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1、第20章胚胎学总论和畸形学概论GENERALEMBRYOLOGYANDTERATOLOGY目的与要求ò掌握受精的概念、过程、部位和意义ò掌握卵裂、桑椹胚及胚泡的概念ò掌握植入的概念、过程、部位及异常植入ò掌握二胚层及其相关结构的形成ò掌握三胚层及其相关结构的形成ò掌握三胚层分化ò熟悉胎膜的组成及其作用ò胎盘的一般结构和功能以及胎盘屏障的结构和功能ò了解双胎和联体的成因ò熟悉先天性畸形的发生原因ò掌握致畸敏感期OUTLINEPrimordialgermcellsappearinthewalloftheyolksacinthefourthweekandmigrate
2、totheindifferentgonad,wheretheyarriveattheendofthefifthweek.Inpreparationforfertilization,bothmaleandfemalegermcellsundergogametogenesis,whichincludesmeiosisandcytodifferentiation.Maturemaleandfemalegameteshave,respectively,22plusXor22plusYchromosomes.Beforespermatozoacanfertilizethe
3、oocyte,theymustundergo(a)capactation,duringwhichtimeaglycoproteincoatandseminalplasmaproteinareremovedfromthespermatozoonhead,and(b)theacrosomereactionduringwhichacrosinandtrypsin-likesubstancesarereleasedtopenetratethezonapellucida.Duringfertilization,thespermatozoonmustpenetrate(a)
4、thecoronaradiata,(b)thezonapellucida,and(c)theoocytecellmembrane.Assoonasthespermatocytehasenteredtheoocyte,(a)theoocytefinishesitssecondmeioticdivisionandformsthefemalepronucleus;(b)thezonapellucidabecomesimpenetrabletootherspermatozoa;and(c)theheadofthespermseparatesfromthetail,swe
5、lls,andformsthemalepronucleus.Theresultsoffertilizationarea)restorationofthediploidnumberofchromosomes,(b)determinationofchromosomalsex,and(c)initiationofcleavage.Cleavageisaseriesofmitoticdivisionsthatresultsinanincreaseincells,blastomeres.Afterthreedivisions,blastomeresundergocompa
6、ctiontobecomeatightlygroupedballofcellswithinnerandouterlayers.Compactedblastomeresdividetoforma16-cellmorula.Asthemorulaenterstheuterusonthethirdorfourthdayafterfertilization,acavitybeginstoappear,andtheblastocystforms.Theinnercellmass,whichisformedatthetimeofcompactionandwilldevelo
7、pintotheembryoproper,isatonepoleoftheblastocyst.Theoutercellmass,whichsurroundstheinnercellsandtheblastocystcavity,willformthetrophoblast.Theuterusatthetimeofimplantationisinthesecretoryphase,andtheblastocystimplantsintheendometriumalongtheanteriororposteriorwall.Iffertilizationdoesn
8、otoccur,then
