Anatomy Glands First Proff 2022-2023.pdf

Anatomy Glands First Proff 2022-2023.pdf

1. Endocrine System
Pharm D 1
st
Prof
Bahauddin Zakariya University Multan
Waseem Ashraf

2. Recommended Books:
•Fundamentals of Anatomy & Physiology. Martini F, Nath JL, Bartholomew EF. 10th Edition
•Principles of Anatomy and Physiology. Tortora GJ, Derrickson B. 13th Edition

3. Pituitary Gland
Pituitarygland,orhypophysisissmall,ovalglandliesnestledwithinthesellaturcica,adepressioninthesphenoid
bone.Thepituitaryglandisinferiortothehypothalamus.Itisconnectedbytheslender,funnel-shapedstructurecalled
theinfundibulum.Thebaseoftheinfundibulumliesbetweentheopticchiasmandthemammillarybodies.Cradled
bythesellaturcica,thepituitaryglandisheldinpositionbythesellardiaphragm,aduralsheetthatencirclesthe
infundibulum.Thesellardiaphragmlocksthepituitaryglandinpositionandisolatesitfromthecranialcavity.The
pituitaryglandhasanteriorandposteriorlobesthatdifferinfunctionanddevelopmentalanatomy.
Itreleasesnineimportantpeptidehormones.
Sevencomefromtheanteriorlobeandtwofromtheposteriorlobe.
Allninehormonesbindtomembranereceptors,andallnineusecAMPasasecondmessenger.

5. Anterior Lobe of Pituitary Gland
Theanteriorlobeofthepituitarygland,alsocalledtheadenohypophysis,containsavarietyofendocrinecells.The
anteriorlobehasthreeregions:
1.theparsdistalis(distalpart),thelargestandmostanteriorportionofthepituitarygland;
2.anextensioncalledtheparstuberalis,whichwrapsaroundtheadjacentportionoftheinfundibulum;and
3.theslenderparsintermedia,anarrowbandborderingtheposteriorlobe.
Anextensivecapillarynetworkradiatesthroughtheseregions,givingeveryendocrinecellimmediateaccesstothe
bloodstream.
TheHypophysealPortalsystem
Thehypothalamuscontrolstheproductionofhormonesintheanteriorlobeofthepituitaryglandbysecreting
specificregulatoryhormones.Atthemedianeminence,aswellingneartheattachmentoftheinfundibulum,
hypothalamicneuronsreleaseregulatoryfactorsintothesurroundinginterstitialfluids.Theirsecretionsenterthe
bloodstreamquiteeasily,becausetheendothelialcellsliningthecapillariesinthisregionareunusuallypermeable.
Thesefenestrated(fenestra,window)capillariesallowrelativelylargemoleculestoenterorleavethebloodstream.

6. The Hypophyseal Portal system
Thecapillarynetworksinthemedianeminencearesuppliedbythesuperiorhypophysealartery.Beforeleavingthe
hypothalamus,thecapillarynetworksunitetoformaseriesoflargervesselsthatspiralaroundtheinfundibulumto
reachtheanteriorlobe.Intheanteriorlobe,thesevesselsformasecondcapillarynetworkthatbranchesamongthe
endocrinecells.Thisvasculararrangementisunusualbecauseitcarriesbloodfromonecapillarynetworkto
another.Incontrast,atypicalarteryconductsbloodfromthehearttoacapillarynetwork,andatypicalveincarries
bloodfromacapillarynetworkbacktotheheart.
Bloodvesselsthatlinktwocapillarynetworksarecalledportalvessels.Inthiscase,theyhavethehistological
structureofveins,sotheyarealsocalledportalveins.Theentirecomplexisaportalsystem.
Portalsystemsarenamedfortheirdestinations.Thisparticularnetworkisthehypophysealportalsystem.

8. Hypothalamic Control of the Anterior Lobe
Twoclassesofhypothalamicregulatoryhormonesexist:releasinghormonesandinhibitinghormones.
Areleasinghormone(RH)stimulatesthesynthesisandsecretionofoneormorehormonesattheanteriorlobe.In
contrast,aninhibitinghormone(IH)preventsthesynthesisandsecretionofhormonesfromtheanteriorlobe.
Releasinghormones,inhibitinghormones,orsomecombinationofthetwomaycontrolanendocrinecellinthe
anteriorlobe.Theregulatoryhormonesreleasedatthehypothalamustraveldirectlytotheanteriorlobebythe
hypophysealportalsystem.
Negativefeedbackcontrolstherateatwhichthehypothalamussecretesregulatoryhormones.

11. Hormones of the Anterior Lobe
Thefunctionsandcontrolmechanismsofsevenhormonesfromtheanteriorlobearereasonablywellunderstood.
1.Thyroid-stimulatinghormone;
2.Adrenocorticotropichormone;
3.Twogonadotropinscalledfollicle-stimulatinghormoneandluteinizinghormone;
4.Prolactin;
5.Growthhormone;and
6.Melanocytestimulatinghormone.
Ofthesixhormonesproducedbytheparsdistalis,fourregulatetheproductionofhormonesbyotherendocrine
glands.Thenamesofthesehormonesindicatetheiractivities.
Thehormonesoftheanteriorlobearealsocalledtropichormones(trope,aturning).They“turnon”endocrine
glandsorsupportthefunctionsofotherorgans.(Somesourcescallthemtrophichormones[trophe,nourishment]
instead.)

12. Thyroid-StimulatingHormone.
Thyroid-stimulatinghormone(TSH),orthyrotropin,targetsthethyroidglandandtriggersthereleaseofthyroid
hormones.TSHisreleasedinresponsetothyrotropin-releasinghormone(TRH)fromthehypothalamus.Thenas
circulatingconcentrationsofthyroidhormonesrise,theratesofTRHandTSHproductiondecline.
AdrenocorticotropicHormone.
Adrenocorticotropichormone(ACTH),alsoknownascorticotropin,stimulatesthereleaseofsteroidhormonesby
theadrenalcortex,theouterportionoftheadrenalgland.ACTHspecificallytargetscellsthatproduceglucocorticoids,
hormonesthataffectglucosemetabolism.ACTHreleaseoccursunderthestimulationofcorticotropin-releasing
hormone(CRH)fromthehypothalamus.Asglucocorticoidlevelsincrease,theratesofCRHreleaseandACTH
releasedecline.

13. Gonadotropins.
Thehormonescalledgonadotropinsregulatetheactivitiesofthegonads.(thetestesinmalesandtheovariesin
females—producereproductivecellsaswellashormones.)
Gonadotropinreleasinghormone(GnRH)fromthehypothalamusstimulatesproductionofgonadotropins.An
abnormallylowproductionofgonadotropinsresultsinhypogonadism.Childrenwiththisconditiondonotmature
sexually,andadultswithhypogonadismcannotproducefunctionalsperm(males)oroocytes(females).
Thetwogonadotropinsarefollicle-stimulatinghormoneandluteinizinghormone.
Follicle-stimulatinghormone(FSH),orfollitropin,promotesfollicledevelopmentinfemalesand,in
combinationwithluteinizinghormone,stimulatesthesecretionofestrogensbyovariancells.Estradiolisthemost
importantestrogen.Inmales,FSHstimulatesnursecells,specializedcellsintheseminiferoustubuleswheresperm
differentiate.Inresponse,thenursecellspromotethephysicalmaturationofdevelopingsperm.
FSHproductionisinhibitedbyinhibin,apeptidehormonereleasedbycellsinthetestesandovaries.(Theroleof
inhibininsuppressingthereleaseofGnRHaswellasFSHisunderdebate.)

14. Gonadotropins.
Luteinizinghormone(LH),orlutropin,inducesovulation,theproductionofreproductivecellsinfemales.It
alsopromotesovariansecretionofestrogensandprogesterone,whichpreparethebodyforpossiblepregnancy.
Inmales,thisgonadotropinissometimescalledinterstitialcell–stimulatinghormone(ICSH),becauseitstimulates
theproductionofsexhormonesbytheinterstitialcellsofthetestes.Thesemalesexhormonesarecalledandrogens.
Themostimportantoneistestosterone.
LHproduction,likeFSHproduction,isstimulatedbyGnRHfromthehypothalamus.Estrogens,progesterone,and
androgensinhibitGnRHproduction.

15. Prolactin.
Prolactin(pro-,before+lac,milk)(PRL)workswithotherhormonestostimulatemammaryglanddevelopment.In
pregnancyandduringthenursingperiodthatfollowsdelivery,PRLalsostimulatesmilkproductionbythemammary
glands.ThefunctionsofPRLinmalesarepoorlyunderstood,butevidenceindicatesthatPRLhelpsregulateandrogen
productionbymakinginterstitialcellsmoresensitivetoLH.
Prolactinproductionisinhibitedbytheneurotransmitterdopamine,alsoknownasprolactin-inhibiting
hormone(PIH).Thehypothalamusalsosecretesseveralprolactin-releasingfactors(PRF).Fewofthesehavebeen
identified.CirculatingPRLstimulatesPIHreleaseandinhibitsthesecretionofPRF.
AlthoughPRLexertsthedominanteffectontheglandularcells,normaldevelopmentofthemammaryglandsis
regulatedbytheinteractionofseveralhormones.Prolactin,estrogens,progesterone,glucocorticoids,pancreatic
hormones,andhormonesproducedbytheplacentacooperateinpreparingthemammaryglandsforsecretion.
Milkejectionoccursonlyinresponsetooxytocinreleaseattheposteriorlobeofthepituitarygland.

16. GrowthHormone.
Growthhormone(GH),orsomatotropin,stimulatescellgrowthandreplicationbyacceleratingtherateofprotein
synthesis.Skeletalmusclecellsandchondrocytes(cartilagecells)areparticularlysensitivetoGH,althoughvirtually
everytissuerespondstosomedegree.
TheproductionofGHisregulatedbygrowthhormone–releasinghormone(GH–RH,orsomatocrinin)and
growthhormone–inhibitinghormone(GH–IH,orsomatostatin)fromthehypothalamus.Somatomedinsinhibit
GH–RHandstimulateGH–IH.
Melanocyte-StimulatingHormone.
Theparsintermediamaysecretetwoformsofmelanocyte-stimulatinghormone(MSH),ormelanotropin.Asthe
nameindicates,MSHstimulatesthemelanocytesoftheskin,increasingtheirproductionofmelanin,abrown,black,
oryellow-brownpigment.DopamineinhibitsthereleaseofMSH.

17. ThePosteriorLobeofthePituitaryGland
Theposteriorlobeofthepituitarygland,alsocalledtheneurohypophysis,containstheaxonsofhypothalamic
neurons.Neuronsofthesupraopticandparaventricularnucleimanufactureantidiuretichormone(ADH)and
oxytocin(OXT),respectively.Thesehormonesmovealongaxonsintheinfundibulumtoaxonterminals,whichend
onthebasementmembranesofcapillariesintheposteriorlobe.Theytravelbymeansofaxoplasmictransport.
AntidiureticHormone
Antidiuretichormone(ADH),alsoknownasvasopressin(VP),isreleasedinresponsetoavarietyofstimuli,most
notablyariseinthesoluteconcentrationinthebloodorafallinbloodvolumeorbloodpressure.Ariseinthesolute
concentrationstimulatesspecializedneuronsinthehypothalamus.Theseneuronsarecalledosmoreceptorsbecause
theyrespondtoachangeintheosmoticconcentrationofbodyfluids.Theosmoreceptorsthenstimulatethe
neurosecretoryneuronsthatreleaseADH.
TheprimaryfunctionofADHistoactonthekidneystoretainwateranddecreaseurination.Withlosses
minimized,anywaterabsorbedfromthedigestivetractwillberetained,reducingtheconcentrationsofelectrolytesin
theextracellularfluid.Inhighconcentrations,ADHalsocausesvasoconstriction,anarrowingofperipheralblood
vesselsthathelpselevatebloodpressure.AlcoholinhibitsADHrelease.

18. Oxytocin
Inwomen,oxytocin(oxy-,quick+tokos,childbirth)(OXT)stimulatessmoothmusclecontractioninthewallofthe
uterus,promotinglaboranddelivery.Afterdelivery,oxytocinpromotestheejectionofmilkbystimulatingthe
contractionofmyoepithelialcellsaroundthesecretoryalveoliandtheductsofthemammaryglands.
Untilthelaststagesofpregnancy,theuterinesmoothmusclesarerelativelyinsensitivetooxytocin,buttheybecome
moresensitiveasthetimeofdeliveryapproaches.Thetriggerfornormallaboranddeliveryisprobablyasuddenrise
inoxytocinlevelsattheuterus.Thereisgoodevidence,however,thattheuterusandfetussecretemostofthe
oxytocininvolved.Oxytocinfromtheposteriorlobeplaysonlyasupportingrole.
Oxytocinsecretionandmilkejectionarepartofaneuroendocrinereflexcalledthemilklet-downreflex.The
normalstimulusisaninfantsucklingatthebreast,andsensorynervesinnervatingthenipplesrelaytheinformationto
thehypothalamus.Oxytocinisthenreleasedintothecirculationattheposteriorlobe,andthemyoepithelialcells
respondbysqueezingmilkfromthesecretoryalveoliintolargecollectingducts.Anyfactorthataffectsthe
hypothalamuscanmodifythisreflex.Forexample,anxiety,stress,andotherfactorscanpreventtheflowofmilk,
evenwhenthemammaryglandsarefullyfunctional.Incontrast,nursingmotherscanbecomeconditionedtoassociate
ababy’scryingwithsuckling.Inthesewomen,milklet-downmaybeginassoonastheyhearababycry.

19. Oxytocin
Thefunctionsofoxytocininsexualactivityremainuncertain,butitisknownthatcirculatingconcentrationsof
oxytocinriseduringsexualarousalandpeakatorgasminbothsexes.
Evidenceindicatesthatinmen,oxytocinstimulatessmoothmusclecontractionsinthewallsoftheductusdeferens
(spermduct)andprostategland.Theseactionsmaybeimportantinemission—theejectionofsperm,secretionsofthe
prostategland,andthesecretionsofotherglandsintothemalereproductivetractbeforeejaculation.
Studiessuggestthattheoxytocinreleasedinfemalesduringintercoursemaystimulatesmoothmusclecontractionsin
theuterusandvaginathatpromotethetransportofspermtowardtheuterinetubes.

22. Thyroid Gland
Thethyroidglandcurvesacrosstheanteriorsurfaceofthetracheajustinferiortothethyroid(“shield-shaped”)
cartilage,whichformsmostoftheanteriorsurfaceofthelarynx.Thetwolobesofthethyroidglandareunitedbya
slenderconnection,theisthmus.Whensomethinggoeswrongwiththisgland,ittypicallybecomesvisibleasit
enlargesanddistortsthesurfaceoftheneck.
Thesizeoftheglandvaries,dependingonheredityandenvironmentalandnutritionalfactors,butitsaverageweight
isabout34g(1.2oz).Anextensivebloodsupplygivesthethyroidglandadeepredcolor.
ThyroidFolliclesandThyroidHormones
Thethyroidglandcontainslargenumbersofthyroidfollicles,hollowsphereslinedbyasimplecuboidalepithelium.
Thefolliclecellssurroundafolliclecavitythatholdsaviscouscolloid,afluidcontaininglargequantitiesofdissolved
proteins.Anetworkofcapillariessurroundseachfollicle,deliveringnutrientsandregulatoryhormonestothe
glandularcellsandacceptingtheirsecretoryproductsandmetabolicwastes.
Folliclecellssynthesizeaglobularproteincalledthyroglobulinandsecreteitintothecolloidofthethyroidfollicles.
Thyroglobulinmoleculescontaintheaminoacidtyrosine,thebuildingblockofthyroidhormones.

23. Thyroid Gland
Theformationofthyroidhormonesinvolvesthefollowingbasicsteps:
1.Iodideionsareabsorbedfromthedietbythedigestivetract,andthebloodstreamdeliversthemtothethyroid
gland.TSH-sensitivecarrierproteinsinthebasementmembraneofthefolliclecellsactivelytransportiodideions
(I−)intothecytoplasm.Normally,thefolliclecellsmaintainintracellularconcentrationsofiodidethataremany
timeshigherthanthoseintheextracellularfluid.
2.Theiodideionsdiffusetotheapicalsurfaceofeachfolliclecell,wheretheyloseanelectronandareconvertedto
anatomofiodine(I
0
)bytheenzymethyroidperoxidase.Thisreactionsequence,whichoccursattheapical
membranesurface,alsoattachesoneortwoiodineatoms(I
0
)tothetyrosineportionsofathyroglobulinmolecule
withinthefolliclecavity.
3.Tyrosinemoleculeswithattachediodineatoms(I
0
)becomelinkedbycovalentbonds,formingmoleculesof
thyroidhormonesthatremainincorporatedintothyroglobulin.Thyroidperoxidaseprobablycarriesoutthepairing
process.Thehormonethyroxine,alsoknownastetraiodothyronineorT4,containsfouriodineatoms.Arelated
moleculecalledtriiodothyronine,orT3,containsthreeiodineatoms.Eventually,eachmoleculeofthyroglobulin
containsfourtoeightmoleculesofT3orT4hormonesorboth.

24. Thyroid Gland
ThemajorfactorcontrollingtherateofthyroidhormonereleaseistheconcentrationofTSHinthecirculatingblood.
TSHstimulatesiodidetransportintothefolliclecellsandstimulatestheproductionofthyroglobulinandthyroid
peroxidase.TSHalsostimulatesthereleaseofthyroidhormones.
UndertheinfluenceofTSH,thefollowingstepsoccur:
4.Folliclecellsremovethyroglobulinfromthefolliclesbyendocytosis.
5.lysosomalenzymesbreakdownthethyroglobulin,andtheaminoacidsandthyroidhormonesenterthecytoplasm.
Theaminoacidsarethenrecycledandusedtosynthesizemorethyroglobulin.
6.ThereleasedmoleculesofT3andT4diffuseacrossthebasementmembraneandenterthebloodstream.About90
percentofallthyroidsecretionsisT4,andT3issecretedincomparativelysmallamounts.
7.About75percentoftheT4moleculesand70percentoftheT3moleculesenteringthebloodstreambecome
attachedtotransportproteinscalledthyroid-bindingglobulins(TBGs).MostoftherestoftheT4andT3inthe
circulationisattachedtotransthyretin,alsoknownasthyroid-bindingprealbumin(TBPA),ortoalbumin,one
oftheplasmaproteins.Onlytherelativelysmallquantitiesofthyroidhormonesthatremainunbound—roughly0.3
percentofthecirculatingT3and0.03percentofthecirculatingT4—arefreetodiffuseintoperipheraltissues.

26. The C Cells of the Thyroid Gland and Calcitonin
Thethyroidalsocontainsasecondpopulationofendocrinecells.ThesecellsaretheC(clear)cells,orparafollicularcells.
Theyliesandwichedbetweenthecuboidalfolliclecellsandtheirbasementmembrane.Theyarelargerthanthecellsofthe
follicularepitheliumanddonotstainasclearly.
Ccellsproducethehormonecalcitonin(CT),whichhelpstoregulateCa
2+
concentrationsinbodyfluids.
TheneteffectofcalcitoninreleaseisadropintheCa
2+
concentrationinbodyfluids.Calcitonin(1)inhibitsosteoclasts,
whichslowstherateofCa
2+
releasefrombone,and(2)stimulatesCa
2+
excretionbythekidneys

28. TSHplays a key role in both the synthesis and the release of thyroid hormones. In the absence of TSH, the thyroid
follicles become inactive, and neither synthesis nor secretion occurs.
TSH binds to plasma membrane receptors and, by stimulating adenylate cyclase, it activates key enzymes involved in
thyroid hormone production

30. Adrenal Gland
Theadrenalglands,consistingofacortexandmedulla,capthekidneysandsecreteseveralhormones.
Ayellow,pyramid-shapedadrenalgland,orsuprarenalgland,sitsonthesuperiorborderofeachkidney.Each
adrenalglandliesnearthelevelofthe12thrib.Adensefibrouscapsulefirmlyattacheseachadrenalglandtothe
superiorportionofeachkidney.Theadrenalglandoneachsidenestlesamongthekidney,thediaphragm,andthe
majorarteriesandveinsthatrunalongtheposteriorwalloftheabdominopelviccavity.Theadrenalglandsprojectinto
theperitonealcavity,andtheiranteriorsurfacesarecoveredbyalayerofparietalperitoneum.likeotherendocrine
glands,theadrenalglandsarehighlyvascularized.
Atypicaladrenalglandweighsabout5.0g(0.18oz),butitssizecanvarygreatlyassecretorydemandschange.The
adrenalglandhastwopartswithseparateendocrinefunctions:asuperficialadrenalcortexandaninneradrenal
medulla.

31. The Adrenal Cortex
Theyellowishcoloroftheadrenalcortexisduetostoredlipids,especiallycholesterolandvariousfattyacids.The
adrenalcortexproducesmorethantwodozensteroidhormones.Theyarecollectivelycalledcorticosteroids.Inthe
bloodstream,thesehormonesareboundtotransportproteinscalledtranscortins.
Corticosteroidsarevital.Iftheadrenalglandsaredestroyedorremoved,thepersonwilldieunlesscorticosteroidsare
administered.likeothersteroidhormones,corticosteroidsexerttheireffectsbyturningontranscriptionofcertain
genesinthenucleioftheirtargetcellsanddeterminingtheirtranscriptionrates.Theresultingchangesinthenature
andconcentrationofenzymesinthecytoplasmaffectcellularmetabolism.
Deeptotheadrenalcapsulearethreedistinctzonesintheadrenalcortex:(1)anouterzonaglomerulosa;(2)a
middlezonafasciculata;and(3)aninnerzonareticularis.Eachzonesynthesizesspecificsteroidhormones.

35. The Adrenal Cortex
ZonaGlomerulosa
Thezonaglomerulosaistheouterregionoftheadrenalcortex.Itproducesmineralocorticoids,steroidhormones
thataffecttheelectrolytecompositionofbodyfluids.Aldosteroneisthemainmineralocorticoidofthezona
glomerulosa.
Thezonaglomerulosaaccountsforabout15percentofthevolumeoftheadrenalcortex.Aglomerulusisalittleball,
andasthetermzonaglomerulosaimplies,theendocrinecellsinthisregionformsmall,denseknotsorclusters.This
zoneextendsfromthecapsuletotheradiatingcordsofthedeeperzonafasciculata.
Aldosterone.
Aldosteronestimulatestheconservationofsodiumionsandtheeliminationofpotassiumions.Thishormone
targetscellsthatregulatetheioniccompositionofexcretedfluids.Itcausestheretentionofsodiumionsbythe
kidneys,sweatglands,salivaryglands,andpancreas,preventingNa+lossinurine,sweat,saliva,anddigestive
secretions.AlossofK+accompaniesthisretentionofNa+.Asasecondaryeffect,theretentionofNa+enhancesthe
osmoticreabsorptionofwaterbythekidneys,sweatglands,salivaryglands,andpancreas.Theeffectatthekidneysis
mostdramaticwhennormallevelsofADHarepresent.

36. The Adrenal Cortex
ZonaGlomerulosa
Inaddition,aldosteroneincreasesthesensitivityofsaltreceptorsinthetastebudsofthetongue.Asaresult,a
person’sinterestin(andconsumptionof)saltyfoodincreases.
AldosteronesecretionoccursinresponsetoadropinbloodNa+content,bloodvolume,orbloodpressure,ortoarise
inbloodK+concentration.ChangesineitherNa+orK+concentrationhaveadirecteffectonthezonaglomerulosa,
butthesecretorycellsaremostsensitivetochangesinpotassiumlevels.Ariseinpotassiumlevelsisveryeffectivein
stimulatingthereleaseofaldosterone.AldosteronereleasealsooccursinresponsetoangiotensinII.

37. The Adrenal Cortex
ZonaFasciculata
Thezonafasciculata(fasciculus,littlebundle)producessteroidhormonescollectivelyknownasglucocorticoids,due
totheireffectsonglucosemetabolism.Thiszonebeginsattheinnerborderofthezonaglomerulosaandextends
towardtheadrenalmedulla.Itcontributesabout78percentofthecorticalvolume.Theendocrinecellsarelargerand
containmorelipidsthanthoseofthezonaglomerulosa,andthelipiddropletsgivethecytoplasmapale,foamy
appearance.Thecellsofthezonafasciculataformindividualcordscomposedofstacksofcells.Adjacentcordsare
separatedbyflattenedbloodvessels(sinusoids)withfenestratedwalls.
TheGlucocorticoids.
WhenstimulatedbyACTHfromtheanteriorlobeofthepituitarygland,thezonafasciculatasecretesprimarily
cortisol,alsocalledhydrocortisone,alongwithsmalleramountsoftherelatedsteroidcorticosterone.Theliver
convertssomeofthecirculatingcortisoltocortisone,anotheractiveglucocorticoid.Negativefeedbackregulates
glucocorticoidsecretion:Theglucocorticoidsreleasedhaveaninhibitoryeffectontheproductionofcorticotropin-
releasinghormone(CRH)inthehypothalamus,andonACTHintheanteriorpituitarylobe.

38. The Adrenal Cortex
EffectsofGlucocorticoids.
Glucocorticoidsspeeduptheratesofglucosesynthesisandglycogenformation,especiallyintheliver.Adiposetissue
respondsbyreleasingfattyacidsintotheblood,andothertissuesbegintobreakdownfattyacidsandproteinsinstead
ofglucose.Thisprocessisanotherexampleofaglucose-sparingeffect.
Glucocorticoidsalsoshowanti-inflammatoryeffects.Thatis,theyinhibittheactivitiesofwhitebloodcellsandother
componentsoftheimmunesystem.

39. The Adrenal Cortex
ZonaReticularis
Thezonareticularis(reticulum,network)formsanarrowbandborderingeachadrenalmedulla.Thiszoneaccountsfor
onlyabout7percentofthetotalvolumeoftheadrenalcortex.Theendocrinecellsofthezonareticularisforma
folded,branchingnetwork,andfenestratedbloodvesselswindamongthecells.UnderstimulationbyACTH,thezona
reticularisnormallyproducessmallquantitiesofandrogens,thesexhormonesproducedinlargequantitiesbythe
testesinmales.Onceinthebloodstream,someoftheandrogensfromthezonareticularisareconvertedtoestrogens,
thedominantsexhormonesinfemales.Adrenalandrogensstimulatethedevelopmentofpubichairinboysandgirls
beforepuberty.Adrenalandrogensarenotimportantinadultmen,butinadultwomentheypromotemusclemassand
bloodcellformation,andsupportthesexdrive.

40. AdrenalMedulla
Theboundarybetweentheadrenalcortexandtheadrenalmedullaisirregular,andthesupportingconnectivetissues
andbloodvesselsareextensivelyinterconnected.Theadrenalmedullaispalegrayorpink,dueinparttothemany
bloodvesselsinthearea.Itcontainslarge,roundedcells—similartocellsinsympatheticgangliathatareinnervated
bypreganglionicsympatheticfibers.
Thesympatheticdivisionoftheautonomicnervoussystemcontrolssecretoryactivitiesoftheadrenalmedullae.
Theadrenalmedullacontainstwopopulationsofsecretorycells:
Oneproducesepinephrine(adrenaline),theothernorepinephrine(noradrenaline).Evidencesuggeststhatthetwo
typesofcellsaredistributedindifferentareasandthattheirsecretoryactivitiescanbeindependentlycontrolled.The
secretionsarepackagedinvesiclesthatformdenseclustersjustinsideplasmamembranes.Thehormonesinthese
vesiclesarecontinuouslyreleasedatlowlevelsbyexocytosis.Sympatheticstimulationdramaticallyacceleratesthe
rateofexocytosisandhormonerelease.

41. Epinephrineandnorepinephrine
Epinephrinemakesup75–80percentofthesecretionsfromtheadrenalmedullae.Therestisnorepinephrine.These
hormonesinteractwithalphaandbetareceptorsonplasmamembranes.Stimulationofα1andβ1receptors,themost
commontypes,speedsuptheuseofcellularenergyandthemobilizationofenergyreserves.
Activationoftheadrenalmedullaehasthefollowingeffects:
Inskeletalmuscles,epinephrineandnorepinephrinetriggermobilizationofglycogenreservesandacceleratethe
breakdownofglucosetoprovideATP.Thiscombinationincreasesbothmuscularstrengthandendurance.
Inadiposetissue,storedfatsarebrokendownintofattyacids,whicharereleasedintothebloodstreamforother
tissuestouseforATPproduction.
Intheliver,glycogenmoleculesarebrokendown.Theresultingglucosemoleculesarereleasedintothebloodstream,
primarilyforusebyneuraltissue,whichcannotshifttofattyacidmetabolism.
Intheheart,thestimulationofβ1receptorstriggersanincreaseintherateandforceofcardiacmusclecontraction.
ThemetabolicchangesthatfollowthereleaseofcatecholaminessuchasEandNEreachtheirpeakabout30seconds
afteradrenalstimulation,andtheypersistforseveralminutes.Asaresult,theeffectsofstimulatingtheadrenal
medullaeoutlasttheothersignsofsympatheticactivation