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when is the embryonic period?
fertilization > 8th week
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When is the fetal period?
9th week > birth
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What is the most critical stage of development?
first trimester?
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When does the initial appearanc eof all major organ systems occur?
first trimester?
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when is the fetus most vulnerable to effects of drugs, radiation, and microbes?
first trimester?
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Which trimester is the fetus nearly completed development of organ systems?
second
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which trimester has the most rapid fetal growth?
third
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What does the sperm penetrate during fertilization?
- corona radiata
- zona pellucida
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What does the sperm bind to during fertilization?
zona pellucida
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what happens when the sex cell's membranes fuse?
- oocyte completes meiosis and divides
- pronuclei form and fuses
- results in a zygote
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how many cells is in a zygote?
2 > 4 > 8
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what is a morulla?
zygote with 16 cells in it
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what happens in the first week of development?
- blastocyst formation from the morula
- ---inner mass becomes embryoblast
- --- outer wall is trophoblast
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where does the zygote implant during the first week?
- fundus or body of uterus
- blastocyst attaches to endometrium
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what happens during the second week of development?
- trophoblast develops into 2 laters
- embryoblast develops into bilaminar embryonic disk
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what are the 2 layers of trophoblast(Chorion) in the second week?
- syncytiotrophoblast
- cytotrophoblast
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what forms in the hypoblast?
yolk sac
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what forms where the epiblast is?
amniotic cavity
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What happens during the third week of development?
gastrulation produces trilaminar embyonic disc
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what are the 3 primary germ layers that form during the third week of development?
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what does ectoderm later become?
epidermis of skin, nervous system
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where does endoderm later become?
- epithelial linings of GI tract,
- respiratory tract,
- urinary tract,
- and many glands
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Whhere does the mesoderm form?
between ectoderm and endoderm
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what doest he mesoderm later become?
muscles, bones, C.T, peritoneum
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