ovum | physiology - Britannica

ovum, plural ova, in human physiology, single cell released from either of the female reproductive organs, the ovaries, which is capable of developing into ... ovum TableofContents ovum Introduction FastFacts Facts&RelatedContent Media Images More MoreArticlesOnThisTopic Contributors ArticleHistory Home Health&Medicine Anatomy&Physiology ovum physiology Actions Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/ovum GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). FeedbackType Selectatype(Required) FactualCorrection Spelling/GrammarCorrection LinkCorrection AdditionalInformation Other YourFeedback SubmitFeedback Thankyouforyourfeedback Oureditorswillreviewwhatyou’vesubmittedanddeterminewhethertorevisethearticle. JoinBritannica'sPublishingPartnerProgramandourcommunityofexpertstogainaglobalaudienceforyourwork! ExternalWebsites FactMonster-Science-Ovum Print Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/ovum Feedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). FeedbackType Selectatype(Required) FactualCorrection Spelling/GrammarCorrection LinkCorrection AdditionalInformation Other YourFeedback SubmitFeedback Thankyouforyourfeedback Oureditorswillreviewwhatyou’vesubmittedanddeterminewhethertorevisethearticle. JoinBritannica'sPublishingPartnerProgramandourcommunityofexpertstogainaglobalaudienceforyourwork! ExternalWebsites FactMonster-Science-Ovum Alternatetitles:ova By TheEditorsofEncyclopaediaBritannica • EditHistory TableofContents KeyPeople: KarlErnstvonBaer FrankRattrayLillie EdwinGrantConklin OskarHertwig ...(Showmore) RelatedTopics: egg coronaradiata corticalgranule secondaryovum pellucidzone ...(Showmore) Seeallrelatedcontent→ ovum,pluralova,inhumanphysiology,singlecellreleasedfromeitherofthefemalereproductiveorgans,theovaries,whichiscapableofdevelopingintoaneworganismwhenfertilized(united)withaspermcell.Theoutersurfaceofeachovaryiscoveredbyalayerofcells(germinalepithelium);thesesurroundtheimmatureeggcells,whicharepresentintheovariesfromthetimeofbirth.Ahollowballofcells,thefollicle,encompasseseachovum.Withinthefollicletheovumgraduallymatures(seeoogenesis).Ittakesaboutfourmonthsforafollicletodeveloponceitisactivated.Somefolliclesliedormantfor40yearsbeforetheymature;othersdegenerateandneverdevelop.Duringchild-bearingyears,300to400folliclesmatureandemiteggscapableofbeingfertilized.Bythetimeawomanreachesmenopause,mostremainingfollicleshavedegenerated. BritannicaQuiz HumanBody:FactorFiction? Howdeepisyourbodyofknowledgeabouttheinnerworkingsofhumans?Testitwiththisquiz. Afollicle-stimulatinghormone,secretedintothebloodstreambythepituitary,causesovumgrowth.Aftertheeggmatures,asecondhormonefromthepituitary,luteinizinghormone,isliberated;thiscausestheegg’srelease,calledovulation(q.v.).Astheovumdevelops,thewallsofthefollicleexpandbyaddingnewcells.Thefollicleandovumslowlymigratethroughthetissueoftheovaryuntiltheycauseabulgeinthesurfaceoftheorgan.Thehollowcavitybetweentheeggandthefollicularwallusuallycontainsafluidsecretedbythefollicularcells.Thiskeepstheovummoistandprovidesasuitablegrowingenvironment.Whenthefollicleruptures,theeggisreleasedfromtheovaryandisthencapturedandguidedbythefallopiantubes.Muscularcontractionsofthefallopiantubesmovetheeggtothecavityoftheuterus.Theovumitselfhasacentralnucleusthatcontainsthefemale’sgeneticmaterial;this,withthegeneticmaterialinthespermcell,determinestheinheritedcharacteristicsofthechild.Surroundingthenucleusisacellplasma,oryolk,thatcontainsnutritionalelementsessentialtothedevelopingeggcell. Ifaneggdoesnotbecomefertilizedwithin24hoursofitseruption,itbeginstodegenerate.Aftertheeggisfertilizeditundergoesaseriesofcelldivisions.Ifatanearlystageofitsdevelopmentthefertilizedeggsplitsintotwopartsthatcontinuetogrow,identicaltwinswillresult;incompletedivisionwillresultinSiamesetwins,bornphysicallyjoined.Fraternaltwinsresultwhentwoseparateeggsarereleasedandindependentlyfertilized.Seealsoimplantation. GetaBritannicaPremiumsubscriptionandgainaccesstoexclusivecontent. SubscribeNow