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ReproductiveBiologyChapterOne:ReproductiveSystemreproductivesystemsAnimals’reproductivesystemscanbedividedintotheinternalreproductiveorgansandtheexternalgenitalia.Thegonadsaretheactualorgansthatproducethegametes.Inthemale,testes(singular=testis)producesperm,andinthefemale,ovariesmakeeggs.Diversityofreproduction
AsexualreproductionParthenogenesisHermaphroditesSequentialhermaphrodites-protogyny(FM)orprotoandry(MF)Sexualreproduction
Male/femalereproductivestrategyAsymmetricalgametesize(anisogamy異配生殖)meansthesexwithsmallergametesshouldusuallycompeteforaccesstothesexwithlargergametes.Thisresultsingreatervariationamongmalesthanamongfemalesforreproductivesuccess.Inmostanimals,individualsareeitherdefinitemalesordefinitefemales.However,insomespecies,individualorganismsarebothmaleandfemale.Hermaphroditismiswhenoneorganismhasbothsexes.Earthwormsandgardensnailsalwayshavebothmaleandfemaleorgans,andwhen,forexample,twoearthwormsmate,theyfertilizeeachother.Aspecialvariationonthethemeissequentialhermaphroditism(順序型雌雄同體
),inwhichanorganismchangessexduringitslife.Ifanorganismisfemalefirstandlaterchangestomale,thatorganismisprotogynous(雌性先熟,如巨石斑魚),andiftheorganismismalefirstandchangestofemale,itissaidtobeprotandrous(雄性先熟).Indifferentspecies,sequentialhermaphroditismcanbeinfluencedbytheorganism’sageorsizeorbyvariousenvironmental/climaticfactors.
Anthinesareexamplesofsynchronousprotogynoushermaphrodites.Theyarebornwithanundifferentiatedgender,laterturnintofemales,andthencanbecomemaleswhenprovidedwiththerightcues.Picturedhere,a
Pseudanthias
squamipinnisisinanintermediatestagebetweenfemaleandmale.Keeponlyonemalepertank,andfeedsmall,frequentportionsoffood(2-3timesdaily).PhotobyAnthonyCalfo.ParthenogenesisWhilemosthigheranimalsreproducesexually,therearesomespeciesinwhichthefemalescan,undercertainconditions,produceoffspringwithoutmating.Parthenogenesis
istheabilityofanunfertilizedeggtodevelopandhatch.Thisseemstobeespeciallyprevalentamonginsects.Someofthegiantwalkingsticks(竹節(jié)蟲)attheZooarefemaleswho,withoutmating,layeggsthathatchintomorefemalesgenerationaftergeneration.Otherinsects,likesomeaphids(蚜蟲),havecomplicatedlifecyclesthatinvolvesexually-reproducinggenerationsalternatingwithparthenogenicallyproducedgenerations.Inhoneybees,fertilizedeggsturnintofemales(workersandqueens),whileunfertilizedeggs,whichareonlyproducedinthespring,turnintomales.external/internalfertilizationInsexualreproduction,theremustbesomewayofgettingthespermtotheegg.Sincespermandeggsaredesignedtobeinawateryenvironment,aquaticanimalscanmakeuseofthewaterinwhichtheylive,butterrestrial(陸生)animalsmust,insomeway,providethewetenvironmentneededforthespermtoswimtotheegg.Thereare,thus,twomajormechanismsoffertilization.Inexternalfertilization,usedbymanyaquaticinvertebrates,eggsandspermaresimultaneouslyshedintothewater,andthespermswimthroughthewatertofertilzetheegg.Ininternalfertilization,theeggsarefertilizedwithinthereproductivetractofthefemale,andthenarecoveredwitheggshellsand/orremainwithinthebodyofthefemaleduringtheirdevelopment.MannersofReproductionInspecieswithexternalfertilization,atanappropriatedevelopmentalstage,theeggshatch,andthenewyoungsimplyswimaway.However,femalesofspecieswithinternalfertilizationmust,atsomepoint,expelthegrowingyoung.Therearethreegeneralwaysofdoingthis:Oviparous(卵生)organisms,likechickensandturtles,layeggsthatcontinuetodevelopafterbeinglaid,andhatchlater.Viviparous(胎生)
organisms,likehumansandkangaroos,arelive-bearing.Thedevelopingyoungspendproportionatelymoretimewithinthefemale’sreproductivetract,portionsofwhicharespecially-modifiedforthispurpose.Youngarelaterreleasedtosurviveontheirown.Ovoviviparous
(卵胎生)organisms,likeguppies(孔雀魚),gartersnakes(
肉食性束帶蛇),andMadagascarhissingroaches(馬達加斯加發(fā)聲蟑螂),haveeggs(withshells)thathatchastheyarelaid,makingitlooklike“l(fā)ivebirth.”MaleReproductiveSystemThemalereproductivesystemisillustratedtotheright.Spermareproducedinthetesteslocatedinthescrotum(陰囊).Normalbodytemperatureistoohotthusislethal(致命的)tospermsothetestesareoutsideoftheabdominalcavitywherethetemperatureisabout2°C(3.6°F)lower.Becarefulofyourbluejeans!!!Temperatureissoimportantforthesperm!Notealsothatawoman’sbodytemperatureislowestaroundthetimeofovulationtohelpinsurespermlivelongertoreachtheegg.Ifamantakestoomanylong,veryhotbaths,thiscanreducehisspermcount.Undescendedtestes(testesaresupposedtodescendbeforebirth)willcausesterilitybecausetheirenvironmentistoowarmforspermviabilityunlesstheproblemcanbesurgicallycorrected.EpididymisFromthere,spermaretransferredtotheepididymis,coiledtubulesalsofoundwithinthescrotum,thatstorespermandarethesiteoftheirfinalmaturation.Ejaculationandvasdeferens
Inejaculation,spermareforcedupintothevasdeferens(plural=vasa
deferentia).Fromtheepididymis,thevasdeferensgoesup,aroundthefrontof,overthetopof,andbehindthebladder.Avasectomyisafairlysimple,outpatient(門診患者)operationthatinvolvesmakingasmallslitineachscrotum,cuttingthevasa
deferentia
nearwheretheybegin,andtyingoffthecutendstopreventspermfromleavingthescrotum.Becausethisisarelativelynon-invasiveprocedure(ascomparedtodoingthesametoawoman’soviducts),thisisapopularmethodofpermanentbirthcontrolonceacouplehashadallthechildrentheydesire.Couplesshouldcarefullyweightheiroptions,becausethis(andthecorrespondingfemaleprocedure)isnotdesignedtobeareversibleoperation.ejaculatoryducts/seminalvesicles/semen/urethra
Theendsofthevasa
deferentia,behindandslightlyunderthebladder,arecalledtheejaculatoryducts.Theseminalvesiclesarealsolocatedbehindthebladder.Theirsecretionsareabout60%ofthetotalvolumeofthesemen(=spermandassociatedfluid)andcontainmucus,aminoacids,fructoseasthemainenergysourceforthesperm,andprostaglandinstostimulatefemaleuterinecontractionstomovethesemenupintotheuterus.Theseminalvesiclesemptyintotheejaculatoryducts.Theejaculatoryductsthenemptyintotheurethra(which,inmales,alsoemptiestheurinarybladder).prostateglandTheinitialsegmentoftheurethraissurroundedbytheprostategland(notespelling!).Theprostateisthelargestoftheaccessoryglandsandputsitssecretionsdirectlyintotheurethra.Thesesecretionsarealkalinetobufferanyresidualurine,whichtendstobeacidic,andtheacidityofthewoman’svagina.Theprostateneedsalotofzinctofunctionproperly,andinsufficientdietaryzinc(aswellasothercauses)canleadtoenlargementwhichpotentiallycanconstricttheurethratothepointofinterferringwithurination.Mildcasesofprostatehypertrophy(肥大、增生)canoftenbetreatedbyaddingsupplementalzinctotheman’sdiet,butseverecasesrequiresurgicalremovalofportionsoftheprostate.Thissurgery,ifnotdoneverycarefullycanleadtoproblemswithurinationorsexualperformance.bulbourethralglandsThebulbourethralglandsorCowper’sglandsarethethirdoftheaccessorystructures.Theseareasmallpairofglandsalongtheurethrabelowtheprostate.Theirfluidissecretedjustbeforeemissionofthesemen,thusitisthoughtthatthisfluidmayserveasalubricantforinsertingthepenisintothevagina,butbecausethevolumeofthesesecretionsisverysmall,peoplearenottotallysureofthisfunction.Penis/Theurethragoesthroughthepenis.Inhumans,thepeniscontainsthreecylindersofspongy,erectiletissue.Duringarousal,t
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