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Exercise 44

Exercise 44. Survey of Embryonic Development. Objectives:. Fertilization, zygote, morula, blastocyst, gastrula, fetus, chorion, chorionic villi, placenta, amnion, yolk sac, umbilical cord Embryonic structures and functions. Fertilization.

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Exercise 44

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  1. Exercise 44 Survey of Embryonic Development

  2. Objectives: • Fertilization, zygote, morula, blastocyst, gastrula, fetus, chorion, chorionic villi, placenta, amnion, yolk sac, umbilical cord • Embryonic structures and functions

  3. Fertilization • Fusion of two haploid (1n) gametes, occurs in uterine tube usually within a day after ovulation • Sperm • Delivers paternal chromosomes to fertilization site • Egg • Provides all the cellular organelles, nourishment, genetic programming for development AND maternal chromosomes • ~2000x the volume of the sperm cell • Secondary oocyte has been suspended in Metaphase II until now Fig. 29-1

  4. Zygote • Product of fertilization (union of gametes) • Contains 46 chromosomes (normal # for a somatic cell) Fig. 29-1

  5. Prenatal Development **Atlas Diagrams • 1st trimester • Embryological & early fetal development • Beginnings of organ systems appear • 2nd trimester • Organs and systems nearly complete • 3rd trimester • Rapid fetal growth • Most organ systems functional

  6. Embryonic Development: MORULA • Day 3-4 of development/cleavage (cell divisions) • Solid multicellular (> 4-cell stage) ball • Morula = “mulberry” • Reaches uterus on day 4 Fig. 29-2

  7. Embryonic Development: BLASTOCYST • Over next 2 days • Hollow ball with inner cavity • Outer cellular layer (“trophoblast”, provides nutrients) • Inner layer of cells (clustered at one end, will form the embryo) • Implants in uterine wall Fig. 29-2

  8. Embryonic Development: GASTRULA • Day 12 • Third layer forms—cells on surface migrate to central line: “primitive streak” • Migrating cells move between the 2 layers • Now have 3 embryonic layers: • Ectoderm • Mesoderm • Endoderm Fig. 29-4

  9. Embryonic Germ Layers Neural tissue Ectoderm Mesoderm Endoderm Connective tissues Epithelia & glands Muscle tissue Fig. 29-4

  10. Embryo to Fetus • Fetus: • Start of month 3 to delivery Fig. 29-5

  11. Extra-embryonic membranes • Yolk sac • Endoderm & mesoderm • Amnion • Ectoderm & mesoderm • Allantois • Endoderm & mesoderm • Chorion • Mesoderm & trophoblast

  12. Yolk sac • Endoderm + mesoderm • Pouch • Important site of blood cell formation Fig. 29-5

  13. Amnion • Ectoderm + mesodermal cells form this two layered structure • Enlarges throughout development • Amniotic cavity contains amniotic fluid • Surrounds, cushions developing embryo/fetus Fig. 29-5

  14. Chorion • Mesoderm and trophoblast cells form this vascular layer • Provides transport of nutrients to the growing embryo/fetus (multicellular now, so diffusion alone won’t suffice) • Chorionic villi: branches in contact with maternal tissues • Embryonic blood vessels in each • Supplies embryonic heart (beating by week 3) • Gases and nutrients diffuse between embryonic and maternal circulations—no mixing of actual blood (separated by trophoblast)

  15. Chorion Fig. 29-6

  16. Placenta • Appearance of blood vessels in the chorion = 1st step in creation of a functional placenta • Temporary structure in uterine wall that allows the diffusion between fetal and maternal circulatory systems • Fetal side • Maternal side Fig. 29-6

  17. Umbilical cord • Connection between fetus and placenta • Contains the allantois, placental blood vessels, & yolk stalk of the yolk sac Fig. 29-6

  18. Fig. 29-8

  19. Fig. 29-10

  20. Video: The Miracle of Life

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