BIOL 1412 Lecture Notes - Lecture 5: Amniotic Sac, Yolk Sac, Fallopian Tube
6 Jun 2017
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Early human development: pre-embryonic period = first 2 weeks, zygote (1 cell, diploid) Undergoes rapid mitotic divisions called cleavage divisions: morula (72 hours) Solid ball of 16-32 cells (cells called blastomeres) Same size as ovum/zygote: blastocyst (5 days) ~ 5-7 days after fertilization after implantation: inner cell mass forms a 2-layered (bilayered) embryonic disc composed of: a) Epiblast will undergo mitosis to form: i. ii. amnion with a fluid filled amniotic cavity. Hypoblast will undergo mitosis to form the yolk sac: embryonic period. 3rd week to end of the 8th week. 3 germ layers are now present forming the embryo (each layer was formed from mitosis and differentiation of epiblast cells): Ectoderm will form the nervous system and the epidermis of the skin. Mesoderm will form muscles, cardiovascular system, dermis, and most bones. 9th week to end of 40th week growth and maturation or organs occurs.
