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ch. 8 300-313 - p 300-313 Early Mammalian Development The...

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p. 300-313 Early Mammalian Development The Unique Nature of mammalian Cleavage o Fertilization in ampulla o Unique orientation of mammalian blastomeres 1 st cleavage = normal meridional division 2 nd cleavage- rotational cleavage – one blastomere divides meridionally and other divides equatorially o Asynchrony of early cell division – mammalian blastomeres do not all divide at the same time, embryos contain odd numbers of cell o Mammalian genome activated during early cleavage o Nuclei produce proteins for cleavage/development Compaction o Crucial diff. btwn mammalian cleavage and all others = compaction o Phenomenon where after 3 rd cleavage blastomeres huddle together and form ball of cells held by tight junctions o Cells of ball divide to produce morula – small group of internal cells surrounded by large group of external cells o Internal cells – inner cell mass (ICM) – give rise to embryo o Trophoblast – comes from external cells, produces no embryonic structures, forms tissue of chorion, embryonic portion of placenta o Chorion – enable fetus to get o2 and nourishment from mom, secretes hormones that cause mom’s uterus to retain fetus, produces regulators of immune response so mom wont reject embryo o Trophoextoderm – 1 st differentiation event in mamm. Development, external cells adhere to uterine lining o Which cells become trophoblast and which become ICM = chance o Cells of ICM gives rise to embryo and yolk sac, allantois, amnion
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o ICM will support trophoblast by secreting proteins like Fgf4 that stimulate trophoblast cells to divide o
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