REPRODUCTIVEPHSYIOLOGY

PhysiologyUnit4

InPhysiologyToday

Gonads

• Gonadshave2functions– Gametogenesis• Spermatogenesis• Oogenesis

– Secretesteroidhormones• Testosterone• Estrogens(3forms)

– Estradiol,producedbyovaries,placenta

• Progesterone

SexHormonesMalesSexHormones

• Androgens– generalmasculinizingactions– Producedbyadrenalcortex– DHEAisanexample

• Testosterone– Producedbytestes– Maintainsmalereproductive

function

FemaleSexHormones• Estrogens

– Estradiol• Primaryformofestrogen

produced• Producedbyovariesandplacenta

– Estrone• Producedbyovariesandplacenta

– Estriol• Usuallyonlyinpregnantwomen• Producedbytheplacenta

• Progesterone– Producedbyovariesandplacenta

MaleReproductivePhysiology

• Functionofthetestes–Meiosis• Formationofsperm

– Spermatogenesis• Maturationofsperm

– Emission,ejaculation• Expulsionofsperm

– Secretionofmalesexhormone• Testosterone

HormonalControloftheTestes• Hypothalamus(Brain)– PulsatilesecretionsofGnRH– Every90minutes

• Anteriorpituitary– FSHandLHreleasedbysamecelltype– Alsoshowpulsatility

• Testes– TestosteronesecretionbyLeydigcellsstimulatedbyLH

SertoliCells

• ActivatedbyFSHandtestosterone• Regulatethemicroenvironmentofdevelopingsperm– Formstheblood-testisbarrier– Nourishdevelopingsperm– Secreteandrogenbindingprotein(ABP)

• Maintainshighconcentrationoftestosteroneinlumenofseminiferoustubules

• Preventsimmunesystemfromattackingdevelopingspermcells

• Phagocytosisofdefectivesperm

Spermatogenesis

• Spermatogenesistakes64days

• Malesproduce30millionsperm/day

• Differentiationrequiresextensivecellularremodeling

PubertyinMales

• Reproductiveorgansmatureandreproductionbecomespossible– 12-16yearsofageinmales

• Firstsignsofpubertyareduetoincreasedsecretionsofadrenalandrogens(ACTHcontrolled)

• Allotherdevelopmentsinpubertyreflecttheincreasedactivityofthehypothalamic-anteriorpituitary-gonadalaxis

PubertyinMales

• IncreasedGnRHsecretionatpuberty– IncreasedsecretionofFSH,LH

• Testosterone– Changesinaccessoryreproductiveorgans

• Ducts,glands,penis

– Developmentofmalesecondarysexualcharacteristics– Sexdrive

ReflexPathwaysforErection

• Underrestingconditionssympatheticinputdominant– NEcausesarteriolesmoothmuscletocontract• Vasoconstrictionofbloodvesselssupplyingbloodtoerectiletissue

• Duringerectionsympatheticinputisinhibited• NeuronsreleaseNO– NOcausesarteriolesmoothmusclerelaxation• Vasodilationofbloodvesselssupplyingbloodtoerectiletissue

Ejaculation

• Primarilyaspinalreflex(spinalnervesS2,S3,S4)

• Dividedinto2stages1. Spermandglandularsecretionsintotheurethra

(emission)2. Semenisexpelledfromtheurethra(ejaculation)• Averagevolume3mL• 300,000,000sperm

SeminalFluidSeminalGlands

• SeminalGlands(Vesicles)– Producesmajorityofseminalfluid– Producesaprotein,semenogelen• Semenogelenencasesejaculatedsperminaprotective“gel” toprotectitfromtheacidicenvironmentinthevagina• Secretionscontainfructose,nourishesspermcells

SeminalFluidProstateGland

• ProstateGland– Producesabout1/3volumeofseminalfluid– Producesanalkalinefluid– ProducesProstateSpecificAntigen(PSA)• PSAisaproteasethatcleavessemenogelen• PSAisinhibitedbyhigh[zinc],presentinsemen• Vaginahaslow[zinc],activatesPSA

– PSAcleavessemenogelenallowingthespermtomovefreely– Capacitation

FemaleReproductivePhysiology

• Functionsoftheovaries–Meiosis– Formationofova(eggs)

– Oogenesis–Maturationoftheoocyte

– Ovulation• Expulsionofanoocyte

– Secretionoffemalesexhormones• Estrogens• Progesterone

Oogenesis• Earlyfetaldevelopment• Oogonia undergomanyroundsofmitosis

• 7monthsgestation– 6-7millionoogonia– Meiosisceases

• Atbirth– 2-4millionoocytesremain(atresia:programmedcelldeath)

• AtPuberty– Ovariesbecomeactive– 2-400,000oocytes remain(atresia)– Approximately400ovawillbeovulated(atresia)

Oogenesis

• Iftheeggisfertilized,thenmeiosisIIoccursinthefallopiantube– Ovum retainsalmostallofthecytoplasm

– 2ndpolarbody released,againmuchsmallerthanovum

– MeiosisIIcompletedafterfertilization

GranulosaCells

• Primarycellsofthefollicle• HavereceptorsforFSH• Regulatethemicroenvironmentinwhichtheovumdevelops– Secreteestrogen(estradiol)– Produceoneormorefactorsthatactonprimaryoocytesthatmaintaintheminmeioticarrest

• Folliclegrowsbymitosisofthegranulosacells• Secretefluidthatformsandfillstheantrum

FollicleDevelopment1. Throughoutinfancyandearlychildhood– Theprogression/growthofsomeprimordialfolliclesoccurs

2. Atthebeginningoftheeachmenstrualcycle– 10-25ofthosefolliclesbegintodevelopintolargerfollicles

3. Aboutoneweekintothecycle– OnlyonedominantfolliclewilldevelopintoaGraafianfollicle

– Non-dominantfolliclesenlargeandundergoatresia– Theeggswithinthedegeneratingfolliclesdie

FollicleDevelopment

Ovulation

• TriggeredbyLH• Folliclebulgesoutfromthesurfaceoftheovaryasitenlarges(1.5cm)

• Ovulationoccurswhenthethinwallsofthefollicleandtheovaryrupture

• AGraafianfolliclerupturesandexpels:– Secondaryoocyte– Zonapellucida(spermcellbinding)– Coronaradiata(2or3layersofgranulosacells)

CorpusLuteum

• Thefolliclecollapsesafterthedischargethethefollicularfluidandtheegg

• Granulosa cellsenlargeformingthecorpusluteum– Secretesestrogen,progesterone

• Ifimplantationdoesnotoccur,thecorpusluteumreachesismaximumsizewithin10days,thendegenerates(apoptosis)toformthecorpusalbicans

HormonalControlofOvaries• Hypothalamus– PulsatilesecretionsofGnRH– Frequencyandamplitudeofthesepulsesduringa24hourperiodchangeoverthecourseofthemenstrualcycle

• Anteriorpituitary– FSHandLH

• Ovaries– Estrogen– Progesterone

OvarianCycle

OvarianCycle

PubertyinFemales

• Averageageofonsetofpubertyis10-12• IncreasedsecretionofGnRHresultsinanincreasinglevelsofestrogen– Developmentofsecondarysexualcharacteristicsandtheonsetofthemenstrualcycle

• Increasinglevelsofleptin– Secretedbyadipocytes– StimulatessecretionofGnRH

MenstrualCycle

• MenstrualPhase– Day1isthefirstdayofmenstrualflow• Endometriumdegenerates

• ProliferativePhase– Endofmenstruationtoovulation

• SecretoryPhase– Ovulationtotheonsetofthenextmenstrualphase

Changesinuteruscausedbyestrogenandprogesterone

Pregnancy

• Introductionofspermmustoccurbetween5daysbeforeand1dayafterovulation– Spermviablefor4-6days– Eggviablefor1-2days

SpermCapacitation

• Spermcellscannotfertilizetheegguntiltheyhaveresidedinthefemaletractforseveralhours– Actedonbysecretionsofthefemalereproductivetract– calledcapacitation

– Changesinthepatternoftailmovementallowspermtopropelforwardinstrongsurges

– Sperm’splasmamembranebecomesalteredsothatitmayfusewiththeplasmamembraneoftheovum

Fertilization• Only100-200sperm

reachtheegg• Manyspermbindtothe

zona pellucida• Zona pellucida proteins

actasreceptorsforspermsurfaceproteins

• Bindingtriggerstheacrosome reaction– Vesiclescontaining

digestiveenzymesreleasedfromspermanddigestthezona pellucida

ImplantationandPlacentaFormation

• Trophoblastcells(fetalcells)producehumanchorionicgonadotropin(hCG)– Maintenanceofcorpusluteum(preventsmenstruation)

– Promotesangiogenesisinuterinevasculature– Blocksimmune/macrophageactionfrommotheronforeign,invadingplacentalcells

– Bloodtitersdoubleeverydayuntil10th week• 10thweek– DeclineinhCG

• Placentabecomessecretory– 5th-6thweek– Secretesprogesterone(maintainsendometrium)

PlacentalExchangeofMolecules

• Nomixingofmaternalandfetalblood• Diffusion– O2 &CO2

– Nutrientmolecules&wasteproducts• Highmetabolicrateinplacenta– Utilizes1/3maternaloxygen&glucose– Rateofproteinsynthesisexceedsliver

HormonalChangesDuringPregnancy