ENDOCRINESYSTEM

PhysiologyUnit3

InPhysiologyToday

HormoneClassification

• AmineHormones– Tyrosine– Tryptophan

• Peptide/ProteinHormones–Watersoluble

• SteroidHormones– Lipidsoluble

AmineHormones

• DerivativesofTyrosine– Catecholamines

• Epinephrine

– Thyroidhormones• T3,T4

• DerivativesofTryptophan– Serotonin(5-HT)– Melatonin

• pinealgland

PeptideandProteinHormones

• PeptideHormones– <200aminoacids– ADH,ACTH,insulin,PTH,Calcitonin,ANF,GItracthormonesandothers

• ProteinHormones– TSH,LH,FSH,erythropoietin,renin

SteroidHormones

• Derivedfromcholesterol

• Producedby– Adrenalcortex– Gonads• Testosterone• Estrogens• Progesterone

SteroidHormonesHormonesoftheAdrenalCortex

• Aldosterone– Regulatesbloodpressure

• Cortisol– Releasedinresponsetostress– Increasebloodsugar– Aidinmetabolism

• Dehydroepiandrosterone(DHEA)– Androgen– Prohormone(precursor)forsex

steroids

HormoneTransportintheBlood

MechanismofHormoneActionHormoneReceptors

• Signal-transductionmechanism• Receptormodulation– Up-regulation– Down-regulation

• LocationofReceptor– Lipidsoluble–Watersoluble

MechanismofHormoneActionHormoneInteractions

• Synergisticeffects- Epi/NEonheart

• Permissive/Potentiation• HormoneAmustbepresentforafullstrengthofhormoneB’seffect

• Antagonisticeffects– Insulin/Glucagon– Calcitonin/PTH

TheHypothalamusandPituitaryGland

Hyothalamus-Pituitary Axis

PVN and SON send axons to both the poserior

pituitary and the portal vessel to the anterior

pituitary

PosteriorPituitaryHormones• PosteriorPituitaryisaneuralextensionofthehypothalamus• Neuronswhichprojectfromthehypothalamus

• Hormonessynthesizedinthehypothalamus• Hormonespackagedintovesiclesmovedowntheaxonsinto

theposteriorpituitary• Stimulioftheneuronsgenerateactionpotentialswhich

triggerthereleaseofthehormones• Hormonesreleased– Oxytocin

– Actsonsmoothmuscleoftheuterusandmammaryglands

– Antidiuretichormone(ADH)– Decreaseswaterloss– Stimulatesthirst

HypothalamusReleasingHormones

Somatocrinin = GHRH

HypothalamusandtheAnteriorPituitaryHormones

• Hypothalamusneuronssecretehormonesthatcontrolthesecretionofalltheanteriorpituitaryhormones– Hypothalamusreleasingorinhibitinghormones

• Eachofthereleasinghormonesisthefirstinathree-hormonesequence1. Hypothalamusreleasinghormone2. Anteriorpituitarystimulatinghormone3. Endocrineglandhormone

• Allowsforfeedback,amplificationofresponse• AllarepeptidehormonesexceptDA

AnteriorPituitaryHormonesandtheHypothalamus

AHypophysiotropic hormoneisreleasedfromthehypothalamusandbindstoreceptorsintheAnteriorPituitary

AnteriorPituitaryHormones

Atropichormonehasanotherendocrineglandasitstargetorgan

Hypothalamic-AnteriorPituitarySystem

Short-LoopandLong-LoopNegativeFeedback

ThyroidHormones• Follicularcells– secreteTH

• Producestwoiodinecontainingmolecules– Thyroxine(T4)– Triiodothyronine(T3)– T4 generallyconvertedintoT3 intargetcells

– Thyroglobulin• Thyroidbindinghormoneinthyroidfollicles

SynthesisofThyroidHormones

ControlofThyroidFunction

• BasiccontrolofThyroidHormoneproductionislong-loopnegativefeedback

• TheprimaryroleofT4 inthebloodistofeedbacktotheanteriorpituitaryANDthehypothalamus

ActionsofThyroidHormones• THreceptorspresentinthenucleiofmostcellsofthebody

• MetabolicActions– Maintainsrelativelyhighmetabolicrate– StimulatestheactivityofNa+/K+/ATPasepumps– Inducesgenetranscriptionandproteinsynthesis

• PermissiveActions– Potentiatestheactionsofcatecholamines

• GrowthandDevelopment– PotentiatesGH– Developmentandfunctionofthenervoussystem– Normalcognitioninadults

EndocrineControlofGrowthBoneGrowth

• GrowthHormone• Insulin-LikeGrowthFactorsIandII• Thyroidhormones• Insulin• Testosterone• Estrogens• Peptidegrowthfactors– Paracrine/autocrineagentstostimulatedifferentiation,celldivision

Ghrelinregulatesenergy

homeostasis

EndocrineControlofGrowthGrowthHormone

• Growthhormone(GH)–Mostimportanthormoneforpost-natalgrowth– Stimulus:exercise,stress,fasting,lowplasmaglucose,sleep

– Stimulatescelldivisioninmanytissues– Promotesbonelengthening– Stimulatesproteinsynthesisinmuscle– StimulateslivercellstosecreteIGF-I

EndocrineControlofGrowthInsulin-LikeGrowthFactors

• Insulin-LikeGrowthFactorI(IGF-I)– PotentiatesGHeffectsonbonegrowth• Stimulateschondrocytes

– Requiredforfetaltotalbodygrowth,maturationoffetalnervoussystem

• Insulin-LikeGrowthFactorII(IGF-II)– Importantmitogenduringprenatalperiod

EndocrineControlofGrowthThyroidHormonesandInsulin

• Thyroidhormones– Potentiatesgrowthhormone

• Insulin– Uptakeofglucoseandaminoacidsbycells– Stimulatesstorageoffat– Inhibitsproteindegradation– Promotescelldivisionanddifferentiationinfetaldevelopment

EndocrineControlofGrowthSexHormones

• Sexhormonesecretionbeginstoincreasebetweentheagesof8and10andplateausoverthenext5-10years

• Pubertalgrowthspurt– Growthoflongbones,vertebrae

• StimulatesthesecretionofGHandIGF-I• Testosteroneexertsadirectanaboliceffectonproteinsynthesis– Increasesmusclemass

EndocrineControlofCa2+Homeostasis

• Ca2+homeostasisisvitalforsurvival– Lowplasma[Ca2+]Hypocalcemia• Increaseexcitabilityofnerve,musclemembranes

– Highplasma[Ca2+]Hypercalcemia• Causescardiacarrhythmias• Causesdepressedneuromuscularexcitability

• Ca2+homeostasisinvolvesbone,kidneys,parathyroidgland,skin,thyroidgland,GItract

EndocrineControlofCa2+HomeostasisBone

• 99%oftotalbodyCa2+iscontainedinbone

• Osteoclast/osteoblastactivity

• Ca2+fluxinto/outofboneisparamountincontrollingplasma[Ca2+]

• Hydroxyapatiteiswheremineralsaredeposited– Ca2+,PO4

3-

EndocrineControlofCa2+HomeostasisKidneys

• ControlofCa2+excretionisexertedmainlyinthekidneys

• Reabsorptiondecreaseswhenplasma[Ca2+]increases,andvisversa

• HormonalcontrolsofCa2+alsoregulatePO43-

balance

EndocrineControlofCa2+HomeostasisParathyroidGland

• Normal,day-to-dayregulationofplasma[Ca2+]

• ParathyroidHormone(PTH)• Resultsinanincreaseinplasma[Ca2+]– Decreasedplasma[Ca2+]stimulatesPTHsecretion

• Stimulatesosteoclastactivity• Stimulates1,25-dihydroxyvitaminD• IncreasesCa2+reabsorptioninthekidneys

EndocrineControlofCa2+HomeostasisSkin

• Normal,day-to-dayregulationofplasma[Ca2+]

• 1,25-dihydroxyvitaminD(calcitrol)istheactiveformofVitaminD

• Resultsinanincreaseinplasma[Ca2+]• Synthesizedintheskin• Dietarysupplement• IncreasesabsorptionofCa2+andPO4

3- bytheintestines

EndocrineControlofCa2+HomeostasisThyroidGland

• Not involvedinnormal,day-to-dayregulationofplasma[Ca2+]

• Calcitonin– Peptidehormonesecretedbyparafollicularcellsofthethyroid

• Resultsinadecreasesplasma[Ca2+]– Stimulatedbyanincreaseinplasma[Ca2+]

• Inhibitsosteoclasts

EndocrineControlofGlucoseHomeostasisPancreas

• Insulin– Producedbypancreaticisletβcells

– Stimulatedbyincreasedbloodglucose

– Stimulatescellularuptake(liver,skeletalmuscle,adipocytes)andutilizationofglucose

• Glucagon– Producedbypancreaticisletαcells

– Stimulatedbydecreasedbloodglucose

– Stimulates livertoreleaseglucose

– Stimulates skeletalmuscle,adipocytestodecreaseglucoseuptakeandutilization