Development

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Development

• Chapter 29

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Fertilization
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• Zygote undergoes a series of mitotic cell
  divisions called cleavage
• zygote ? 2-cell stage ? 4-cell stage ? 8-cell
  stage ? morula ? blastocyst? gastrula
• Morula solid sphere of cells (day 5)
• Blastocyst hollow ball of cells (days 6-7), it
  produces human chorionic gonadotropin (hCG)
  hormone which can be detected in the womans
  urine during a pregnancy test source of
  embryonic stem cells
• Gastrula differentiation starts contains three
  germ layers (ectoderm, endoderm, mesoderm days
  7-10)

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Late Gastrula
Endoderm
Ectoderm
Mesoderm
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• Three germ layers in gastrula
• Ectoderm gives rise to the nervous system and
  skin
• Endoderm gives rise to lining of the gut and
  internal organs
• Mesoderm gives rise to skeleton, muscles,
  circulatory system, reproductive system

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• Pregnancy becomes established during days 10 -14
• Fluid filled amniotic cavity starts to form
• Yolk sac starts to form (will make blood cells,
  germ cells)
• Embryo starts to form from embryonic disc
• Chorion (placenta) starts to form and will supply
  the embryo with nutrients and eliminate wastes
• Woman misses period

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Development of the Placenta
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• Embryo the term used until the 8th week from
  Greek swelling within
• Fetus the term used from the 8th week until
  birth from Greek offspring
• Pregnancy can be divided into three trimesters
• First trimester body systems form (during this
  time the embryo is extremely sensitive to smoking
  drugs)
• Second third trimesters continued body growth

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BIRTH

• 3 parts
• Dilation of cervix
• Expulsion of the baby
• Expulsion of the placenta

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