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Unformatted text preview: 9-16-10Prenatal DevelopmentFertilization of EggGenerally during 3-7 day journey of mature egg down fallopian tube to uterus3 stages of prenatal development (not referring to trimesters)1.Zygote (Germinal Period)2.Embryo3.FetusI.Period of ZygoteA. Begins with fertilization, ends when zygote firmly implants into uterine wall.B. Usually takes 2 weeksC. Implantation tendrils from zygote penetrate uterine wallD. 25-65% of zygotes survive Many that do not survive have severe genetic defectsII. Embryonic perioda.Begins firm implantation. Ends roughly aboutb.Period of most rapid cell differentiation: Cells become different in form and functionb.i.Most organs formed and crudely functioningb.ii.First step of differentiation: 3 layers formb.ii.1.Ectoderm (outer layer) out of which comes: e.g., outer skin, nervous systemb.ii.2.Mesoderm: (middle) e.g., muscle, skeleton, bloodb.ii.3.Endoderm: (inner) e.g., lungs, digestive trackc.Auxiliary structure developc.i.Amniotic sac contains...
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- Fall '08