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11.4 (Stages in oogenesis (Germinal epithellium cells divide rapidly via…
11.4
Stages in oogenesis
- Germinal epithellium cells divide rapidly via mitosis
- Diploid germinal epithelium cells grow larger and become primary oocytes
- Primary oocytes start the first division of meiosis but stop during prophase I. a primary follicle is formed
- When a baby is born it contains 400,000 primary follicles
- Every menstrual cycle a few primary follicles start to develop and the primary oocyte completes the first meiotic division. The products are one large secondary oocyte and a polar body (due to an unequal division)
- The secondary oocyte starts the second meiotic division but stops during Prophase II. The follicle cells proliferate and follicular fluid forms.
- After fertilization the oocyte completes the second meiotic division forming an ovum.
7.When the mature follicle bursts, at the time of ovulation, the egg that is released is still a secondary oocyte.
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Stages in fertilization
- Arrival of sperm due to chemical signal released by the oviduct. Fertilization is succesful if many sperm reach the egg.
- The first sperm to break through the layers of follicle cells binds to the zona pellucida. This triggers the acrosome reaction
- The acrosome contents of the sperm are released and these are enzymes which digest a path in the zona pellucida which allows the sperm to reach the plasma membrane of the egg
- The plasma membranes of the sperm and egg fuse and the sperm nucleus enters the egg and joins the egg nucleus. This causes the cortical reaction.
- Small vesicles called cortical granules move to the plasma membrane of the egg and fuse with it, releasing their contents by exocytosis. These enzymes cause a hardening of the zona pellucida, which helps avoid polyspermy.
6.The nuclei from the sperm and egg do not fuse together, but instead both carry out mitosis using the same centrioles and spindle of microtubules. A two cell embryo is prodyced.
Stages in Gametogenesis
- Mitosis to generate large numbers of diploid cells
- Cell growth so the cells have enough resources to undergo two divisions of meiosis
- Meiosis to produce haploid cells
- Differentiation of haploid cells into gametes with structures needed for fertilization
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Function of the placenta
8 weeks after fertilization, bone and tissue develop and the body is known as a fetus, which develops a placenta and an umbilical cord
The placenta is a disc-shaped structure with many projections called placental villi, it facilitates the exchange of materials between mother and child
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