01:119:116 Lecture Notes - Lecture 17: Inner Cell Mass, Primitive Streak, Polarity In Embryogenesis
15 Mar 2016
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Fig 47. 2 development events in the life cycle of a frog. After cleavage, rate of cell division slows down. Morphogenesis: cellular and tissue-based processes by which animal body takes shape, occurs during last two stages of embryonic development. Morphological process by which hollow blastula becomes a gastrula. Embryonic germ layers: ectoderm, endoderm lines embryonic digestive tract, mesoderm. Infolding of a sheet of cells into embryo. 2nd opening mouth: sequence of events. Mesenchyme cells at tip of archenteron produce filopodia. Filopodia- thin extensions: extend toward blastocoel wall. Cilia function in feeding and movement: fig 47. 8. Each germ layer contributes to distinct set of structures. More cells invaginate and blastopore extend around both sides of embryo. Ends eventually meet and blastopore forms circle. Sheet of cells spread out of animal hemisphere. Rolls inward over dorsal lip: involution. Blastopore becomes smaller because ectoderm growing and spreading downward over surface. Circular blastopore surrounds plus of yolk- filled cells: fig 47. 10.
