BIOL 1410 Lecture Notes - Lecture 5: Umbilical Cord, Allantois, Circulatory System
16 Nov 2016
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Undergoes rapid mitotic divisions called cleavage divisions. Solid ball of 16 - 32 cells (cells called blastomeres) Same size as ovum/zygote: fluid-filled cavity develops (called blastocoel/blastocyst cavity) Cells will divide and differentiate (undergo changes to become more specialized) to form the embryo: trophoblast (made of trophoblast cells) Cells will divide and differentiate to form the chorion. Provides nutrients to developing embryo blastocoel trophoblast cell inner cell mass. Features: zygote (1 cell, diploid, inner cell mass, morula (72 hours, blastocyst (5 days) Topic v: early human development: pre-embryonic period = 1st 2 weeks after implantation: Blastocyst moves from uterine tube and attaches to the endometrium of uterine wall = implantation. Inner cell mass forms a 2-layered (bilayered) embryonic disc composed of: Embryonic membranes form, including: chorion, amnion. Chorionic villi= projections of the chorion containing the blood vessels that will form the fetal part of placenta. Function of fluid - shock absorption, temperature regulation: yolk sac.
