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Prenatal Development


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Prenatal Development

  1. 1. The Stages of Prenatal Development
  2. 2. <ul><li>Induction </li></ul><ul><ul><li>During prenatal development differences in cytoplasmic composition trigger changes in genetic activity </li></ul></ul><ul><li>Gestation periods </li></ul><ul><ul><li>Three trimesters </li></ul></ul>Embryonic and Fetal Periods
  3. 3. SECTION 29-4 The First Trimester
  4. 4. <ul><li>Cleavage </li></ul><ul><ul><li>Zygote becomes a preembryo then a blastocyst </li></ul></ul><ul><li>Implantation </li></ul><ul><ul><li>Blastocyst burrows into uterine endometrium </li></ul></ul><ul><li>Placentation </li></ul><ul><ul><li>Blood vessels form around blastocyst and placenta develops </li></ul></ul><ul><li>Embryogenesis </li></ul><ul><ul><li>Formation of a viable embryo </li></ul></ul>The First Trimester
  5. 5. <ul><li>A series of cell divisions that subdivides the cytoplasm of the zygote </li></ul><ul><ul><li>Trophoblast – outer layer of cells </li></ul></ul><ul><ul><li>Inner cell mass – cluster of cells at one end of blastocyst </li></ul></ul>Cleavage and blastocyst formation
  6. 6. Cleavage and Blastocyst Formation Figure 29.2
  7. 7. <ul><li>Occurs about 7 days after fertilization </li></ul><ul><li>Trophoblast enlarges and spreads </li></ul><ul><ul><li>Maternal blood flows through open lacunae </li></ul></ul><ul><li>Gastrulation </li></ul><ul><ul><li>Embryonic disc composed of germ layers </li></ul></ul><ul><ul><ul><li>Endoderm </li></ul></ul></ul><ul><ul><ul><li>Mesoderm </li></ul></ul></ul><ul><ul><ul><li>Ectoderm </li></ul></ul></ul>Implantation
  8. 8. Stages in Implantation Figure 29.3
  9. 9. The Inner Cell Mass and Gastrulation Figure 29.4
  10. 10. <ul><li>Gastrulation </li></ul><ul><ul><li>By day 12 surface cells move toward the primitive streak </li></ul></ul><ul><ul><li>A third germ layer forms </li></ul></ul><ul><li>The three germ layers are: </li></ul><ul><ul><li>Ectoderm – superficial cells that did not migrate </li></ul></ul><ul><ul><li>Endoderm – cells facing the blastocoele </li></ul></ul><ul><ul><li>Mesoderm – migrating cells between ectoderm and endoderm </li></ul></ul>Germ layers
  11. 11. <ul><li>Four extraembryonic membranes: </li></ul><ul><ul><li>Yolk sac </li></ul></ul><ul><ul><li>Amnion </li></ul></ul><ul><ul><li>Allantois </li></ul></ul><ul><ul><li>Chorion </li></ul></ul>Extraembryonic Membranes
  12. 12. Extraembryonic Membranes and Placenta Formation Figure 29.5a, b
  13. 13. Extraembryonic Membranes and Placenta Formation Figure 29.5c, d
  14. 14. Extraembryonic Membranes and Placenta Formation Figure 29.5e
  15. 15. <ul><li>Yolk sac </li></ul><ul><ul><li>Important site of blood cell formation </li></ul></ul><ul><li>Amnion </li></ul><ul><ul><li>Encloses fluid that surrounds and cushions developing embryo </li></ul></ul><ul><li>Allantois </li></ul><ul><ul><li>Eventually becomes bladder </li></ul></ul><ul><li>Chorion </li></ul>Embryo Anatomy