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Embryo2(7) - General Biology 101 Dr Morrison Lecture...

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General Biology 101 Dr. Morrison Lecture: Embryonic Development -- Part II Human Development Pre-embryonic period (first 2 weeks) -- includes cleavage, implantation and gastrulation. Embryonic period (3rd - 8th week) -- includes induction. Fetal period (3rd to 9th month) -- includes growth and development. Pre-embryonic period Cleavage Begins 1.5 days after fertilization. Completed in 5-6 days, before implantation. Zygote becomes a hollow blastula. Late blastula composed of: -- inner cell mass -- trophoblast layer Late blastula Implantation Trophoblast cells “digest” their way into the uterine lining. Trophoblast cells will become the chorion. Urine tests for pregnancy detect hCG (human chorionic gonadotrophin). Gastrulation Formation of the three primary germ layers Epiblast migrates inward through the primitive streak to form both mesodern and endoderm. Gastrulation Begins with 2-layered embryo. Hypoblast (lower layer) grows down around “yolk” to form yolk sac. Epiblast (upper layer) -- grows up to form amnionic sac. --invaginates through primitive streak to form mesoderm and endoderm.
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