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11 Cards in this Set
- Front
- Back
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List the 3 main stages before birth |
week 1 - preimplantation stage weeks 2-8 - embryonic stage (organogenesis) weeks 9-38 - foetal stage (growth and development) |
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What are the critical developmental landmarks that occur in the first 10 weeks (9)? |
day 0: zygote forms day 1: cleavage begins week 1: implantation of blastocyst week 2: formation of bilaminar disc week 3: gastrulation weeks 3-8: organogenesis week 4: heart starts beating and limb buds form week 8: foetus begins to resemble a baby week 10: expression of genitalia |
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Explain what happens during week 1 |
- fertilized oocyte undergoes mitotic divisions, though remains the same size - cluster of cells called a morula forms by day 4 and enters the uterus - by day 5 the blastocyst has begun to form - at around 7 days, fluid begins enter through the zona pellucida. This eventually causes it to hatch and implant into the uterus |
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Explain what happens in week 2? |
- embryo implants into uterine wall - enzymes help the trophectoderm burrow into the endometrium - embryo takes form bilaminar disc (upper layer=epiblast; lower layer=hypoblast) extraembryonic membranes and cavities form |
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What happens in week 3? |
- Cellular movements occur in the epiblast, pushing cells down through the primitive streak -INVAGINATION - Mesoderm layer is formed from these cells - Cells remaining in the epiblast form the ectoderm layer - Hypoblast cells get pushed aside allowing formation of the endoderm layer - End of gastrulation results in a three layered embryo which can give rise to all body tissues |
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What happens in week 4? |
• Changes in body form –Embryo “rolls up” from a flat disc into a closed cylinder along its long axis –Growth of the embryo makes the embryo fold laterally –Head and tail ends curl under the fast growth of the neural tube • The embryo now resembles a human form |
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Give 5 examples each of tissues formed in the ectoderm, mesoderm and endoderm |
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Describe the three extra-embryonic membranes, when they are present, and their function |
- amnion contunous with epiblast persists until birth provide protection for developing embryo - yolk sac continuous with hypoblast important for nutrient transfer weeks 2-3 disappears around week 20 - chorion forms the foetal component of the placenta chorionic cavity appear early in preganancy disappears when amnion expands |
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What are the rules to remember for weeks 2,3 and 4? |
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