32

9The Endocrine SystemA racing biker feels that he needs an edge so that

he can get a better time on each leg of the Tour de France. A baseball player wants to hit more home runs. A championship track star wants to break a world record. In many instances, athletes such as these have turned to performance-enhancing drugs to achieve their goals.

Many performance-enhancing drugs are actu-ally natural chemicals called hormones. For example, erythropoietin is a hormone that signals the bone mar-row to make more red blood cells, which increases the ability of the blood to carry oxygen to working muscles. Because it increases oxygen-carrying capacity, it en-hances an athlete’s endurance. Human growth hormone and steroid hormones, such as testosterone, increase the growth of skeletal muscles. Increased muscle mass enables athletes to run faster and become stronger.

Unfortunately, these performance-enhancing drugs can have harmful side effects, not to mention the unfair competitive advantage they may give athletes. Many athletic agencies such as the International Olympic Committee, National Baseball League, and National Football League forbid players from using these sub-stances. Furthermore, athletes must submit blood and urine samples periodically to be tested for banned sub-stances. The consequences for using these substances can be severe. In some cases, athletes even face crimi-nal charges for using and distributing these substances.

In addition to the hormones that enhance perfor-mance, the body produces many hormones that are necessary for normal functions. Let’s look at the various hormones that the body produces, how the endocrine system uses them, and their physiological functions.

CHAPTER OUTLINEHormones Act on Target Cells 4

• TheEndocrineSystemHasManyComponents• SteroidHormonesGoDirectlyintotheTargetCell• NonsteroidHormonesBindtoReceptorson

theTargetCellMembrane

Endocrine Glands Regulate Key Body Functions 7• ThePituitaryGlandandHypothalamusControl

ManyEndocrineGlands• TheThyroidGlandRegulatesMetabolism• ParathyroidGlandsRegulateCalciumLevels• PancreaticEndocrineCellsRegulateBlood

SugarLevels■ WhataHealthProviderSees:

GestationalDiabetes

Endocrine Glands Regulate Other Key Body Functions 19

• AdrenalGlandsRegulateManyFunctions• TheHypothalamus,PituitaryGland,andGonads

RegulateReproduction• ThePinealGlandSetsDailyCycles

The Endocrine System Coordinates the Stress Response 25

• TheStressResponseHasThreeStages• SeveralOrgansandHormonesAreInvolvedin

theStressResponse

Aging Alters the Endocrine System 28

❑ Studythepictureandreadtheopeningstory.

❑ ScantheLearningObjectivesineachsection: p.4❑ p.7❑ p.19❑ p.25❑ p.28❑

❑ Readthetextandstudyallvisuals.Answeranyquestions.

Analyze key features:

❑ ProcessDiagramp.5❑ p.6❑ p.11❑ p.13❑p.15❑ p.17❑ p.20❑ p.21❑

❑ InSight,p.24❑ p.28❑

❑ WhataHealthProviderSees,p.18

❑ Stop:AnswertheConceptChecksbeforeyougoon: p.7❑ p.18❑ p.24❑ p.27❑ p.29❑

End of chapter:

❑ ReviewtheSummaryandKeyTerms.

❑ AnswertheCriticalandCreativeThinkingQuestions.

❑ AnswerWhatishappeninginthispicture?

❑ CompletetheSelf-Testandcheckyouranswers.

CHAPTER PLANNER ✓✓

HormonesActonTargetCells5

1 Lipid-soluble steroid hormone enters thetarget cell directly through the cell membraneand binds to a specific receptor (activation).

Blood capillary

The activated hormone-receptorcomplex binds to specific genesof the target cell’s DNA andcauses these genes tobe expressed.

NucleusReceptor

mRNA

2

3 Messenger RNA (mRNA)from the hormone-activatedgenes leaves the nucleusand starts making newproteins.

DNACytosol

Target cell

New proteins alter the cell’sactivity in some specific way.

4

Transportprotein

Free hormone

Ribosome

Newprotein

Pineal gland

Trachea

ParathyroidGlands(behind thyroidglands)

Hypothalamus

PituitaryGland

Thyroid Gland

Trachea

Thymus

Heart

Stomach

Kidney

Uterus

Ovary

Testes

Skin

Thyroidgland

Scrotum

Lung

Liver

Male

Female

AdrenalGlands

SmallIntestine

Pancreas

ParathyroidGlands

Hormones Act on Target CellsLEARNING OBJECTIVES1. Define endocrineglands,hormones,hormone

receptors,andtargetcells.2. Describe howsteroidhormonesact.3. Describe hownonsteroidhormonesact.

Tomaintainasteadystate,thebodymustreg-ulate many parameters, such as heart rate,breathing,bloodglucose,fluidbalance,andsoon.Thenervoussystemregulatesmanyofthese

on a moment-by-moment basis and is ready to rapidly re-spondtochangeswithinseconds.Besidesthenervoussystem,the endocrine system regulates many parameters chemi-cally.Let’slookatthecomponentsoftheendocrinesystem.

• Some organs—such as the hypothalamus, pancreas,thymus, ovaries, testes, heart, liver, and kidneys—containendocrinecells.

• Sometissues,suchasadiposetissue,secretehormones.

Theendocrinesystemalsocontrolslong-termchanges,suchasgrowthandtheonsetofpuberty.

The components of the endocrine system function inthisgeneralmanner.Indirectresponsetoachangeinsomephysiologicalparameterorbystimulationfromthenervoussystem,anendocrinecell secretesachemical signalcalleda hormone into the bloodstream. Although the hormonecirculatesthroughoutthebody,itactsonlyonspecificcells,calledtarget cells.Thetargetcellscontaintheappropriatereceptorforasecretedhormone,calledahormone receptor;imaginethehormonereceptorasalockthatcanbeopenedonlybyaspecifickey(thehormone).Thehormone–recep-torcomplexelicitssomeactionwithinthetargetcellsthatrestoresthechangedparametertonormallevels.Oncenor-mallevelsarerestored,thesecretionoftheendocrinecellsisusuallystoppedvianegativefeedback(seeChapter1).Inthisway,theendocrinesystemhelpsmaintainhomeostasis.

Hormonescomeintwomajortypes,steroidandnon-steroid.Steroid hormonesdissolveinfatsorlipids,whilenonsteroid hormonesdissolveinwater.Steroidhormonesaremadefromcholesterol,whilenonsteroidhormonesareusually made from small amino acids, peptides, or large

proteins.Steroidhormonescangodirectlythroughthetar-getcellmembrane,whichismadeoflipids,whilenonster-oidhormonesusuallymustbindtoahormonereceptoronthesurfaceofthecellmembranetoenterthecell.Thesetwomodesofentryleadtoentirelydifferentmechanismsofaction.Let’slookatsteroidhormonesfirst.

Steroid Hormones Go Directly into the Target CellSteroidhormonespassdirectlythroughthecellmembraneandstimulatespecificgenestomakenewproteins,whichaltertheactivityofthetargetcell(Figure 9.2).Becausenewproteinsmustbemade,steroidhormonestakelongerto act than their nonsteroid counterparts. However, theeffectsofsteroidhormonesaregenerallylongerlasting.

Differentendocrinecellsproducevarioussteroidhor-mones,whichactonavarietyoftargets.Forexample,theovaries,testes,andadrenalglandsproduceandrogensandestrogens,whichactonmanycells toproducemaleandfemalecharacteristics.Theadrenalcortexsecretesmin-eralocorticoids,whichactonthekidneystoincreasesodi-umandwaterreabsorptionandpotassiumexcretion.Thekidneysproducecalcitriol, theactive formofvitaminD,whichactsontheintestinalliningtopromoteabsorptionofcalciumandphosphate.

Now,let’slookathownonsteroidhormoneswork.

The Endocrine System Has Many ComponentsTheendocrinesystemconsistsofseveralcomponents(seeFigure 9.1a):

• Endocrine glands are glandsthat secrete a chemical signaldirectly into the bloodstreamrather than through a duct ortube. For example, the salivarygland is an exocrine gland; itsecretes saliva through a duct.Incontrast,thepituitary,thyroid,parathyroid,adrenal,andpinealglandsareendocrineglandsbecausetheysecretechemicalsintothebloodstream.

Components of the endocrine system • Figure 9.1

Thisfigureshowsthemajorendocrineglands(red),organsthatcontainendocrinecells(blue),andsomenearbyorgansforreference(a),andindicatesthefunctionalcomponentsoftheendocrinesystem(b).

endocrine system A system of glands and hormone-secreting cells that regulate body func-tions through chemical messages (hormones).

a. Location of endocrine glands b. How endocrine components work.

Endocrine glands orEndocrine cells

Target cells(cell activity gets changed

by hormone)

Hormone

Blood

How steroid hormones work • Figure 9.2

Steroidhormonesgodirectlyintothetargetcellandstimulatethemakingofnewproteins,whichalterthecell’sactivity.Theentirepro-cessofsteroidhormoneactiontakesasignifi-cantamountoftime(minutestohours).

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6CHAPTer9 Theendocrinesystem endocrineglandsregulateKeyBodyFunctions7

pothalamus makes antidiuretic hormone (ADH), whichisreleasedfromthepituitaryglandandactsonthekid-neystoreabsorbwater.Thepituitaryglandalsoproducesfollicle-stimulatinghormone(FSH),whichstimulatessexcellproductionintheovariesandtestes.Thepancreasse-cretesinsulin,whichactsonmostcellsinthebodytotakeupglucoseandstorelipids.

1. How doesanendocrineglandcommunicatewithatargetcell?

2. How doesasteroidhormoneexertitsaction?3. What istheroleofthesecondmessenger?

LEARNING OBJECTIVES1. Identify thehormonessecretedbythepituitary

glandandtheirphysiologicaleffects.2. Outline theprocessesofsecretionandthe

functionsofthyroidhormones.

Nonsteroid Hormones Bind to Receptors on the Target Cell MembraneNonsteroid hormones are water-soluble and cannot passthroughthecellmembrane.Instead,theybindtoreceptorsonthesurfaceofthecell.Thehormone–receptorcomplexelicitstheformationofasecond messengerinsidethecell,whichaltersthetargetcell’sactivity(Figure 9.3).Secondmessengersincludecyclic AMP (cAMP) andcalcium.cAMP

is made from adenosine triphosphate (ATP) but does notparticipateinenergytransformations.Instead,itisachemi-cal second message inside targetcells.Insomecells,calciumcanactas a second messenger. The bind-ingof a nonsteroidhormone to itsreceptoropenscalciumchannelsinthemembranethatallowcalciumtoflowintothecell,altertheactivitiesofenzymes,andelicitresponses.

cyclic AMP (cAMP) A form of adenosine monophos-phate in which the phosphate is in a ring structure.

Because second messengers elicit a multistep pro-cess,theireffectsareamplified.Thismeansthatasmallamountofnonsteroidhormonecanproduceanexagger-ated and greatly diversified set of responses in the tar-getcells.NotethatthisamplificationoccursineachstepdepictedinFigure9.3:Onehormonemoleculecanelicitchanges inmanyproteins.Also,becausenonsteroidhor-monesdonotinvolvemakingnewproteins,theygenerallyactfaster,buttheireffectsaremoreshort-livedthanthoseofsteroidhormones.

A variety of endocrine cells make nonsteroid hor-mones that act on many target cells. For example, theadrenalmedullamakesepinephrineandnorepinephrine,which are also called adrenaline and noradrenaline, re-spectively.Thesehormones increaseheartrate,contractblood vessels to increase blood pressure, and stimulatethe liver to break down glycogen into glucose. The hy-

Endocrine Glands regulate Key Body Functions

3. Explain therolesofparathyroidglandsinregu-latingcalciummetabolism.

4. Describe theroleofthepancreaticisletsinglu-cosehomeostasis.

The endocrine glands, organs containing en-docrine cells, andendocrine tissues secreteapproximately30differenthormones.Theyregulate and control many body functions,

includingchemicalcompositionandvolumeofblood,me-tabolism,contractionsofsmoothandheartmuscles,se-cretionsofendocrineglands,theimmunesystem,growthanddevelopment,reproduction,anddailyrhythms(cir-cadianrhythms).

Diseases or endocrine disorders may involve dimin-ished secretions of endocrine glands (hyposecretion) orincreasedsecretionsofendocrineglands(hypersecretion).Some hormone secretions are associated with more than

oneendocrinegland,asyouwillseewiththehypothalamic–pituitary–thyroid axis. Diminished hormonal secretion byanendocrineglandmayhaveoneoftwocauses:

• Primary hyposecretion—This is a defect in a gland thatdirectlysecretesahormone.

• Secondary hyposecretion—This isadefect inaglandthatprovidesastimulatinghormoneorreleasinghormonetotheglandthatdirectlysecretesahormone.

Let’slookatthefunctionsoffourmajorelementsoftheendocrinesystem:thehypothalamus/pituitarygland,thyroidgland,parathyroidgland,andpancreas.

4 The many phosphorylated proteins alter thecell’s activity to elicit physiological responses.

1

2

3

5

The hormone-receptor complexstimulates the formation of asecond messenger inside the cell,such as cyclic AMP (cAMP).cAMP is made from ATP by anenzyme called adenylate cyclase.

cAMP only lasts for a short timebefore it becomes degraded.

cAMP activates proteinkinase enzymes, whichactivate many otherproteins by phosphorylation(adding a phosphategroup to them from ATP).

Water-soluble non-steroid hormoneis the first chemical message.It binds to a specific receptoron the cell membraneof the target cell (activation).

How nonsteroid hormones work • Figure 9.3

Nonsteroidhormonesdonotenterthecellbutratheractthroughsecondmessengers,suchascAMP,insidethecell.Theyachievetheirphysiologicaleffectsbyactivatingexistingpro-teinsratherthanmakingnewones.Theireffectsarerelativelyshort–lived.

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8CHAPTer9 Theendocrinesystem endocrineglandsregulateKeyBodyFunctions9

The pituitary gland secretes nine nonsteroid hor-mones, many of which control other endocrine glands.However, thepituitarygland itself is controlledby thebrain, specifically the hypothalamus. The posterior pi-tuitary is essentially an extension of the brain—axonsandterminalsofspecializednervecellsfromthehypo-

thalamus called neurosecretory cells makeuptheposteriorpitu-itary lobe. The cells dump theircontents directly into the bloodvessels supplying the posteriorpituitary lobe. The anterior pitu-itary shares a blood supply withthe hypothalamus—some neuro-secretory cells within the hypo-

thalamus synapse on blood vessels that are connectedto blood vessels of the anterior pituitary lobe. Secre-tionsfromtheseneurosecretorycellsinfluencethecells

Capillariesof posteriorpituitary

Hypothalamicneurosecretorycell

Hypothalamic neurosecretorycells release hormones into theblood supplying the anterior pituitary.

Artery

Sphenoid bone

AnteriorpituitaryVeins

Infundibulum –stalk that connectsthe pituitary to thehypothalamus.

Hypothalamus

Pituitary gland

Capillaries of posteriorpituitary

Posteriorpituitary

Hypophysealfossa

Artery

Posterior Anterior

Capillaries ofhypothalamus

Hypothalamus

Hypophyseal portalveins connect capillariesin hypothalamus tocapillaries in anteriorpituitary.

Veins

Capillaries of anterior pituitary

Hypophysealportal veins

Path of releasing andinhibiting hormones

Hypothalamic neurosecretory cellsextend into the posterior pituitary wherethey release hormones directly into the blood.

The structure and blood supply of the pituitary gland • Figure 9.4

Thehypothalamuscontrolsthesecretionsofthepituitaryglandintotheblood.Somehypothalamicneurosecretorycellsmakeuptheposteriorpituitary,whileothersinfluencetheanteriorpituitarybysecretingreleasingandinhibitinghormonesintoacommonbloodsupply.

The Pituitary Gland and Hypothalamus Control Many Endocrine GlandsThepituitary gland,whichisaboutthesizeofagrape,islo-catedjustbeneaththebrain(Figure 9.4).Itconsistsoftwoparts, the largeranterior pituitary lobeandthesmaller

posterior pituitary lobe;thelobesofthepituitaryareof-tenreferredtomerelyastheanteriorpituitaryandthepos-teriorpituitary.Athirdregionofthepituitarygland,calledthepars intermedia (intermediate lobe),atrophiesduringhumanfetaldevelopmentandceasestoexistasaseparatelobeinadults;however,someofitscellsmigrateintoadja-centpartsoftheanteriorpituitary,wheretheypersist.

neurosecretory cells A specialized form of nerve cells that secrete a neu-rotransmitter into the bloodstream rather than into a synaptic cleft.

oftheanteriorpituitary lobe.Thehypothalamicsecre-tions can either stimulate the pituitary gland (releas-inghormones)orinhibitthepituitarygland(inhibitinghormones).

Hormonesof theanteriorpituitary regulategrowth,metabolism, sexual maturation and reproduction, milkproduction,glucocorticoidproduction,andmelanocyteac-tivity(Table 9.1).Fourofthehormonessecretedbythean-teriorpituitary(TSH,FSH,LH,andACTH;seeTable9.1)alterbodyfunctionsindirectlybyinfluencingthehormonesecretion of other endocrine glands (the thyroid gland,ovaries,testes,andadrenalgland).Thesecretionsoftheanteriorpituitaryarecontrolledbyhypothalamicreleas-inghormones(GHRH,TRH,GnRH,CRH,andPRH;seeTable9.1)andhypothalamicinhibitinghormones(GHIHandPIH;seeTable9.1).Remnantcellsfromthepars in-termedia secretemelanocyte-stimulatinghormone(MSH),butitsroleinhumansisnotknown.

A s k Yo u r s e l f

1.Whichlobeofthepituitaryglanddoesnotsynthesizethehormonesitreleases?2.Whereareitshormonesproduced?3.Whatistheroleoftheinfundibulum?

Hypothalamic hormones and corresponding anterior pituitary hormones Table 9.1

Hypothalamic hormone Anterior pituitary hormone Target cell Action

Growth-hormonereleasinghor-mone(GHRH)promotesgrowthhormonesecretion.

Growth-hormoneinhibit-inghormone(GHIH)inhibitsgrowthhormonesecretion*

Humangrowthhormone(hGH) Varioustissues(e.g.,liver,muscle,bones,cartilage)

Makesinsulinlikegrowthfactor(IGF)intar-getcellstocontrolgrowth(stimulatecelldivisioninmuscle,bone,andcartilage)

Thyrotropin-releasinghormone(TRH)†

Thyroid-stimulatinghormone(TSH)

Thyroidfolliclecells

Secretesthyroidhormones(T3,T4)tocon-trolmetabolism

Gonadotropin-releasinghor-mone(GnRH)

Follicle-stimulatinghormone(FSH) Ovaries,testes Promoteseggandspermdevelopment

Luteinizinghormone(LH) Ovaries,testes Controlsovulationandproductionofes-trogen,progesterone,andtestosterone

Prolactin-releasinghormone(PRH)stimulatesprolactinrelease.

Prolactin(PRL) Breastcells Producesmilk

Prolactin-inhibitinghormone(PIH)inhibitsprolactinrelease.

Corticotropin-releasinghor-mone(CRH)

Adrenocorticotropichormone(ACTH)

Adrenalcortexcells

Producesglucocorticoidtobreakdownproteinsandfats,formglucose,andre-duceinflammation

Melanocytestimulatinghormone(MSH);excessiveCRHcanstimu-lateMSHrelease

Melanocytes Haveanunknownfunctioninhumans,butitmayinfluencebrainactivity

Notes

* Hypothalamic-inhibitoryhormonesaredenotedinblueandhaveoppositeeffectsofthereleasinghormones.

† Theterms(orendings)tropic(TRŌ-pik)hormones,trophic(TRŌ-fik)hormones,andtropinsrefertohormonesthatactonotherendocrineglands.

10CHAPTer9 Theendocrinesystem endocrineglandsregulateKeyBodyFunctions11

head trauma, or damage to thepituitary gland, pituitary stalk,or hypothalamus during surgery.Diabetes insipidus leads to ex-cessivethirst, frequenturination,andlargevolumesofurine.Whileanormalpersoncantoleratedehy-dration for several days, individu-als with diabetes insipidus cannottoleratedehydrationforevenaday.

Whentheanteriorpituitarysecreteseithertoolittleortoomuchhumangrowthhormone(hGH),severaldisordersaremanifested.Theseincludepituitary dwarfism(Figure 9.5a),gigantism(Figure 9.5b)andacromegaly(Figure 9.5c).Abnormalsecretionsthatresultindwarfismorgigan-tismusuallyoccurpriortopuberty,whileacromegalyresultsfromabnormalsecretionsafterpuberty.Whenatumoristhecauseofexcesssecretion,theconditionmaybetreatedwitheithersurgeryorchemotherapytoshrinkthetumor.

Pituitary dwarfism, gigantism, and acromegaly are caused by abnormal levels of secretion of human growth hormone • Figure 9.5

b. Gigantism Atumoroftheanteriorpitu-itaryexistingpriortopubertycausessecretionoftoomuchhumangrowthhormone,result-ingingigantism.Theaccel-erationofbonegrowthinthisconditionresultsinapersonwithnormalproportionsbuttaller-than-normalheight.

Effect of ADH secretions on body water and blood pressure levels • Figure 9.6

ThehypothalamussenseschangesinosmolarityanddirectsneurosecretorycellstosecreteADHthroughtheposteriorpituitary.

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Other hypothalamic neurosecretory cells make andsecreteantidiuretic hormone (ADH) throughtheposte-riorpituitary (Figure 9.6).Thesecells sense increasesin the salt concentration in the blood (osmolarity) andreleaseADH.ADHactsonthekidneys,sweatglands,ar-terioles,andbraintoconservebodywaterandincreasebloodpressure.

The most common pituitary disorder is diabetes insipidus, which is caused by a lack of ADH secretion.Diabetesinsipidusismostoftencausedbybraintumors,

antidiuretic hormone (ADH) A hormone secreted through the posterior pituitary lobe that conserves body water and increases blood pressure.

Theanteriorpituitarymaybe involved inendocrinedisordersofotherendocrineglands.Wewilldiscussthesediseaseswhenwediscussthoseglands.

Hypothalamicneurosecretorycellsmakeandsecreteoxytocinthroughtheposteriorpituitary.Oxytocininflu-encesbirthandmilkrelease(lactation).Duringbirth,oxy-tocinstimulatesmusclecontractionsintheuterus.Afterbirth, oxytocin stimulatesmilk releaseor let-down frombreasttissuewhentheinfantsuckles.

▲

c. AcromegalyAtumoroftheanteriorpituitaryafterpubertycauses

excesssecretionofhumangrowthhormone,resultinginacromegaly,aconditioninwhichlongbonescan

nolongergrow.Instead,thebonesofthehands,feet,face,andjawthickenandgrowlarger.

▲

Osmoreceptors

Hypothalamus

2

5

3

1

ADH acts on these target tissues: • Kidneys to retain water • Sweat glands to reduce water loss • Arterioles to constrict and increase blood pressure • Brain to stimulate drinkingThese actions restore normal osmolarity and blood pressure.

4

ADH

Target tissues

Water retention reduces blood osmolarity and inhibits hypothalamic osmoreceptors.

Dehydration causes high blood osmolarity, which is sensed by hypothalamic osmoreceptors.

6Osmoreceptors stimulate neurosecretory cells that make and release ADH.

Reduced osmoreceptor activity reduces or stops secretion of ADH by hypothalamic neurosecretory cells.

Nerve impulses of the neurosecretory cells release ADH from terminals in the posterior pituitary into the bloodstream.

a. Pituitary Dwarfism Whenthelevelsofsecretionofhu-mangrowthhormone(hGH)bythe

anteriorpituitaryareinsufficientpriortopuberty,bonegrowthis

impairedandtheindividualdoesnotgrowtonormalheight.Aperson

withpituitarydwarfismhasnor-malbodyproportionsbutoverall

shorter-than-normalheight.

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12CHAPTer9 Theendocrinesystem endocrineglandsregulateKeyBodyFunctions13

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LM

location and structure of the thyroid gland • Figure 9.7

Follicularcellsofthethyroidglandmakethyroidhormonesandstorethemincavities.Parafollicularcellsliebetweenthefolliclesandmakethehormonecalcitonin.

P u t I t To g e t h e r

1.The__________cellssecreteT3andT4.2.The__________cellssecretecalcitonin.

The Thyroid Gland Regulates MetabolismThe thyroid gland wraps around the trachea just be-lowthevoicebox(Figure 9.7).Thespongythyroidtis-sueiscomposedofmanysmallsacscalledfollicles.Inthewallsofthefollicles,follicular cellsmakethyroidhormones, thyroxine and triiodothyronine (trī-ī-ō-dō-THĪ-rō-nēn),whichare stored in thecavitiesof thefollicles.Locatedbetweenthefolliclesaretheparafol-licular cells,whichmakethehormonecalcitonin.

Thyroid hormones are made from the amino acidtyrosineandhave threeor four iodineatomsadded tothem (thyroxine [T4] has four iodines, and triiodothy-ronine [T3] has three). Eventhoughtheyarenotlipid-soluble,the thyroid hormones are smallenough to pass through the lip-ids of the target cell membranewithoutasurfacereceptor.Insidethecell,T4getsconvertedtotheactive form T3. T3 binds to the

calcitonin A hor-mone secreted by the parafollicular cells of the thyroid gland that inhibits osteoclast ac-tivity and lowers blood calcium levels.

thyroid hormone receptor, which is located on nuclearDNA.OnceT3isboundtothereceptor,newproteinsgetmade. T3 has the following effects on targetcells,whicharemostcellsinthebody:

• It stimulates the breakdown of glucose andfattyacidsforATPproduction(increasingthebasalmetabolismrate).

• During ATP production, cells use moreoxygenandreleasemoreheat.

• Proteinsynthesisincreases.

thyrotropin- releasing hormone (TRH) A hormone secreted by the hypo-thalamus that stimu-lates the anterior pitu-itary gland to secrete thyroid-stimulating hormone (TSH)

A s k Yo u r s e l fWhataretheeffectsonthebodywhenthethyroidglandsecretestoolittlethyroidhormonesecretion?

regulation of thyroid hormone secretion by the hypothalamus and pituitary gland • Figure 9.8

Thehormonesofthehypothalamus,pituitarygland,andthyroidmakeupanegativefeedbackloopthatcontrolsthyroidhormonelevelsintheblood.

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Thyroidhormonesincreasetheexcretionofcholester-ol,therebyreducingits level intheblood.Togetherwith

insulinandhGH,thyroidhormonesstimulatebodygrowth.

The hypothalamus and anterior pitu-itaryglandregulatethesecretionsofthyroidhormones by using a negative-feedback loopinvolving thyrotropin-releasing hormone (TRH), thyroid-stimulating hormone (TSH),andthyroxine(Figure 9.8).

Parafollicular cells of the thyroid secretecalcitonin, which inhibits a type of bone cell

14CHAPTer9 Theendocrinesystem endocrineglandsregulateKeyBodyFunctions15

Whenthethyroidglandsecretestoomuchthyroxine,hyperthyroidism occurs. In the most common form ofthiscondition,calledGraves disease,theimmunesystemproducesantibodiesthatbindtotheTSHreceptor,mimicTSH,andoverstimulatethethyroid.PatientswithGravesdiseasemayhaveanenlargedthyroidcalledagoiter(Fig-ure 9.9a)and/orpeculiarpuffinessintheeyescalledex-ophthalmos(Figure 9.9b).Gravesdiseasecanbetreat-edwithdrugsthatblockthesynthesisofthyroidhormone,bydestroyingthyroidtissuewithradiation,orbysurgicallyremovingthyroidtissue.

Parathyroid Glands Regulate Calcium LevelsTheparathyroid glandsaresmallglandsembeddedintheposteriorsideof the thyroidgland(Figure 9.10). The parathyroid glandssecrete a protein hormone calledparathyroid hormone (PTH),which acts on bone cells (osteo-clasts) to release calcium and onkidneycellstoreducecalciumex-cretionandtoreleasecalcitriol.

Theparathyroidglandsandthe parafollicular cells of thethyroid gland are thought towork together to control bloodcalcium levels (Figure 9.11).The calcium level in the bloodmustbemaintainedwithinnar-rowlimitsforproperfunctioningof nerves and muscles, particu-larly the heart muscle, vascularsmooth muscle, and intestinalsmoothmuscles.

Whentheparathyroidglandsare damaged, which happensmostoftenduringsurgeryonthethyroid, the circulating levels ofPTH fall. Hypoparathyroidismleads to a fall in blood calciumlevels, which especially affectsnerveandmusclecells.Itcanof-tenbe treatedwithcalciumandvitaminDsupplements.

calcitriol The active form of vitamin D, which is secreted by the kidneys and stimu-lates the intestine to absorb calcium from food into the blood, thereby increasing blood calcium levels.

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P u t I t To g e t h e rTheprimarytargettissuesforPTH,calcitonin,andcalcitriolare________,________,________.

location of the parathyroid glands • Figure 9.10

Theparathyroidglandsaresmallglandsembeddedintheposteriorsideofthethyroidgland.

called osteoclasts. Osteoclasts“eat” bone mineral and releasethecalciumintotheblood.Byin-hibitingtheactivityofosteoclasts,calcitonincandecreasethelevelsofcalciumintheblood.However,the normal physiological role of

calcitonin remains a mystery because calcitonin can bepresent in excess or completely absent without causinganyabnormalphysiology.

Whenthethyroidglanddoesnotsecreteenoughthy-roidhormone,aconditioncalledhypothyroidismresults.Ifitoccursatbirth,itiscalledcongenital hypothyroid-ism; if it occurs later in life, it is referred to as myx-edema.Congenital(orprimary)hypothyroidismcausesabnormaldevelopmentandmentalretardation,butitcanbetreatedwithoraldosesofthyroxine;bylaw,newbornsmustbescreenedforproperthyroidfunction.Myxedema(secondaryhypothyroidism)ischaracterizedbypuffinessintheface,slowheartrate,sensitivitytohotandcold,andmuscleweakness.Primaryhypothyroidismiscausedbyde-fectsinthefollicularcellsofthethyroid,whilesecondaryhypothyroidismcanbecausedbydamageordefectsinthehypothalamus(diminishedTRH)ortheanteriorpituitarylobe(diminishedTSH).

osteoclasts A type of bone cell that resorbs, or “eats,” bone mineral and releases its cal-cium into the blood.

b. ApuffinessintheeyescalledexophthalmosisanothersymptomofGravesdisease.

Graves disease • Figure 9.9

The activity of calcitonin and parathyroid hormone • Figure 9.11

Calcitoninandparathyroidhormoneactinconcerttoregulatebloodcalciumlevels.

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a. PatientswithGravesdisease(hyperthyroidism)mayhaveanenlargedthyroidcalledagoiter.▲

16CHAPTer9 Theendocrinesystem endocrineglandsregulateKeyBodyFunctions17

Pancreatic Endocrine Cells Regulate Blood Sugar LevelsThepancreas,whichisbothanexocrineglandandanen-docrinegland,islocatedoffthefirstsectionofthesmall

intestine, called the duodenum (Figure 9.12). Its exo-crine function concerns digestion, which you will learnmore about in Chapter 14. In this chapter, we are con-cerned with its endocrine functions, which occur in thecellsof thepancreatic islets,or islets of Langerhans.

b. Pancreatic islet and surrounding acini

Blood capillary

Exocrine cells

Alpha cell(secretes glucagon)

Beta cell(secretes insulin)

Pancreas

Kidney

a. Anterior view

Spleen(elevated)

Duodenum of small intestine

Pancreas

Abdominal aorta

Celiac trunk

c. Pancreatic islet and surrounding acini

Exocrinecells

Alpha cell

Beta cell

200x

Pancreatic islet

The structure of the endocrine pancreas • Figure 9.12

Thepancreasliesintheabdomennexttothesmallintestine.

Withintheisletsaretwotypesofcells:al-phacells,whichsecreteglucagon,andbetacells,whichsecreteinsulin.Bothglucagonand insulinareproteinhormones thatactmainly on the liver and skeletal muscle;they have opposite effects on the levels ofglucose intheblood(Figure 9.13).Main-tenance of normal blood glucose levels isimportantfortheproperfunctioningofthenervoussystem.

The secretions of glucagon and insulinare coordinated to prevent blood glucosefromrisingtoomuchafteramealandfallingtoo much between meals. Abnormal levels

of insulin, glucagon,and/or glucose inthe blood can indi-cate hypoglycemia,hyper glycemia, orthe presence of dis-eases such as diabe-tesmellitus,themostcommondisorder.

There are two types of diabetes mel-litus, which affects about 7.8% of the U.S.population:

• Type I—Type I diabetes involves a lackof insulin because the patient’s immunesystemhasdestroyedthebetacellsofthepancreas.TypeIdiabetesusuallydevelopsearly in life and has been called juvenilediabetes.

• Type II—Type II diabetes involvesdecreased sensitivity of target cells toinsulin.TypeIIdiabetesisoftenassociatedwithobesity,usuallydevelopslaterinlife,andhasbeencalledadult-onsetdiabetes.Patients with type II diabetes may havenearly normal levels of insulin in theirblood.This typeofdiabetes isagrowingepidemic in America, mainly due to theriseinobesity.

Bothtypesofdiabetesarecharacterizedbyelevatedbloodglucoselevelsandimpairedglucosetolerance(seeWhat a Health Provider Sees),presenceofglucoseintheurine,exces-sivethirst,excessivehungerandeating,andfrequenturination.InbothtypeIandtypeIIdiabetes,thebodyactsasifitisstarving.El-evatedglucagonandcortisollevelscausethe

hypoglycemia A condition in which blood glucose levels are below normal.

hyperglycemia A condition in which blood glucose levels are above normal

breakdownofliverglycogentoreleaseglucose,triglyceridestoreleasefattyacids,andmuscleproteinstoreleaseaminoacids.Becausemostcellsofthebodydonottakeupexcessglucosefromtheblood,thebloodbecomeshypertonic(Chapter3).Thiscondition,alongwithincreasedexcretion by the kidneys, leads to dehydration, circulatory problems,andtissuedamage.Diabetesmellitusoftenleadstodeathduetocar-diovasculardamageandkidneyfailure.IndividualswithtypeIdiabetescanbetreatedwithbloodglucosemonitoring,changesindiet,exercise,andadministrationofinsulin.IndividualswithtypeIIdiabetescanbetreatedwithbloodglucosemonitoring,changesindiet,exercise,andmedicationsthatstimulateinsulinsecretion.

regulator of blood glucose by glucagon and insulin • Figure 9.13

Glucagonandinsulinhaveoppositeeffectsonskeletalmuscletoregulatebloodglucoselevels.

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18CHAPTer9 Theendocrinesystem endocrineglandsregulateotherKeyBodyFunctions19

TestNormal blood glucose (mg/dL)

Other blood glucose (mg/dL) Diagnosis or treatment

Fasting <100 100–126 AdministerGTT

1-hourOGTT(50gglucose → bloodsamplein1hour)

<140 >140 Gestationaldiabetes;maytake3-hourtestand/orretakethetestin4weeks

3-hourOGTT(100gglucose→bloodsampleat1,2,and3hours)

Fast <951 <1802 <1553 <140

Valuesgreaterthannormal

Gestationaldiabetes

1. How ishumangrowthhormonesecreted,andwhatareitseffects?

2. How dothehypothalamusandpituitaryglandinteracttocontrolthesecretionofthyroidhor-mone?

3. What istheeffectofparathyroidhormoneonbloodcalciumlevels?

4. How doesthepancreashelpcontrolbloodglu-coselevels?

Gestational Diabetes

Jenna is pregnant and has her blood glucose checked during her regular obstetrical visits. During one of her tests, her fasting

blood glucose is greater than normal. She fears that she might have gestational diabetes, a type of diabetes that affects about 4% of pregnant women, representing about 135,000 new cases in the United States each year. Although the exact cause is unknown, it’s thought that hormones released by the placenta during pregnancy block the action of the mother’s insulin (that is, cause insulin

resistance). The mother’s pancreas secretes more insulin than usual but not enough to remove glucose

adequately. The increased blood glucose and other nutrients stimulate the baby’s pancreas

to hypersecrete insulin. As a result, the baby gains additional fat during development, which

presents complications for delivery, low blood glucose at birth, and risk for obesity and

type II diabetes in the mother.

Jenna’s physician orders a one-hour oral glucose tolerance test (OGTT), usually done between weeks 24 to 28. To prepare for this test, Jenna fasts for 8 to 12 hours prior to the test. A technician takes a blood sample and then gives her a high-glucose drink (~50 g). She has blood drawn 1 hour later. Her blood glucose level is higher than normal (see the table below), so the physician orders a 3-hour OGTT. Jenna prepares for this test in the same way but drinks a higher-glucose drink (100 g) and has blood drawn at 1-hour intervals for 3 hours. When her test results show higher-than-normal responses, her physician diagnoses gestational diabetes.

For treatment, Jenna goes on a restricted carbohydrate diet, begins a new exercise program, and uses a blood glucose meter to monitor her blood glucose daily. Also, because Jenna may require two or three times the normal insulin levels, she requires daily insulin injections. This treatment will continue until she gives birth. For many women, gestational diabetes goes away after birth, but some women become diabetic permanently.

WHATAHeAlTHProviDersees

1. Why does hypersecretion of insulin by the fetus cause the baby to gain excess weight?2. Why might Jenna require two or three times the normal insulin levels?

T h i n k C r i t i c a l l y

Adrenalglands Adrenal

cortex

b. Section throughleft adrenal gland

Left adrenalgland

Right renalartery

a. Anterior view

Left renalartery

Left renalvein

Abdominalaorta

Kidney

Right adrenalgland

Capsule

Adrenalmedulla

Right renalvein

Inferiorvena cava

Adrenal cortex:

Zona glomerulosasecretesmineralocorticoids,mainly aldosterone

Zona fasciculatasecretesglucocorticoids,mainly cortisol

Adrenal medullachromaffincells secreteepinephrine andnorepinephrine (NE)

Zona reticularissecretes androgens

c. Subdivisions of the adrenal gland

50x

Capsule

Endocrine Glands regulate Other Key Body Functions

LEARNING OBJECTIVES1. List themajorhormonesoftheadrenalgland

andexplaintheireffectsonthebody.2. Describe theinfluenceofthehypothalamus

andpituitaryglandonthehormonesofthegonads.

3. Identify thehormonesecretedbythepinealglandanditsfunction.

4. List thehormonessecretedbyendocrinecellsnotlocatedinendocrineorgansandtheirsub-sequenteffects.

In addition to the hypothalamus/pituitarygland,thyroidgland,parathyroidgland,andpancreas,otherendocrineglandscontrolsev-eralbodyfunctions,includingchemicalcom-

positionandvolumeofblood,metabolism,contractionsofsmoothmusclesandheartmuscles,reproduction,anddai-lyrhythms(circadianrhythms).Theseglandsincludetheadrenalglands, thegonads(ovariesandtestes),andthepinealgland,alongwithendocrinecellscontainedwithinotherorgans.Let’sstartwiththeadrenalglands.

Adrenal Glands Regulate Many FunctionsAnadrenal glandsitsontopofeachofthekidneys(Figure 9.14).Eachglandconsistsofanoutercortexthatsurroundsan innermedulla.Thecortex secretes three typesof ste-roidhormones—mineralocorticoids,glucocorticoids,andan-drogens—eachfromdifferentlayers.Themedullasecretesepinephrineandnorepinephrine.Let’stakeacloserlookateachofthesehormones,theireffects,andtheirsecretion.

The structure of the adrenal glands • Figure 9.14

Theadrenalglandsrestontopofthekidneys.Eachglandhastwoparts(cortex,medulla)surroundedbyacapsule.Cellswithineachpartsecretedifferenthormones.

20CHAPTer9 Theendocrinesystem endocrineglandsregulateotherKeyBodyFunctions21

mineralocorticoids Steroid hormones secret-ed by the adrenal cortex that regulate the mineral composition of the blood.

Mineralocorticoids regulate mineral composition of the blood Cellsintheouterzoneoftheadrenalcortexsecreteste-roid hormones called mineralocorticoids.Oneof these,aldosterone, actson thekid-neys to reabsorb sodium into the blood and

excrete potassium in response to dehydra-tion,bloodloss,orsodiumdeficiency.Aldoste-roneactsinconcertwiththehormonesreninandangiotensintochangethemineralcom-positionofthebloodandinfluencebothbloodvolumeandbloodpressure(Figure 9.15).

• Fat (adipose) tissue—Cortisolstimulates fat cells to breakdown triglycerides into fattyacids, which are released intotheblood.Other cells canusethefattyacidstomakeATP.

Glucocorticoids also suppress white blood cells fromparticipatingintheinflammatoryresponse.Inhighdoses,cortisolsuppressesimmuneresponses.Therefore,cortisol(hydrocortisone)isoftenprescribedasananti-inflamma-torytreatmentforrashesandallergicresponses.Inaddi-tion,cortisolisusedtotreatchronicinflammations,suchasarthritis,andtodecreasetheriskoftissuerejectionbytheimmunesysteminorgantransplantrecipients.

Thehypothalamusandpituitaryglandcontrolsecre-tionofglucocorticoidsfromtheadrenalglandthroughanegative feedback loop involving corticotropin-releasinghormone (CRH),adrenocorticotropichormone (ACTH),andcortisol(Figure 9.16).

If blood pressure is restored to normal, then reninandaldosteronesecretionsstop.Withseverebloodloss,the renin–angiotensin–aldosterone system cannot fullycompensateforthedropinbloodvolumeandpressure.Secretionsofreninandaldosteronewillstoponlywhenthe blood loss is fixed (for example, when a wound isrepaired) and when blood volume is restored by othermeans(suchastransfusion).

Glucocorticoids regulate energy balance Thecellsinthemiddlelayeroftheadrenalcortexsecreteglu-cocorticoids,mainlycortisol.Cortisolactsonmanytis-suestomobilizeenergyresources:

• Skeletal muscle—Cortisolcausesthebreakdownofmuscleproteins into amino acids, which get released into theblood.

• The liver—Cortisolstimulateslivercellstoconvertaminoacidsintoglucose,whichisreleasedintotheblood.

glucocorticoids Steroid hormones se-creted by the adrenal cortex that regulate energy balance.

renin–angiotensin–aldosterone system • Figure 9.15

Inacomplexseriesofeventsinvolvingseveralorgans,therenin–angiotensin–aldosteronesystemrestoresbloodvolumeandbloodpressure.

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Control of glucocorticoid secretion by the hypothalamus and pituitary gland • Figure 9.16

Thehypothalamusandpituitaryglandcontrolsecretionofglucocorti-coidsfromtheadrenalglandthroughnegativefeedback.

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a. Release of renin

c. Production of angiotensin II

ACE

angiotensinogen angiotensin I (AI)renin

angiotensin I angiotensin II (A II)ACE

5

renin

angiotensinogen3

restore blood pressure

10

increases bloodvolume

9

reabsorb sodiumand water

7

release aldosterone

1

b. Production ofangiotensinogen

d. Actions of angiotensin II (AII)

e. Actions of aldosterone

4

6

8

f. Combined effectsof aldosteroneand angiotensin II

2

angiotensin converting enzyme (ACE)

angiotensin II (A II)

4

5

2

3

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22CHAPTer9 Theendocrinesystem endocrineglandsregulateotherKeyBodyFunctions23

Secretionoftoomuchcortisolbytheadrenalglandcausesacon-dition called Cushing’s syndrome.Cushing’s syndrome can be caused byadrenaltumorsorbypituitarytumorsthatresult inoversecretionofACTH.Cushing’s syndromecanalsoresultfromusinghighdosesofcortisonefortreatingar-thritis.Overstimulationbycortisolcausesmusclestobreakdownandfattoberedistributed.Oneobvioussymptomisa round,flushed-looking face (Figure 9.17),alongwithahumpedbackandhangingabdomen.Complicationsincludeincreasedbloodpressure,elevatedbloodglucose,weakness,brittle bones, and decreased resistance to stress. Depend-ingonthecause,Cushing’ssyndromecanbetreatedusingdrugsthatinterferewithcortisolsynthesisorbysurgicalre-movaloftheadrenalglandsorpituitarygland.

When the adrenal cortex does not secrete enoughcortisoloraldosterone,theresultisararediseasecalledAddison’s disease. Addison’s disease can be caused byantibodies attacking the adrenal tissue or damage tothe pituitary gland due to surgery or trauma that leadsto insufficientACTHsecretion.Due to the lossof corti-solandaldosterone,Addison’sdiseasepatientsoftenhavesymptomsincludinglowbloodsugar,weightloss,nausea/vomiting,muscleweakness,lowbloodpressure,dehydra-tion,andheartproblems(forexample,arrhythmias,lowcardiacoutput).Addison’sdiseaseisusuallytreatedwithartificialglucocorticoidsandmineralocorticoids.

Adrenal androgens influence sexual character-istics and behaviors Inbothmalesandfemales,theinnerzoneoftheadrenalcortexsecretesadrenalandro-gens. Before puberty, adrenal androgens contribute togrowthofarmhairandpubichairinmalesandpre-pubertalgrowth spurts in females. Adrenal androgens have littleinfluenceafterpubertyinmalesbecausethetestessecretefarmoreandrogens(testosterone)thantheadrenalgland.Adrenalandrogenshavegreatereffects in femalesafterpuberty; they influence sex drive and become convertedtoestrogens(femalehormones).Whileafemaleisfertile(between puberty and menopause), the ovaries are theorgans primarily responsible for the secretion of estro-gens.(Youwilllearnmoreabouttheovariesshortly.)Aftermenopause,theconversionofadrenalandrogensintoes-trogensbecomestheonlysourceofnaturalestrogen.

Epinephrine and norepinephrine regulate the body’s response to stress and exercise The cells of theadrenal medulla are like post-ganglionicnerve cells of the autonomic nervous sys-tem. Upon nervous stimulation, they se-crete thehormonesepinephrine (adrena-

line)andnorepinephrine(noradrenaline).These hormones act on many tissues to ac-

complishthefollowingfunctions:

• Increase heart rate and force of contraction, whichincreasesbloodpressureandbloodflow

• Constrictbloodvesselsandraisebloodpressure

• Increase blood flow to the heart, liver, and skeletalmuscles

• Dilateairwaysofthelung,whichincreasesventilation

• Break down liver glycogen into glucose, which isreleasedintotheblood

• Breakdownadipose tissue fats into fattyacids,whicharereleasedintotheblood

These responses help the body during activities such asexercisebymobilizingenergyreserves,bringingmoreoxy-genintothebodythroughthelungs,andincreasingoxy-gendeliverytoworkingmuscles.

The Hypothalamus, Pituitary Gland, and Gonads Regulate ReproductionThe gonads, or sex-cell-producing organs, are the ova-ries,whicharelocatedinthepelvisofthefemale,andthetestes,which lie inthescrotalsacofthemale.Theova-riesproducethehormonesestrogenandprogesterone.Thesefemalesexhormonesstimulatethedevelopmentoffemalesexcharacteristicsatpuberty(forexample,femalebodyshape,pubichairgrowth,breastdevelopment),reg-ulate themenstrual cycle,andmaintainpregnancy.Theovariesalsoproduceotherhormones,inhibinandrelaxin,thathaverolesinpregnancy.

Thetestesproducetestosterone,whichisresponsiblefordevelopmentofthemalesexcharacteristicsatpuber-ty (for example, muscle growth, thickening of the vocalcords, increased facialandpubichair)andspermdevel-opment. The testes also produce inhibin, which inhibitssecretionofFSHfromthepituitarygland.

Let’stakeabrieflookathowthehypothalamus,ante-riorpituitary,andgonadsworktogethertocontrolthese-cretionsofsexhormones,determinetheonsetofpuberty,andmaintainnormalsexualfunctions(Figure 9.18).WewillreturntothistopicingreaterdetailinChapter16.

Cushing’s syndrome • Figure 9.17

OnesymptomofCushing’ssyn-drome,whichresultsfromexcesscortisol,isaround,flushedface.

• Neurosecretory cells in the hypothalamus of bothmales and females secrete pulses of gonadotropin-releasing hormone (GnRH) into the pituitary bloodsupplyatregularintervals.

• GnRHstimulatestheanteriorpituitarylobetosecretesimilar pulses of follicle-stimulating hormone (FSH)andluteinizinghormone(LH)intothebloodstream.

• Inthemale,FSHandLHstimulatespermdevelopmentandtestosteroneproductionbythetestes.Testosteronein the blood inhibits secretions of GnRH from thehypothalamus and LH and FSH secretions from thepituitarygland.

• In the female, LH and FSH cause the egg cells tomatureandtoproduceestrogen:

• Astheestrogenlevelincreasesandaneggdevelops,therecomesapointwhenamassivereleaseofLHandFSHfromthepituitaryglandoccurs,leadingtoovulation.

• Afterovulation,theremnantsofthefollicle(corpusluteum)continuetoproduceestrogenand progesterone, whichsuppress GnRH secretionfrom thehypothalamusandLHandFSHsecretionsfromthepituitarygland.

• Inhibin produced by theovaries helps to suppressFSH secretion from thepituitary gland and inhibitthe development of othereggcells.

• During pregnancy, theovariesproducerelaxintoincreasetheflexibilityofuterine and vaginal smooth muscle in preparationforchildbirth.

regulation of sex hormone secretions by the hypothalamus, pituitary gland, and gonads • Figure 9.18

gonadotropin-releasing hormone (GnRH) A hormone released by the hypothalamus that stimulates the anterior pituitary gland to secrete hormones—specifi-cally luteinizing hormone (LH) and follicle stimulating hormone (FSH)—that act on the ovaries and testes.

-Anteriorpituitary

Anteriorpituitary

Ovaries

FSH

GnRH

ProgesteroneEstrogen

LH

Hypothalamus Hypothalamus

- + +

+

+

+

Testes

FSH

GnRH

Testosterone

LH

+

+

+

+

GnRHstimulatesthe anteriorpituitary tosecreteLH and FSHat regularintervals.

2

3a FSH and LH act on the testes andlead to testosterone production, whichexerts effects on the hypothalamusand pituitary via negative feedback.

3b

The hypothalamus releases pulsesof GnRH at regular intervals.

1Female Male

FSH and LH act on the ovary and lead to development of an egg and production of estrogen and progesterone. These hormones influence the hypothalamus and pituitary via either positive or negative feedback, depending on the point in the menstrual cycle when secretion occurs.

ThecoordinationofGnRH,FSH,andLHsecretion,alongwiththesecretionofsexhormonesbythegonads,signaltheonsetofpubertyandgameteproductioninbothmalesandfemales.Inaddition,thisprocesssignalsovulationandmaintenanceofpregnancyinfemales.

24CHAPTer9 Theendocrinesystem TheendocrinesystemCoordinatesthestressresponse25

THE PlAnnEr✓✓InSight EndocrineFunctionsinNon-EndocrineGlands • Figure 9.19

TheendocrinesystemCoordinatesthestressresponse2524CHAPTer9 Theendocrinesystem

Therearemanycellsinvariousnon-endocrineorgansthatsecretehormones.

All cells except red blood cells secrete two hormones that are derived from fatty acids: leukotrienes (loo-ko-TRI-ens) and prostaglandins (pros'-ta-GLAN-dins). Unlike most other hor-mones, these act locally (that is, close to their sites of release), so they are not found in significant quantities in the blood. Leukotrienes stimulate the movement of white blood cells and me-diate inflammation.The prostaglandins alter smooth muscle contraction, glan-dular secretions, blood flow, reproduc-tive processes, platelet function, respi-ration, nerve impulse transmission, fat metabolism, and immune responses. Prostaglandins also have roles in in-flammation, promoting fever, and in-tensifying pain.

The Pineal Gland Sets Daily CyclesThepineal gland (PĪN-ē-al) is attached to the roofof thethirdventricleinthemidlineofthebrain.Thepinealglandconsistsofmassesofneurogliaandsecretorycellscalledpine-alocytes(pin-ē-AL-ō-sītz).Thisglandsecretesthehormonemelatonin,whichisderivedfromtheaminoacidserotonin.Melatoninisthoughttobeinvolvedinsettingthebody’sdailyclock.Thepinealglandreceivesinputfromtheeyes,indicat-ingthatlightanddarkmayinfluenceitsactivities.Insupportof this hypothesis, melatonin secretion is greatest duringsleepandindarkness(almost10timesgreaterthanatothertimes).Forpatientswhohavetroublefallingasleep,smalldosesofmelatoninmaybetakenorallytopromotesleep.

Overproduction of melatonin may be the cause of atype of depression called seasonal affective disorder (SAD).SADafflictssomepeopleduringthewintermonths,when day length is short. To provide relief from this dis-order,full-spectrumbright-lighttherapy(thatis,repeateddosesofseveralhoursofexposuretoartificiallightasbright

assunlight)isused.AnotherdisorderthatmaybesimilartoSADisjetlag,fatiguesufferedbytravelerswhoquicklycrossseveraltimezones.Threetosixhoursofexposuretobrightlightappearstohelpspeedrecoveryfromjetlag.

Therearecellsinnon-endocrineorgansthatsecretehormones.SeeFigure 9.19tolearnaboutsomeimpor-tantendocrinefunctionsinthesenon-endocrineglands.

1. What istheroleofaldosteroneintherenin–angiotensin–aldosteronesystem?

2. How isovulationcontrolledbyhormones?3. What isthoughttobethefunctionofthepineal

gland?4. What arethefunctionsofhormonessecreted

byendocrinecellsthatarenotlocatedinendo-crineglands?

The Endocrine System Coordinates the Stress responseLEARNING OBJECTIVES1. Describe thestagesofthestressresponse.2. List theglandsoftheendocrinesystemin-

volvedinthestressresponse.

Imaginethatyouaredrivingtoclassandyounarrowlyavoidacollisionwithanothervehi-cle.Thesoundoftheothercar’shornstartlesyou.Youimmediatelyrealizewhathappened.

Yourheartbeatsfasterandharder.Youarebreathingmoreheavily.Youmaybesweating.Whenyougettoclass,yourprofessorspringsapopquizforwhichyouareunprepared,andthesamesymptomsappearagain.Theseeventsarestressors,andweencountersucheventseveryday.Someotherexamplesofstressincludefear,anxiety,otherstrong

emotions,exposuretotoxinsorallergens,changesintem-perature,exercise,injurytrauma,anddisease.

The body has a series of physiological responses tostress,whichiscalledthestress response,orgeneral ad-aptation syndrome.Thestressresponse,whichhasthreestages,strivestomaintainhomeostasis.

The Stress Response Has Three StagesWhateverthecauseofstress,thebodyrespondsinstages. The fight-or-flight stage prepares the body for immediatephysicalactivity.Theresistance stageinvolvesprolongedre-sistancetothestressor.Theexhaustion stagefeaturesanin-abilitytoresistprolongedexposuretothestressor.

Let’slookattheresponsesineachstage.

Adipose tissue releasesleptin, which suppressesappetite.

Placenta – During pregnancy, the placenta secretes human chorionic gonadotropin (hCG), which allows the ovary to continue secreting progesterone and estrogen to maintain pregnancy.

26CHAPTer9 Theendocrinesystem TheendocrinesystemCoordinatesthestressresponse27

diverts blood flow to working skeletal muscles, theheart,andthelungs.

• Stimulates sweat glands in the skin, which leads toincreasedsweating.

• Dilatestheairwaysofthelungsandincreasestherateofbreathing.

• Stimulatesreleaseofepinephrineandnorepinephrinefromtheadrenalmedulla,enhancingtheeffectsofthesympatheticnervoussystemandcausingtheliverandadiposetissuetobeginmobilizingenergyreserves.Intheliver,glycogenbreaksdownintoglucose,whichisreleasedintotheblood.Inadiposetissue,triglyceridesbreak down into fatty acids, which are released intotheblood.

Intheresistancestage,thehypothalamusstimulatesthepituitarygland,thethyroidgland,theadrenalglands,theliver, and muscle, and adipose tissues (see Figure 9.18).ThehypothalamussecretesCRH,GHRH,andTRH,whichactontheanteriorpituitarylobe(seeTable9.1).Thean-teriorpituitarysecretesTSH,hGH,andACTH.TSHactsonthethyroidglandtoreleasethyroidhormones,whichincreasemetabolism.hGHactsontheliverandothertis-suesthroughIGFstosustainthebreakdownofglycogenand triglycerides. ACTH stimulates the adrenal cortexto release cortisol, the major stress hormone. Cortisolacts on the liver, adipose tissue, and skeletal muscle tomaintainthemobilizationofenergyreservesandreduceinflammation. So, the resistance stage mobilizes energysources(glucose,fattyacids,aminoacids)thattissuescanuse tomakeATP.Because theresistancestagereliesonchemicalmessages, it takes longerto initiate,but itcanbesustainedforalongperiodoftimetocombatastressor.

Exhaustionoccursduetoprolongedexposuretocorti-sol,which,amongothereffects,depletesthebody’senergyresources, wastes away muscles, and suppresses the im-munesystem.Prolongedstressor frequent stressesmayweakenthebodyandmakeitsusceptibletootherdiseases.However,theexactroleofstressindiseasesisnotknown.

1. What arethestagesofthestressresponse?2. How arethecomponentsoftheendocrine

systemandtheirtargetorgansinvolvedineachstageofthestressresponse?

The stress response • Figure 9.20

Bysecretingnorepinephrineandvarioushypothalamicreleasingfactors,thesympatheticnervoussystemandhypothalamuscoordinatethesecretionsofotherglandsandactivationofvariouspro-cessestomakeanimmediateandsustainedresponsetostress.(Greenarrowsrepresentnervousactivity,redarrowsrepresentprimaryhormonesecretions,andblackarrowsindicatesubsequenthormonesecretions.)

Thyroid hormones

Key:

b. Resistance reactiona. “Fight-or-flight” responses

Liver

Adipose tissue

Skeletal muscle

CRH

GHRH

TRH

TSH

hGH

ACTH

Fight-or-flight stage In the fight-or-flight stage,thesympatheticnervoussystem(Chapter7)kicksinandstimulatesheart,lungs,bloodvessels,andtheadrenalme-dulla(seeFigure 9.20):

• Sympatheticstimulationoftheheartandbloodvesselsincreases heart rate, blood pressure, and blood flow,especiallytoskeletalmuscles.

• Sympathetic stimulation of the lungs dilates airwaysandincreasestherateofbreathing.

• Sympathetic stimulation of the adrenal medullareleasesepinephrineandnorepinephrine.

Thesecoordinatedresponsesincreasetheavailabilityofoxygenandfueltoworkingmuscles.However,thisini-tialstagecannotbesustainedforlong.

resistance stage The resistance stage takes overwhenthefight-or-flightstageisalmostcomplete.Inthisstage,thebody’senergyreservesaretappedtoprovideen-ergytoworkingmusclesorothertissues,suchassitesofinjury.Theresistancestageinvolvesthehypothalamus,pi-tuitarygland,adrenalcortex,andthyroidgland.Depend-ingonthetypeandseverityofthestress, theresistancestagemaybesuccessfulincombatingthestressorandre-turningthebodytonormal.However,whenanindividualcannotdefeatapowerfulstressor,suchasseveretrauma,thebodybecomesexhausted.

Exhaustion stage Theexhaustion stageoccurswhenthe body’s energy resources become depleted, muscleswasteaway,andtheimmunesystemissuppressed.

Several Organs and Hormones Are Involved in the Stress ResponseThe sympathetic nervous system and the hypothalamusdirectthestressresponsebystimulatingotherorgansandglands,suchastheadrenalglands,thepituitarygland,thethyroid gland, the liver, and skeletal muscle (see Figure9.20).Let’sdiscussthemateachstageofthestressresponse.

In the fight-or-flight stage, the sympathetic nervoussystemisactivatedandreleasesnorepinephrine,which:

• Stimulatestheheart,whichincreasesheartrate,bloodpressure,andbloodflow.

• Constrictsbloodvesselstovisceralorgans,suchasthedigestivesystemandskin.Thisreducesdigestionand

InSight Overviewoftheeffectsofagingonthemajorendocrineglands • Figure 9.21 THE PlAnnEr✓✓

AgingAlterstheendocrinesystem2928CHAPTer9 Theendocrinesystem

Aging Alters the Endocrine SystemLEARNING OBJECTIVE1. Describe theeffectsofagingontheendocrine

system. Aging alters the secretions of various endo-crineglands.Becauseseveralendocrinefunc-tionsinvolvemorethanoneendocrineglandthrough negative-feedback loops, aging may

cause different hormonal changes; some glands may in-creasesecretions,whileothersmaydecreasesecretions.

In general, the size or secretions of many endocrineglandsdiminishasthebodyages(Figure 9.21).Hormonalchangesincludediminishedoutputbyendocrineglands,diminished sensitivity of target tissues to hormonalstimulation, and increased secretions of some glands asa consequence of failed negative-feedback loops withintheendocrinesystem.Forexample,thecessationofse-cretionsof estrogenandprogesterone fromtheovariescauses one of the most dramatic changes in the female

endocrine system—menopause (see Chapter 16). Also,insufficientdietarycalciumleadstoelevatedPTHsecre-tionanddiminishedsecretionsofcalcitoninandcalcitriol;theseeventsleadtoosteoporosis,weakeningofboneandincreasedoccurrencesofbonefractures(seeChapter5).

1. How doesagingaffecttheovariesinwomen?

Mostoften,asweage,thesecretionsofmajorendocrineglandsdiminish,andsomeendocrineglandsmayshrink.

Pineal gland – Secretion ofmelatonin is reduced with age,which may disrupt normalsleep-wake cycles.

Pituitary gland• hGH secretion decreases, leading to muscle atrophy and weakness.• TSH secretion may be elevated due to negative feedback by thyroid hormones.• Slightly higher levels of ACTH due to failure of negative feedback by cortisol.• LH, FSH secretions decrease probably due to decreasing GnRH from hypothalamus.

Hypothalamus• GHRH secretion from the hypothalamus may also diminish with age.• TRH secretion may be elevated due to failure of negative feedback by thyroid hormones.• Slightly higher levels of CRH due to failure of negative feedback by cortisol.• GnRH secretion decreases.

Thyroid gland• Thyroid hormone secretions diminish, resulting in reduced rate of metabolism. A reduction in metabolism encourages the formation of more body fat and increases sensitivity to cold temperatures.

• Calcitonin secretion diminishes.

Male

Female

The thymus gland shrinks significantly, resulting in decreased immune cell production and decreased resistance to disease.

30CHAPTer9 Theendocrinesystem

THE PlAnnEr ✓✓byhypothalamicCRHsecretionandpituitaryACTHsecretion.

• Theadrenalmedullasecretesepinephrineandnorepinephrine,whichincreaseheartrate,bloodpressure,andbloodflowandmobilizeenergysources.

• Theovariessecreteestrogenandprogester-one.Secretionsarecontrolledbythehy-pothalamusviagonadotropin-releasing hormone (GnRH)andthepituitaryglandviafollicle-stimulatinghormone(FSH)andluteinizinghormone(LH).Thesehormonescontrolthemenstrualcycle,initiateovulation,andmaintainpregnancy.

• Thetestessecretetestosteroneundercontrolofthehypothalamus(GnRH)andpituitarygland(LH,FSH).Testos-teronesupportsspermdevelop-mentandmaintainsmalesexualcharacteristics.

• Otherbodytissues(forexample,heart,kidney,intes-tine)secretedifferenthormonesthathaveavarietyoffunctions(forexample,controlbloodvolume,increaseredbloodcellproduction,stimulateinsulinsecretion).

The Endocrine System Coordinates the Stress Response 25

• Asshownhere,thestressresponsehasthreestages:fight-or-flight,resistance,andexhaustion.

5

summary31

1Summary

Hormones Act on Target Cells 4

• Theendocrinesystemconsistsofbothendocrineglandsandendocrinecellsofotherorgans.Theendocrinesystemregulatesmanyphysiologicalparameterschemically.

• Endocrinecellssecretehormonesthatbindtoreceptorsintargetcellsandcausesomeactionsinthetargetcellstoevokephysiologicalresponses.

• Hormonescanbeclassifiedassteroidhormonesornonste-roidhormones.

• Steroidhormonescangodirectlythroughthetargetcellmembrane,andstimulatespecificgenestomakenewpro-teins,whichaltertheactivityofthetargetcell.

• Asshown,nonsteroidhormones,usuallymustbindtoahormonereceptoronthesurfaceofthecellmembrane,andelicittheformationofa“secondmessenger”insidethecell(forexample,cyclic AMP,calcium),whichaltersthetargetcell’sactivity.

Endocrine Glands Regulate Key Body Functions 7

• Theendocrineglandsandorganscontainingendocrinecellssecreteapproximately30differenthormonesthatregu-lateandcontrolmanybodyfunctions,includingchemicalcompositionandvolumeofblood,metabolism,contractionsofsmoothandcardiacmuscles,secretionsofendocrineglands,growth,development,andreproduction.

• Endocrinedisordersinvolveeitherhyposecretionorhyper-secretionofhormones.Causesofdisorderscanbeeitherprimary(withintheaffectedgland)orsecondary(withinaglandthatregulatestheaffectedgland).

• Thehypothalamusandpituitaryglandregulatemanyendocrineglandsandbodyfunctions.Thehypothalamussecreteshormones(ADH,oxytocin)directlyintotheblood-streamthroughtheneurosecretory cellsoftheposteriorpituitary.Antidiuretic hormone (ADH)affectsfluidreab-sorptioninthekidneys.

• Thehypothalamussecretesreleasinghormones(GnRH,GHRH,thyrotropin-releasing hormone (TRH),CRH,PRH)andinhibitinghormones(GHIH,PIH)intoacommonbloodsupply,wheretheyaffecttheanteriorpituitary.

• Theanteriorpituitarysecretesmanyhormonesthataffecthumangrowth.

• Otheranteriorpituitaryhormones(TSH,ACTH,FSH,LH,PRL)controlthesecretionsofthethyroidgland,theadrenalglands,theovaries/testes,andbreastdevelopmentandmilkproduction.

• Asshownhere,thethyroidglandsecretesthy-roidhormones(thyroxine,triiodothy-ronine)thatincreasebasalmetabolism,andcalcitonin,whichdecreas-esbloodcalciumlevelsbyinhibitingtheactivityofatypeofbonecellcalledosteoclaststhatreleasecalciumintotheblood.

2• Theparathyroidglandssecreteparathyroidhormone,

whichmobilizescalciumfrombone,increasescalciumreabsorptioninthekidneys,andstimulatescalcitriolsecretionbythekidneys.Calcitriolstimulatescalciumabsorptionbythesmallintestine.Parathyroidhormoneandcalcitoninactinoppositewaystocontrolbloodcalciumlevels.

• Thepancreas,asseenhere,secretesglucagonandinsulin.Bothglucagonandinsulinactmainlyontheliverandskeletalmuscle;theyhaveoppositeeffectsonbloodglucose.Inresponsetolowbloodsugarlevels(hypoglycemia),glucagonmobilizesenergysourcestoraiselowbloodglucosebystimulatingthebreakdownofliverglycogenintoglucose,adiposetissuetriglyc-eridesintofattyacids,andmuscleproteinsintoaminoacids.Inresponsetohighbloodsugarlevels(hypergly-cemia),insulinlowershighbloodglucosebystimulatingallcellstotakeupglucosefromtheblood,andithastheoppositeeffectofglucagononliver,adiposetissue,andskeletalmuscle.

3

4

Endocrine Glands Regulate Other Key Body Functions 19

• Theadrenalcortexsecretesamineralocorticoidcalledaldosterone,whichaffectssodiumreabsorptionandpo-tassiumexcretioninthekidneys.Aldosteronesecretion,whichiscontrolledbytherenin–angiotensin–aldoste-ronepathway,influencesbloodvolumeandpressure.

• Asshown,theadrenalcortexalsosecretesaglucocor-ticoidcalledcortisol,whichmobilizesenergysourcesfromskeletalmuscle,theliver,andadiposetissue.Corti-solalsoreducesinflammation.Itssecretioniscontrolled

nonsteroid hormones • Figure 9.3

• Nonsteroidhormonesgenerallyactfaster,buttheireffectsareshorterthanthoseofsteroidhormones.

Thyroid hormone levels • Figure 9.8

Control of glucocorticoid secretion • Figure 9.16

The pancreas • Figure 9.12a

CRHGHRHTRH

TSHhGHACTH

The stress response • Figure 9.20

32CHAPTer9 Theendocrinesystem

5PinealGland

PituitaryGland

ThyroidGland

Ovary

Testes

AdrenalGlands

Pancreas

ParathyroidGlands

Aging Alters the Endocrine System 28

• Thesizeorsecretionsofmanyendocrineglands,asshownhere,diminishwithaging.

• Secretionsofgrowthhormone,thyroidhormones,cortisol,aldosterone,estrogen,andprogesteronealldecreasewithaging.

• Thesympatheticnervoussystemstartsthefight-or-flightstage.Theadrenalmedullasecretesepinephrineandnor-epinephrine,whichincreasebloodflowandmobilizeenergysources.

• Activityofthehypothalamusandpituitaryglandcontinueduringtheresistancestagebystimulatingsecretionofcortisol,growthhormone,andthyroidhormones.Thesehormonesmobilizeenergysources(glucose,fattyacids,aminoacids)thattissuescanusetomakeATP.Resistancecanbesustainedforalongperiodoftimetocombatastressor.

• Theexhaustionstageoccurswhenresistancecannolongercombatthestressorandbodyreservesaredepleted.

Key Terms• acromegaly10

• Addison’sdisease22

• adrenalgland19

• aldosterone20

• androgen22

• anteriorpituitarylobe8

• antidiuretichormone(ADH)11

• calcitonin12

• calcitriol15

• congenitalhypothyroidism14

• cortex19

• cortisol21

• Cushing’ssyndrome22

• cyclicAMP(cAMP)6

• diabetesinsipidus11

• diabetesmellitus17

• endocrinegland4

• endocrinesystem4

• epinephrine22

• estrogen22

• exhaustionstage27

• exophthalmos14

• fight-or-flightstage27

• follicle12

• follicularcell12

• generaladaptationsyndrome25

• gestationaldiabetes18

• gigantism10

• glucagon17

• glucocorticoid21

• gonadotropin-releasinghormone(GnRH)23

• Gravesdisease14

• hormone5

• hormonereceptor5

• hyperglycemia17

• hyperthyroidism14

• hypoglycemia17

• hypothyroidism14

• insulin17

• medulla19

• melatonin24

• mineralocorticoid20

• myxedema14

• neurosecretorycell9

• nonsteroidhormone5

• norepinephrine22

• osteoclast14

• oxytocin10

• pancreaticisletsorisletsofLangerhans16

• parafollicularcell12

• parathyroidgland14

• parathyroidhormone(PTH)15

• pineal24

• pinealocyte24

• pituitarydwarfism10

• pituitarygland8

• posteriorpituitarylobe8

• progesterone22

• resistancestage27

• seasonalaffectivedisorder(SAD)24

• secondmessenger6

• steroidhormone5

• stressresponse25

• targetcell5

• testosterone22

• thyrotropin-releasinghormone(TRH)13

• thyroxine12

• triiodothyronine12

Critical and Creative Thinking Questions1.Twoteenageboys,BobandBill,arediagnosedwithdiabetes.

Bobisslightlyunderweightforhisage,whileBillisover-weight,possiblyobese.Bobmusttakedailyinsulininjectionstocontrolhisdiabetes,whileBillmustwatchhisdietandtakeoralmedications.Identifythereasonsforthedifferenttreat-mentsandexplainwhatisgoingonineachoftheirbodies.

2.Joe’swifeof20yearshasnoticedchangesinhisappearance.Whentheyweremarriedatage18,Joewasatall,handsometeenager.AsJoehasaged,hishands,feet,andjawshavethickened,andhisheadhasbecomeelongated.WhatmightbehappeningtoJoe?Whattestsmightyouconducttosup-portyourhypothesis?

3.Ascientisthastwoculturesofthesametypeofcell.SheadministersHormoneAtoonecultureandHormoneBtotheother.ShenoticesthatHormoneAhasanimmediateeffectontheculture,whiletheculturewithHormoneBtakesabout90

minutestoshowanyactivity.Whenthescientistexaminespro-teinsynthesisinbothcultures,shenoticesthatnewproteinsaremadeonlyinthecultureexposedtoHormoneB.Explainthedifferencesbetweenthetwohormonesandindicatewhattypestheymightbe.

4.Laurarecentlysufferedaheadinjuryinacaraccident.Assheisrecovering,shenoticesthatsheisalwaysthirsty,urinatesfrequently,andpasseslargevolumesofurine.Ifshedoesnotdrinkoften,shefeelsweak,faint,andnauseated.WhatmighthavehappenedtoLaura,andwhatisgoingoninherbodythatwouldexplainthesesignsandsymptoms?

5.Michaelisa45-year-oldmanwhowasrecentlydiagnosedwithhighbloodpressure.Hisphysicianprescribedadrugcalledanangiotensin-convertingenzyme(ACE)inhibitor.HowwillthedrugaffectMichael’sabilitytowithstanddehydra-tion?Explain.

What is happening in this picture?Allthesegirlsare15yearsold,butoneofthemlooksverydiffer-entfromtheothers.Atonly23.5inchestall,JyotiAmgeisalleg-edlytheworld’ssmallestperson.

1. What endocrine problem might make Jyoti so much smaller than the other girls?2. How would it affect her size?

T h i n k C r i t i c a l l y

33

Components of the Endocrine System • Figure 9.1

• TSH,PTH,LH,andFSHsecretionsincreasewithaging.

• Asabodyages,thepancreassecretesinsulinmoreslowly,andtissuestakelongertorespondtoinsulin.

34CHAPTer9 Theendocrinesystem self-Test35

Self-Test(CheckyouranswersinAppendixXX.)

1. Whichofthefollowingdoesabodyneedforsuccessfulendocrinecommunication?

a.endocrinecellb.hormonec.targetcelld.alloftheabove

2. TheletterCindicatesthe__________.

a.adrenalglandsb.thyroidglandc.pinealglandd.pituitarygland B

C

A

D

E

3. Intheabovefigure,theendocrineglandthatcontrolsreproductivefunctionsislabeled__________.

a.A d.Db.B e.Ec.C

4. Oftheglandslabeledinthefigureabove,theonethatismostinvolvedintheresistancephaseofthestressresponseis__________.

a.A d.Db.B e.Ec.C

6. Thefigureabovedemonstratestheactionofthehormone__________.

a.cortisol c.epinephrineb.insulin d.parathyroidhormone

7. Thehormone__________wouldrequireasecondmessengerforitsaction.

a.cortisol c.aldosteroneb.epinephrine d.estrogen

8. Thehormone__________isessentialtoreproduction.

a.CRH c.ACTHb.hGH d.GnRH

5. Thehormone__________wouldbeelevatedinanindividualwithprimarythyroidhormonedeficiency.

a.ADH c.TSHb.GnRH d.ACTH

9.Theendocrineglandindicatedbyarrowsinthefigureaboveregulates__________.

a.thegrowthoflongbones c.bloodvolumeb.bloodcalciumlevels d.basalmetabolism

10. Theglandpicturedinthefigureabovealsoplaysarolein__________.

a.reproduction c.typeIdiabetesb.stressresponse d.gigantism

11. Themineralocorticoidsecretedfromtheglandinthefigureaboveoriginatesinthe__________.

a.hypothalamus c.thyroidglandb.anteriorpituitarylobe d.kidneys

13. Thehormone____________hastheoppositeeffectsofglucagon.

a.cortisol c.epinephrineb.insulin d.ADH

14. Whatmightbethecauseoftheconditionshowninthephotoabove?

a.secretionoftoomuchhGHduringadulthoodb.lackofhGHsecretionduringchildhoodc.secretionoftoomuchhGHduringchildhoodd.secretionoftoomuchcortisolduringadulthood

15. Elderlypeopleoftenhaveosteoporosis.Whatmightcontributetothiscondition?

a.notenoughthyroidhormoneb.secretionoftoomuchcalcitoninc.highlevelsofparathyroidhormoned.highlevelsofcortisol

12. Thepersonshowninthephotoabovelikely__________.

a.lacksinsulinb.secretestoomuchaldosteronec.secretestoomuchthyroidhormoned.lacksparathyroidhormone

ReviewyourChapterPlanneronthechapteropenerandcheckoffyourcompletedwork.

THE PlAnnEr ✓✓