the walls of the ( il tract mia
jre 19.1 Organs of the digestive system and related structures.
Organs of the gastrointestinal (GI) tract are the mouth, pharynx, esophagus, stomach, small intestine, and large
intestine. Accessory digestive organs are the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
and
[land)
iditjtilar gland
lland)
feophegus
Mouth (oral cavity)
contains teeth
and tongue
Sublingual gland
(salivary gland)
Pharnyx
Stomach
Pancreas
Transverse
colon
Descending
colon
Sigmoid colon
Reclurn
Anal canal
Anus
Functions of the Digestive System
1. Ingestion: taking food into the mouth.
2. Secretion: release ol water, acid, buffers, and enzymes into the
lumen oi the GI tract.
3. Mixing and propulsion: churning and pushing lood through ihe GI
Iract.
4. Digestion: mechanical and chemical breakdown ol food.
5. Absorption: passage of digested products from ihe GI trad into
the blood and lymph.
6. Defecation: elimination of feces Horn the GI tract.
flight lateral view ol head and neck and anterior view of trunk
■Which accessory digestive organs assist in the physical breakdown of food?
474 Chapter 19 The Digestive System
food and secretions and propel them toward the anus.
The ability of the (II trace K) nlia arid move material
along its length is termed motility.
4. Digestion. Mechanical and chemical processes break
down ingested food into small molecules. In mechanical
digestion the teeth cm and grind fund before it is swal-
lowed, and ihen smooth muscles of the stomach and
small intestine churn the food. As a result, food mole-
cules become dissolved and thoroughly mixed with diges-
tive enzymes. In chemical digestion the Luge carbohy-
drate, lipid, protein, and nucleic acid molecules in food
are broken down into smaller molecules by digestive
en /.vines.
5. Absorption. The entrance of ingested and secreted tlu-
IdSj ions, and the small molecules that are products of di-
gesiion into the epithelial cells fining the lumen ol the
(il tract is called absorption, The absorbed substances
pass into interstitial fluid and then into blood or lymph
and circulate to cells throughout the body.
6. Defecation. Wastes, indigestible substances, bacteria.
cells shed from the lining oi the CI tract, and digested
materials thai were not absorbed leave the body through
the anus in a process called defecation. The climinatr
materia] is termed feces.
m CHECKPOINT
1. Wlijch components nf the digestive system are Cil irau
organs ami which are accessory digestive organs?
2. Which organs of the digestive system come in coins!
with food, and what are some of their digeMiv< I n
LAYERS OF THE Gl TRACT
AND THE OMENTUM
objective • Describe the four layers that form the
wail of the gastrointestinal tract.
The wall of the (il tract, from the lower esophagus to die
anal canal, has the same basic, four-layered arrangeme
tissues. The four layers of the tract, from the inside m
the mucosa, suhtnucosa. muscularis, and serosa (Figi
Figure 19.2 Layers of the gastrointestinal tract Variations in this basic plan may be seen in the stomach
(Figurfl IS .8), small intestine (Figure 1 9 13), and large intestine (Figure 19.16).
ft*?
The four layers of the Gl tract from inside to outside are the mucosa, submucosa, muscularis, and serosa.
Duel of gland
outside tract
<such as
pane: n
Lymphatic tissue
Lumen
MUCOSA.
Epithelium
Lamina propria
Muscularis mucosae
SUBMUCOSA
Mesentery
MUSCULARIS.
Circular muscle
Longitudinal musclo
What is the function of the nerves in the wall of the gastrointestinal tract?
SEROSA:
Areolar connective tissue
ELpit helium
Mucosa. The mucosa, or inner lining of the tratt
mucous membrane. It is composed of a layer ol epithe-
lium in direct contact with the contents of the GI tract, a
layer of areolar connective tissue called the lamina
propria, and a ihin layer of smooth muscle called the
muscularis mucosae. Contractions of the muscularis
mucosae create folds in the mucosa chat increase rhe sur-
face area for digestion and absorption. The mucosa also
contains prominent lymphatic nodules that protect
against the entry ol pathogen;) through the GI tract
Suhnuicosa. The sub mucosa consists ol areolar 'riiiiiee-
tivc tissue that binds the mucosa to rhe muscularis. It
contains many blood and lymphatic vessels that receive
absorbed food molecules. Also located in the suhmucosa
are networks of neurons ih.it are a part ol the enteric
nervous system (ENS), the 'lira in of rhe gut." ENS neu-
rons within the suhmucosa control the secretions ol the
is of ilie GI tract.
Muscularis. As its name implies, the muscularis of the
Cd tract is .1 thick layer of muscle. In the mouth, pharynx,
ami upper esophagus, it. consists m pan of skeletal mitstk
that produces voluntary swallowing. Skeletal muscle also
ibfms the external anal sphincter, which permits volun-
tary control til defecation. Recall that a sphincter is a
thick circle of muscle around an opening. In the rest ol
Layers ol Ihe GI Tract and the Omentum 475
the tract, the muscularis consists oi smooth muscle, usually
arranged as an inner sheet of circular fibers and an outer
sheer of longitudinal fibers. Involuntary contractions i
these smooth muscles help break down food physically
mi\ it wilh digestive secretions, and propel it alontr the
tract. ENS neurons within die muscularis control the
frequency and strength of its contractions.
4. Serosa and peritoneum. The serosa^ the outermost
layer around organs ol the GI tract below the diaphragm,
is ;i membrane composed of simple squamous epithelium
and areolar connective tissue. The serosa set n tes a slip-
pery, watery fluid that allows the tract to glide easil]
against other organs. The serosa k also called the vtectral
peritonea at (per'-i-to-NF.-um == to stretch over). Recall
from Chapter 4 that the peritoneum is the largest serous
membrane of the body. The parietal periwumtn lines the
wall of the abdominal cavity; die visceral peritoneum
covers organs in the cavity.
In addition to binding the organs to each other and to
the walls of the abdominal cavity, the peritoneal folds contain
blood vessels, lymphatic vessels, and nerves that supply the
aUlonunal organs. The greater omentum io-\lf\"l um =
fat skin) drapes over the transverse colon and small intestine
like a "la try apron" (Pigurt ' I he mar!} lymph nodes
of the greater omentum contribute macrophages and ami-
Figure 19.3 Views of the abdomen and pelvis. The relationship of Ihe parts ol the peritoneum
(greater omentum and mesentery) to each other and to organs o( the digestive system is shown
v"~.'~
The peritoneum Is the largest serous membrane in the body.
Liver
Stomach
Transverse colon
GREATER
OMENTUM
Urinary bladder
GflEATER OMENTUM
Transverse
colon
—
Jejunum
MESENTERY
Descending colon
Ileum
Sigmoid colon
Urinary bladder
Y
(a) Anterior view
(b) Anierior view (greater omentum
lifted and small intestine reflected
to right side)
Which part of the peritoneum binds the small intestine to the posterior abdominal wall?
476 Chapter 19 The Digestive Syslem
producing plasma cells that help combat and contain
i ions of ihe Gl tract. The greater omcniuin normally
contains considerable adipose tissue. Its adipose tissue cbri-
iL-rii can greatly expand with weight gain, giving rise to the
characteristic "beer belly" seen in some overweight indivnlu-
als. A part of the peritoneum^ isbc mesentery <.YlKZ-en-ter'-e;
nits- = middle), binds the sm-.il I intestine in the posterior ab-
dominal wall (Figure 19.3b),
I A common cause of peritonitis, an acute inl];immation of
die peritoneum, is contaitunation of the peritoneum by in-
fectious microbes, which can result from accidental or sur-
gical wounds in the abdominal wall, or from perforation or
rn|iiiirc of abdominal organs.
■ CHECKPOINT
3. Where along the 01 tract is the muscularis composed of
skeletal muscle? Is control of" tins skeletal muscle
voluntary or involuntary?
4. Where are the visceral peritoneum and parietal peri
toneuni local. T
MOUTH
^
OBJECTIVES • Identity the locations of the salivary
glands, and describe tlie (unctions of their secretions.
« Describe the structure and functions of the tongue.
• Identify the pans of -i typical moth, and compare
deciduous and permanent dentitions.
The month or oral cavity is formed by the cheeks, hard mid;
soA palates, and tongue (Figure 1^.4). The cheeks form theba
era! waJIs ol the oral cavity- The ftps are fleshy folds around ilit
opening of the month. Both the cheeks and lips are covt*rct! oj
the outside by skin and on the inside by a mucous membrane
During chewing, the lips and cheeks help keep foot! U
the upper and lower teeth. They also assist in speech.
The hard palfltt' y consisting of the maxillae and palatin
hones, forms mojsi oi the roof of the mouth, The rest
formed by the muscular soft pnhttt: I langtng I nun ih
palate is 9 projection called the uvula (U-vu-ia). During swa|
lowing, the inula moves upward with the soli palate.
prevents entry of su allowed foods and liquids into flu
Figure 19.4 Structures of the mouth (oral cavity).
The cheeks, hard and soft palates, and tongue form the mouth.
Hard palate
Soft palate
Ivula
Cheek
Molars
Premolars
Cuspid (canine
Incisors
Anterior view
What are the functions of the muscles of the tongue?
Upper ||p
Gingivae (gums)
Palatine tonsil
Tongue
Lingual frenulum
Opening ot duct of
submandibular gland
Gingivae (gums)
Lower lip
aviiy. At t he- back of the soli palate, eke mouth opens into
the oropharynx. The palatine tousih are just posterior u> rite
^ing.
rogue
Monpie forms the flour of the oral cavity. It is an acces-
w digestive organ composed of skeletal muscle covered
jth mucous membrane (See Figuri Li .4 on page 292).
The muscles of the tongue maneuver food for chewing,
m the food into a rounded mass, force the food to tin:
;ck o! the mouth for swallowing-, and alter the shape and
i>i the tongue lot swallowing and speech. The lingual
tiiuluni il.lNCi-gwal FREN-ii-lum; lingua ~ tongue;
tutu = bridle), a fold ol mucous membrane in ihe midline
ft.k uiulersurface of the tongue, limits the movement of
ngfle posteriorly (Figure 19.4). Ihe lingual tonsils lie at
llltbiise of the tongue (sec ! igure 12.4a). The upper surface
. les of the tongue are covered with projections called
.;>.... v PH.-d some of which contain taste buds.
■
Mouth 477
gums and arc lined with the peYiOeltmtal Hgttmmt (peri- =
around; odont- — tooth). This dense fibrous connective tissue
anchors the teeth to bone (Figure 19>.5),
A typical tooth has three major externa] regions: the
crown, root, and neck. The crown is the visible portion above
the level of the gums. The root consists of one to three pro-
jections embedded in rhc socket. The neck is the junction
line ol the crown and root, near the uunt line.
Internally, dentin forms the majority of the tooth.
Dentin consists of a calcified connective tissue thai gives fcfoe
tooth its basic shape and rigidity. The dentin of the crown is
covered b) enamel that consists primarily of calcium phos-
phate and calcium carbonate. I'tuiniel, the hardest substance
in the body and the richest in calcium SftltS (flboW 95% of its
dry weight), protects the tooth from the wear and tear of
chewing. It is also a barrier against acids that easily dissolve
the dentin. The dentin of the root is coveted by cementnm, a
bonclike substance that attaches to ihe rout to the periodon-
tal ligament. The dentin of a tooth encloses the pulp cavity, a
Salivary GJands
|c three pairs of sativmy glands arc accessor} organs ofdi-
ption that lie outside the mouth and release their secretions
ducts emptying into the oral cavity (sec Figure 19„1),
Ibe pa cat id glands are located inferior and anterior to the
m> between the skin and the massctcr muscle. The sub-
Mjidibidar glands are found in the floor ol the mouth; the]
Kmalial and partly inferior to die mandible. 1 "be sublingual
>ds ctre beneath the tongue and superior to the sub-
d) Iml sir glands.
pic fluid secreted by the salivary glands, called saliva, is
i1 99.5% water and 0.5% solutes. The water in
issolve foods so they can be tasted and digestive
gflons cm begin. One of the solutes, the digestive enzyme
amylase, begins the digestion of starches in the
f. Mucus in saliva lubricates food SO it can easily be
d. The en/.yme lyso/.ymc kills bacteria, therein' pro-
the mouth's mucous membrane from infection and
teeth from decay.
hi ol saliva, called salivation (sal-i-VA-shun), is
I hy the autonomic nervous system, Normally,
Hynip;iihctic stimulation promotes continuous secretion
aodemte amount of saliva, which keeps the mucous
banes moist and lubricates the movements of the
lips during speech. Sympathetic stimulation doui-
fo'during stress, resulting in dryness ol the mouth.
lh
leetb {denies} are accessory digestive organs located in
f sockets of the mandible and maxillae. The sockets axe
yngivac (JTN-ji-ve; singular is gmgfaa) or
Figure 19.5 Parts of a typical tooth.
There are 20 teeth in a complete deciduous set and 32 teeth In a
complete permanent set.
Sagittal ptane
CROWN -
NECK — £
ROOT —
t n,-iiii'-;i
Dentin
Gingiva <gum)
Pulp In pulp cavity
Cementuin
Root canal
Alveolar bone
Periodontal
ligament
Nerve
Blood supply
Sagittal section ol a mandibular (lower) molar
What type of tissue is the main component of teeth?
478 Chapler 19 The Digestive System
space in the crown filled with pulp, a connective tissue con-
taining blood vessels, nerves, and lymphatic vessels. Narrow
extensions of the pulp cavity run through the root of the
tooth and are called root canals. Each root canal has an open*-
iug at its base through which blood vessels bring nourish-
ment, lymphatic vessels offer protection, and nerves provide
sens;! lion.
Humans have two sets of teeth. The deciduous teeth be*
gin to erupt at about 6 months of age, and one pair appears
about each month thereafter until all 20 are present. They
are generally lost in the same sequence between 6 and 12
vcars of age. The permanent teeth appear between age 6 and
adulthood. There are 32 teeth in a complete permanent set.
Humans have different teeth for, different lunctions (see
I, Incisors are closest to the midline, are chisel-
shaped, and are adapted For cutting into lood; cuspids (ca-
nines) arc next to the incisors and have one pointed surface
(cusp) to tear anil shred food; premolars have two cusps to
crush and grind food; and molars have three or more blunt
cusps to crush and grind food.
Root canal therapy is a muhisrep procedure in which all
traces of pulp tissue are removed from the pulp cavity and
root canals of a badly diseased tooth. After a hole is made
in the tooth, the root canals are filed out and irrigated to
remove bacteria, 'I hen, the canals are treated with medi-
cation and sealed tightly. The damaged crown is then
red.
Digestion in the Mouth
Mechanical digestion in the mouth results from chewing, or
mastication (mas -ii-K.A-shun = to chew), in which food is
manipulated by the tongue. ground by the teeth, and mixed
with saliva. As a result, the food is reduced to a soft, flexible.
easily swallowed mass called a bolus ( - lump).
Dietary carbohydrates are either monosaccharide and
disaccluu ide sugars or complex polysaccharides such as
glycogen and starches (see page 31). Most of the carbohy-
drates we eat are starches from plant sources, but only mono-
saechandes (glucose, fructose, and galactose) can be absorbed
into the bloodstream. Thus, ingested starches must lie bro-
ken down into monosaccharides. Salivan amylase begins the
breakdown of starch In breaking particular chemical bonds
between the glucose subunils. The resulting products include
the disaccharide maltose (2 glucose siihuniis). the trisnecha-
ride maltotriose (} glucose suhuniis), and larger fragments
called devtrins (5 i icose subunits). Salivary amylase in
die swallowed fond continues to act for about an hour until it
is inactivated by stomach acids.
■ CHECKPOINT
5. What structures form the mouth (oral cavitj )■
6. I low is saliva secretion regulated?
7. What is a bolus? I low is it formed?
PHARYNX AND ESOPHAGUS 1
OBJECTIVE • Describe the location, structure, and
functions of the pharynx and esophagus.
When food is swallowed, ii passes from the mouth
pharynx (FAlRhiks), a tunnel-shaped tube that is on;
of skeletal muscle and lined by mucous membrane. It
from the internal uares to the esophagus posteriorly until
larynx anteriorly (Figure 19, 6a). The nasopharynx is
iit respiration (see Figure 18 J. on page 447); food that,
swallowed passes from the mouth into the orophan tJ
I nrvn go pharynx before passing into the esophagus, \hisd
contractions of the oropharynx and laryngophanmx ln-lppni
pel food into the esophagus.
The esophagus (e-SOF-a-gus = eating gullet) is ;i rnu
cillar tube lined with stratified squamous epithelium thntlij
posterior to the trachea. It begins at the end of the hna
gopharynx, passes through the mediastinum and dnip
and connects to the superior aspect of the stomach. Ittruj
ports food to the stomach and secretes mucus. Vi uu
the esophagus, the muscularis forms two sphincu
upper esophageal sphincter (VES) (e-sof -a-JK-al). ubk
consists of skeletal muscle, and the lower esophageal sptim
ter (LES), which consists of smooth muscle. The
esophageal sphincter regulates the movement ol I
the pharj ax into the esophagus; the lower esophageal «
ter regulates the movement of food from the esophagus]
the stomach.
Swallowing, the movement of food from the mmitlij
the stomach, involves the mouth, pharynx, and t
and is helped by saliva and mucus. Swallowing is divided 1 ]
three stages; the voluntary, pharyngeal, and csophj
stages.
In the voluntary stage of swallowing, the bolus is l>
to the back of the mouth cavity and into the oraphaj
the movement ol the tongue upward and backward d
the palate. With the passage of the bolus into the
ynx, die involuntary pharyngeal stage of swallowing
I ire 19.6b). Breathing is temporarily interrupted. j|
die soft palate and uvula move upward to close off the i
so pharynx, the epiglottis seals off the larynx, and thet
cords come together. Alter the bolus passes tin
oropharynx, the respirator) passageways reopen and br
Pharynx and Esophagus 479
Figure 19.6 Swallowing. During the pharyngeal stage of swallowing (b). Ihe tongue rises against the
palate, the nasopharynx is closed off, Ihe larynx rises, the epiglottis seals off the larynx, and the bolus
passes Into the esophagus. During Ihe esophageal stage of swallowing (c), food moves through the
esophagus into the stomach via peristalsis.
- ' **"*• .-
Swallowing moves food from the mouth into ihe stomach.
Nasopharynx
Hard palate
Soft palate
Uvula
Esophagus
Oropharynx
Epiglottis
Laryngopharynx
Larynx
(a) Position of structures before swallowing
<b) During Ihe pharyngeal stage of swallowing
Bolus
Stomach
(c) Esophageal stage ol swallowing
Is swallowing a voluntary or an involuntary action?
480 Chapter 19 The DigastivB System
ing resumes. Once die upper esophageal sphincter relaxes,
the bolus moves into the esophagus.
In the esophageal stage, food is pushed through the
esophagus by a pfoeess called peristalsis Q i
Q The circular muscle fibers in the section of esophagus
above the bolus contract, constricting the wal3 of the
esophagus and squeezing the bolus downward.
Q Longitudinal muscle fibers around the bottom of the bo-
lus contract, shortening the section ol the esophagus he-
low the boln.s .mil pushing its walls outward.
^ After die bolus moves into the new section of the esopha-
gus, the circular muscles above it contract, and die cycle
repents. The contractions move the bolus down the
esophagus toward the stomach. As the bolus approaches
the end of the esophagus, the lower esophageal sphincter
relaxes and the holus moves into the stomach.
Sometimes, after food has entered the stomach, the lower
esophageal sphincter Tails to elose adequately and the
stomach contents can hack up (reflux) into the lower
tSOphagUS, a condition known as gastroesophageal re-
flux disease (GERD). Reflux ol acid from the stomach
can irritate the esophageal wall, causing a burning sensa-
tion known as heartburn, Although it is experienced in a
I region very near the heart, heartburn is unrelated to any-
cardiac problem. GERD also may increase the risk of
esophageal cancer.
■ CHECKPOINT
8. How does a bolus pass from the mouth nun the sum
STOMACH
OBJECTIVE * Describe the location, structure, and
functions of the stomach.
The stomach is a J-shnped enlargement of die Gl tract d
rectly below the diaphragm. The stomach connects
esophagus to the duodenum, the first part of the small im
tine {figure \ l K~). Because a meal can be eaten mud
quickly than the intestines can digest and absorb ii.oiin
the functions of" ihe stomach is cb serve as a misting .dip
and holding reservoir. At appropriate intervals after fo
ingested, the stomach forces a small quantity ofrrtal
the duodenum. 1 he position and si/.i ol the siotniH'h
continually; the diaphragm pushes it mferiorly with cudim-
Figure 19.7 External and internal anatomy of the stomach. The dashed lines indi-
cate the approximate borders of the regions of the stomach.
.,. n
The four regions of the stomach are the cardia, fundus, body, and pylorus.
A Pyloric x PYLORUS
sphincter
Duodenum (first portion
oJ small intestine)
Anterior view
", Does your stomach still have rugae after a very big meal?
FUNDUS
Serosa
Muscularis:
Longitudinal layer
Circular layer
Oblique layer
Rugae of mucosa
halation and pulls it superiorly with each exhalation. Empty,
i is about rhe size of a large sausage, but it is rhc niiost elastic
wn of the <L i J tract and can acconimocta a large quantity 0I
mod,
Structure of the Stomach
Ik stomach has lour main regions: cardia, Fundus, body, and
its (Figure 19.7). 'The cardia (CAR-de-a) surrounds the
Superior opening of rhe stomach. The stomach then curves
. ,i. The portion superior and to die left or" the cardia is
jc fundus (FUN-dus). Inferior tp the fundus is the large
11:1111. il portion of rhe stomach, railed the body, The narrow,
Kt inferior region is the pylorus (pi-LOR-ns; pyl- = gate;
= guard). Between the pylorus .md duodenum is the
py/onV sphincter.
The stomach wall is composed of the same four basic lay-
fias the rest of the CI tract (mucosa, submucosa, museu-
ms, serosa), with certain differences. When the stomach is
iprv, the mucosa lies in large folds, called rugae (ROO-je =
,1. The surface of the mucosa is a layer ol nonciliated
Stomach 481
simple columnar epithelial cells called surface mucous cells
(Figure I '■' )■ E piihclial cells also Extend downward and form
columns ol secretory celts called gastric glands that lim- in
row channels called gastric pits. Secretions rrom the gastric
glands flow into the gastric pits and then mio the lumen of
the stomach*
'i'he gastric glands contain three types a£ exocrine gland
tills that secrete their products into the stomach lumen: mu-
cous neck cells, chief cells, and parietal cells. Both surface
mucous cells and nnicaus neck cells secrete mucus (Figure
) The chief cells secrete an inactive gastric enzyme called
pepsinogen. Parietal cells produce hydrochloric acid, wl
kills many microbes in food and helps convert pepsinogen to
die active digestive enzyme pepsin. Parietal cells also secrete
intrinsic factor, which is involved in the absorption of vitamin
B| : . inadequate production of intrinsic faci-ir can result in
pernicious anemia because vitamin B|i is needed for red
blood cell production. The secretions of the mucous, chief,
Anc\ parietal cells are collectively called gastric juice. The G
cells, a fourth type of cell in the gastric glands, secrete the
hormone gastrin into the bloodstream.
Figure 19.8 Layers of the stomach.
Secretions from the gastric glands flow into the gastric pits and then into the lumen of the stomach.
Lumen aJ stomach
- MUCOSA
Lymphatic nodule
MuseuJarls mucosae
Lymphatic vessel
Venule
Arteriole -
Oblique layer ol muscle
Circular layer oi muscle
Enteric neurons
m rnuscularis
Longitudinal
layat of muscle
Three-dimensional view of layers of the stomach
Which stomach layer is In contact with swallowed food?
- SUBMUCOSA
- MUSCULARIS
SEROSA
482 Chapter 19 The Digestive System
Figure 19.9 Sectional view of gastric glands and types of cells in the stomach mucosa.
Gastric juice is the combined secretions of mucous cells, chief cells, and parietal cells.
Simple
columns
epithelium
Areolar
connective
tissue
Gastric
glands
Surface mucous cell
(secretes mucus)
Mucous neck ceil
(secretes mucus).
Parietal ceil
(secretes hydrochloric
acid and intrinsic factor)
Chief cell (secretes
pepsinogen)
Muscularis
mucosae
Subm
G cell (secretes
the hormone gastrin)
Which type of cell shown here is part of the endocrine system (secretes a hormone)?
The submueosa of the stomach is composed of areolar
connective tissue ili.u connects the mucosa to the muscularis.
The muscularis has three rather than two layers of smooch
muscle: an outer longitudinal layer, i middle circular layer,
and ;m inner oblique layer (see Figure 19.7). 'Hie serosa cov-
ering the stomach, composed ol simple squamous epithelium
and areolar connective tissue, is part of the visceral peri-
ii'iKinn.
Digestion and Absorption in the Stomach
Once food readies die stomach) the stomach wall is stretched
and the pi I of I he stomach contents increases because pro-
teins in food have buffered some of the stomach acid. These
changes in the stomach trigger uerve impulses that stimulate
ilk: flow nl gastric juice and initiate mixing waves, gentle,
rippling peristaltic movements of the muscularis. These
waves macerate food and mix it with the secretions of the
gastric glands, producing chyme (KiM = juice), a chick liquid
with the consistency of pea soup. Kach mixing wave forces a
small amount of chyme through the partially closed pyloric
sphincter inwi the duodenum, a process called gastric empty-
ing. Mom of the chyme is forced hack into the hodyoj
stomach. The next mixing wave pushes clnme forward™
and forces a little more into the duodenum. Khar I
ach has emptied some ol its contents into the dimdur
Ilexes begin to slow the exit of .chyme from the stomadt,
prevents overloading oi the duodenum with more d
than it can handle, hoods rich in carbohydrate spend the
time in the stomach; high-protein foods remain sc-KM
longer, and gastric emptying is slowest after a meal urn
ing large amounts of fat.
Vomiting is the forcible expulsion "I the coments
Upper C j T tract (stomach and sometimes duodenum
through the mouth. The strongest stimuli lor vouiitiiigfui
irritation and excessive distension of the stomach. COT
stimuli include unpleasant sights, general anesthesia, djfl
ness, and certain drugs such as morphine. Prolonged vwid
itingi especially in infants and elderly people, can be sets
ous because the loss of acidic gastric juice can lead J
alkalosis (higher than normal blood pll). delivdr.iunn.aj
damage to the esophagus and teeth.
Pancreas 48!
The main event of chemical digestion in the stomach is
|t beginning of protein digestion hy the enzyme pepsin.
Kich breaks peptide bonds between the amino acids ol pro-
Ens. \s a result, the proteins become fragmented into /><#-
ti,h\ smaller strings of amino acids. Pepsin is most effective
in tin: very acidic environment of the stomach, which has a
jH ol 2. What keeps pepsin from digesting the protein in
li cells along with the food? First, recall that chief cells
, , pepsin in an inactive form (pepsinogen), It is not con-
feted into active pepsin until it contacts hydrochloric acid in
juice. Second, mucus secreted by mucous cells coats
nc »sa, forming a thick barrier between the cells ol the
o ill lining and the gastric juice.
The epithelial cells of the stomach are impermeable Ha
p materials, so little absorption occurs. However, mucous
of the stomach absorb some water, ions, and short-chain
Is, as well as certain drugs (especially aspirin) and
,hnl.
CHECKPOINT
J, What are the components of gastric juice?
10, What is die role of pepsin? Why is ii secreted in an
inactive form?
11, What substances are absorbed in the stomach?
PANCREAS
objective • Describe the location, structure, and
functions of the pancreas,
From the stomach, chyme passes into the small intestine. He-
cause chemical digestion in the small intestine depends on
activities of die pancreas, liver, and gallbladder, we first con-
sider these accessory digestive organs and their contributions
to digestion in the small intestine.
Structure of the Pancreas
The pancreas {pint- - all; -evens = flesh) lies behind the
stomach (see Figure 19J). Secretions pass from the pancreas
to the duodenum via the pancreatic duct, which unites with
the common bile duct from the liver and gallbladder, forming
a common duct to the duodenum (Figure 1°. 10).
The pancreas is made up of small clusters of uUndulnr
epithelial cells, most of which are arranged in clusters called
acini (AS-i-nl). The acini constitute the twerm portion of
the organ (sec Figure 13;11 on page 328). The cells within
acini secrete a mixture of fluid and digestive eu/unes called
pancreatic juice. The remaining 1% of the cells irt
[Figure 19.10 Relation of the pancreas to the liver, gallbladder, and duodenum. The inset shows details ol the
[amnion brie duct and pancreatic duel forming the common duct.
Pancreatic |uice in the pancreatic duct and bile in the common bile duct both flow into the common duct to the duodenum.
Falciform
Igament
Gallbladder
Duodenum
Lett hepafic duct
Common hepatic duct
Common bile duct
Pancreatic
duct
Common bile duel
Common duct to
duodenum
Mucosa
of duodenum
Pancreatic duct
Common due!
Eo duodenum
^^
I
Jejunum
/
Anterior view
Sphincter at entrance
to duodenum
What substances are present In pancreatic juice?
484 Chapter 19 The Digestive System
m/.ed nuo clusters called pancreatic islets (islets of Longer-
bans), the mdwint portion of the pancreas. These cells se-
crete the hormones glucagon, insulin, somatostatin, and pan-
creatic polypeptide, which arc discussed in Chapter L3.
Pancreatic Juice
Pancreatic juke is a clear, colorless liquid that consists
mi i' hi water, some salts, sodium bicarbonate, and en-
zymes. The bicarbonate ions give pancreatic juice a slightly
alkaline pH (7.1 to 8.2),. which inactivates pepsin from the
stomach and creates the optimal environment for aeiivin of
enzymes in the small intestine. The enzymes in pancre-
i ■■' fuicc include a starch-digesting enzyme called pancreatic
amylase, several protein-digesting enzymes including trypsin
(TRIP-sin), chymotiypsin (ki'-ino-TRIP-sin), and ear-
boxypeptidase (kar-hok'-se-PKP-ii-das); i he main triglyc-
ende-digesting enzyme in adults, called pancreatic lipase:
anil nucleic acid- -digesting cn/.ymes called > ihonmieiise and
deoxyrilwmcIea.se. The protein-digesting enzymes are pro-
duced in an inactive Form, which prevents them from digest-
ing the pancreas itself. Upon reaching the small intestine, the
inactive form ul trypsin is activated by .m enzytne called en-
terokinase. In turn, trypsin activates the other protein-
digesting pancreatic enzymes-
Pancreatic cancer usually affects people over 50 years of
age and occurs more frequently in males. Typically, there
are few symptoms urn i I ilu disorder reaches an advanced
stage and often not until it has metastasized to other parts
ul the hotly such as the lymph nodes, liver, or lungs. The
disease is nearly always fatal and is the fourth most com-
mon cause of death from i ancer in die EJnited States. Pan-
creatic cancer has been linked to fatty foods, high alcohol
consumption, genetic (actors, smoking, and chronic pan-
creatitis.
■ CHECKPOINT
12. What are the pancreatic acini: How do their lunclions
differ from those of the pancreatic islets?
13. Wli.ii is the role ofenterokinase?
LIVER AND GALLBLADDER
OBJECTIVE • Describe the location, structure, and
functions of the liver and gallbladder.
In an average adult, die liver weighs ! .4 kg (about > lb) and,
after the skin, is the second largest organ of the hods, It is lo-
cated below the diaphragm, mostly on the right side of the
■ . ft connective tissue capsule covers the liver, which in
turn is covered by peritoneum, the serous membrane that
covers all ihe viscera. The gallbladder (gall- bile) is ,i
shaped sac that hangs from the lower front margin n| M
liver (l-'imm 1 9.10); "
Structure of the Liver and Gallbladder
The lobes of the liver arc made up of many functional
called lobules (Figun I 1 ' ! 1 ). \ lobule consists of special
epithelial cells, called hepatocytes {hepat- = liver; -cytoA
cells), arranged around a central vein. In addition, the
has highly-permeable capillaries called sinusoids. Also proJ
em. in the sinusoids are lived phagocytes called Kupffcr am
which destroy worn-out blood cells, bacteria, and othe
eign matter in the venous blood draining from ihe <rasl.i'<>m-
testing 1 tract.
Bile, which is secreted In hepatocytes, enters Ink ctmA
mil (kan'-a-LlK-u-ll = small canals), which are narrow
cellular canals thai empty into bile titters at ihe periphery
the lobules. The bile duels merge ,md eventually form
right and left hepatic ducts, which unite and exil the ]jm
the common hepatic duct (see I igure 19.1(1). farther on,
common hepatic duct joins the cystic duct (cystic = blddi
from the gallbladder to form the common bile duet. \\\
the small intestine" is empty, ihe sphincier around die
mon duel at die entrance to the duodenum closes, ami
backs up into the cystic duet to ihe gallbladder for storage,
Bile
Bile salts in bile aid in etnulsifhation. the breakdown oflaiw
lipid globules into a suspension ol small lipid globules. ;il)<Ijjj
absorption of lipids following their digestion. The- small lit
globules formed as a result of em unification present a vn|
large surface area so that pancreatic lipase can digesi
rapidly. The principal bile pigment is bilirubin, which •
rived from heme. When worn-out red blood cells arc brofl
down, iron, globin, and bilirubin are released. The iron 1
globin are recycled, but some of. the bilirubin is ewiv.oi
bile, Bilirubin eventually is broken down in the inn-
one of us breakdown products (stercobilin) gives feustd
normal brown color .(sec Figure I i. 1 * on paee ^th Alter thJ
have served as emulsifying agents, most bile salts arc red
sorheil by active transport in the final portion ol the snwllflj
testine (ileum) and enter portal blood flowing toward i fit- In J
The components of bile sometimes crystallize and kitjfl]
gallstones. As they grow in size and number,
mas cause intermittent or complete obstruction
flow of bile from the gallbladder into the duodenum
Treatment consists of using gaUstone-dissolviu
lithotripsy, a shock-wave therapy that smashes ihi
stones into particles small enough to pass throtu
ducts. For people with recurrent gallstones or for uli
drugs or lithotripsy is not indicated, r/Woy.^ Vrvwi —
removal of the gallbladder and its contents — is n
Liver and Gallbladder 485
Figure 19.11 Structure of the liver.
A liver lobule consists of hepatocytes arranged around a central vein.
Liver lobule
Central vein
Branch of
hepatic artery
Branch of hepatic
portal vein
Bile duct
Liver
Interior vena cava
Hepallc artery
Hepatic portal vein
(a) Overview ol a liver lobule
Sinusoid
To hepatic
vein
Central vein
Sinusoids -
Bite canaliculi
Bile duct
Branch oi hepatic portal vein
Branch ol hepatic artery
Hepatocyte
Kuprfer cell
Connective tissue
(b) Details ot a portion of a liver lobule
Which cells in the liver are phagocytes?
ictions of the Liver
to: liver performs many other vital functions in addition to
taction of bile and bile salts and the phagocytosis oi
md dead or foreign material by the Kuprfer cells.
these arc related to metabolism and are discussed in
ffl. Briefly, however, other functions of the liver in-
ude the following:
1. Carbohydrate metabolism. The liver is especially in
porcam in maintaining a normal blood glucose level.
When blood gluCOSC is low, the liver can break down
glycogen to glucose ;iud release ulumse int« v lite blood-
stream. The liver can also convert certain amino acids
and lactic acid Co glucose, and it ean convert other sugars,
such as fructose ami galactose, inn. ghlpOSe, W hen blood
486 Chapter 19 The Digestive System
glucose is high, as occurs just after eating a men], the
liver com crts glucose to glycogen -jinl triglycerides for
storage.
2. Lipid metabolism. Hepatocytes store some criglyc-
erid.es; break down laity acids to generate ATP; synthe-
size lipoproteins, which transport fatty acids, triglyc-
• , and cholesterol in ,im.l from body cells; synthesize
cholesterol; and use cholesterol tso make bile salts.
3. Protein metabolism. I lepatocytes remove the amino
group (-\ T H : ) from amino acids so that the amino acids
can be used tor ATP production or convened to carbo-
hydrates or hits. 7 hey also convert the resulting toxic
ammonia (\ll;» into the much less toxic urea, which is
excreted in urine. Hepatocytes also synthesize most
plasma proteins, such :is globulins, albumin, prothrom-
bin, and fibrinogen.
4. Processing of drugs and hormones. The liver cm
detoxify substances such as alcohol or secrete drugs such
us penicillin, erythromycin, and sulfonamides nun bile. It
can also inactivate thyroid hormones and steroid hor-
mones such as estrogens and aldosterone.
5. Excretion of bilirubin. Bilirubin, derived from the
heme of aged red blood cells, is absorbed by the liver
from the blood and secreted mm bile. Most of the biliru-
bin in bile is metabolized in the small intestine by bacte-
ria and eliminated in feces.
6. Storage of vitamins and minerals In addition to stor-
ing glycogen, the liver stores certain vitamins ( \, \). I\
and K) and minerals (iron and copper), which are re-
leased from the liver when needed elsewhere in the body.
7. Activation of vitamin D. The skin, liver, and kidneys
participate in synthesizing the active form of vftamiti D.
■ CHECKPOINT
14. flow are die liver and gallbladder connected to the duo-
denum 2
15. What is the function nt bile:
16. List all of the functions ol the liver.
SMALL INTESTINE
OBJECTIVE • Describe the location, structure, and
functions of the small intestine.
Within 2 to 4 hours alter eating a meal, the stomach has
emptied its contents into die small intestine, where the major
events of digestion and stbsoroaon occur. The rwall hiiestitw
averages 2.5 em (] in.) in diameter; its length is about 3 ra
i 10 hi in a living person ami about 6.5 m (21 ft) in a cadaver
due in the loss of smooth muscle tone a her death.
Structure of the Small Intestine
The small imestine has three portions (Figure Is 1 , I2,i): tn
duodenum, the jejunum, and the ileum. 'The chmknm
(doo'-o-Dll-nuin), the shortest part (about 25 cm or 111,
in.), attaches to the pylorus of the stomach. DiioJaiui
means '"twelve"; the structure is SO named because
aboill as long as the width of 12 lingers. The fejlffllfPlM
JO( )-nuin = empty) is about 1 m (3 ft) long ami m
named because it is empty at death. The final portion oft
small intestine, the ileum (II. -e urn twisted), nieiui
about 2 m (6 ft) and joins the large intestine at the i/«oroflj
sphincter (il'-c-o-SE-Lal ).
Figure 19.12 External and internal anatomy of the small in*
testine. (a) Portions of the small intestine are the duodenum, j
junum, and ileum, (b) Circular folds increase the surface area lor
gestion and absorption in the small intestine.
in,
01 j
V
Most dfgestion and absorption occur in the small intestine.
SMALL
'NTESTINE:
DUODENUM
JEJUNUM
IlLuM
Large
inlaw
(a) Anterior view ol external anatomy
Circular tolas
T>
(b) Internal analomy of the jejunum
Which segment of the small intestine is the longest?
Small Intestine 487
The wall ol the small intestine is composed of ehe satne
four layer's tViat make up most of the GY tract* mucosa, safer
mucosa, muscular is f and serosa (Figure L9.ll). 'Hie epithelial
I Hi of the small intestinal mucosa consists <>i simple colum-
cpiihelium thai contains mum types of cells. Absorptive
St of" the epithelium contain microvilli and digest and nb-
irh nutrients in small intestinal chyme. Also present in the
Kelium are gofrfet cells, which secrete munis. The small
retinal mucosa contains intestinal glands, which are deep
'ices lined I iv epithelial cells that secrete intestinal juice.
Bes absorptive cells and goblet cells, intestinal glands also
(onto in three types of endocrine cells that secrete hormones
|lu the bloodstream: 5 cells-, CCK cells, :vnd K cells, which
:atc secretin (se-KRE-tin), cholecystokinin (ko-le-sis'-to-
BX-in) or CCK, and gtucose-dependent insult not topic pep-
■ft, or ft//*, respectively (see Ihhle 19.2 on page #95 form-
ttoin .iiul Ct.'K and Table I I J on page TvJ for GIB). The
Lima propria ol" the small intestinal mucosa contains areolar
biective tissue that has an abundance of lymphatic tissue.
i helps defend ajrainsr pathogens in food. The subtnu-
Bsaol the duodenum contains duodenal glands that secrete
p. alkaline mucus. It helps neutralize . acid in the
iyrtie. I he muscukiris of the small intestine consists ol two
layers of smooth muscle — ;m outer longitudinal layer and an
inner eucular V.vyer. Tke serosa is Composed of simple squa-
mous epithelium and areolar eoimecuve tissue.
Even though the wall of the small intestine is composed
of die same four basic layers as the rest of the Cil tract, spe-
cial structural features of the small irirestine facilitate the
process of digestion and absorption, fhese structural features
include circular folds, villi, and mierovilli. Circular folds are
peninment ridges of the mucosa and submucosa that enhance
absorption by increasing surface area and causing the chyme
to spiral, rather than move in a straight line, as it passes
through the snv.ill intestine (see Figure 19 I lb). Also present
in the small intestine are numerous villi ( = tufts of hail - ; sin-
gular is villus), fingerlike projections of the mucosa that in-
crease the surface area of the intestinal epithelium. Each
villus consists of a b.tycr of simple columnar epithelium sur-
rounding a core of lamina propria. Within the core are an
arteriole, a venule, a blood capillary network, anil q lacteal
(I , \K-te-al = milky), which is a lymphatic capillary. Nutri-
ents absorbed in the epithelial cells covering the villus pass
through the wall of a capillary or a lacteal to enter blood or
lymph, respectively. Besides circular folds and villi, the small
intestine also has microvilli Oui-kro \'TL-i; micmr = small), tiny
Figure 19.13 Structure of the small intestine.
i Circular folds, villi, and microvilli increase the surface area for digestion and absorption in the small intestine.
Lumen of small intestine
Lacteal
Simple columnar
epithelium
Lamina propria
Opening of intestinal gland
Lymphatic nodule
Musculans mucosae
Arteriole ■
Venule —
Lymphatic vessel
Circular layer of muscle
Enteric neurons
In muscularis
Longitudinal layer
ol muscle
MUCOSA
SUBMUCOSA
MUSCULARIS
SEROSA
Three-dimensional view ol layers ol the small intestine showing *1
Where are the cells located that absorb dietary nutrients?
488 Chapter 19 The Digestive System
projections of the plasma membrane of absorptive cells thai in-
crease the surface area of these cells (sec Figure 19 14). Thus,
digested nutrients can move rapidly into absorptive ceils.
Intestinal Juice
Intestinal juice, secreted by the intestinal "lands, is a watery
clear yellow fluid with a slightly alkaline pjrl of 7.6 that con-
rains some mucus. Together, pancreatic and intestinal juices
provide a liquid medium that aids absorption of substances
from chyme as they come in contact with die microvilli. In
cesdnaj enzymes arc synthesized in the absorptive cells that
line the villi. Most digestion by enzymes of the* small intes-
tine occurs in or on the surface ol these absorptive cells.
Mechanical Digestion in the Small Intestine
Two types of movements contribute to intestinal motility in
the small intestine: segmentations and peristalsis. Segmenta-
tions are localized contractions that slosh chyme back and
forth, mixing' it with digestive juices and bringing food parti-
cles mto contact with the mucosa lor absorption. The move-
ments are similar to alternately squeezing the middle and the
ends Etf ;i capped tube of toothpaste. They do not push the
intestinal contents along rite tract.
After most of a meal has been absorbed, segmentation
Stops; jit.-rist.ikis begins in the lower portion ot the stomach
and pushes chyme forward along a short stretch of small in-
testine. The peristaltic wave slowly migrates down the small
intestine, reaching the end of the ileum in 90 to 120 minutes.
Then another wave of peristalsis begins in the stomach. Alto-
gether, chyme remains in the small intestine lor 3 to 5 hours.
Chemical Digestion in the Small Intestine
The chyme entering cfoe small intestine contains partially di-
gested carbohydrates and proteins. The completion of diges-
tion in me small intestine is a collective effort or* pancreatic
the final products of digestion are ready for Absorption.
Starches \\\m\ dcxirins not reduced to maltose by the rime
eJiyme Leaves the stomach are broken down by pancreatic
amylase, an enzyme in pancreatic juice that acts in the small
inivsiine. Three enzymes located at the surface of small in-
u-.tin.il absorptive cells complete the digestion or disaecha-
rides, breaking them down into monosaccharides, which are
small enough to be absorbed. Maltose splits maltose into two
molecules of glucose. Sucrose breaks sucrose into a molecule
of glucose m-\{\ a mdleeafe of Brtictose. Lactase digests lactose
into a molecule of glucose and a molecule of galactose.
In some people the absorptive cells of the Small intestine
fail to produce enough lactase. This results in a condition
called lactose intolerance, in which undigested lactose in
chyme retains fluid in the feces, and bacterial fermentation
of lactose produces gases. Symptoms of lactose intolerance
include diarrhea, gas. bloating, and abdominal aramJH
vlier consumption ol milk and other dairy products. Tm
severity of symptoms varies from relatively minor to suffi-
ciently serious to require medical attention.
Enzymes En pancreatic juice (trypsin, chymotrypsin, am
tase, and earboxypeptidase) continue the digestion of pro-
teins begun in the stomach, though their actions differ soma!
what because each splits the peptide bond between different
amino acids. Protein digestion is completed by peptulasd
enzymes produced by absorptive cells that line the villi. 1 "he
final products of protein digestion arc amino acids, dipepj
tides, and tripeptides.
in an adult, most lipid digestion occurs m the small int
tine. In the Ersi step of lipid digestion, bile salts cinulsi
large globules ol triglycerides and lipids into small lipid
ules. giving pancre.irie lipase easy access. Recall thai tdfg|
elides consist ol a molecule ol glycerol with three ;uu.
fury acids (see Figure 2.10 on page 53). In the second 1
pancreatic lipase, found in pancreatic juice, breaks dowaJ
triglyceride molecule by removing two of the three |
acids from glycerol; the third remains attached Co tl
erol. Thus, fatty acids and monoglycerides are the caul prnj*
UCtS ot triglyceride digestion.
Pancreatic juice contains two nucleases; rihoimc
which digests RNA, and deoxyribonnckase, whicj
D\"-V. The nucleotides that result from the action of the
nucleases arc further digested by small intestinal eir/.n
into pentoses, phosphates, and nitrogenous biases,
[able 19.1 summarizes the enzymes thai contributcB
ilieorion.
Absorption in the Small Intestine
.Ml the mechanical and chemical phases of digestion iiniiii
iwovtfh down through the small intestine are divert
changing food into molecules that can undergo ahm {
Recall that absorption refers to the movement of smailiT|
cules through the absorptive epithelial cells or the nni
into the underlying blood and lymphatic vessels. About]
of all absorption takes place in the small intestine, i
10% occurs in the stomach and large intestine. Vhsn
the small intestine occurs by simple diffusion, lacilitaicili|
fusion, osmosis, and active transport, Vnj umligest
absorbed material left in the small intestine is puss
rhe large intestine.
A bsorption of Monosaccharides
All carbohydrates are absorbed as monosaccharides, lib
\\m\ galactose are transported into absorptive cells ot lbs]
by active transport. Fructose is transported by hicilbtHj]
fusion (FigUM I'M hi OH page W). \fter ahsorpiHi
saccharides are transported out of the epithelial cdkliyi
Enzyme
Carbohydrate Digesting
Salivary amylase
Pancreatic amylase
Maltase
Sucrase
Lactase
Protein Digesting
Pepsin
Trypsin
Chymotrypsln
Carboxy peptidase
Peptidases
Lipid Digesting
Pancreatic lipase
cleases
Rlljonuclease
Deoxyri bo nuclease
Table 19.1 Summary of Digestive Enzymes
Source
Substrate
Salivary glands.
Pancreas.
Small Iniesiine
Small iniesiine.
Small intestine
Stomach (chief cells).
Pancreas.
Pancreas.
Pancreas.
Small intestine.
Pancreas.
Pancreas.
Pancreas.
Starches.
Starches.
Maltose.
Sucrose.
Lactose
Proteins-
Proleins.
Proteins.
Amino acid at carboxyl (acid)
end ol peptides.
Amino acid at amino end of
peptides and dipaptides.
Triglycerides (lars) that have been
emulsified by bile salts.
Ribonucleic acid.
Deoxyribonucleic acid.
Small Intestine 489
Product
Maltose (disacciiande).
maltotnose (trisaceharide).
and dextrins
Maltose, maltotnose,
and dextrine
Glucose.
Glucose and fructose,
Glucose and galactose.
Peptides.
Peptides.
Peptides.
Peptides and
amino acids.
Peptides and
amino adds.
Fatty acids and
monoglycerldes
Nucleotides.
Nucleotides,
irjteil diffusion into the blood capillaries, which drain into
^ of the villi. From here, monosaccharides arc carried
irvia the hepatic portal rein, then through the heart
bathe general circulation (Fi
WrrptioH of Amino Acids
break down dietary proteins into amino acids,
s, and tripeptides, which are absorbed mainly in the
mlcnuin and jejunum. About half of the absorbed amino
■tare present in food, but half come from proteins in df-
.1, fujees and de^\ cells that slough off the mucosa!
Bio adds, dipeptides, and tripeptides enter absorptive
J of the villi via active transport. (Figure l () . 14a). Inside
jftthelial cells, peptides arc digested into amino acids.
llVl via diffusion and enter Mood capillaries. Like
Saccharides, amino acids are carried in hepatic portai
the liver 1 1 igurc 19.14b). [fnot removed by liver
lino acids enter the general circulation, From there.
r cells take up amino acids for use m protein synthesis
reduction.
mm of Ions and Water
Live cells lining the small intestine also absorb most ol
Mud water that enter the C il tract in food, drink, and di-
Uvmiu: secretions. Ma|or ions absorbed in the small intestine
include sodium, potassium, calcium, iron, magnesium, chloride,
phosphate, nitrate, and iodide. All water absorption in the Gl
tract, about 9 liters (a little more than 3 gallons) dairy, occurs
via osmosis. When monosaccharides, amino acids, peptides,
and ions are absorbed. they "pull" water along In osmosis.
Absorption of Lipids and Bile Salts
Lipases break down triglycerides into monoglycerides and
fatty acids. The flatty acids can be either short-chain I'.un
acids (with fewer than 10-12 carbons) or long-chain fatty
acids. The short-chain fatty acids are absorbed via simple dif-
fusion into absorptive cells of the villi and then pass into
blood capillaries along with monosaccharides and amino
acids I ]v.l-ki). Bile saJts emulsify the larger lipids,
forming' many micelles (mi-SKI.Z - small moiwefsi. tiny
droplets thai include some bile salt molecules along u'lth the
long-chain fatly acids, nionoglycei'idcs. cholesterol, arid
other dietary lipids (Figure 19.14a). From micelles, these
lipids diffuse into absorptive cells of the villi where they are
packaged into chylomicrons, large spherical particles that are
coated with proteins. Chylomicrons leave the epithelial veils
via cxoeyrosis imtl enter lymphatic fluid within a lacteal.
Thus, most absorbed dietary lipids In pass the hepatic portal
490 Chapter 19 The Digestive System
Figure 19.14 Absorption of digested nutrients in the small intestine. For simplic-
ity, all digested foods are shown In the lumen of the small intestine, even though some
nutrients are digested ai the surlace of or in absorptive epithelial cells of the villi.
Long-Chain fatty acids and monoglycerides are absorbed into lacieais: other products
of digestion enter blood capillaries.
Lumen of
small intestine
Glucose and
galactose
Microvilli
Fructose
Actjve
transport
Facilitated
diffusion
Dipeptides
Tripeptides
Active
transport
Short-chain _
(any acids
■
Long-chain
/a\"^ fatty acids
Micelle Monoglycerides
Simple
diffusion
. Simple .
diffusion
Epithetfal
cells of villus
Monosaccharides
^^. Facilitated
diffusion
Amino acids
Diffusion
*■
Diffusion
■*■ o
To blood
capillary
of a villus
Triglyceride
lacteal
us
Chylomicron
(a> Mechanisms lor movement of nutrients through absorptive epithelial cells of the villi
Left subclavian
vein
Heart
o,
Short-
chain
fatly acid
Liver
\
_ Hepatic
portal Amino acid
Thoracic duct - — |l( vein
^r Monosaccharide -
Venule
Villus (greatly enlarged)
Chylomicron
Blood
capillary
Lacteal
Arteriole
Bioo
Lymphatic vessel ^
"^ ' Lymph
(b) Movement of absorbed nutrients Into the blood and lymph
How are fat-soluble vitamins (A, D, E, and K) absorbed?
iruhiuon because they enter lymphatic vessels instead of
capillaries. Lymphatic fluid caminu chyloinkrons
he small intestine passes into the thoracic duct and in
ic course empties into the left subclavian vein (Figure
I, As blood passes thrcjugh capillaries in adipose tissue
and the liver, chylomicrons are removed and their lipids are
•Stored lor I mure use.
When chyme reaches the ileum, most of the bile salts are
kirbsorhed anil returned by the blood to the liver for reev-
pmg. Insufficient bile salts, ihw to either obstruction of the
nets or liver disease, can result in the loss of up to 40%
lilieuin lipids in feces due to diminished lipid absorption,
ikorptjoti of lltam his
Fat-soluble vitamins (A, D, E, unci K) are Included along with
htestcd dietary lipids in micelles and are absorbed via simple
Bffusion. Most water-soluble vitamins, such as the U vitamins
ii. . liamin {.. are absorbed by simple diffusion. \ nam hi B L .
Ipust be combined widi intrinsic factor (produced by die stom-
• lor its absorption via active transport in the ileum.
|| CHECKPOINT
1J. In what ways are the mucosa mkI submucosa of the small
intestine adapted for digestion \mA absorption;
J8. 1 \plain the function c » I each digestive enzyme.
Large intestines 491
19. Define absorption. I low are the end products of carbo-
hydrate and protein digestion absorbed? I low are the
end products of lipid digestion absorbed?
20. P>\ what routes do absorbed nutrients reach the liver"-
LARGE INTESTINE
OBJECTIVE • Describe the location, structure, and
functions of the large intestine.
The large intestine is tile Ijsi part of the ( d tract. (tS QVW&B
functions are the completion of absorption, the production of
iciiain vitamins, the formation of feces, and tin- expulsion of
feces from the body.
Structure of the Large Intestine
The large intestine averages about 6.5 cm (.2.5 in.) in diame-
ter and about LS m (5 It) in length. It extends from the ileum
tO the 8JWBS and is attached to the posterior abdominal wall
l>> its mesentery (.see Figure [9.3b), The large intestine lias
four principal regions: cecum, colon, rectum. .uu\ mal canal
(Figure I9J -\.
Rgure 19.15 Anatomy of the large intestine.
The regions of the large Intestine are the cecum, colon, rectum, and anal canal.
TRANSVERSE COLON
1
RECTUM
ANAL CANAL
ANUS
(a) Anterior view of large intestine showing
major regions
DESCENDING
COLON
Longitudinal
band of smooth
muscle
SIGMOID
COLON
Rectum
Anal canal
Anus
(b) Frontal section of anal canal
Internal ami
sphincter
(Involunlaiy)
External anal
sphincter
(voluntary)
What are the functions of the large intestine?
492 Chapter 19 The Digestive System
At the opening of the ileum into the large intestine is a
valve called the ileocecal sphincter. It allows materials from
the small intestine to pass mi" the large intestine. Inferior to
the ileocecal sphincter is the first segment of large intestine.
called die cecum. Attached to the cecum is a twisted coiled
cube catted the appendix.
3 he open end ol the cecum merges with the longest per-
il. >n of the large intestine, called the colon ( = rbnd passage).
The colon is divided into ascending, tea us verse, descending,
ami Sigmoid portions. I lie ascending colon ascends on tile
right side of the abdomen, reaches the undersnrfece of the
and turns to the left. The colon continues across the
abdomen to the left side as the fran.nersc colon. It curves be-
neath the lower border of the spleen on the left side and
passes downward as the descending colon. The S-shaped
sigmoid colon begins near the iliac crest of the left hip hone
and ends as the reefttm.
i he last 2 to 3 cm (1 in.) ol the rectum is called the anal
canal. The opening of the anal canal to die exterior is called
the anus. It has an internal sphincter of smooth (involuntary)
muscle and an external sphincter of skeletal (voluntary) tDOS
cle. Normally, the anal sphincters are closed except during
the elimination o! feces.
The wall of the large intestine contains the typical four
layers found in the rest of the (il tract: mucosa, stihmiicosa.
muscularis, .)\n\ serosa. The epithelium of the mucosa is sim-
ple columnar epithelium that contains mostly absorptive cej
ami goblet cells i 19.16). The cells form long tuhffl
called intestinal ^hnnis. The absorptive cells function priraaJ
fly in ion ami water absorption. The goblet cells secrete inii-
COS that lubricates the contents of the colon. Lymphatic nod]
ules a I KB are found in the mucosa. Compared to the small
intestine, the mucosa of the large urtestme does not haved
many structural adaptations thai increase surface area. Then
are no circular folds or villi; however, microvilli of the ab-
sorptive cells are present. Consequently, much more absorp-
tion occurs in the small intestine than in the large \\\u ■
The muscularis consists of" an external layer ol" longitudinal
muscles and an internal layer of circular muscles. 1'ulila'
other parts of the gastrointestinal tract, the outer lonjnttfdi-
nal layer of the muscularis is luuulled into three I < oi^mniioal
hands that run the length of most of the large intestine (see
e l l] I Ml. Contractions of the muscularis gather the
colon into a series of' pouches, which give the colon a puck
ercd appearance.
Polyps in che colon are generally slow -developing benira
growths that arise from the mucosa of the large inn. mm
ten. they do not cause symptoms. If symptoms dt
include diarrhea, blood in die feces, and mucus disc
from the anus. The polyps are removed by colonuso
singer)' because some of them may become cancerous.
Figure 19.16 Structure of the large intestine.
Intestinal glands lormed by absorptive cells and goblet cells extend the full thickness of the mucosa.
Lumen of large intestine
""
Openings of
Muscuians mucosae
Lymphatic vesse
Arteriole
Venule
Circular layer ol muscle
Enteric neurons in muscularis
Longitudinal layer of muscle
Three-dimensional view ol layers of the large intestine
How does the muscularis of the large Intestine differ from that of other parts of the Gl tract?
- MUCOSA.
_-SUBMUCOSA
-MUSCULARIS
SEROSA
Digestion and Absorption
In the Large Intestine
The passage of chyme from the ileum into the cecum is regu-
lated by tlit- ileocecal sphincter. The sphincter normally re-
paitte slightly contracted so that the passage of chyme is
iiMf.illy a slow process. Immediately niter a meal, a reflex
"i' risili p< i istalsis, forcing any chyme in the ileum into the
Peristalsis occurs in the Luge intestine m .1 slower
ban in other portions of the Gl tract. Characteristic of
Bie large intestine is mass peristalsis, 3 strong peristaltic wawe
icg'ins in the middle ol the colon and drives the colonic
nrs into rhc rectum, hood in Lite stomach initiates mass
fttstalsis, which usually takes place three or lour times a day,
Muring or immediately after -.1 meal.
The final srage of digestion occurs in die colon through
liviiy of bacteria ihat normally inhabit the lumen. The
lanJs nl the large intestine secrete mucus but no enzymes.
.1 ferment any remaining carbohydrates and release
fdrop-cii, carbon dioxide, and methane gases. These gases
tribute to flatus (gas) in the colon, rertned jLtatiaicc when
is excessive, Bacteria also break down die remaining pro-
I \u amino acids and decompose bilirubin to simpler pig-
cluding scercdbjlio, which give feces their brown
■, Several vitamins needed for normal metabolism, ra-
111I111L' some B vitamins and vitamin K. are bacterial prod-
t that arc absorbed in the colon.
Uthough most water absorption occurs in the small in-
feline, the large intestine also absorbs a significant amount
Kb large intestine also absorbs ions, including sodium and
Monde, and some dietary vitamins.
time chyme has remained in the large mtcsime 3
10 hours, it has become solid or semisolid as a result of
r absorption and is now called feces. Chemically; feces
water, inorganic salts, sloughcd-off epithelial cells
■.the mucosa of the gastrointestinal tract, bacteria, prod-
rs nf bacterial decomposition, tmabsorbed digested rnateri-
IQtl indigestible parts ol lood.
10 Defecation Reflex
nltic movements push fecal material from the sigr
[liiU'oliin into the rectum. The resulting ili.sten.sion ol the
til-wall stimulates stretch receptors, which initiates a ehje-
m reflex thai empties the rectum. Impulses from the
nul cord travel along parasympathetic nerves to the de-
eding colon, sigmoid colon, rectum, and anus. The result-
Egontraction ol the longitudinal rectal muscles shortens
. n, 1 hereby increasing the pressure within it. This
ilus parasympathetic stimulation opens the internal
meter. The external sphincter is voluntarily controlled. If
f-vohmtanli relaxed, defecation occurs and the feces ate
1 ii the .mux it' it is voluntarily constricted.
Phases of Digestion 493
defecation can he postponed. Voluntary contractions of die
diaphragm and okiominal muscles aid defecation foj increas-
ing the pressure within the abdomen, which pushes the walls
of the sigmoid colon and rectum inward. If defi attOfl does
not occur, die feces back up into the sigmoid 1 olon mutl the
next wave of mass peristalsis stimulates the stretch receptors.
In infants, the defecation relle\ causes automatic eiuph u
the rectum because voluntary control of the external anal
sphincter has not yet developed*
Diarrhea (dl-a-RF.-a; $&- = through; rrhea - Sow} is tio
increase in the frequency, volume, and fluid content ofthfi
feees caused by increased motility of and decreased
sorption by the intestines. When chyme passes loo uuiekly
through rhc small intestine and feces pass too quickl)
through the large tJltesdhe, there is not enough turn
absorption. Frequent diarrhea can i-esull in dehydration
and electrolyte imbalances. Excessive motility mav be
caused by laelose intolerance, stress. mu\ microbes that ir-
ritate 1 he gastrointestinal mucosa.
Constipation (kon'-sti-PA-shun,; am- = together; jgfe-
" to press) refers 10 infrequent or difficult defecation
caused by decreased motility of the intestines. Because the
feces remain in the colon for prolonged periods, excessive
water absorption occurs, and the feces become dry and
hard. Constipation may be caused In poor habits (delating
defecation), spasms of the colon, msufhdi-ni liber in ilk-
diet, inadequate fluid intake, lack of exercise, emotional
stress, or certain drujjs.
■ CHECKPOINT
21. What activities occur m the large intestine to change its
contents into feces:
22. What is defecation and how does it occur?
PHASES OF DIGESTION
objectives • Describe the three phases of digestion.
• Describe the major hormones that regulate digestive
activities.
Digestive activities occur in three overlapping phases: die
cephalic phase, the gastric phase, and the intestinal phase.
Cephalic Phase
.During the cephalic phase of digestion. 1 he smell, sight,
smmd, or thought of' fi»,J scdvates neural centers in i/h:
brain. The brain then activates the facial (\'1U. ijJos.sopJjaryn-
Focus ON
M
Emotio.
Consumed by
Food
In addition to keeping Us alive, eating
serves countless psychological, social,
and cultural purposes. We cat to eele-
bratc, punish, comfort, defy, and deny,
lilting in response CO emoliona! drives.
mi.;Ii as feeling stressed, bored, or Bred,
rather than in response to true physical
hunger, is called mictiantd eating.
Food as I motional Rescue
Emotional eating is so common that,
within limits, it is considered well
anthill die range of normal behavior.
hasn't at one time or another
headed for the refrigerator after a bad
day" Problems arise when emotional
eating becomes so excessive that it in-
terferes with health. Physical health
problems include obesity and assocr-
aied disorders Mich as hypertension and
he. in disease. Psychological health
problems include poor self-esteem; an
inability to cope effectively with feel-
inc. of stress; and in extreme cases, eat-
ing disorders;
For emotional eaters, the drive to
eat often masks unpleasant feelings
such as boredom, loneliness, depres-
sion, anxiety, an^cr, or fatigue. Eating
provides comfort and solace, numbing
pain and "feeding; the hungry heart."
Some emotional overeaters say that
stuffing themselves with food heticrai.es
a metaphor for suppressing undesirable
feelings.
Eating may provide a biochemical
"lix" is well. Emotional eaters Ly pi call)
overeat carbohydrate foods (sweets and
starches), which may raise brain sero-
tonin levels and lead to feelings of rc-
lasaiiou. Food becomes a way to self-
medicate when negative emotions arise.
( onsumed U\ bond
In extreme cases, eatmg becomes an
addiction, and the drive to consume ex-
cessive amounts of food begins to take
avei i person's life. People with bu-
limia or hinge-eating disorder have an
overwhelmingly urgent and totally un-
controllable drive to car, causing them to
consume huge volumes of food several
times a week, sometimes several times a
day. People with bulimia try to purge the
calories they have consumed by vomit-
ing, exercising excessively, or using la\a-
ti\cs and diuretics, but people vv-i ih
I hi ige-eatmg disorder usually do not.
Fating disorders can he very dnn-
iu rous and even lethal. reqtririlM
prompt, comprehensive, and in-deptl
professional treatment thai helps
cope with the underlying psychological
issues. "Therapy for emotional carers re-
quires addressing the emotions thai
ger overeating and devising effective
coping strategies that eliminate the
m deal with stress by overeating.
Why might repeated attempts to lose might With vtery restt ictive diets Itm
emotional overeating?
geal (IX), and vugus (X) nerves, The facial and glossopharyn-
geal nerves stimulate the salivary glands to secrete saliva, while
the V^gOS nerves stimulate the gastric glands to secrete gastric
juice. The purpose of the cephalic phase oi digestion is to pre-
pare the- mourn and stomach for food that is about to he eaten,
Gastric Phase
1 > food reaches the stomach, die gastric phase ol diges-
tion begins. "The purpose of this phase of digestion is to con-
tinue gastric secretion and to promote gastric motility. Gas-
tric secretion during the gastric phase is regulated by the
hormone gastrin. Gastrin is released from the G cells ol the
gastric glands in response to several stimuli: stretching oJ the
494
stomach In chyme, partially digested proteins in ehyuJfycB
feme in chyme, and the high pi I ol chyme due fn v
ence of" food in the stomach. Gastrin stimulates gastric giant!
to secrete large amounts of gastric juice. It also stre atM
die contraction of the tower esophageal sphincter to pptwl
re-ili ix of acid chyme into the esophagus, increases iiiotifilM
the stomach, and relaxes the pyloric sphincter, which pro-
motes gastric emptying.
Intestinal Phase
The intestinal phase of digestion begins once food eaten
small intestine. In contrast to the activities initiated .luritj
the cephalic and gastric phases, which stimulate stomachs]
Aging and the Digestive System 495
amy actiyi'ty and motility, i 1 currinir during the in*
final phase have inhibitory effects chat slow the exii of
nine from the stomach and prevent overloading of the duo-
denum with more chyme than it can handle. In addition, re-
ises occurring during the intestinal phase promote rhe
iiftihued digestion oi food.*; thai have reached the small in-
fos.
rite activities of the intestinal phase sire mediated bj two
hormones secreted by die small intestine: cfaolecysr
Itokinin and secretin. Cholecystokiniij (CCK) is secreted by
cells in intestinal glands of rhe small intestine in re-
t'i chyme containing amino acids from partially <ii-
proteins and tatty acids from partial!} digested triglyc-
Rdes. CCK stimulates secretion of pancreatic juice that is
pli in digestive enzymes, h also causes contraction of the
1 the gallbladder, which squeezes stored bile out of the
'" ladder into the cystic duct and through the common bile
tin addition. CCK slows gastric emptying by promoting-
inaction of the pyloric sphincter, and it produces satiety
feeling lull to satisfaction) b\ acting on the hypothalamus in
pt' brain.
Acidic chyme entering the duodenum stimulates the
: of si-cretin from S cells in intestinal glands of the
KDdll intestine. In turn, secretin stimulates the flow of pau-
juice that is rich in bicarbonate (HCO J ions to
tn the tcidic chyme that enters the duodenum from the
fch.
I V.J summarizes the major hormones that control
i-»n.
CHECKPOINT
arc the stimuli that cause the eephalic phase of
itinn:
Gnmpare and contrast thv. activities that occur during the
gastric phase ol digestion with those that occur duruig
me, intestinal phase of digestion.
AGING AND THE
DIGESTIVE SYSTEM
objective * Describe the effects of aging on the
digestive system.
Changes in the digestive system associated with aging include
decreased secretory mechanisms, decreased moiihu of the
digestive organs, loss of strength and tone of the muscular
tissue ami its supporting structures, changes in sensory feed-
back regarding enzyme and hormone release, and diminished
response to pam and internal sensations, in the upper portion
ol the CI tract, common changes include reduced sensilivitj.
to mouth irritations and sores, loss of taste, periodontal dis-
ease, difficulty in swallowing, hiatal hernia, gastrins, in.l
peptic ulcer disease. Changes that ma) appear in the small
intestine include duodenal ulcers, maldigestion, and malab-
sorption. Other pathologies that increase in incidence with
flge are appendicitis, gallbladder problems, |auiidice. cirrhosis
of the liver, and acute pancreatitis. Changes fo the large m-
usiiiu- sikh is constipation, hemorrhoids, and diverticular
disease may also occur. The incidence of cancer of the col.m
or rectum increases with age.
■ CHECKPOINT
25. List several changes in rhe upper ami lower portions of
i he ( ii tract associated with aging.
Now that our exploration of the digestive system is com-
pleted, you can appreciate the uum\ ways that this system
contributes to homeostasis of other bod) systems by examin-
ing locus on Homeostasis; The Digestive System on page
VKk Next, in Chapter 2(), you will discover how the nutrients
absorbed by the Gl tract arc utilized in metabolic reactions
hy the body tissues.
Table 19.2 Major Hormones That Control Digestion
[tone
Where Produced
Stimulant
Action
Stomach mucosa
(pyloric region).
Stretching of stomach, partially
digested proleins and caffeine in
stomach, and high pH o| stomach chyme.
Stimulates secretion. ol gastric [ui.ee.
i creases motility ol Gl trad and
relaxes pyloric sphincter.
Secretin
Intestinal mucosa.
Acidic chyme that enters the
small Intestine.
Stimulates secretion ol pancreatic
|uice rich in bicarbonate Ions.
bnoteystc
kinln
InlestlnaJ mucosa.
Amino acids and fatty acids in chyme
in small intestine
Inhibits gastric emptying, stimulates
secretion ol pancreatic juice rich in
digestive enzymes, causes ejection
of bile from the gallbladder, and Induces
a feeling ol- satiety (leeling full So
satisfaction).
FOCUS
ON
HOMEOSTASIS
Body System
For all body
systems
The Digestive System
Contribution of the Digestive System
The digestive system breaks down dietary nutrients into forms that can be absorbed and used
by body cells for producing ATP and building body tissues; absorbs water, minerals, and vita-
mins needed for the growth and functions of body tissues; and eliminates wastes from body titt-
sues in feces.
Integumentary
system
Skeletal system
Muscular system
Nervous system
The small intestine absorbs vitamin D, which the skin and kidneys modify to produce the hor-
mone calcitriol. Excess dietary calories are stored as triglycerides in adipose cells In the dermis
and subcutaneous layer.
S*
The small intestine absorbs dietary calcium and phosphorus salts needed to build bone extra-
cellular matrix.
The liver can convert lactic acid produced by muscles during exercise to glucose.
Gluconeogenesis {synthesis of new glucose molecules) in the liver plus digestion and absorb
tion of dietary carbohydrates provide glucose, needed for ATP production by neurons.
Endocrine
system
J
The liver inactivates some hormones, ending their activity. Pancreatic islets release insulin and
glucagon. Cells in the mucosa of the stomach and small Intestine release hormones that regu-
late digestive activities.
Cardiovascular
system
The Gl tract absorbs water that helps maintain blood volume and iron that is needed for the
synthesis of hemoglobin in red blood cells. Bilirubin from hemoglobin breakdown is partially
excreted in feces. The liver synthesizes most plasma proteins.
Lymphatic
system and
immunity
The acidity of gastric juice destroys bacteria and most toxins in the stomach.
Respiratory
system
The pressure of abdominal organs against the diaphragm helps expel air quickly during a fori
exhalation.
Urinary system
*
Absorption of water by the Gl tract provides water needed to excrete waste products in urine.
Reproductive
systems
v / \
Digestion and absorption provides adequate nutrients. Including fats, for normal developmental
reproductive structures, for the production of gametes (oocytes and sperm), and tor feta! grmfej
and development during pregnancy.
496
Common Disorders 497
COMMON
DISORDERS
Dietary Fiber and the Digestive System
wary fiber consists of indigestible plant substances, such as cellu-
rt, lignin, and pectin, found m fruits, vegetable grains, and
(OS, Insoluble fiber, which docs HOI dissolve in water, includes the
Rural parts of plums such as Fruit and vegetable skins and the
oaring around wheat and corn kernels, insoluble fiber passes
; the <■ .'I traei largely unchanged and speeds up the passage
il through the tract. Soluble fiber, which does dissolve in
■nns .1 gel that slows tin- passag< of materials through chc
:i. h is found in abundance in beans, oats, barley, broccoli,
pies, and drras fruits. It lends to slow the passage til ma-
lign the tract
•u.-pk- who house a fiber-rich diet may reduce their risk of de-
obesity, diabetes, atherosclerosis, gallstones, hemorrhoids.
i>. appendicitis, and colon cancer. Insoluble fiber may
ptotcel ngainsi colon cancer, mv\ soluble liber may help lower
olcsterol level.
Dental Caries
)ml caries, or tooth decay, involves a gradual deminer.ili/aiioji
Bltraimg] of the enamel and dentin by bacterial acids. If untreated,
(j-iiiu- microorganisms may invade the pulp, causing inflammation
i .!,:crion with subsequent death of the pulp. Such leedi
Btfttd by root canal therapy.
[periodontal Disease
HtnitMl tlise/ise relets to j variety of conditions characterized bj
pjiumiaaon and degeneration of the gums, hone, periodontal liga-
■Wil. iivl * riiienuiin. Periodontal diseases are often caused by poor
by local irritants, such as bacteria, impacted food, and
nK-.mii :;niHke;orbya pi Mir "bite."
jpeptic Ulcer Disease
percent of die I S. population develops peptic ulcer dis-
Tt,(PlD) each year, \n nicer is a cratcrlikc lesion m .1 membrane;
1 1 levelop in areas of the C ,1 tract exposed to acidic gastric
1 I peptic ulcers; The most common complication of
tit ulcer» is bleeding, which can lead to anemia. In acute cases,
can lead to shock and death. Three distinct causes ol
o;mr/.ed: (1) the bacterium Helicobacter pylori, (-> nons-
nnti-mfkminatory drugs (NS-UDs) such as aspirin, and ( <i
. ton of! ICI
mdicitis
is an inflammation ol ! ippendfc. Appendectomy
mtival of the appendix) is recommended in all suspected
cases because it is safer to operate than to risk gangrene, rupture,
and peritonitis.
Colorectal Cancer
Colorectal cancer is among the deadliest of malignancies. An in-
herited predisposition contributes to more than half of all cases
p£ colorectal cancer. Intake of alcohol and diets high m animal tat
and proteitl are associated with increased risk ol colorectal can-
cer; dietary filler, retinoids, calcium, and selenium tnaj be pnu.ee
Give. Signs and symptoms of colorectal cancer include diarrhea,
c.insiipitiu.M. erainping, didomirial pain, ,\\ti\ rectal bleeding.
Screening ton colorectal cancer includes testing tor Mood m the
feces, digital rectal examination, sigmoidoscopy, colonoscopy, md
barium enema.
Diverticular Disease
Diverticulum is die development of diverticula, saclike uiiip.
ings of the wall of the colon in plat es where the nrasculnris has l>.
come weak. Many people who develop di\ erticulosis have npsymp-
ujiii-, ami experience no complications, About 1.5% •»( people with
divcrticulosis evemualb develop an inflammation known as diver-
ticr/litis, characterised by pain, either constipation or inc..
frequency of defecation, nausea, vomiting, and km-grade fever.
Patients who change to high-liber diets often show marked relief of
symptoms.
Hepatitis
Hepatitis is ,111 inflammation of the liver caused by virus; 5, ,l, ■ ■
and chemicals, including alcohol.
Hepatitis A (infections hepatitis), caused h\ the hepatitis \
virus, is spread by fecal contamination of food, Joining. loy v
utensils, and so forth {fecal- oral route). Ii does 101 cause I
liver damaji
Hepatitis B, caused In the hepatitis B virus, is spread prima
by sexual contact and contaminated syringes and transfusion equip-
ment It can also be spread h\ an\ secretion \ ia saUVa and te.n
patitis B can produce chronic liver infhmun.uioi av.nl
able for hepatitis Ii and are required for * ui.un individuals, SUGfl as
health-care provi<!ers.
Hepatitis C, caused by the hepatitis ( virus, is clinically similar
to hepatitis B. It is often spread by blood Transfusions and can CUUSt
cirrhosis and liver cancer.
Hepatitis 1) is caused In the hepatitis D \irus. It is transmitted
like hepatitis II. A person must be infected with hepatitis IJ to con-
tract hepatitis I) I Icpatiris D results in. severe liver damage and has
a fatality rate higher than that due to infection with hepatitis H virus
alone.
Hepatitis E is caused by die hepatitis I urns -.mA is spread like
hepatitis \. Although it does not cause chrome liver disease, the he-
patitis ]•'. virus is responsible for a very high death rate in pregnant
women.
498 Chapter 19 The Digestive System
MEDICAL TERMINOLOGY AND CONDITIONS
.Ittonxj/i nervosa A chrome disorder characterized by self-induced
weight loss, negative perception <>l body Image, and phvsioloej-
changes thai result Itorn mn i iti. »nnl depiction. Patients have
a fixation on weight control arid often abuse laxatives, which
(yOrsens their fluid arid electrolyte imbalances arfd nutrient de-
ikks. The disorder is found predominantly in young, sin-
femflles, and a may be inhaijcwL Individuals may become
emaclatced and mac ulrnnatel) die of starvation or one of its
complications.
Bulimia (Am- = ox; -limia = hunger) or binge- purge syndrome \
disorder charade ciked by overeating at teast twice a week fol-
lowed by purging by sell-induced vomiting, strict dieting or
tastine, vigorous exercise, or use of Lix.it ives or diuretics; it oe-
curs in response to tears of being; overweight, stress, depres-
sion, and physiological disorders such .is hypothalamic tumors.
Canker sore 0KAM( .-ker.) Painful ulcer on the mucous membrane
of the mouth that iflfeets females more often than moles, nsu-
iil 1 y between ages 10 and 40: ii may be SB autoimmune reaction
or result from a food allergy.
Cbotecystitis (ko'-le-sis-Tl-ris; chute- - bile; tyg£- - bladder; -iris =
inflammation of) in some cases, .m autoimmune inflammation
of die gallbladder: other cases are caused In ■ ihsti union of the
;u. duet by Ink' ^Umcs.
rbosis Distorted or scarred liver as a ivsnh. O'J chronic inflamma-
tion ikii- to lu-|i.itti,'s. chemicals Ehai destroy hepatocyteS, para>
sites that infect the liver, or. alcoholism: the hepatocytes ate re-
placed by fibrous or adipose connective tissue. Symptoms
include jaundice, edema in the leys, uncontrolled bleeding:, and
increased sensitivity to drugs.
Colostomy (ko-I.OS-to-me: -stowy = provide an opening) The di-
version ol the tee;] I stream through an opening in the colon,
creating a surgical "■stoma" (artificial opening) that is affixed io
the exterior of the abdominal wall, litis opening ci
substitute anus through which feces are eliminated nitiu!
VVOfctf mi tlie abdomen.
Inflammatory bowel disease (in-l I.AAl .i-to'-re BOW I
tluu exists in two lorms: (I) Crohn's d is
the gastrointestinal tract, especially the distal ilium .uttlprnj
mal colon, in which the inflammation nun eMeml
mucosa through the serosa, and (2) u leer alive colitis,
inarion of the mucosa of the gastrointestinal n.n'i. u
ited to the large intestine and usuallj accompanied Yinfl
bleeding,
Irritable bowel syndrome (IBS) Disease of the entire gnstrciia
nal tract in which a person reacts to stress by Jcvclopjrmsyt]
tonis (such as cramping anil abdominal pain) associated with
leriiatiug patterns ol diarrhea and constipation. | \ (l v
amounts ol mucus mm appear in feces; other symptom?
elude flatulence, nausea, and Ions of appetite.
Malocclusion (mal'-o-KLOO-zhun; mal-- bad; ocdusion = nM
f&geriier) Condition in which the surfaces of the maxillary
per) and mandibular (lower) teeth fit togethei poorly.
Nausea (NAW'SS-a = seasickness) Discomfort charaeterimlb
loss of appetite and the sensation of impending vomiting^
causes include local irritation ofthe ga s i rouuesti mil tract, u^
temtc disease, brain disease or injury, overexertion, ui
lects ol tnedicatiou or. drug Overdose.
Ih/veler's diarrhea Infectious disease of the gastrointestinal tn
that results in loose, urgent bowel movements; iT.uupriii:. j'n
dnminai pain; malaise; nausea; and occasionally level t
dration. It is acquired through ingestion til food or water co
laminated with fecal material typical!) containing I i.icKri
(especially Escherichia ,-oliv, druses or protozoan pat»fi(e§
less common cause.
'H'
STUDY OUTLINE
Introduction (p. 472)
1. The breakdown of larger tood molecules into smaller molecules
is called digestion; the passage of these smaller molecules into
blood and lymph is termed absorption,
2. The organs thai collectively perform digestion ami absorption
constitute the digestive system.
Overview of the Digestive System (p. 473)
1. The Cil tract is a continuous rube extending from the mouth to
the anus.
2. The aceesson iligcsii'.c organs tncliMk i. | h, tongue, sali-
vary glands, fiver, gallbladder, and pancreas
3. Digestion includes six basic processes: ingestion, secretion,
mixing and propulsion, mechanical anil chemical digest ion, ab-
sorption, and defecation.
Layers of the Gl Tract and Omentum (p. 474)
1. The basic arrangemem of layers hi tnosi of the gascrointestinaJ
tract, from the inside to the outside, is the mucosa, submiii
imisriilaris, ;unl serosa.
2. Parts of" the pcrjioncum include the incseiiten iihl
omentuiii.
Mouth (p. 476)
1. The mouth is formed by the cheeks, hard and soli p.tl.itc
arid tongue, which aid mechanical digestion.
2. Tlie tongue forms i he lie. or of the oral canity Ii i
skeletal muscle covered with raucous membrane. I lie
.Shi lace and lateral areas ofthe tongue are covered with
lac. Some papillae contain taste buds.
3. Most saliva is secreted bj the sahvaa glands, which lie uuujj
the mouth ami release their secretions into duets tltat ennj
iii". the riral cavity. There arc three pairs of saliv.m ji:mif
parotid, submandiliiilar. ^m.1 sublingual. Saliva luhru
arid starts the chemical digestion of carbohydrates. Saliviii
Controlled by the autonomic nervous system.
4, 1 he tcedi, or denies, project into the mouth and arc adapted
I for mechanical digestion. \ typical tooth consists of three prin-
L-i | >;i i portions; crown, root, and neck. Teeth ate composed pri-
marily of dentin and ate covered b$ enamel, the hardest sub-
stance in tlit body. 1 taians have two sets of teeth: deciduous
.in. I permanent.
Through mastication, food is mixed widi saliva and shaped mm
,i bolus.
'4 Saliva n amylase begins the digestion of starches in the mouth.
Pharynx and Esophagus (p. 478)
L 1"*hih1 that is .swallowed passes from the mouth into die
ornphan nx.
From the oropharynx, food passes into the laryngophan n\.
pe esophagus is a muscular cube that connects the pharynx to
the stomach.
[lowing moves a bolus from the mouth CO the Stomach by
feistaJsis, 1 1 consists of a voluntary stage, pharyngeal stage (in-
lolttntary), and esophageal stage finvoiunun >.
Stomach (p. 480)
j. The stomach connects die esophagus to the duodenum.
Tin- iii-.im regions oFfJic stomach are the cardia, fundus, body,
and pylorus.
oris mC the stomach lor digestion include rugae.; glands
ih.u produce mucus, hydrochloric acid, a protein -digesting en-
mnc (pepsin), intrinsic factor, and gastrin; and a three-layered
laris for efficient mechanical movement.
L Mechanical digestion consists of mixing waves that macerate
fuod and mix it with gastric juice, forming- chyme.
digestion consists of the conversion of proteins into
peptides by pepsin.
, ili; stomach wall is impermeable to tnost substances. Among
I; substance!! the stomach can absorb arc water, ions, ifapft-
: itry acids, some drugs, and alcohol.
^tncreas (p. 483)
- ..-us pass from the pancreas to the duodenum via the
iiu duct.
reatic islets (islets of Langerhans) secrete hormones and
constitute the endocrine portion of the pancreas.
ir cells, which secrete pancreatic juice, constirace the ex
• portion ol the pancreas.
puicreatic juice contains enzymes thai digest starch (pair.cn
mylase); proteins (trypsin, chymotrypsm, and car-
•sei: triglycerides t pancreatic lipase); and nucleic
i nucleases).
furor and Gallbladder (p. 484)
liver has left mm\ right lobes. The gallbladder ts a sac b-
; in a depression under the liver that stores and coneen-
hik produced 1% the liver.
BL 1, , liver are made up of lobules rhar contain hepa
liver cells), sinusoids, Kupfler cells, and a central vein.
uvtes produce bile thai is earned bj a duct system to the
plllibdilcr for concern ration and temporary storage.
Study Outline 499
4. Bites conrnluition to iligestion is the emulsilication of dietary
lipids.
5. The liver also functions in carbohydrate, lipid, and pn.iein me-
tabolism; processing "f drugs and hormones; excretion oj
bilirubin: synthesis of bile salts; storage of vitamins and miner-
il : phagocytosis; and acrivation of vitamin D.
Small Intestine (p. 486)
1. Idle small intestine extends from the pyloric sphincter to die
ileocecal sphincter. Ii is divided into the duodenum, the je-
junum, and die ileum.
2. The small intestine k highly adapted for digestion and absorp-
tion- Its glands produce enzymes and mucus, and the microvilli,
villi, and circular folds of its wall provide a large surface area
for iligestion and absorption.
>. ,Mei .-hanicat digestion in the small intestine involves segmenta-
tions and migrating waves of peristalsis.
4. Enzymes in pancreatic juice, bile, and the microvilli o| ih, fljj
sorpiivc cells of the small intestine bile break down disaccha-
rnles to monosaccharides: protein digestion is complei. I I
peptidase cn/yuies: (triglycerides are broken down into bitty
acids and monoglycerides by pancreatic lipase; and nucleases
break down nucleic acids to pentoses and nitrogenous bases.
5. Absorption is die passage »i nutrients from digested food in
the gastrointestinal tract into the blood or lymph, \bsorp-'
which occurs mostly in the small intestine, occurs bj means ol
simple diffusion, facilitated diffusion, osmosis, and active
transport.
6. Monosaccharides, amino acids, and short -chain fatty acids pass
into the blood capillaries-.
7. Long-chain fatty adds and moitogh/cerides are absorbed as
part of micelles., rcsynihcsi/.ed to t.ngha-i nie-, and ir.msporreil
in chylomicrons to the lacteal of a vill
S. The small intestine also absorbs water, electrolytes, -^^ vita-
mins.
Large Intestine (p. 491)
1. The large inn •stine extends from the ileocecal sphincter to the
anus. Its regions include die cecum, colon, rectum, and anal canal*
2. The mucosa contains numerous absorptive cells that absorb
water and goblet cells that secrete mucus.
t, Mass peristalsis k a Strong peristaltic w av e that drives die con-
tents of the colon into the rectum.
4. In the large intestine, substances are further broken down, and
some vitamins are synthesized through bacterial action,
5. The large intestine absorbs water, electrolytes, and vitamins.
6. Feces consist of Water, inorganic salts, cpiihclial cells, bacteria.
and undigested foods,
7. The elimination of feces from the rectum is called defecation.
Defecation is a reflex action aided bj voluntary contractions ol
i: iphragm and abdominal muscles am\ relaxation ol the <-\
ocFnatiraitfspAmceBR
Phases of Digestion (p. 493)
I. Digestive activities occur in three overlapping phases: cephalic
phase, gastric phase, and intestinal phase,
500 Chapter 19 The Digestive System
2, During the cephalic phase of digestion, salivary glands secrete
'.•-"liv.i -.mil gastric gtacls secrete gastric Juice in order to prepare
the mouth and stomach |<>r innd ||);U Is a hi ml CO be eaten.
$« I lit- presence ol food iti the stomach causes the gastric phase of
jestion, which promotes gastric juice secretion and gastric
motility.
4. During the inrcstin-.il phase ol digestion, fowl i-< dtgesjjed in the
small intestine. In addition, gastric rtidttlfty "id gastric secre-
rioi; decease in order i<> slovi the exit of chyme from the stom-
ach, which prevents the smaJJ intesrJiic from being overloaded
with more chyme than if cm handle,
5. The activities that occur during the- various phases of digcsdiM
are coordinated l>y hormones, fable 1 0.2 on page 4 ( >5 surra
ri/.es the major hormones that control digestion.
Aging and the Digestive System {p. 495)
1. General changes with age include decreased seereton, ul
nisms, decreased motility, and loss of ton*.
2. Specific changes may include loss of taste, hernias, peptic
disease, constipation, hemorrhoids, and diverticular disease;
12
SELF-QUI
1. Which of the following is NOT an accessor? digestive organ?
a. teeth b. salivary "hinds <.-. |i\<)- d. pancreas
■ _ £& i|i|'i.i;^!-.
2. ( Ifoewing food is an example of
a, absorption b. mechanical digestion c. secretion
cl. chemical digestion e. ingestion
3. Which ol the following is mismatched?
a, submucosal enteric nervous system Q NS)
b. inuscularis, lacteal c, serosa, greater- omentum
il. mucosa, villi e. serosa, viscera] peritoneum
4. Most chemical digestif, n OCCWtS in the
a. liver b. stomach c. duodenum d. colon
e. pancreas
5. Absorption is defined :ts
a. the elimination of solid wastes from chj digestive system
b. .i reflex action controlled In the autonomic tiervous system
c. the breakdown of foods by enzymes
d. i he passage of nutrients from the gastrointestinal cpaei into
the bloodstream
e. die mechanical breakdown of triglycerides
6. I In: exposed portions of the teeth that you clean with 9 tooth-
brush arc the
a. crowns b. periodontal ligaments c. roots
d. pulp cavities c. gingivae
7. The smell ol yom l.iv -rite lood cooking makes "'yom mouth
water"; this is due to
a, <vmp.iiitctn, siuiuii-itii.il o£th't salivary glands
b. tn-.wtic.uion
C, pai.isynipalhctir Stimulation ol the saliva!) glands
d. increased mucus secretion by the pharynx
e. the enteric nervous sj stem
A. p\ lone sphinctt
B. circular tulds
C. micelles
D. cystic duct
E. ileocecal splitnnj
i'". rugae
C chylomicrons
II. acini
H. Match the followinfp
a. carries bile
l>4 proteins combined with
triglycerides and cholesterol
c. surrounds die opcniiig
between the stomach and
duodenum
d. secrete pancreatic juice
e. increase surface area in
small intestine
f. bile salts combined' with
partially digested lipids
gr located be ween
the opening of the small
and huge intestine
h. targe mucosal fold*.
in stomach
9. which of the Allowing correctly describes the esophagi
a. Food enters the esophagus frotn tin- pyloric regie
the stomach.
b. The movement oftbotl through the entire esophi
<ler voluntary control.
c. It allows the passage ol thyme.
d. It produces several ciuymcs that aid in the diuotumj
food.
e. It is a muscular tube extending from the pharvns
stomach.
10. Jf an incision were made into the stomach, the tissuei
would be i tu in what order?
a. mucosa, muscularis, serosa. subnuK'osa
b. mucosa, inns, ufari'.. suhniucosa, serosa
c. serosa, inuscularis. mucosa, subintieosn
d. musculans. submucos;). mucosa, serosa
t\ serosa, inuscularis. submucosa. mucosa
1 1. A'losi water absoj ption in the digestive tract occurs in tk
a. small intestine h. stomach c. moutll d.
e. large intestine
Critical Thinking Applications 50
E. Which of the following would NOT result ln secretion oi
gastric juices in the stomach;?
a. secretion of gastrin
b. stimulation by the vagus nerves
c. the presence of piirr.ialk digested proteins
d. stretching of she stomach
e. stimulation by die sympathetic nervous system
% Bile
a. is produced in the gallbladder
b. is an cn/yine lhai breaks down carbohydrates
c. c'liuilsifies triglycerides
d. rs requtad for the absorption of ammo adds
c. enters the small intestine through the right hepatic dud
4. Winch of the following is [M< > 1 a function of the liver?
a. processinf new!) ahsorhed nutrients
|i. producing' envyenes that digest proteins
c. breaking down old red hlooi! c Us
pi fletoxin/ing certain poisons
oductng Wile
. 1 1 purpose of villi in the small intestine is to
a. aid in the movement of food dwOugfe the BJOnll intestines
I b. phagoeytr/e microbes
c, produce digestive eii/.yin -
(1, increase the surface area for absorption oi digested nutrients
e, produce acidic secretions
h of the follow ing is NO I* produced in the stomach?
.,. iotliimi bicarbonate (Nal IC< ' I
b. gastrin
c. pop si no yen
il. in
c. hydrochloric ackl (\ 1CI)
17. Which of the follow niLf is Mi 1 1 eon-eetlj paired?
a. esophagus, peristalsis
h. mouth, mastication
c. large iiHesune. in.iss peristalsis
d. small intestine, segmentations
e. stomach. emuisillcaiSon
18. The cu/yme pancreatic lipase digest iriclyccrides into
n. glucose.
b. amino acids
c. fan y acids and mnnoglyccrides
d. nucleic acids
e. aunb-.
19. Pfiee die following in the eon-eel order as food passes from die
small intestine:
L sigmoid colon
2. transverse colon
$. ascending colon
4. reel u in
5. cecum
6. descending colon
a. 1.^.2.6.5.4 bi 5. 1.6,2, 1.4 c. 4. I, 6. _\ S, 5
d. 2.3.5.6.4. I e. 5, 3.2.6,1.4
20. Lacicals function
a, in the absorption of lipids in ch\ lomicrons
b. to produce Ink- in the liver
c 111 1 he ahsorption of electrolytes
d. in the fermentation of carbohydrates in the large intestine
e. co produce salivary aiwj las
ICALTHINKING APPLICATIONS
uiu of live dentists think that VOW should chew sugarless
n. Inn all five think that you should brush your teeth. Why:
discussion around the bridge table was growing heated.
convinced that lactose intolerance is the cause ot
I: | . itiparion. (Jcrcrude insists that lactose intolerance has
ildiliitii! to do with bowel problems but is the cause til her
fearrrmrn. Of course, neither ol these ladies has eaten efflirj
1 1. for years (which may help explain their osteoporosis).
pif.iSL settle the argument.
put a plastic spider in hi- sisters drink as a joke. Onfortn-
teaclv, his mother doesn't think die joke was wcxj fuimj be-
his sister swallowed il and now they're all at the KR
tanergencT room), The doctor suspects that the spider may
have lodged ai i he junction ofthe stomach and the duodenum.
Name the sphincter .11 this function. Trace the patio taken bj
die plastic spider on its journey CO its neu home. What proce-
dure COUld llu doctor use I" View the interior nl iIr siriniach?
Wh.u siTii.-iures may be viewed hi the stpmaeh (besides the
spider):
4. Jerry hadn't eaten all tkj when he bough l a dried out. luke-
warm hot doe from a stTfiCt vendor lor lunch. \ lew Jioui- later,
he was a victim of fetid pOfeonJUg and was desperately seeking a
bathroom, Vfter vomiting several dines. Jem noticed thai he
was expelling a mei-nish-yeliow liquid. I he hot tlog may have
li.ni a bit shriveled, but it w.isn'i green! What is lite soul
this colored fluid-
502 Chapter 19 The Digestive System
^ANSWERS TO FIGURE QUESTIONS
1 9. 1 The teeth eut and grind food.
19.2 \rrvr. in its wall help regulate secretions and contractions
of the gastrointestinal tract.
19.3 Mesentery bunds die small intestine tcj die posterior abdominal
irafl
19.4 Muscles of die tongue maneuver food lor chewing, shame
food into .i bolus, force food m the back of the mouth Eor
swallowing, and alter the shape of the congui Ebi swallowing
arid speech production.
19.5 The main componeni of teeth k a connective tissue tailed
denim.
L9.6 Swallowing is bptfc voluntary and involuntary. Inn ml i< m I il
swallowing, carried out by skeletal muscles, is voluntary.
i jil.-imn of swallowing — moving- a bolus along; the
esophagus and into the stomach — involves peristalsis of
Miinoili muscle and is itnoluntary.
19.7 Alter a very targe meal. the stomach probably docs not have
rugae bet aose as the stomach fills, the rugate stretch out.
19.8 The simple columnar epithelial cells of the mucosa j re in
contact wiili food in die stomach.
19.9 (i cells, which secrete the hormone gastrin, are part fifths
endocrine system.
19.10 Pancreatic juice is a mixture of water, salts, bicarbonau
and digestive etwymes.
19. 1 1 Kuplk-r pells In the liver are phagocytes,
19.12 rhc iltaun is the loiigesl portidn^ die small intestine.
19. 1 3 The absorptive cells cover the surface qjf the villi.
19.14 Kat-soluhk- vitamins are absorbed by diffusion front micelles.!
19.15 Ttmcnonv i.t'iiu- targe intestine Include completion of aW
sorption, synthesis of certain vitamins, formation of feaa
ami elimination 61 fi ei •
19.16 The tnuscularis of the large intestine forms three longitudSj
n:d bunds that gather the colon into 6 scries of pouches
NUTRITION AND METABOLISM
chapter 20
Wk
i\\6 you know?
hen energy intake
{hire: many Calories you consume) exceeds energy
expenditure (how many Calories you bum), the ex-
tra energy is saved in the form of body fat. Over the
years excess fat storage can lead to obesity. The
[remedy f Eat less and exercise more, in order to cre-
I ate an energy imbalance that coaxes the body into
I using stored fat for fuel. Sounds simple, but many
[people have a very difficult time losing weight and
I keeping it off. Studies of people who win at losing
\wight have found that significant, lifelong changes
in eating and exercise behaviors are the key to
long-term weight control success.
Focus on Wellness, page 518
www wiley.com/co4lege/apcantral
± he food we eat is our
only source of energy for
I >erforming biological
work. Many molecules
needed to maintain cells and tissues can be made from build-
ing blocks within the body; others must be obtained in food
because we cannot make them. Food molecules absorbed by
the gastrointestinal (GT) tract have three main fates:
1 . 1» supply energy for sustain bag Life processes, Mich as active
transport, DNA replication, protein synthesis, muscle
contraction, maintenance of body temperature, and cell
division.
2. la s&Vje as building blocks for the synthesis of more complex
molecules, such as muscle proteins, hormones, :ind enzyflnes.
3. Stvntgc for fiitnrc use. For example, glycogen is Stored in liu-r
cells, and triglycerides are stored in adipose cells.
In this chapter we will discuss the major groups ol nutrients;
guidelines for healrh\ c;iimg; how each group of nutrients is
used for \TP production, growth, ami repair of the body; m\\\
how various factors affect die body's metabolic rate.
looking back to move ahead
Main Chemical Elements In the Body {page 23)
Enzymes (page 37)
Carbohydrates, Lipids, Proteins (pages 31-37)
Negative Feedback System (page 8)
Functions ol the Liver (page 485)
Hypothalamus and Body Temperature Regulation (page 254)
503
504 Chapter 20 Nutrition and Metabolism
NUTRIENTS
OBJECTIVES • Define a nutrient and identify the six
main types of nutrients.
• List the guidelines for healthy eating.
Nutrients are chemical substances m food that body cells use
for growth, maintenance, and repair- The six main types of
nutrients are carbohydrates, lipids, proteins, water, minerals,
and vitamins. Essential -nutrients are specific nutrient mole-
cules that die body cannot make in sufficient quantity to
meet its needs and thus mum he obtained from die diet. Some
amino acids, some Fatty acids, vitamins, and minerals are es*
•-L-nri.il nutrients. The structures and funcd'ons ol carbohy-
drates, proteins, lipids, and water were discussed in Chapter
2. In this chapter, we discuss some guidelines for healthy eat-
ing and the roles of minerals arid vitamins in metabolism.
Guidelines for Healthy Eating
Each gram of protein or carbohydrate in fond provides about
4 Calories; 1 cram of tat (lipids) provides about 9 Calories.
not know with certainty what levels and types of car-
bohydrate, fat, and protein are optimal in the diet. Different
populations around the world eat radically different diets that
are adapted to their particular lifestyles. However, many ex-
perts recommend the following distribution of calories:
50-60% from carbohydrates, with less ih;m 15% from sim-
ple sugars; less than 30% from fats (triglycerides are the I
type of dietary fat), with no more than 10% as saturated tars;
a , m I 1 1 ii .i 1 1 12—15 % from proteins.
The guidelines for healthy eating are to:
■ Eat a variety of bods.
■ M a i i un i n a h eal rh y u e i i; I u .
■ Choose foods low in fat, saturated fat. and cholesterol.
■ Bat plenty of vegetables, fruits, and grain products.
■ Use sugars in moderation only.
In 2005, the United Suites Department of Afficillture
(US DA) introduced a new food pyramid called My Pyramid,
which represents a jKrsmutlizcd approach to making healthy
food choices and maintaining regular physical activity. By
consulting a chart, it is possible to determine your calorie
level based on your gender, age. mi\ activity level. ( )nce this
is determined, you can choose the type and amount, of food
to be consumed.
If you carefully examine the My Pyramid in Figure 20J,
you will note that the sis color bands represent the live basic
food groups plus oils. Foods from all bands are needed each
i . \lso note that the overall size of the bands suggests the
proportion of food a person should choose on a daily basis.
The wider base of each hand represents Foods witb tittle or
no solid tats or added sugars and these foods should he se-
lected more often. The narrower top of each band represents
foods with more added sugars and solid fats, which should be
selected less frequently. The person climbing the steps Ls a
reminder of -the need lor daily physical activity.
As an example of how the My Pyramid works, letft J
sume based upon consulting a chart that the calorie lu
an lS-year-old moderately active female is 2000 Calori<
that of an I s-y ear-old moderately active male is 280(1 I
ries. Accordingly, it is suggested that the following
should be chosen in the following amounts:
Calorie level
2000
2B0C
FrUitS (includes ail fresh, frozen, canned,
Bfit) dried fruits and fruit juices)
Vegetables (Includes all fresh, frozen, canned,
and dried vegetables and vegetable |i.nces)
Grains (Includes all foods made from wheat.
rice, oats, cornmeal. and barley SUQl ! I I
bread, cereals, oatmeal, rice, pasta,
crackers, tortillas, and grits)
Meats and beans (includes lean meal, poultry,
Ush. eggs, peanul butter, beans, nuts, and
seeds)
Milk group (includes milk products and !oods
made from milk that retain their calcium
content such as cheeses and yogurt)
Oils (Choose mostly lats that contain
monounsajurated and polyunsaturated
tatty acids such as fish, nuls, seeds, and
vegetable oils)
2 cups 2.5 cups-
2.5 cups 3.5 CHOI
6 0Z 10 02 |
5.5 oz 7 o:
3 cups '-i.::/.
6 tsp 8 tsp
in addition, you should choose and prepare foods with
little salt In fact, sodium intake should be less than 2>00 tnfl
per day. If you choose to drink alcohol, it should head
sinned m moderation (no more than I drink per Jay m
women and 2 drinks per day for men), \ drink is defined!
1 2 o/. of regular beer. > oz of wine, or I J A oz of 80 proof dj
tilled spirits.
Minerals
Minerals are inorganic elements that constitute a bo
the total body weight and are concentrated most lk-;nilt i
the skeleton. Minerals with blown functions in the
include calcium, phosphorus, potassium, sulfur, soi
chloride, fluoride, magnesium, iron, iodide, manguj
cobalt, copper, /me. selenium, and chromium. Outers—
minum, boron, silicon, and molybdenum are present
may have no functions. Typical diets SUpplj .ulequ
amounts of potassium, sodium, chloride, and m,L
Some attention must be paid to eating foods dun prorij
Nutrients 505
1
Figure 20.1 My Pyramid.
fe£
ly Pyramid is a new personalized approach to making healthy food choices and maintaining regular
physical activity.
MEAT&
BEANS
5 ) What does the wider base ot each band mean?
i calcium, phosphorus, iron, and iodine Excess amounts
minerals are excreted in the urine and feces.
A major role of minerals is to help regulate enzyrnatic re-
ittis, Calcium, iron, magnesium, and manganese are pari
feme coenzymes. Magnesium also serves as a catalyst lor
i conversion of \DP to \TP. Minerals such as sodium and
horns work in buffer systems, which help control the
';h,i both fluids. Sodium also helps regulate the osmosis of
Brand, with other ions, is involved In the generation of
jtt-e impulses. lable 20. J describes the roles of several nun-
Kilsm Mirions hod}- functions.
[Vitamins
,jtnk nutrients required in small amounts to maintain
Uth and normal metabolism are called vitamins;. Unlike
mljnhvd rates, lipids, or proteins, vitamins do not provide
Idwrcy'or serve as the body's building materials. Most vita-
■is with known functions serve as coenzymes.
Mm si vitamins cannot be synthesized by the body and
Jibe ingested. Other vitamins, such as vitamin K. are pro-
h bacteria in the Cil tract and then absorbed. The
I assemble some vitamins if the raw materials, called
pviltimim, arc provided, for example, vitamin A is pro-
\hd hv die body from the provitamin beta -carotene, a
chemical present m orange and yellow vegetables such as car-
rots and in dark green vegetables such as spinach. Ha angle
food contains all the vitamins required by the body— one of
the best reasons to eat a varied diet.
Vitamins are divided into two main groups; fat-soluble
and water-soluble. The fa/soltth/c vitamins are vitamins V.
1). E, anil K. They are absorbed along tilth dietary lipids in
the small intestine mu\ packaged into chylomicrons. They
earn lot be absorbed in adequate quantity unless they are in-
gested with other lipids. Fat-soluble vitamins mav be StOJfid
in cells, particularly in the liver. 'The vatctsolithk vitamins
include the B vitamins and vitamin C. They are dissolved in
body fluids. Excess quantities «»f these vitamins are nm stored
bin instead are rxcreted in the urine.
Besides their other functions, three vitamins C. I\ and
beta-carotene (a provitamin)— are termed antioxidant vita-
wins because they inactivate oxygen free radicals. Recall thai
free radicals are highly reactive ions or molecules thai
an unpaired electron in their outermost electron shell. Free
radicals damage cell membranes. DNA, anil other cellular
structures and contribute to the formation of atherosclerotic
plaques- Some free radicals arise naturally in the body, and
others come from environmental hazards such as rol
smoke and radiation. Antioxidant vitamins arc thought to
play a role in protecting against some kinds of cancer. redliC
506 Chapter 20 Nutrition and Metabolism
Table 201 Minerals Vital to the Body
Mineral
Calcium
Phosphorus
Potassium
Sulfur
Sodium
Chloride
Magnesium
Iron
Iodide
Manganese
Copper
Cobalt
Zinc
Fluoride
Selenium
Chromium
Comments
Most abundant mineral In body. Appears In combination with
phosphates. Aboul 99% is stored in bone and leeth. Blood Ga-
level is conirolled by parathyroid hormone (PTH). Calcilriol
promotes absorption of dietary calcium, Sources are milk, egg
yolk, shellfish, and leafy green vegetables.
About 80% is lound in bones and teeth as phosphate salts.
Blood phosphate level is controlled by parathyroid hormone
(PTH). Sources are dairy products, meat, fish, poultry.
and nuts.
Major cation (K ) in intracellular fluid. Excess excreted in unne.
Present In most foods (meats, fish, poultry, fruits, and nuts).
Component of many proteins (such as insulin and chondroitin
sulfate!, electron earners in electron transport chain, and some
vitamins (thiamine and biotin), Sources include b$ef,
liver, lamb, fish, poultry, eggs, cheese, and beans.
Most abundant cation (Na') in extracellular fluids; some found
in bones. Normal intake ol NaCl (table salt) supplies more
than the required amounts
Major anion (CI ) in extracellular fluid. Sources include table
salt <NaCl), soy sauce, and processed foods.
Important cation (Mg 3 ") in intracellular fluid. Excreted in urine
and feces. Widespread in various foods, such as green
leafy vegetables, seafood, and whole-grain cereals.
About 66% found In hemoglobin of blood, Normal losses of iron
occur by shedding of hair, epithelial cells, and mucosal cells,
and Jn sweat, urine, feces, bile, and blood lost during
menstruation. Sources are meat, liver, shellfish, egg yolk.
beans, legumes, dried fruits, nuts, and cereals.
Essential component of thyroid hormones. Sources are
seafood, iodized salt, and vegetables grown in
iodine-rich soils.
Some stored in liver and spleen.
Some stored In liver and spleen. Sources include eggs,
whole-wheal flour, beans, beets, liver, fish, spinach, and
asparagus.
Constituent of vitamin B , *
Important component of certain enzymes Widespread in
many foods, especially meats.
Components of bones, teeth, other tissues
Important component ol certain enzymes. Found in seafood,
meat, chicken, tomatoes, egg yolk. milk, mushrooms, and
garlic, and cereal grains grown in selenium-rich soil.
Found in high concentrations in brewer's yeast. Also lound in
wine and some brands of beer.
Importance
Formation of bones and teeth, blood clotting, normal muscle
and nerve activity, endocytosis and exocytosis. cellular nullify
chromosome movement during cell division, glycogen
metabolism, and release ol neurotransmitters and hormones.
Formation of bones and teeth Phosphates constitute a maj
butter system ol blood. Plays important role in muscle
contraction and nerve activity. Component of many enzyrnBs.
tved in energy transfer (ATP) Component ol DNA and R"
Needed for generation and conduction ol action potentials
in neurons and muscle libers.
As component ol hormones and vitamins, regulates various
body activities. Needed for ATP production by election
transport chain.
Strongly affects distribution ol water through osmosis. Parlol,
bicarbonate bulfer system. Functions in nerve and muscle
action potential conduction.
Plays role In acid-base balance ol blood, water balance, and
tormation o! HCI in stomach.
Required for normal functioning ol muscle and nervous tissnt
Participates in bone formation. Constituent of many
coenzymes.
As component of hemoglobin, reversibly binds 0* Com
of cytochromes In electron transport chain.
IN*
ipflwrt
Required by thyroid giand to synthesize thyroid hormones,
which regulate metabolic rate.
Activates several enzymes. Needed lor hemoglobin synitieas,
urea formation, growth, reproduction, lactation, and bona
formation.
Required with iron lor synthesis of hemoglobin. Conwsnja
coenzymes in eiedron transport chain and enzyme nece
for melanin formation.
As part of vitamin B„. required lor erythropoiesls.
As a component of carbonic anhydrasa. import... >
dioxide metabolism. Necessary for normal growth and '
healing, normal taste sensations and appetite, and normal
sperm counts in males. As a component ol peptidases, It is
Involved in protein digestion.
Appears to Improve tooth structure and inhibit tooth decay,
Needed for synthesis ot thyroid hormones, sperm motility,;
proper functioning of the Immune system. Also functions asa^
antioxidant Prevents chromosome breakage and may ptajnf
role in preventing certain birth delects, miscaniage, pn
cancer, and coronary artery disease.
Needed for normal activity of insulin in carbohydrale and ft
metabolism.
Metabolism 507
the buildup of atherosclerotic plaque, delaying some ef-
fects of aging, -ni'l ilt.'L-iv.isin^ tin chance of cataract forma-
tion in the lenses of the eyes. Tabic 20.2 lists the principal vi-
umins. their sources, their functions, and related deficiency
disorders.
Mtisi nutritionists recommend eating a balanced diet that
includes :i variety of foods rather than taking vitamin
supplements or mineral supplements, except in special
instances. Common examples of necessary supple*
entations include iron for women who have excessive
ftroal bleeding; iron and calcium for women who are
nant or breast-feeding; folic acid (folate) for all
n who may become pregnant, to reduce the risk of
neural tube defects; calcium lor most adults, because
tltcv do not receive the recommended amount in their di-
k and vitamin Bp for strict vegetarians, who eat no
meat. Because most North Americans do not ingest in
food the high levels of antioxidant vitamins thought
c beneficial effects, some experts recommend sup-
enting vitamins C and I- . Mure is not always better;
Inrger doses of vitamins or minerals can be very harmful.
CHECKPOINT
1. Describe the My Pyramid and give examples of foods
front each food group.
Briefly describe die functions of the minerals calcium
and sodium in the body.
J, Explain how vitamins are different from minerals, and
ilLstinguish between a hit-soluble vitamin and a watcr-
soluhlc vitamin.
METABOLISM
objectives • Define metabolism and describe its
I'fthporiance in homeostasis,
i Explain how the body uses carbohydrates, lipids, and
.proteins.
ibolisin (me- IMJ-o-li/an; mvtahtrf- = change) refers to
chemical reactions of the body. Recall from Chapter 2
^chemical reactions occur when chemical bonds between
Jwanccs are formed or broken, and that enzymes serve as
ysts i" speed up chemical reactions. Some enzymes te-
lle presence of an ion such as calcium, iron, or /inc.
enzymes work together with coenzymes, which func-
1 35 tempt irary carriers of atoms being removed from or
Ded to n substrate during a reaction, Main coenzymes are
i from vitamins. Examples include the coenzyme
j ': lived from the B vitamin niacin, and the coenzyme
rived from vitamin B_> (riboflavin).
The body's metabolism may be thought of as an ener
balancing' act between anabolic (synthesis) ;ind cauholie (de-
composition) reactions. Chemical reactions that combine
simple substances into more complex molecules arc collec-
tively known as atudmlhm U-N \|5 n li/ui; nun- = upward i.
Overall, anabolic reactions use more energy than thev pro-
duce. The energy they use is supplied In carabolic reactions
i '•..' ). ( )ne example of an anabolic process is the for-
mation of peptide bonds between amino acids, combining
them into proteins.
The chemical reacrions that break down complex organic
compounds into simple ones are collective!) known as cattib-
otis-iu (ka- TAB-o-li/.m; calu- = downward). (."anabolic reac-
tions release the energy stored in organic molecules. This en-
ergy is transferred to molecules of PCI P and then used to
power anabolic reactions. Important: sets of catahnlic reac-
tions occur during glycolysis, ihe Krelis cycle, and the elec-
tron transport chain, which are discussed shortly.
■\bout 40% of the energy released in catabolism is used
for cellular functions; the rest is converted to heat, some of
which helps maintain normal body temperature. Excess heat
is lost to the environment. Compared with machines, which
typically convert only 10-20% of energy into work, the In
efficiency of the body's metabolism is impressive. Still, the
body has a continuous need to take in and process external
sources of energy so that cells can synthesize enough ATP to
sustain lire.
Figure 20.2. Role of ATP in linking anabolic and catabolic re-
actions. When complex molecules are split apart (catabolism, at
left), some of the energy is transferred to form ATP and the rest is
given off as heat. When simple molecules are combined to form
complex molecules (anabolism. at right), ATP provides the energy
for synthesis, and again some energy is given olf as heat.
i The coupling of energy-releasing and energy-requiring reactions
is achieved through ATP.
Heat
released
Simple molecules such as
glucose, amino acids,
glycerol, and fatty acids
Catabolic reaction::,
transfer energy Irorn
complex molecules
to ATP
Anabolic reactions
transfer energy from
ATP to complex
molecules
Complex molecules such
as glycogen, proteins, and
triglycerides
Heat
released
I In a pancreatic cell that produces digestive enzymes, does an-
abolism or catabolism predominate?
508 Chapter 20 Nutrition and Metabolism
Table 20.2 The Principal Vitamins
Vitamin
Fat-soluble
Vitamins
A
E (tocopherols)
Comment and Source
Functions
Deficiency Symptoms and
Disorders
All require bile salts and some dietary
lipids for adequate absorption.
Formed (rom provitamin bela-carotene
(and olher provitamins) in Gl tract.
Stored In liver. Sources ol carotene
and other provitamins include orange,
yellow, and green vegetables; sources
ol vitamin A include liver and milk.
In the presence of sunlight, the skin.
liver, and kidneys produce the active
form ot vitamin D (calcilnol). Stored in
tissues to slight extent Most excrBted
in bile. Dietary sources include lish-Hver
oils, egg yolk, and fortified milk.
Slored in liver, adipose tissue, and
muscles. Sources include fresh nuts
and wheat germ, seed oils, and green
leafy vegetables.
Produced by Intestinal bacteria Slored
in liver and spleen, Dietary sources
include spinach, cauliflower, cabbage,
and Jlver,
Maintains general health and vigor of
epithelial cells. Beta -carotene acts as
an antioxidant to inactivate Iree radicals,
Essential for formation of light-sensitive
pigments In photoreceptors ol retina.
Aids in growth of bones and teeth by
helping to regulate activity of
osteoblasts and osteoclasis.
Essential for absorption of calcium and
phosphorus from Gl tract. Works with
parathyroid hormone (PTH) to maintain
Ca 2 homeostasis
Inhibits catabolism of certain fatty acids
thai help form cell structures, especially
membranes. Involved In formation of
DNA. RNA. and red blood cells. May
promote wound healing, contribute to
the normal structure and functioning ol
1he nervous system, and prevenl
scarring. Acts as an antioxidant to
inactivate free radicals.
Coenzyme essential for synthesis of
several dotting factors by
liver, including prothrombin.
Atrophy and keratinization of
epithelium, leading to dry skin ami
hair; increased incidence ol ear. sinus
respiratory, urinary, and digestive
system infections; inability lo gam
weight; drying ol cornea; and skin
sores,
Night blindness or decreased ability
lor dark adaptation.
Slow and faulty development cf
bones and teeth.
Defective .utilization of calcium by
bones leads to rickets in children
and osteomalacia in adulfs
Possible Joss of muscle tone,
Abnormal structure and fund
mitochondria, lysosomes, andplaura
membranes, A possible consaquwei,
is hemolytic anemia
Delayed clotting lime results in
excessive bleeding.
Water-solubte Dissolved in body fluids. Most are not
Vitamins stored in body. Excess intake is
eliminated in urine.
B, (thiamine) Rapidly destroyed by heal. Sources
irc.i.ide whole-grain ptoducts, eggs,
pork. nuts, liver, and yeast.
Acts as a coenzyme for many different
enzymes that break cerbon-to-carbon
bonds and are Involved In carbohydrate
metabolism of pyruvic acid to CO ? and
H a O Essential lor synthesis of the
neurotransmitter acetylcholine.
Buildup of pyruvic and laciic acids I
and insufficient production of ATPta
muscle and nerve cells leads to;
(1] beriberi, partial paralysis of s
muscle of Gl tract, causing digestm
disturbances, skeletal muscloi
and atrophy of limbs; (2) potyt\
duo to degeneration of myelin \
impaired reflexes, impaired ser
touch, stunted growth In chlldte
and poor appetite.
Metabolism 509
Vitamin
Comment and Source
Functions
Deficiency Symptoms and
Disorders
Water-soluble (continued)
B z (riboflavin)
Niacin
(nicotinamide)
8,(pyridoxine)
locobalamin)
antothenic acid
'Folic acid
(folate, folacin)
Biotin
{.(ascorbic acid)
Small amounts supplied by bacteria of
Gl tract. Dielary sources include yeast,
liver, beet, veal. lamb, eggs, whole-grain
products, asparagus, peas, beets, and
peanuts.
Derived Irom amino acid tryptophan.
Sources include yeasl, meats, liver,
fish, whole-grain products, peas,
beans, and nuts.
Synthesized by bacteria ol Gl trad.
Stored In liver, muscles, and brain. Other
sources Include salmon, yeasl.
tomatoes, yellow corn, spinach, whole
grain products, liver, and yogurt,
Only B vitamin not found In
vegetables: only vitamin containing
cobalt. Absorption from Gl tract
depends on intrinsic factor secreted
by the stomach mucosa. Sources
Include liver, kidney, milk, eggs,
cheese, and meat.
Some produced by bacteria of Gl tiacl.
Stored primarily in liver and kidneys.
Other sources include liver, kidneys,
yeast, green vegetables, and cereal.
Synthesized by bacteria ol Gl tract.
Dietary sources includs green leafy
vegetables, broccoli, asparagus, breads.
dried beans, and citrus fruits.
Synthesized by bacteria ol Gl tract.
Dielary sources Include yeast, liver,
egg yolk, and kidneys.
Rapidly destroyed by heal. Some
stored in glandular tissue and plasma.
Sources Include citrus fruits,
strawberries, melons, tomatoes, and
green vegetables.
Component of certain coenzymes dor
example. FAD and FMN) in carbohydrate
and protein metabolism, especially in
cells ol the eyes, skin, mucosa of the
intesiine. and blood.
Essential component ot NAD and
NADP, coenzymes In oxidation-
reduction reactions In lipid metabolism,
Inhibits production ol cholesterol and
assists m triglyceride breakdown.
Essential coenzyme tor normal amino
acid metabolism. Assists production
of circulating antibodies. May function
as coenzyme in triglyceride metabolism.
Coenzyme necessary for red blood
cell formation, formation of the amino
acid methionine, entrance ol some
amino acids into Krebs cycle, and
synthesis of choline (used
to make acetylcholine).
Constituent ol coenzyme A. winch is
used to transfer acetyl groups into
Krebs cycle; conversion ol lipids and
amino acids into glucose, and synthesis
of cholesterol and steroid hormones,
Component of enzyme systems
synthesizing nitrogenous bases of DNA
and RNA, Essential for normal
production of red and white blood cells.
Essential coenzyme for conversion of
pyruvic acid to oxaloacetic acid and
synthesis of laity acids and purines.
Promotes protein synthesis including
synthesis ol collagen in connective
tissue. As coenzyme, may combine
with poisons, rendering them harmless
until excreted Works with antibodies,
promotes wound healing, and functions
as an antioxidant.
Faulty use of oxygen resulting in
blurred vision, caiaracts, and corneal
ulcerations. Also dermatitis and
cracking of skin, lesions of intestinal
mucosa, and one type of anemia.
Pellagra, characterized by dermatitis,
diarrhea, and psychological
disturbances.
Dermatitis of eyes, nose, and mouth,
relarded growlh, and nausea.
Pernicious anemia, neurapsyd" i |i
abnormalities (ataxia, memory loss.
weakness, personality and mood
changes, and abnormal sensations),
and impaired activity of osteoblasts.
Fatigue, muscle spasms, Insufficient
production of adrenal steroid
hormones, vomiting, and Insomnia
Production of abnormally large red
blood cells. Higher risk ol neural tube
defects in babies born to tolic
acid-deficient mothers.
Mental depression, muefiuiai pain,
dermatilis. fatigue, and nausea.
Scurvy; anemia; many symptoms
related to poor collagen formation,
including lender swollen gums
loosening ol teeth, poor wound
healing, bleeding, impaired immune
responses, and retardation of growth
510 Chapter 20 Nutrition and Metabolism
Carbohydrate Metabolism
During digestion, polysaccharide and disaccharide carbohy-
drates arc eataboli/ed to monosaccharides — glucose, fruc-
tose, and galactose — which are absorbed in the small intes-
tine. Shortly after their absorption, however, fructose and
galactose arc converted to glucose. Thus, the story oj carho-
hv fliitc metabolism is really the story of glucose tnetabofisnk
Because glucose is the body's preferred source for synthe-
sizing VIP. the late of glucose absorbed from the diet de-
pends on the needs of body cells. If die cells require \TP im-
mediately, they oxidize the glucose. Glucose not needed l,,r
immediate ATP p r r » c 1 1 1 c- 1 i c i n niaj lie converted to glycogen
for storage in li\er cells and skeletal muscle fibers. II these
glycogen stores are full, the liver cells c;in transform the glu-
tei triglycerides for storage in adipose tissue. At a later
when the cells need more ATP, the glycogen and
triglycerides enn be converted back to glucose. Celt
throughout the body also can use glucose to make certai/i
amino acids, the building blocks of proteins.
Before glucose can be used by bod}' cells, it must pass
through the plasma membrane by facilitated diffusion and
enter the cjtosol. Insulin increases the rate of facilitated
fusion of glucose.
Glucose CataboHsm
The catabolism of" glucose to produce YIP is known is cellu-
lar respiration. Overall, its many reactions can be suimna-
rized as follows,
1 glucose j 6 oxygen — *- .>f»-. >s AI'P
+ 6 carbon dioxiile + 6 water
Pour interconnecting sets uf chemical reactions contrilnireto
cellular respiration (Fij : h
Figure 20.3 Cellular respiration.
, The catabolism of glucose to produce ATP Involves glycolysis, the formation of acetyl coenzyme A, the
Krebs cycle, and the electron transport chain.
O GLYCOLYSIS
in cytosol
Mrtochondnon
© FORMATION
OF ACETYL
COEN2YME A
D
KREBS
CYCLE
.-_- . jt 32-34 < ATP
O ELECTRON _^jft V- ^2?
TRANSPORT
CHAIN
How many molecules of ATP are produced during the complete catabolism of one molecule of glucose?
During glycolysis (gli-J&E >l.-i •SIS; g^«?- - sugar: -ij^/s =
breakdown), reactions that take place in the eytosol con-
vcri one six-carbon glucose molecule Lata two three-
carbon pyruvic acid molecules. The reactions ol glycol]
sis direct h produce two .VI Ps. They also transfer some
chemical energy, in the form of hhrh -energy electrons.
from glucose to llie coenzyme NAI)\ forming two
\ A I.) I I + H'. Because glycolysis does IKfl require oay-
gen, u is a way to produce ATP anaerobic-ally (without
lis known as anaerobic cellular respiration. Tt
oxvgen is available, however, most cells next convert
pyruvic acid to acetyl coenzyme A.
Q The formation of acetyl coenzyme A rs a transition step
that prepares pyruvic acid fox entrance into the Krebs cy-
cle. First, pyruvic acid enters a mitochondrion and is con-
verted to a i^vo-carbon fragment In removing a molecule
ofcarboii dioxide (Q h)< Molecules oFCOj produced dur-
ing glucose cataholism diffuse into the Mood and are even-
tually exhaled. Then, the coenzyme NAD* takes awaj a
hydrogen atom (I l : ), in the process becoming NADH +
]i'. Finally, the remaining atoms, called an acetyl group,
beg attached m coenzyme A, to form acetyl coenzyme V
The Krebs cycle is a series of reactions that transfer
the chemical cneruv from acetyl coenzyme A to two
other coenzymes— NAD and FAD — thereby forming
NADU . n .in,] FADHi. krebs cycle reactions also
produce CO.. and one ATP for each acetyl coenzyme A
that enters the Krebs cycle. To harvest the energy m
NADU and I-AD1 k their high-energy electrons must
ni',i go through the electron transport chain.
Metabolism 51 1
Through tlie reactions of the electron transport chain,
the energy in N'ADtl + IT ami FAD1P is used to svn-
thesize ATP, As the coenzymes pass their high-energv
electrons through a series of "electron earners." All 1 is
synthesized. Finally, lower-energy electrons are passed ro
oxygen in a reaction that prdtktces water* Because the
krebs cycle and the electron transport: chain together re-
quire oxygen to produce ATP they arc known as aerobic
cellular respiration
(i Incase A nabolis'/n
Even though most of the glucose m die hod\ is catabohzed
to generate ATP. glucose limy take part in or he formed V«J
several anabolic reactions. One is the synthesis of gheogen;
another is the synthesis of new glucose molecules from some
of the products of protein ami lipid breakdown.
If". glucose is not needed immediately for All 3 produc-
tion, ir combines with many other molecules of" gluco>e t<>
form a long-chain molecule called glycogen (Figure 2Q.4)«
S\mhesis of glycogen i 1 - siiinulated by insulin. The bodv
cai] Store about 500 grains (about LI lb) of glycogen,
roughly 75% in skeletal muscle fibers and the rest in liver
cells.
ff blood glucose level falls below normal, glucagon is pi
leased from the pancreas and epinephrine is released Iroin
the adrenal luedultae. These hormones stimulate breakdown
of glycogen into its glucose subuniis 1 1 , ':). \ ,i\ er cells
release this glucose into the blood, and hod\ cells pick it up
to use for ATP production. Glycogen breakdown usually oc-
curs between meals.
Figure 20.4 Reactions of glucose anabolism: synthesis of glycogen, breakdown of
glycogen, and synthesis of glucose from amino acids, lactic acid, or glycerol.
u;
About S00 grams (1 1 lb) of glycogen are stored in skeletal muscles and the liver.
GLYCOGEN
LACTIC ACID
X
CERTAINO
AMINO ACIDS
GLUCOSE
I
GlyceraldehydeCl
3-phosphale
t
Pymvrcadd
GLYCEROL
Fatty acids
Triglycerides
Key:
Synthesis of glycogen (stimulated!!
by insulin)
Breakdown of glycogen ( stimu fated D
by glucagon and epinephrine)
Gkiconeogenesis (stimulated □
by con i so I and glucagon]
Catabollsm of triglyceridesfJ
(lipoiysisj
r ) Which body cells can synthesize glucose trom amino acids?
V
512 Chapter 20 Nutrition and Metabolism
The amount of glycogen stored in the liver, and skeletal
muscles varies and bain be completely used up during long-
term athletic endeavors, Thus, many marathon runners
and other endurance athletes follow a precise exercise and
dietary regimen that includes eating forge amounts of
aplfex earholu d rates, such as pasta and potatoes, in tlie
three days before an event. This practice, called carbohy-
drate loading-, helps maximize the amount of glycogen
available for ATP production in muscles. For athletic
events lasting more than an hour, carbohydrate loading
has been shown to increase an athlete s endurance.
V\ hen your liver runs low on glycogen, it is time to eat.
If you don't, your bodj starts catabolizing triglycerides Mats)
and proteins. Actually, the body normally catahcilizes some of
its triglycerides and proteins, but large-scale triglyceride and
protein cata holism does nor happen unless you are starving,
eating very few carbohydrates, or suffering from an en-
docrine disorder.
Liver cells can convert the glycerol part ol triglycerides,
lactic acid, and certain amino acids to glucose (Figure 20.4).
The series of reactions that form glucose from these nonear-
bohydrate sources is called gluconcofrencsis (qloo"-ko-ne'-6~
II N -e-sis; two- — new). I his process releases glucose into
the blood, thereby keeping blood glucose level normal dur-
ing the hours between me n glucose is nor being ab-
sorbed. Gluconeogenesis occurs when die liver is stimulated
by Cortisol from the adrenal cortex and glucagon from the
pancreas.
Lipid Metabolism
Lipids, like carbohydrates, may be cataboiized to produce
ATP. Ji the body has no immediate need to use lipids in this
way, they arq stored as triglycerides in adipose tissue
throughout the body, and in the liver. \ fev lipids are used as
structural molecules or to synthesize other substances. Two
essential fatty acids that the body cannot synthesize are
linoleic acid and liriolenic acid. Dietary sources of these lipids
include vegetable oils and leafy vegetables.
Lipid Catabolism
Muscle, liver, and adipose cells routinely caralxdize fatty
adds Irom triglycerides to produce VI II Liist, die triglyc-
erides are split into glycerol and lain acids — a process railed
lipolysis (li-POL-i-sis) (Figure 20.5). The hormones epi-
nephrine, norepinephrine, and Cortisol enhance lipolysis.
The glycerol and tatty acids that result frotn lipolysis are
catahohzed via different pathways. Glycerol is converted by
many ceils of the body to glyceraldehyde 3-phosphate, Tf the
ATP supply in a cell is high, glyceraldehyde 3- phosphate is
converted into glucose, an example of gluconeogcnesis. If the
ATP supply in a cell is low. glyceraldehyde J -phosphate en-
ters the cat.aholic paihway to pyruvic acid.
Fatty acid catabolism begins as enzymes remove two J
boia atoms ai a time Irom die fatty acid and attach diemd
molecules of coenzyme A, forming acetyl coenzyme A (ace J
CoA). Then the acetyl CoA enters the Krebs cycle (FiguS
i. A 16-carbon ratty add such as palmitic acid can WcldJ
many as I 29 ATPs via the Krebs cycle and the electron
port chain.
.As part of normal fatty acid cataholism, the liver coj
some acetyl CoA molecules into substances known a* krone
bodies (Figure 20-5X Ketone bodies then leave the liver J
enter body cells, where they are broken down into acetyl
CoA, which enters the Krebs cycle.
The level of ketone bodies in the blood normally is vm
low because other tissues use them lor ATP product-ion*!
fast as they are formed. When the concentration of ketonn
bodies in the blond rises above normal — a conditioa
called ketosis — the ketone bodies, most of which ar*^
acids, must be buffered. If too many accumulate, blood pH
I alls. When a diabetic becomes seriously insulin dcticienr.
one of the telltale signs is the sweet smell on tin
Irom the ketone body acetone. Prolonged ketosis can
to acidosis, an abnormally low blood pH that can result to
death.
Lipid Anabolism
Insulin stimulates liver cells and adipose cells m MmhcMK
triglycerides when more calories arc consumed than aj
needed to satisfy ATP needs [V (.) S ), Excess diem
carbohydrates, proteins, and Fats all \v,nc the same fate— thfl
are converted into triglycerides. Certain amine, aenls un ,in-
dergo the following reactions: amino acids -*- acetyl CoA •*!
laity acids ■*■ triglycerides. The use of glucose to form lipid
rakes place via two pathway s:
1. glucose -*- glyceraldehyde 3-phosphate -*- glycerol; and]
2. glucose -*- glyceraldehyde 3-phosphate -*■ accryl CoA-*
fatty acids.
The resulting glycerol and fatty acids can undergo
reactions to become stored triglycerides, or rhej i
through a series of anabolic reactions to produce other lipid
such as lipoproteins, phospholipids, and cholesterol.
Lipid Transport in Blood
AIosl lipids, such as triglycerides and cholesterol, are
water-soluble. Lor transport in watery blood, such moled
first are made more water soluble by combining them nfl
proteins. Such lipoproteins .in: spherical particles with a
outer shell of proteins, phospholipids, and cholesterol
cuies surrounding an inner core of triglycerides and oi|
lipids. The proteins in the outer shell help the lipopt
particles dissolve in body fluids and also have speeifit tiincJ
lioir..
Metabolism 513 \
i
Figure 20.5 Metabolism of lipids. Lipolysis is the breakdown of triglycerides into glycerol and tatty acids. Glycerol
may be converted to glyceraldehyde 3-phosphate, which can then be converted to glucose or enter the Krebs cycle.
Fatty acid fragments enter the Krebs cycle as acetyl coenzyme A Fatty acids also can be converted Into ketone bodies.
ft*
Glycerol and fatty acids are catabolized in separate pathways.
TRIGLYCERIDES
CERTAIN
AMINO ACIDS
Key:
Lipolysis (stimulated I ■.• • rv Mirlne,
norepinephrine, and Cortisol)
->• Synthesis of lipids (stimulated by insulin)
Breakdown of ketone
bodies in most body cells
Formation of ketone
bodies in liver cells
KREBS
CVCLE
Ketone bodies
) Which cells form ketone bodies?
rotcins Lire transport \ chides: They provide dfiliv-
jud pickup services so that lipids can be mailable when
Beed them or removed when they are nor needed,
proteins are categorized and named mainly according
■Br size nn»l density. From largest and lightest to smalb
Bfld heaviest, the tour major types of" fipoproteioa are
pmierons, very low-density lipoproteins, low-densii\
Jjbroteins, and high-density lipoproteins.
I. Chylomicrons form in absorptive epithelial cells of the
K II intestine and transport dietary lipids to adipose tis-
p] storage,
low-density lipoproteins (W.DIjc) rnmsporr trfglyc-
I trifles made in liver cells to adipose cells for storage; Al-
ipositing some of their triglycerides in adipose cells,
VI DLs are converted Co LDLs.
1 bwrdensity lipoproteins (LOU) carry about 73% of the
total eholesterol in blood and deliver it to cells through-
out the hod}' for use in repair ot ceil membranes and syn-
. : steroid hormones and bile salts.
E High-density lipoproteins (HDLs) remove excess eholes-
I'rom body cells and transport it to the liver for
Kminau'on.
en present in excessive numbers, LDLs deposit choles-
terol in and around smooth muscle fi\)£is in arteries, Form?
ing tatty plaques that increase the risk of coronary an en
disease (see page 579); For this reason, the cholesterol in
LDLs, called LDL -cholesterol, is known 3s "bad" cho-
lesterol. Eadng a high-fat diet increases the product ion ol
VLDLs, which elevates the LDL level and increases die
formation of tatty plaques. Because 111)1 s prevent accu-
mulation of cholesterol in the blond, a IttLrJi HDL level is
associated with decreased risk ot coronary artery disease.
For this reason, I IDL-choIcstcrol is known as "good"
cholesterol,
Desirable levels of blood cholesterol in adults are to-
tal cholesterol under 200 mg/dL. LDL under I.U)mg/dL,
and DDL over 40 mg/dL. The ratio of total cholesterol
to HDL cholesterol predicts the risk of developing coro-
nary artery disease. A person with a total cholesterol ol
ISO mg/dl. and HDL of oil mg/dL has a risk nuio ol h
Ratios above 4 are considered undes.ira.ble; the higher the
ratio, the greater the risk of developing coronary artery
disease.
514 Chapter 20 Nutrition and Metabolism
Protein Metabolism
During digestion, proteins arc broken dawn into amino
acids. L nlike carbolu -d rates and triglycerides, proteins are
not warehoused for future use. Instead, their amino acids arc
cither oxidized to produce ATP or used to synthesize new
proteins for growth and repair ofbod\ tissues. Excess dietary
amino adds are converted into glucose (ghicaneogertesis) or
i _v rill us.
The active transport of amino acids into body cells is
stimulated by insulinlike growth factors (Ids) ;ind insulin.
Almost immediateh after digestion, amino acids are reassem-
bled into proteins. Many proteins function as enzymes; other
proteins are involved in transportation (hemoglobin) or serve
as antibodies, clotting lactors (fibrinogen), hormones (in-
sulin), or contractile elements in muscle libers (aeim and
myosin). Several proteins serve as sixucairal components oF
the hudy (collagen, elastin, ami keratin).
Protein Catabolism
A certain amount of protein catabolism occurs in the bodj
each day, stimulated main!) by Cortisol from the adrenal cor*
te\. Proteins from worn-out cells (such 9S reii blood cells) .ire
broken down into ammo acids. Some amino acids are con-
verted into other ammo acids, peptide bonds are reformed,
and new proteins are made as part of tin- recycling process.
Liver cells convert some amino acids CO baity acids, ketone
bodies, or glucose. Figure 20.4 shows the conversion of
annuo acids into glucose (gluconeogencsis), Figure 20.5
shows the conversion ol amino acids into talis acids or ke-
tone bodies.
Amino acids also are oxidized to generate ATP. Before
amino acids can enter the Krebs cycle, however, their amino
group ( — NH-) must first be removed, a process called
cieainination (de-am '-i-\A-slum). De a mi nation occurs in
liver cells and produces ammonia (Nik), Liver cells then
convert the highly toxic ammonia co urea, a relatively barm-
less substance that is excreted m the urine.
Protein Anabolism
Protein anabolism, the formation of peptide bonds bciwecn
amino acids to produce new proteins, is carried out on the ri-
bosomes of almost every cell in the body, directed by the
ccIN' DMA and R\'V. Insulinlike growth factors, thyroid
hormones, insulin, estrogens, and testosterone stimulate pro-
it'in synthesis. Because proteins are a main component ol'
most cell structures, adequate dietary protein is especially es-
sential during the growth years, during pregnancy, and when
tissue has been damaged by disease or injury. Once dietary
intake of protein is adequate, eating more protein does noi in-
crease bone Or muscle mass: only a regular program of force -
hil. weight-bearing muscular activity accomplishes that goal.
Ol fk 20 unino acids in the human body; 10 are essen-
tial amino acids: They must be present in the diet becauw
they cannot be Synthesized in the body in adeqiui
amounts. Nonessential amino acids are those svnthesi .
by the body. I hey are formed by the transfer o! an .iiiii...
group from an amino acid to pyruvic acid or to an a I
the Kvebs cycle. Once the appropriate essential and
nonessential amino aeids are present in cells, protein *vj*
thesis occurs rapidly- Cable 20.3 summarizes the proce
occurring in botii catabolism mm\ anabolism of carbohy-
drates, lipids, and proteins.
Phenylketonuria <fcn' il l:e to \( )0-rv-a) or PkT is
generic error ot protein metabolism characterized hv
vated blood levels of the amino acid phenylalanine.
children with phenylketonuria ha\e a mutation in the
that codes for the enzyme needed to convert pheini,
nine into the amino acid tyrosine, which can ei
krebs cycle. Because the enzyme is deficient, plum lam
nine cannot be metabolized, and what is not used in pro-
tein synthesis builds up in die blood. If untreated, i
order causes vomiting-, rashes, seizures,
deficiency, i\m\ severe mental retardation. Newborns an
screened lor PKU, and mental retardation can be Dig
vented by restricting the child to a diet that suppBa
only tiie amount of phenylalanine needed for gjo
though learning disabilities may still ensue. Because da
artificial sweetener aspartame (NutraSueet' » e<j
phenylalanine, its consumption must be resi
children uithPkl 1 .
■ CHECKPOINT
4. What happens during glycolysis?
5. What happens in the electron transport chain?
6. Which reactions produce VIP during the com]
dation of a molecule of glucose?
7. What is gluconeogenesis, ami why is it important:
8. \\ hut is the difference between anabolism and
lismr
9. 1 low does VTP provide a link between anabolism anjjj
ta holism:
10. What are the functions of the proteins in lipopri
11. Which lipoprotein panicles contain "good" an
cholesterol, and whj are these terms used:
12. Where are triglycerides stored in rhe body?
13. V\ lull are ketone bodies? What is ketosis?
14. What me the possible hues of the amino acids troniB
;.. in catabolism?
Process
Carbohydrate Metabolism
Glucose catabolism
Glycolysis
Krebs cycle
Electron transport chain
Glucose anabollsm
Jpld Metabolism
Triglyceride catabolism
Triglyceride anabolism
Protein Metabolism
Catabolism
Anabolism
Metabolism anil Body Heal 515
Table 20.3 Summary of Metabolism
Comment
Complete calabollsm of glucose (cellular respiration) is the chief source of ATP in most cells. II consists of glycolysis,
the Krebs cycle, and the eleclron transport chain. One molecule ol glucose yields 36-38 molecules ol ATP
Conversion of glucose Into pyruvic acid, with net production of two ATP per glucose molecule: reactions do not re-
quite oxygen (anaerobic cellular respiration)
Series ol reactions in which coenzymes {NAD and FAD) pick up high-energy electrons- Seme ATP is produced.
COji. H 2 0, and heat are byproducts. Reactions are aerobic (aerobic cellular respiration).
Third sel of reactions in glucose catabolism in which electrons are passed from one earner to the ne*t and most of
die ATP is produced. Reactions are aerobic (aerobic cellular respiration)
Some ojucose Is converted into glycogen lor storage if not needed immediately lor ATP production. Glycogen can be
converted back to glucose for use in ATP production. Gluconeogenesis Is the synthesis of glucose from amino acids,
glycerol, or lactic acid.
Triglycerides are broken down Into glycerol and fatty acids. Glycerol may be converted into glucose (gluconeogene-
sis) or caiabollzed via glycolysis. Fatty acids are converted info acetyl CoA that can enter the Krebs cycle for ATP
production or be used to form ketone bodies
Synthesis of triglycerides from glucose and ammo acids. Triglycerides are stored in adipose tissue.
Amino acids are deaminated to enter the Krebs cycle. Ammonia formed during deamination Is converted to urea In
the liver and excreted in the urine. Amino acids may be convened into glucose (gluconeogenesis). fatty acids, or ke-
tone bodies,
protein synthesis is directed by DNA and uses the cell's RNA and rlbosomes.
ITABOLISM AND BODY HEAT
IECT1VES • Explain hovv body heat is produced
lost.
Describe how body temperature is regulated.
tow i&naidcr the relationship of foods to body heat, heat
ilirnutn and loss, and the regulation of foody temperature.
;uring Heat
,1 form of energy that can he measured as tempera-
expressed in units called calories. \ calorie (cat) is
his the amount of heat required to raise the teinpera-
1 gram of water l°C. Because the calorie is a reJa-
Ltn.it, the kiiocalorie (knit) or Caloric (Oil) (al-
rel'led with an uppercase C.) is often used t<> measure
ccaboiic race and to express the energy eorioeat
LA kibcalorie equals L000 calories. Thus, when we
it a particular fond item contains 500 Calories, we
tattially referring; to kilocalories. Knowing the caloric
.-...Is is important. If we know the amount of en-
iod\ uses for various activities, we can adjust our
Food intake by taking in only enough kilocalories to sustain
our activities.
Body Temperature Homeostasis
The body produces more or less heat depending on the rates
of metabolic reactions. Homeostasis of Body temperature ran
he maintained only if the rate ol heat production by metftbc
lism equals the rate ol heat loss from the body. Thus, it is im-
portant to understand the ways in which lieu can be pro*
dticed and lost.
Hotly Heat Production
Most of the heat produced fey the body comes from the ca-
tabolism of die food we ear. The rate at which this heal is
produced, the metabolic rale, Is measured m kilocalories. Be-
cause many factors affect metabolic rate, it 13 measured under
standard conditions, with the had) w a quiet, testing) and
lasting condition called the basal state. The measurement
obtained is the basal metabolic rate (BMR). BMR is 1200 to
1800 Calories per daj b adults, which amounts to about 24
(Calories per kilogram of body mass in adult males and 21
Calories per kilogram ut adult females,
516 Chapter 20 Nutrition and Metabolism
The added Calories needed to support daily activities,
such as digestion and walking, range from M)(i Calories [or a
sum 1 1, relative] v scdentarv person to over 3000 Calories for a
person in owning For Olympic-level eompcririons. The fol-
lowing factors affect metabolic v.wc:
1. Exercise. During strenuous exercise the metabolic rate
ages by :is much .is 1 5 to 20 times the IS Nil-!.
2. Hormones- Thyroid hOrrnones are die mam regulators
ol BMR, which increases as the blood levels of thyroid
hormones rise. Testosterone, insulin, and human growth
hormone can increase the metabolrc pate b\ 5— I ; > % ,
3. Nervous system. During exercise or in a stressful siuta-
iHiii. the sympathetic division of die autonomic nervous
system releases norepinephrine, and it stimulates release
of the hormones epinephrine and norepinephrine hy die
adrenal medulla. Both epinephrine and norepinephrine
increase the metabolic rate of body cells.
4. Body temperature. The higher the body temperature.
i In. higher the metabolic rate. As a result, metabolic rare
is substantially increased during a lever.
5. Ingestion of food. The ingestion of food, especially
proteins, can raise metabolic rate by It) 20
6. Age, The metabolic rate of a child, in relation to its size,
is about double that of an elderly person due to the high
rates ol growth-related reactions in children!.
7. Other factors. Other factors that affect metabolic rate
are gender (lower in females, except during pregnancy
and lactation), climate (lower in tropical regions), sleep
(loweifc and malnutrition (lower').
Body Heat Loss
Because body beat is continuous^ produced by metabolic re-
actions, heai must also he removed continuously or body
temperature would rise Steadily. The principal routes ol hcai
loss from the hotly to the environment are radiation, conduc-
tion, convection, aiul evaporation.
1. Radiation is the transfer of heat in the form ©f infrared
rays between a warmer object and a cooler one without
physical contact. Your bod) loses heat hy radiating more
infrared waves than it absorbs from cooler objects. If sur-
rounding objects are warmer than you are, you absorb
more heat In radiation than you lose.
2. Conduction is the heat exchange that occurs between
two materials that are in direct contact. Bod] heat is lost
by conduction CO solid materials in contact with the body,
such as your chair, clothing, and jewelry. I leat can also he
gained by conduction, for example, while soaking in a
h oi tub.
3. Convection is the transfer of heat by the mowmeni of a
gas mi a liquid between areas of different temperatures.
"The contact ol airoi watea with your body results in heat
transfer bj both conduction and convection. U hen co.ol
air makes contact with die body, it becomes wartftecj .sin
is carried awaj by convection currents. The fastei
moves lor example, hy a breeze or a Ian — the histei
the rate of convection.
4. Evaporation is the conversion of a liquid to a vapor, t'n-
der'tvpieal resting conditions, about 22% ofheat lossoffi
curs through evaporation of water — a daily lossofabod
300 ml. in exhaled air and 400 ml. from the skin surface;
Evaporation provides the main defense against overheat
ing during exercise. Under extreme conditions, a num
mum of ilu nit 3 liters of sweat can he produced eacj
hour, removing more than 1700 kcal of heat if all ofi
evaporates. Sweat chat drips off the body rather than
'■ poradng removes very little heat.
Regulation of Body Temperature
ff the amount ol' heat production equals the amount ol lit
loss, you maintain a nearly constant body temperature
37°C (°8.6 n F). II your heat-producing mechanisms l'ciut
more heat than is lost In your heat-losing mechanisms. 3
body temperature rises, For example, strenuous exe
some infections elevate body temperature. If you In-;
faster than you produce it. your bod) temperature falls,
mei'Moii m cold water, certain diseases such as hypnriij
roidism, and some drugs such as alcohol and antidepresfl
can cause bodj temperature to fell. \n elevated tempers
may destroy body proteins, and a depressed tern pern tun; :
cause cardiac arrhythmias; both can lead to death.
The balance between heat production and heat Iowa
controlled by neurons in the hypothalamus. These no
generate more nerve impulses when blood temperature
creases and fewer impulses when hlood Temperature d9
creases. If body temperature falls, mechanisms diat hdpeqj
Serve heal and increase heat production act hy raeaua
several negative feedback loops to raise the body tcmpeian
to normal (Figure 20.6), Thermoreceptors send nerve ni
pulses to the hypothalamus, which produces a rele.iM
mone called diyrotropin-releasing hormone (TRH), T
turn stimulates die anterior pituitary to release tlvyrokl-
uladng hormone (TSH). Nerve impulses from the hvpi:
auuis and LSI I then activate several effectors:
■ Sympathetic nerves cause blood vessels of the skin m
constrict (vasoconstriction). The decrease of hlood 1
slows the rate of heat loss from the skin. IK
heat is lost, bod) temperature increases even iftliemej
hoi re rate remains the same.
■ Sympathetic nerves stimulate the adrenal medulla io,f|
lease epinephrine and norepinephrine into the blow
I hesc hormones increase cellular metabolism, which l
crease heat production.
■ The hypothalamus stimulates parts of die brain thai
crease muscle tone. As muscle tone increases in cnemifl
Metabolism and Body Heal 517
cle (the agonist), & e small contractions stretcn muscle
Spindles in its antagonist muscle, Ungating a stretch re-
\\c\. The resulting contraction in the antagonist stretches
muscle spindles in the agonic, and 1 levelops a
stivu'h reflex This repetitive cycle— called shiveri&g-
■j\\'-m\\ increases tta race of beat production. During
maximal shivering, hotly be&t production can rise to
irboui four times die basal rate te jusi ii few minutes.
■ The thyroid gland responds u> TSI I l.y n leasing man
thyroid hormones into the blood, increasing the meta-
bolic rate.
If l.mly temperature rises above normal, a negative feed,"
hick systoru opposite CO the one depicted in Pij " gOCj
into action. The higher temperature of the blood stimulate!
tliC hypothalamus. Nerve impulses ftLUSe dilution ol blOQj
Figure 20.6 Negative feedback mechanisms that increase heat production.
When stimulated, the heat-promoting center in the hypothalamus raises body temperature.
Some stimulus disrupts
homeostasis by
Decreasing
Thermoreceptors in
skin and hypothalamus
Return to homeostasis
whan response brings
body temperature back
to normal
Vasoconstriction
decreases heat
loss through Ihe
skin
Adrenal medulla
releases hor-
mones lhat
increase cellular
metabolism
Skeletal muscles
contract in a
repetitive cycle
called shivering
i
Thyroid gland
releases thyroid
hormones, which
increase meta-
bolic rate
Increase in body temperature
What (actors can increase metabolic rate and thus increase heat production?
Focus on Well
Exercise Training -
Metabolic
Workout
Hrhletes spend hours a day training
for their sports. Many physiological
changes occur as a result of* all this
training, including an Increased ability
in produce ATI J tor muscle contrac-
tion. These improvements .ire specific
in the metabolic pathways that are used
during the training. Athletes design
their training programs to challenge
the ATP production system or systems
most \ 11 al to their spons.
Metabolic Power
Some sports require a short burst of
power, high eiterg) output that lasts
only a few seconds. Such events include
the 100-meter spnnc, the shot put, the
discus throw, and the JS-merer swim.
Muscle contraction for these events is
supplied primarily \>v existing ATP and
creatine phosphate. (Recall from Chap-
ter <S that creatine phosphate can do-
nate a phosphate group to ADP CO re
score ATR)
Athletes improve their ability to
generate power by practicing their
events, over and over. Power lifting —
forcefully lifting very heavy weights —
also challenges the muscles to produce
more ATP faster. In response to such
training, the concentration qf enzymes
required for these ATP-production
pathways as well as the levels of VI T
and creatine phosphate increases in
trained muscles.
Going lor the Burn
Many athletic events require well-
trained glycolytic pathways. Anaerobic
glycolysis, combined with ATP :-\m.\
creatine phosphate, rovkles most of
the energy for high-intensity exercise
lasting up to 9.0 seconds, such as a 400-
meter run or a 100-meter swim. .Many
sports, such as basketball, soccer, and
tennis, require bursts ol high-ATP pro-
duction by anaerobic glycolysis inter-
spersed with somewhat lower energy
output.
Athletes train the anaerobic gly-
colytic pathway by exercising at high
intensities lor periods of a minute or
longer. Interval I raining includes both
high-intensity work and periods
lower-intensity work or rest. In
spouse to high-intensity exercise,,
concentration of enzymes required
anaerobic glycol) sis increases,
Going the Distance
Most athletic events, including
events lasting longer than a feu
utes, require aerobic cellular re
tion. \ihleivs improve the;
production pathuays by exerojtM
moderate to vigorous inrcniitic
tended periods of lime, with or
high-intensity intervals-. Wi'oIhi
ing increases the size an
mitochondria as well as the COGt
lion ol enzymes required For ATP 'id
duct ion by aerobic pathways
► Think I
\!OU think that the burning sensation that can develop with biyjt-intum
'.vr, producing ATP vid anaerobic glycolysis, represents the brtakdwak
adipose tissue?
vessels in the skin. The skin becomes warm, and the excess
'i.-.u is tost to cite environment by radiation .w\<] conduction
as an increased volume of blood flows from the warmer inte-
rior of the body into the cooler skin. At the same time, meta-
bolic rate decreases, and die high temperature of the blood
stimulates sweat glands of the skin by means of hypothalamic
it ion of sympathetic nerves. As the water in sweat evap-
orates from the surface of the skin, the skin is cooled. All
these responses counteract heai-promoiing effects and help
return body remperarurt CO normal.
Hypothermia is a lowering of core body temperature to
55 d C (95°F) or below. Causes ol hypothermia include an
whelming cold stress (immersion m icy water), meta-
bolic diseases (hypoglycemia, adrenal insufficiency, or hy-
pothyroidism), drugs (alcohol, antidepressants. sccLiDVtj
or tranquilizers), burns, and malnutrition. Sympi
hypothermia include sensation of cold, shivering, u-nfo.
sion, vasoconstriction, muscle rigidity, slow heart rate itaj
ol spontaneous movement, and coma. Death is ll^uuIT
caused by cardiac arrhythmias. Because the eltterl
reduced metabolic protection against a cold en
coupled with a reduced perception of cold, tin
greater risk For developing hypothermia,
■ CHECKPOINT
15. fn what ways can a person lose heat to or nam I
the surroundings? How is it possible for n pi —
heat on a sunny beach when the temperature is ^
(I04'T) and the humidity is 85 percent;
518
Study Outline 519
H I
Common
disorders
Fever
M&veris .111 elevation of hotly temperature that results. From a rc-
• iu uf the hypothalamic thermostat. The most common causes
: u\ uril hi I. iii aerial infections and bacterial toxins; other
Rp« are ovulation, excessive secretion oi thyroid hormones, Oi-
n. and reactions to vaccines. When phagocytes ingest certain
: riiey arc stimulated to secrete, a pyrogen (PI-n>gen;
ir a | lute), a fe\ei-producJng substance. '1 he
reflates do the hypothalamus and induces secretion oi
jglandins. Some prostaglandins can reset the hypothalamic
nn -ut ,u a higher temperature, and temperamre-regiikring re-
mechanisms then act to bring body temperature up to this new
ftttrini;. jntipyrwes are agents that relieve or o rluce fever. I 1 xainples
ilujv aspirin, acetaminophen (Tylenol'* 1 ), and ibuprofen (Advil 1 i.
| of which reduce fever by inhibiting Synthesis of certain
ij»lan.dins.
bthougb death results if eore temperature rises above
(112-1 14°F), up to a point, lover is beneficial. For exans-
)lCALTERMINOLOGY AND CONDITIONS
pie, a higher temperature intensifies die ■lie. i of interferon and The
[.li.iLiocyiic activities of macrophage- while hindering replicqtio
some pathogens, Because fever increases heart rate, infection -fighl
big white liloi.il cells are delivered to sites of infection more rapidly.
In addition, antibody production and T cell proliferation increase,
Obesity
Obesity is ho.ly weight more than 20% above a desirable standard
due i-i an excessive accumulation "I adipose tissue; it affects one*
tlijrd of the adult population in the United States, (Ail athlete may
he "Va-Vfiifbr due to a higher-ihan-uorm-d amount, of muscle tissue
within being obese.) Even rnodeiiate obesity is hazardous to health;
it is implicated as ;i risk factor in cardiovascular disease, hyperten-
sion, pulmonary disease* non-insulin-dependent diabetes ruellitus,
arthritis, certain cancels (breasti uterus, and colon), varicose veins,
and gallbladder disease.
In a few cases, obesity may result from irauma to or tumors in
..od- regulating centers in the InpoihaJaunis. In most cases of
obesity, no specific cause can be identified. Contributing factors in-
clude genetic factors, eating habits taught early in life, overeating u>
relieve tension, and social customs.
tips Cramps that result from profuse sweiumg. The salt
\.,-a in sweal causes painful contractions ol muscles; such
cramps lend to occur in muscles used while working but do not
until the person relaxes once the work is done. Drinking
wilted liquids usually leads to rapid improvement.
ttitmkc (sunstroke) A severe and often fatal disorder caused by
Biposure to high temperatures, Blood flow to the skin is de-
I. perspiration is greatl) reduced, and body temperature
-is-.-s i.lr.n |i|\ because of failure of the hypothalamic thermostat.
Dwli temperature may reach 4?°C (1 IQ°F>. Treatment, which
lie undertaken immediately, consists of cooling the body
o immersing the victim in cool water and by administering
Lfluids anil electrolytes.
frfrrfor (kwash'-e-OR-kor) \. disorder in which prutehi intake
flcicnt despite normal or nearly normal calorie intake.
characterized In edema of the abdomen, enlarged liver, de-
creased blood pressure, low pulse rate:, lower than normal i I
tempera lure, and sometimes mental retardation. Because the
main protein in com lacks two essential amino adds, which are
iiLidcd for growth .m<.\ tissue repair, mum Mucin children
whose diet consists largely ol corniitea] develop kwashiorkor.
Malnutrition [nutl- = bad) Vn imbalance of total Cflloric intake or
intake of specific nutrients, which can be either inadequate or
fxcessive.
MamsimtS (mar-AZ-mus) A type of undernutrition that results
from inadequate intake of both protein and calories. Its charac-
teristics include retarded growth, tow weight, muscle wasting,
emaciation, dry skin, and thin, dry, dull hair.
STUDY OUTLINE
tlon (p. 503}
„ s > fund we eat is our only source of energy For performing
(iln-jie.'.l work; u also provides essential substances that we
1 1 1 1 arhesiw.
„,„ molecules absorbed by the gastrointestinal tract are
lo supply energj for life processes, serve as building
blocks during synthesis of compiles inuleeiiles. or arc m i ■
for future use.
Nutrients (p. 504)
1. Nutrient* unhide c.irhohydratcs, lipids, protein*., voter, miner-
als, and ^ itamins.
520 Chapter 20 Nutrition and Metabolism
2. Nutrition experts suggest dietary calories be 50-60% from car-
hoh\ ih :iii's. >0% nr less from I'.its, unci 12-15% from proteins.
3. The My Pyramid guide represents a personalized approach to
making healthy food choices and maintaining regular physical
activity.
4. Some minerals known to perform essential functions include
calcium, phosphorus, potassium, sodium, chloride, magnesium,
(Ton, lUii.nganese. copper, and JfiUlC. HiCH" luncl.ious MC summa-
n/.nl in fable 20 J on page 506.
5. Mi.tniins arc organic nutrients that maintain growth and nor-
mal metabolism. Many (unction as coenzymes.
6. Lai-soluble uiainins arc absorbed with tilts and include vita-
mins A, D, F, and K: water-soluble vitamins arc absorbed with
water and include the B vitamins and vitamin (.'..
7. The functions of the principal vitamins -^A their deficiency
disorders are summarized in I il ii JO on pages 508-509.
Metabolism (p. 507)
i. Metabolism refers to all chemical reactions «»f tin Nod) ami has
mo phases: cataholism arid aonbaliSrn. Anabohsm consists oi
reactions that COmbmc simple substances iulo uh.iv complex
molecules. Cataholi.sm consists of reactions that break down
complex organic compounds Into simple ones.
2. Metabolic reactions are catalyzed by enzymes, proteins that
Speed up chemical reactions without being changed.
3. Anabolic reactions require energy, which is supplied by c.\\.\-
boHc reacaom
4. During digestion, polysaccharides and disaccliarides are con-
vened op glucose.
5. Glucose moves into cells by facilitated diffusion, which is stim-
ulated by insulin. Some glucose is ccmiboli/.ecf by cells to pro-
duce ATP. Excess glucose can be stored by the liver and skeletal
muscles as glycogen or converted to fat.
6. Glucose catabolism is also called cellular respiration. The com
lili iv eaialiolisni .j| glwcost I" [iroiluce A IP involves glycolysis.
tin Kivlis cycle, and the electron transport chain. It can be
represented as follows: I glucose • 6 oxygen — * 56 or 38 ATI'
f 6 carbon dioxide + 6 water.
7. Glycolysis is also called anaerobic respiration because it occurs
Without oxygen. During glycolysis, which occurs in the cytosol.
one glucose molecule is broken down into two molecules oi
pyruvic acid. Glycolysis jdekls a net of two ATP and two
wnn - h\
8. When oxygen is plentiful, most cells convcrl pyruvic acid to
aeetj I coenzyme A, which enters the Krebs cycle.
9. Ihc Knlis cycle occurs in mitochondria. The chemical en-
ergy originally contained in glucose, pyruvic acid, and acetyl
coenzyme v is transferred co the coenzymes NADU and
I \I)TL.
10. The electron transport chain is a series of reactions that occur
in mitochondria in which the energy in the reduced coenzymes
is transferred to YI'R
11. The conversion of glucose to glycogen for storage occurs ex-
tensively in liver and skeletal muscle libers and is stimulated b)
insulin. The bod} cu, store iboUi SQ§ goftglycogen.
12. The breakdown ol glycocen io iducose occurs niainlv between;
meals.
13. < ihrconeogencsis is the conversion of glycerol, lactic acid, or]
amino acids ro glucose.
14. Sonic triglycerides may be eaniboHzcd to produce ATP; othert
are Stored m adipose tissue. < >thcr lipids are used as stnictun|
molecules or to synthesize other substances.
15. Triglycerides must be split into fatty acids and glycerol Ur r
they can he catahoHzcd. Glycerol can lie transformed imoghd
Cose by conversion into glyceraUehyde 3 -phosphate, hnv
adds arc catabolizcd through formation of acetyl coenzyme^
which can enter the Krebs cycle.
16. The formation o1 ketone bodies bj the liver is a normal phari
of fatty acid carnholism. but an excess of ketone bodies, railed]
kci. »Kiis, rnaj cause acidosis,
17. d he conversion Ol glucose or amino acids into lipids is snmu-J
lated hy insulin.
18. Lipoproteins transport lipids in the bloodstream '[yyw of J
lipoproteins include chylomicrons, vs hich carry dietary lipids-'w
adipose tissue; very-low-deilstty lipoproteins (VI.DLsJ, whjcftl
carry triglycerides Irom die liver to adipose tissue; l<m-.|
lipoproteins (LDLs), which deliver cholesterol to hoily cells um||
high-density lipoproteins (HDLs), which remove excess chultfl
u rol Irom body cells and transport it to the liver lor cliiiiirutii:
19. Amino acuk under the influence of insulinlike growth &j
anil insulin, enter body cells by means of active transport i
side cells, amino acids are reassembled into proteins that I
Lion as enzymes, hormones, structural elements. ,iml •
stored as la' or glycogen; or used for All 1 production.
20. Before amino acids can be cataholizcd, they must deauuiKinA
Liver cells convert the resulting ammonia to urea, whit
crcted in urine.
21. Amino acids may also be converted into glucose, i
and ketone bodies.
22. Protein synthesis is stimulated by insulinlikc growth vjuisaM
thyroid hormones, insulin, estrogen, and testosterone. It kJM
rccrcd by l.)NA and UNA and carried out on ribosomes.
23. lablt • • hi page 515 summarizes carbohydrate, lipid. «M
protein metabolism.
Metabolism and Body Heat (p. 515)
1. \ calorie is the amount ol energy required to raise the wmwA
.iLure oi 1 gram ol water 1°C
2. The Calorie is the unit of heat used to express d . ilori
of foods and to measure the body's metabolic rate. ( Jji i
equals loon calories, or I kilocalorie.
3. Most body heat is a result of eatabolrsm of die fowl we 1
The rate at which this heat is produced is known as- the rani
bolic rate ami is affected by exercise, hormones, tl
i1 mi. body temperature, ingestion of food, age, genflojl
mate, sleep, ami nutrition.
4. Aleasurenicni of the metabolic rate under basal condiuffl
called the basal metabolic rate (13MR).
5. Mtu lunisiii.s iif heal loss are radiation, eondui ti-m. cortjj
md ev-viioramm.
. Radiation is the transfer of heai from a warmer object to a
cooler object without physical contact.
t. i (induction is the transfer of heat between two objects in con-
tact with each other.
Convection is die- transfer of heal bj the movement of a liquid
mt gas between areas ot different temperatures,
I imporation is the conversion of a liquid to ;i vapor; in the
process, heat is lost.
Sell-Quiz 521
10. A normal body temperature is maintained by negative feedback
loops that regulate heat-producing ami heal losing mecha-
nisms.
11. Re spouses rhat produce or retain heal when bod) temperature
falls are vasoconstriction: release of epinephrine, norepineph-
rine. and.,rliyroid hormones: and shivering.
12. Responses that increase hc.it loss when body temperature rises
include vasodilation, decreased metabolic rate, and evaporaiio]
of sweat.
treating a protein from amino adds is an example of
a. deflJiiinarion b. anabolism
• bconeogenesis d. catabolism
B cellular res' pi rati on
2. tree radicals
q. .ire a type of provitamin
li, art essential amino acids
c. ran cause damage to cellular si i
il. In lp regulate enzymatic reactions
c. are a form of energy
of the following statements about vitamins is M'T
n
n. Mnst viuunins are synthesized by the body cells,
b; \ itarains tan act as coenzymes.
c. Vitamin K is produced In bacteria in the Gl tract,
d, Upitl-Soluble vitamins may he stored in the liver,
B. J wess water-soluble vitamins are excreted in urine.
ptch the following:
__ a. precursor for vitamin A
h. form in which lipids are
transported in the blood
plasma
c. needed Lot* invert
©Pto VI V
_il. derived Iroin vitamin ftj
(riboflavin)
iper.iuirc is controlled by the
pons b. thyroid gland
liy[n>th;iJ.iniiis d. adrenal inedtilla
inomic nervous system
tpioval of an amino group ( — NIK) from amino acids
en ig the Krebs cycle is know n as
ijcinii nation b. convection c. kctogeuesis
lipuK i c. aerobic respir.i tii >u
jr diet is low in carbohydrates, which eompound(s) does
: liodv Ik-gin tocatabolize next for VTP production?
vitamins b. lipids c. minerals d. cholesterol
• icids
A. lipoproteins
li. IAD
C, beta-carotene
D. magnesium
8. Cellular respiration includes the following steps in order:
a. Krebs cycle, glycolysis, electron transport chain
b. Krebs cycle, electron transport chain, glycolysis
c. glycolysis, electron transport chain, kiebs cycle
d. electron transport chain, Krebs cycle, glycolysis
e. glycolysis. Krebs cycle, electron transport chain
9. Which of the following is most often used to synthesize YIT-
a. galactose b. triglycerides c. amino acids
d. glucose c. glycerol
10. How does glucose enter the eytosol of cells?
a. facilitated diffusion b. simple dillusum
c. active transport d. osmosis c. electron transport
11. Sweat drying' from a person's skin surface causes loss oi bod]
hear by
a. radiation b, conduction c. convection
d. evaporation e. conversion
12. Glycolysis
a. requires the presence of Oxygen
b. produces two ATP molecules per glucose molecule
C. lakes place in mitochondria
d. is also known as the Krebs cycle
e. is the conversion ofgjhicose to glj i •
13. Which of the following statements is NO'f true?
a. Triglycerides are scored in adipose tissue.
b. Chylomicrons enter the blood by w.i_\ oj lacieals m the in-
testines.
C Most of the body's rlmk sterol is carried in li.wdei.--iu
lipoproteins.
d. Lipids can lie siored in the liver.
e. I ligh-densiry lipoproteins contribute to die lunnaiioi) of
fatty plaques.
14. Which of the following equations sunim complete
eaiabolism of a molecule of glucose?
a. glucose i 6 water—* 3o or 38 VII' i (S< 0; I 6Gj
b. glucose f 6 Qj -* 16 or 18 vn* i o ( K i i 6 water
e. glucose I VI P -»3'J of 18 CO- I 6 wan i
d. glucose + pyruvic acid -* 56 or 1$ VI I' - 60
c. glucose ■ citric acid -* 31 or J8 ATP * n( O
522 Chapter 20 Nutrition and Metabolism
15. Those amino acids thai cannot bj Bynt&itfij&d by the body and
must lie obtained from the diet arc kno\» ,
a. coenzymes b. ketones c. essential ammo acids
d. nonessential amino acids e. polypeptides
16. Which Of the following would NOT increase the metabolic
irate?
a. increased levels of thyroid hormones
b. epinephrine
c. old age
d. fever
e. exercise
17. FAD :mtl NAD' are examples of
a. nutrients b. antioxidants c. pyrogens
d. coenzymes e. minerals
IH. The process by which 14luco.se is formed from amino acids is
a. glueoneogenesis l>, deamination c. anaerobic
respiration il. ketogenesrs c, glycolysis
19. All of 1 he following can contribute to an increase ir
temperature EXCEPT
a. shivering
Ii. release of thyroid hornioncs
c. syinpaUictic stimulation of the adrenal medulla
d. vasodilation ol'lilooil vessels in the skin
c. activation oi the nyijotlialarans
20. Match the following;
a. eon version of glucose A. catahulism
to pynnii- acid ij. anaboifsm
b. die complete I ireakd'iu n C. glycolysis
"Ulueose I), cellular respira J
C buildinir simple molecules g krebs cvcle
into more complex ones
d. \ \l> and I \\) pick up
liieli-ciicPi)- electrons
e. the breakdown of organk
compounds
m
CRITICAL THINKING APPLICATIONS
1. Carla and Ashley, members 0? their college's tennis tram, ate
lunch at McDonald's before dieir afternoon practice, Carla had
.j Quarter Pounder with cheese, small trench tries, and a small
chocolate shake; Ashley had a Chicken VlcCJrili (plain, without
mayonnaise), .1 garden salad with fat-free vinaigrette, and a
of \% low-fin milk. ( rif&fguc their choice^ based on the
recommended distributions of calorics. I low many calorics arc
ir breakfast; dinner, and snacks?
Quarter Founder Meal
^percentages of total
calories):
total fats - 41'
saturated fats = IT
1 carbohydrates = 469
simple saga
proteins i V i
1 mi. 1 1 ( lalories Hiss
Grilled Chicken .Sandwich .Meal
(pcrcentaires ol total calorics):
total fats ■ 24%
satoatcd rajs 9%
total carbohydrates - •)
simple sugars = 15%
proteins - 29%
total (. ialorit 1
2. Its noon on a hot summer clay, the sun is directly ovhOh
ami a croup of sunbathed roasts on die beach. What mc
iiisni causes their body temperature to increase? Several of tl
sun bathers jump into the cool water. What niecbms
decrease their body temperature?
3. Shannon is a morning person hue her roommate Darla 1*1
In fact. Shannon teases Dark for being a classic examples
"BA1R" (barely mentallj responsive) during her 8 \.m I
What dor-- BMR really mean- I low is metabolism
4. Roh swallows a multivitamin tablet even morning ami id
antioxidant tablet containing bcta-camtcnc, vitamin C, mim
aiiun V. with his dinner every night. What are ilie f tines*
antioxidants m the body" What happens to the .urn
an\ exceed his daily requiremenT
f ANSWERS TO FIGURE QUESTIONS
20.1 The wider base ofeacfo \>.\\h\ repress tits foods with little or
tin solid fatS Ol added stilus.
20.2 The formation of digestive en/ymes m the pancrca-. is pan
uf auaholism.
20.3 Complete catabolism of glucose yields 36- 38 ATP.
20.4 I aver cells can carry out gluconeogenesis.
20.5 Liver cells form ketone bodies,
20.6 Exercise, the sympathetic nervous system, In inn
nephrinc. norepinephrine, thyroid hormones, test
human growth hormone), elevated body tcinperanin,',
11 stion of food increase meiaholic rate.
THE URINARY SYSTEM
chapter 21
jtL kidney stone is a hard mass,
usually composed of calcium oxalate, uric acid, or cal-
jffii phosphate crystals. The medical term for a kidney
stone is renal calculus. Researchers do not yet know
why some people are predisposed to developing kidney
stones. About 90% of stones will pass on their own
within three to six weeks, so patients are usually ad-
ded to try lifestyle changes before going on to medical
treatment, increased fluid intake (3 to 4 quarts of
fluid, preferably water, per day), and changes in diet
iind medications are often sufficient treatment.
Focus an Wellness, page 535
wvMW.wiley.com/collegB/apcenlral
j/ls body cells carry out their
metabolic functions, they consume
oxygen and nutrients and produce
substances, such us carbon dioxide.
that l-Kivc no useful functions and need to be
eliminated from the body. While the respiratory system
rids the body of carbon dioxide, the urinary sysu-ui dis-
poses of most other unneeded substances. As you will
learn in this chapter, ridwe^SCi the urinary system is not
merely concerned with waste disposal; it carries out a
number of other important functions as well.
lookinq back to move ahead
Transport Across the Plasma Membrane (page 47)
Simple Cuboidal Epithelium (page 75)
Transitional Epithelium (page 82)
Actions of Antidiuretic Hormone (AOH) (page 322)
Vitamin D. Calcitriol.and Calcium Homeostasis (page 326)
Renin-Angiotensin-Aldosterone Pathway (page 331)
Filtration and Reabsorption in Capillaries (pages 388-389)
Stood Colloid Osmotic Pressure (page 388)
52c
524 Chapter 21 The Urinary System
OVERVIEW OF THE URINARY
SYSTEM
objective • List the components of the urinary sys-
tem unci their general functions.
The urinary system consisis oi two kidneys, two ureters, one
iinnarj bladder, and one urethra (Figure 21.1). Alter the kid-
neys filter blood, they return must of the water and many ol
the solute to the Midstream. The remaining water and
sulnl.es constitute urine, which passes through the ureli tt*S
and is stored m the urinary bladder until it is expelled Irom
the body through the urethra. Vephroltigy (ncr'-ROL-o-je;
m'phm- = kidney; -kgp - study of) is ihe scientific siiuk of
the anatoim, physiology, and disorders of the kidneys. The
branch ol' medicine thvir deals with the male and female uri-
ij stems and the nude reproductive system is urology
(Ti-kOL-o-je; tifo- - nriiu). \ physician who specializes jji
this branch of medicine is called a urolagist (u ROI -&-pst>,
The kidneys qb the major work of the urinary system.
The other parts of the system are primarily passageways and
temporary storage areas. Functions of the kidneys include tiii
Following:
■ Regulation of ion levels in the blood. The kiclra
help regulate the blood levels ol several ions. in<
portnntly sodium ions (No 1 ), potassium ions (K 1,
Hum ions it. a' >. chloride ions (CI ), and phosphate id
<III><V ).
■ Regulation ol* blood volume and blood prcsstffl
The kidneys adjust the volume of blood in the bad)}l
returning water to die blood or eliminating it o
the mine. They help regulate blood pressure by scccen
the enzyme renin, which activates the renin-*
giotensin— aldosterone pathway (see Fijriirc
|..ii( 131), by adjusting blood How into and our ofl
kidneys, and In adjusting blood volume.
■ Regulation of blood pH. The kidneys regulate
ceiur.uion of II in the blood In excreting a vor" '
amount of II in the mine. The\ also conserve bib
carbonate ions (HGO ? ), an important buffi
Bom activities help regulate blood pH.
Rgure 21.1 Organs of the female urinary system in relation to surrounding structures.
^
Urine formed by the kidneys passes first into the ureters, then to the urinary bladder lor
storage, and finally through the urethra for elimination from the body,
RIGHT KIONEY
Right renal artery
RIGHT URETER
URINARY -
BLADDER
URETHRA
Diaphragm
Esophagus
Left 'adrenal
(suprarenal) gland
Left renal vein
LEFT KIDNEY
Abdominal aorta
nlenor vena cava
LEFT URETER
Rectum
Left ovary
Uterus
Anterior view
Which organ of the urinary system does most of the work to form urine?
Functions of the Urinary System
1. The kidneys regulate blood volume and compel
regulate blood pressure and pH, produce two hi
and excrete wastes,
2. The ureters transport urine Irom the kidneys lo :
bladder.
3. The urinary bladder stores urine and expels il iriiofitf
urethra,
4. The urethra discharges urine from the body.
Production of hormones. The kidneys produce two
hormones. Qikimot, the active form of vitamin D, helps
legukte calcium homeostasis (see Blgtic I klQ on pa^e
827), and eryiirropoietm stimulates product! on qj red
blood cells (see i . _ 1 1 re 1 4.4 on page 3 5 1 ).
I vcretion of wastes. By forming mini', the kidneys
help excrete wastes — substances that have no uschil
function in the body. Some wastes excreted in urine re-
sult from metabolic reactions in the body. These in-
clude ammonia and urea from the breatkdbwn of amino
:kids; bilirubin from the breakdown ol hemoglobin;
jtearifcine from the breakdown ot" creatine pbosphate in
muscle fibers; and uric acid from the breakdown of rai-
cleic acids. Other wastes excreted in urine are Foreign
Instances from the diet, such as drugs and environ
mental toxins.
I CHECKPOINT
What are wastes, and how do the ladneys take pari in
their removal from the body?
Structure of trie Kidneys 525
STRUCTURE OF THE KIDNEYS
OBJECTIVE • Describe the structure and blood supply
Of the kidneys.
The kidneys '{bLID-UL'/,) are a pair of reddish organs shaped
like kidney beans (Figure 21. 1). They lie on either side oi
the vertebral column between the peritoneum and the back
wall of the abdominal cavity ai the level of the 12 th thoi u
and feat three lumbar vertebrae. The 11th and Uih pairs of
ribs provide some protection for die superior pare of the
kidneys. The right kidney is slightly lower than ihe left be-
cause the liver occupies a targe area above the kidney on the
I'i^hl si !
External Anatomy of the Kidneys
\n adult kidney is about the si/.e of a bar of bath soap. W.ir
the center of the medial border is an indentation called the
renal hiltim (Ilt-ium), through which die ureter leaves the
Figure 21.2 Structure of the kidney.
A renal capsule covers the kidney. Internally, the two main regions are the renal cortex and the renal medulla.
Renal
hllurn.
Renal cortex'
Renal medulla
Renal column
Rerlal pyramid
|n renal medulla
Renal papilla
Renal capsule
Nephron
Palh of urine drainage.
Collecting duct
I
Minor calyx
Major calyx
Renal pelvis
Urinary bladder
Frontal section ol right Kidney
Where in the kidney are the renal pyramids located?
526 Chapter 21 The Urinary System
kidney and blood vessels. lymphatic vessels, and nerves enter
and exit. Surrounding each kidney is the smoolli, transparent
re mt I Ci/psul^, a connective tissue slie;uli that helps maintain
die shapes of the kidney and serves as s barrier agiiinst trauma
(Figure 21.2), Adipose (fatty) tissue surrounds the renal cap-
sule and cushions the kidney Atony with a thin layer of dense
irregular connective tissue, the adipose tissue anchors the
kidney to the posterior abdominal wall.
Internal Anatomy of the Kidneys
Internally, the kidneys have two main regions- ajj outer light-
red region called the renal cortex {corrcx - rind or hack:) and
an inner, darker red-brown region called the renal medulla
{//ndulht — inner portion) (Fij ')■ Within die renal
medulla are several cone-shaped renal pyramids. Extensions
of the renal cortex, called renal columns, fill the spaces b<
renal pyramids.
I rine formed in the kidney drains inio a large, funnel-
shaped cavity called the renal pelvis {petit- - basin). The rim
of the renal pelvis contains cuplike structures caller! major
and minor calyces (KM -i-se/ = cups; singular is calyx).
Urine (lows from several ducts within the kidney into a mi-
nor caiy\ and from there through a major ealyx into die renal
pelvis, which connects to a ureter. Water and solutes \n the
fluid that drains into the renal pelvis remain in the urine and
are excreted (eliminated from the hodv).
Renal Blood Supply
About 20-25% of the testing cardiac dntpttt— 120Q milli-
liters of blood per minure — flows inro the kidneys through
the right and left renal arteries M I i. Within each
kidney, the renal artery divides into smaller and smaller ves-
sels (segmental, interlobar, arcuate, tnterkhnlirr arteries) that
eventually deliver blood to the afferent arterioles (///- = to-
ward; -fare = CO carry). Each afferent arteriole divides into a
tangled capillar) network called a glomerulus (gleVMER-a.-
bs = little ball; plural \5 glomeruli).
The capillaries of the glomerulus reunite to form an ef-
ferent arteriole (ef- = out). Upon leaving the glomerulus,
eaefa efferent arteriole do ides CO lonn a network of capillaries
around the kidney tubules {described shortly). These peri-
tubular capillaries (peri- = around) eventually reunite to
fi.rin in-nuduilur veins, which merge \m>< H'leriuhthtr. arcuate.
and interlobar vcbis. Ulntnatelv, all these smaller veins drain
into the renal vein.
Nephrons
The functional units of the kidney are the nephrons (NEI
ton/), numbering about a million in each kidnej il igtn
on page 528). A nephron consists of two pans: a renal cot-\
pnscle (KOR-pus-ul = tiny body), where blood plasma is lit-
tered, ami a renal tubule into which the tillered fluid, crlln!
glomerular filtrate, passes. As the lluid moves through
renal tubules, wastes and excess substances ire added, i
useful materials are returned to the Mood in die periti
capillaries.
The two parts 'hat make up a renal corpuscle arc
glomerulus and the glomerular (Boiemans) capsule
double-walled cup ol" epithelial cells that surrounds
glomerular capillaries, (ilomertil.tr filtrate first cnrei
glomerular capsule and then passes into the renal tuhnlc. iw
the order that lluid passes through them, the three maiitseof
tions of the reiud tubule are the proximal convoluted
the loop of Henle, and the distal convoluted tabu/c. Pmvmil]
denotes the part of the tubule attached to the glum.
Capsule, and distal denotes the part that is farther away.
rotated means the tubule is tightly coiled rather than straight
I he renal corpuscle and both convoluted tubules lii- within
the renal cortex; the loop of I lenle extends into the TUXm
medulla. The first pari of the loop of Henle begins in then
rial cortex and extends downward into the renal incduHjJ
where it is called the descending limb of the loop of Hem
(Figure 21.4). It then makes a hairpin turn and returns .
renal cortex as the ascending limb of the loop of Henle. \h
distal convoluted tubules of several nephrons emptj into
common collecting duct.
The number of nephrons is constant from birth
nephrons do not form to replace those that are inju
diseased. Signs of kidney damage often are noi apparent
however, until the majority of nephrons are damaged In-
cause the remaining functional nephrons adapt to handle 11
larger-rhan-normal load. Surgical removal of on
for example, stimulates enlargement ofihe remaining tiij.
Iney, which eventually is able to filter blood at K0% of tfej
rate of two normal kidnej S.
■ CHECKPOINT
2. Which structures help protect and cushion the bint
3. What is the functional unit of the kidney- Dcscna
structure.
Fund i o ns ol Ih d N ephron 527
Figure 21.3 Blood supply of the right kidney.
The renal arteries deliver about 25*. of the resting cardiac output to the kidneys.
Glomerulus
Th
Frontal
Renal capsule
Rsnal cortex
Renal pyramid
fii'ranal medulla
Interlobular
artery
Interlobar
artery
Peritubular
capillary
Interlobular
vein
£=- Vasa recta
Segmental artery
Renal artery
Renal vein
Interlobar vein
Arcuate vein
Interlobular vein
(.i> Anterior view ol frontal section of right kidney
Renal artery
Segmental arteries
Interlobar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles
Glomerular capillaries
Efferent arterioles
Peritubular capillaries
Interlobular veins
Arcuate veins
Interlober veins
Renal vein
(b) Path of blood (low
through ilie kidney
How much blood enters the renal arteries each minute?
528 Chapter 21 The Urinary System
Figure 21.4 The parts of a nephron, collecting duct, and associated blood vessels.
Nephrons are the functional units of the kidneys.
Proximal convoluted tutaufe
Peritubular capillary
Renal cortex
Renal medulla
Renal papilla
Minor calyx
Renal capsule
Renal corpuscle:
Glomerular (Bowman's)
capsule
- Glomerulus
Elferent arteriole
Distal convoluted tubule
Afferent arteriole
Interlobular artery
nierlobular vein
Arcuate vein
Arcuate artery
Coilicon'iedullary junction
Loop ol Henle".
Descending limb ol Ihe
loop of Henle
Ascending limb ol ihe
loop of Henle
Collecting duel
Kidney
FLOW OF FLUID THROUGH A
CORTICAL NEPHRON
Glomerular (Bowman's) capsule
*
Proximal convoluted tubule
i
Descending limb of tho
loop of Henle
t.
Ascending limb olthe
loop ol Henle
Dlsial corwcilLrtsd tubule
trnams mo cottacting duct 1 )
i r
Nephron and vascular supply
Renal papilla
Minor calyx
Urine
s A water molecule has just entered the proximal convoluted tubule of a nephron. Which parts of the nephron will it
travel through (in order) to reach the renal pelvis in a drop of urine?
FUNCTIONS OF THE NEPHRON
OBJECTIVE • Identify the three basic functions per-
formed by nephrons and collecting ducts and indicate
where each occurs.
In produce urine, nephrons and collecting ducts perform
three basic processes — glomerular filtration, tubular reab-
M.rpiion, and tubular secretion (Figure 2 L5):
Filtration is the forcing of fluids and dissolved
smaller than a certain size through a membran
sure. Glomerular filtration is the first step of urine i
tum: Blood pressure forces water and most solutes^
plasma across the wall of glomerular capillaries)
glomerular filtrate. Filtration occurs in glomeruli \\
occurs m other capillaries (see ) >onpage$j
Tubular reabmrpi ion occurs as filtered fluid IV
die renal tubule anil through the collet-fin i
Functions ol the Nephron 529
Figure 21.5 Overview of functions of a nephron. Excreted substances remain in the urine and
eventually leave the body.
^ Glomerular filtration occurs in the renal corpuscle; tubular reabsorption and tubular secretion occur
an along the renal tubule and collecting duel.
Renal tubule and collecting duct
Renal corpuscle
Afferent
arteriole
Efferent
arteriole
Peritubular capillaries
* Wnen the renal tubules secrete the drug penicillin, is the drug being added to or removed from the blood?
UrfrtB
(contains
excreted
substances)
Blood
(contains
reabsorbed
substances)
ami duct cells return about 99% ofchfl filtered water ami
m.mv useful solutes to the blood flowing through per-
faxbular capillaries.
I Q Tubular secretion also takes place as fluid Hows along
the tubule and through the collecting duet: The culuik-
duel cells remove substances, such as wastes, dm
and excess ions, horn blood in die peritubular capillaries
mil transport them into the fluid in the renal tubules.
As nephrons perform their luneiinns, they help maintain
;s of the blood's volume and composition. The sk-
is somewhat similar to a recycling center: Garbage
bucks dump refuse into an input hopper, where the smaller
refuse passes onto a conveyor belt (glomerular filtration ol
blood plasma). As the conve\m belt carries the gattbage
along, workers remove useful items, such as aluminum cans,
plasties, and glass containers (reabsorpimn). Other WOtlcers
place additional garbage and larger items onto die com cat
belt (secretion). At the end of the belt, .ill remaining garbage
tails into a truck for transport to the landfill (excretion o|
wastes in urine).
Table 21.1 compares the substances thai are filtered, re-
absorbed, and excreted in urine per day in in adult male. Al-
though the values shown are typical, they van cojisidcr.il <k
according GO diet. The Following sections describe each of the
three steps that contribute to urine formation in more detail.
Table 21 .1 Substances Filtered, Reabsorbed, and Excreted in Urine per Day
Substance
Jum ions {K '
filHfcflcid
'Creatinine
Filtered' (enters renal tubule]
Reabsorbed (returned to blood)
Excreted in Urine
orWe ions (Ch)
ilons(Na')
te Ions (HCCV
180 liters
640 g
579 g
275 g
162 g
54 C]
29.6 g
8.5 g
i.e g
178-179 liters
633.7 g
575 g
274.97 g
162 g
24 g
29.6 g
7.7 g
1 -2 liters
6.3 g
*M.
0.03 g
30 g'
2.0 g'
0.8 g
1.6g
ning glomerular nitration is 180 liters per day.
helnq Filtered and reabsorbed, urea is secreted,
tually all filtered K is reabsorbed in the convoluted tubules and loop ol Henle, a variable amount ol K - Is secreted in the collecting duct
530 Chapter 21 The Urinary System
Glomerular Filtration
'I wo layers of cells compose the capsule thai surrounds the
glomerular capillaries I 1 .6), Think of ilie renal cor-
puscle as a li^i (the glomerular capillaries) pushed into a lnn|>
balloon (the glomerular capsule) until the fist is covered by
two layers or the ha I loon with a space, the capsular space, in
between. The cells chat make up the inner wall of the
glomerular capsule, called podocyt.es, adhere dosel.3 to the en-
dothelial cells of the glomerulus. Together, the podocytes and
glomerular endothelium lonu .1 jtlivatimi wembruue that per-
mits the passage of water and solutes from the blood into the
capsular space, Blood cells and most plasma proteins remain
in the blood because they are too large to pass through the
filtration membrane. Simple squamous epithelial cells form
the Outer layer 61 the glomerular capsule.
Net Filtration Pressure
The pressure thai causes filtration is the blood pressure frl
the glomerular capillaries. Iwu other pressures oppose
glomerular tili.rai.ion: (I) Wood colloid osmotic pressure (see
page 388) and (2) glomerular capsule pressure (due to Jluid
already in the capsular space ami renal tubule). When either
of these presumes increases, Lrlouierular filtration decreases.
Normally, blood pressure is greater than the two opposing
pressures, producing a net filtration pressure of about 10 mm
Hg, Net Station pressure forces a large volume of fluid
into the capsular space, about ISO liters daily in females and
ISO liters daily in males.
Because the efferent arteriole is smaller in diameter than
the afferent arteriole, it helps raise the blood pressure in the
glomerular capillaries. When blood pressure increases ovm
creases slightly, changes in the diameters of the afferent m
efferent arterioles ean actually beep net filtration pressure
steady to maintain normal glomerular filtration. Consilient
oi the afferent arteriole decreases blood How into the
glomerulus, which decreases net filtration pressure. Constriej
Hon of the efferent arteriole stows outflow of blood ami in-
creases net filtration pressure.
Conditions thai greatly reduce blond pressure, for instance
severe hemorrhage, maj cause glomerular blond pressure
in liill SO low that net filtration pressure drops despite con.-
strichon of efferent arterioles. Then, glomerular filtration
slows, or even stops entirely. The result is oliguria (o%- =
scanty; -win - urine production), a daily urine output be-
tween 51) arid 250 ml., or anuria, a daih urine output of j
less than 50 tnL. Obstructions, such as a kidney stone that
blocks a ureter or an enlarged prostate that blocks ti
ihra m 3 male, can also decrease net filtration pressure ami I
thereby reduce urine output.
Figure 21.6 Glomerular filtration, the first step in urine formation.
Glomerular filtrate (red arrows) passes into the capsular space and then into the proximal convoluted tubule.
Afferent
arteriole
Outer layer of
glomerular capsule
Renal corpuscle
< external view)
Capsular space
Ascending limb
of loop of Henie
EHerent arteriole
Proximal
convoluted
lobule
^mf *** Podocyte of inner layer
ol glomerular capsule
Endothelium ol
glomerulus
Renal corpuscle finiernat view)
s Which celts make up the filtration membrane In Ihe renal corpuscle?
Functions of the Nephron 531
Glomerular Filtration Rate
The amount of filtrate that tonus m bpth kidneys every
| minute is called the glomerular jilt mtit>n rule (GFR). In
adults, the ( il*R is about 1 05 ml./min in females and
BS mL/min in males. It is very important for the kidneys to
Lintain a constant GFR. If the GFR is too high, needed
Instances pass so quickly through the renal tubules that ilie\
are unable to be reabsorbed and pass out ol the body as part
of urine. On the other band, if the ( iFR is too low, nearly all
jg filtrate is reabsorbed, and waste product* are not ade-
nine I y excreted,
Atrial natriuretic peptide (.IMP) is a hormone dial pro-
loss of sodium iuns and water in die mine in part be-
cause ii increases glomerular filtration rate. Cells in die atria
heart secrete more ANP if die heart is stretched more,
as occurs when Mood volume increases. \NP then acts on
the kidneys to increase loss of sodium ions and water in
fenc, which reduces the blood volume bac& to normal.
Like most blood vessels of the body, those of the kidneys
ire supplied by sympathetic neurons of the autonomic \wr-
L* system. When these neurons are active, they cause vaso-
tonstriction. At rest, sympathetic stimulation is low and the
gerent and efferent arterioles are relatively dilated. With
iter sympathetic stimulation, as occurs during exercise ot
morrhage. die afferent arterioles arc constricted more tiuin
Liferent arterioles. As a result, blood How into glomerular
;anillaries is greatlj decreased, net filtration pressure de-
... and ( l-FR drops. These changes reduce urine output,
helps conserve blood volume and permits greater
pel flow to other bod) tiss ■■
feibular Reabsorption and Secretion
tybultrr reaftsorption — returning most of the filtered water
Mid mam of the filtered solutes to the blood— is the second
Function of the nephrons and collecting duets. The
H»ed fluid becomes tubular fluid once it enters the proximal
iJVoltltetl tubule. Due to reabsorption and secretion, the
JJosirion of tubular fluid changes as [t Hows along the
cphron tubule and through a collecting duct. Typically
of die tiltered water is reabsorbed. Only 1% of
Hater in glomerular filtrate actually leaves the body in
w,the fluid that drains into the renal pelvis.
i -lial cells all along the renal tubules mm\ collecting
carry out tubular reabsorption (Figure 21.7). Some
Bare passively reabsorbed by diffusion; others are reab-
bv active transport. Proximal convoluted tubule cells
the largest contribution, reabsorbing 65% ol the 61-
WBter, 100% of the filtered glucose and amino acids,
quantities of various ions such as sodium i\.ri.
jfam (K 1 ), chloride (CI y bicarbonate (HGO3 ), cal-
;.. and magnesium (Mg : j- Reabsorption of
ifllso promotes reabsorption of water m the following
i movement of solutes into peritubular capillaries
decreases the solute concentration of the tubular fluid but in-
creases the solute concentration in the peritubular capillaries.
As a result, water moves by osmosis into peritubular capillar-
ies. Cells located distal to the proximal convoluted tubule
airy om fine-nine reabsorption to maintain liomeostntic bal-
es
ances of water and selected ions, "lb appreciate the huge ex-
tent of tubular reabsorption. look back at Table 21.1 on page
|Z9 and compare the amounts of substances thai are filtered.
reabsorbed, and excreted in urine.
When the blood concentration pfglucOS.fi rises above nor-
ma!, transporters in the proximal convoluted mimics ma\
not be able to work Bast enough to reabsorb all ol the fil-
tered glucose. As a result, some glucose remains in the
urine, a condition called glucosurk(gloo'-ko-SOO re-.i)
The most common cause of glucosuria is diabetes mcllitus,
in which the blood glucose level may rise tar above normal
because insulin activity is deficient. Because "wan ; follows
solutes" as tubular reabsorption takes place., an) condition
that reduces reabsorption of filtered solutes also increases
the amount ol water lost m urine, Polyuria (pol'-e-U -re <
poly- ■ too much), excessive excretion of urine, usir
accompanies glucosuria and is a common symptom <>l
diabetes.
The third function of the nephrons and n.llt-ctiiyi: ducts
is tubular secretion, die transfer of materials from tin blood
through tubule cells ami into tubular fluid. As is the case for
tabular re-absorption, uilnikir secretion takes place all along
the renal tubules and collecting ducts and occurs via both
passive diffusion and active transport processes. Secreted sub-
stances include hydrogen ions ill ), K . ammonia (Ml
urea, creatinine ui waste from creatine in muscle cells), anil
certain drugs such as penicillin. Tubular secretion helps dim
mate these substances from the bodj.
Ammonia is a poisonous waste product thai is produced
when amino groups are removed from amino acids. Liver
cells convert most ammonia to urea, uhtch is a l$RHtOlfc
compound. Although tiny amounts of urea mA ammonia are
present m sweat, most excretion of these nitrogen- containing
waste products occurs in rhe urine. Urea and ammonia in
blood are both filtered at the glomerulus and secreted by prox-
imal convoluted tubule cells mio the tubular fluid. Secretion ol
excess K' for elimination in the urine also is veiy important.
Tubule cell secretion of K' varies with dietary intake ol
sium to maintain a stable level ofK m bodj fluid,.
Tubular secretion also helps control blood pi I. \ norma!
blond pll of 7.55 to 7.45 is maintained, even though the i\ p
ical high-protein diet, in North America provides more acid
producing foods than alkali-producing foods, lb eliminate
acids, the cells of the renal tubules secrete II ' into the tubu-
lar fluid, which helps maintain the pll of blood m the normal
range. Due to H secretion, urine is typically acidic (has a
pH below 7).
532 Chapter 21 The Urinary System
Figure 21.7 Filtration, reabsorption, and secretion in the nephrons and collecting ducts. Percent-
ages refer to the amounts initially filtered at the glomerulus.
|fe?
Filtration occurs in the renal corpuscle; reabsorption occurs all along the renal tubule and collecting ducts.
RENAL CORPUSCLE
Glomerular filtration rate:
105-125 mUmin
Filtered substances: water and all solutes
present In blood (except proteins) Including
ions, glucose, ammo acids, creatinine
PROXIMAL CONVOLUTED TUBULE
Reabsorption unto Wood) ol liltered:
Water
65% (osmosis)
Glucose
100%
Amino acids
100%
Na-
65%
tC
65%
cr
50%
H®
80-90%
GrfVJMg*
variable
Urea
50%
Secretion (into urine) of:
H"
variable
Ammonia
variable
Urea
variable
Creatinine
small amoun. 1
1
Urine — ( ")
LOOP OF HENLE
Reabsorptl
in (into biood) of:
Water
1 5% (osmosis in
descending limb)
Na"
20-30% {ascending limb)
K*
20-30% (ascending limb)
er
35% (ascending limb)
hco/
10-20%
Ca 7 '. Mo/''
variable
Secretion (Into urine) o(:
Urea
variable
DISTAL CONVOLUTED TUBULE
Reabsorption (into blood) ol:
Water 10-1 5% (osmosis)
Na" 5%
CI S%
Ca ? " variable
LAST PART OF DISTAL TUBULE
AND COLLECTING DUCT
Reabsorption (into blood) ot:
Water 5-9% (insertion ol water
channels stimulated, by ADH)
Na"
HCO a
Urea
1-4%
variable amount
variable
Secretion (into urine) ol:
K' variable amount to
adjust tor dietary Intake
(leakage channels)
H' variable amounts to
maintain acid-base
homeostasis (H* pumps).
Tubular fluid leaving the collecting dud is dilWa
when ADH tevel is low and Goncentratfid
ADH level is high.
In which segments o» the nephrons and collecting ducts does secretion occur?
Functions ot the Nephron 533
Hormonal Regulation of Nephron Functions
Hormones affect the extern olf-NSa . CI", and waUer reabaorp-
idoa as well as K 1 secretion by the renal tubules, I lit- most
mportant hormonal regulators of ion reabsorptapn and se-
cretion are angiotensin 11 and aldosterone. In the proximal
luted tubules; angiotaum II enhances ceabsorption of
and ( 1 . Angiotensin II also stimulates the adrenal eor-
ic> release aMosfcetoiie, a hormone that in run* stfnplates
e collecting ducts to reabsorb more Na' and C] and se-
more K'. When more Na' and CI arc reabsorbed,
more water is also reabsorbed bj osmosis, \ldosterom-
ated secretion ofK rs the major regulator ol blood K
l.-vil. An elevated level of K m plasma causes serious dis-
bnnces in -cardiac rhythm or even cardiac arrest Besides
,u mi' glomerular filtration rate, the hormone atrial na-
muretic peptide (ANP) plays a minor role in inhibiting the
Labsorption of Na (and CI and water) by fc renal
nilmk-s. As GFR increases and Na ' , CI . and water reah-
ajjprion decrease, more water and salt are lost in the urine,
ll effect is io lower blood volume.
The major hormone that regulates water rcaibsorption is
itiittrctic hormone (ADH), which operates via negative
dback (Figure 21.8). When the concentration of water in
Is blood decreases by us little as 1%, osmoreceptors in the
|rjirithalamiis stimulate release of ADIT from the posterior
irv. A second powerful stimulus for AD1 1 secretion is a
i in Wood volume, as occurs in hemorrhaging or se-
..n. ADH acts on tubule cells in the last part ol
i convoluted tubules and throughout the collecting
, In die absence of \D\ i, these parts of the renal tubule
.i very low permeability to water. ADH increases the
r foertneabilitj ol these tubule -cells by causing insertion
(items that rtinerion as water channels into their plasma
ires. When the water permeability of the tubule
increases, water molecules move from the tabular fluid
the cells and then into the blood. The kidneys can pm-
irrle as 400-500 ml. of vers concentrated urine
day when \l)l I concentration is maximal, tor instance
severe dehydration. When ADI1 level declines, the
^channels are removed from the membranes. The kid-
produce ii large volume of dilute urine when ADH
is tow.
Sties are substances that slow reabsorpiion of water
\c kidneys and thereby cause diuresis, an elevated urine
. Naturally occurring diuretics include cqffffim in
.. tea, and cola sodas, which inhibits Na rcahsorp-
i, jtul alcohol in beer, wine, and mixed drinks, which in-
pife -secretion of ADM. In a condition known a.s diabetes
\\)\ I secretion is inadequate or the ADI 1 recep-
i inky, and a person may excrete up to 20 liters ol
dilute urine daily.
Figure 21.8 Negative feedback regulation ot water reabsorp-
tion by ADH.
When ADH level is high, the kidneys reabsorb more water.
*~
me stimulus disrupts
homeostasis by
Decreasing
Blood water
concentration
Receptors
Osmoreceptors
in hypothalamus
input
Control cent
Nerve
impulses
Hypothalamus and
posterior pituitary
ADH
/
Return to homeostasis
when response brings
concentration of water in
the blood back Jo normal
Output
Increased release
of ADH
Electors
Cells hi DCT
and collecting _^
dud become
more perm*:
to water, which increases
water reabsor'pfion
Increase in blood
water concentration
Would blood ADH level be higher or lower than normal in a per-
son who has just completed a 5-krn run without drinking any
water?
Components of Urine
An analysis of the volume and physical, chemical, and micro
scopic properties of urine, called a urinalysis, u-lls us much
about the suite of die bodv. [able 2\.l summarizes the prin-
cipal physical characteristics of urine.
534 Chapter 21 The Urinary System
Table 21.2 Physical Characteristics of Normal Urine
Characteristic
Description
Volume One m two liters (about 1 to 2 quarts) in 24 hours but
varies considerably.
Color Yellow or amber, but varies with urina cortcemralion and
diet. Coior is due to urochrome (pigment produced Irom
breakdown of bile) and urobilin (from breakdown ot he-
moglobin). Concentrated urine is darker in color. Diet,
medications, and certain diseases affect color-
Turbidity Transparent when freshly voided, but becomes Turbid
(cloudy) after a while.
Odor Mildly aromatic but becomes ammonia-like after a time.
Some people Inherit the ability to lorm methylmercaptan
from digested asparagus, which gives urine a character-
istic odor.
pH Ranges between 4:6 and 8.0; average 6.0: varies con-
siderably with diet BIgh-protein diets increase acidity;
vegetarian diets increase alkalinity.
Specific gravity Specific gravity (density) is the ratio of the weight of a
volume of a substance to the weight of an equal volume
ot distilled water. Urine specific gravity ranges from
1 ,001 to 1 .035. The higher the concentration of solutes,
the higher the specific gravity.
The volume of urine eliminated per day m ;t noi
adult is 1 to 2 liters (about 1 to 2 i|ii.nts). Water accounts
aboui 95% i»l the toted volume of urine, in addition toiintfj
trcLitiuinL!, potassium, and ammonia, typical solutes nnr
really present in urine include uric acid .is well as soctititi
ehloride* magnesium, sulfate, phosphate, and calciunj
ions.
It disease alters body metabolism or kidney runotionj
traces of substances not normal!) present ma) appear in ihr
urine, or nnnmil constituents may appear in abnornuti
amounts. Table 21.3 lists several abnormal constiments in
urine thai may be detected as pan of a urinalysis,
■ CHECKPOINT
4. How does blood pressure promote filtration of Itluod irt
the kiilnevsr
5. What solutes are reabsorbed and secreted as fluid movw
along the renal mlmles?
6. How do angiotensin II, aldosterone, and untitlin
hormone regulate tubular real isorpi ion and seeivinm :
7. Wbal are the characteristics of normal tinn
ntii
Table 21.3 Summary of Abnormal Constituents in Urine
Abnormal Constituent
Comments
Albumin
Glucose
Red blood cells
(erythrocytes)
White blood cells
(leukocytes)
Ketone bodies
Bilirubin
Urobilinogen
Casta
Microbes
A normal constituent of blood plasma that usually appears "m only very small amounts In urine because il is tootargeio
be filtered. The presence of excessive albumin in the urine, albuminuria (al'-bu-mi-NOO-re-a). indicates an Incros
me permeability of filtering membranes due to injury or disease, increased blood pressure, or damage to kldne-,
Glycosuria, the presence of glucose in the urine, usually indicates diabetes mellitus.
Hematuria (hem-a-TOO-re-a), the presence of hemoglobin from ruptured red blood cells in the urine, can occur with
acute inflammation of the urinary organs as a result of disease or irntation from kidney stones, tumors, trauma, and
kidney disease-
Trie presence ol white blood cells and other components of pus in the urine, referred to as pyuria (pT-U-ra-a). Ind
infection (n the Kidneys or other urinary organs.
High levels of ketone bodies in the urine, called ketonuria (ke-td-NOO-re-a). may indicate diabetes mellitus. mosam
Starvation, or too Utile carbohydrate In the diet.
When red blood cells are destroyed by macrophages, the giobin portion of hemoglobin Is spilt off and the heme is coo
verted to blliverdfn. Most of the billverdln is converted lo bilirubin. An above-normal level of bilirubin in urine Is cal
bilimbrnuria (bit -e-roo-bi-NOO-re-a)
The presence of urobilinogen (breakdown product of hemoglobin) iri urine is called urobilinogenuria (u -ro-bl-lln -o-|s-
NOO-re-a). Trace amounts are normal, but elevated urobilinogen may be due to hemolytic or pernicious anc
tious hepatitis, obstruction of bile ducts, |aundice, cirrhosis, congestive heart failure, or Infectious mononucleosis.
Casts are tiny masses of material that have hardened and assumed the shape ot rhe lumen of a tubule in which thay
formed. They are flushed out of the tubule when glomerular filtrate builds up behind them Casts are named altar the.
cells or substances that compose them or based on their appearance. For example, there are white blood cell cask rsd
blood cell casts, and epithelial cell casts (cells from renal tubules).
The number and type of bacteria vary with specific infections in the urinary tract. One of the most common is £ coll The
most common fungus to appear in urine is Candida albicans, a cause of vaginitis. The most frequent protozoan
Trichomonas vaginalis, a cause of vaginitis In females and urethritis in males.
Transportation, Storage, and Elimination oi Urine 535
FniKirv tract infections (I'Tls) are the
i common bacterial infections and
second must common illness (after
Irk) among women. About 10-15%
(omen develop L'TJs several times a
lib. Men get I'TIs, too. but much
uentiy. The female's shorter
l^erhra allows bacteria to enter the uri-
btadder more easily, la addition,
fat urethral and anal openings are
loser in females. Most lirst-tiine U'l'Is
paused by Escherichia ceii iE. coJt)
that have migrated do the ure-
iiiim the anal area. E. foii bacteria
:cessary for proper digestion and
lelcome in the intestinal tract, but
By cause much pain and suffering; if
i lie tirinan. system.
son Prevention
■i.il hygiene is the first line of
iri'venrinn. Care must be taken to
• .importing bacteria from the
area Co the urethra. Girls should
taught to wipe from front to back
wash hands thoroughly after
the toilet. When bathing,
[en and girls should wash from
IfruMtu hack ns well.
Menstrual blood provides an excel-
lent growth medium for bacteria. Sani-
tary napkins and tampons should be
changed often. Some women find that
switching from tampons CO napkins Or
from napkins to tampons reduces the
frequency of U I Is. Deodorant lam-
|)ons ami cianMus and s&perabsorbent
tampons can increase irritation.
People who are po IQC to L' 1 Ls
should drink at least 1 to 2.5 liters of
fluid daily. Drinking cranberry and
blueberry juice may help to decrease
rial growth in the urinary bladder.
Voiding frequently, every - to I hours,
helps prevent recurrent I I Is because
w expels bacteria and eliminates the
urine needed for their growth.
Partners in Health
Sexual intercourse is frequently associ-
ated wiili the onset of IH'ls in women.
Women who Hud that sex brings on
L'Tls learn to develop and teach their
partners stringent personal hygiene.
Women should drink plenty of water be-
fore and after sex and urinate as soon af-
terward us possible. I lus flushes i HK bac-
teria thru ma\ have entered the urethra.
At limes a woman's partner may be
the source ol liacterial transmission.
When L'Tls continue to recur, he
should be tested for asymptoniaiie ure
thtitis, which is the term for am hade
rial infection of the urethra other tlmn
gonorrhea. Sometimes treating the
part net with antibiotics cures both
parties.
One of the basil tetteu of tire wellness philosophy rV thai the heal ys-
tcm works best when patients work as partners with their providers to under-
stand, treat, arid prevent illness. Explain why treatment rmti IfUs is
a good Illustration of this belief.
TRANSPORTATION, STORAGE
ID ELIMINATION OF URINE
ACTIVE • Describe the structure Am] functions of
jters, urinary bladder, and ure thra.
I earlier in the chapter, urine produced by the
:>ns drains into the minor calyces, which join to be*
,r calyces that unite to form the renal pelvis (see
). From the renal pelvis, urine drains first into the
ureters and then into the urinary bladder; urine is. then dis-
charged from the body through the urethra (see Figure J 1.1).
Ureters
Each of the two ureters (U-re-tcrs or fi-RE-ters) transports
urine from the renal pelvis of one of the kidneys to Ebfi uri-
nary bladder (see I gyre 21.1). The ureters pass under the
Urinary bladder for several centimeters, causing die bladder
to compress the ureters and tllUS prevent backllow oi urine
when pressure builds up m the bladder during urination. If
536 Chapter 21 The Urinary System
Siologicd valve is noi Operating;, cystitis (urmarv
bladder inflammation) ma\ develop into a kidney infection.
The wall of the ureter consists of three layers. The inner
layer is the mucosa, containing transit miull cpuht'luirn (see
[able 4. 1 1 on page 80) with an underlying layer of areolar
connective tissue. Transitional epithelium is able to stretch —
j marked advantage for any organ that must accommodate a
variable volume OJ fluid. Mucus secreted b\ (he sroblei evils
of the mucosa prevents the cells from coining in contact with
urine, the solute concentration and pi 1 of which may difier
drastically from the cytosol of cells that I'onn the wall of the
ureters, The middle layer consists of smooth muscle. Urine is
transported irom the renal pelvis to the urinary bladder pri-
marily by peristaltic contractions of this smooth muscle, but
the fluid pressure of the urine and gravity may also con-
tribute. The outer layer consists of areolar connective tissue
containing blood vessels, K mphatic vessels, and nerves.
page 557). In females, it is in hunt of the vagina and below
the uterus. Folds of the peritoneum hold the urinary bladdej
in position. The shape of the urinary bladder depends on how
much urine it contains. When empty, it looks like a deflate
balloon. It becomes spherical when slightly stretched at
urine volume increases, becomes pear-shaped and rises inio
the abdominal cavity. Urinarj bladder capacity avera
700 800 mL. Tt is smaller in females because the uterus occj
pies the space just superior to the urinary bladder. Toward rjj
base of the bladder, the ureters drain into the urinan hjodda
via the (ttTterdl opening?. Like the ureters, the mucosa of tb|
urinary bladder contains transitional epithelium. The musi'ii-
lar layer of the urmarv bladder wall consists of three In
smooth muscle called the detrusor muscle (de-TR( )()-scr -
to push down). The peritoneum, which covers the superid
surface of die urinary bladder, forms a serous on let coat; tH
rest of the urinary bladder has a fibrous outer covering.
Urinary Bladder
The urinary bladder is a hollow muscular organ situated in
the pelvic cavity behind the pubic symphysis li ignrc 2 1 |J ). In
males, it h directly in front oftfoe rectum (see ' ■ • I Oil
Urethra
Thcvretbra in -RE ihrai, the terminal portion of the urinaql
system, is a small tube leading From the floor of the urimu
bladder to the exterior of the body 1 1 ipure 2 i .'>). In In
Figure 21.9 Ureters, urinary bladder, and urethra (female).
Urine is stored in the urinary bladder until it is expelled by micturition.
<7
Frontal
plane
Detrusor
muscle
Ureihra
Hip bone ■
(pubis)
Anterior view ol Ironlal section
Rugae ol mucosa
Peritoneum
nlernal urethral sphincter
(involuntary)
External ufethral sphincter
in deep muscles ol the
perineum (voluntary)
External urethral sphincter
External urethral orilice
What is a lack ol voluntary control over micturition called?
Aging and the Urinary System
637
I lies dlreedy behind the pubic symphysis and is embedded in
|c front wall of the vagina. The opening: of the urethra to die
feerior, die external urethral orifice, lies between the clitoris
and vaginal opening. In males, the urethra passes vertically
through the prostate, the tleep perineal muscles, and finally fche
penis ( SC c 21 .1 and 23.6 on pages 557 -and 564).
\mund the opening CO the urethra is an internal ure-
thral sphincter composed of smooth muscle. The opening
fed closing of the internal urethral sphincter is mvoluiuary.
Mm the internal sphincter is the external urethral sph'Mt-
lur, which is composed of skeletal muscle and is under volun-
Irj control. In both mules and female*, the urethra is the pas-
Igewaj for discharging urine from the body. The male urethra
SO serves as the duct through which semen is ejaculated.
[Micturition
The urinary bladder stores urine prior to its elimination and
then expels urine into the urethra by an act called micturition
aik'-too-Rl-shun = to urinate), commonly known as mm*
bcturition requires a combination of involuntary and vol-
uiir.nv muscle contractions. When the volume of urine in the
Enary bladder exceeds 201) to 400 ml,, pressure withm die
i increases considerably. and stretch receptors in ils wall
lit nerve impulses into the spinal cord, These impulses
ate to the lower part of die spinal cord and trigger a re-
flex called die micturition reflex. In this reflex, parasympathetic
impulses from the spinal cord cause contraction of the detrusor
; and relaxation of the internal urethral sphincter muscle.
i i ilrancouslv, the spinal cord inhibits somatic motor neurons,
sing relaxation of skeletal muscle in the external urethral
.incur. Upon contraction of the urinary bladder wall ami re-
jtion of the sphincters, urination takes place. Urinary bladder
fee causes a sensation of fullness that initiates a conscious de-
t > urinate before the micturition reflex actually occurs. \\-
m emptying of the urinary bladder is a reflex, in early
JEoptl we learn to initiate it and slop it voluntarily. Through
trol of the external urethral .sphincter muscle and
..mn muscles of the pelvic lloor. the cerebral cortex can initi-
: micmriiion or dek) it for a limited period ol time.
inability to prevent micturition is termed inconti-
I Under about two years of age, incontinence is nor-
., because neurons to the external urethral sphincter
ire not completely developed. Infants void wben-
1 1] .,-.an Madder ts sufficiently distended to trigger
reflex. In strep memtmettce, physical stresses that in-
|se abdominal pressure, such as coughing, sneezing,
filing, exercising, pregnancy, or simph walking, cause
Sage of urine from the urinary bladder. Smokers have
fee the risk of developing incontinence as nonsmokers.
■ CHECKPOINT
8. What forces help propel urine from the renal pehis io
the urinary bladder?
9. What is micturition? How docs ihe micturition reflex
occur?
10. How does the location of the urethra compare in males
and females?
AGING AND THE
URINARY SYSTEM
OBJECTIVE • Describe the effects of aging on the
urinary system.
With aging, the kidne\s shrink in size, have a decreased
blood Bow, and niter less blood. The mass of the two kidneys
decreases from m average of 260 g in ZQ-year-oIds to less
than 200 g by age HO. likewise, renal blood How and filtra-
tion rave decliiic In 50% between ages 40 and 70. Kidney
diseases that become more common with age include acute
and chronic kidney inflammations and renal calculi (kidney
stones). Because die sensation of thirst diminishes with age,
older individuals also are susceptible to dehydration. Urinary
tract infections are more common among die elderly, as are
polyuria, nocturia (excessive urination fit night), increased
Frequency of urination, dysuria (painful urination), urinary
retention or incontinence, and hematuria (blood in the
urine).
■ CHECKPOINT
11. Why are older individuals more susceptible io dclndra-
lion"-
In appreciate the many ways that the urinan system
contributes £P homeostasis oi other bod) systems, examine
Focus on Homeostasis: The Urinary System on page
538. Next, in Chapter 22, we will see how the kidneys
and lungs contribute t<> maintenance of homeostasis O.I
body fluid volume, ion levels in body fluids, and acid base
balance.
FOCUS
ON
HOMEOSTASIS
Body System
For ail body
systems
The Urinary System
Contribution of the Urinary System
The kidneys regulate the volume, composition, and pH of body fluids by removing wastes and
excess substances from blood and excreting them in the urine. The ureters transport urine fron
the kidneys to the urinary bladder, which stores urine until it is eliminated through the urethra.
Integumentary
system
The kidneys and skin both contribute to the synthesis of calcitriol, the active form of vitamin D.
Skeletal system
The kidneys help adjust the levels of blood calcium and phosphates needed for building bone
extracellular matrix.
Muscular system
The kidneys help adjust the level of blood calcium, needed for contraction of muscles.
Nervous system
Endocrine
system
Cardiovascular
system
i
The kidneys perform gluconeogenesis (synthesis of glucose from certain amino acids and lactk
acid), thereby providing glucose for ATP production in neurons, especially during fasting or star
vation.
The kidneys participate in the synthesis of calcitriol, the active form of vitamin D, and release
erythropoietin, the hormone that stimulates the production of red blood cells.
By increasing or decreasing reabsorption of water filtered from the blood, the kidneys help ad-
just the blood volume and blood pressure. Renin released by the kidneys raises blood pressure,
Some bilirubin (from hemoglobin breakdown) is converted to a yellow pigment (urobilin), which
is excreted in the urine.
Lymphatic
system and
immunity
Respiratory
system
0%
By increasing or decreasing the reabsorption of water filtered from blood, the kidneys help
adjust the volume of interstitial fluid and lymph. Urination flushes microbes out of the urethra,
The kidneys and lungs cooperate in adjusting the pH of body fluids.
Digestive system
The kidneys help synthesize calcitriol, the active form of vitamin D, which is needed for absorp-
tion of dietary calcium.
Reproductive
systems
538
* j /
In males, the portion of the urethra that extends through the prostate and penis is a passagewq
for semen as well as urine.
Common Disorders 539
COMMON
DISORDERS
Glomerulonephritis
Glomerulonephritis is an Laflammatiofl of the glomeruli oEchc Idd-
• a of rhe mast common causes is an aUei|fie reaction to the
produced by streptococcal bacteria that have recently in-
I ! mother part of i he body, especially the throat. Because in-
hmnJ and swollen glomeruli allow blood cells and plasms proteins
,.r the filtrate, the urine contains many red blood cells (hcina-
rtuOand large amounts of protein.
[iRenal Failure
Renal failure is n decrease or cessation of glomerular filtration. In
Jtorfi renal failure (ARF) the kidneys abruptly stop working en-
■ nlinost entirely). Ilu mint feature of ARF is die suppres-
uriiie [low, lending to oliguria or anuria. Causes include low
pod vol trine [for example, due to hemorrhage); decreased cardiac
[otrt|HH: damaged renal tubules; kidney stones; or reactions to the
used to visualize blood vessels in angiograms, nonsteroidal
Rammaiory drugs, and some antibiotic drugs.
Chronic renal fail are (CRF) relets to ,t progressive .mil usually
Me decline in 12.lon1cn1l.11 filtration i.ite (GFR)« CRF may
MEDICAL TERMINOLOGY AND CONDITIONS
fpjalysis tdi-AL-i-sis; dwfyt) = 10 separate) is the separation of l.ir -.
solutes from smaller ones bj diffusion through a selectively
|iermenhlc membrane. It is used to cleanse a person's blood ar-
feially when the kidneys are so impaired In disease or injury
liar they are unable to function adequately. One method of
is hemodialysis (he-m««-di- Al.-i sis; ham- = blood)
which filters the patient's blood directly bj reiBmring wastes
and excess electrolytes and fluid and: then returning the
ideansed blood to the patient. Blood removed from lite bod} is
delivered to a hemodwlvzer (artificial kidney). Inside the he-
,i\/er. blood Hows through a dialysis mewbntne, which
contains pores large enough to permit the diffusion ot small
\ special solution, called the Salysate idi-AI.-r-vu) is
pumped into the hetnodiidy/er so chat it surrounds the dialysis
1 ,me. The dialysate is specially formulated to maintain
ion gradients thai remove wastes from the blood (for ex-
ample urea, creatinine, uric acid, excess phosphate, potassium,
tlfate ions) and add needed substances ilor example, glu-
p& and bicarbonate ions) to it As a rule, most people on he-
• tiysvi require about 6-12 hours a week, typically divided
inro three sessions.
fcajrif i.lis-l 1 re a; ttys - painful; una = urine) Painful urination,
-u-RF.-sis; = to void urine") Involuntary voiding ol
uriiii- alter rhe age at which voluntary control has typically
I ken attained.
result from chronic glomerulonephritis, pyelonephritis, polyi
kidney disease, or traumatic loss ol kidncj tissue. I he final stage of
CRF is called end-stage, renal failure and occurs when about
of the nephrons have been lost. At this Stage, GFR diminish.
Ill ls% of normal, oliguria is present, and blood levels o\
nitrogen-containing wastes and creatinine arc high, People with
end-stage renal failure require dialysis therapj and arc possible can-
didates lor a kidney transplant operation.
Polycystic Kidney Disease
Polycystic kidney disease (PKD) is one ol die moS! cnnmioii inher-
ited disorders. In PKD. the kidney tubules become riddled with
hundreds OF thousands Of cysts f lluid-litled cavities}. In addition, in-
appropriate apoptosis (programmed cell death) of cells in mxu
tubules leads it. progressive impairment of renal function and even-
tually BO end-Stage renal failure.
People witfe I'M.) also may kn<. iv-is and apoptosis in the
liver, pancreas, spleen, and gonads; increased ri.sk of cerebral
aneurysms; heart \alvc defects; and dnertintli in the colon. 1 v 1 n
cally, symptoms are noi noticed until adulthood, when patients may
have back pan. urinary tfaCI infections, blood in the urine, hyper-
tension, and large abdominal masses. Using drugs to restore normal
blood pressure, restricting protein and salt in the diet, and control-
ling urinary tract infections may slou progression ro renal failure.
Iniracenoas pyeiagrant tin' tra -\ I -mis IM-cl-o-gram ': fattV
within: irnii- = \ cin; pyrin- - pelvis of kidney: -grof/l = record)
or UP Radiograph (x-ray lilm) of the kidney* alter u-nous
injection ol n d\e.
Kidney stones Insoluble stones occasionally formed from solidtfica-
m m ol the crystals of urine sahs. C '.-.m be caused by ingestion of
excessive mineral salts, insufficient water intake, abnormally al-
kaline or acidic urine, or overactive parathyroid glands. I sually
fonn in the renal pelvis. Often cause intense pain. Also termed
renal ailcuii.
\'(iitarnnl enuresis fuok- 1 L R-nal en'-u-RI' sisi Discharge ol
urine during sleep, resulting in bctt-wcttingj oecura b about
15% of 5 -year-old children and generally resolves sponta-
neously, afflicting only about 1% < if adults. Possible causes in-
clude smaller-than-normal urinary bladder capacity, faihr
awaken in response to a lull urinary bladder, ,\\w\ above-normal
production of urine at night. Also termed nocturia.
Urinary retention A failure to Completely or normally void urine;
may be <~\^e to an obstruction in the urethra or neck of the uri-
nary bladder, to nervous conn-action of the urethra, or to lack
..I urge i" urinate. In men, an enlarged prostate may constrict
the nicilua and cause urinary retention. If urinary retention IS
prdlongedj P catheter (slender rubber drainage tube) must be
placed into the urethra 10 drain
540 Chapter 21 The Urinary System
STUDY OUTLINE
%
Overview of the Urinary System (p. 524)
1. The nrrans c>! the urinary system include the kidneys, ureters,
urinary bladder, and urethra.
2. \tii-r i In- kidneys filter blood and return mosi oFfhs waW "and
rm-inv solutes to the brood, the petiiufning water and solutes
constitute urine.
3. The kidneys regulate blood tonic composition, Wood volume,
btOOd pressure, hhI blood pi I.
4. 'I"he kidneys ftls© i ck..ise- ealcitriol and erythropoietin .in.l ex-
crete flfastes and foreign substances.
Structure of the Kidneys (p, 525)
1. The kidneys lie on eirher side of the vertebral column between
the peritoneum and the buck wall of the abdominal cavity.
2. Each kidney is enclosed in a renal capsule, which is surrounded
fey adipose tissue.
3. hnern.db. tfte kidney*- consist of .i renal cortex, renal medulla.
renal pyramids, renal columns, calyces, .Vnd a renal pelvis,
4. Blood eiilers the kidney through "In. renal ftfftcrj and leaves
through the renal vein.
5. The nephron is the functional unit "I ihe kidney. A nephron
eonsisis ol a renal corpuscle (glomerulus and glomerular or
Hovu nan's capsule) and a renal tubule (proximal convoluted
tubule, descending Ihnb of the loop of Henle. ascending limb
of the loop of I It nle, and distal convoluted tubule). The distal
pottvokttedtulnilesofse.ee i ms empty into a common
collecting duet.
Functions of the Nephron (p. 528)
i. Nephrons perform three basic casks! glomerular filtration,
tubular reflhsorpUlVI, and tulnjlar secrenon.
2. i i it: tj trior, the podocytes and glomerular endothelium form a
leaky hltrvition membrane that permits the passage ofwater and
solutes from the blood into the capsular space, Blood cells :md
most plasma proteins remain in die blood because tiHe) are coo
large 60 pass through the [titration membrane. The pressure
dial causes filtration is the blood pressure in the glomerular
i millaries.
3. tabic -l I on pag< 5 ''• dcscril&es the substances chat are til-
lered, reabsorbed, and excreted in urine on a daily basis.
4. The amount of libra U: that forms in both kidnevs every minute
is die glomerular filtration rate (GFR); Atrial natriuretic pep-
r n I ■. : i.WT) increases (II'R; sympathetic stimulation decreases
GFR.
5. Epithelial cells all along the renal tubules and collecting duets
carrv out tubular reahsorpiion and tubular secretion. Tubular
reahsorpiion retain?, substances needed by the body, including
filter, glucose, amino acids, anil ions such as sodium (Ha I
potassium 'Is ). chloride K.I ). bicarbonate (IfCX), ), calcium
.' ,r i. and magnesium (Mg
6. Angiotensin il enhances reabsorption of Na and CI
giotensin D tls© snmulat.es the adrenal concx to release aldta
teioiie, which siimuiates the collecting ducts to reabsorb iminc
Na % andCI and secrete mon. Is . Itrtal natriuretic p
inhibits reabsorption of N,i (and O and water) by tin
tubules, which reduces blood volume,
7. Most water is reabsorbed by osmosis together with reahsn i
solutes, mainly in the proximal convoluted tubule. Real
tion of the remaining water is regulated by antidiuretic lior-
n e (M'lf) in i i if List pan ol the distal convoluted uilnik-
and collecting duct.
8. Tubular secretion discharges chemicals not needed by tin I
into the urine, Included are excess ions, nitrogenous
hormones, and certain drugs. The kidneys Kelp maintain II
pi I bj secreting H~. Tubular secretion also helps inaiiitaijq
proper levels of K m die blood,
9. Table 21.2 on page 534 describes the physical clvar.u iu ;-a .
urine that arc evaluated in a urinalysis: color, odor, uirkkiity,
pi I, and specific gravity.
10. Chemically, normal urine contains about 95 '• water and ?l lti
solutes.
11. [and 21 I on page 534 lists the abnormal constituents thai
be diagnosed through urinalysis, including albumin, tglucasj
red blood cells, white blood cells, ketone bodies, bilirubin, uroj
bilinogen, casts, and microbes.
Transportation. Storage, and Elimination of Urine (p. 535)
1. The ureters transport urine from the renal pelves of thi
and left kidneys to the urinary bladder Mti\ consist of a rnueq|
uiuscufaris. ,\m\ adventitia.
2. The urinary bladder is posterior to the pubic symphysis
function is to store urine prior to mieturuton,
3. The mucosa, of the urinary bladder contains stretchy \rm
Clonal epiihehurn. The muscular layer of the wall coiiaajfl
three layers of smooth muscle together referred to as tin
snr muscle.
4. The urethra is a tube leading from the lloor ol the
bladder to the exterior. Its function is ro discharge urine htn
the body.
5. The micturition tefieJi discharges urine from the itrinnr
der by means ol parasympathetic impulses that cause cimlraj
tion of the detrusor muscle and relaxation of the inicrinl uu-
thral sphincter muscle, and by inhibition ol somatic tnntfll
neurons to the external urethral sphincter.
Aging and the Urinary System (p. 537)
1. With a'.'ing. die kidneys shrink in size, haw lowcii
flow, and hirer less bio u\.
2. Common problems related to aging include urinan tract m!w
lions, increased frequency ol urination, urinan, rcienti
continence, and renal calculi (kjdne\ stemes).
ir\
SELF-QUIZ
1. Which of the Mowing is NOT a fonptioa ->i fhf urinary
\ stei i-
a. rciiiil.iii" «n ofblond volume and composition
b. stimulation of red blood cell production
c. regttlsitiofl of hotly temperature
il. regulation of blood pressure
e. regulation of blood pi I
2. Which of the following structures is located in the renal cortesl
I the Teiial pyramid b. (he renal coluinn
c. the major calyx d. the minor caly\
,-. the renal corpus* tc
I Winch of the following increases water Geabsorption in the dis-
tal convoluted tubules and collecting ducts-
a. antidiuretic hormone (,M)I I) b. angiotensin 11
c. atrial natriuretic peptide (ANP) d> diuretics
c. glucosuria
4. The major openings located in the base of the bladder -arc the
a. renal artery, renal vein, urethra
li. renal artery, renal vein, ureter
c. ureter, urethra, collccdng Bubes
il. urethra and two ureters
. . external urethral sphincter and papillary ducts
| • ich statement does NOI describe the kidneys?
a. I hey are protected bj the 1 hh and 12th pairs ofribs.
li. I he average adult kidney is 1 1 cm (-4 indies) long ami 6 cm
(2 inches) wide,
i rhe left kidnej is lowei than the rigfa to accommodate the
large si/.c oi the liver.
<[. [ aehkidnej is surrounded bj adipose and connective tissue
c. The kidneys are surrounded by a renal capsule.
|fc Place the following structures in the correct order for the 8om
ol urine:
|. renal tubules 2. minor calyx
4b major calyx 5. collectinj> ducts
,.i, I 2,4, J, 6, 5 b. 5, 1.4,2.3.6
d. 5,5, 1.2.4.6 e. I. \ l,fi
functional unit of rhe kidncj where urine is produced is
tk
| n. nephron b* pyramid c. pelvis d. glomerulus
i i
jes nitration of plasma across the filfcrarion membrane?
, a lull urinary bladder
council by the nervous system
r retention
I the pressure of the blood
MS, the pressure of urine id the glomerulus
3. renal pelvis
6. ureters
c. \ 1.2,4,3.6
9. Glomerular filtration rate (( il'R) is the
a. rate of urinary bladder filling
b. amount ol filtrate Formed in both fcidneyseach minute
c. amount ol filtrate reabsorbed ai the colJecrillg duets
d. amount of blood delivered to die kidneys ea Hi minute
e. .iniouni (4 urine torined peVhour
10. Which of tbe following is secreted into the urine Ironi the
blood?
:i. hydroiicn ions (I I ) b. amino acids c\ gkcose
d. water e, white blood cells
11. In the nephron, tubular fluid that is reabsorbed from the renal
tubules enters ihe
a. glomerulus b. pcrmibulur i tpilbries
c. efferent arteriole d. afferent arteriole c. renal artery
12. Place the following siruetures in the correct order as ili«_-\ arc
involved in the formation of urine in the nephrons.
1. distal convoluted tubule
2. renal corpuscle
3. descending limb of loop ol Henlc
4. proximal convoluted tubule
5. collecting duet
6. Ascending' limb ol loop ol Henle
a. 4. 1 . 6, 3. 2, 5 b. 2. 6. 3. 1.5.4 c. 2. -1. I, 6, >, I
(1. J, 1.4,3,6,2 e. :,4, v-, 1,5
13. Blood is carried qui of die glomerulus bj the
a. renal artery
b. afferent nrieriole
c. peritubular venule
d. segmental artery
e. efferent arteriole
H. V\ Inch of the following increases glomerular filtration rate (GFR):
a. atrial natriuretic peptide iAM'
h. constriction of (he afferent arterioles
c. increased sympathetic cumulation to the afiFcreni arterioles
d. ADM
c. angiotensin II
15. Which of i he following statements concerning tubular rcab-
sorption is \< )T trad
a. Most reabsorption occurs in the proximal convoluted tubules.
k lubtiLir reabsorprioN is a selective process.
Ci Tubular rcabsorption of excess potassium tons t'K") main-
tains the correct blood level o! K ' .
d. The reabsorption ofwatef In the proximal convoluted
tubules depends upon sodium low (Na * reabsorotion,
e. Tubular reabsorption allows rhe body to retain most filti
nutrients.
542 Chapter 21 The Urinary System
16. The micturition reflex
a. is under the control of hormones
b. a activated foj low pressifM in the urinan bladder
C. depends upon contraction of the internal urethral sphincter
muscle
d. is an involuntary reflex over M hich normal adults have vol-
untary control
c. i 1 - also known as incontinence
17. Which ul the following is NOT normally present in glomeru-
lar filtrate?
a. blood cells b. glucose
c nitrogenous wastes such as urea d. amino acids
e. water
18. Urine Formation requires which of the following?
a. glomerular filtration arid tubular secretion • >uK
h. glomerular filtration and tubular ceabsorpnoti only
c. glomerular filtration, tubular reahsorpnon, aiul tubular
secretion
d. tubular reabsorprion. tubular liluation, and mtonlar set
lion
e. tubular secreriorj unci tubular i^eabsorpition only
19. The* transport of urine ironi the renal pdvtti into the i.mnnr
bladder is the fnncrioii of the
a. urethra b. efferent arteriole c. afferent arteriole
d. renal pyramids c. ureters
20. Incontinence i%
a. In i lure ol the urinary bladder to expel urine
b. a lack ol vol on tan control over the micturition reflej
e. an inability .if the kidneys to produce urine
d. an ahilru to consciously control micturition
e. a lorin of kidnev dialysis
I
fl CRITICAL THINKING APPLICATIONS
1. Yesterday; vou attended a large, outdoor part)' where beer was
ilu- only beverage available, You remember having to urinate
many, many times yesterday, and today you're ven thirsty
What hormone is affected l>v alcohol, and how, does this allcct
your kidney function?
2. Sarah is an "above average" l-year-old whose patents would
like her to he the firs! toilet -trained child in preschool. Ilou-
ever, in this case ai least, Sarah js average for her age and
remains incontinent. Should her parents be concerned by this
lack of success?
3. Kayla is a healthy, VERi active 4-year old. Sin driest]
lake die time to go to the bathroom because, as she
might miss somuthin'." Her mother is worried that KuylaV Id-
neys mav stop working when her urinary bladder is lull.
her mother be concerned?
4. Assume that the length of a nephron's twisted and eunvulmew
renal tubules is about the same as the width of the kidney. Hum
many meters of tubules would one kidney contain?
<s~
^ANSWERSTO FIGURE QUESTIONS
21.1 Hy- forming urine, the kidneys do the major work of the uri-
nary system.
21.2 Tile renal pyramids are located in the renal medulla.
21.3 About 1200 ml. of Mood enters the kidneys each minute.
2 1 .4 The water molecule will travel from the proximal convoluted
tubule — * descending limb of the loop of I Jenle — * ascending
limb of the loop of'Hcnle — » distal convoluted tubule — col-
lecting duct — *■ minor calyx — major calyx —* renal pelvis.
21.5 Secreted penicillin is being removed from the blood.
21.6 Podocytes and the glomerular endothelium make uptlieflffl
tration membrane.
21.7 Secretion occurs in the proximal convoluted tobuli
of Henle, the last part of ihe distal convoluted Nil
the colled mil duct.
21.8 The blood level of ADI1 would be higher than normal a!
a 5-fcrf| n\[-\, flue to loss of hody water in swear.
21 .9 A lack o! voluntary control over micturition is tct n
tinence.
FLUID, ELECTROLYTE, AND
ACID-BASE BALANCE
2
did you know?
Jtligh blood pressure often responds to
lifestyle treatments, such as increasing physical activity and
tin eloping better eating habits. The DASH (Dietary Ap-
proaches to Stopping Hypertension) diet is the most success-
ful dietary treatment for hypertension. It may work partly
improving flu id balance through changes in the concen-
n 1 /
n-nhons of many of the body's electrolytes. The DASH diet
is low in sodium, and high in calcium, potassium t and
magnesium. The DASH diet also encourages the consump-
mi; <f law-fat dairy products, and plenty of fruits, vegeta-
bles, and whole grains. Fish, poultry, dried beans, and nuts
tire on the menu, but only smalt
< .-, ^ amounts of red meat, sweets, and salty
foods are permitted.
Focus on Wellness, page 551
www.wiley.coTn/college/apcentral
in Chapter 21
you learned how
the kidneys form
urine. One important function of the kidneys is to
help maintain fluid balance in the body. The water
mi dissolved solutes in the body consulate die
body fluids. Regulatory mechanisms involving die
kidneys and other organs normally maintain home-
ostasis of the body fluids. Malfunction in any or all
(i I" i hum may seriously endanger the functioning of
organs throughout the body. In this chapter, we
will explore the mechanisms that regulate the vol-
ume and distribution of body fluids and examine
the factors that determine the concentrations of
solutes and the pi I of body fluids.
looking back to move ahead
Acids, Bases, and pH (page 30}
Intracellular and Extracellular Fluid (page 47)
Osmosis (page 49)
Antidiuretic Hormone (ADH) (page 322)
Hormonal Regulation of Calcium in Body Fluids (pages
325-327)
Renin -Angiotensin -Aldosterone Pathway (page 331)
Control of Breathing Rate and Depth (page 461 )
Ions Reabsorbed and Secreted in the Kidneys (page 531)
Negative Feedback Regulation of ADH Secretion (page 533)
543
544 Chapter 22 Fluid. Electrolyte, and Acid-Base Balance
FLUID COMPARTMENTS AND
FLUID BALANCE
OBJECTIVES ■ Compare the locations of intracellular
fluid (ICF) and extracellular fluid (ECF), and describe
the various fluid compartments of the body.
• Describe the sources of water and solute gain and
loss, and explain how each is regulated.
In lean adults, body fluids make up between 55% and 60% of
total body mass GPigure 22.1% Fluids are present in two main
"compartments"— inside cells and "inside cells. About run-
time Is of body fluid is intracellular fluid (ICF) {intra- —
within) or cytosof, the fluid within cells. The oilier third,
Called extracellular fluid (ECF) (extra- = outside), is out-
side cells and includes all Other body fluids. About HO of
the F.CF is interstitial fluid (fitter- = between), which oc-
cupies the spaces between tissue cells, and about 20% of the
ECF is blood plasma, the liquid portion of the blood. Other
extracellular fluids that are grouped with interstitial fluid
include lymph in lympharte vessels; cerebrospinal fluid in
the nervous system; synovial Quid in joints; aqueous humor
and vitreous body in the eyes; endolymph xm\ perilymph m
the ears; ,md pleural, pericardial, and peritoneal Fluids be-
tween serous membranes ol the brigs, heart, and abdominal
organs.
'I wo "barriers" separate intracellular fluid, interstitial
fluid, ami blood plasma.
1. The plumm membrant of each cell separates intracellular
lluid from the surrounding interstitial fluid. You learned
in Chapter 3 that the plasma membrane is a selectively
permeable barrier: It allows some substances to cross but
blocks the movement of other substances. In addition.
active transport pumps work continuously to inainujo
different concentrations o\ certain ions in the cytnsol aaij
interstitial lluid.
2. Blood vessel wails separate the interstitial fluid Irom h i
plasma. Only in capillaries, the smallest blond vessels, ail
the waits thin enough and leak) enough to pennii dit .
change of water and solutes between blood plasma MA
interstitial fluid.
The body is in fluid balance when the required amuunsJ
of water and solutes are present and are correctly prnpnr-j
tionol amoiiii the various compai'tments. Water is U 1'artfl
Figure 22.1 Body fluid compartments.
In lean adults, fluids make up 55-60% ol body mass.
Total body mass (female)
Total body mass (male)
Total body
fluid
2/3
Intracellular
fluid (ICF)
Extracellular
fluid
1/3 80%
. 1/3 I( , Interstitial
Extracellular ||l)ld
fluid (ECF)
20%Plasrna
(a) Distribution of body solids and fluids in an average lean, aduh female and male
s Wbat is body fluid?
(b) Exchange of water among
body lluid compartments
I,
Igest single compoiient of the body, making up 45-75% of
i . .1 ii body mass, depending on age atftl gender.
The processes of filtration, reabsorption, diffusion, and
>js provide for the continual exchange of water and
tables among body fluid compartments (! lb). Vet,
fee volume of fluid in each comparrmem remains remarkably
foible. Because osmosis is the primary means of water move-
ment between intracellular fluid and interstitial fluid, the eon-
1 1 linn of solutes in these fluids determines the dirmhi/ ol
wiua movement. Most solutes in body fluids arc electrolytes.
iniHg-.tmc compounds that break apart into ions when dis-
i. They are the main contributors to the os-
Iftotic movement of water. Fluid balance depends primarily i hi
olyie balance SO the two are closely interrelated. Because
jintake of water and electrolytes rarely occurs in exactly the
toe proportions as their presence in bo<1\ Hinds, die ability
pthe kidneys to excrete excess water by producing dilute
it, or to excrete excess electrolytes by producing coneen-
:d urine, is of utmost importance in the maintenance of
istasis.
tources of Body Water Gain and Loss
The bodv can gain water by ingestion and by metabolic
pons (1 fim ' - 2 ). The mam sources of body water are
liquids (about 1600 ml.) and moist foods (about
Oil ml.) absorbed from the gastrointestinal (Gl) tract.
bieh total about 2300 mL/day. The other source of water
mebolic water that is produced in the body during chem-
.icrions. Most of it is produced during aerobic cellular
...lion (see I igim on page 51 0) and to a smaller e\-
during dehydration synthesis reactions (see I c
32). Metabolic water gain accounts for about
_/day. Thus, daily water gain Iptals about 2500 mL.
Normally, body fluid volume remains constant because
, equals water gain. Water loss occurs in four ways
>). Each day the 3 excrete about 1500 ml
ik. about 600 mL evaporates from the skin surface, the
i exhale about 300 mL as water vapor, and the gastroin-
... tract eliminates about ](M) ml. in feces. In women of
ilucuve age, additional water is lost in menstrual flow. On
laily water loss totals about. 2500 ml.. The amount of
by a given route can vary considerably over time.
example, water may literally pour from the skin in the
■ a luring strenuous exertion. In other cases, water
51 in vi unit or diarrhea during a GI tract infection.
julation of Body Water Gain
ijfta in the hypothalamus known as the thirst center governs
ui drink. When water loss is greater than water cam.
lion — a decrease in volume and an increase in osmotic
j of body fluids— stimulates thirst (Figure 2 ! >). When
reases by 2% due to fluid loss, mild dehydration
^A decrease in blood volume causes blood pressure to tall.
Fluid Compartments and Fluid Balance 545
Figure 22.2 Water balance: Sources of dally water gain and
loss under normal conditions. Numbers are average volumes for
adulls.
C^-^
Normally, dally water loss and water gain are both equal to
2500 mL.
Volume of
water (mL)
2500
2000
liuu
10D0
500
WATER GAIN
Metabolic water
<20OmL)
WATER LOSS
Gl tract nOOmL)
How would a diuretic drug affect a person's water balance?
This change stimulates the kidneys to release renin, which pro-
motes the formation of angiotensin 11. Osmoreceptors in the
hypothalamus and increased angiotensin II in the blood both
stimulate the thirst center in the hypothalamus. Other signals
thai stimulate thirst come from neurons in the mouth that de-
fect drvness due CO a decreased flow of saliva. \s a result; the
sensation of thirst increases, which usually leads to increased
fluid intafcfi (if fluids are available) and restoration of normal
fluid volume. ( Kvrall, fluid gain balances fluid loss.
Sometimes the sensation of thirst does not occur quickly
enough or access to fluids is restricted, and significant dehy-
dration ensues. This happens most often in elderly people, in
infants, and in those who are in a confused mental state. In
situations where heavy sweating or fluid loss from diarrhea or
vomiting occurs, it is wise to start replacing body fluids |jj
drinking fluids even before the sensation ol thirst appears.
Regulation of Water and Solute Loss
F.limmation of mm body water or solutes occurs mainly by
;oiitrolliiiL the amount lost in urine. The extent of wmary
Si/lt (SuCI) loss is the main factor that determines body fluid
cnhuii,'. The reason is that in osmosis "water follows solutes."
Figure 22.3 Pathways through which dehydration stimu-
lates thirst.
Dehydration occurs when water loss Is greater than water gain.
Dehydration
I
^
Increased blood
osmotic pressure
Decreased
blood volume
Dry mouth Stimulates
♦
and
pharynx
Decreased
osmoreceptors in blood
hypothalamus pressure
;
Increased
renin release
by kidneys
i
Increased
angiotensin II
formation
Stimulate
thirst center in
hypothalamus
Increases thirsl
t
Increases Water intake
Increases body
water to normal
level and relieves
dehydration
Does regulation of these pathways occur via negative or positive
feedback? Why?
.md i lie two main solutes m euracellular fluid (unci in urine)
are sodium tons (Na ) and chloride ions (CI ). Because our
.talk diet contains a higHy variable amount o1 NnC "I, urinary
excretion of Ma* ami CI jnu.st .tlsn vary CO maintain homcosut-
sis. Three hormones regulate the extent Of renal Na ' and CI
reabsorption (unci thus how much is lost in die mine): atrial
natriuretic peptide (ANP)> angiotensin 11, and aldosterone
i depicts the sequence of changes Chat occur
after a salty meal. The resulting increase ra blood volume
stretches the atria of the heart and promotes the release ul
atria] natriuretic peptide; ANP promotes natrinresis, ele-
Figure 22.4 Hormonal regulation of renal Na 1 and CI res
sorption.
v The three main hormones that regulate renal Na* and CI real
sorption (and thus the amount lost in the urine) are an-
giotensin II. aldosterone, and atrial natriuretic peptide.
Increased intake ol Na'Ci
I
Increased plasma concentrations
ol Na" and CI
*
Increased osmosis of water
from intracellular fluid lo
interstilial fluid to blood plasma
Increased stretching of
atria of heart
♦
Decreased release of renin
by kidneys
Increased release of
atrial natriuretic peptide
Decreased formation ol
angiotensin II
Decreased release ol
,-. Ida st t-M.
Reduced reabsorption ol
Na'Cl by kidneys
\
Increased (oss o! Na' and CI
in Urine (natriurosisi
i
Increased loss of water
m urine by osmosis
1
Decreased blood volume
How does excessive aldosterone secretion cause edema"?
Nted Liruiiiry loss "i N'n [mid CI~) and waser, which de-
creases blood volume. The initial increase in blood volume
Iso slows release of renin from the kidneys- As renin level
Mines, less angiotensin TT is formed. With less angiotensin
I. the kidney tubules reabsorb less Na', Cl~, and water. In
adiliiit hi. less angiotensin II leads to less aldosterone and tur-
ner slowing of Na"* -and CI reabsorptaom in the renal
tubules. .More filtered Na ' and CI thus remain in the tubu-
lar fluid to be excreted in the urine. The osmotic conste-
jdence of excreting more Na ' and C] is loss of more water
l',urine, which decreases blood volume nml blood pressure.
|jr contrast, when someone becomes dehydrated, higher lev-
angiorensin II and aldosterone promote tirtnarj reab-
nn of Na' and CI (and water by osmosis with the
s) and i hereby conserve the volume of body fluids by
jpcittg urinary loss.
The major hormone that regulates water Loss is antidi-
httic hormone (ADH). An increase in the osmotic pressure
1} fluids (si decrease in the water concentration of the
fluids) stimulates release ot ADH (see Figure 21.8 on page
vDM pro he insertion oi water channels into the
Bsnui membranes of cells in the collecting ducts of the fefd-
\s a result, the permeability of these cells to water in-
. and water moves from the tubular fluid into the cells
|Ul then into the bloodstream. By contrast, intake of plain
ttr decreases the osmotic pressure of blood and inrersiitial
[tiiiil- Within minutes, AD1I secretion shuts down, and soon
blood level is close to zero. Then, the water channels are
! from the membranes. As the number of water ehan-
h decreases, more water is lost in the urine.
summarizes the factors mat maintain body
Br balance.
mfltssssodium ions remain in the bod) because the kidneys
to excrete enough of them, water is also osnmtiealK
id. 'I he result is increased blood volume, increased
pressure, and edema, an abnormal accumulation of
Kraal fluid. Renal failure and excessive aldosterone se-
iii are two causes of Na " retention. Excessive urinary
;;i . b\ contrast has me osmotic effect of causing ex-
ilter loss, which results in hypovolemia, an abnor-
Fluid Compartments and Fluid Balance 547
mally low blood volume, I Iypovoleinia related to NJ : , j@8S ^
most often due t< > inadequate secret ton of «ll( losterone.
Movement ot Water Between
Fluid Compartments
Intracellular and interstitial lluiils normally have (he same os-
motic pressure, so cells neither shrink nor swell. An increase
in the osmotic pressure of interstitial fluid draws water o ■
cells, so thc\ shrink slightly. A decrease- m the osmotic pres-
sure of interstitial fluid causes cells to swell. Changes in os-
motic pressure most often result from changes m die concen-
tration of Na'. A decrease in the osmotic pressure of
interstitial fluid inhibits secretioB of ADII. Normally lune-
boning kidneys then excrete excess water in the urine, which
raises the osmotic pressure of body fluids to mutual. \s fl re-
sult, body cells swell only slighilv. ami only for ,i brief period
of nine.
When a person steadily consumes water faster than i!i>
kidneys can excrete it (the maximum unne flow rate is
about 15 mT./min) or when kidney function is poor, the
decreased \"a ' concent ration of iimrauial fluid CJpseS
water to move by osmosis from interstitial fluid into intra-
eelJular lluid. The result may be water intoxication, a
State in which excessive body water causes cells to swell
dangerousk producing convulsions, eoina, ami possibly
death. To prevent this dire sequence of events, solutions
given for intravenous or oral rehydration therapy
(ORT) include a small amount of table salt (NaCl),
CHECKPOINT
What is the approximate volume of each ot vonr body
fluid compartments?
\\ "Inch routes of uater gain and loss from the body arc-
regulated ?
How dd angiotensin II, aldosterone, atrial natriuretic
peptide, and antidiuretic hormone regulate the volume
and osmotic pressure of body Hinds?
2.
3.
Table 22.1 Summary of Factors that Maintain Body Water Balance
Mechanism
Effect
fllliB! center In hypothalamus
Stimulates desire to drink fluids.
■foiensln n
Stimulates secretion of aldosterone
BSterone
By promoting urinary reabsorption of Na ' and CI" , increases water
reabsorplion via osmosis.
Ifti natriuretic peptide (ANP)
Promotes nalriuresis. elevated urinary excretion of Na ' (and CI },
accompanied by water.
■Mureilc hormone (ADH)
Promotes inserlion of waler-channel proteins into the plasma membranes
ot cells in the collecting ducts of the kidneys. As a result, Ihe water
permeability of these celfs increases and more water is reabsorbed
Water gain if Ihirst is quenched.
Reduces loss of water in urine.
Reduces loss of water in urine.
Increases loss of water In urine.
Reduces loss of water in urine.
548 Chapter 22 Fluid, Electrolyte, and Acid-Base Balance
ELECTROLYTES IN BODY FLUIDS
OBJECTIVES • Compare the electrolyte composition
of the three major Huid compartments: plasma, intersti-
tial fluid, and intracellular fluid.
• Discuss the functions of sodium, chloride, potassium,
and calcium ions, and explain how their concentra-
tions are regulated.
The ions formed when electrolytes break apart serve four
general functions in die body:
1. Because they aire largely confined to particular fluid cotn-
parfmenrs and are more numerous than nonclcctrokies,
certain ions control the osmosis trfiotitier Im-cm fluid tom-
pttrti/rcnts.
2. Ions help fimintuin the uad- bust Ihihmcc required for nor-
mal cellular activities.
3. Ions carry, ilea nail cuirvfit, which allows production of
action potentials.
4. Several ions <tr.r as aifihtrm needed for optimal activity
of enzymes-
re 22.5 compares rhe concentrations of the mmn
electrolytes and protcm anions m extracellular fiutd (blood
plasma and interstitial fluid) and intracellular fluid. Thee
difference between the two extracellular Fluids is thatH
plasma contains many protein anions, but interstitial
serv lew. Because normal capillars membranes are unu
impermeable m proteins, only a few plasma proteins ■
of brood vessels into the interstitial fluid. This tlificrcntcl
protein concentration ts largely responsible for the bkwjj
loid osmotic pressure, the difference in osmotic pressure:!
nveen blood plasma and interstitial fluid. The other eomp
Bents or rhe two extracellular Hinds are similar.
The clectrokie content ol intracellular fluid diffi
siderahly from thai of extracellular fluid. Sodium inns (\VJ
are the most abundant extracellular ions, rcpresuitn
90% of extracellular cations, Na' plays a pivotal rule in 'luifl
and electrolyte balance because ii accounts for almost fall
the osmotic pressure of extracellular fluid, \a rs n<
for the generation and conduction of action potential-; i
neurons ami muscle libers. As you learned earlier in
chapter, the Na ' level in the blood is controlled k
terone. antidiuretic hormone, and atrial natriuretic
Chloride ions (CI ) are the most prevalent iminns^H
tracellular fluid. Because most plasma membrane
many CI leakage channels, CI moves easily between rhe el
tracellular ami intracellular compartments. For this
CI can help balance the level of anions in different llull
Figure 22.5 Electrolyte and protein anion concentrations in blood plasma, interstitial fluid, and
intracellular fluid. The height of each column represents the milliequivalents per liter (mEq/lrter), the total
number of cations or anions (positive or negative electrical charges) in a given volume of solution.
v The electrolytes present In extracellular fluids are different from those present in Intracellular fluid.
*r ,
I
175
150
125
100
7b
50 -
25 -
- ..,.145
Na'
' -:"i
44
K'
What is the major cation in ECF?
m
in,.:
3 0.2 * 2
Ca'" M'i '
CO
Key:
Blood plasma
Interstitial fluid
Intracellular Huid
100
, $
1 1
Extracellular
fluids
M
20 20
L
CI HCCy hpo/ so,- Protein
(organic) anions
Electrolytes in Body Fluids 549
ppartments. As you also learned earlier, ADM helps regtt-
SteCJ" balance in body fluids by regulating the extent of wa-
ter loss in urine. Processes that increase or decrease Feral
j&alisorption of sodium ions also affect reabsorptinn of chin-
be ions. The neg-.itivcly charged CT Follows the positively
prged Na' due to the electrical attraction of oppositely
gfrarged particles.
Potassium ions (K '), the most abundant cations in Intra-
LiliiLn fluid, play a key role in establishing the resting mem-
Bane potential and in the repolarization phase of action po-
ttmtals in neurons and muscle fibers. When K moves inio
il ntoi ells, ii often is exchanged tor It' and thereby helps
late the pi I of body fluids. The level of k in blood
dtanu >s controlled mainly by aldosterone When bit >•
|jsma K is high, more aldosterone is secreted into the
limn-]. Aldosterone then stimulates the renal collecting ducts
rete more K 1 and excess K is lost in the urine. ('.on-
ly, when blood plasma K" is low, aldosterone secretion
jses ;md less K" is excreted in urine.
\honi 99% ol the calcium in adults is in the skeleton and
teeth, where II is combined with phcisphute^ to lorm mineral
salts. In body fluids, calcium is nr.unb an extracellular cation
i(..\' ). Besides conm^taig to the hardness of bones and
ceeth, Ca 2 plays important roles in Wood clotting, neuro-
transmitter ft-lease. maintenance of muscle lone, and ex-
citability of nervOuS and muscle rissue.
The two twin regulators of Cr' level in blood plasma
are parathyroid hormone (PTlh and calciiriof the lorm ot
vitamin D that acts as a hormone (sec I i| are 13,10 on page
327). A low plasma Cr level promotes release of more
PTH. which increases bone resorption bj stimulating osteo-
clasis in bone tissue to release Cr (and phosphate) front
mineral salts of hone matrix. PTH also enhances ftitfoorption
of (,r from L>]omeruhir filtrate back into blood and in-
creases production of calciiriol (which in turn increases C;i '
idmirptioii fn.uu the gastrointestinal »raci).
! ih describes the imbalances that result I'mm i lie
deficiency or excess of several electrolytes.
Table 22.2 Blood Electrolyte Imbalances
Electrolyte*
Bpdlum {Na*)
K-14B mEq/IWor
pi
fir.Eq/liler
fom(K)
i mEq/iitar
t(Ca")
^-10,5mg/ctL
i 4.5-5.5 rtiEq/Hter
Deficiency
Excess
Name and Causes
Hyponatremia
(ht-po-na-TRE-ma-a) may be
due to decreased sodium
intake: increased sodium loss
through vomiting, diarrhea.
aldosterone deficiency, or
taking certain diuretics snd
excessive water intake.
Hypochloremia
(hi-po-klo-RE-me-a) may be
due to excessive vomiting,
water intoxication,
aldosterone deficiency.
congestive heart failure, and
therapy with certain diuretics
such as furosemido (Lasiirr).
Hypokalemia
(hi-p6-ka-LE-me-a) may result
from excessive fluid loss due
to vomiting or diarrhea, de-
creased potassium Intake, al-
dosterone excess, kidney dis-
ease, or therapy with some
diuretics.
Hypocalcemia
(hi-po-kal-SE-me-a) may be
due to increased calcium
loss, reduced calciilm Intake,
elevated levels ol phosphate,
or parathyroid hormone
deficiency.
Signs and Symptoms
Name and Causes Signs and Symptoms
Muscular weakness; dizzi-
ness, headache, arid hy-
potension; tachycardia and
shock; mental contusion,
stupor, and coma.
Muscle spasms, metabolic
alkalosis, shallow ventila-
tions, hypotension, and
tetany.
Muscle fatigue, flaccid
paralysis, mental confusion,
increased urine output,
shallow ventilations, and
changes in the
electrocardiogram,
Numbness and Jingling of
the fingers; hyperactive
reflexes, muscle cramps,
tetany, and convulsions;
bone fractures: spasms of
laryngeal muscles thai can
cause death by
asphyxiation.
Hypernatremia may
occur with
dehydration, water
deprivation, or
excessive sodium In
the diet or in
intravenous fluids.
Hyperchloremla may
result from dehydra-
tion due to water loss
or water deprivation,
excessive chloride
intake, or severe renal
failure, aldosterone
excess, certain types
of acidosis, or some
drugs.
Hyperkalemia may be
due to excessive
potassium intake,
renal failure, aldos-
terone deficiency, or
crushing injuries to
body tissues,
Hypercalcemia may
result from hyper-
parathyroidism, some
cancers, excessive
intake ol vitamin D,
and Paget's disease of
bone.
Intense thirst,
hypertension, edema.
agitation, and
convulsions.
Lethargy, weakness.
metabolic acidosis, and
rapid, deep breathing.
irritability, nausea.
vomiting, diarrhea,
muscular weakness; cap
cause deaih by inducing
ventricular fibrillation.
Lethargy, weakness,
anorexia, nausea,
vomiting, polyuria,
itching, bone pain,
depression, confusion.
paresthesia. &tupor, and
coma
5«re normal ranges ol blood plasma levels in adults.
550 Chapter 22 Fluid, Electrolyte, am) Acid-Base Balance
People who arc at risk for fluid and electrolyte imbal-
ances include those who depend on others for llnid and
food, such as infants, the elderly, and the hospitalized. Also
iit risk are individuals undergoing medical treatment that
iv lives intravenous infusions, drainages r^r Suctions, and
urinary catheters. People who recent.- diuretics experience
excessive fluid losses and require increased fluid intake;
those who experience fluid retention and have fluid re-
strictions are also at risk. Finally at risk are postoperative
dtuils, severe burn or trauma cases, individuals with
chronic diseases (congestive heart failure, diabetes, chronic
obstructive lung disease. and cancer), people in confine-
ment, and individuals with altered levels of consciousness
who may he unable to communicate needs or respond to
thirst.
■ CHECKPOINT
4. What are the Einicrions of electrolytes in the body?
ACID-BASE BALANCE
OBJECTIVES • Compare the roles of buffers, exhala-
tion of carbon dioxide, ajid kidney excretion of H in
maintaining: the pH of body fluids.
« Define acid-base imbalances, describe their effects on
the body, and explain how they are treated.
From our discussion thus far, it should be clear that various
ions play different roles in helping to maintain homeostasis.
A major homeosratic challenge is keeping the H ' level (pH)
of body tluiils m the appropriate range. This task —the main-
tenance of acid-base balance — is of critical importance be-
cause the three-dimensional shape of all body proteins, which
enables thern to perform specific functions, is very sensitive
to the most minor changes m pi I. When the diet contains a
large amount ol protein, as is typical in North America, cel-
lular metabolism produces more acids than bases and thus
tends to aci«.lif\ the blood.
In a healthy person, the pf I of systemic arterial blood re-
mains between 7.35 and 7.45. The removal oFH' from body
fluids and its subsequent elimination from the hody depend
Oil three major mechanisms; buffer systems, exhalation of
carbon dioxide, and kidney excretion ol I I ' into the urine.
The Actions of Buffer Systems
Buffers arc substances ihai act tjuickh io temporarily bind
IT' v removing the highly reactive, excess 11 ' from solution
but not from the body. Buffers prevent rapid, drastic changes
in the pi I of a body fluid by converting strong acids and
liases into weak acids and bases. Strong adds release H'
more readily than weak adds and ihus contribute more- Ira-
hydrogen ions. Similarly, strong bases raise pM more than
weak ones. The principal buffer systems of die body fluuli
are the protein buffer system, the carbonic acid -bicarb
buffer system, .in, I the phosphate buffer system.
Protein Buffer System
Alam- proteins can act as buffers. Altogether, protein
body flunk comprise the protein buffer system, which
most abundant buffer in intracellular fluid and plasma. He-
moglobin is an especially good buffer wuhiri red blood cells,
and albumin is the main protein buffer in blood plasma. Re-
call that proteins are composed ol amino acids, organic mofej
cules that contain at least one carboxyl group (— CO( )J I) and
at least one amino group (-NI t : ); these groups are the func-
tional components of the protein buffer system. The carbojyl
group releases II when pH rises. The 11' is then ablctoifJ
act with any excess Oil io the solution to lorm water. The
annuo group combines with IT, forming an -N1 I, ■■
when pi I falls, Thus, proteins can buffer both adds and
bases.
Carbonic Acid - Bicarbonate Buffer System
The airborne acid -bicarbonate buffer system IS based
bicarbonate ion (HCO f ), which can act as a weak base
carbonic acid (ITCO») T which can act as a weak acid. I ICO
is a significant anion in both intracellular and cxtracetlubtl
fluids (!■ .•<). Because the kidneys reabsorb fihqtl
HCO j . this important buffer is not lost in the urine. It
is an excess ol" I I \ the I ICO, can function as a weak bi«j
and remove the excess H" as follows:
II + HCO:, — ► IbCO,
! j . I igen i"i>
Bic-.irlnin.iii.- ion
(weak base)
■nu acid
(Conversely, if there is a shortage of II'. the ll< I
function as a weak acid and provide 1 1 is follows:
H;CO;
*■
II
r
IK . :
( htrlioiiK acid
(weak .io ij)
1 IuliutfL-n inli
HicarbonaicJd
Phosphate Buffer System
The phosphate buffer system acts via a mechanism suni
the carbonic add— -bicarbonate buffer system. The compJ
nents of the phosphate buffer system are the ions Jihfam
phosphate (I -T..PO. ) and monohydrogvn phosphate (HPQJ
Recall that phosphates arc major anions m intracellular 8m
and minor ones in extracellular fluids (Figure 22.S). The'9
hydrogen phosphate ion acts as a weak acid and is enpafifej
buffering strong bases such as OH , as follows:
OB
I Hydroxide ion
(>iil.i:l'.' busc)
lldH):
Diljydri iai n
i tsphatc
(weal .I. ni
II
Wllcl
+ HPQJ
Mttiiohyift
iyw I
Acid-Base Balance 551
*■
Activity — A Challenge
lo Fluid and
Electrolyte Balance
ivv or pnjlojiged phystcaj activity
n lead no dehydration and disrupt
nrcl electrolyte balance* Strenuous
isfl in bot weather rnaj cause the
|iBSof over 2 liters (aboul 2 qfc) of wa-
jijer hour from the skin and togs.
fij losses can lead to dehydration and
rated body temperature it fluids are
■jt replaced.
Jon'i Sw
^hydration is a loss of hotly fluid that
lunmiiits to \% or more ol total body
h is most common during
activity at a high temperature
[man also occur during strenuous ex-
.u lower temperature. Fluid
ire common in athletic
.nth as football soccer, tennis.
and long-distance running. Syinptotns
include irritability, fatigue, and loss of
appetite.
With dehydration, water is lost
from all hotly Hind compartments. 'The
decrease in blood volume impairs phys-
ical performance because il decreases
the amount ol blood (he heart
pump per beat. Muscles need oxygen CO
work; as cardiac output is reduced,
muscle performance declines. The
bod) tries to. maintain blood volume to
the muscles by constricting blood ves-
sels LO the skin, s<j less heal is Inst and
body temperature rises. Intracellular
el< qtraryte changes may also occur.
rhirsi is die body's signal thai its
water level is getting too low. Union u-
naicly ihirsi is not a reliable indicator
of fluid needs. People lend to drink just
enough to relieve 1 heir parched throats.
The thirst mechanism is especially un-
reliable in children -muI older adults.
Airing decreases the kidneys" abilin to
retain water when the bod) needs flu-
ids, which increases ihe susccptil'iliu
to dehvi I ration.
► Think It Ove
Sports tit inks contain tkctralytes such as sodium and potassium* Wfap might
stub drinks help a dehydrated person regain novum! hydration levels l><
than plain water?
Tie monohvdrogen phosphate ion. in contrast, acts as a
and is capable of buffering the il' released by a
ffirttid such as hydrochloric acid (HC3)i
+ HPCX, 2 — >■
II
i
Mutinluiln.^L"!
phosphate
i. ..
TITO,
i >ih\ drogen
phosphate
(wcik acid)
In concentration of phosphates is highest in in>
tdliiLir lluid, die phosphate hulkr system is an important
n of pfi in the cytosol. It also acts to a smaller degree
icel'lular fluids, and it buffers acids in urine.
ilation of Carbon Dioxide
Jays an important role in maintaining the pi I of
[fluids. An increase in the carbon dioxide (COJ concert -
rn hotly fluids increases H ' concentration and thus
..ithc pi I intakes body fluids more acidic). Conversely, a
it the CO.? concentration ofbody fluids raises the
Offices fluids more alkaline). These chemical inter-
ili* are illustrated bv the following reversible reactions.
CO • II, =f^ H 2 CO
Carbon U'.ircr Cartnoiiic
tliuxufc and
II + IKO
i- 'i Riuihiiiuu'
IIM1
Changes in the rate and depth of breathing can alter the
pH ofbody fluids within a couple of minutes. Willi increased
ventilation, more COa is exhaled, the reaction goes from
right CO lcli, I I concentration falls, and blood pi I rises, tlf
ventilation is slower than normal, less carbon dioxidt is ex-
haled, and the blood pi I falls.
The pi I ofbody fluids :\\m\ the rate and depth of breath-
ing interact via a negaiive feedback loop (limine 12 M). When
mi, bib id acidity increases, the decrease in pi I (increase in
concentration of II ) is detected by chemoreeeptsoES in the
medulla oblongata ami in the aortic and carotid bodies, both
of which stimulate the inspiratory area in the medulla ohlon-
^ala. As a result, the diaphragm and other respirator), mus-
cles contract more forcefully and frequently, so more ( '< ) is
exhaled, driving the reaction to the left. As less 1 1 ( .1); forms
and fewer II arc present, blood pi I mereases. When the re-
sponse brings blood pM (IT concentration) back to normal,
there is a return to acid -base homeostasis.
552 Chapter 1Z Fluid. Eleclrolyle. and Acid-Base Balance
Bv contrast, if flu: pi I of the blood increases, the respira-
tory center is inhibited and the rule and depth of breathing
decreases. Then, CO2 accumulates in the blood and its H*
concentration increases. This respiratory mechanism is pow-
erli.ll, hut it can only uegdlate the concentration oJ Clfie
acid — carbonic acid.
Kidney Excretion of H '
The slowest mechanism lor removal of acids is also the onl\
way to eliminate most acids that form in the body: Cells of
:-, nal tubules secretr. I I , which then is excreted ill urine.
Also, because the kidneys synthesize new H€0 3 and reab-
sorb filtered HC(V, tbfe important buffer is not lost in the
urine. Because of the contributions of the kidneys to
acid -base balance, it's not surprising that renal failure ran
.|uickly cause death,
summarises the mechanisms thai maintain pH
of body Quids.
Acid-Base Imbalances
Acidosis is a condition in which arterial blood nil rs below 7.35.
The principal physiological effect of acidosis is depression ol
die central nervous system through depression of synaptic
transmission. If the systemic arterial blood pH falls below 7.
depression of die nervous system is so severe that the individual
becomes disoriented, then becomes comatose, and may die.
In alkalosis, arterial blood pi I is higher than 7.45. A major
phvsiulojrical effect of alkalosis is overexcitahiliiy in both the
central nervous system and peripheral nerves. Neurons GOnduct
impulses repetitive! \, even when not stimulated; the results are
nervousness, muscle spasms, and even convulsions and death,
\ change in blood pi I that leads to acidosis or alkalosis
1 1 nit be countered by irunpcnsatiott, the physiological re-
sponse to an acid -base imbalance dial acts to normalize arte-
rial blood pi I. Compensation may he either rrw//>/cAc, il pi I
indeed is brought within the normal range, or part/at, il sys-
temic arterial blood pi I is still lower than 7.35 or higher than
7.45. II a person has altered blood pi I due to metabolic
causes, hyperventilation or hypoventilation can help bring
blood pli hack coward the normal range; this form of coin-
]k nation, termed respiratory compensation, occurs within
minutes and reaches its maximum within hours. 11, however,
a person has altered blood pH due to respiratory causes, then
renal compensation— changes in secret ton of H and reao-
sorption off ICO : by the kidney tubules— can help reverse
the change. Renal compensation may begin in minutes, bm 11
takes days to reach maximum effectiveness,
■ CHECKPOINT
5. How do proteins, bicarbonate ions, and phosphate ions
help maintain the pi 1 of body Mimbr
6, What are the major physiological effects of acidosis and
alkalosis:
Figure 22.6 Negative feedback regulation of blood pH by
the respiratory system.
, % Exhalation of carbon dioxide lowers the H j concentration of
blood.
Some stimulus disrupts
homeostasis by
i 1
Decreasing
Blood pH (increase
In H* concentration)
Receptors
Chemo- Chemo-
receptors receptors. -
In in aortic
medulla and
oblongata carotid
bodies
I
Return 10 honteofil
when response b
blood pH or H' con
eentration back to
normal
As teraH ? C0 3 tarns
and lower H* are present.
blood pH increases (H
concentration decreases!
■ I
it
If you hold your breath tor 30 seconds, what is likely to I
your blood pH?
echanism
litter Systems
Proteins
Carbonic acid -bicarbonate
Phosphates
jhalation of CO?
iWneys
Table 22.3 Mechanisms That Maintain pH of Body Fluids
Comments
Convert strong acids and bases into weak acids and bases, preventing drastic changes in body fluid pH.
The most abundant buffers in body cells and blood. Hemoglobin is a buffer in the cytosol of red blood cells; albumin is a
butler In blood plasma.
Important regulators of blood pH-The most abundant buffers in extracellular fluid.
Important buffers in intracellular fluid and In urine.
Wilh increased exhalation of CO ? , pH rises (fewer H"). With decreased exhalation of CO a . pH falls (mure H )
Kidney lubules secrete H" into the urine and reabsorb HCO : , so it is not lost In the urine.
AGING AND FLUID,
(ELECTROLYTE, AND
ACID-BASE BALANCE
OBJECTIVE • Describe the changes in fluid, electro-
lyte, and actd-base balance that may occur with aging.
pmparison with children and younger adults, older adults
have an impaired ability CO maintain llitid, electro!) 10,
J&cid-base balance. With increasing age, many people
mk decreased volume of intracellular fluid and decreased
body potassium due CO declining skeletal muscle mass
Eacrcnsing mass of adipose tissue (which contains very lit-
tle water). Age-related decreases in respiratory and renal
hiiuTioniiur may compromise acid -base balance b\ slowing
the exhalaiii'ii oid h mk\ the excretion of excess acids in urine.
Other kidney changes, S»Cfl .is decreased blood Bow, decreased
tdomerular till ration rale, and reduced sensitivity 10 antidiuretic
hormone, have an adverse effect on the ability Co m ai nt ain Said
and electrolyte Waftce. Due to a decrease in the number and
efficiency of sweat gjands, water loss from the sMn declines
uidi age. Because of these age-related changes, older adults ate
susceptible to several fluid and electrolyte disorders.
■ CHECKPOINT
7. How are skeletal muscle mass and adipose tissue related
to fluiil and electrolyte imbalam
STUDY OUTLIN
I Compartments and Fluid Balance (p. 544)
Hit water and dissolved solutes in the body constitute the
viik
I i two-thirds of the body's fluid is lucated within cells and
, d imteellular fluid (ICF). Hie other one-third, called
: lUihir fluid (l-'.CF), includes all other body fluids. About
,| ilu If :i' is interstitial fluid, which occupies the micro?
sonic spaces between tissue cells, and about 20% of the ECF
UsWnod plasma, the liquid portion of the blood,
fluid balance moans that the various body compartments eon-
nuimal amount of water and solutes.
is die largest single component in the body, abomi
il total body mass in lean adults,
leccmlytc is an inorganic substance thai dissociates into
i solution. Hind balance and electrolyte balance are to-
lied
water gain -.md loss are each about 250P nil.. Sotirc
are ingested liquids and foods ami wafer produced
".
S.
9.
bv metabolic reactions (metabolic water). Water is lost Irons
the body through urimutoii. evaporation from the skin surlaee,
exhalation of water vapor, and defecation. In women, men
flow is an additional route for loss ol both water.
'The mam \va\ 10 regulate body water gata is by adjusting the
volume of- water intake. The thirst center in the liypothalaiffUS
governs the urge to drink.
Angiotensin 11 and aldosterone reduce urinary loss ol N,i and
CI and thereby increase ihe volume of body fluid*-. \trial na-
triuretic peptide promotes n-.tin uresis, elevated exeredon of
i\n* [and CI ) and water, which decreases blood volume,
Tabic 22.1 op page ^"47 si nalfrses ihc factors thai maintain
W it* r balance.
Electrolytes in Body Fluids (p. 548)
1. Electrolytes control die osmosis of water between lluiil COffi
parunents, help maintain acid- base balance. earn electrical
i airrent, and act as en/vuie cotactors.
554 Chapter 22 Fluid. Electrolyte, and Acid-Base Balance
2. Sodium ions (N'a ) are 1 1 u- most abundant extracellular inns.
I hey are involved in actinia potentials, muscle contraction, and
fluid and electrolyte balance. Na level is controlled b\ aldos-
terone, antidiuretic hormone, and atrial natriuretic peptld.e.
3. Chloride ions (CI ) are die major extracellular anions, They
play n role in regulating osmotic pressure and forming I Id in
gastric ftaee. c:i level is controlled by processes thai increase
or decrease kidney rcabsorption oJ N.i ,
4. Potassium ions (K > are the most abundant cations in intracel-
lular fluid, They pla\ a key role in establishing die resting
membrane potential in neurons and muscle fibers, and eon-
tribute in regulation of pi f. k level is controlled by aldos-
terone.
5. Calcium is die most abundant mineral in the body, Calcium
Miiu are structural components of bones and Eeech, Ca
which are principalis extracellular canons, function in - blood
clotting, neurotransmitter release, -i n.i contraction of muscle.
I h level is controlled mainly by paramyloid hormone and
cakiinol.
6. lalilc 22J on page S49 describes the imbalances ilmi rear]
from deficiency or excess. of important bodj clectrorj
Acid-Base Balance (p. 550)
1. The normal pi I of systemic arterial blood is 7.35 u>
2. I looieostasis ol' pi [ is maintained by buffer systems. In nlhh-
don of carbon dioxide, and by kidne) excretion nl II .indr&J
absorption of I ICO , , Rlbie 2 i on page 553 suimim
mechanisms that maintain pj J ofbod) fluids.
5. Vcidosis is ,i systemic arterial blood pi I below 7.>5 i
pal elieet is depression oj the central nervous system
Alkalosis, is a systemic arterial blond pi I above 7.4>; ii
pal el'leet is overc\citability ol the { \S.
Aging and Fluid, Electrolyte, and Acid-Base Balance (p. 553)
1. With increasing age, there is decreased intracellular fluiiholinj
nnd decreased potassium due to declining skeletal muscle moss.
2. Decreased kidney function adverse!} affects fluid
trolyie balance
'Q
SELF-QUI
l. Normally, most of the body's water is lost through
a. dje gastroiflteslinal tract b, celhilaf respiration
c. exhalation In the lungs d. excretion of urine
e. evaporation from die tfkin
?. Substances chat dissociate into ions when dissolved in body lln-
ids are
a. neurotranstni tiers b. enzymes c. nonelcctmlytes
d. hormones c, i k.-ctn >\\ lis
J. Which of the following statements abom \odnim is \OT rrue ;
a, Sodium ions are the most abundant intracellular ions
b. Sodium is ne. • n u generating action potentials in neu-
rons.
c Excess sodium ions can cause edema.
d. Sodimn levels ire regulated by the ktktaeys.
e. Aldosterone helps regulate the concentration of sodium in
the blood.
4. I'ararhyroid hormone if* II h controls blood lew I '- 1
a. magnesium b. sodium c. calcium d. potassium
e. chloride
5. IIliilI movement between J n trace Ilu la r fluid anil extracellular
fluid depends primarily on die concentration of which ion in
extracellular fluid:
a. -...ilium h. potassium C, calcium tt phosphate
e. magnesium
6. Which df the following arc mismatched:
a. the most abundant extracellular anion, CI
b. the most abundant mineral in the body, < a
c. the most abundant extracellular cation, Na
d. the most abundant intracellular cation, K*
e. the most abundant intracellular anion. 1 tCOg
7. Which of the following statements concerning aciil-lnalj
aiuv in the bfdv is Ps't ) I ma
a. An increase in respiration rate increases pi I ol Iic.lv iluuk
b. Normal pi I ofextraccllutar fluid is 7.35 to". 45.
c. Buffers are an rmportanr mechanism in the rnajrtlciiara tj
pi I balance.
d. \ Wood |d I of 7,2 is called alkalosis,
e. Respiratory acidosis is characterized by a high lev
in body fluids.
8. Most human buffer systems consist of
a. a weak add and a weak base
b. a strong acid and a strong base
c. a strong acid Mieh as I K'.l
d. an electro!} le and uoiielectrolvte
e. a weak base and a gas
9. The most abundant buffer in body cells and plasi
buffer system.
a. hemoglobin b, carbonic add c. protein
d. bicarbonate e. phosphate
10. VTosi (80%) of the extracellular fluid i> pari of" the Id
a. interstitial fluid b. lymph c. eerebrospir
d. plasma e. synovial fluid
1 1 . Which hormone stimulates the kidne) s !<■ secrete mure K*?
a. atrial natriuretic peptide b. angiotensin
C aldosterone d. antidiuretic hormone
e. parathyroid hormone
12. Most ofthe body's water comes from
a. cellular respiration b. adipose KftSSUt!
c. urine production d. water intoxication
e. ingested liquids and foods
J
14.
"
"I lie thirst cencez 1 caii bK activated bj .ill of Che following
I SCI i-,
j. angiotensin II
b. an increase in blood volume
c. n decrease in flow from salivary glands
d. a decrease ui blood pressure
A. an increase in blood Osmotic pressure
The center Tor thirst is located in the
a. kidneys h. adrenal cortex c. hypothalamus
il. cerebral cortex e, Jivcr
..' i i- of th< fallowing is NOT one of the fractions pfelcc^
> in the bodj :
a. control of fluid movement between the extracellular and
intracellular compartments
b. reguhtion of pi I
c. enzyme cefaclor
d. energy source
e. carriei »felectri< current
Mdostcrone is secreted in response to
j. increased blood pressure b« decreased Ijkiod. volume
c. increased calcium lewis cl. increased sodium levels
c. increased water levels
Answers Id Figure Questions 555
17. What U the importance of buffer systems in the body?
at. They help maintain ihc calcium and phosphate balances of
bone.
b. Tney control the body's vv.iter balance.
c. They prevent drastic changes in the In »h s pi I.
d. They help regulate blond volume.
e. Hi ey ate responsible fc>i the operation of the body's sodium
pump.
18. Match r,hc follow ing:
. a. extracellular cation: struelur.il
component ol bones and teeth
J>. most abundant anion in extra -
ccl hilar fluid
c. most abundant extracellular
cation; needed for generation
and conduction oj action
potentials
d. most abundant cation in
intracellular fluid;
ittvoh eil in nerve ami muscle
homeostasis
\. ofllchim
B. chloride
C. potassium
D. sodium
I
CRITICAL THINKING APPLICATIO!
I
'
Jose was grafting his way through lunch by eating - at street ven-
,1'u-.. 1 1 1 had a large order of fries with extra salt, then a foot-
fang hot dog with ketchup (a very high sodium content lunch).
\,.\i. Jiise bought a large bottled -water and drank the entire
liui.ile. How will his bod) respond to this lunch?
Onc-venr-old Timon had a busy morning at the "mom and lot"'
swim program. loday's lesson included lots ot underwater cxer-
mses in blowing bubbles. After die lesson, Timon seemed dis~
lied and then suffered a convulsion. The emergency room
i thinks ihc: swim class Iras something to do with Timon s
m, What is wrong whJi Timon;
VllU and Jennie arc the same height and both weigh 150 lb.,
Iiut when Mike and JeUnie measured their blood alcohol after
drinking identical alcoholic beverages, Jennie's blood alcohol
level was higher than Mikes. In the body, alcohol is transported
in the body fluids, L se your knowledge about die differences in
hodv water between males and females to explain the difference
in alcohol level.
4. \lex was 1 5 minutes late for A&P class. While searching for his
pen. he thought be heard the instructor sa) something ahout
the heart affecting water balance but he had thoughi it was the
oilier way around. Ucx JUSI decided to ignore the whole thini;.
Bad move, Mc\l Explain the relationship of the heart to fluid
balance.
fi
ANSWERS TO FIGURE QUESTIONS
p,l The term body lluid refers to body water ami its dissolved
substances.
ii i cue drug increases urine flou- rate, thereby increasing
il fluid from die body and decreasing the volume of
bnch fluids.
Hi Negative feedback is in operation because the result tan in-
crease in fluid intake] is opposite to die initiating stimulus
dralion).
22.4 Elevated aldosterone promotes abnormally high renal reab-
sorption ol" N'aCI and water, which expands blood vol tunc
am! increases blood pressure. Increased blo.nl pressure
causes more fluid in filter GUI of capillaries and accumulate
in the inicrsittial fluid, a condition called edema.
22.5 The major cation in IICV is \a .
22.6 Breath holding causes blood pi I to ilccrease stlEhd) as CO.
and 1 1 accu inulate.
chapter 23
';.".■
THE REPRODUCTIVE SYSTEMS
A,
did you know?
bstainingfrom sexual
contact prevents the risk of sexually transmitted
infections. For couples who engage in sexual
contact, safer-sex practices at least reduce
the risk of acquiring an infection. Safer sex-
practices mean avoiding contact with oral or
genital sores ana' avoiding the exchange of
body fluids, such as semen, blood, and vaginal
secretions. Latex condoms provide the best
protection against sexually transmitted infections
for couples having sexual intercourse. Studies
of couples in which one partner was infected
■with HIV have found that when latex condoms
were used consistently, HW tram-mission to
partners was ve?y low (zero in one study,
2 out of 111 in another).
Focus on Wellness, page 576
VAVw.wiley.com/GOllege/apcentral
KJexaal reproduction is the process In which
organisms produce offspring by making
germ cells cdkd gametes <( IAM-ets = spouses).
Ahcr fertilization, when the male gamete
(sperm cell) unites with the female gamete (secondary oocyte), the
resulting cell conmins one set of chromosomes from each pa.reni.Tlw
organs that make tip the male and female reproductive systems i
grouped by function. The gonads— testes in males and u\ aries in
females — produce gametes and .secrete sex hormones. Various ducts
then store and transport die gametes, and accessory sex glands pro
substances dial protect die gametes and facilitate then- inovenn hi
Finally, supporting structures, such as the penis and the uterus, assist the
delivery and joining of gametes and, in females, the growth of the
embryo and fetus during pregnancy.
Gynecology (p -ne-KOL^6-je; gyneco- = woman; -%y = stii
is the specialized branch of medicine a jncernei I with the diagnnsi
treatment of diseases of the female reproductive system. As noted In
Chapter 21, urology (ii-ROL-o-je) is the study of the urinary system.
Lid |r agists also diagnose and treat diseases mm\ disorders of the male
reproductive system. The branch of medicine that deals with male
disorders, especially infertility and sexual dysfunction, is called/?//,
(an~DROL-o-je; W/?;- = masculine).
looking back to move ahead
■ Somatic Cell Division (page 62)
• Sympathetic and Parasympathetic Divisions of the Autonomic
Nervous System (page 274)
• Hormones of ihe Hypothalamus and Pituitary Gland (page 319)
556
Male Reproduclive System 557
IALE REPRODUCTIVE SYSTEM
UECTIVES • Describe the location, structure, and
tbns of the organs of the male reproductive system.
:m :i ibe how sperm cells are produced.
Explain the roles of hormones in regulating mate re-
productive functions.
jhe organs of the mtiie reproductive system are ilu- teste?"; a
n of duets (epididymis, ductus deferens, ejaculacory
id urethra); accessory sex "-lands (seminal vesicles,
[pate, and bulbourethral glands); and several supporting
pictures, including the scrotum and the penis fFfgure 23.1).
The testes produce sperm and secrete hormones. Sperm are
transported ami stored, helped Co mature, and conveyed to
i lie exterior by a system of ducts. Semen contains sperm plus
the secretions provided by die accessory se\ glands.
Scrotum *
The scrotum (SKRO-tum = bag) is a pouch thftl supports
rhe testes; it consists nf loose skin, superficial lasna. and
smooth muscle (Figure 23.1). Internally, a septum divides the
scrotum into twosa.cs, each containing a single testis,
"ilie production and survival ol sperm is optimal at a
temperature that is about 2-3°C below normal body temper-
ature, litis lowered body tcmperaiiire is iiwintained within
Figure 23.1 Male organs of reproduction and surrounding structures.
, Reproductive organs are adapted to produce new individuals and pass genetic material from one generation to the next.
Functions of the Male Reproductive System
t, Testes: produce sperm and the male sex hormone testosterone,
2. Ducts: transport, store, and assist in the maturation of sperm.
3. Accessory sex glands: secrete most ot the liquid portion of semen
4. Penis: contains the urethra, a passageway lor ejaculation ot semen
and excretion ot urine.
Seminal vesicle
Coccyx -
Rectum
Ejaculalory duel
Anus
Testis
Scrotum
Sagittal section
Urinary bladder
Ductus fvas) deferens
Pubic symphysis
Prostate
Deep muscles ol perineum
Bulbourethral gland
Corpora cavernosum penis
Urethra
Penis
Corpus spongiosum penis
Glans penis
Prepuce (foreskin)
External urethral orifice
Among the male organs of reproduction, how is the penis classified functionally?
558 Chapter 23 The Reproductive Systems
h scrotum because n is outside the pelvic cavity. On expo-
sure to cold, skeletal muscles comma to elevate the testes,
moving them closer to the pelvic cavity, where ihe\ can ab-
sorb body beat Exposure co warmth causes relaxation of the
skeletal rnuscles ;,nu descent of die testes, increasing the sur-
face area exposed to the air, s,, that the testes can give off ex-
cess heat K> their surroundings.
Testes
The testes (TES-tcz; singular is testis), of testicles* are paired
oval glands chat develop on the embryo's posterior abdominal
uall am! usually begin their descent into the scrotum in the
seventh month of fetal development.
The testes are covered hy a dense ivhite fibrous capsule
that extends inward and divides each testis into internal com-
partments called lobules ( ; ), Each of the 200 to
300 Lobules contains one eg three tighrb coiled seminiferous
tubules (semht- = seed; fir- = to carry) dial produce sperm
U\ a process called spermatogenesis (described sliorth ).
Seminiferous ttihtiles are lined with Sper m atog e tlic (sperm-
rbrmtng) cells (Figure 23 J b). Positioned against the basement
membrane, toward the outside of tfafi tubules, are the sper-
matogonia (sper-ina'-io-(i(Vne-a; -gut ia ~ offspring), the
stem cell precursors. Toward die lumen ol the tubule are layers
of cells in order of advancing maturity: primary spermatocytes,
secondary spermatocytes, spermatids, and sperm cells, Alter a
sperm cell or spermatozoon (sper'-ma-to-ZO-on: -zami — lire)
has formed, it is released into rhe lumen ol' the seminiferous
tubule.
Large Sertoli cells, located between the develop
sperm cells in the seminiferous tubule-., support, protect, and
nourish spermatogenie cells; phagocyti/.e degenerating sper-
matngenic cells: secrete fluid lor sperm transport; and release
the hormone inhibin, winch helps regulate sperm produc-
tion. Between the seminiferous tubules are clusters of Leydig
cells. These cells secrete the hormone testosterone, the most
important androgen. An androgen (AN-dro-jen) is a hormone
that promotes the development ol masculine characteristics,
testosterone also promotes a mans libido (sex drive).
ondition in which the testes do not descend into the
scrotum is called cryptorchidism (krip-TOR-ki-di/.m;
ii-n: orchid = testis), b occurs in about 3% of
rm infants and about 30% of premature infants. Un-
treated bilateral cryptorchidism causes sterility due to the
higher temperature of the pelvic cavity. The chance of tes-
ticular cancer is 30 ro sO times greater in cryptorchid
. poSStblj clue to abnormal division of germ cells
caused by rhe higher temperature of the pelvic cavity. I "he
testes of about HO'/i of boys widi cryptorchidism will <le-
1 spontaneously during the lirst year of life. When the
S remain undescended, the condition can be corrected
surgically, ideally fie tore IS months of age.
Spermatogenesis
The process by which the seminiferous tubules of the
produce sperm is called spermatogenesis (sper-ma'-to |1,\
e-sis). It consists of three stages: meiosis I, meiosis II. ir i
spermiogenesis. We begin with meiosis.
Ovi -kvu-u of MEIOSIS As you learned in Chapter v no
body cells (somatic cells), such as brain cells, stomach cellsj
kidney cells, and so forth, contain 25 pairs ol chromoson -
or a total of 46 chromosomes. One member ol each pair is]
Inherited front each parent. The two chromosomes that
make up each pair are called homologous chromosomes (hi>
AlOL-o-gus: Iw/uv- = same): they contain similar gents I
arranged in the same (or almost the same) order. BecauscsS
matic cells contain two sets of chromosomes, they are tertnea
diploid cells (DIP-loyd; dip/- — dottble; -aid - lomi), sym-
bolized as In, ( iamei.es differ from somatic cells because
contain a single set of 23 chromosomes, symbolized as fl
the) .we thus said t.i In. haphid (I I M'-lnyd; hapl- = singlfl
In sexual reproduction, an organism results from the M
sion ol tWO dillvrent gametes, one produced by each parent,]
II each gamete had the same number of chromosomes as4
matic cells, then rhe number oJ chromosomes would J out.
each time Icriili/.arion occurred. Instead, gametes receffl
single set of chromosomes by means of a special type 01 1
productive cell division called meiosis (rnl-O-sIs; mct-
ening; -osts - condition of). Meiosis occurs in two succtssim
stages: meiosis I ,i\\t\ meiosis 11. First, we will examine fan
meiosis occurs during spermatogenesis. Later in the chapter
we will follow the steps of meiosis during oogenesis, the ar*
duetion of female gametes.
Stages of Spermatogenesis Spermatogenesis begins <itf
ing puberty and continues throughout life. The time Irunoi
set of cell division in a spermatogonium- until spen i
leased into the lumen ol a seminiferous tubule is 65 to ~5di]jfl
The spermatogonia contain the diploid number of cfoOB
somes (46). After a spermatogonium undergoes itiiui
celt stays near the basement membrane as a spermatogonhijl
BO Stem cells remain for future mitosis (Figure 23.3 on
560), "The other cell differentiates into a prima ly spcniiatofjM
(sper-A'IA-to-sIt'). Like spermatogonia, prim an spc mi
are diploid. Spermatogenesis proceeds as follows:
I. Aleiosis I. During the interphase that precedes n
the chromosomes replicate, as also occurs in the nut
phase before mitosis in somatic cell division (see
62), The 46 chromosomes, now each made up of
identical "sister" chromatids, line up as 23 pairs
mologous chromosomes. (By contrast, pairing, or [n.
ogous chromosomes does not occur during mitosis)
iVittr chromatids ol each homologous pair then
around one another. At this time, portions of one 3
matid may he exchanged with portions of am
an exchange is termed crossing- over*. Crossini
suits in genetic recombination, the formation of
Male Reproductive System 559
Frgure 23.2 Anatomy and histology of the testes, (a) Spermatogenesis occurs In the seminiferous
tubules- (b) The stages ol spermatogenesis. Arrows in (b) indicate the progression from least mature to most
mature spermaiogenic cells. The (n) and (2n) refer to haploid and diploid chromosome number, to be de-
Scribed shortly.
The male gonads are the testes, which produce haploid sperm.
k
L^
Sagiita
plane
jT
U
Ductus (vas) deferens
Ductus epididymis
Epididymis
(a) Sagittal seciron ol a testis showing
seminiferous lupulas
Leydig cell
Blood capillary
Basement membrane
Sertoli cell nucleus
Spermatic cord
Blood vessels
and nerves
While fibrous capsule
l.obute
Seminiferous tubule
«»
SPERMATOGENIC CELLS.
Spermatogonium [2n)
{stem cell)
i
Primai y spermatocyte [2ri)
Secondary spermatocyte (n
J
Spermatid (n)
Sperm celf or
spermatozoon in)
(b) Transverse section of a part of a seminiferous tubute
Which spormatogenic cells in a seminiferous tubule are least mature?
560 Chapter 23 The Reproductive Systems
Figure 23.3 Spermatogenesis. The designation 2n means
diploid (46 chromosomes); n means haploid (23 chromosomes).
> Sf
Spermiogenesis is the process whereby spermatids mature into
sperm.
Basameni membrane
ol seminilerous lubiiie
Superficial
Seme spermatogonia remaJrj
as precursor siern cells
Spermatogonium
Some spermatogonia
pushed away l".nn
basemen! membrane
MEjOSIS
Differentiation I
Primary spermatocyte
MeioBts
Meiosis
DNA replication
and cros3|ng-ovor
Secondary spermatocytes
fM /i Eacl1
JLmj chromosome
has two
chromatids
Spermatids
SPERMIOGENESIS
\BB\
♦ ♦ * +
Spermatozoa
f" f f"
Lumen of seminiferous tubule
Whet Is ihe significance of crossing-over?
combinations of genes. As a result, the sperm, eventually
produced are genetically unlike one another and unlike
the parent cell th.u produced them.
Next, the members of each homologous pair sepa-
rate, wirh one member of each pair moving to opposite
ends of the cell. The sister chromatids, held by a eefl-
immcre, remain together. (During mitosis, the sister
chromatids move to opposite ends of the cell,) The net
effect of meiosis I is that each resulting cell contains a
haploid sei of chromosomes.
The cells formed by meiosis I me haploid secondary
spermatocytes, having 25 (replicated) chromosomes.
Each chromosome within a secondary spermatocyte is
up of two chromatids (two copies of the DNA) Still
attached by a centromere. The genes on each chromatid
may lie rearranged as $ result ol crossing-over.
2. Meiosis II. In meiosis fl there is no further repli
of DNA. The chromosomes of the secondary spermatqj
cytes line up in single file near the center of the nucleus,
and this time the chromatids separate, as also occurs in
mitosis. Ihe cells formed from meiosis 11, termed spcr-
ma/ids, contain 23 chromosomes, each of which is conk
posed of a single chromatid.
3. Spermiogenesis. In the final stage of spermatogcneSK
called spermiogenesis (sper'-me-o-JEN-e-sis), each hap-
loid spermatid develops into a single sperm cell (sei
ure23.2kr).
Sperm
Sperm are produced at the rate of about 500 million pi
( taice ejaculated, most do not survive more than 48 hours in
i hi female reproductive tract. The major parts of a sperm eel
are rhe head and the tail (Figure 23.4). The head contains thl
nuclear material (DNA) and an acrosome {aero- = acq
vesicle containing enzymes that aid penetration by the spent)
Figure 23.4 Parts of a sperm cell.
About 300 million sperm mature each day.
... «,
Acrosome
Nucleus
Neck
Mitochondria
Middle piece
Principal
piece
— HEAD
— TAIL
End piece
What is the function of the sperm middle piece?
Male Reproductive System 56
cell into a secondary oocyte. The tail of -a sperm cell is subdi-
into four parts: neck, middle piece, principal piece, :nu|
end piece. The twk is the constricted region just behind the
n ;i I The middle piece contains mitochondria that: provide
AIL* lor locomotion. 1 he principal piece is die longest portion
ill' the tail and the end piece is the terminal, tapering portion
lithe tail
Figure 23.5 Hormonal control of spermatogenesis and ac-
tions of testosterone and dihydrotestosterone (DHT). Dashed
red lines indicate negative feedback inhibition.
t v Release ot FSH Is stimulated by GnRH and Inhibited by inhlbin;
- release of LH is stimulated by GnRH and Inhibited by testos-
• •« ■
terone.
Hormonal Control of the Testes
At the tinsel of puberty, neurosecretory cells in the hypothal-
increase their secretion of gonadutrnpiii-releasing hor-
mone {GnRH). This hormone, in turn, stimulates the ante-
rior pi mi rarv to increase its secretion of luteinizing hormone
[LH) and follicle-stimulating hormone (FSH). Figure 23.5
shows the hormones and negative feedback cycles that con-
fed i he Leydig and Sertoli cells of the testes and stimulate
iiiogenesis.
IT I stimulates Leydig cells, which are located between
seminiferous tubules, to secrete the hormone testosterone
fes-TOS-te-ron). This steroid hormone is synthesized from
gjwlesterol in die testes and is the principal androgen.
iTestosterone acts in a negative fecdhack manner to suppress
Secretion of LH by the anterior pituitary and to suppress se-
cretion of" GnRT-I by hypothalamic neurosecretory cells. In
targel cells, such as those in the external genitals and
prostate, an enzyme converts testosterone to another andro-
gen called dihydrotestosterone (DHT),
FSH aiul testosterone act together to stimulate sper-
(ttitogenesis. Once the degree of spermatogenesis required
for male reproductive functions has been achieved. Sertoli
cells release inhibhi, a hormone named for its inhibition of
fefi secretion by the anterior pituitary (I "■)■ Inhibin
thus inhibits the secretion of hormones needed for spej ana to -
wenesis. If spermatogenesis is proceeding too slowly, less in-
libin is released, which permits more FSH secretion and an
;i ceased rate ol spermatogenesis.
Testosterone and dihydrotestosterone both bind to die
jme androgen receptors, producing several effects:
Prenatal 'development. Before birth, testosterone siimu-
htes the male pattern of development of reproductive
fystem duct* aflflf the descent of the testes. DHT. bycori-
testosterone also is converted in the brain to estrogens
(feminizing hormones), which may play a role in the de-
velopment of certain regions of the brain in males.
Development of male sexual characteristics, Vt puberty.
'terone and DHT bring about development and en-
largement of the male sex organs ami the development of
masculine secondary sexual characteristics. These include
fcroscular and skeletal growth that results in wide shoul-
, ls,rs and narrow hips; pubic, axillary, facial, ami chest hair
Hypothalamus
Testosterone decreases
'elease of GnRH and LH
Anterior pituitary
Inhlbin decreases
release ol FSH
Together with
testosterone,
FSH stimulates
spermatogenesis
LH si i mutates
testosterone
secration
I Spermatogenie
/ cells
Sertoli cell
Dihydro-
testosterone
(DHT)
Leydig cells secrete
testosterone
I
1 Male pattern of development (before birth)
1 Enlargement ol male sex organs
and expression of male secondary
sex characteristics (starting at pui
AnaboJism (protein synthesis)
Key:
W LH
_"'.-.■ . ■-■ .
Which cells secrete Inhibin?
# FSH
562 Chapter 23 The Reproductive Systems
i .% i r hin hereditary limits); thickening of the skin; in-
creased sebaceous Coil) gland secretion; and enlargement
of the larynx ami consequent deepening of tin- voice.
■ Development of sexual junction. Androgens contribute
to mule sexual behavior and spermatogenesis and to sex
drive (libido) in both males and Females. Recall chat the
adrenal cortex is die mum source of androgens in fe-
males.
■ Stimulation of anabolistn. Androgens are anabolic hor-
mones; that is, they stimulate protein synthesis. This ef-
ivci is obvious in the heavier muscle and bone mass of
most men as Compared to women.
■ CHECKPOINT
1. i -low does the scrotum protect the- testes?
2. What are die principal events ol spermatogenesis and
where do they 0C< iir:
3. What are the roles of FSH, LH, testosterone, and in-
hibin in the male reproductive system? How is secretion
of i hese hormones controlled?
Ducts
FoHowaag spennatogeoesiS} pressure generated by the con-
tinual release of sperm and fluid secreted by Sertoli cells pro-
pels sperm ami fluid through the seminiferous tubules and
into the epididymis (see Figiitt
Epididymis
M' epididymis (ep'-i-DID-i-mis; epi- = above or over;
-didymis - testis: plural is epididymides) is ,\ comma-shaped
organ that lies along the posterior border of' the testis (see
. 1 and 2 5. 2 a). Each epididymis consists mostly of
the tightly coiled ductus epididymis. Functionally, the ductus
epididymis is the site of sperm mafatraiitm, the process by
which sperm acquire motility and the abihu to fertilize a sec-
ondary oocyte. This occurs over :i 10- to 1 -4- - . 1 ,i y period, ' "he
ductus epididymis also stores sperm and helps propel them
during sexual arousal by peristaltic contraction or its smooth
muscle into the ductus (vas) deferens. Sperm may remain in
storage in the ductus epididymis for several months. \m
stored sperm tluit are not ejaculated by that rime are even-
tually reabsorbed.
Ductus Deferens
\i. ilk- end ni die epididymis, the ductus epididymis becomes
lcs> convoluted, and its diameter increases. Beyond the epi-
didymis, the duct is termed the ductus deferens or vas defer-
ens (VAS DI-T-er-enz; pas = vessel; de- - away). See I
r3.2a. The duct us deferens ascends along the posterior bor-
der ot die epididymis and penetrates the inguinal canal, a
passageway m the ln>nr abdominal wall. Them it enters the
pelvic cavity, where it loops over the side anil down the po&*
cerior surface of the urinary bladder (see |, The
ducitis deferens has a heavy coat of three layers of rmisdfl
Functionally the ductus deferens stores sperm, which can re-
main viable here for up lo several months. The ductus .
ens also conveys sperm from the epididymis toward thelitis
thra during sexual arousal by peristaltic contractions (if the
muscular coat.
\ceoni |>a nying the ductus deferens as it ascends in rfa|
scrotum are blood vessels, autonomic nerves, and lymphatic
vessels that together make up the spermatic cord, a suppi
struct ure of the male reproductive system (see ( _
Ejaailatory Ducts
The ejaatfatory ducts (e-JAK-yu-la-to'-re; ejaad- = to «i
(see Figure 23.1) are formed by the union of the dun tn.m
the ductus deferens and the seminal vesicles (to be described I
shortly). The ejaculatory ducts eject sperm into the ureiiir
Ure thru
The urethra is the terminal duet of the male reprc-nlm
system, serving as a passage wa} for both sperm and urine. In
the male, the urethra passes through the prostate, deep per-l
inenl muscles, and penis (se< I ). The opening of t&!
urethra to the exterior is Galled the external urethral orifia
Accessory Sex Glands
The ducts oi the male reproductive system store and i
pott sperm cells, but the accessary sex glands secrete n
the liquid portion (if semen.
The paired seminal vesicles (VES-i-kuls) are pom
structures, lying posterior to the base of the urinarv bhddpfi
and anterior to the rectum (see I- • 1 ). Thcv
alkaline, viscous fluid that contains fructose, prostaglan
ami clotting proteins i unlike those found in blood). The .lib-
line nature of the fluid helps to neutralize the acidic enviruti*
mem of the male urethra and Female reproductive tract thai
otherwise would inactivate and kill sperm. The fructose m
used For ATP production by sperm. Prostaglandins
tribute to sperm motility anil viability and may also stimulate |
muscular contraction within the female reproductive
(Jotting proteins help semen coagulate after ejacul i
Fluid secreted by the seminal vesicles normally constitM
ahoUt 60% of the volume of semen.
The prostate (PROS-tat) is a single, doughnur-shapd
gland about the siae of a golf hall (see J "igun ..' :; 1 ). It is iiifisj
rior to the urinary bladder and surrounds the upper jn
of the urethra. The prostate slowly increases in size frojffl
birth to puberty, and then it expands rapidly The size ail
tained by age 30 remains stable until about age 45, when
rher enlargement may occur. The prostate secretes a milhj]
slightly acidic fluid (pi I about 6.5) that contains 1 1 j
which cm be used liy sperm for ATP production wa the
pebs cycle (see page 511): (2) aekl phosphatase (the function
'which is unknown); and (3) several protein-digesting cn -
such as prostare-specijk mtigett (PSA). Prostatic secret
! make up about 2>% of the volume of semen.
The paired bulbourethral (buMioMi-RF.-ihral) glands are
abovit the size of pens. I"hc\ ;ire located inferior to the
r,n^iu on either side of the urethra (sec Figure 2 1 1 ). Dur-
k sexual arousal, the bulbourethral glajids secrete an alkaline
Bbstance into the urethra that protests the passing sperm by
Uitrali/ing acids from urine in die urethra, kt the same time,
lev secrete mucus that lubricate* the end of the penis and the
of the urethra, thereby decreasing the number of spenn
■ ,1 during ejaculation.
Semen
Sanai I - seed) is a mixture of sperm mul the secretions of
seminal vesicles, prostate, and bulbourethral glands. The
Lwlume ol semen in a typical ejaculation is 2.5 to 5 milliliters,
iO to 150 million sperm per milliliter. When the niiiii-
. ails below 20 million per milliliter, the male is likely to
fertile, \ ver\ large number of sperm is required for fer-
itjiiii because only a tiny fraction ever reaches the see-
onilan oocyte,
Despite the slight acidity of prostatic fluid, semen has a
tody alkaline pi I of 7.2 to 7.7 due to die higher pi I and
feer "volume of fluid from the seminal vesicles. The prosta-
Lietion gives semen a milk) appearance, and fluids from
jsctrunal vesicles and bulbourethral glands give it a sticky
.nsisteney. Semen also contains an antibiotic that can de-
rm certain bacteria. The antibiotic may help control the
lance ol" naturally occurring bacteria in the semen and
the lower female reproductive tract, l'he presence ol
.Del in semen is called hemospermia (he-mo-SPKR-me a;
= blood: -spen/M = seed). In most cases, it is caused by
arniruuinn of the blood vessels lining the seminal vesicles;
■usually treated with antibiotics.
jnis
hs penis contains the urethra and is a passageway for the
■dilation of semen and the excretion of urine (see Figure
hi). Ji is cylindrical in shape and consists of a root, a body,
fad the glans penis. The root of the penis is the attached por-
proximal portion). The body of the penis is composed SJ
Bree cylindrical masses of tissue. The two dorsolateral!
ses are called the corpora cavernosa penis {corpora =
m bodies; cavernosa = hollow). The smaller mklventral
VS. the corpus spongiosum pvuis, contains the urethra. All
masses are enclosed b) fescia fa sheet of fibrous con-
i n tissue) and skin and consist of erectile tissue perme-
Inod sinuses.
The distal end of the corpus spongiosum penis is a
slightly enlarged region called the gla t is penis: In the glans
penis is the opening of the urethra (the external urethral
orifice) to die exterii r < '< ivering the glans in an uneircumeised
penis is the loosely fining prepuce (PR1 po,.s\ of foreskin.
i *
Circumcision ( = to cut around) is a surgical procedure
m which part or the entire prepuce is removed. It is usu-
ally performed just after delivery, 3 to 4 days after birth, or
on the eighth day as part of a Jew hh rel - ite. Although
most health-care professionals find no medical justification
lor circumcision, some feel that it has benefits, such as D
lower risk of urinary tract infections, protection against pe-
nile cancer, and possibly a lower risk for sexualh iranMiiin. -d
diseases. Indeed, studies in several African villages have
found lower rates of I J1V inl'eciion among circumcised men.
Most of the rime, the penis is flaccid (limp) because its
arteries are vasoeonstrieted. which limits blood flow. The
first visible sign of sexual cuitemem is erection, die enlarge
ment and stiffening of the penis. Parasympathetic impulses
cause release of neurotransmitters and local hormones in-
cluding the gas nitric oxide, which relaxes vascular smooth
muscle in the penile arteries. The arteries supplying the penis
dilate, and large quantities of blood enter the blood sinuses.
Expansion of these spaces compresses the veins draining the
penis, so blood outflow is slowed.
Ejaculation (e-jak-u-L A-shun; lyectus- - pa throw out);
die powerful release of semen from the urethra to the exte-
rior, is a sympathetic reflex coordinated by the lumbar por-
tion of the spinal cord. As part of the reflex, the smooth ntus
cle sphincter at the base of the urinary bladder closes. Thus.
urine is not expelled during ejaculation, and semen does n«u
enter the urinary bladder. Even before ejaculation occurs.
peristaltic contractions in the ductus deferens, seminal vesi-
cles, ejacularoiy ducts, and prostate propel semen into the
penile portion of the urethra. "\\ pically, this leads to emission
te-MISiUun), the discharge of a small volume of semen be
fore ejaculation. Emission may also occur during sleep (noc-
turnal emission). The penis returns to its flaccid state when
the arteries constrict, and pressure on the veins is relieved.
Erectile dysfunction (ED), previously termed impotence.
is the consistent inability of an adult male CO i laeulate or
to attain or hold an erection long enough for sexual inter-
course. Many cases of impotence are caused by insufficient
release of nitric oxide. The drug sildenafil tViagra" 7 '} en-
hances the effect of nitric oxide.
■ CHECKPOINT
4. Trace the course of sperm through the system of ducts
from the seminiferous n.rbtlles dlTOHgll the ureihiM
5. 'What is semen? What is its EuhceLobJ
564 Chapter 23 The Reproductive Systems
FEMALE REPRODUCTIVE
SYSTEM
OBJECTIVES • Describe the location, structure, and
functions of the organs of die female reproductive system.
• Describe how oocytes are produced.
The organs of the female reproductive system (figure 2 IXt)
unlink- the ovaries; the uterine (fallopian) tubes, nr oviducts;
i he uterus; die vagina; and external organs, which are collec-
tively called the vulva, or pudendum. The mammary glands
:ils. i uv considered part of the female reproductive system.
Ovaries
The ovaries ( = egg receptacles) are paired organs thai
■■■■ secondary oocytes (cells that develop into mature dm
br Eggs, following fertilization) and hormones, such .is firug.
usti-i-onc .in. I estrogens (die female sex hormones), mhiftM
and relaxiTi. The ovaries aria from the same embryonic til
sue as the testes, and they are the size and shape nfunshell
monds. One ovary lies on each side of the pelvic cavitv, h eiil in
place by ligaments. Figure 2 ! , sin >ws die histoh >gy of an owna
The germinal epithelium is a layer of simple epithelial
(low cmboidaJ or squamous) that covers the surface of the
ovary Deep in the germinal epithelium is the ovarian coifex,
Figure 23.6 Female organs of reproduction and surrounding structures.
£^ The female organs of reproduction include the ovaries, uterine (fallopian) tubes, uterus, vagina, vulva, and
- mammary glands.
Functions of the Female Reproductive System
1 . Ovaries: produce secondary oocytes and hormones, including
estrogens, progesterone, inhibin, and relaxin.
2. Uterine lubes: transport a secondary oocyte to the uterus, and
normally are the sites where ferlilizalion occurs.
3. Uterus: site of Implantation of a fertilized ovum, development ol th»
fetus during pregnancy, and labor,
4. Vagina: receives the penis during sexual intercourse and is a
passageway lor childbirth.
5. Mammary glands, synthesize, secrete, afid ejeel milk for nourtetrmW'
of the newborn.
Vagina
Anus
\
m\>v
Sagittal section
What term refers to the external genitals of the female?
Ulenne (fallopian) tube
Fimbriae
Ovary
Uterus
Cervix
Urinary bladder
Pubic symphysis
Mons pubis
Clitoris
Urethra
Labium majus
External urethral orifice
Labium minus
Female Reproductive System 565
Figure 23.7 Histology of the ovary. The arrows indicate the sequence ol developmental stages that
occur as part of the maturation of an ovum during the ovarian cycle.
■
Pit
The ovaries are the female gonads; they produce haploid oocytes.
.
Frontal plane
Germinal
epithelium
■
Growing
lolficles
Ovanan cortex
Ova nan
blood vessels
Corpus albicans
5 )
Degenerating Blood clot x Corpus
corpus Luteum luteum
Frontal section
What structures in the ovary contain endocrine tissue, and what hormones do they secrete?
Follicular fluid
Mature (graalian) talkie
Ovarian medulla
Ruptured follicle
Ovulation (expulsion ol
a secondary oocyte)
feon of dense connective tissue drat contains ovarian fol-
ich ovarian follicle ifotticuhts = little hag) consists of
oocyte and a variable number of surrounding cells ihar
Un.sh the developing oocyte and begin to secrete estrogens
i!k follicle grows larger. The follicle enlarges until it is a
m (graafian) follicle, a large, fluid-filled follielc tfi-ai is
w> rupture ami expel a secondary oocyte. The rem-
" ovulated follicle develop into a carpus luteum
im Ixah .). The corpus luteum produces progesterone,
i.vtus. relaxin. and inhibin until it degenerates and turns
fibrous tissue called a corpus albicans ( = white body).
|fcwv»vVj// medulla is ;i region deep to the ovarian cortex
ists of loose connective tissue and contains blood
- Is i. ci phatic vessels, and nerves.
rvarian cyst i-- a fluid-filled sae in or on an ovary.
ts are relatively common, are usually noncancer-
itnd freuuendy disappear on their own. Cancerous
emote likely to occur in women over 40. Ovarian
cysts may cause pain, pressure, a dull ache, or fullness in
the abdomen; pain during sevnal intercourse; delayed.
painful, or irregular menstrual periods; abrupt onset of
sharp pain in the lower abdomen-, and/or vagina] bleeding.
M.ist nvatian cysts require no treatment, but larger ones
(more than 5 cm or 2 in.) may he remold surgically.
Oogenesis
Formal ion ol ga meres in the ovaries is termed oogenesix
({>' -o-JKN-e-sis; 00- = egg). Unlike spermatogenesis, which
begins in males at puberty, oogenesis begins in females be-
fore diey are even born. Also, males produce new sperm
throughout life, while females have all the eggs they will ever
have by birth. Oogenesis occurs in essentially the same man-
ner as spermatogenesis. Ii involves meiosis and maturation.
Ml ioms I During early fetal development, cells in the
ovaries differentiate into oogonia (o -o-li< )-ne-a). which
can give rise to cells that develop into secondare oocytes
566 Chapter 23 The Reproductive Systems
i : i- Ik-fore birch, most of these cells degenerate,
'Ma i lew develop Ejitq larger cells called primary oocytes (O-
n-Mb), These cells begin meiosis I .during teta] development
luir do not complete it until after (puberty. \t birth, 200,000
to 2,000,000 |uin!:ir\ oocytes remain in each ovary. Of these,
il.<nn -}ii. IKK) remain at puberty, l>nr only 400 go on to ma-
ture and ovulate during a woman's reproductive lifetime. The
remainder degenerate,
•Viler puberty, hormones secreted by the anterior piiu-
itiiiA stimulate the resumption ol oogenesis each month.
Meiosis 1 resumes in several primary oocytes, although in
each cycle onU one follicle typically teaches the maturity
needed for ovulation. The diploid primary oocyte completes
iiiLitMs I, resulting in two haploid cells of unequal size, both
> nli 23 chromosomes («) ol" two chromatids each. The
smaller cell produced In rneiosis I, called \\k- fnyt poinr body.
Figure 23.8 Oogenesis. Diploid cells (2/1) have 46 chromo-
somes; haploid cells (n) have 23 chromosomes.
-i In
In an oocyte, meiosis II Is completed only if fertilization occurs.
Oogonium
9
Primary oocyte
Meiosis
4
First
polar body
/ \
\pvulation,w i^.
Secondary
oocyte
\, <•
Sperm
cell
+ Secondary
oocyte
During letal development
meiosis I begins.
After puberty, primary oocytes
complete meiosis I, which
produces a secondary oocyte
and a first polar body that
may or may not divide again.
The secondary oocyte begins
meiosis II.
A secondary oocyte (and first
polar body) is ovulated.
Meiosis II
Fertilization
Ovum
Second
polar body
After fertilization, meiosis II
resumes. The oocyte splits
into an ovum and a second
polar body.
The nuclei of the sperm cell
and the ovum unite, terming
a diploid (2n) zygote.
Zygote
How does the age of a primary oocyte in a female compare with
the age of a primary spermatocyte in a male?
is essentially a packet of discarded nuclear material; die latjffl
cell, known as the secondary oocyte, receives most of the d
toplasm. Once a secondary oocyte is formed, it begins tads
sis II and then stops. The follicle in which these events are til-
inn place — die mature (graafian.) follicle — soon ruptures m
releases«its secondary oocyte, a process blown as ovulation.
■VIkiosin ii At ovulation, usually a single secondary no
(with the first polaa body) ls expelled into the pelvic
and swept inn. the uterine (fallopian) tube. If a sperm pene-
trates the secondary oocyte (fertilization), meiosis II reaumts
The secondary oocyte splits into rwo haploid (w) cells nr un-
equal size. The larger cell is the ovum, or mature egg; the
smaller one is the u-auui poi-tr body. The nuclei of the sjienti
cell and the mum then smite, forming ;i diploid {In) zypm
I lie lust polar body may also undergo another division to
produce two polar bodies. If it does, the primary oocyti
mulch gives tisc to ;i single haploid (;/) ovum and three hap-
loid f» polar bodies. 1 hns, each primarj oocyte gives
a single gamete (secondary oocyte, which becomes an
after fertilization); in contrast, each primary spermatocyte
produces four gametes (sperm).
Uterine Tubes
Females have two uterine {fallopian) tubes that extend law
ally from the uteres and transport the secondary na
from die ovaries to the uterus (1 igi n ! ■ '>). The open, fun^
net-shaped end of each tube, the iitfuiiriihuliwi , lies close toij
the ovary but is open to the pelvic cavity. It ends in ;i Irin
of fingerlike projections called fimbriae (HM-hiv-
fringe). From the iofundibulum, the uterine tuibi
medially, attaching to the upper and outer comet \
uterus.
After ovulation, local currents produced by movej
<it the fimbriae, which surround the surface of die mature
liclc just before ovulation occurs, sweep the secondary aucjrl
into the uterine tube. The oocyte is then moved along
tube la cilia in the tubes mucous lining and peristal!;.
tractions of iLs smooth muscle layer.
The usual sue for fertilization of a secondary oocyte In i
sperm cell is in the uterine tube. Fertilization ma\ nccu
time up to about 24 hours after ovulation. The Icnilttd
ovum i /a gore) descends inro the uterus within seven days
Unfertilized secondary oocytes disintegrate.
Uterus
1 he uterus {ivomh) serves as pan ol ihe pathway for
deposited in the vagina to reach the uterine tubes. It iulsj
the site ol implantation of a fertilized ovum, development!
the fetus during pregnancy, and labor. During reprailuctnt
cycles when implantation does not occur, the uterus
source of menstrual How. The uterus is situated U-un.
Female Reproductive System 567
Figure 23.9 Uterus and associated structures. In the left side of the drawing, the uterine tube and uterus
have been sectioned to show internal structures,
The uterus Is the site of menstruation, implantation of a fertilized ovurn, development of a fetus, and labor.
Infundibulum of
uterine tube
Fimbriae ot uterine tube
View
Ulenne cavity
Endometrium
Myometrium
Cervix of uterus
Uterine
(fallopian)
lube
Ovary
ligament
Body of
uterus
Uioiei
Lateral to mix
Vagina
Which part of the uterine lining rebuilds after each menstruation?
Posterior view
inn bkdder and the rectum ami is shaped tike an inverted
bar.
Parts "I flit uterus include the dome-shaped portion su-
■ ■ ■ in the uterine tubes called the fimdus, the tapering
i portion called the body, and the narrow portion open-
■ i the vagina called the cervix. The interior or the body
She uterus is called the uterine cavity (Figure - \Sf),
The middle muscular layer of die uterus, the myti-
tlttn (j/ryo- - muscle), consists of smooth musde and
bulk of the uterine wall. During childbirth, coordi-
Jted contractions of uterine musc/es help expel the fetus.
i in. innermost part of the uterine wall, the endometrium
\ ithin), is a mucous membrane. It nourishes ;i grow-
fetus or is shed each month during menstruation \f fertil-
ization does not occur. The endometrium contain- man\
endometrial glands whose secretions nourish sperm and the
zygote.
Hysterectomy (hiss-ter I "k -to -me; by>tcr- = uterus), the
surgical removal of the uterus, is the most common gyne-
cological operation. It maybe indicated in conditions such
as librojck endometriosis, peine mlhiminatop, di$\
rcaincnt avurinn cysts, excessov uterine iilcctlinir. Md
tneer oi the cervix, uterus, or ovaries; In a pttntui
hyytoTcio/iiy, the btnK of tlie uterus is removed hut the
cervix is left in place. A. co?r/,plett hyxtvfectomy is tlie rcmov ,il
of both the bodv and cervix of the uterus.
568 Chapter 23 The Reproductive Systems
Vagina
The vagina (sra-JI-iia = sheath) is ti tubular canal that ex-
tends from the exterior "I die body hi die uterine cervix i
1,9). It is ihc receptacle for the penis during sexual in-
tercourse, the outlet for menstrual How, and the passageway
lor childbirth. I he vagina in situated between the urinary
bladder and the reel urn, A recess, called the fornix ( = arch
Of vault), surrounds the cervix. When properly inserted, a
contraceptive diaphragm rests on the fornix, covering the
cervix.
The mucosa of the vagina contains large stores of glyco-
gen, the decomposition ol which produces organic acids. The
resulting acidic environment retards microbial growth, but it
barn ml to sperm. Alkaline components of semen,
i]i.:ml\ frotn the seminal vesicles, neutralize the acidit\ ol "the
vagina and increase viability ol sperm. The muscular layer is
composed of smooth muscle ih:it can stretcb to receive the
s during intercourse and allow for childbirth. There naaj
In: q i hin fold of mucous membrane called the hymen
(= membrane) partially covering the vaginal orifice, the
vaginal opening (see Figi IQ).
Perineum and Vulva
The perineum (per'-i-NF.-um) is the diamond-shaped area
between the thighs and buttocks ol both males and females
that contains the external genitals and anus (Figure 2 5.10);
Thejrcrm vulva (VUL-va * to wrap around), oi \ puden-
dum (pu-DEN-duui). refers to the external genitals of the fe-
male I "). The mons pubis (MONZ PU-bis; wow
= mountain) is ati elevation of adipose tissue coveted bj
coarse pubic hair, which cushions the pubic symphysis,
the mons pubis, two longitudinal Folds oi skin, the labia ma-
jot a H.A-be-a ma-JO-ra; labia — lips; majora — larger). e,v-
u nil down and back (singular is labium -trntjits). In females the
labia majora develop from the same embryonic tissue that
the scrotum develops from in males. The labia major;.
tain adip.-se i issue and sebaceous (oil) and sudoriferous
(swear) glands. Like the mons pubis, they are covered bv pu-
bic hair. Medial to the labia majora are two folds of
called the labia minora (mJ-NO-ra = smaller; singular n
labium minus). The labia minora do nor contain pubic hair or
lat and have few sudoriferous (sweat) glands; the) do, how-
ever, contain numerous sebaceous (oil) glands.
Figure 23. 10 Components of the vulva.
Like the penis, the clitoris is capable of erection upon sexual stimulation.
Mons pubis
Labia majora (spread)
Labia minora (spread
exposing vestibule)
Hymen
Prepuce of dltons
r irtorls
External urethral orifice
Vaginal onlice (dilated)
Anus
Inferior view
What surface structures are anterior to the vaginal opening?
The clitoris (KUTT-o-tos) is a small, cylindrical mass of
becale tissue ami nerves. It is located .n the anterior junction
withe labia minora. A layer of 4m called the prepuce (PRE-
|oos), also known as the fbmkm, is foniiod ai a point where
ill. labia minora unite \uu\ cover the body of the clitoris.
The exposed portion of the elitaris i- 6w gftmur, Lilee the
pons, the clitoris is capable of enlargement upon sexual
stimulation.
The region between the labia minora is called the
vestibule. In me vestibule are the hymen (if present): vagiiml
orifice, die opening of the vagina to rhe exterior; external
urethral orifice, the opening y| the iiivihi.i to rhe exterior:
and on either side of the external urethral orifice, the open-
I the ducis of the pai mirethral glands. These glands in
I ill of the urethra secrete mucus, The males prostate de-
velops from the same embryonic tissue as the females para-
gtfethral glands. On cither side of the vaginal orifice itself are
the greater vestibular glands, which produce a small quantity
■ mucus during sexual arousal ami intercourse that adds to
1. ..I mucus and provides lubrication. In males, the hul-
thral glands are equivalent structures.
Female Reproductive System 569
During childbirth, if the vagina is too small to accommo-
date the heml of an emerging fetus, the skin, vaginal epj
tliehum, subcutaneous tat, and muscle of the perineum
may tear. MoreOYer, the tissues ol 'the lecturn may be dam-
aged'. Io avoid such damage, a small incision called an cpis-
iotomy (e-piz-e-OT-n-me; rpisr- - vulva or pubic re-
gion; -otwry = incision) is made in the perinea] skin and
underlying tissues just prior to delivery Utcr delivery, the
episioiomy is sutured in layers.
Mammary Glands
The mammary glands {mumma = breast), located in the
breasts, are modified sudoriferous (sweat) glands that pro-
duce milk. The breasts lie over the peetoralis major and ser-
ratus anterior muscles and are attached to ihem In a layer of
connective tissue figure 23/11). Each bseast has one pig-
mented projection, the nipple, with a series ofclosdj spaced
openings of ducts where milk emerges. The circular pig-
mented area of skin surrounding the nipple is called the
jre 23.11 Mammary glands.
The mammary glands function in the synthesis, secretion, and ejection of milk (lactation).
Suspensory ligament ol
the breast (Cooper's ligament)
- Peetoralis majo
muscle
Lobule containing
alveoli
Milk duct
Nipple
Areola
Adipose lissue
in superficial
fasoa
(a) Sagittal seciron (bl Anterior view, partially sectioned
What hormone regulates the ejection of milk from the mammary glands?
570 Chapter 23 The Reproductive Systems
(inula (a-RE-o-la = small space). This region appears rdu^li
because it contains modified sebaceous (oil) glands. Inri.rn.ilfv.
each mammary gland consists of 15 to 20 /»Aev arranged radi-
ally and separated by adipose tissue and strands of connective
tissue called suspensory ligaments of the breast (Coopers Hg~
aments), which support the breast. In each lobe are smaller
lobules, in which milk-secreting glands called alveoli
[- small cavities) are found. When milk is being produced; h
passes from die alveoli inio a series of tubules that drain to-
ward the nipple.
\i birth, the mammary glands are undeveloped and ap-
pear as slight elevations on the chest Willi the Onset "I |>n-
nnder the influence ol estrogens and progesterone, the
female breasts begin to develop. The duel system matures
and hit is deposited, which increases breast size. The areola
and nipple also enlarge and become more darkly pigmented.
The functions ol the mammar\ glands are the synthesis,
secretion, and ejection of milk; these functions, called lacta-
tion, are associated Avirh pregnancy and childbirth. .Milk pro-
duction is stimulated largely In the- hormone prolactin from
the anterior pituitary, with contributions from progesterone
anil estrogens. The ejection ol milk is stimulated by ox\ toem,
which is released from the postedoi pituitary in response to
L'he sucking of .in infant on tin- mother's nipple (suckling).
The breasts oi females are highly susceptible to cysts and
tumors. In fibrocystic disease, the most common cause of
breast lumps in females, one or more Cysts (fluid- filled
sacs) and thickening of alveoli develop. The condition,
which occurs mainly in females between! the ages of 10 and
50, is probably due to a relative excess of estrogens or a
deficiency of progesterone in the posrovulatory phase of
the reproductive cycle (discussed shortly). Fibroevstic
disease usualb causes one or both breasts l:o become
lumpy, 5WOUen, and tctkiei I week or so before menstrua-
tion begim
■ CHECKPOINT
6. Describe the principal events of oogem - ■!•-.
7. Where are the uterine tubes located? What is their runc-
lic.nr
8. Describe the histology of the uterus.
9. What IS the function of the vagina? Describe its histol-
10. Describe the structure of the mammary glands, t low are
thev supported?
THE FEMALE
REPRODUCTIVE CYCLE
OBJECTIVE • Describe the major events of the ovar-
ian and uterine cycles.
During their reproductive wars, nonpregnant females nor-
mally exhibit cyclical changes in the ovaries and uterus. l.\d:
cacIc takes about: a month and involves both oogenesis and
preparation of the uterus CO receive a fertilized ovum. Hor-
mones secreted by the hypothalamus, anterior pituitary, ami
ovaries control the main events. You have already h
about the ovarian cycle, the series of events in the uvun'a
that Occur during :md after the maturation of an oocyttj
Steroid hormones released by the ovaries control the uterha
(menstrual) cycle, i concurrent series of changes in the en-
domeiriitm of die uterus to prepare it for the arrival «•! ., feu-
lili/id i>\ uin that will develop there until birth. II Tenili/nttuii
dues not occur, the levels of ovarian hormones deer
which causes part of the endometrium to slough off.
general unit female reproductive cycle encompass,
ovarian and uteri ne cycles, the hormonal changes that regulan
them, and the related cyclical changes in the breasts andccrvii
Hormonal Regulation of the Female
Reproductive Cycle
Gonurfotropin-refeasitifr hormone (GnRJl) secreted bv the J
hypothalamus controls the ovarian and uterine cycles (figure I
12:), (ink! I stimulates the release ol' fotlicle-stimiiliHmi
hormone (I SI I) and luteinizing hormone (J J I) from the mi
lerior pituitary. FSH, in turn, initiates follicular growth
the secretion of estrogens by the growing follicles. LH.stinjjp
uhucs the further development of ovarian follicles and their
raj secretion of estrogens. At midcycle. I.I I triggers tivuh-
tion and then promotes formation of the corpus lutcum, the
reaso.ii for die name luteinizing hormone. Stimulated I)} I. II.
the corpus luteum produces and secretes estrogens, pri
terone, rclaxin, and inlnbin.
Estrogens secreted by ovarian follicles have several up]
portent functions throughout the body:
■ Estrogens promote the development and maintenance ui
female reproductive structures, reinlnine secondan
characteristics, anil the mammary glands. Hie sccoitdan|
sex characteristics include distribution of adipose tissue'^
the breasts, abdomen, mojis pubis, and hips; a bro;
and the pattern of hair growth on the head and body.
■ Estrogens stimulate protein synthesis, acting together with
insulinlike growth (actors, insulin, and thyroid humiowed
■ Estrogens lower blood cholesterol level, which is ,
bly the reason that women under age >0 have a muoll
lower risk of corona r\ after) disease than do men ui
comparable age.
The Female Reproductive Cycle 571
Figure 23.12 The female reproductive cycle. Trie length' of the female reproductive cycle typically is 24 to 36
days; the preovulatory phase is more variable in length than the other phases, (a) Events in the ovarian and uterine
cycles and the release of anterior pituitary hormones are correlated with the sequence of the cycle's tour phases. In
the cycle shown, fertilization and implantation have not occurred. <b) Relative concentrations of anterior pituitary hor-
nftnes (FSH and LH) and ovarian hormones (estrogens and progesterone) during the phases of a normal female re-
productive cycle.
Estrogens are secreted by the dominant follicle before ovulation: after ovulation, both progesterone and estrogens
- are secreted by the corpus luteum.
Hypothalamus
Ovarian cycle
iiWfine (menstrual)
cycle
Endometrium
Corpus
albicans
I I I I I I I I I I I I I I I I II I I I I I I '
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 1
Menstrual Preovulatory I Postovulatory
phase phase Ovulation phase
(a) Hormonal regulation of changes in the ovary and uterus
Hormone
concentration
Progesterone
X.
: — f— >~- »--r — ■»-— 1 1 — -r r-n— i 1
10 14 36 18 20 22 24 :,'ti 28
Days P-
fb) Changes in concentration of anterior pituitary and ovarian hormones
v Which hormones are responsible for the proliferative phase of endometrial growth, for ovulation, for growth
Vol the corpus luteum, and for the surge of LH at midcycle?
572 Chapter 23 The Reproductive Systems
Progesterone, secreted mainly by cells of the Corpus lu-
teuin, acts together with estrogens to prepare :i n c I then main-
tain the endometrium for implantation ol a fertilized ovum
and to prepare the mammary glands for milk secretion.
\ small i|uantiiy oj relaxift, produced by the corpus lu-
teuin during' each monthly cycle, relaxes the uterus by in-
hibiting contractions of the myometrium. Presumably, im-
plantation of a fertilized ovum occurs more readily in fl
"quiet" uterus. During pregnane} - , the placenta produces
much more relnvin. and it continues to relax uterine smooth
muscle. At the end of pregnancy, relaxin also u1crea9.es the
flexibility of the pubic symphysis and helps dilate the uterine
cervix, both of which ease dehverv of die baby.
tiihihin ih secreted by growing foilktes and by die corpus
iuteiim a ft cr ovulation. It inhibits secretion ofFSH and. to .1
lesser extent, LI I.
Phases of the Female Reproductive Cycle
I be duration of the female reproductive cycle varies from 24
io 55 days. For this discussion we assume a duration oi t%
i-id divide it into four phases: the menstrual phase, the
preovulatory phase. Ovulation, and the postovulntory phase
!)« Because they occur ai the same time, die
events of the ovarian cycle {events in ilu ovaries) and men-
strual cycle {events in the litems) will be discussed together,
Menstrual Phase
llie menstrual phase (MLN-stroo-al). also called menstrua-
tion (men-str<!o-\-shiini or metises ( - month), lasts for
roughly the first five days ol the cycle. (By convention, the
first day of menstruation marks the firai day oJ a new eyde).
Events in it it Ovaries During the menstrual phase, agr-
eed Ovarian follicles grow and enlarge.
EVENTS in iiii UtSJROS Menstrual flow from the litems
consists of SO to 150 tnL of blood and tissue cells titan the
endometrium. This discharge occurs because the declining
level 6i ovarian hormones (progesterone and estrogens)
causes the uterine arteries to constrict. As a result, the cells
the\ supply become o\\ gen-deprived and star! to die, Even-
tually, part of the endometrium sloughs off. 'J 'he menstrual
flow passes from the uterine cavity Ep Eh? cervix and through
the vagina to the exterior,
Preovulatory Phase
The preovulatory phase is the rime between the end of men-
struation and ovulation. The preovulatory phase of the cycle
accounts for most of the variation in cycle length. In a 28-day
1 is from days 6 to 13.
is in 1 ill « )\ IRIES Under the influence of I'M 1, sev-
eral follicles continue to grow and begin to secrete estrogens
and mhibin. By about day 6, a single follicle in one of the two
ovaries has outgrown all the others to become the dwiinm
follicle. Ksirogens and inhibin secreted In, the dominant idli-
cle decrease ihe secretion of LSI 1 (Figure * '■ I ?h, see dmi
to II), which causes other, less we II -developed follicles d
Stop growing and die.
The* one dtmiinant follicle becomes the matm
(graafian) follicle. The mature follicle continues to enlarrtj
until it is ready for ovulation, forming a blisterlike bulge an
the surface of the ovary. During maturation, the follicle con
twines to increase its production of estrogens under the influ-
ence oi an increasing level of LI I.
With reference to the ovarian cycle, the menstrual
:in>\ prei will ah ay phase 1 1 ige 1 her ale termed I he folliaihr
phase (fo-LIK-u-lar) because ovarian follicles are showing
and developing.
IT l NTS IN "I 1 IJ UTERUS Estrogens liberated into the I tin
growing ovarian follicles stimulate the repair of die en-
dometrium. As the endometrium thickens, the short, strain
endometrial glands develop, and the arterioles coil and lengthen
Ovitlatiati
Ovulation, the rupture of the mature (graafian) rollick
the release of the secondary oocyte into the pelvic cavity
ally occurs on day 14 in a 28-day cycle.
The high levels ol estrogens during the last part of tl
preovulatory phase e\en a positive feedback effect on lioili !.
and GnRU. A high level of estrogens stimulates the hjiji
thalamus to release more gonadotropin-releasmg honnl
(CinRH) and the anterior pituitary to produce more IJ
GnRH then promotes the release ol even more LI I. I V
suiting surge of I I I 1 • ; I M.l) brings about - rupture 1
the mature (graafian) follicle .wu\ expulsion of a seeotd
oocyte. An over-the-counter home test that detects die!
surge associated with ovulation can be used to predict am
rion a day in advance.
Postnvnlatory Phase
The postovulatury phase of the female reproductive ryehiji
the time between ovulation and onset ol the next meiisiniu-j
rion. This phase is the most constant in duration and
14 days, from days 15 to 28 in a 28-day cycle.
I \ 1 \ 1 s in am OVKKI Alter ovulation, the mature
collapses. Stimulated by LI L the remaining follicular'
enlarge and form the corpus Iuteiim, which secretes prpfl
hi one. estrogens, relaxin, and inhibin. With referem
ovarian cycle, this phase is also called the luteal phase.
Subsequent events depend on whether or not theoffl
I iili^ed. If the oocyte is not fertilized, the corpus into
lasts lor only two week-., after which jis secretory activity!
dines, and it degenerates into a corpus albj
23.1 - ). As the levels of progesterone, estrogens, and ir
decrease, release of (in R 1 1, FS1 I. and LI I rises dm
Kgatn mk suppression by the ovarian hormones. Then,
follicular growth resume-sand a new ovarian cycle begins.
If the secondary oocyte is in-iilizcd and begins bodli [cte, the
torpus luteum persists past its normal two-week lifespan. It is
*l«scLie«r horn dt.frener.mon by hitman chorionic gotuulotropin
! ' -ON-ik) (hCG). a hormone produced by the em Inyo he-
ginning about eight days alter fertilization. Like I..! 1. hCG sriin-
Rktes rhe secretor) activity of. the corpus futeum. The presence
ill bCG in maternal blood or urine is -.in indicator f»l pretmanrw
lUid hCG is the hornn ine i jetectfid In home pregnancy tests.
The Female Reproductive Cycle 573
I'm vis i\ nil L iikhs Progesterone and eatra^ns pr<>-
duced by the corpus luteum promote growth of die' endome-
trial glands, which begin to secrete glycogen, and vascul.u iza
tion and thickening of Che endometrium. These preparatory
changes peak, about one week after ovulation, at the lime a
fertilized ovum might arrive at the uterus.
''';- I summarizes die hormonal interactions and
cyclical changes in the ovaries and uterus during the ovarian
and menstrual cycles-
Figure 23.13 Summary of hormonal interactions in the ovarian and menstrual cycles.
H.
Hormones from the anterior pituitary regulate ovarian function, and hormones from the ovaries regu-
late the changes in the endometrial lining of the uterus.
High levels of
estrogens (without
progesterone)
stimulate release
QlGriRR IH.and
FSH
Moderate levels of
estrogens inhibit
secr&ripn of GnRH,
FSH. and LH
Inhibin inhibits
secretion ot FSH
andLH
Low levels of
progesterone
and estrogens
promote secretion
of GnRH, FSH.
andLH
Increasing secretion
\ ^_ of estrogens and
inhibin by
granulosa cells
Increased secretion of
progesterone and
estrogens by ceils
of corpus luteum
Increased secretion
ol inhibin by celts of
corpus luteum
Formation of
corpus
albicans
Uterus
T
T
No secretion of
progesterone and
estrogens by
corpus albicans
Repair and proliferation
of endometrium
V
Preparation of
endometrium for arrival
of fertilized ovum
Menslruatiq.n
When declining levels of estrogens and progesterone stimulate secretion of GnRH, is this a positive
or negative feedback effect? Why?
574 Chapter 23 The Reproductive Systems
■ CHECKPOINT
11. Describe the function of each of the EoHowng hormones
in the uterine and ovarian cycles: GnRH, FSH, LH, es-
trogens, progesterone, and inhibLn.
12. Brieflj outline the major events and hormonal changesof
each phase "I the uterine cycle, and correlate them with
the events of the ovarian cycle.
13. Prepaid a labeled diagram of the major hormonal
changes that occur during the uterine and ovarian cycles.
BIRTH CONTROL METHODS
AND ABORTION
Table 23.1 Failure Rates of Several Birth
Control Methods
OBJECTIVE • Compare the various types of birth con-
trol methods and outline the effectiveness of each.
No single, ideal method of hirth control exists. The only
method of preventing pregnancy that is 100% reliable is total
abstinence, the avoidance of sexual intercourse. Several other
methods are available, including surgical sterilization, hor-
monal methods, intrauterine devices, spermicides, barrier
methods, and periodic abstinence, [able 23J provides the
failure rales for each method of birth control. We will also
discuss induced abortion, the intentional termination of
pregnancy,
Failure Rates'
Method
Perfect Use T
Typical Use
None
85%
85%
Complete abstinence
0%
0%
Surgical sterilization
Vasectomy
o.to%
0.15%
Tubal ligation
0.5%
0.5%
Hormonal methods
Oral contraceptives
o is.
3% :
Depo-provera #
0.05%
q ua
Intrauterine device
Copper T380A
0.6%
0.8%
Spermicides
6%
26% !
Barrier methods
Male condom
3%
14%'
Vaginal pouch
5%
Diaphragm
6%
20','
Periodic abstinence
Rhythm
9%
25%'
Sympto-therma!
2%
*DeIined as percentage of women having an unintended pregnancy during
the first year ol use.
'Failure rate when the method is used correctly and consistently.
'Includes couples who forgol lo use the method.
Surgical Sterilization
Sterilization is a procedure that renders an individual MlGa-
pahle of reproduction. The most common means of steriliza-
tion of males is vasectomy (va-SEK-to-me; -ectomy = cur
out), in which a portion of each ductus deferens is removed
Even though sperm production continues in rhe testes after a
vasectomy, sperm can no longer reach the exterior, lustful.
thev degenerate and are destroyed by phagocytosis. Blood
testosterone level is normal, so a vasectomy has no effect on
sexual desire or performance. Sterilization in females most
often is achieved by performing a tubal ligation <h-(;A-
shun). in which both uterine tubes are lied closed and then
Gilt. As a result, rhe secondary oocyte cannot pas.s through
the uterine rubes, and sperm cannot reach the oocyte.
Hormonal Methods
Aside from total abstinence or surgical sterilization, hor-
monal methods are the most effective means ol birth control.
by 50 million women worldwide, oral contraceptives
('"the pill") contain various mixtures of synthetic estrogens
and progestins (chemicals with actions similar to those ol
progesterone). They prevent pregnancy mainly by negative
feedback inhibition ol anterior pituitary secretion ol VS.
and LI I. The low levels of KS11 i\\\d LI I usually prevent
\elnpmetit of a dominant follicle. Asa result, the level, on
trogens does not rise* tin- midcycle LIT surge does noi w
and ovulation is not triggered, Thus, there is no seeef
oocyte available for lertili/ation. It taken properly, the pi!
close to 100% effective.
Among the noncomraceptive benefits of oral content!
lives are regulation of the length of menstrual cycles and
i reused menstrual How (and therefore decreased risk ol"
mia). The pill also provides protection against endmnetriil
and ovarian cancers and reduces the risk of endometrit
However, oral contraceptives may noi be advised forwomi
with a history ofbiood clotting disorders, cerebral hlninlvts-]
sel damage, migraine headaches, hypertension, liver uinlninc-J
don, or heart disease. Women who lake the pill ami smt
face far higher odds of having a heart attack or stroke thant
nonsmoking pill users. Smokers should quit smoking or.™
an alternative method of birth control.
The same hormones Found in oral contraceptjv
used for emergency contraception (EC), the so-called "raoii
nig-after pill." The relatively high levels of estrogens and
progestin in EG pills provide negative feedback inhibition of
l-\i I and I -I I secretion. Loss of the stimulating effects of
these gonadotropic hormones causes the ovaries i«» cense se-
cretion of their own estrogens and progesterone. Tn rum, cle-
j&iing levels of estrogens and progesterone induce shedding
.of the uterine lining, therein blocking implantation.
i ithcr hormonal methods of contraception .ire also avail-
tble:
I Norplant® consists of" six slender hormone-containing
capsules that are surgically implanted under the skin ol
the arm using local anesthesia. Thej slowly and continu-
ally release a progestin, winch Inhibits ovulation and
thickens the cervical mucus. The effects last lor 5 years,
and Norplant** is about as reliable as sterilization. Re*
moving the Norplant* capsules restores fertility.
Depo-provera®. which is given as an intramuscular in-
fection once even' 3 months, contains progestin that pre-
vents maturation of the ovum 2nd causes changes in the
uterine lining that make pregnancy less likely.
Lunelle® is a once a-moiuh intramuscular infection. It
contains estrogens ;in l I progestin and acts like .111 oral
contraceptive.
Birth control skin patches contain estrogens mil prog-
estin and are placed on the skin once a week for three
weeks. Each week the patch is removed and a new one is
1 on a different area of the skin. During the fourth
. , . L no patch is used so that menstruation can occur.
The vaginal ring is a doughnut-shaped ring that fits in
the vagina and releases either a progestin alone or a
progestin and an estrogen. It is worn for 3 weeks and re-
mou-.l for 1 week to allow menstruation to occur.
Intrauterine Devices
nhautcrine device (IVD) is a small object made of plas-
toper, or stainless steel that is inserted into the cavity ol
jti-rus IL'Ds cause changes in the uterine lining that pre-
implantation of a fertilized ovum. The IUD most coia-
,1 in the United States today is the ( lopper i' >H0A,
pproved for up to 10 years of use and has long-term
ss comparable to that of tubal ligation. Some
1 uim use lUDs because of expulsion, bleeding, or
jjnfort.
rmicides
foams, creams, jellies, suppositories, and douches that
niaui sperm-killing agents, or spermicides, make the vagina
1 unfavorable for sperm survival and are available
It prescription. The most widely used spermicide is
Mynol-9, which kills sperm by disrupting their plasma
Birth Control Methods and Abortion 575
membrane. A spermicide is more effective when used together
with a barrier method such as a diaphragm or a condom.
Barrier Methods
Burikr methods are designed to prevent sperm Iroiu gaining
access to the uterine cavity and uterine tubes. In addition to
presenting' pregnancy, barrier methods may also pi ■
some protection against sexually transmitted diseases tS'l'Ds)
such as \I1)S. In contrast, oral contraceptives and IUI)s con-
fer no such protection. Among the harrier methods are use of
a condom, a vaginal pouch, or a diaphragm'.
A condom is a nonporous. latex coveting placed over the
penis that prevents deposition of sperm in the female repro-
ductive tract. A vaginal pouch, sometimes called a female
condom, is made of two flexible rings connected by a
polyurethane sheath, One ring lies inside the sheath and is
inserted to fit over the cervix; the other ring remains outside
die vagina and covers the female external genitals.
A diaphragm is a rubber, dome-shaped structure that fits
over the cervix and is used in conjunction with a spermicide,
it can be inserted up CO 6 hours before intercourse. The di-
aphragm stops most sperm from passing into the cervix, and
the spermicide kills most sperm that do get by. Although di-
aphragm use does decrease the risk of some STDs, it does
not fully protect against HIV intc-nion.
Periodic Abstinence
A couple can use their knowledge o\~ the physiological
changes that occur during the female reproductive cycle to
decide either to abstain from intercourse on those days when
pregnancy is a likely resuli. or to plan intercourse on those
days if they wish to conceive a child. In females with noriii.il
and regular menstrual cycles, these physiological events help
to predict the day on which ovulation is likely to occur.
The lii'st physiologically based method, developed in the
1930s, is known as the rhythm method (natural family plan-
ning). It takes advantage of the tact that a secondary oocyte is
fertilizahle for only 24 hours and is available for only 3 to 5
days in each reproductive cycle. During this time days be-
fore ovulation, the day of ovulation, and > days alter ovula-
tion) the couple abstains from intercourse. The effectiveness
of the rhythm method for birth control is poor in many
Women due to the irregularity of their cycles.
Another system is the syinpto-tbermal method, in which
COVIples are instructed to know and understand certain signs
of fertility. The signs .if ovulation include increased basal
body temperature; the production of abundant clear, stretch)
cervical rrracus; and pain associated with ovulation (mit-
telschmer/.y If a couple abstains from sexual intercourse
when the signs of ovulation are present and for > days after-
ward, the chance of pregnancy is decreased. A big problem
with this method is that fertilization is very likcij t'J inter-
course occurs one or two days btfuir ovulation.
a*
Focus ON
m
The Female
Triad — Disordered
Eating, Amenorrhea,
and Premature
Osteoporosis
I he female reproductive cycle can be
disrupted by many factors, including
weight loss, low body weight, disor-
dered caring, and vigorous plr
activity. Many athletes experience in-
tense pressure trom coaches, parents,
peers, and themselves no lose weight CO
improve performance. Consequently,
many develop disordered eating be-
haviors and engage in other harmful
weight-loss practices in a straggle co
maintain a ven low body weight. The
athletes with the highest rates of men-
strual irregularity include runners,
gymnasts, dancers, figure skaters, and
divers.
Sticks anil Slimes and . . . the
Female Athlete Triad?
.Menstrual irregularity should never be
ignored, because n may be caused by a
serious underlying disorder for which
the athlete should receive prompt med-
ical treatment Even when menstrual
irregularity is apparently caused by dis-
ordered earing and physical training,
and not associated with another physi-
cal disorder, it is still a cause for con-
cern. One reason is thai women with
amenorrhea, die absence ol menstrual
cycles, are at increased risk for prema-
ture osteoporosis. The observation that
three conditions — disordered eating,
amenorrhea, and osteoporosis — tend
to occur together in female athletes led
researchers to coin the term "female
athlete triad."
Win osteoporosis? Remember that
the ovarian follicles produce estrogens
when stimulated In KM 1 and LI J. II
ovulation is not occurring, then the
ovarian follicles, and later the corpus
lutetun, are not producing estrogens.
Chronically low levels o| estrogens are
associated with loss of bone minerals.
as estrogens help hones retain Calcium.
The loss of the protective effect of es-
trogens explains why many women ex-
perience a decline in bone density alter
menopause, when levels of estrogens
drop. Amenorrheic runners have been
shown to experience a similar effect. In
one study, amenorrheic runners in their
20s had bone densities similar to those
of postmenopausal women 50 ;
pears old- Short periods of menstrual
irregularity in young athletes uwy
cause no lasting harm, but long-teqffl
cessation ol the menstrual cycle in ii
accompanied In a loss of bone mass taj
in adolescent athletes, a failtin
achieve an adequate bone mass, limbo
which can lead to premature ostco
porosis and irreversible bone danmgt
It is ironic that dedicated athlctB
should experience premature
porosis, because physical activm
general is associated with a redtt
of osteoporosis. I'.vercise has bed
shown, to increase bone dens it;,
dally if the exercise involve '
stress, such as running and
dancing. However, in the presences
disordered eating and overtraining; a
erci.se may simply add insuli to itljlg
► Think It Over
r ujifiK that girts and women should be discouraged jrom- participate
'hletJes and other forms ofvigat ous physical activities because o) tbi
k athlete triad?
576
Abortion
tih/iio/i refers Co the premature expulsion of the products or'
^inception from the uterus, usually before the 20di week of
Stagnancy. An abortion may be spontaneous (naturally oceur-
riiie: also called a VttSCttiritlge) or induced (intentionally per-
formed). Induced abortions m,u he performed by vacuum as-
Mration (suction), infusion of a saline solution, or surgical
Evacuation {scraping).
Certain drugs, most notably RL' 486, can induce a so-
called nonsurgical abortion. RU 4S6 (mifepristone) blocks
the action oi progesterone by binding to and blocking prog-
esterone receptors. Within 12 hours after taking RU 486. die
gjulornetriiim starts to degenerate, and wiihm ~2 hours, it
begins to slough off. A form of prostaglandin V, (misopros-
tol). which stimulates uterine contractions, is given after RU
H86 to aid m expulsion of die endometrium. RU 486 can be
tjLn up to 5 weeks after conception. One side effect of the
(ini'j' is uterine bleeding,
I CHECKPOINT
14. How do oral contraceptives reduce die likelihood of
pregnane} •
15. Why do some methods of birth control protect, against
Sexualh transmitted diseases, but others do nor?
AGING AND THE REPRODUCTIVE
SYSTEMS
ABJECTIVE • Describe the effects of* aging on the re-
jmnkicttve systems.
Dnr-iiti the first decade of life, the reproductive system is in a
\i aboui age 30. hormone-directed changes
to occur in both sexes. Puberty (PU-ber-te = a ripe age)
\Q period when secondary sexual characteristics begin to
slop and the potential for sexual reproducrJOE is reached.
set of puberty is marked In bursts of LIT and FSH secre-
, each triggered by a burst of GnRJl. The stimuli that
ftse the GnRH bursts are still unclear, but a role for the
ne feptin is starting to unfold. Just before puberty, fep-
Hdcvels rise in proportion to adipose tissue mass. Leptirt
^Signal the hypothalamus that long-term energy stoivs
1 lo in adipose tissue) are adequate for reproductive
ictions to begin.
Aging And The Reproductive Systems 577
In females, the reproductive cycle normally occurs once
each month from mstwrcbe (inc-NAR-keK the first menses,
to menopause, the permanent cessation of menses. Thus, the
female reproductive system has a time-limited span of fertil-
ity between menarche and menopause. Between the ages of
40 and 50 the poo] of remaining ovarian follicles heeomes ex-
hausted. As a result, the ovaries become less responsive to
hormonal stimulation. The production of estrogens declines,
despite copious secretion ofFSH and LI I !iy the anterior pi-
tuitary. Many women experience hot Bashes and heavy su cur-
ing, which coincide with bursts of (inUIl release. Other
symptoms of menopause are headache, hair loss, muscular
pains, vaginal dryness, insomnia, depression, weight gain, and
mood swings. Some atrophy of the ovaries, uterine tubes,
uterus, vagina, external genitalia, and breasts occurs in post-
menopausal women. Due CO loss of estrogens, most women
also experience a decline in bone mineral density after
menopause. Sexual desire (libido) does not show a parallel
decline; it may lie maintained by adrenal androgens. The risk
of having uterine cancer peaks at about 65 years of age, but
cervical cancer is more common in younger women.
In males, declining reproductive function is much more
subtle than in females. Healthy men often retain reproduc-
tive capacity into their eighties or nineties. At about age 55 a
decline in testosterone synthesis leads to reduced muscle
strength, fewer viable sperm, and decreased sexual desire.
I lowever, abundant sperm may be present even in old see,
Enlargement of die prostate to two to four times its nor-
mal size occurs in approximately one-third of all males over
age 60. This condition, called benign prostatic hyperplasia
(BPH), is characterized by frequent urination, nocturia (bed-
wetting), hesitancy in urination, decreased force of urinan
stream, postvoiding dribbling, and a sensation of incomplete
emptying.
■ CHECKPOINT
16. What changes occur in males and females at puberty?
17. What do the terms menarche and menopause rneanr
lo appreciate the many ways that the reproductive sys-
tems contribute to homeostasis of other body systems, exam-
ine Focus on Homeostasis: The Reproductive Systems on
vS. Next, in Chapter 24, you will explore the major
events that occur during pregnancy and you will discover
how genetics (inheritance) plays a role in the development of
a child.
FOCUS
ON
HOMEOSTASIS
The Reproductive Systems
Body System
Contribution of the Reproductive Systems
For all body
systems
The male and female reproductive systems produce gametes (oocytes and sperm) that unite to
form embryos and fetuses, which contain cells that divide and differentiate to form all of the or-
gan systems of the body.
Integumentary
system
Skeletal system
Muscular system
Androgens promote the growth of body hair. Estrogens stimulate the deposition of fat in the
breasts, abdomen, and hips. Mammary glands produce milk. Skin stretches during pregnancy as
the fetus enlarges.
Androgens and estrogens stimulate the growth and maintenance of bones of the skeletal system,
Androgens stimulate the growth of skeletal muscles.
Nervous system
Endocrine
system
*
Androgens influence libido (sex drive). Estrogens may play a role in the development of certain
regions of the brain in males.
Testosterone and estrogens exert feedback effects on the hypothalamus and anterior pituitary
gland.
Cardiovascular
system
£
Estrogens lower blood cholesterol level and may reduce the risk of coronary artery disease In
women under age 50.
Lymphatic
system and
immunity
Respiratory
system
J)
The presence of an antibiotic-like chemical in semen and the acidic pH of vaginal fluid provida
innate immunity against microbes in the reproductive tract.
Sexual arousal increases the rate and depth of breathing.
Digestive system
Urinary system
578
«
The presence of the fetus during pregnancy crowds the digestive organs, which leads to heart'
bum and constipation.
In males, the portion of the urethra that extends through the prostate and penis is a passageu
for urine as well as semen.
Common Disorders 579
35
COMMON
DISORDERS
Reproductive System Disorders in Males
Ihticnlar Cancer
liitiiitiar ameer is the most common cancer, and also one ol the
post curable, in males between the nges of 20 and 55. An curly sign
i nihil cancer is a mass in the testis, often associated with a
jensacion of testicular heaviness or a chill ache in the lower ab-
. pain usually does not occur. All mules should perform regu-
■ i ■-■ ul a r self- exa mina tio ns -
hastate Disorders
Because die prostate surrounds pari of the urethra, any prostatic in-
i. enlargement, or tumor can obstruct the flow of urine.
and chronic infections of the; prostate are common in adult
m in association with inflammation ol the urethra. In
ptf t prostatitis, the prostate becomes swollen and tender. Chronic
wxtatitis is one of the most common chronic infections in men ol
ruddle and later years; on examination, the prostate feels en-
soft, and very tender, and its surface outline is irregular.
Prostate cancer is the leading cause of death front cancer in
,,, in the United States, A blood resi can measure the level of
Mpstatc-specitk antigen (PSA) in the blood. The amount of PSA,
is produced only by prostate epithelial cells, increases with
incut of the prostate and may indicate infection, benign en-
tintuiient. or prostate cancer. Males over the age of -10 shotitd have
•an aniui.il examination ol' the prostate. In a digital rectal exam, a
i;|i i :ian palpates- the prostate through die rectum with the fingers
il ■ . Mam physicians also recommend an annual I'SA test for
over 50. Tivaimcru for prostate cancer may involve su;i
i n. hormonal therapy, and chemotherapy. Because many
. g03# 9ttf) slowly, some urologists recommend
■btchful waiting" before treating small tumors in men over age 70.
■productive System Disorders in Females
. Premenstrual Syndrome
frrwciistrtMl syndrome (PMS) is a cyclical disorder ol severe
plr.Mial and emotional distress. Il appears during the postovulatory
male reproductive cycle and dramatically disappears
then menstruation begins. The signs and symptoms are highly
t from Din- woman to another. They may include edema,
!%. _hi train, breast swelling and ten . abdominal distension,
itoorarhc. joint pain, constipation, skin erapvions. fatigue and
■uliuri-v. urcacer ac<-</ tar sAvp. Ji-arc^imi or .i/txicty, imuhilm.
KkhI swings, headache, poor coordination and clumsiness, and
Rjbg5 for sweet or salty foods. The cause ol PUS is unknown.
ime women, getting regular exercise; avoiding caffeine, salt,
lukolml: and eating a diet that is high in complex carbohydrates
•il ii'ii! proteins can bring considerable relief.
Endometriosis
Endometriosis Ceu'-do-iue-ire-O-sis; cmfa- = within; metri- -
uterus; -<xis - condition of or disease) is characterized In the
growth of endoTuetrial tissue outside the uterus. Tin tissue enters
the pelvic eavitj vi.i the open uicrine tubes ami may be found in anj
of several sites — on the ovaries, tin- outer 5UT&CC "I the uieius. the
sigmoid colon, pelvic and abdominal lymph nodes, the cervix, the
abdominal wall, the kidneys, and die urinary bladder- Endometrial
tissue responds to hormonal fluctuations, whether it is mstdc or
outside the uterus, by first proliferating; and then breaking down
ami bleeding. When this occurs outside the uterus, it can cause in-
flammation, pain, scarring, and infertility. Symptoms include pre-
menstrual pain or unusually severe menstrual pain.
Breast Cancer
One in eight women m ihe United States feces the prospect ol
breast cancer, the second -lead me, cause ol lemale deaths from can-
cer. Early detection by breast selt-examination ;md i nan nn< grains is
the best waj to increase the chance or survival.
The most effective technique For detecting tumors less dian 1 an
(0.4 in.) in diameter is mammography (maui-OCi-ia-te; -gn
to record), a type of radiography using very sensitive x-ray film.
The image of the breast, called a mammogram^ is best obtained In
compressing die breasis, one ,u a lime, using Bat plate--. A supple-
mentary procedure for evaluating breasi abnormalities is
ultrasonography. Although ultrasonograph} cannoi detect tumors
Smaller Chatl 1 cm in diameter, it can be used to determine whether
a lump is a benign, fluid-iilled cyst Or a solid (arid ihcrerorc possibly
malignant) tumor.
Among the factors ihat increase the risk Of developing breasi
cancer are (1) a family history of breast cancer, especially in a
mother or sister; £2) never having I ".rue a child or having a first
« hib I after age 55: (>> previous cancer in one breasi: <4) exposure to
ionizing radiation, Mieh .is v. -rays; ($) scessive alcohol intake: .i]u\
(6) cigarette smoking.
The American Cancer Society recommends the following steps.
CO help. diagnose breast cancer as early as possible:
■ All women over 20 should develop the habit of uionil h
breast self-examination.
■ A physician should examine the breasts every three years
when a woman is between the ages of 20 and j9; and every
)cai alter age 40.
■ A mammogram should be taken in women between chic
ages of 55 and 39,tobeused later for comparison (baseline
mammogram).
M Women w'nh na symptoms should h:tvc .? mamjnpgtaui
even year alter age 40.
■ Women of any age with a history ol breast cancer, a strong
family history ol the disease, or other risk factors should
consult a physician to determine a schedule for inainiinig
raphy.
580 Chapter 23 The Reproductive Systems
Treatment lor liraist caflcer may involve hormone therapy,
chemotherapy, radiation therapy, lumpectomy (removal of die tu
mar and the immediate surrounding tissue), a modified or radical
mastectomy* m a combination of these approaches, A radical uuts-
tecloniy {mast: ~ breast i involves removal of the alfeeted breast
along with the underlying pectoral muscles ami the axillary lymph
mule-.. 1 1 .ymph nodes are removed because rhe spread of cancerous
cells usualh occur;, through lymphatic or blood vessels.) Radiation
treatment ivml chemotherapy may follow the surgery to ensure the
destruction of any stray timcer cells. In softie eases of metastatic
(spreading) beast cancer. I Lerceptin" . .1 monoclonal antibody drug
that targets an flanagoB on the surface of hrcasi cancer cells, can
ISC regression of the uminh and ret, ml progression of ilie dis
. i'iitally. rwo promising drugs for breast earner pn;u-nri»n arc
n, m m i lit- market ramoxifen (Nolvadex" ) and raloxifene (Rvisra w ).
Ovarian Cancer
Ovarian cancer is die sjxrii most common form of cancer in fe-
males, luit the leadingcau.se of death from all gynecological malig-
nancies (excluding Ureast cancer) because h is difficult to dense* he-
fore U metastasizes {spreads! beyond the ovaries. Risk factors
ava .dated wuh < .vari-an cancer include age (usually over age s'>V;
race (whites are ai highest risk); family IlifitOrj oj ovarian cancer;
more than 40 jnetftS of active ovulation} n!iiU(uiri!\ (no pregnancies i
or 6lSt pregnancy after age *0: a high-fa l. W-iiU.-r. utainin , A-
deficient diet; and prolonged exposure to asbestos ami cafe. lark
ovarian cancer may bave BO symptoms of mild ones such as abdom-
inal discomfort, heartburn, nausea, loss of appetite, bloating, and
flatulence. Later-Mage signs and symptoms indudc an enlarged ab-
domen, nhdominal and/or pelvic pain, persistent gastrointestinal
disturbances, urinary coin plications, menstrual inveularirics, anil
heavy menstrual bleeding.
Cervical Cancer
Cervical cancer, cancer of the uterine cervix, starts with cervical
dysplasia (dis-PL/Wha). a change in the shape, growth, ami num-
ber, of cervical cells. The cells may cither return to normal or
progress to cancer. In most cases cervical cancer may be detected m
it- earliest stages by Pap smear. Some evidence links cervical can-
cer to the virus that causes genital waits (human papilloma virus}.
Increased risk is associated With a large number pi gea»1 partners,
lirM tuicrcouiv u > yowg age, ami smoking cigarettes.
I aivovagifial Candidiasis
I • \ ... albkaw is a yeastlike fnngu.s that commonly grows OQ mu-
cous membranes of die gastrointestinal and genitourinary D3H E5,
lln organism is responsible for vulvovaginal candidiasis \\\\V \ ■-
\ \J-i-nal can'-di-Dl u si.i, the most common form of vaginitis
(vaj '-i-M'-tis). intlammauori of the vagina. Candidiasis, commonly
referred to as a yeast infection, is characterized by severe itching; a
thick, yellow, cheesy discharge; a yeasty odor; and pain- The disorder,
experienced at least once by about 75% of lemales. IS usually ,i result
of proliferation of the fungus following antibiotic therapy lor another
condition. Predisposing conditions- include the use ol oral contracep-
tives or cortisone-like inedicarions, pregnancy, :uu\ diabetes.
Sexually Transmitted Diseases
\ sexually transmittal disease (STD) is one that is spiv a
contact. AIDS and hepatitis B, which are sexually transmitted 4|
cases that also may be contracted in other ways, are h
Chapter's I" and l l ». respectively.
Chlamydia
Chlamydia (kla-Mll)-e-a) is a sexually transmitted disease Cflafl
by the bacterium Chlamydia trachomatis {chlamy- = cloak
usual bacterium cannot reproduce outside bod) cells; it "cloalcj'fl
self inside cells, where it divides. At present, chlamydia
prevalent sexually transmitted disease in the I mied Suites. I
cases the initial infection is asymptomatic and thus diffici [1
ogiii/e clinically. In males, urethritis is the principal resti
a clear discharge and binning, frequent, and painful urmitJi*
Wiilioiir treatment, the epididymides may also become infm
leading to male sterility, Tn 70% of females with chlamydia, qj
corns are absent, but chlamydia is the leading- cause nfpeh
matory disease. The uterine tubes mav also become inflami
inn rases the risk of female infertility due to the foi n
tissue in the tubes.
Gonorrhea
Gonorrhea (gon'-o-RE-a) Is caused by the bacterium >
ordm-tit'. Discharges from infected mucus membranes art
source of bransmisstoti of the bacteria cither during grxnal cc
or during the passage of a newborn through the birth canal. ,\hf
usually experience urethritis with profuse pus drainage and pin
urination. In females, infection typically occurs in tin. vagina,
with a discharge of pus. In females, the infection .m>\ eunseqiii
llauunatioii can proceed from the vagina into the uterus;
tubes, and pelvic cavity. Thousands of women are made inl't
imuorrhea evei'v rear as -» result of scar tissue tonnation thsl
the uterine lubes. Transmission of bacteria in die birth canal
eyes ol a mulimn can result in blindness.
Syphilis
Syphilis, caused bj die bacterium Tnponcmu pallidum, is rj
through sexual contact or exchange of blood, or chrougl :
ceiua to a fetus. The disease progresses through several.
During die {rrhnmy stage, the chief sign is a painless i
called a chancre (SI I \^< t-kcr), ai the point ol eonra< i 'I In. tj
ere heals within 1 to 5 Weeks, from 6 to 24 weeks later.
symptoms such as a skin rash, lever, and aches m the iniiuf
muscles lisher in the secondary stage, which is syro
en ui spreads to all major bpdy systems. When signs oftw
eration appeair, the disease is said to be in the tertiary m&>
ncrvOUS system is involved, the tertiary stage is called »Cli
\> motor areas become extensively damaged, victims inaybel
to control urine and bowel movements-, eventually tht
come bedridden, unable even to Iced themselves. I 1
cerebral cortex produces memon loss and persona I it) change**
range from irritability to hallucinations.
Study Outline 581
Genital Herpes
(unitnl herpes is caused by type J herpes simplex virus JllSV-2),
producing painiul blisters on the prepuce, gl.ms penis, and penile
slmit in males, and mi the vulva or sdoiptunes high up in the vagina
in females, The blisters disappear ;irul reappear in must patients,
MEDICAL TERMINOLOGY AND CONDITIONS
hut die virus iisdf remain-* in the bocfy; there is no cutE \ related
virus, type 1 herpes simplex virus (I ISV-I ). causes eold sores on tlu
mouth .hhI lips. InkcLttl iiirli v h1m:i U typically experience eeem
rences of symp'i'iiis several rimes ;i year.
Amenorrhea <.i--nien' -fj-RF.-a; rf- = without; mgo- ■ momh-,
-irhtui = a flow) The absence of menstruation; ii trmy I'te caused
by .» hormone unbalance, ohesm, e>:irenie weight loss, or very
Inu bodj I it 3S ni;iv uicur during rigorous athletic training.
Dysmenorrhea (dis-men -o-RF -•;»; tiyt- = difficult or painful)
Painful menstruation; the term is usually rmtu'iI to describe
menstrual symptoms that are severe enough to preveni a
woman I mm lun<:l m minii normally for one or more days each
month. Sonie eases are Caused by uterine tumors, ovarian cysts,
pelvic inflammatory disease, or intrauterine devices.
mdocervieal curettage tku'-re-TAII/TI; am/tit? = scraper) A pjeo-
eedure in which the cervix is dijated and the endometrium of
i hi uterus is scraped with a spoon-shaped instrument called a
curette; commonly called .1 D and ( . oJii.uiou and curettage).
njjlrroids (Fl-broyds; fUm* liber; -eidaa - resemblance) Non-
cancerous tumors in the myometrium of the uterus composed
6f muscular and fibrous tissue. 'I 'heir growth appears to be re-
lated to high levels of estrogens. I hc\ do not occur before pu-
bcrt\ and usually stop growing alter menopause. Symptoms in-
clude abnormal menstrual bleeding, and pain or pressure in die
pelvic area.
wfttorrhagfa (men-o-'RA-je-a; maw- — menstruation; 'thagt — to
hurst forth). Excessively prolonged or profuse menstrual pe-
riod. May be due to a disturbance in hormonal regulation of
the menstrual cycle, pelvic infection, medications (anticoagu-
lants), fibroids, endometriosis, or intraoterini devices;
Oophorectomy (6'-of-iVUl ; k-to-me; mpfar- - bearing eggs) 11.
moval of the ovaries.
Ovarian cyst The musi common form of ovarian tumor, in which a
fluid-filled follicle or corpus hiteuni persists and continues
grow inc.
Papanicolaou teat (pa '-pj-ni'-lco-LA-oo). or Pap xmear A test to
detect Uterine cancer in which a few cells from the cervix and
the pan of rjyj eagiJM sin rounding the cervix are removed with
.1 -wall and examined mkragiSCOpECalJjK Vlahgnam cells haw .1
characteristic appearance that allows diagnosis eveil before
symptoms occur.
Pelvic inflammatory disease (PID) A collective \xsfbi for anj enasia
sive bacterial inlcction of the pebie organs, especially the
uterus, uterine rubes, or ovaries, which is characterised bj
pelvic soreness, lower Lack pain, abdominal pain, and mvihn
ris. ( M'ten the early symptoms of I'll) o.eCUt [kxsi tfftq menstrua-
rion. As infection spreads and cases advance, lever m.u develop,
rdongwith painful absce-.c- ol the reproduce
Salpingectomy (sa|'- 1 pin-JB£-t6-mei salpingo - mk-i Renjova] 61 p
uterine (fallopian) tube.
Smegma (SMFCi-ma* The secretion, consisting pnn. .-ipally of
sloughed oil epithelial cells, found cluelh around die evierual
genitals anil especially under the Ion : I: ,
JTUDY OUTLIN
1
•* Introduction (p. 556)
Sexual reproduction is the process of producing offspring bv
die union n| gametes (oocytes and sperm).
The organs of reproduction are grouped as gonads [produce
gametes), ducts (transport and store gametes 1, accessory scs
panda (produce materials thai support gametes), and support-
11114 structures.
Hale Reproductive System (p. 557)
|J. The male reproductive system includes ehe testes, epididymis
iIuluis uasj deferens, ejaculaiorj ducts, urethra, seminal vesicles,
prostate, bulbourethral (( !< •■ pi 1 i) glands, scrotum \\nd penis.
jl The scrorum is a sac that supports and regulates the tempera*
iiire of the testes.
3. The male gonads include the testes,, oval-shaped organs in the
sen Hum thai contain the seminiferous ruluiles. in which sperm
cells develop; Sertoli cells, which nourish sperm cells and pro-
duce tnhibiu; and l.eulig cells, which produce the male ses
hormone testosterone.
4. Spermatogenesis occupy it) the testes and consists of metosis I.
u.ehKis IT, and spenwiogencais. Ii results in the formation or
lour haploid Sperm cells from a primary sperm.irocs ll
5. Mature sperm consist of a head and a lail. Their iuticinm 1-. to
lertili/e a secondary oocyte.
6. At puberty, gonadotropin-relc3si)ig hormone id.nKll) stimu-
l.u- anterior pituii.irv secretion of Id I and FSI1. I.ll stimu-
LatCS Leydig cells to produce testosterone. FSI J and testns
terone initiate spermatogenesis.
I
582 Chapter 23 The Reproductive Systems
7. Testosterone controls the growth, development, ami mainte-
nance of sex organs; stimulates bone growth, protein an-
.il.ulisin, and sperm maturation; ami stimwJatea development of
male secondary se.v c.:hurnc.i.c'ri:-Liu.' I .
8. IiiliiUin is produced U\ Seitoli ccJIsj its inhibition of T SF I helps
regulate the ran- ol spermatogenesis.
9. Sperm aire transported out of the testes into -.in adjacent organ,
die epididymis* where their motility increases.
10. "I "Jit- ductus (vas) deferens $t0t6& Sperm and propels them to-
ward i|ie urethra during ejaculation. Removing part of the vas
deferens t«) prevent feriili/.ation is called vasectomy.
11. The ejaculatory ducts are formed by the union pj the ducts
in mi ihe seminal vesicles and vas deferens, and thej eject
sperm Late the urcihra.
12. The m-.ile urethra passes through the prostate, deep perineal
muscles, and penis.
13. The seminal vesicles secrete ;m alkaline, viscotis fluid thai eon
grftuces about fill";, of the volume of semen and contributes to
sperm vkbilitp;
14. The prostate secretes a slightly acidic fluid that constitutes
about 2i'V' of the volume of semen and contributes Co sperm
motility.
15. The bulbourethral glands Secrete mucus fat lubrication and an
alkaline substance that ncuvmli/r li id
16. Semen is a mixture of Sperm and seminal fluid; it provides the
liiFul in which sperm are transported, supplies nutrients, and
in iur,ili/.cs the acidity of the male urethra and the vagina.
17. The penis consists ofa root, a body, and a gfans penis, It func-
tions to iniroduee sperm into the vagina, [expansion of its
blood sinuses under die rnlhi, ft e SCgUal exeitatfafn is Called
erection
Female Reproductive System (p. 564)
1. I he female organs of reproduction include die ovaries (go-
nads), uterine (fallopian; tubes, uterus, vagina, and vulva.
2. The mammary glands are also considered part of die reproduc-
tive system,
h The female gonads are the ovaries, located in the upper pelvic
•, on either sick of the Uterus.
4. Ovaries produce secondary oocytes; discharge secondary
oocytes (die process of ovulation)] and secrete estrogens, prog-
esterone, rchiNin, and inluhm.
$ . Oi . product t<m of hapfoid seeundary oocytes) begins in
the ovaries. The oogenesis sequence includes meiosts 1 and
ineiosis II. Meiosis li is completed only idler an ovulated see-
OndatJ «»oryie is fertilized by a sperm cell.
6. The uterine (fallopian) tuhej which transports a secondary oocyte
from an Ot at) to the uterus, is die normal site of fertili/ation.
7. The uterus is ;iu organ the size and shape of an inverted pear
that functions m menstruation, implantation of a fertilized
ovum, development of a fetus during pregnancy, and labor. It
also is part of the pathway for sperm to reach a uterine tube to
fertilize a secondary oocj te,
8. The innermost layer of the uterine wall is the endometrium,
which undergoes marked chance- during Hie- menstrual cycle.
9. The vagina is a passageway for the menstrual flow, the n i
de fof the penis during sexual intercourse. and the lower pod
tion of the birth canal. The smooth muscle of the vaginal
malies u capable of considerable stretching.
10. 1 he vulva, a collective term for the external genitals »] the fe-
male, consists of the uions pubis, labia maiora. labia minur
clitoris, vestibule, vaginal and urethral orifices, paraiuc
glands. Hi'! greater vestibular glands.
11. The mammary glands of the female breasts are rnodiiieii •
glands located over the pectoruhs major muscles. Their ftmtj
tion is to secrete and eject milk (lactation),
12. Ylamman. gland development depends 0*1 estrogens and prrj
gestcione.
13. Milk production is mmulated by prolactin, estrogens, awl J
progesterone: milk election i<- stiniuJflted by oxytocin.
Female Reproductive Cycle (p. 570)
1. The female reproductive cycle includes the ovarian am! umi
siriial cycles. The (unction ol the ovarian cycle IS d( • • I r
of a secondary oocyte; that of the menstrual cycle is put
tion of the endometrium each month to receive a ler
2. The ovarian anil menstrual cycles are controlled liy I
from the hypothalamus, which stimulates the release of
and LI I bj die anterior piiuit Irj
3. FS1 1 stimulates development of follicles and initiates sccretkg
of estrogens by the follicles. 1.11 stimulates hirtlier dewjl
metil of die follicles, seeietioii of estrogens by follicular
ovulation, formation of the corpus [uteum, and the sccrendftt
progesterone and estrogens In the corpus luleum
4. Estrogens stimulate the growth, development, and muiiire- 1
nance of female reproductive structures: the develnpn •
secondary sex characteristics; and protein synthesis.
5. Progesterone works together with estrogens to prepare thu cfttl
domctriun) for implantation anil the mammary glands
synthesis.
6. Relaxin increases the Ik-vihility of ihe pubic sytriphysi-
helps dilate the uterine cervix to case deliver) o! a baby
7. During the menstrual phase, purl of the endometrium is slug
discharging blood and tissue cells.
8. During die preovulatory phase, a group ol follicles in th
ovaries begins to undergo maturation. One follicle outgrows I
Others and becomes dominant while the others die \i tin- -am
lime, endometrial repair occurs In the uterus. I 'snog-,.
dominant ovarian hormones during the preovulatorj phase,
ft, ( Kulation is the rupture of the dominant mature (ulaaliaiufo
licle and the release of a secondan oocyte into the pcT
It is hroughi aboui by a surge oi' 1,1 ['.
10. During the posiovulatory phase, both progesterone atld
gens are secreted in large quantity by the corpus lutetini ol"
.nary, aiul the uterine endometrium thickens in ruadinesw
uiii«l.uUation,
11. If fertilisation and implantation do not occur, the corpus lu-
icuiii degenerates, and the resuldng low level of progesterone
and estrogens allows discharge of the endometrium (naenstrua-
iic.ni followed in iln.- initiation of another reproductive cycle,
12. It fmili/ntH.ii and implantation occur, the corpus lutcum is
maintained In hCG.
Blrtii Control Methods and Abortion (p. 574)
U. Birth control methoLls include surgical sterilization (vasectomy,
tubal ligation), hormonal methods, intrauterine devices, sper-
micides, barrier methods ("condom, vaginal pouch, diaphragm),
ond periodic abstinence. I on j>age 574 provides fail-
ure rates oi the various methods oi biftib control. Abstinence is
the only foolproof met In n I of birth control.
• ontraveptive pills of the cdd&£ti*$ori type contain estrogens
and progestins in concentrations that decrease the secretion of
Sell-Quiz 583
ESH and If I and therein inhibit development of ovarian loll i-
eles ami ovulation.
& An abortion is the premature expulsion from the uterus tX the
products of conception; li m.u he spontaneous or induced. RL
486 can induce abortion by blocking the action of proges-
terone. *
Aging and the Reproductive Systems (p. 577)
I. Puberty is the period of time v. hen secondary sex characteris-
tics begin to develop and the potential lor sexual reproduction
arises. In older females, levels of progesterone and estrogens
decrease, itSqJting in changes in menstruation and ilur,
menopause.
2. In older males, decreased levels of testosterone are associated
with decreased muscle strength, waning sexual desire, .md
fewer liable sperm; prostate disorders are common.
1. I he testes are located in the scrotum because
ft. they must he separated from all other orpins or sterility can
occur
h. Sperm and hormone production and survival require a tem-
perature lower than the normal body tempcran
c. die scrotum supplies the necessary hormones for sperm
i nutation
d. sperm in the testes cannot survive without the nutrients
.supplied by rhe scrotum
e. rhe scrotum produces alkaline fluids thai neutralize the acids
in the male urethr.i
''■' li ll die following:
a. cells that support, protect
and nourish developing
spermatogonia
b. contain developing oocytes
c, immature sperm cells
d. cells that secrete testosterone
c. produce progesterone and
ogens
I}. Removal of the prostate would
ii. interfc re with sperm production
b inhibit testosterone release
c. decrease the ralume of semen bj about 75-96
ise semen to become more acidic
semen dotting
ieh of die following is truer
the process by which somatic (bodj I cells divide
'. J he liaploid chromosome number is symbolized by 2n
sis I results in diploid spermatocytes.
Gametes contain the liaploid chromosome number.
Gametes contain 46 chromosomes in ihvw nwla.
A. COrpuS luteum
B. Lcyili'j. cells
C. Sertoli cells
D. follicles
E. spermatogonia
5. lite uterus is the site of all of the following exccpl
a. menstruation
b. iiiipf.Hii.niou of ii fertilized ovum
c. ovulation
d. labor
e. development of i In- fetus
6. Menstruation is triggered by .,
a. rapid rise in bteinizing hormone (1.1 1)
b. rapid fall in luteinizing hormone (f .1 \)
c. drop in estrogens and progesterone
d. rise in estrogens and progesterone
e. rise m inbibni
7. An inflammation ,,i die seniiuilerous tubules would interfere
with the alwlih in
a. secrete testosterone b. produce sperm
e. void urine d. make semen alkaline
e. regulate the temperature in the scrotum
8. I recti on of the penis involves the release of which neurotrans-
mitter?
a. norepinephrine b, serotonin
c. glycine d. dopamine
c. nitric oxide
ft vUu'c/i of the i'ollou inu is \< l !'.; huicno/i nfsancn-
Su transport sperm
b. hi I a ic . i te i h e re prod tieti ve tra c t
c. provide an acidic environment needed for fertifi/.uion
d. provide nourishment for sperm
e. produce antibiotics to destroy some baetcria
10. Prior 10 ejaculation, sperm arc stored in the
a. Leydig cells b. scrotum c. Sertoli cells
d. prostate e. ductus (ViS) deferens
584 Chapter 23 The Reproductive Systems
11. Mace the following m the correct order for the passage of
sperm horn the iL'sics m the ...inside of lire body.
3. urethra
2. ductus (vas) deferens
3. seminiferous till
iacutory onci
5. external urethral orifice
6. epididymis
a. 6. 3, 2. 4, 1 , 5 b. 3, 2, 6, 4, I, 5 c. 1, 6, 2, 4, 1 , 5
d. 5,6,2, 1.3, I e. 2, 4,6, |,S,5
12. fn nifiles, I In: gland that surrounds iJicr urethra at the Ui.sc of
the urinary bladder is the
a. glans penis b. prostate
c. seminal vesicle d. bulbourethral gland
e. greater vestibular gland
13. An Oocyte is moved towards the uterus In
i. peristaltic contractions of' the uterine- (Fallopian} cubes
b. contraction of (he uterus
c. eT.iMty
d. swimming
e. flngetla
14. Fertilization normally occurs in the
a. Vitt-ina b, cervix •-. uterus d,
e. uterine pi.be
15. In the female reproductive system, lubrivaung mucus js p«o-
l luted by the
a. vulva
b. clitoris
c. nunis pubis
d. greater vestibular glands
e. sudoriferous glands
16. Ovarian follicles mature during
a. menstruation
b. Qvuiat i i
c. the jioscovulnioiy phase
d. ihe preovulatory phase
e. the see re ton phase
A. emission
B. ejaculadon
C. erection
I), spermingen
17. Match the following;
, _.». The enlargement and
Stiffening of the penis
. b. The discharge ol a small volume
of semen before ejaculation
* c. "I he maturation of
spermatids into sperm
d. The powerful release of semen
from the urethra to the exterior
18. Ihe portion of the uterus responsible for us conn action is the
a. fundus b. infundibulum c. endometrium
d* myometrium e. perineum
19. Witch ihe following:
a. released by the hypothalamus
to regulate the ovarian eyele
b. stimulates the nM[i,\\ secretion
i 'i estrogens In growing
follicles
A. luteinizing
horinniH
B. gonadotropin- I
releasing I
iC.nKlb
C. rclilxin
D. progesterone
E. inhibit)
F. lollicle-
stimulating
hormone il SI I
G. estrogens
c. stimulates ovulation
d. stimulate growth. devclop-
mem, and maintenance of the
female reproductive system
e. works with estrogens to
prepare the uterus for implan-
tation of, i u rttlfacd ovum
f. assists with labor by helping
to dilate the cervix and
increase flexibility of the
pubic symph) sis
_g. inhibits release OJ I SI I by the
anterior pituitary
20. Bifth control pills are a combination of ovarian horOToriCSjO
prevent pregnane) by
a. iiLMiiriili/int; the pi 1 ol the vagina
b. inhibiting motility of the sperm
c. causing eark ovulation, before the folliele is mature
cl. preventing sperm from entering the uterus
e. inhibiting- the secretion of I 1 1 and I'M I from the pituitary
n
I
CRITJCALTHINKING APPLICATIONS
1, Thirty-five year-old Janellc has been advised to haw a coin- 3.
ptete hysterectomy due to medical problems. She is worried
that the procedure will cause menopause. Explain what is
involved in the procedure m<\ the likelihood that the procedure
will result in menopause.
2. Phil has promised his wife thai he will get a vasectomy after the 4.
birth of their next child. Re is a little concerned, however,
about the possible effects on his virility. What would you tell
Phil about the procedure?
Julio and his wife have been trying unsuccessful!) to bam
preuiiaul. The fertility clinic suggested that the problem fl
have something io do with Julio's habits of wearing very d<
tig briefs during the day and taking a long niglnl
his hot tub. What elVecl could this have oti fertilu |
Your uncle Mike has just been diagnosed with an inlanjfl
prostate (benign prostatic hyperplasia)'. What are the win; :.
of this condition 1 ' What is the effect uii the semen of remmJ
of the prostate?
Answers to Figure Questions 585
^F )
ANSWERS TO FIGURE QUESTIONS
23.1
23.2
Z3.3
2.1.4
23.5
1\. 6
23,7
Functionally, the penis is considered •• swpportifig structure.
Sperraatqgonia (seem eells) are the least mature.
Crossing-over permits the formation of new eombmauonsof
l es from maternal and paternal chromosomes.
The middle piece contains mitochondria, whieb produce
VI p thai provides energy for locomotion ofsperju.
The Sertoli cells secrete nhftrin.
The female externa] genitals are collectively referred CO SS
the vulva or pudendum.
Ovarian follicles secrete estrogens, and the corpus luteum
secretes estrogens, progesterone, rda.vm, and inhibiu.
Primary oocytes arc present in the ovarj at birth, so they are-
as old as the woman is. In males, primary spermatocytes ti*
f
continually being formed from Spermatogonia and thus are
only a few days ctkii
23.9 The eodomtrnum is rebuilt after each mciismuiion.
23.10 The mons pubis, clitoris, prepuce, and external urethra] ort-
lice are anterior to the vaginal Opening.
23.11 Oxytocin regulates milk ejection from the mammary glands.
23.12 The hormones responsible for the proliferative phase ol en-
dometrial growth are estrogens; for ovulation, LK; for
growth of the corpus luteum, 1.11: and Tor the mid,.
surge of II [.estrogens.
23.13 This is ueyalixe feedback because the response is opposite to
i lu stimulus. Decreasing levels of estrogens and proges-
terone stimulate release of<5ra&H, which, in turn, increases
production ami release ofescrogens.
chapter 2
DEVELOPMENT AND INHERITANCE
ft
did you know?
uman milk provides'
pel feet nutrition for ha mail infants. It also
supplies important digestive enzymes and
hormones that promote healthy development.
Breast milk contains important substances that
help babies fight infections. These include secre-
tory immunoglobulin A (IgA) antibodies,
formed by the mother in response to infectious
agents in the mother's (and baby's) environ-
ment. These antibodies summon an immune
response without harming helpful flora in the
gastrointestinal (GI) tract or causing inflam-
mation, a process that can harm the baby more
than the infection. Human milk also contains
mucins, oligosaccharides (sugar chains), and
glycopi oteiiis (curb oh ydi ate -pi o tein co mp on nds)
that bind to microbes and prevent them from
infecting the babys
(7/ tract.
Focus an Wellness, page 603
www, wiley.com/collBge/apcenlral
C/nce sperm and a secondary oocyte have
developed through meiOgls MM.\ maturation,
and the sperm have been deposited in l he vagina,
pregnancy can occur. Pregnancy is ;i sequence of
events that begins with fertilization, proceeds to implantation, embiw
onic development, and fern I development, and normal!} ends with
birth about 38 weeks later, or 40 weeks alter the last menstrual paim!
Developmental biology is the study of the extraordinary
sequence of events from the fertilization of a secondary oocyte to
the formation of an adult organism. From fertilization rhrouqti the
eighth week of development, the developing human is called an
embryo (cm- - into; -hyo = grow), and this is the embryonic pe-
riod. Embiyology (em-bre-OL-6-je) is the study of development
from the fertilized egg- through the eighth week. The fetal period
begins at week nine and continues until birth. During this time,
the developing human is called n fetus ( I I ,-uis = offspring).
Obstetrics (ob-S'lTVI-riks; obstetrix = midwife) is the branch of
medicine that deals with the management of pregnancy, labor. ,ind
the neonatal period, the lirsi 2S days after birth. Prenatal develop*,
mint (pre-NA-tal; pre- ^ before; natal = birth) is the time from fer-
tilization ro birth and includes both the embryonic and fetal pe
In this chapter, we focus on the developmental sequence from
fertilization through implantation, embryonic and fetal development.
labor, and birth. We will also consider the concept of inheritance.
looking back to move ahead
Somatic Cell Division {page 62)
Testes and Ovaries (pages 558, 564)
Uterine Tubes and Uterus {pages 565-567)
Estrogens and Progesterone (page 570)
Positive Feedback System (page 8)
Mammary Glands (page 569)
Oxytocin {page 322)
Prolactin (page 320)
586
EMBRYONIC PERIOD
OBJECTIVE • Explain the major developmental events
that occur during the embryonic period.
First Week of Development
] ik' firs! week of development is chataccerixed by several sig-
iinic:;int events including fertilization, cleavage of the zygote,
BfestQcysi lot niaiion, anil implantation.
fertilization
During fertilization (fer-til-i-Z A-sluin; fertil- = fruitful),
die genetic material from :\ hnploid sperm cell and n h;tp-
" I ■■ indan oocyte merges listo a single diploid nucleus
I.I), Of approximately 300 million sperm intro-
.1 eil into the vagina, fewer than 1 million reach the cervix
at the uterus and only aboul 200 reach the secondary
-. Fertilization normall) occurs in the uterine (fallop-
ian) tube within 12 to 24 hours after ovulation. Sperm can
i'Lir;uii viable for about 48 hours after deposition in the
ISgina, although a secondary oocyte is viable for only aboul
r- alu-i ovulation. Thus, pregnane) is most likely to
occur it intercourse takes place during a 3-day "window" —
2 days before ovulation to i day after ovulation.
Sperm swim From the vagina into the cervical canal pro-
pelled In the whiplike movements of their rails (llagclla). The
ol sperm through the rest of the uterus and then into
ilk Uterine tube results mainly from contractions of the walk
Figure 24,1 Fertilization. A sperm cell penetrating the corona
radiata and zona pellticida around a secondary oocyte.
During fertilization, genetic material from a sperm cell and a sec-
ondary oocyte merge to form a single diploid nucleus.
Sperm eel
PATH OF SPERM
CELL:
- Corona radlata
I
Ftel
1
9
*••
Zona pelfuclda
I
Plasma membrane
of secondary
oocyte
T
Gyioplasm of
secondary oocyte
What Is capacitation?
r
Embryonic Period 587
ol these organs- Prostaglandins m semen are believed to
stimulate uterine motility at the time of intercourse and to
aid in the movement ol sperm through the uterus and into
the uterine tube. Sperm that reach the vicinity of the OoCj i
within miliums after ejaculation ( //v not. «v//v/M- of fertilizing it
until about seven hours later. During this tune in the female
reproductive tract, mostly in the uterine tube, sperm undergo
capacitation (ka-pas'-i -'| A-shun; capacit- - capable of), a se
ries of functional changes thai cause the sperm's tail to beat
even more vigorously and prepare its plasma membrane to
fuse with the oocyte's plasma membrane.
for fertilization to occur, a sperm celJ firsi must pene-
trate the corona radiata (ko-RO-na = crown; ra-dc -A-ta =
Co shine), the ceils that surround the secondary oocyte, ami
then the zona pcllmitin (ZO-wa = /one; pe-LOO-si-da = al-
low i mi passage of lights the clear glycoprotein layer between
the corona radiata and the oocyte's plasma memhrane(! -
I >nc .il the glycoproteins in the zona pelhicida acts as fl
sperm receptor, lis binding to specific membrane proteins in
the sperm head triggers the release of enzymes from the
acrosome 1 . '1 Tie acrosomal enzymes digest a path through the
zona pelhicida as the lashing sperm tail pushes the sperm cell
onward- Although mam sperm liind CO the zona pelhicida
and release their enzymes, only the first sperm cell EC pene
ttate the entire zona pelhicida s \m\ reach ihc oocyies plasma
membrane fuses wiih lire oocyte. The fusion of a nemo with
.i Secondary oocyte sets in morion events that block fertiliza-
tion by more than one sperm cell.
Once ,i sperm cell enters a secondary oocyte, the oocyte
lii st must complete meiosis II. It divides into a larger ovum
(mature egg; and a smaller second polar body I hat fragments
and disintegrates (see figure 2 l£ on page 566), The nucleus
in the head of the sperm and the nucleus of the fertilized
ovum. Rise, producing a single diploid nucleus that contains
23 chromosomes from each cell. Thus, the fusion of the km
bid (ft) cells restores the diploid number (2//) of 46 cferamo-
• im.-s. The fertilized ovum now is called a zygote (Zl-gnr;
zygan — yolk).
Dizygotic (fraternal) levins are produced irom the inde
pendent release of two secondary oocytes ami the subse-
quent fertilisation of eacii by different Sperm, I he;.
rhe same age a.ml in the uterus al the same lime, but the}
are genetically as dissimilar as are any other siblings. 1 )izy
gotic twins may or may not be the same sex Because
monozygotic (identical) twins develop from a single fer-
tilized ovum, they contain exactly the same genetic mater-
ial and are always the same sex. Monozygotic twins arise
from separation of the developing zygote mm two em
hrvos, which occurs within 8 days after feriili/aiion '
of die time. Separations that occur later than H days are
likely to produce conjoined twins, a situation m which
rhe rwins are joint-/) together m?/) sfeaw same hoth
structures.
588 Chapter 24 Development and Inheritance
Early Embryonic Development
After fertilization, rapid mitotic cell divisions of the zygote
called cleavage (KLEV-ij) cake place (Figure 24J), The first
division of the zygote begins about 24 hours after fertiliza-
tion and is completed about 6 hours later. Each succeeding
division takes slight!) less time. By the second day after lettil-
ization, the second cleavage is completed and there are four
cells (Figure 24.2b). By the end of the third day, i litre :ire 16
cells. The progressively smaller cells produced by cleavage
are called blastomeres (BLAN-to-mer/.; Nt/stu- - germ or
sprout; -mtm ~ parts). Successive cleavages eveimially pro-
duce a solid sphere ol cells called the morula (AlOR-u-la
= mulberry). "The morula is still surrounded be rhe zona
pellucida and is about the same si/e as the original zygote
i nre 24.2i i
\\\ the end of the fount) day, the number of cells in the
morula increases as it continues to move through the uterine
tube toward the uterine Cavity. When the morula enters the
uterine cavity on da\ 4 or 5, a glycogen-rich secretion from
the glands of the endometrium of the uterus penetrates the
morula, collects between the blastomeres, and reorganizes
them ground a large fluid-filled cavity culled the blastocyst
cavity (BLAS-to-sist; blasm- a germ or sprout; *fjpt - hag)
!. With the formation oi this cavity, the devel-
oping mass is then called the blastocyst. Though it now has
hundreds, of eel Is. the blastocyst is still about ihe same size as
the original zygote. Further rearrangement of the blas-
fonieres results in the formation of two distinct structures:
rhe inner cell mass and trophohlast (Figur . )« The inner
cell mass is located internally and eventually develops into
the embryo. The trophoblast H !<!< T-d-Uast; iropkn- = de-
velop or nourish) is an outer superficial layer of cells that
forms the wall of the blastocyst, b will ultimately develop
into ihe feral portion ot the pheenta. the site of cvehange of
nutrients and wastes between the CHOI her and fettlS.
Stem cells are unspeeiali/.ed cells (cells without a particu-
lar I unction) that have the ability to divide for long periods
and develop into specialized veils. Based on their potential,
stem ceils are classified into thr. (
tii Totipotent stmt cells Oo-TIP-M-ient; torus- = whole:
•potwtwi = power) have the potential to form all cells
of an entire organism. An example is a zygote (fertil-
ized ovum l
l2) Pfaripiitmt stem cells (ploo-RIP-o-tenr: phrr- - several)
have the potential to develop into main (but not all.)
different types of cells ol" an organism. Examples are
inner cell mass veils.
(3) Mf/lnpuitvt slew cells (mul-TJP-6-tent) have the ;
rial to develop into a few different types of cells uf Q
organism, Examples are myeloid and lymphoid swrifl
GfeUs that develop into blood veils.
Pluwpotent stem veils currendy used in researcr
derived from (1) extra embryos that were destined to UJ
used for infertility treatments but were not i
from (2) nonliving fetuses terminated during th
trimester of pregnane)'. Ik-cause pluri potent stem cm
give rise to almost all cell types in the body, the}
tremel) important in research and health care. Fnrcxiiflj
pie, they might be used to generate cells and ussi
transplantation to treat conditions such as cancer, i
son and Alzheimer disease, spinal cord injury, Jin
heart disease, stroke, burns, birth defects, osteoiiri
and rheumatoid arthritis.
On October 13, 2001, researchers reported el
the first human embryo to grow celts to treat hum;!
eases. Therapeutic cloning is envisioned as a pjt-x
in which the genetic material of a patient with a par-
disease is used to create pluripoteni stem cells to m
disease. Using the principles of therapeuti einrunj
enlists hope to make an embryo clone of a patient
move the pluripoteni stem cells from the embryo
then use them to grow tissues to treat particular J,
and disorders.
Scientists are also investigating the potential elinira
plications of using atliih stem cells, stem cells thai rem i
the body throughout adulthood. Studies have sat;
that stem cells in human adult red hone marrow !i.
ability to differentiate into cells of the liver, kidney, I
lung, skeletal muscle, skin, and organs of ih
nal tract. In theory, adult stem cells from red hone in
could be harvested Irom a patient and then used to repari
other rissnes and organs in that patients hcwlv \w
having to use stem cells from embryos.
The blastocyst remains tree within the iiteriri
for a bou i t days before it attaches to the uterine wall. \\»
d !\s after fertilization, the blastocyst loosel\ attach
endometrium, a process called implantation (J
As the blastocyst implants, it orients wirh the in net
toward the endometrium (Figure 2
The major events associated with the first wee!
opinent are summarized in Figure 24.4 on page
Figure 2-4.2 Cleavage and the formation of the morula and
blastocyst.
^ Cleavage refers to the early, rapid mitotic divisions of a zygote.
Polar bodies
Blastomeres
Zona pellucida
f'.'(a) Cleavage of
zygote two -eel I
stage Iday 1
5 Cleavage.
tour-cell stage
(day 2)
Nucleus
Cytoplasm
|Mdrula
[day 4)
) Blastocyst.
external view
m
^Blastocyst.
Internal view
Py5)
_ Inner cell mass
Blastocyst cavity
Trophoblasi
> What is the hlstofoglcaf difference between a morula and a
blastocyst?
Embryonic Period 589 |
Figure 24.3 Relation of a blastocyst to the endometrium of
the uterus at the time of implantation.
Implantation, the attachment of a blastocyst to the endometrium,
occurs about 6 days after fertilization.
Frontal
plane
Uterine
cavity
Endometrium ol uterus
Blood
Frontal section
through uterus
Endometrial gland
Opening ol
endometrial gland
Trophoblasi —
Inner cell
mass
Blastocyst
cavity
Frontal section through endometrium of uterus and
blastocyst, about 6 days after fertilization
) How does the blastocyst merge with and burrow Into the
j endometrium?
Ectopic pregnancy (ek-7'OI>-ik; ec-^dm ofj -topic =
place) is the development of ;in embryo or fetus outside
the uterine Gavityi An ectopic premium \ usualjj occurs
when movement of die fertilized ovum throu^i the literfrie
tube is impaired. Situations that impair movement include
scarring clue to a prior tubal infection, decreased motility ol
the uterine tube smooth muscle, or abnormal tubal
anatomy. Although the most common site of ectopic preg-
nancies is the uterine tube, ectopic pregnancies may also
occur in ihe ovary, abdominal cavity, or uterine cervix. I He
signs and symptoms of ectopic pregnancy include one or
two missed menstrual cycles Followed by bleeding and acute
abdominal and pelvic pain. Unless removed, the di I \\
embryo can niprurc the uterine tube, «.iu-n resulting in
death or' the mother.
590 Chapter 24 Development and Inheritance
Figure 24.-4 Summary of events associated with the first week of development.
<, Fertilization usually occurs in the uterine tube.
Frontal plane
V
3, Morula
(3-4 days atler fertilization)
2. Cleavage
(first cleavage
completed about 30
hours after fertilization)
4. Blastocyst
(4Tfr-5 days
fertilization
Uterine cavity
5. Implantation
(occurs about
6 days after
fertilization)
1. Fertilization
(occurs within
uterine tube
12-24 hours
alter ovulation)
Ovulation
Ovary
Uterus
Endometrium
Myometrium
Frontal section through uterus, uterine tube, and ovary
At implantation, how is the blastocyst oriented?
■ CHECKPOINT
1. Where does fertilization normally occur?
2. Describe the layers of a lihistocw and their eventual
fetes.
3. When, where, and rum does implantation occur?
Second Week of Development
About 8 days after fertilization, the trophoblast develops
into two l;i v L-rs: a syucytiotrophohlast (sin-sit'-e-o TROE-
6-blast) .incl a lytatropbuhfast {si-\;i>-' \'R()V-( >-\>\<\s[} (Figure
). The two layers of trophoblast become paj?t of the
chorion (one of the fetal membranes) as they undergo fur-
i he- r growth (see ! igun 24.8 inset). During implantation,
the syncv Monophobias! seereles en/.} tries that enable the
blastocyst to penetrate the uterine lining. Another secre-
tion ?)l tlie trophoblast is human chorionic gonadotropin
(hCX i), a hormone which sustains secretion of progCS
rone and estrogens by the corpus lui.euin. These hor-
mones maintain the uterine lining- in a secretory state and
therein prevent menstruation. About the ninth week of
pregnancj die placenta is lulls developed and produces the
progesterone and estrogens that continue to sustain the
pregnancy.
Cells of die inner ceil mass also differentiate into tv
layers around 8 days alter fertilization a hypoblast {prir,
endodcrm) and epibias't (primitive ectoderm) (Figuri
Cells of the hypoblast and epihlasr together form a flat
referred to as the trilaminar embryonic disc (hi-f ..Wl-in-ar
two-layered). In addition, a small eavitj appears within the;
epiblast and eventually enlarges to form the amniotic cavity
(am-ne-OT-ik; ammo- = lamb).
V rhe amniotic cavity enlarges, a thin protective a
brane called the amnion (AYI-ne on) develops from ilu-
hlast i v-'ii). With growth ol the embryo, the amnfc
eventually surrounds the entire embryo (see 1
inset), creating the amniotic cavity that becomes filled '
amniotic fluid, Amniotic fluid serves as a shock absorber!
the fetus, helps regulate fetal body temperature, helps
vent drying 0|| t, ;||1l I prevents adhesions between tin 5]
the Ictus and surrounding tissues.
I Embryonic cells are normally sloughed off into amnion
fluid. They can he examined in a procedure called amnio-
centesis (am'-ne-o-sen-TK-sis; amnio- — amnion;
= puncture to remove fluid), which involves withdrawn
some of rhe amniotic fluid that bathes the developui
and analyzing the fetal ceils and dissolved sub
page mi).
Embryonic Period 591
Figure 24.5 Principal events of the second week of development.
.. At
About 8 days after fertilization, the trophoblast develops into a syncytiotrophoblast and a cytotrophoblast; the
inner cell mass develops into a hypoblast and epiblast (bilaminar embryonic disc).
Endometrium of uterus
Endometrial gland
Formation
of yolk sac
Bilaminar
embryonic disc;
Hypotrfasl —
Epiblasi
Cytolrophoblast
SyncyiioEropnoWast
Amnion
Amniotic cavity
Blastocyst cavity
Blood vessel
i mn is
Uterine cavity
S; .Ik r„-:i
Lacunar
network
Uterine cavity
(a) Frontal section through endometrium ot uterus showing blastocyst,
about 8 days after fertilization
Endometrium of uterus
Chorion;
Extraembryonic mesoderm
Syncytiotrophoblast.
Cytoirophoblast
Amnion
Amniotic cavity
Bilaminar embryonic disc:
Epiblast
Hypoblast
Endometrial gland (right)
and maternal blood vessel (left)
emptying into lacunar network
(b) Rental section through endometrium of uterus showing
blastocyst, about 1 2 days after lertlllzation
1 How is the bilaminar embryonic disc connected to the trophoblast?
' , m the eighth day after fertilization, cells of the hy-
ht migrate and cover the inner surface nf the blastocyst
i re J4.^;i) T forming the wall of the yolk sue, formerly
Che blastocyst cavitj ( I. The yolk sac has
ml important functions in humans. Ft supplies nutrients
co the embryo during the second and third weeks of develop*
nK-ni. is the source of blood cells from the third thm
sixth weeks, contains che first cells (primordial genu cells)
that will eventually migrate into the developing gonads, and
forms part of the gut (gastrointestinal tract). Finally, tin
592 Chapter 24 Development and Inheritance
sac functions as 1 shock absorber and helps prevent drying
0>Ut of the embryo,
On die ninth day after fertilization, the blastocyst be-
comes completely embedded in the endometrium and small
spaces called lacunae (la-MH)-iie -little lakes) develop
within the croprioblast (Figure 24.5b). Bj the twelfth day of"
development, die lacunae fuse to form larger, interconnect-
ing spaces called lacunar networks. Vl-.nemal blood and glan-
dular secretions enter the lacunar networks, serving lis both a
rich source of materials for embryonic nutrition and a dis-
posal site lor the embryo's wastes.
About the twelfth day after fertilization, mesodermal
cells derived Irom the yolk sac form a connective tissue < mes-
enchyme) around the amnion and yolk sac called the ex-
t rat mhryonic mesoderm (I ». The extraembryonic
iderm iftd the two layers of the trophoblast together
form the chorion (KOR-e-on = membrane) (Her: i),
It surrounds the embryo and, later, the fetus (see Rgttre 24. S
inset). Eventually the chorion becomes the principal embry-
onic part of the placenta, the structure for exchange of mate-
rials between mother and fetus. The chorion protects the
embryo and fetus from the immune responses of the moiher
and alsO produces human chorionic gonadotropin (hCCJ), an
important hormone of pregnancy.
By the end of the second week of development, the bi-
laminar embryonic disc becomes connected to the tro-
phoblast by a band ol extraembryonic mesoderm called die
connecting (body) stalk (see Figu] I mset). the future
umbilical cord
■ CHECKPOINT
4. What are the functions of the trophobhist?
5. Describe the formation of the amnion, yolk sac, and
chorion ;md explain their functions.
Third Week of Development
1 he third week ol development begins a six-week period of
rapid embryonic development and differentiation. During
the third week, the three primary germ layers are established
and Isarj the groundwork for organ development in weeks four
through eight.
Gastrnlation
The first major event of the third week of development is
Called gastrulation (gas'-rroo-LA-shun). In this process, the
bilaminar (two-layered) embryonic disc transforms into a tri-
laminar (three-layered) embryonic disc consisting of three
primary germ layers, die ectoderm, mesoderm, and endoderm.
The primary germ layers are the major embryonic tissues
from which the various tissues and organs of the body develop.
\s part of gastruhilion, cells of the epibiast move in-
ward and detach from it (Figure 24.6b). Some of the cells
push DM other cells ol the hypoblast, forming the endo-
derm Undo- - inside; -derm = skin). Other cells remain
between the epiblast and newly formed endoderm to form
the mesoderm {m?s<>- = middle). Cells remaining in the
epiblast then form the ectoderm [c,lt>- outside). As the
embryo develops, the endoderm nltimatelv becomes the
epithelial lining ol the gastrointestinal tract, respii
tr;ici. atrd several other organs. The mesoderm gives rise to
muscle, bone, \-\m\ other connective tissues. The ectoderm
develops into the epidermis of the skin and die nervous
MStClJI.
\l"Uit 22 to 24 days after fertilization, mesodermal cells
form a solid cylinder of cells called the notocbord (w
KORD; tiata- = back; -chard = cord). It stimulates mesodcfl
mal cells to form parts of the backbone and intervertebral
discs. The notoehord also stimulates ectodermal cells merit
to form the neural plate (sec Figure 24.9a). By the end
third week, the lateral edges of the neural plate Income mora
elevated and form the neural fold. The depressed mklngmn
is tailed the neurit I groove. Generally, the neural fold
proach each other and fuse, thus concerting the neural plate
into a neural tube. Neural tube cells then develop into
brain and spinal cord. The process by which tin neural
neural folds, and neural tube form is called nemuUmm \
(noor-oo-LA-shun).
Neural tube defects (NTDs) are caused by problem^ J
| with the normal development and closure of die lu-unl
i tube. These include spina bifida (discussed on \\
and anencephaly (an'-en-SEPl I-a-le; an- - without: m-
cephaf = brain). In anencephaly, the cranial bone
develop and certain parts of the brain remain in cor
with amniotic fluid and degenerate. Usually, die part of j
die brain that controls vital functions such as breathing
and regulation of the heart is also affected. Infants with
anencephaly are stillborn or die within a feu days
[ birth. The condition occurs about once in every NXlfl
births and is 2 to 4 times more common in female in!
than males. Neural tube defects are associated with taw
levels of folic acid, one of the B vitamins.
Development of the Allantois, Chorionic I '////,
and Placenta
The wall ol the yolk sac forms a small vascularized miipoudi-l
ing called the allantois (a-LAN-to-is: alUmt- = sa
mset). In most other mammals, the allantois fcl
used lor gas exchange and waste removal. Because oftl
ol the human placenta in these activities, the allantois is nodi
prommenl structure in humans. Nevertheless, it dues fuiic-J
tion in earl) formation of blood and blood vessels and ii
soeiated with the development of the urinary bladder.
By the cm\ of the second week ol development, chorkim
villi (ko-re-ON-ik MT.-l) begin to develop. These Umvh
projections consist of chorion (syncyriotrophohlasi surrotuffl
bvcytotrophoblast) and contain fetal blood vessels (1
on page ^'H). By the end of the third week, blood capillaries]
Embryonic Period 593
Figure 24. G Gastrulation.
\ Gastrulation involves the rearrangement and migration of cells from the epiblast.
Amnion
Amniotic
•cavity
Yolk sac
Cylotraphoblast
Connecting alalk
Bilaminar embryonic disc:
Epi blast
Yolk sac
(a) Dorsal and partial sectional views of
embryonic disc, aboul 15 days alter fertilization
Transverse
plane
^- Primitive node
^ Amnion
y^' •*
^ Connecting stalk
TAIL
END
^
"^ Primitive streak
^%»-
Bilaminar embryonic disc
^ Epfblasi
^ Hypoblast
Primitive sireak
Trilaminar embryonic dtsc:
Ectoderm
Mesoderm
Endodeiin
Yolk sac
(b) Transverse section of trilaminar embryonic disc,
about 16 days after fertilization
I What is me significance of gastrulation?
viinji in die chorionic villi connect to t Iil einbiyonic heart In
■ol the umbilical arteries and umbilical vein. As \ result, m.i-
Bternnl and fetal blood vessels are in close proximity. Note, how -
br. tlnii. maternal and fetal blood vessels do not join, and the
l!ic\ cany dm not normally mix. Instead, oxygen and
nutrients in die mother's blood diffuse across the cell mem-
branes into the capillaries of the chorionic villi. Waste prod
such as ciirhou dioxide diffuse in the opposite direction,
The placenta (pla-SF.N-ta = ll;u cake) is die- sin- of ill.
i vehange of nutrient.*: and wastes between the mother an I I
594 Chapter 24 Development and Inheritance
tus. The placenta is unique because it develops from rwo sep-
arate individuals, die mother and die Fetus. By the beginning
of i he twelfth week, the ptacenta has two distinct parts: (I)
the fetal portion formed in the chorionic villi and (2) the ma-
ternal portion formed by part of ihe endometrium of the
uterus m i. When fully developed, the placenta is
shaped like a pancake >; 1 ,81 1). Most microorganisms
cannot pass through it, but certain viruses, such as those that
cause AIDS, German measles, ehickenpox, measles, en-
cephalitis, and poliomyelitis, can cross the placenta as well as
many drugs, alcohol, and some other substances thai can
cause birth detects. The placenta also stores nutrients such as
carbohydrates, proteins, calcium, and iron, which are re-
leased into lvt.il circulation as required, and it produces sev-
eral hormones that are necessary to maintain pregnancy (dis-
cussed later i.
The actual connection between the placenta and embn i -
and later the fetus, is through the umbilical card (um-BIL-i-
kul = navel), which develops from the connecting stalk. The
umbilical cord consists of two umbilical arteries that carry
decocygenated k-ial blood to the placenta, one umbilical vein
thai carries oxygenated maternal blood into the fetus, and
supporting mucous connective tissue. A layer of amnion sur-
rounds the entire umbilical cord and gives \\ a shiny appear-
ance 1 I ijgtrre 24,8a).
Vfter the hirth of the baby, rhe placenta detaches In-m
the uterus and is i here fore termed the afterbirth. At this
time, the umbilical cord is tied off and then severed, leaving
die baby on its own. The small portion (about an inch) of the
cord that remains attached to the infant begins to wither and
falls off, usually within I- to 1.5 days after birth. The area
where the cord was attached becomes covered by a thin layer
of skin, and scar tissue forms. The scar is rhe umbilicus
(navel).
Pharmaceutical companies use human placentas as a
source of hormones, drugs, and blood: portions of placentas
are also used lor burn coverage. The placental and umbilical
cord veins can also be used in blood vessel grafts, and cord
blood can be frozen lo provide a future source af'.piuripotejlt
stem cells, for example, CO repopulate red bone marrow fol-
lowing radiotherapy for cancer
m some cases, the entire placenta or part of it may become
implanted in the inferior portion of die uterus, near or
covering the cervix. This condition is called placenta pre-
■■ : : TKI. vc-a tie fore or m Iront of), Although placenta
previa may lead to spontaneous abortion, it also occurs in
approximately I in 250 live births. It is dangerous to the
ictus because it may cause premature birth and intrauter-
ine hypoxia due to maternal bleeding, Maternal mortality
is increased (\\.\c to hemorrhage and infection. The must
important symptom is Midden, painless, bright-red vaginal
bleeding in the third trimester. Cesarean section is the
preferred method of delivery in placenta pre\ ia.
Figure 24.7 Development of the chorionic villi.
A.^ Blood vessels in the chorionic villi connect lo Ihe embryonic
heart via the umbilical arteries and umbilical vein.
S,
Amniotic cavity
Embryo
Yolk sac
Blood capillary
n chorionic vliltis
Umbilical vein
Umbilical
artories
Intervillous
space
Connecting
stalk
Chorionic villus
MatemaJ blood
Frontal section through uterus showing an embryo and
its vascular supply, about 21 days after lertilrzaiion
Why is development of the chorionic villi Important?
Fourth Through Eighth Weeks of
Development
The fourth through eighth weeks of development atteSJ
significant in embryonic development because all major
gang appear during this time. By the end ol the eighth m
all the maior body- systems have begun to develop, altlloilj
their functions lor the most part are minima!.
During rhe fourth week after fertilization, theembr
dergoes dramatic changes in shape and size, nearly tripling in
size. It is essentially converted from a flat, two-diinensiuni]
trilaminar, embryonic disc to a three-dimensional cylinder, a'J
process calico 1 embryonic folding.
Ihe Inst distiiiLruishiihlc structures are those in lite head
area. The first sign of a developing ear is a thickened are
ectoderm, the otic placode (future internal ear), which i
distinguished about 22 days alter fertilization (see Figond
% "The eyes also begin their development about 21
after fertilization. This is evidenced by a thickened m
ectoderm ca lied the lens placode (see I \ ).
By the middle of the fourth week, the upper limbs Ctiffl
their development as outgrowths of mesoderm cover©
ectoderm called upper limb buds (see figure M.'\\ il). I.
end of t lie fourth week, the lower limb buds develop. Tire
heart ,\\s<> forms a distinct projection on the ventral suri n
the embryo called th e heart prominence (see I iiiun 'A »cj
tail is also a distinguishing feature of an embryo at the c
the fourth week (see I i ■•.
During die fifth week of development, there is
rapid development of the brain, so growth of die head is con-
Embryonic Period 595 j
Figure 24.8 Placenta and umbilical cord.
The placenta is formed by the chorionic villi of the embryo and part of the endometrium of the mother,
Amniotic
fluid in
amniotic
cavily
Endometrium Chorion
(maternal portion (fetal portion
of placenta) ol placenta)
Chorionic
villi
Malernat
endometrial
venule
Intervillous
space
containing
maternal blood
Maternal
endometrial
arteriole
Fetal
blood
vessels
Umbilical cord'
Umbilical
arteries
Umbilical
vein
Mucous
connective
tissue*
Amnion
Umbilical cord
(a) Details of placenta and umbilical cord
Umbilical vBins
Umbilical arteries Amnion covering letal surface ol placenta
(b) Fetal aspect of placenta
What is the function of the placenta?
treble. By the end of the sixth week, die bead grows even
relative to the trunk, and the limbs show substantia] de-
ip . In addition, the neck and mink begin to steaighteni,
heart is now four-chambered. By the seventh week, die
(ions regions of the limbs become distinct and the begin-
ning of digits appear (see Figure 2 1 "a At the sun of tfog
irhth week, the final week of the embryonic period, the digits
of the hands are short antl webbed aftd the tail is still visible,
but shorter. In addition, the eyes are open and die auricles oi
the cars arc visible. Bj the end of the eighth week, all regions
of the limbs are apparent and the digits are distinct and no
longer webbed. Also, the eyelids come together and m;iv ft&s-e,
die tail disappears, and die external genitals begin to differen-
tiate. The embryo now has clearly human eharacieris'iL s,
596 Chapter 24 Development and Inheritance
■ CHECKPOINT
6. Mow do the three prirrtviry jjenn layers 1<»nn"- Why are
they important?
7. Describe how nc urn I at ion occurs. Why is it significant?
8. How does the placenta form and what is its Function?
9. Why are the second through fourth weeks of develop-
ment SO crucial?
10. V\ hiit changes occur in the limbs during the seeonii half
oi ihe embryonic pern I
FETAL PERIOD
OBJECTIVE • Define the fetal period and outline
major events.
During the Fetal period, tissues and organs that developed
during the cjnhruuiie period ;jrow ;uul difFercntiure. Vera
few new structures appear during rhe Fetal period, but the
rate of body growth is remarkable, especially during the
second half of intrauterine life, lor example, during the
Table 24.1 Summary of Changes During Embryonic and Fetal Development
Time
Approximate Size
and Weight
Representative Changes
Embryonic Period
1 -4 weeks
5-8 weeks
Fetal Period
9-12 weeks
13-16 weeks
17-20 weeks
21-25 weeks
26-29 weeks
30-34 weeks
35-38 weeks
0.6 cm (3/16 in.)
3 cm (1 .25 in.)
1 g (1/30 oz)
Primary germ layers and notochord develop. Neurulation occurs. Brain development beams.
Blood vessel formation begins and blood forms in yolk sac, allantois, and chorion.
Heart forms and begins to beat. Chorionic villi develop and placental formation begins. The
embryo folds. The primitive gut and limb buds develop, Eyes and ears begin to develou
forms, and body syslems begin to form.
Brain development continues. Limbs become more distinct and digits appear.
Heart becomes four-chambered. Eyes are far apart and eyelids are fused. Nose develop? and
is fiat. Face is more human-like. Ossification begins. Blood cells start to form in liver. External
genitals begin to differentiate. Tail disappears. Mafor blood vessels form. Many internal organs
continue to develop.
7.5 cm (3 in.)
30 g (102)
18 cm {6.5-7 in.)
100g(4oz)
25-30 em (10-12 in.)
200-450 g (0.5-1 lb)
27-35 cm (11 -14 in.)
550-800 g (1.25-1,5 lb)
32-42 cm (13-17 in)
1110-1350 g (2.5-3 lb)
41 -45 cm (16.5-18 in.)
2000-2300 g (4.5-5 lb)
50 cm (20 In.)
3200-3400 g (7-7.5 lb)
Head constitutes about naif the length of the fetal body, and fetal length nearly doubles. R-
continues to enlarge. Face is broad, with eyes fully developed, closed, and widely separated.
Nose develops a bridge. External ears develop and are low set. Ossification continues. Upper
limbs almost reach final relative length but lower limbs are not quite as well developed. Heart-
beat can be detected. Gender Is distinguishable from external genitals. Urine secreted byteius
is added lo amniotic fluid. Red bono marrow, thymus, and spleen participate in blood cell forma-
tion. Fetus begins to move, but its movements cannot be felt yat by the mother. Body systems
continue to develop.
Head is relatively smaller than rest of body. Eyes move medially to their final positions, and ears
move to their final positions on the sides of Ihe head, Lower limbs lengthen. Fetus appear* - .
more humanlike Rapid development of body systems occurs.
Head i3 more proportionate to rest of body. Eyebrows and head hair are visible. Growth skws
but tower limbs continue to lengthen, Veipix caseosa (fatty secretions of sebaceous glands ana
dead epithelial cells) and lanugo (delicate fetal hair) cover fetus Brown fat lorms and Is thi-
of heat production. Fetal movements are commonly felt by mother (quickening).
Head becomes even mora proportionate lo rest of body. Weight gain is substarillal, and skin is
pink and wrinkled, By 24 weeks, lung cells begin to produce surfactant.
Head and body are more proportionate and eyes are open. Toenails are visible. Body lai is 3:1
of total body mass and additional subcutaneous fat smoothes out some wrinkles. Testes bogfn
to descend toward scrotum at 28 to 32 weeks. Red bona marrow is major site of blood cell
production. Many fetuses born prematurely during this period survive if given intensive care
because lungs can provide adequate veniilation and central nervous system is developed
sufficiently to control breathing and body temperature.
Skin is pink and smooth. Fetus assumes upside down position. Pupillary reflex is present by
30 weeks. Body fat is 8% of total body mass, Fetuses 33 weeks and older usually survive
born prematurely.
By 38 weeks, circumference of fetal abdomen is greater than that of head. Skin Is usually
bluish-pink, and growth slows as birth approaches. Body fat is 16% of total body mass. Testes
are usually in scrotum In full-term male infants. Even afterbirth, an infant Is not completely
developed; an additional year is required, especially for complete development of Ihe nervous
system.
last two and one hall' months of intrauterine life, half of the
full-term weight is added- \t the beginning of the Feint pe-
rioi.l, the head is half the length of the body. By the tm\ of
ill; Fetal period, the head size is unly one-quarter ilie
length of the body. During the same period, the fetal limbs
Kfeo increase in size from one-eighth to one-hall the fetal
fength. The fetus is also less vulnerable 10 the damaging ef-
fects ;-i drugs, radiation, and microbes rhan it was as an
BTtbryo.
Fetal Period 597
A summary of the m:ijor developmental events of the em-
bryonic and feral period is presented in Ihble 2 II and illus-
trated in i - i
■ CHECKPOINT
11. What are 1 the general developmental trends during the
fetal period?
12, Using rafale _4. 1 as a guide, select any one body stnit
tore in weeks 9 through 12 anil trace il.s development
through the remainder of the feral period.
598 Chapter 24 Development and Inheritance
Figure 24.9 Summary of representative developmental events of the embryonic and fetal periods.
The embryos and fetuses are nof shown al their actual sizes.
t*
Development during the fetal period is mostly concerned With the growth and differentiation of tissues and
organs lormed during the embryonic period.
Cut edge
of amnion
Yolk sac
(a; 20-day embryo
(c) 32 -day embryo
Neural
plate
Neural
UK...HV.
Lens placode
Heart prominence
Upper limb bud
Tail
Lower limb bud
(b) 24-day embryo
(d) 44-day embryo
Developing
brain
Heart
prominence
Developing
spinal cord
Otic placode-
Developing i
Upper limb
Lower limb
Umbilici!.
Fetal Period 599 j
Umbilical Lower
cord limb
— Yolk sac
Umbilical
cord
placenta
(e) 52-day embryo
(t) Ten-week fetus
Mouth
Upper
limb
Lower
limb
(g) Thirteen-week fetus
.(h) Twenly-six-week fetus
How does mid-fetal weight compare to end-fetal weight?
600 Chapter 24 Development and Inheritance
MATERNAL CHANGES
DURING PREGNANCY
OBJECTIVES • Describe the sources and functions of
the hormones secreted during pregnancy.
o Describe the hormonal, anatomical, and physiological
changes in the mother during pregnancy.
Hormones of Pregnancy
During die fbst 3 co 4 months of pregnancy, the corpus
luteum in the ovary continues In secrete progesterone and
estrogens, which maintain die lining of die uterus during preg-
nancy and prepare the mammary glands to secrete milk. The
amounts secreted by the corpus luteuin, however, are only
slightly more than those produced alter ovulation in a normal
menstrual cycle. From the third month through the remain-
der of the pregnancy, the placenta itself provides the high
levels of progesterone and estrogens required. The chorion
secretes human chorionic gonadotropin (hCG) into the
1 1. In turn f hCG stimulates the corpus Inteum to con-
tinue production of progesterone and estrogens — -an activity
required CO prevent menstruation ami for the continued at-
tachment of the embryo md fetus to the lining of the uterus.
By the eighth day alter Fertilization, hCG can he detected in
the blood and urine of a pregnant woman. Peak secretion of
hCG occurs at about the ninth week of pregnancy. During
i he fourth and filth months the hCG level decreases sharply
and then levels off until childbirth.
The chorion begins to secrete estrogens alter the first 3
to 4 weeks of pregnancy and progesterone by the sixth week.
These hormones are secreted in increasing quantities until
the rime of birth. From the third month to the ninth month,
the placenta supplies the levels of progesterone and estrogens
and progesterone needed to maintain the pregnancy. t\ high
level of i progesterone ensures Chat the uterine myometrium is
relaxed and that the cervix is tightly closed. After delivery, es-
trogens and progesterone in the blood decrease to normal
levels.
Rehtxin, n hormone produced first by the corpus luteum
of the ovary and later by die placenta, increases the flexibility
of the pubic symphysis and ligaments of the Sacroiliac and
sacrococcygeal joints and helps dilate the uterine cervix dur-
ing labor. Both of these actions ease deliverv of the baby.
\ third hormone produced by the chorion of the pla-
centa is human placental lactogen (hPL), The rate QJ secre-
tion of hPL increases in proportion to placental mass, reach-
ing maximum levels after 32 weeks and remaining relatively
constant after that. It is thought to help prepare the mam-
mary glands lor lactation, enhance maternal growth f»\ in-
creasing protein synthesis, and regulate certain aspects of
metabolism in the mother and fetus.
The hormone most recently found to be produced h\
placenta is corticotropin-relcarinir hormone (CRH), which in
nonpregnant people is secreted only by the hypothalamus
Ckl l is now thought to he part of the "clock" that establishd
the timing of birth. Women who have higher levels ofCRH
earlier in pregnancy are more likely to deliver prematurely]
those who have low levels are more likely to deliver after CM
due date. CRH from the placenta has a second important cfi
feet: It increases secretion of Cortisol, which is needed for
maturation of the fetal lungs and the production of surfactants
Early pregnancy tests detect tin nott ills of human
chorionic gonadotropin (h(Xi) in the urine that begin to
be excreted about 8 Jays after fertilization. The test
can detect pregnancy as early as the first day of a missed
menstrual period — that is. at about 14 clays alter lerttli i
rion. Chemicals in the kits produce a color change if a re-
action occurs between hC(i in the urine and hCXJ anti-
bodies included in the kit.
Changes During Pregnancy
By about the end of die third month of pregnancy, the uterus
occupies most of the pelvic cavity. \s the Ictus continues to
grow, the uterus extends higher into the abdominal cavils
Toward the end of a full-term pregnancy, the uterus H
most the entire abdominal cavity, reaching almost to th
xiphoid process of the sternum. It pushes the maternal in-
testines, liver, and stomach superiorly, elevates the dia^
phragm, and widens the thoracic cavity.
Changes in the. skin during pregnancy are more apparent
in some women than in others. Included are increased pig-
mentation around the eyes and cheekbones in a masklikt pa
tern, in the areolae of the breasts, and in the lower abdomen
Striae (stretch marks) over the abdomen can occur .is rlic
uterus enlarges, and hair loss increases. Pregnancy -indue
physiological changes include weight gam due to the fetus,
amniotic fluid, the placenta, uterine enlargement, and in-
creased total bod)' water; increased storage of proteins,
triglycerides, and minerals; marked breast enlargement m
preparation for lactation; and lower back pain due to lordosis.
Several changes occur in the maternal cardiovascular sys-
tem. Stroke volume increases by about >0% and cardia<
put rises by 20-30% due to increased maternal blood iW i.
the placenta and increased metabolism. Heart rate iiu
It)- 1 5% and blood volume increases 30-50%. most A
ing the second half ol pregnancy. These increases are rini-.-
sai v, to meet the additional demands of the fetus for mm
and oxygen.
Pulmonary function is also altered during pregnancy
meet the added oxygen demands of the fetus. Tidal voS
can increase by 30 — K)%, expiratory reserve volume cu
Labor and Delivery 601
reduced by up to 40%, minute ventilation (the total volume
of nir inhaled and exhaled each minute) can increase In up EO
and total body oxygen consumption can increase by
about 10-20%. Dyspnea (difficult breathing) also occurs as
i expanding uterus pushes on the diaphragm.
With regard to the gastrointestinal tract, pregnant
women experience an increase in appetite. Pressure on [he
■i .rich may force the stomach contents superiorly into the
:'«>('■ hagus, resulting in heartburn. A general decrease in Cil
tract motility can cause constipation, delay gastric emptying
rime, and produce nausea, vomiting, and heartburn. Pressure
on the urinary bladder by the enlarging uterus can produce
urinary symptoms, such as increased frequency and urgency
of urination, and stress incontinence,
Changes in the reproductive system include edema and
ed blood How to die vagina. The uterus increases from
its nonpregnant mass oi 60-80 g to 900-1200 g at term bc-
icmise of increased numbers of muscle fibers in the my-
cmetrium in early pregnane)' and enlargement of muscle
1 rs dining the second Dm] third trimesters.
I CHECKPOINT
13. list the hormones involved in pregnancy, and describe
the (auctions of each.
14. What Structural and functional changes occur in die
mother during pregnancy?
t
EXERCISE AND PREGNANCY
OBJECTIVE * Explain the effects of pregnancy on
exercise and of exercise on pregnancy.
[Only a few changes in early pregnancy affect exercise. A
bregnant woman may tire more easily than usual, or innrn-
ickness (nausea and sometimes vomiting) may inter-
fere with regular exercise. As the pregnancy progresses,
lit rs gained and posture changes, so more energy is
fieeded to perform activities, and certain maneuvers (sud-
jjen stopping, changes m direction, rapid movements) are
metre difficult to execute. In addition, certain joints, espe-
cially the pubic symphysis, become less stable in response
1 10 the increased level of the hormone relaxin. As comperi-
toUion. many mothers-to-be walk with widely spread legs
fliul a shuffling motion.
Although blood shifts From viscera (including the uterus)
ItDthe muscles and skin during exercise, there is no evidence
of inadequate blood How to die placenta. The heat generated
Poring exercise may cause dehydration and further increase
btnly temperature. During early pregnancy especially, exces-
: exercise and heat buildup should be avoided because ele-
i:<:ii body temperature has been implicated in neural tube
delects. I'.xercise has no known cilect on lactation, provided a
woman remains hydra ted and wears a bra that provides good
support. Overall, moderate physical activity does not endan-
ger the fetus of a healthy woman who has a normal pregnancy.
Among the benefits of exercise to the mother during
pregnancy are a greater sense of well-being and fewer minor
complaints,
■ CHECKPOINT
15- 1 low do changes during ear!) and late pregnancy affect
the ability to exercise"'
LA BOR AND D E LIVERY
OBJECTIVE « Explain the events associated with the
three stages of labor.
Lab/Or is the process by which the fetus is expelled from the
uterus through the vagina. Ptirtitriiion (par'-ioor-LSH-im;
pannrit- = childbirth) also means giving birth.
Progesterone inhibits uterine contractions. Toward the
end of pregnancy, the levels of estrogens in the mother's
blodd rise sharply, producing changes that overcome the in-
hibiting effects of progesterone. Estrogens also stimulate the
placenta to release prostaglandins. Prostaglandins induce
production of enzymes that digest collagen libera in. the
Cervix, causing it to soften. High levels ol "estrogens cause
uterine muscle libers to display receptors for oxytocin, the
hormone that stimulates uterine contractions. Relaxin assists
by increasing the flexibility of the pubic symphysis ami help-
ing dilate the uterine cervix.
The control of labor contractions occurs via a positive
feedback cycle. Uterine contractions force the babys head or
body into the uterine cervix, which Stretches the cervix. This
stimulates stretch receptors in the cervix to send nerve im-
pulses to the hypothalamus, causing it to release oxytocin.
Oxytocin stimulates more forceful uterine contractions.
which stretches the cervix more, and promotes secretion of
more oxytocin. The positive feedback system is broken with
the birth of the infant, which decreases stretching of the
cervix.
Uterine contractions occur in waves (quite similar to
peristaltic waves) that start at the top of the uterus and move
downward, eventually expelling the fetus. True labor begins
when uterine contractions occur at regular intervals, usually
producing pain. As the interval between contractions short-
ens, the contractions intensity. Another sj mptoin of true ta-
bor in some- women is localization of pain in the hack thai is
intensified by walking. The reliable indicator of true labor is
dilation of the cervix and die- "show." a discharge ol a blood-
containing mucus that appears in the cervical canal during la-
602 Chapter 24 Development and Inheritance
bor. \n false labor, pain is fck mi the- abdomen at irregular in-
tervals, bin n does not intensify and walking does riot alter n
significantly. There t£ no "show" and no cervical dilation.
True labor can be dfa ided into three stages;
1. Stage of dilation. The time from the onset of labor to
the complete dilation ol the cervix is the stage of
dilation. This stage, which typically lasts 6-12 hours,
features regular contractions of the uterus, usually a
rupturing ofthe amniotic sac, and complete dilation (to
IQ cm) of the cervix. It" the amniotic s;ic does not rupture
spontaneously, it is ruptured intentionally.
2. Stage of expulsion. The time (10 minutes ro several
hours) from complete cervical dilation to delivery of the
baby is the stage of expulsion.
3. Placental stage. The time (5-30 minutes or more) after
ili livery until the placenta or "afterbirth" is expelled by
powerful uterine connections is the placental stage.
These contractions also constrict blood vessels that were
torn during delivery, thereby reducing the likelihood of
hemorrhage.
As n rule, labor lasts longer with first babies, typically
about 14 hours. For women who have previously given birth,
the avei age duration ol labor is about 8 hours — although the
time varies enormously among births.
Delivery of :i physiologically immature bain Carries
certain risks. A premature infant or "preemie" is generally
considered a baby who weighs less than 2500 g (5.5 lb) at
birth. Poor prenatal care, drug abuse, history of a previous
premature delivery, and mother's age below \6 or above 3 5
increase the chance of premature delivery. The body of a
premature infani is not yei ready ro susrnin some critical
functions, and thus its survival is uncertain without medical
intervention. The major problem after delivery of an infant
under 36 weeks of gestation is respiratory distress syn-
drome (RDS) of the newborn due to insufficient surfactant.
RiJS can be eased by use of artificial surfactant and a venti-
lator that delivers oxygen until the lungs can operate on
their own.
About 7% of pregnant women do not deliver by 2 weeks
after their due date. Such infants are called post term babies or
post, date hbies. They curry an increased risk of brain damage
to the fetus, and even fetal death, due to inadequate supplies
of oxygen and nutrients from an aging placenta. Post-terro
deliveries may be facilitated by inducing labor, initiated bv
administration oJ oxytocin (Pitocin®), or by surgical delivery
i can section).
hollowing the deliver) of the baby and placenta is a 6-\veek
period during which the in.itcrn.il reproductive organs and
physiology return to the prepregnancy state. This period is
called die paerperiuin (pu'-er- I'KR-e-um).
Dystocia (dis-T()-se.-a; ays- = painful or difficult; iw- ■
birth), or difficult labor, may result either from an a
mal position (presentation) of the fetus or a birth c.malnf
inadequate size to permit vaginal deliver),'. In a breech
presentation, for example, the fetal buttocks ui
is, rather than the head, enter the birth canal lit
occurs most often in premature births- If fetal or maierna]
distress prevents a vaginal birth, the baby may lit 1 deli'
surgically through an abdominal incision. V low, ho
tal cut is made through the abdominal wall and low,;
tion of the uterus, through which the baby and placenta
are removed. Even though it is popularly assoi
the birth of Julius Caesar, the true reason this p
termed a cesarean section (C-section) is becnust
described in Roman Law, lex uesana, about 600 years be-
fore Julius Caesar was born. Even a history of ttiultlj
sections need not exclude a pregnant woman from .it-
tempting a vaginal delivery.
■ CHECKPOINT
16. What hormonal changes induce labor?
17. What happens during the stage of dilation, ilk
expulsion, and the placental stage of true labor?
LACTATION
OBJECTIVE • DisCUSS
lactation.
die hormonal control uf
iMctation (lak'-TA-shun; imt- = milk) is the product
ejection of milk from the mammary glands. A principal hql
mane in promoting milk production is prolactin iPHL),
which is secreted from the anterior piruiturv idanil. Etw
though prolactin levels increase as the pregnancy pi
no milk production occurs because progesterone inhibit
effects of prolactin. After delivery, the levels of progi
and estrogens in the mothers blood decrease, mid the nihil*
tion is removed. The principal stimulus in mainuiimng pro-
lactin production during lactation is die sucking action of d
infant Suckling initiates nerve impulses from stretch reed
tors in the nipples to the hypothalamus, and more prolaEffl
is released by the anterior [limitary.
Oxytocin causes the release of milk into the iiiumnwJ
ducts. Milk forme* I by the glandular cells of the keaitf 9
stored until die baby begins active suckling. Stimulation ■
touch receptors in the nipple initiates sensnn nerve tmpuld
mat are relayed to die hypothalamus. In response, sccreD'qJj
•wtoein from the posterior pituitary increases.
Lactation 603
Breast
Nature's Approach to
Infection Prevention
Physicians in both industrialized and
developing countries Slave long observed
thai breast-fed babies contract fewer in-
fections than da babies ted formula.
Mis difference is tint--, in pan, Co ;i num-
il ingredients in breast milk that en-
bnce .in infant's ability eo fight disease,
i 'liner iinri bodies and some immune
Beeping the Trad Intact '.
?r Attack
Several substances in breast milk en-
Sjiance immunity in the baby's gastroin-
|i -uruil {('At tract. One family of these
ij I-, :iit wtrtr/ry hmimntiglobiilm A (IgA)
odies. When the baby's mother
unlets pathogens, she manufac-
tures antibodies specific to each one.
he antibodies pass into her breast
Ulk and escape breakdown in the
iak's GI tract because thev are pro-
i.l b\ the so-called secreton com-
loneru. Once in the bain's (il tract,
the antibodies bind with the targeted
infectious agents ,um\ prevent them
i passing- through the lining ot the
met. This protection is especially
irtatil in the earliest days ot' life,
uaause the infant does not beem to
make his or bur own secretary IgA im-
lil several weeks or months after birth.
The secretory tgA antibodies dis-
able pathogens without harming help-
ful GI tract flora or causing inllamma-
ti«»n. This is important because
although inlhnnination helps Ggfat
infection, sometimes the process over-
u helms the (il tract. An inlant may
suffer more from the inflammaton,
process than the infection itself when
inflammation destroys healthy tissue.
The targe quantities of the immune
system molecule infcrU'ttkin-IO found
in breast milk also help inhibit inflam-
mation. And a substance called ftinynea'm
enhances the phagocytic activity of
macrophages, inhibits inrlaminanon.
and helps repair tissues damaged by
inflammation.
Several other breast-in.il k mole-
cules help disable harmful microbes.
Mucins. certain oligosaccharides (sugar
chains), and glycoproteins (carbohy-
drate-protein compounds) bind to
microbes and prevent them from gain-
ing a foothold on the lining of the (il
tract. Al.an>' of breast milk's immune
cells, including T lymphocytes and
macrophages, attack invading microbes
directly.
Breast-milk compounds help in
other ways as Well, Some decrease the
supply of nutrients Mich as icon and
vitamin B|> needed by harmful bacte-
ria to survive. \ substance called /•/-
fidtts factor promotes the growth of
helpful gin flora, which help crowd
our pathogens, Rvthwic i/tvV/y, a group
ot vitamin \ precursors, reduce the
ability of viruses to replicate. And
some of the hormones and growth
factors present in breast milk stimu-
late the baby's GI craci to fiumm
more umekh. making it less vulnera-
ble to dangerous in\ adcrs.
► Thin
ii by dn yon think that preventing in feci ion through brtast-fetdhig is prefsr-
tthh- to giving babies antibiotics?
Oxytocin stimulates contraction of smooth-musclc-like
Els surrounding the glandular cells and ducts. The resi.ih
Compression moves the milk from the alveoli of the mammary
■jbfkK 'I'hu ilr.- mammary ducts, where it can be suckled.
During late pregnancy and the first few days after birth,
ie maiinii;ir\ glands secrete ;i cloudy fluid called colostrum
' >S-trum). Although it is not as nutritious as milk — -it
contains less lactose .in*l virtually no fat — colostrum serves ad-
unri'l the appearance oi true milk on about the fourth
mi olosirum and maternal milk contain important antibod-
I i protect the inlant during the first few months of life.
Lactation often blocks ovarian cycles for the first few
months following delivery, if the frequency of sucking is
abpUl 8- K) rimes a day. This effect is inconsistent, hov.
and ovulation commonly precedes the first menstrual period
after delivery of :i baby. As a result, the mother can never be
certain she is not fertile. Breast-feeding is therefore not a
very reliable birth control measure-
A pnmarv benefit of breast- feeding is nutritional: Hu-
man miik js a sterile solution that contains amounts oi lain
acids, lactose, amino acids, minerals, vitamins, and water that
are ideal for the kiln's digestion, Brain development, and
604 Chapter 24 Development and Inheritance
growth. Breast-feeding also benefits infants in oilier way., as
indicated in the 'Focus on Wellness on page 603,
Years before oxytocin was discovered, ir was common
practice in midwifery co let a first-born twin nurse at the
mother's breast to speed the birth of the second child, Now
we know why this practice is helpful — it stimulates the re-
lease of oxytocin. Ivcn after a single birth, nursing promotes
expulsion of the placenta (afterbirth) and helps the uterus re-
turn to its normal size. Synthetic oxytocin (Pitocirr : ) is often
riven to induce labor or to increase uterine tone and control
hemorrhage just alter parturition.
■ CHECKPOINT
18. Which hormones contribute to lactation? What is che
Junction (.if each?
INHERITANCE
OBJECTIVE * Define inheritance, and explain the
inheritance of dominant, recessive, and sex-linked
traits.
\s previously indicated, the genetic material of a father and a
mother unite when a sperm cell fuses with a secondary
oocyte to form a zygote. Children resemble their parents be-
cause they inherit traits passed down from both parents. We
now examine some of the principles involved m that process,
called inheritance.
Inheritance is the passage of hereditary traits from one
generation to the next. It is the process by winch yon acquired
your characteristics horn your parents and may transmit some
of your traits to your children. The branch of biology that
de. lis with inheritance is called genetics ( je-NT.T-iks). 7'he
area ul health care dial oilers advice on genetic problems (or
potential problems) is called frenetic counseling.
Genotype and Phenotype
'The nuclei ol all human cells except gametes contain 23 pairs
of chromosomes — the diploid number {In). One chromo-
some in each pair came from the mother, and the Other came
Iroin the father. Each botnoiog — one of the two chromo-
somes that make up a pair — contains genes that control the
same traits. If a chromosome contains a gene for bodv hair,
tor example, its homolog will also contain a gene lor body
hair in the -,:iuie position on the chromosome. Such alterna-
tive forms of a gene that code for the same trait and are at the
same location on homologous chromosomes arc called alleles
(ah-I.ELZ). For example, one allele of a body hair gene
might code for coarse hair, ami another allele for fine hair. A
mutation (uui -T A-shinv. tmitti- = change) is a permanent
heritable change in an allele that produces i different variant
of die same trait.
The relationship of genes to heredity is illustrated b]
ainining the alleles involved in a disorder called plienj/im
tonuria or PAT 7 . People with PKU lack phcii)
hydroxylase, an enzyme that com ens the amino n.i.l phenol
Ialanine into tyrosine, another ammo acid. IT infant
PKL' tat foods containing phenylalanine, high levels 9
phenylalanine build up in the blood. The result
brain damage and mental retardation. The allele that natifE
for phenylalanine hydroxylase is symbolized as P; Lrn
tared allele that fails to produce a functional cnzvttn
bolized as />. The chart in figure M.W, which shows the pd
sible combinations of gametes from two parents who encji
have one P and one p allele, is called a Punmtt xqu
constructing a Punnett square, the possible paternal .tlldcs.ini
sperm are written at the left side and the possible mm
alleles m ova (or secondan oocytes) are written at the
The tour spaces on the chart show how the alleles.
bine in zygotes formed by the union of these sperm arm
to produce the three different genetic makeups, o
(Jli-no-tipsi: pp, pp, or pp. Notice from the Punnetl
thai 25% of the offspring will have the PP ircnuu
will have the Pp genotype, and 25% will have the
type. People who iriherit PP or Pp genotypes do
PKU: those with a pp genotype suffer from the djsovdw
though people with a Pp genotype have one PKU allele]
the allele that codes for the normal trait [P] is mart! Jtiti
nam. An allele that dominates or masks die pi
oilier allele and is full) expressed (P in this example) issaidi
be a dominant allele, and the trait expressed is called a I
nam trait. 1 he allele whose presence is complete!) mask
in this example) is said to be a recessive allele, and the D
controls is called a recessive trait.
By tradition, the symbols lor genes are written in tt
with dominant alleles written in capital letters and rec
alleles in lowercase letters. \ person with the same dleliM
homologous chromosomes (for example, PP or pp)
be homozygous for the trail. PP is homozygous d
and/'/' is homozygous recessive. An individual with M
alleles on homologous chromosomes (for example, .
ro be- heterozygous for the trait.
Phenotype (IT-no-tip; pbeno- = showing) refer;
the genetic makeup is expressed in the body; it is the nhyn
cal or outward expression ol a gene. A person vnh
(a heterozygote) has a different genotype from a pet
PPU homozygote), but both have the same phertotypt— ro»
production of phenylalanine hydroxylase. Iletero/V! :i
viduals who earn, a recessive gene but do not expn
can pass the gene on to their offspring. Such ituliviti
called i v// v very of the recessive gene.
Alleles that code for normal traits do not always
nate over those that code for abnormal ones, hut don
alleles for severe disorders usually are lethal :m.\ est
Ol the embryo or fetus. One exception is Huntings
(HD), which is caused by a dominant allele thai doesnol
press itself until adulthood, both homozygous dominant]
Inheritance 605
Figure 24. 10 Inheritance of phenylketonuria (PKU).
, Genotype refers to genetic makeup; phenotype refers to the
physical or outward expression of a gene.
Homologous chromosomes
of heterozygous lather
Possible '
sperm
types
Miosis
II
Homologous chromosomes
of heterozygous mother
/ V
pp p P
Possible
ova types
Possible
genotypes
of zygotes
(in boxes)
Possible
genotypes
r> offspring
Possible
phenotypes
ol offspring
Punnetl square
\pp 2Pp ipp
Homozygous Heterozygous Homozygous
dominant
^PP
laminant
2Pp
Do not have PKU
Has PKU
A If parents have the genotypes shown here, what is the percent
I chance that their first child will have PKU? What is the chance of
PKU occurring in their second child?
us people exhibit the disease; homozygous reces-
re people are normal. I ID causes progressive degeneration
he nervous system and eventual death, but because symp-
...jcnllv do not appear until alter age 30 or 40, many
acd' indrvUtuals have already passed the allele for the
on to their children.
fn incomplete dominance, neither member oi an allelic
I is dominant over the other, and the hetcrozytgbte has a
i , intermediate between the homozygous donainami
Jie homozygous recessive phenotypes. An example ol m-
Bjfete dominance in humans is the inheritance of sickle-
Msease (SCO). People with the homozygous dominant
llh'Hlr 1 fbnn normal hemoglobin; those with the
■us recessive genotype HI^Hh' have sickle-cell dis-
icverc anemia. Although they arc usually healthy,
h the heterozygous genotype Hl> '/-//■ v have minor
... uh anemia because half their hemoglobin is nor-
n,j half is not. Heterozygotes are carriers, and the) arc
Jiahave mkle-ceU trait.
plough a single individual inherits only two alleles for
;. some genes may have more than two alternate
forms, and this is the basis for multiple-nitric inherit/nice.
One example of multiple- allele inheritance is the inheritance
of the ABO blood group. The lour blood types (phenotypes)
of the ABO group — \ R, AB, and O — result from the in-
heritance of Six combinations of three different alkies ol a
Single gene called the / gene: (1) allele I' produces the \ ami -
gen, (2) allele /" produces the B antigen, and ( >) allele r pro-
duces neither A nor B antigen. Each person inherits two J-
gene alleles, one from each parent, that give rise to the
various phenotypes. The six possible genotypes produce four
blood types, as fallows:
Genotype
l"! 11 or Pi
a
Blood lypeUMiem.tvpe)
B
At!
o
Notice that both /' and i !; are inherited as dominant
trails, and i is inherited as a recessive trait. An individual with
type \l' blood has characteristics of both type A and type B
red biodd cells.
Autosomes and Sex Chromosomes
When viewed under a ttiicroscQpe, the 46 human ohrorno-
somes in a normal somatie cell can be identdied by their si/.e,
shape, and staining' pattern tq be members of 23 different
pairs of chromosomes. In 22 of the pans, the homologous
chromosomes look alike and have the same Rppearancfi tn
both males and females; these 22 pairs are c:\Wci\antosoiiics.
The iw<> members of the 23d pair are termed the sex
chromosomes, they look different in males and leraafcs
(Figure 24.1 la). In females, the pair consists of two chromo-
somes called \ chromosomes. One X chroinosoBfle Is also
present m males, but its mate is a much smaller chromosome
called a Y chromosome.
When a spermatocele undergoes meiosis to retluce its
chromosome number, it gives rise to two sperm that contain
an X chromosome and two sperm that contain a V chromo-
some. Oocytes have no Y chromosomes and produce only X
containmii gametes. If the secondary oocyte is fertilised Bj
an X-beaHng sperm, the offspring normally is female (XX).
Fertilization by a Y-fieariiig sperm produces a male (XY).
I bus, an individuals SO is determined by the father's chro-
mosomes (Rgttrc 24.1lb). The prime male-determining
is one called SRY (sex-determining region oj the Y chromo-
some). XATacts as a switch to turn on the male pattern ol de-
velopment. Only if the NAM' gene is present and functional m
a fertilized ovum Will the fetus develop testes and dii'ferenti-
Bte into a male; in the absence of SRY, the fetus will develop
ovaries and differentiate into a female.
The Sex chromosomes also are responsible for the trans-
mission of several nonsexual traits. Many ol the genes for
Ehese traits are present on X chromosomes but are absent
606 Chapter 24 Development and Inheritance
Figure 24.11 Inheritance of gender (sex). In (a) the sex chro-
mosomes, pair 23. are indicated in the colored box.
Gender Is determined at the time of fertilization by the sex chro-
mosome of the sperm cell.
» "*J U ft fi » tt*
1 2 3 -1 5 6 7 6
H a Jr a u a a a
10 11 12 13 14 15
m W n aa w & x1*y
17 13 |9 20 21 22 23
I
(a) Normal human male chromosomes
XY
Sex chromosomes
of lather
/ \
x
Possible
sperm
types
Meiasis
XX
Sex chromosomes
of mother
/ \
Q ©
Possible
ova types
Possible sex
chromosomes of
zygotes (In boxes)
Possible gender
ol offspring
Punneti square
2 XX £XY
Females Males
(b) Sex determination
What are chromosomes other than sex chromosomes called?
horn V chromosomes. This feature produces a pattern ol
heredity, termed sex-linked inheritance, that is diffemnl
from Hit- patterns already described.
One example of sex-linked inheritance is red-green color
blindness, the most common type of color Umdness. This
condition is characterized In 2 deficiency in either red- or
green-sensitive cones, so red and green arc seen as the same
color (either red or given, depending on which cone is pre-
sent). The gene for red-green color bJJtaduess is a recessive
one designated c. Normal color vision, designated C, domi-
nates. The C/c genes are located only on the X chromosome,
and thus the ability tO see COlotS depends crilireh on the X
chromosomes. The possible combinations me as follows
Genot) pe Phertotype
Y'.Y Normal female
X' A' Normal female (Inn a carrier of the
recessive gene)
Y\ Reel greet] color-blind female
Y \ Normal imiL-
XY kid green color-htinJ male
Only females who have two V genes are red-
blind. This rare situation can result only from the mating od
color-blind male ;\\m} a color-blind or carrier female. (In \ V
females rhe trait is masked by the normal, dominam L!UUfl
Because males do nol have a second X chromosome ffifl
could mask the trait, all males with an X i>cnt; \ufl ln»
ra\- green color blind. Figure 24.1 1 illustrates the mhrnianq
of red-green color blindness in the offspring ol i imnnal
male and a carrier female. Traits inherited in the m
desei'i I >ed are ca I led sex-linked (rails. I lie un >st ei mimon ty|W
ol [hemophilia — a condition in which the blood Lni
clots very slowlj after an injury — is also a sex-linked .
■ CHECKPOINT
19. What do the terms genotype, phenotype, dominjmc
cessive, homozygous, and heterozygous mean}
20. Define incomplete dominance and give an example,
21. Whal is muhiple-allele inheritance 1 Give an
22. I low is the development ol gender detcmiinedi
23. Define and provide an example of sex-linked inheritaiKlj
Figure 24.12 An example of the inheritance of red-green
color blindness.
Mfe
Red-green color blindness and hemophilia are examples olse-
linked traits.
X-Y
Norrnal male
/ \
t 9
Possible
sperm
types
Meiosis
X X
Normal female who
carries recessive gene
/ \
^ ^
Possible
ova types
Possible
genotypes
ol zygotes
(in boxes)
Possible
phenotypos
ol offspring
Punnett square
tfx? xfx
Normal Normal
lemale female
(carrier)
X Y
Normal Color-blind
malB male
V
What is the genotype of a red-green color-blind female?
608 Chapter 24 Development and Inheritance
Cmiceptns (kon-SFI'-tus) Includes all structures that develop from a
zygote and includes an embryo plus die embryonic pan of the
placenta arid associated membranes (chorion, amnion, yolk sac,
and allantoic).
Ernests gravidarum (EM-e-sis yra-VID-ar-imv. cwco = to voimi,
yrttvhb - a pregnant woman) Episodes of ii;ilisi.:.i Slid possibly
. -iiiiting that are most likely to occur in die morning during
the ctrlv stages of pregnancy; also called morning sickness. Its
cause is unknown, but die high levels of human chorionic
tadotrctpin (h(."(i) secreted In ihe pl.ueisu. and of ptpgjss?
terone secreted by die ovaries, have been Implicated. Ln some
women the severity ol tfogse syroptsosas requires hospitalization
for intravenous feeding.
Fertilization age Two weeks less than die gestational age, Stride n
secondary nnnn 1 is not fertilized until about two weeks artier
die l.isi normal menstrual period (LN'MP).
Fetal alcohol syndrome (FAS) A Specific pattern of fetal ma I forma -
tion due tn inirauicrmc exposure to alcohol. | ; \S is one of die
most common causes of mental retardation and the most com-
mon preventable cause of birth detects in the I'nirtd States.
The symptoms of FAS may include slow growth before ami
after birth, characteristic facial features (short palpebral fissures,
a thin upper lip, and sunken nasal bridge), defective heart and
other organs, malformed limbs, genital abnormalities, and edi-
ted! nervous system damage- Ivchavioral problems, such as
hyperactivity, extreme nervousness, reduced ability to concen-
trate, and an inability to appreciate liiim. uul ..■fleet relation-
ships, are common.
Fetal surgery A surgical procedure performed on a fetus; in some
cases i he uterus is opened and die fetus is operated on directly;
Fetal surgery has been used to repair diaphragmatic hernias
and remove lesions in the lungs.
Fetal ultrasonography (til '-n ra-snn-( K ! -ra -ft) V prenatal diagnostic
procedure that uses ultrasound to confirm pregnancy, identify
multiple pregnancies, determine fetal age, evaluate fed
i i ihility and growth, determine fetal position, identify fetal*
maternal abnormalities, and assist in procedures such asaHiauj
eentesis.
Gestational age (jes- iA-shun-al; gestjitus = to bear) I Ik. aj
embryo or Ictus calculated from the presumed Erst dai >
last normal menstrua] period fLNMP).
Lethal gene (I. J*. -thai fen; letbmn = death) A gene that, whdtt|
expressed, results in death cither in the embryonic sin. . <
shortly alter birth,
MiUifemale syndrome A sex chromosome disorder characterised In
at least three X chromosome-- i.YWt diat occurs about
every 701) births. These females have Underdeveloped geniul
organs and limited fertility. Generally, they arc mental]
retarded.
Preeclampsia (prc-e-KLAMP-w-w) \ syndrome of pregnane) char-
acterized by Sudden hypertension, large amounts of pro*
urine, and generalized edema; possibl) related
autoimmune or allergic reaction to the presence iif .i fetdl
When the condition is also associated with convulsions -»ul
cinua, it is referred to as eclampsia.
Puerperal fever (puTT-pcr-al; pner - child) A maternal infe'em
disease of childbirth, also called puerperal sepsis and cliikllied
fe\er. The disease, which results from an infection origiiiitnl
in the birth canal, alleets the endometrium.. It may spread to
Other pelvic structures and lead to septicemia.
I'erattigeu (TLR-a-to-jen; temto- — monster, -gai - creatine) \nv
agent or influence thai causes developmental delects in the
embryo. Examples include alcohol, pesticides, industrial chemi- 1
eak anrilii.itKs, thalidomide, LSI), and cocaine.
DY OUTLII
Embryonic Period (p. 587)
1. Pregnancy is a sequence of events mat begins with fertilization
and proceeds to implantation, embryonic development, and fe-
tal development. It normally ends in birth.
2. During fertilization a sperm cell penetrate*; a secondary oocyte
and their nuclei unite. Penetration ol the KOlia pellucida is
facilitated by enzymes in the sperms acrosome. The resulting
cell is a zygote.
3>; Normally, onlj i imj sperm cell fertilizes a secondary one) te.
4. Early rapid cell division ol a zygote is called cleavage, arid the
cells produced hy cleavage arc called blastomeres. The solid
sphere of cells produced by cleavage is a morula.
5. The morula develops into a blastocyst, a hollow ball of cells
differentiated into a trophoblast and tin inner cell mass.
6. The attachment of a blastocyst to the endometrium is
implantation.
7. J he trophoblast develops into the syneyciotrophobl
cyiotrophoblast. both of which become part of die cJioriotJ
8. The inner cell mass differentiates into hypoblast and epibbj
ihe hi laminar (two-layered) embryonic disc
9. The amnion is a thin protective membrane that develops'
the cyiotitiphijlilasi.
10. The hypoblast forms ihe yolk sac, "Inch transfers nutric
the embryo, forms blood Cells, produces primordial gen |
and forms part of the gut.
11. Ml.iod and secretions enter lacunar networks to supply
tie hi to and remove wastes from ihe embryo.
I he extraembryonic mesoderm and iropholilast form the
chorion, the princip;il embryonic part of the placenta.
The third week ol development is characterized by g.istnilation.
inversion of the bflaminar disc inro a trilaminar (three- la v-
enetl) embryo consisting of ectoderm, mesoderm, and endoderm.
I he three primary germ Fayers form nil tissues and organs of
die developing organism.
Tin: process by which the neural plate, neur.il folds, and neural
tiihe form is called neurulat ion. [lie brain and spinal cord
develop Ji'om the neural tube.
Chorionic villi, projections of the chorion, eonnea to the
embryonic heart so that mafcertial and fetal blood vessels are
brought into close proximity. Thus, nutrients and Wastes arc
exchanged between maternal and fetal bloods
Pjacentauon refers ro formation ni the placenta, the site of
exchange of ntrerients and wastes between the pKither mi fe-
EOS. 1 he placenta also functions as a protective barrier. ■> i
nutrients, and produces several hormones to maintain preg-
nancy.
The actual connection between the placenta, and embryo (and
later the fetus) is the umbilical cord.
Ihe formation of body organs and systems occurs during the
tourth week ol development.
By the end of the fourth week, upper and lower limb buds de-
velop and l»y the end of the eighth week the embryo has clearly
human features.
Fetal Period (p. 596)
1. The lew! period is primarilj concerned with the growth .um]
differentiation of tissues mid organs thai developed during
embryonic period.
2. Hie rate oi body growth is remarkable, especial!) durinii the
ninrh and sixteenth weeks.
J. The principal changes associated with embryonic and fetal
i!i a re summarized in I i!T. M on pages 596 597.
Maternal Changes During Pregnancy {p. 600)
1. Pregnancy is maintained by human chorionic gonadotropin
1 1 'i X J), -,'■.! n igcns, and progesterone
2. Relaadn increases flexihility of the pubic symphysis ami helps
dilate the uterine cervix near the end of pregnancy.
1, Human placental lactogen (hPL) contributes to breast cleveIo|>'
mem, protein anabolism. and catabolism of glucose and l'ao\
acids.
f, OHticotropm-releasing hormone, produced by the plaeenta, is
thought to establish ihe timing of birth, and Stimulates the
tion ol Cortisol by the fetal adrenal gland
I During pregnane), several anatomical and physiological
changes occur in the mother.
Study Outline 609
Exercise and Pregnancy (p. 601)
1. During pregnancy, some fowJs l« ...in, less stable, and certain
maneuvers aft more difficult to execute.
2. Moderate physical activiu does n.,t endanger the reins in a
normal pregnant J
Labor and Delivery (p. 601)
1. Labor is the process by u hieh ihe fetus i, expelled from die uterus
through ihe vagina to die OUCHde. True l.ibor involves dilation of
the cervix, expulsion oftiu- fetus, and deliver; of die placenta,
2. Oxytocin stimulates uterine contractions.
Lactation (p. 602)
1. Lactation refers to the production and ejection of milk by the
mammary glands.
Milk product-ion is influenced by prolactin (PR3 i estrogens,
and progesterone,
Millc erection is stimulated by oxytocin.
A few of the many benefits of breast-feeding include ideal
nutrition for the infant, protection from disease, and decreased
likelihood ol devel oping allergies.
Inheritance (p. 604)
1. Inheritance is the passage of hereditary traits from one genera-
tion to ihe i
2. 1 he genetic: makeup of an Organism is called its genotype; the
u.nts expressed are called its phenotypc.
3. Dominant genes control a particular trait; expression oi' reces-
sive genes i* masked by douunam genes.
fo incomplete dominance, neither member of an allelic pair
dominates} phemuypieally, the betcrozygote is intermediate
between the homozygous dominant and the homozygous
recessive. An example is sickle-cell disease.
In miilliple-allele inheritance, genes have more than two alterna-
tive forms. \n example is the Inheritance: oi AIM } blood groups,
bach somatic ecl! has 46 chromosomes — 22 pairs of autosomes
and 1 pair of sex chromosomes.
in females, the sex chromosomes are two X chromosomes; m
males, they are one X chromosome and :i much smaller Y dim
inosotne, which normally includes the prime malc-detcniibing
ge lie. called .S'AT.
II die iSWgenc is present and functional rn a fertilized ovum,
the Ictus will develop lestcs and differentiate tflflO.iR male. In the
absence of Sh>)\ the ictus mil develop ovaries .md differentiate
into a female.
Red-green color blindness and beinopiuli.i result from M i .
sivt genes locatecl on the X chromosome. They arc se\-lmU:..l
traits that occur primarik in Cnafcs because of the absence ol
amy counterbalancing dominant g( u >l,r V ,|„ „„■
L
5.
6.
7.
8,
'■>.