3 Embryology and development

3 Embryology and development - 29-1HOW DO TWINS...

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Unformatted text preview: 29-1HOW DO TWINS DEVELOP?29-2Embryology, Growth and Development29-3Where it all Began29-4Prenatal Development•From conception to birth: three stages1.Germinal period: first 2 weeks of development during formation of primitive germ layers2.Embryonic period: second to end of 8th week, organ systems develop3.Fetal period: last 30 weeks, organ systems grow and mature29-5FertilizationBinding of ZP3Acrosomal Reaction29-6Fertilization29-7Fertilization•Binding to α6β1Fast Block to Polyspermy•depolarization Slow Block to Polyspermy•intracellular release of Ca – exocytosis of H2O•oocyte shrinks – zona pellucida denatures•ZP3 becomes inactivated29-82-cells(day 1)4-cells(day 2)Morula(day 5)TrophoblastFertilizationOvulationImplantation(see figure 29.4)Cells thatwill become theembryo properBlastocyst(day 6)Innercell massBlastoceleMorula and Blastocyst29-9Implantation and Formation of Placenta8-12 daysCells that willbecome theembryo properCytotrophoblastSyncytiotrophoblastinvading uterine wallMaternal arterioleImplantedblastocystUterineendometrium29-10Implantation and Formation of PlacentaImplantation:burrowing of the blastocyst into the uterine wallPlacenta:exchange of nutrients and waste between mother and embryoSynctiotrophoblast– multinucleated cell invades endometriumCytotrophoblast– remains close to the embryonic tissue29-11Implantation and Formation of PlacentaMaternalarterioleSyncytiotrophoblastCytotrophoblastMaternalarteriole wallArteriole wall digested bysyncytiotrophoblastLacuna filled withmaternal bloodConnecting stalkto developing embryo14-20 daysLacunae: syntiotrophoblast surround maternal blood vessels and digests their walls forming pools of blood29-12Implantation and Formation of PlacentaMaternalarterioleSyncytiotrophoblastCytotrophoblastLacuna filled withmaternal bloodEmbryonicvessels forming(contain embryonicblood)MesodermConnecting stalk todeveloping embryoCytotrophoblastcord1 MonthCytotrophoblast provides a protective barrier between maternal and embryonic blood29-13Implantation and Formation of PlacentaChorionChorionic villiUmbilical veinUmbilical arteriesUmbilical cordPlacentaMaternal venuleSyncytiotrophoblastMaternal arterioleEndometriumFetal arterioleFetal venuleMaternal bloodin lacunaBasementmembraneEmbryonicbloodin capillarySeparation betweenmaternal and embryonicblood: The chorion, consisting of the embryonic capillarywall, basement membrane, and syncytiotrophoblastMaternal bloodin lacuna29-14Formation of Germ LayersEMBRYONIC DISK:•Amniotic cavity: forms inside inner cell mass •Forms after implantation–Embryonic disk: composed of ectoderm and endoderm and is part of the inner cell mass–Amniotic cavity eventually surrounds the developing embryo providing a protective fluid bag•Yolk sac: forms inside blastocele from endoderm29-15...
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This note was uploaded on 12/03/2009 for the course KINESIOLOG 1Y03 taught by Professor Parises during the Spring '09 term at McMaster University.

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3 Embryology and development - 29-1HOW DO TWINS...

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