01:119:116 Lecture Notes - Lecture 17: Inner Cell Mass, Primitive Streak, Polarity In Embryogenesis
11 Jan 2020
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Lecture 17 - development ii: gastrulation, sea urchins. Highlights - sea urchins are radially symmetrical. 1. cells at vegetal pole - migrates to blastocoel. 2. cells at vegetal pole flatten - causing invagination. 4. archenteron fuses with blastocoel wall: chickens. Blastocyst has formed and reaches uterus: humans. Trophoblast - outer single layer of cells. It secretes enzymes -> erode area of endometrium. Implantation trophoblast thickens and extends fingerlike projections. Inner cell mass - becomes embryo proper (stem cells) Extraembryonic membranes start to form (10-11 days), and gastrulation begins (13 days) Inner cell mass -> flat disk, two layers. Hypoblast - extraembryonic membranes: organogenesis, neurulation. In vertebrates - nervous system develops first. Some mesoderm solidifies and forms notochord which is a flexible rod. Part of the ectoderm becomes the nervous system. Induction - certain cells influence stimulate neighboring cells (paracrine signaling) Cannot be fixed - results in death. Spina bifida - posterior outside of the body)
