1.The Endocrine Introduction.pdf………………..

An academic article on the introduction to the endocrine system provides a comprehensive overview of the structure, function, and significance of endocrine glands and hormones in maintaining physiological balance. This type of article is typically published in medical or biological science journals and serves as a foundational resource for students, researchers, and healthcare professionals.

1. ENDOCRINE
PHARMACOLOGY
Introduction to the Endocrine
System

2. Major Functions of the Endocrine System:
1)Maintaininternalbodyhomeostasis(cellularmetabolism,
regulationofbodyfluidsandelectrolytes,modulationofthe
immunefunction).
2)Coordinatevariousfunctionsofthebody(Reproduction,
responsestoexternalstimuli,circadianrhythm).
3)Supportcellgrowthanddevelopment.
•Thesefunctionswereachievedbysecretionofchemicalmediators
(Hormones).
Chemicalsubstancesynthesized/released(inresponsetospecificstimuli)
insmallamountsbyanendocrinetissueandcarriedbybloodtothetarget
tissue.

3. Structures of the Endocrine System
•Thesystemconsistsofglands(majorplayer),cells,tissues,and
organs.
•EndocrineGlands:Pituitary,Thyroid,Parathyroids,
Adrenals,andPinealglands.
•Organswithsecondaryendocrinefunction:Hypothalamus,
Thymus,Heart,Kidneys,Stomach,Smallintestine,Liver,and
Gonadscontaincellswithendocrinefunction.
•ThePancreasfunctionsasbothexocrineandendocrinegland.
•ThePlacentaofpregnantmammalsalsoproduceshormonesthat
influenceuterine,fetal,andovarianprocesses.

4. What is a gland?
•Isspecializedcellclusterswhichproducesandreleases
chemicalproducts/mediatorthatperformaspecific
functioninthebody.
•Therearetwotypesofgland:
Endocrineglands:ductlessglandsproduces/releases
hormonesintothevascularsystemtobecarriedoutbythe
bloodtootherplaceinthebody.
Exocrineglands:(e.g.sweatglands,lymphnodes),produces
andreleasestheirproducts(non-hormonal)throughaductto
actwithinthenearenvironment.

5. •ChemistryofHormones:
Amines(Thyroxine,Epinephrine).
Proteins(Insulin,GH,Glucagon).
Peptides(ADHandOxytocin).
Glycoproteins(FSH,LH).
Steroids(Cortisol,Aldosterone,Estrogens,Testosterone).
•Hormonemoleculescanalsobedividedto:
Polarorwater-soluble(cannotorpoorlypassthroughplasma
membranes).
Nonpolarorwater-insolubleandoftenreferredtoaslipophilic
hormones(penetratetheplasmamembraneeasily).

6. HormonesReleaseandTransport:
•Hormonescouldbereleaseddirectlytotheblood,ordiffuseinto
thebloodstreamaftersecretiononextracellularspace.
•Thebloodcarrieshormonestothetargettissuecellswhich
containspecificreceptorsthatbindthehormonesandgivethe
response.
•Water-solublehormonesaresolubleinthebloodstream.
•Lipid-solublehormonesarenotsolubleinblood.Theyare
associatedwithCarrierProteinsviareversiblebonds,allowing
transportthroughthecirculation.
T4andT3aretransportedthroughthyroxine-bindingglobulin(TBG).
Corticosteroidstransportedbycorticosteroid-bindingglobulin(CBG).

7. Hormone Receptors:
1)Membrane-AssociatedReceptors
Bindhydrophilichormonesonthecellsurface.
Transmitsignalsintothecellthroughactivationofsecondmessengeror
byintracellularenzymeactivity.
E.g.FSH,LH,Epinephrine,andInsulinReceptors.
2)IntracellularReceptors:
Bindhydrophobichormones.
Hormone-receptorcomplexcouldmigratetothenucleuswheretheycould
modulatethetranscriptionofspecificgenes.
Modulationofgenetranscriptioninducesynthesisorinhibitsynthesisof
someproteins.
E.g.Thyroidhormones,CortisolandEstrogen.

8. Regulation of Hormones Secretion
•FeedbackLoops:
PositiveFeedback:stimulationofhormonesecretioninresponseto
otherhormonesthatcirculatedinthebloodortoitsoriginalrelease.
NegativeFeedback:inhibitionofhormonesecretioninresponseto
otherhormonesthatcirculatedinthebloodorwhenitexertsitseffects.
•EndocrineStimuli:
Humoralstimuli:release/inhibitionofhormonesinresponseto
changesinbloodlevelsofnon-hormonechemicals.
Neuralstimuli:release/inhibitionofhormonesinresponsetothe
nervoussystem.
•Itmaybecomplex(Prolactinproductionisaffectedbymany
neurotransmittersandhormones).

9. E.G. Feedback Loops
•ReleaseofOxytocinduringchildbirth:
Thefirstcontractionsoftheuterussignalthebodytoreleaseoxytocin(travelstothe
uterusandstimulatesmorecontractions).
Releasedoxytocinsignalthebodytoreleasemore,whichstimulatesmorecontractions.
Thefeedbackloopcontinuesuntilthechildisborn—thecontractionsstop,signallingthe
bodytostopreleasingoxytocin.
•TheTRH(hypothalamus)-TSH(pituitary)-Thyroxine(thyroid)system:
DropofthyroxinelevelsbelownormalsignalsthehypothalamustoreleaseTRH.
ReleasedTRHsignalsthepituitarytoreleaseTSH.
TSHthenstimulatesthethyroidtoproducethyroxine.
HighlevelsofthyroxineinthebloodsignalthehypothalamustostopreleasingTRH.

10. E.G. Endocrine Stimuli
•Humoralstimuli:
SecretionofInsulininresponsetohighlevelofbloodglucose.
SecretionofParathyroidHormoneinresponsetolowbloodcalcium
level.
•Neuralstimuli:
ReleaseofAdrenalineinresponsetoactivationofthefight-or-flight
responsebythesympatheticnervoussystem.
Detectionoflightbythesensoryreceptorsontheretinaoftheeyesinhibit
PinealGlandsecretionofMelatonin(whentheenvironmentgrowsdark,
melatoninproductionisstimulated).

11. Pulsatile Secretion of Hormones:
•Isabiochemicalphenomenoninwhichthehormone
secretedinaregulartemporalpattern.
•Pulsatilitycanbecriticaltothefunctionofmany
hormonestomaintainthedelicatehomeostaticbalance
necessaryforessentiallifeprocesses.
•Variationsoftheconcentrationinacertainfrequency
(constantstimulation)cancausefunctionalinhibitionof
thereceptorduetoprofounddownregulation.

12. HYPOTHALAMUS -PITUITARY COMPLEX
•Thiscomplexcanbethoughtofasthecommandcenterof
theendocrinesystem.
•Italsocoordinatesthemessagesoftheendocrineand
nervoussystems.
•Consistsof:
HypothalamicHormones.
AnteriorPituitaryHormones.
PosteriorPituitaryHormones.

13. HYPOTHALAMUS
•Isasmallstructurelocatednearthebaseofthebrain.
•Itaffectstheendocrinesystemthroughproductionofsix
majorhormones.
Thesehormonesstimulate/inhibitthereleaseofhormones
madeintheanteriorpituitary(alsocalledhypothalamic
regulatoryfactors).
•Alsoproducestwohormones(Vasopressinand
Oxytocin).
Producedbythehypothalamus,transportedtotheposterior
lobeofthepituitaryglandforstorageandsubsequentrelease.

14. HYPOTHALAMIC HORMONES:
1.Somatotropin-ReleasingHormone(GrowthHormone-
ReleasingHormone).
2.Somatotropin-Release Inhibiting Hormone
(Somatostatin).
3.Thyrotropin-ReleasingHormone(Protirelin).
4.Corticotropin-ReleasingHormone.
5.ProlactinInhibitingHormone(Dopamine).
6.Gonadotropin-ReleasingHormone(GnRH).

15. PITUITARY GLAND
•Small,ovalstructurelocatedunderthebrain.
•Ithastwoparts:
•Theanteriorlobe(Adenohypophysis):
Produceandreleasesixhormonesthatinfluencesthe
activityofmanyotherendocrineglands,tissuesor
organs.
•Theposteriorlobe(Neurohypophysis):
•Storesandreleasetwohypothalamushormones.

16. ANTERIOR PITUITARY HORMONES:
•Secretionmaybecontrolledbyhypothalamicregulatory
factorsorotherhormonesthatcirculatedintheblood.
•Allanteriorpituitaryhormonesarereleasedintothe
bloodstreaminapulsatilemanner(bythepulsatile
secretionofhypothalamicregulatoryhormones).
•Secretionmayalsovarieswithtimeofdayor
physiologicalconditions.

17. 1) Growth Hormone (Somatotropin):
•Stimulatelinearbodygrowthandregulatecellularmetabolism.
•Stimulateslipolysis,elevatesbloodglucose,andpromotesprotein
synthesisby:
Directeffectonmanytissues.
Stimulationofhepaticproductionofinsulin-likegrowthfactors
(IGFs/Somatomedins)whichmediateanabolicactionsonmanycell.
•SecretionisregulatedbyGHRHandSomatostatin.
•ReleaseofIGFshasaninhibitoryeffectonGHsecretionbystimulating
Somatostatinreleasefromthehypothalamus.
•Secretionishighinthenewborn,decreasingat4yearstoan
intermediatelevel,maintaineduntilafterpuberty,thenitdeclineto
lowlevels.

18. 2)Thyrotropin(Thyroidstimulatinghormone-TSH):
•Stimulatesthethyroidglandtoproducethyroidhormones
(ThyroxinandT3).
3)Corticotropin(Adrenocorticotropichormone-
ACTH):
•StimulatesproductionofGlucocorticoidsand
MineralocorticoidsfromtheAdrenalCortex.
4)Prolactin:
•Initiatesandmaintainsmilkproductionbythemammary
glandsinthebreast.

19. 5) Gonadotropins (FSH and LH):
•Follicle-StimulatingHormone(FSHorFolliculotropin):
Females:Releasedduringthefollicularphaseofthemenstrualcycle,
requiredfordevelopmentofovarianfolliclesandforestrogensynthesis
fromtheovaries.
Males:Stimulatesspermatogenesisandsynthesisofandrogen-binding
proteinsinthetestes.
•LuteinizingHormone(LHorLuteotropin):
Females:Secretionoccursjustbeforeovulationtoinduceovulation,
progesteroneandandrogensynthesisinthecellsoftheovaries.
Males:Stimulatestestosteroneproductionfromtestescells.
•ProductionofLHandFSHismainlycontrolledbyGnRHfromthe
hypothalamus,andInhibin(producedbygonads).

20. POSTERIOR PITUITARY HORMONES :
•Synthesizedinthehypothalamusandtransportedtotheposterior
lobeofthepituitaryglandforstorageandsubsequentrelease.
1)Vasopressin(AntidiureticHormone,ADH):
Releasedinresponsetodecreasesinbloodvolume.
Actsonthekidneycausingincreasedwaterreabsorption(V2receptors).
Athigherconcentrations,actsonV1receptorstocauseageneral
constrictionofmostbloodvessels.
2)Oxytocin:
Stimulatescontractionofuterinesmoothmuscleinlatephaseof
pregnancy.
Causesmilkreleasefromlactatingmammaryglands.