Posted: May 22nd, 2023
Two haploid cells (sperm and ova) fuse during fertilization in the ampullae of fallopian tubes leading to a cascade of events that culminate in the formation of a fully developed fetus resembling a chimpanzee at the end of gestation. Thirty hours later two cells are formed, forty hours later a four-cell stage, 72 hours later you have 12 â€“ 16 cells and a late morula is formed by day four. This morula is implanted by day six and blastocyst with embryoblast and trophoblast is formed by the end of week one.
The formation of a bilaminar disc is the main event in week two. It has two cell layers (hypoblast and epiblast) and two cavities (amniotic cavity and primitive yolk sac). Week three is heralded by gastrulation with the formation of the trilaminar germ disc that is composed of the epiblast, endoderm, mesoderm, and ectoderm. All the organs of the body originate from these three layers (Cleaver and Krieg 9)
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