BIOL 204 Study Guide - Midterm Guide: Primitive Streak, Germinal Disc, Epiblast
Document Summary
During cleavage, zygote divides to form morula (solid ball of cells). Incomplete and restricted to small region at animal pole of zygote. Cleavage makes blastodisc (flat disk of cells on dorsal side of yolk). Cells of blastodisc form 2 layers: (hollow ball of ells). epiblast and hypoblast. Hypoblast helps guide migration of epiblast cells during gastrulation but does not contribute to embryo. Space between epiblast and hypoblast is blastocoel. Koller"s sickle forms at posterior regions of epiblast. It makes the primitive streak as it moves posterior to anterior. Anterior end of primitive streak is the. Cells from epiblast migrate through through blastopore. Gut formation archenteron gives rise to lumen of digestive tract. During migration these cells keep dividing + start to differentiate. Hensen"s node closes the primitive streak as it moves anterior to posterior. Once it closed a region of chick embryo, gastrulation stops and neurulation begins. Digestive system starts to form during or after gastrulation.
