PSYC 2500 Lecture Notes - Blastocyst, Zygote, Twin
28 Sep 2014
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If it splits into clusters of cells on the way, it can become monozygotic twins, triplets, etc. About 4 days post conception forms a: blastocyst: a zygote of about 100 cells, like a hollow ball. After a week, the blastocyst reaches the uterus and the implantation happens. Implantation: zygote burrows into the uterine wall to establish a connection with the mother"s blood vessels. Takes approximately a week then hormonal changes start in the mother: less than 1mm in size, cells have begun to differentiate. Two layers of differentiation: germ disk: cluster of cells near the centre which become the baby, placenta: layer of cells nearest uterus to form the structure for exchanging nutrients and wastes between mother and child. Period begins once blastocyst is completely embedded in the wall of the uterus. Body structures and organs are formed during this period. 3 layers form: ectoderm: skin, mesoderm: bones, muscles, endoderm: digestive system.
