Anatomy & Physiology

1065 Pages·2016·82.086 MB·English

Sixth Edition
Anatomy &
Physiology
Elaine N. Marieb
Katja Hoehn
Brief Contents
UNIT 1 Organization of the Body UNIT 4 Maintenance of the Body
1 16
The Human Body: An Orientation 1 Blood 554
2 17
Chemistry Comes Alive 19 The Cardiovascular System: The Heart 579
3 18
Cells: The Living Units 54 The Cardiovascular System:
4 Blood Vessels 608
Tissue: The Living Fabric 105
19
The Lymphatic System and Lymphoid
Organs and Tissues 661
UNIT 2 Covering, Support, and Movement of the Body 20
The Immune System:
Innate and Adaptive Body Defenses 672
5
The Integumentary System 134 21
The Respiratory System 705
6
Bones and Skeletal Tissues 152 22
The Digestive System 746
7
The Skeleton 174 23
Nutrition, Metabolism, and Energy
8
Joints 220 Balance 795
9 Muscles and Muscle Tissue 244 24 The Urinary System 834
10 The Muscular System 281 25 Fluid, Electrolyte, and Acid-Base
Balance 866
UNIT 3 Regulation and Integration of the Body
UNIT 5 Continuity
11
Fundamentals of the Nervous System 26
The Reproductive System 888
and Nervous Tissue 345
12
The Central Nervous System 382
13
The Peripheral Nervous System
and Reflex Activity 431
14
The Autonomic Nervous System 504
15
The Endocrine System 521
A00_MARI6415_10_SE_FES.indd 1 14/09/15 9:10 AM
ELAINE MARIEB
is the
most trusted name in all of
A&P. More than 3 million
health care professionals
started their careers with
one of Elaine Marieb’s
Anatomy & Physiology texts.

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LEARN WHY THIS MATTERS
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Matters videos describe how the
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A01_MARI6415_10_SE_FM_i-xix.indd 1 07/10/15 3:30 PM
SEE WHERE YOU ARE HEADED
NEW! Key concept organization presents the material in manageable chunks and helps
you easily navigate the chapter. Each section header states the key concept of that section.
5 why this
The Integumentary
System
matters
<<<
W
Overview of ould you be enticed by an ad for a coat that is waterproof,
Key ConCepTS stretchable, washable, and air-conditioned, that automati-
Key Concepts cally repairs small cuts, rips, and burns? How about one that’s
guaranteed to last a lifetime? Sounds too good to be true, but you
5.1 The skin consists of two layers: the epidermis and already have such a coat—your skin.
dermis 134 The skin and its derivatives (sweat and oil glands, hairs, and nails)
make up a complex set of organs that serves several functions, mostly
5.2 The epidermis is a keratinized stratified squamous protective. Together, these organs form the integumentary system
epithelium 135 (in-teg″u-men′tar-e).
Key Concept 5.3 The dermis consists of papillary and reticular
layers 138 5.1 The skin consists of two layers: the
section header epidermis and dermis
5.4 Melanin, carotene, and hemoglobin determine
skin color 140 Learning Objective
List the two layers of skin and briefly describe subcutaneous
5.5 Hair consists of dead, keratinized cells 141 tissue.
The skin receives little respect from its inhabitants, but architectur-
5.6 Nails are scale-like modifications of the ally it is a marvel. It covers the entire body, has a surface area of 1.2
epidermis 144
to 2.2 square meters, weighs 4 to 5 kilograms (4–5 kg = 9–11 lb),
and accounts for about 7% of total body weight in the average adult. Also
5.7 Sweat glands help control body temperature, and called the integument (“covering”), the skin multitasks. Its functions go
sebaceous glands secrete sebum 144
well beyond serving as a bag for body contents. Pliable yet tough, it takes
constant punishment from external agents. Without our skin, we would
5.8 First and foremost, the skin is a barrier 146 quickly fall prey to bacteria and perish from water and heat loss.
Varying in thickness from 1.5 to 4.0 millimeters (mm) or more in
5.9 Skin cancer and burns are major challenges to the different parts of the body, the skin is composed of two distinct layers
body 148
(Figure 5.1):
● The epidermis (ep″ĭ-der′mis), composed of epithelial cells, is the outer-
most protective shield of the body (epi = upon).
● The underlying dermis, making up the bulk of the skin, is a tough,
leathery layer composed mostly of dense connective tissue.
Only the dermis is vascularized. Nutrients reach the epidermis by
diffusing through the tissue fluid from blood vessels in the dermis.
The variation in skin tone shown here is primarily due to
varying concentrations of the pigment melanin.
<
134
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SEE WHERE YOU ARE HEADED
Check Your Understanding questions end each section and allow you to assess
your understanding of the concept before moving on.
Chapter 5 The Integumentary System 151
Hair shaft
Dermal papillae
Epidermis
Subpapillary
Papillary plexus
layer
Sweat pore
Appendages of skin
Dermis Reticular • Eccrine sweat gland
layer • Arrector pili muscle
• Sebaceous (oil) gland
5
• Hair follicle
• Hair root
Hypodermis
(subcutaneous
tissue; not part
of skin)
Nervous structures
• Sensory nerve fiber
with free nerve endings Cutaneous plexus
• Lamellar corpuscle
• Hair follicle receptor
(root hair plexus) Adipose tissue
Figure 5.1 Skin structure. Three-dimensional view of the skin and underlying subcutaneous
tissue. The epidermal and dermal layers have been pulled apart at the upper right corner to reveal
the dermal papillae.
and accounts for about 7% of total body weight in the average The subcutaneous tissue just deep to the skin is known as
adult. Also called the integument (“covering”), the skin multitasks. the hypodermis (Figure 5.1). Strictly speaking, the hypodermis
Its functions go well beyond serving as a bag for body contents. is not part of the skin, but it shares some of the skin’s protec-
Pliable yet tough, it takes constant punishment from external tive functions. The hypodermis, also called superficial fascia
agents. Without our skin, we would quickly fall prey to bacteria because it is superficial to the tough connective tissue wrapping
and perish from water and heat loss. (fascia) of the skeletal muscles, consists mostly of adipose tissue.
Varying in thickness from 1.5 to 4.0 millimeters (mm) or Besides storing fat, the hypodermis anchors the skin to the
more in different parts of the body, the skin is composed of two underlying structures (mostly to muscles), but loosely enough
distinct layers (Figure 5.1): that the skin can slide relatively freely over those structures.
● Thoutee rempidoestr mprios t(eecpt″ivĭ-ed sehri′emldi so)f, cthoem bpoodsye d(e opfi e=p iuthpeolnia)l. cells, is the Solffid oiunrg bskoidni epsr. oBteeccatsu uses obfy i etsn fsautrtyin cgo tmhapto msitainoyn ,b tlhoew hs yjupsotd ge<lramncies< <
also acts as a shock absorber and an insulator that reduces heat
● The underlying dermis, making up the bulk of the skin, is a loss. Check Your
tough, leathery layer composed mostly of dense connective
tissue. Check Your Understanding Understanding
Only the dermis is vascularized. Nutrients reach the epider- 1. Which layer of the skin—dermis or epidermis—is better
mis by diffusing through the tissue fluid from blood vessels in nourished? self-assessment
the dermis. For answers, see Answers Appendix.
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A01_MARI6415_10_SE_FM_i-xix.indd 3 07/10/15 3:30 PM
Chapter 10 The Muscular System 383
MUSCLE GALLERY
Table 10.17 (continued)
Adductors Hamstrings
Vastus
lateralis
(a)
Femur
Posterior compartment of thigh
Vastus
(flexes leg and extends thigh);
intermedius
innervated by tibial nerve (portion
of sciatic nerve)
10
Rectus femoris
Vastus medialis
(b)
Medial compartment of thigh
(adducts thigh); innervated by obturator nerve
Anterior compartment of thigh
(extends leg); innervated by femoral nerve
(a) Muscles of the thigh
Triceps surae
Key:
Fibula
Posterior
compartment
Fibularis
muscles
muscles
Anterior
compartment
muscles Chapter 22 The Digestive System 755
Medial
compartment
TOOLmuSscles o f thiTgh O HELP YOU P ost eri or OcompartmNent of legYOUR JOURNEY
and lateral
(plantar flexes foot, flexes toes);
compartment
innervated by tibial nerve
muscles of leg
Tongue
Tibialis
Teeth
Paroatind terior
gland
Lateral compartment of leg
Ducts of
NEW! Find study tools online with (prelafnetarr eflnexcees sa ntdo e vMeratss ftoeotr)i;ngA&P® in the book. Tibia
sublingual
Vgilasnitd MasteringA&P for self-study modiunnleesrv, aitnetde brya scutpiveerf Picaainraolitimd dautcitons, virtual lab tools,
fibular nerve
Masseter muscle
aFnrednu lmumore!
of tongue 464(b)< MuscUleNsI To f3 thRee lgeugBloadtyio onf manandd iIbnletegration of the Body
(cut)
Sublingual
gland breakdown reflects somPeo sctehraionr gbeel lyi nof the capillary endothelial Cerebrovascular Accidents (CVAs)
digastric muscle
Practice art labeling
cells or their tight junctions. Anterior compartment of leg
Mylohyoid
muscle (cut) >Study Area>Chapter 10 Submandibular (dorsiflexes fooTht, eex stienngdlse mtoeoss)t; common nervous system disorder and the third
Check Your Undedruscttanding innervated by dleeaedpi nfigb uclaaur snee rovfe death in North America are cerebrovascular
Anterior belly of Submandibular accidents (CVAs) (ser″ĕ-bro-vas′ku-lar), also called strokes.
digastric muscle Figure 10.26 Summ19a.rWy:h Aatc itsi oCnSFs? oWf hmerue siscg illtea pnsdr oodfu tchede? t Whihgaht aaren idtMs lufeucgonuc.st icoenllss? Serous cells
CVAs occur when blood circulation to a brain area is blocked
(a) 20.A brain surgeon is about to make an incisio(nb.) Name all the
and brain tissue dies of ischemia (is-ke′me-ah), a reduction of
tissue layers that she cuts through from the skin to the brain.
blood supply that impairs the delivery of oxygen and nutrients.
Figure 22.10 The salivary glands. (a) The parotid, submandibular, and sublingu aFlo grl aanndssw ers, see AnswerVsi eAwp pheisntodlioxg.y slides The most common cause of CVA is a blood clot that blocks
and their ducts. (b) Photomicrograph of the sublingual gland (150×), a mixed salivary gland >Study Area>
a cerebral artery. A clot can originate outside the brain (from
containing mostly mucous cells (light blue) with a few serous cells (purple).
CLINICAL the heart, for example) or form on the roughened interior wall
12.9 Brain injuries and
NEW! Easily find clinical of a brain artery narrowed by atherosclerosis. Less frequently,
M10_MARI7040_09_SE_CH10_321-387.indd 383 25/07/14 10:17 AM
examples to help you see how disorders have devastating strokes are caused by bleeding, which compresses brain tissue.
others) scattered throughout the oral cavity mucosa augment beneath the mucosa of the oral cavity floor and opens at the
Many who survive a CVA are paralyzed on one side of the
A&P concepts apply to your future consequences
the output slightly. base of the lingual frenulum (see Figure 22.8b). The small,
body (hemiplegia). Others commonly exhibit sensory deficits
carTeheer . mTahjoer cslailniviacray l gclaonndts eanret —paired compound tubulo- almond-shaped sublingual gland lies anterior to the subman-
Learning Objectives or have difficulty understanding or vocalizing speech. Even so,
alveolar glands that develop from the oral mucosa and remain dibular gland under the tongue and opens via 10–20 ducts into
including the Homeostatic
the picture is not hopeless. Some patients recover at least part
connected to it by ducts (Figure 22.10a). The larDgee,s rcoriubgeh ltyh e cautshee f(liof okrn oofw thne) m anoudt hm (aFjiogru rseig 2n2s.1 a0na)d.
Imbalantrciaen gsuelcart ipoanrost,i dc glilnanicda (pl acho-rnott′eidn; tp ar = near, otosy =m tphteo emars) of cerebTrhoev asaslciuvalaryr agclacniddes natrse, cAolmzhpeoismede or’fs two types of soefc trheteoirry l ost faculties, because undamaged neurons sprout new
modulileess a, natenrdio rt htoe t hceh eaapr tbeetrw-eeennd tihneg m asseter musdclies eaansde ,t hPea rkinsocenll’ss: dseisreoauss ea,n adn mdu Hcouunst i(nFgigtuorne’ s2 2d.i1s0eba)s. eS.erous cellsb prraondcuhcees that spread into the injured area and take over some
At stkhine. CItsl inpriocm Cinaesnet dSutcut dpya—rallhelas st hae zygomatic aLrcisht, apniedrc eesx plaina s wevateerrayl steeccrhetnioiqnu ceosn utasiendin tgo e ndziaygmneos,s ieo ns, and a tilnoys tb fiut nofc tions. Physical therapy should start as soon as possible
the buccinator muscle, and opens into the vestibuleb nreaxint tdo itshoer ders.mucin, whereas mucous cells produce mucus, a stritnog yp, rveivs-ent muscle contractures (abnormally shortened mus-
secuonnidf uiepdpe rn mewola rl.ook and feel. cous solution. The parotid and submandibular glandsc lceosn dtauine to2 2differences in strength between opposing muscle
Brain dysfunctions are unbelievably varied and extensive. We
Branches of the facial nerve run through the parotid gland mostly serous cells. Buccal glands have approximately equal
groups).
have mentioned some of them already, but here we will focus on
on their way to the muscles of facial expression. For this reason, numbers of serous and mucous cells. The sublingual glands
Not all strokes are “completed.” Temporary episodes of
surgery on this gland can result in facial paralytsrisa.umatic brain injurcioenst,a ciner meborsotlvya mscuucloaurs a ccecllisd.ents, and degen-
reversible cerebral ischemia, called transient ischemic attacks
erative brain disorders.
(TIAs), are common. TIAs last from 5 to 50 minutes and are
Composition of Saliva
CliniCAl
Homeostatic characterized by temporary numbness, paralysis, or impaired
imbalance 22.3 Traumatic BraiSnali vIan ijsu larrigeelsy water—97 to 99.5%—and therefore is hypo-
speech. These deficits are not permanent, but TIAs do consti-
osmotic. Its osmolarity depends on the specific glands that are
Mumps, a common children’s disease, is 1an2 inflHameamda tiinojnu orife tsh ea re a laecatdivien agn cda tuhsee s toimf auclucsid foenr tsaalli vdaetaiotnh. iAns Na rourlteh, saliva itsu stleig “hrtelyd flags” that warn of impending, more serious CVAs.
parotid glands caused by the mumps virus (myxovirus), which
America. Consider, faocrid eicx a(pmHp 6le.7, 5w tho a7t. 0h0a),p bpuetn itss ipf Hy omua yfo vragreyt. Ittos solutes incAlu CdeV:A is like an undersea earthquake. It’s not the initial tem-
spreads from person to person in saliva. If you check the loca-
tion of the parotid glands in Figure 22.10a, youf acsatne nu nydoeursrt asnedat belt ●a nEdl etchtreonly rteesa r(-Nean+d, Kan+,o Cthl−e, rP cOa4r3.− ,Y aonudr H hCeaOd3 −) blor that does most of the damage, it’s the tsunami that floods
is moving and then stops suddenly as it hits the windshield. the coast later. Similarly, the initial vascular blockage during a
why people with mumps complain that it hurts to open their ● The digestive enzymes salivary amylase and lingual lipase
mouth or chew. Other signs and symptoms inBcrlauidne dmaomdaegraet eis caused( nlinogt uoanl llyip bayse l omcaakleizs eodn liyn aju mryin aotr t choen stritieb uotfi on to osvterroaklle f aits not usually disastrous because there are many blood
fever and pain when swallowing acidic foodst h(pei cbklloews, , gbruapt ea-lso by thdei greicstoiocnh)eting effect as the brain hits the vessels in the brain that can pick up the slack. Rather, it’s the
fruit juice, etc.). Mumps in adult males carrioesp pa o2s5i%te erinskd ooff the s●k uTllh.e proteins mucin, lysozyme, and IgA neuron-killing events outside the initial ischemic zone that
infecting the testes too, leading to sterility. ✚ A concussion is an alteration in brain function, usually tem- wreak the most havoc.
● Metabolic wastes (urea and uric acid)
porary, following a blow to the head. The victim may be dizzy Experimental evidence indicates that the main culprit is
About the size of a walnut, the submandiobru llaors eg lcaonnds cliieosu snesWs. hAelnth doiussgohlv teydp iinc awllayt emr, itlhde a gnldyc sohporortte-ilniv medu,c in forgmlus ttahmicakt e, an excitatory neurotransmitter. Glutamate plays a
along the medial aspect of the mandibular body. Its duct runs mucus that lubricates the oral cavity and hydrates foodstuffs.
even a seemingly mild concussion can be damaging, and multi- key role in learning and memory, as well as other critical brain
ple concussions over time produce cumulative damage. functions. However, after brain injury, neurons totally deprived
More serious concussions can bruise the brain and cause per- of oxygen begin to disintegrate, unleashing the cellular equiva-
manent neurological damage, a condition called a contusion. In lent of “buckets” of glutamate. Under these conditions, gluta-
cortical contusions, the individual may remain conscious. Severe mate acts as an excitotoxin, literally exciting surrounding cells
A01_MARI6415_10_SE_FM_i-xix.indd 4 brain stem contusions always cause coma, lasting from hours to a t0o7/ 1d0/e15a t 3h:3.0 PM
M22_MARI6415_10_SE_CH22_746-794.indd 755 lifetime because of injury to the reticular activating system. A2t2 /p08r/1e5s e5n:24t ,P Mthe most successful treatment for stroke is tissue
Following a head injury, death may result from subdural or plasminogen activator (tPA), which dissolves blood clots in the
subarachnoid hemorrhage (bleeding from ruptured vessels into brain. Alternatively, a mechanical device can drill into a blood
those spaces). Individuals who are initially lucid and then begin clot and pull it from a blood vessel like a cork from a bottle.
to deteriorate neurologically are, in all probability, hemorrhaging
intracranially. Blood accumulating in the skull increases intra- Degenerative Brain Disorders
cranial pressure and compresses brain tissue. If the pressure forces
Alzheimer’s Disease
the brain stem inferiorly through the foramen magnum, control
of blood pressure, heart rate, and respiration is lost. Intracranial Alzheimer’s disease (AD) (altz′hi-merz), a progressive degen-
hemorrhages are treated by surgically removing the hematoma erative disease of the brain, ultimately results in dementia
(localized blood mass) and repairing the ruptured vessels. (mental deterioration). Alzheimer’s patients represent nearly
Another consequence of traumatic head injury is cerebral half of the people living in nursing homes. Between 5 and 15%
edema, swelling of the brain. At best, cerebral edema aggravates of people over 65 develop this condition, and for up to half of
the injury. At worst, it can be fatal in and of itself. those over 85 it is a major contributing cause in their deaths.
M12_MARI7040_10_SE_CH12_430-484.indd 464 8/14/14 11:31 AM
TOOLS TO HELP YOU ON YOUR JOURNEY
Chapter 9 Muscles and Muscle Tissue 281
Epimysium
Bone Epimysium
Perimysium
<
Stunning 3-D art with
Tendon
Endomysium
vibrant colors appears
Muscle fiber
on every page to help in middle of
a fascicle
you better visualize
(b)
and understand key Blood vessel
Perimysium wrapping a fascicle
anatomical structures
Endomysium
and their functions. (between individual muscle fibers)
9
Muscle fiber
Fascicle
Perimysium
(a)
Figure 9.1 Connective tissue sheaths of skeletal muscle: epimysium, perimysium, Practice art labeling
164 UNIT 2 Covering, Support, and Movement of the Body a(Fnodr ae rnedlaotemdy imsiuagme., (sbe)e PAh oBtroiemf iAcrtolagsr oapf hth oef Hau cmroasns sBeocdtiyo, nP loaft ep a2r9t. )of a skeletal muscle (30×). >Study Area>Chapter 9
of the external environment. This slows passive heat loss from Excretion Let’s consider these connective tissue sheaths from exter- Attachments
nal to internal (see Figure 9.1 and the top three rows of
Recall from Chapter 8 that most skeletal muscles span joints
the body, conserving body heat. Chapter 24 discusses body tem- NEW! Making ConneTcabtlie o9.1n).s questions in each chapter aansd katt aycho tou b otneos ( oar opthper lsytru cwturhes)a int a t least two places.
perature regulation. you’Thwveae slt eebsao r(dnayme edmli maoncirinaoa,s tues srd e●l aiif,mmtEh pfuaaiemtsi ncstylrueesdr”eiru)d o minusu .na artndThmi s“ cboetvh oeeeoar pwcucidomhianodtyy”lste oi) sumfs mdiuyoen sn(scfes ltepe s. ″ einwSrĭ-rommiemegtiuraes′ltsoaetimr- , guca emoasen n;lin ntt “edboh-cluetc otinvscodieud shtne igw sasttihhutaheep imnteionWtmrisgosuhtns e ,csn lme oa’so mov reutissgh ctiloneaw. cIaontrn d tth yrteah comet suiu,m tshcm leeb oms vouoafvb tailheble ldo elri bm loeabnssse , ,mt thhoee vo marbiuglesin cbl eto’ysnp ienic, satehlrlye-
cohessuicvhe wuansdtees rasrtea enxdcrinetged toh ei fnd e teuph fraeiscn iabe th.o aPt dliresoy b.feutwseee<n snewighebaotriinng mgu isscl eas onr tihme polire-s proximal to the insertion.
Cutaneous Sensation superficial fascia deep to the skin. Muscle attachments, whether origin or insertion, may be
tant avenue for water ●a nPedri msyasilutm ( asnod dfasicuiclmes. Wcihthlino eraicdh esk)el eltoal smsu.scle, the direct or indirect.
muscle fibers are grouped into fascicles (fas′ĭ-klz; “bundles”) ● In direct, or fleshy, attachments, the epimysium of the mus-
The skin is richly supplied with cutaneous sensory receptors, Check Your Undtehart rsestemabnle dbuinndlegs of sticks. Surrounding each fascicle is cle is fused to the periosteum of a bone or perichondrium of
a layer of dense irregular connective tissue called perimy- a cartilage.
which are actually part of the nervous system. The cutaneous sium (per″ĭ-mis′e-um; “around the muscle”).
● In indirect attachments, the muscle’s connective tissue
receptors are classified as exteroceptors (ek″ster-o-sep′torz) 21. What chemicals pro●d Euncdoemdy siinum t. hThee senkdionm hyseiulmp (penr″odov-midise′e -buma;r “rwieitrhsin to wrappings extend beyond the muscle either as a ropelike
because they respond to stimuli arising outside the body. For bacteria? List at least trthoheu nmrdeuse seca leca”h)n iinsd da i vewidxisuppayll amshiuenasct hlhe ofiofb cweor.n Intt ehccoteniv seic stthiss seoufm efi tnhieca taa rseulosr-- are tneun-droo′ns is()F. iThguere t e9n.1dao)n oorr aasp oan sehuereotsliisk ea nacphoonrse uthreo smisu s(acple″ oto-
protective. lar connective tissue. the connective tissue covering of a skeletal element (bone or
example, tactile (Meissner’s) corpuscles (in the dermal papil-
As shown in Figure 9.1, all of these connective tissue sheaths cartilage) or to the fascia of other muscles.
lae) and tactile discs allow us to become aware of a caress or 22. Which epidermal cealrles c opntlianuyo uas wroithle on ien an botohedr ays wimell ams wuitnh itthye t?endons that Indirect attachments are much more common because of
the feel of our clothing against our skin, whereas lamellar (also 23. How is sunlight impjooonin rth tmeasuens scthle esta ottho s ,bb woonheincsh.e Wt rhahneesnma miltt uthhsce?l ep ufilblienrgs fcoorncetr taoc tt,h teh beoyn peu tlol tlahgeeirn dfiubrearbsi lwityh iacnhd c samn awlli tshizstea. nTde nthdeo nasb raarsei omno ostfl yr otuoguhg hb coonly-
called Pacinian) corpuscles (in the deeper dermis or hypoder- 24. MAKING connectionsbtiec imWtyo ovhfe mde.u nThsc elbe s thliosesaouthed,s ac novdne tarslisbsoue ptelr sosov iimdnee wrtohhuatete ts o df othere tr hnmea teuinrstar lyc e aloansnd- stricpsutroe sje. cBteiocnaus steh aotf wthoeuilrd r teelaatri vaeplayr st mthael lm siozree, mdeolircea ttee nmduosncsl et htiasn-
mis) alert us to bumps or contacts involving deep pressure. Hair or dilate to help maeixnitt oaf tihne bblooodd vye stseelsm anpd enerravet ufibreers, thwat hseircvhe t htey mpuesc loe.f
follicle receptors report on wind blowing through our hair and muscle tissue that you learned about (in Chapter 4) acts as the
effector that causes blood vessel dilation or constriction?
a playful tug on a ponytail. Free nerve endings that meander
throughout the skin sense painful stimuli (irritating chemicals, M09_MARI7040_10_SE_CH09_278-3 2 0F.indod r 2 8a1nswers, see Answers Appendix. 25/07/14 10:15 AM
extreme heat or cold, and others). We defer detailed discussion
5
of these cutaneous receptors to Chapter 13. CLINICAL
5.9 Skin cancer and
Figure 5.1 illustrates all the cutaneous receptors mentioned
above except for tactile corpuscles, which are found only in skin burns are major challenges to the body
that lacks hairs, and tactile cells, shown in Figure 5.2b.
Learning Objectives
Metabolic Functions Summarize the characteristics of the three major types of
A01_MARI6415_10_SE_FM_i-xix.indd 5 skin cancers. 07/10/15 3:30 PM
The skin is a chemical factory, fueled in part by the sun’s rays.
Explain why serious burns are life threatening. Describe
When sunlight bombards the skin, modified cholesterol mol-
how to determine the extent of a burn and differentiate
ecules are converted to a vitamin D precursor. This precursor first-, second-, and third-degree burns.
is transported via the blood to other body areas to be converted
Loss of homeostasis in body cells and organs reveals itself on the
to vitamin D, which plays various roles in calcium metabolism.
skin, sometimes in startling ways. The skin can develop more
For example, calcium cannot be absorbed from the digestive
than 1000 different conditions and ailments. The most com-
tract without vitamin D.
mon skin disorders are bacterial, viral, or yeast infections (see
Among its other metabolic functions, the epidermis makes
Related Clinical Terms on pp. 171–172). Less common, but far
chemical conversions that supplement those of the liver. For
more damaging to body well-being, are skin cancer and burns,
example, keratinocyte enzymes can:
considered next.
● “Disarm” many cancer-causing chemicals that penetrate the
epidermis
Skin Cancer
● Activate some steroid hormones—for instance, they can
One in five Americans develops skin cancer at some point.
transform cortisone applied to irritated skin into hydrocorti-
Most tumors that arise in the skin are benign and do not spread
sone, a potent anti-inflammatory drug
(metastasize) to other body areas. (A wart, a neoplasm caused
Skin cells also make several biologically important proteins, by a virus, is one example.) However, some skin tumors are
including collagenase, an enzyme that aids the natural turnover malignant, or cancerous, and invade other body areas.
of collagen (and deters wrinkles). The single most important risk factor for skin cancer is
overexposure to the UV radiation in sunlight, which damages
Blood Reservoir DNA bases. Adjacent pyrimidine bases often respond by fus-
ing, forming lesions called dimers. UV radiation also appears to
The dermal vascular supply is extensive and can hold about 5%
disable a tumor suppressor gene. In limited numbers of cases,
of the body’s entire blood volume. When other body organs,
frequent irritation of the skin by infections, chemicals, or physi-
such as vigorously working muscles, need a greater blood sup-
cal trauma seems to be a predisposing factor.
ply, the nervous system constricts the dermal blood vessels.
Interestingly, sunburned skin accelerates its production
This constriction shunts more blood into the general circula-
of Fas, a protein that causes genetically damaged skin cells to
tion, making it available to the muscles and other body organs.
commit suicide, reducing the risk of mutations that will cause
sun-linked skin cancer. The death of these gene-damaged cells
causes the skin to peel after a sunburn.
M05_MARI7040_10_SE_CH05_150-172.indd 164 21/07/14 10:04 AM
PRACTICE MAKES PERFECT WITH MasteringA&P
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<
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A01_MARI6415_10_SE_FM_i-xix.indd 6 07/10/15 3:30 PM