BIOL 221 Lecture Notes - Lecture 14: Umbilical Cord, Neural Crest, Neural Groove
4 Mar 2020
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Document Summary
The extra-embryonic membranes are an evolutionary hold-over from distant egg-laying ancestors. The chorion develops from trophoblast cells and forms the fetal part of the placenta (in reptiles and birds, it is important to respiration). The amnion provides a fluid-filled environment that cushions, buoys, and allows increased freedom of movement for the developing embryo/fetus. The yolk sac serves little purpose in human embryos except as the first location for formation of erythrocytes (see topic 1) and blood vessels (in reptiles and birds, it serves to digest the yolk). Neural plate neural groove & neural folds . The outermost primary germ layer is the ectoderm. This layer forms the epidermis of the skin, the nervous system, and the facial bones. Initially, the ectoderm along the mid-dorsal area thickens to become the neural plate. This then invaginates to form the neural groove with neural folds located laterally. The folds join along the midline to form the neural tube.
