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Human Development

Human Development. Fertilization. Must occur within 24hrs postovulation Requires capacitated sperm (6-8hrs) Secondary oocyte completes Meiosis II once sperm enters oocyte Zygote formed with fusion of male and female pronuclei. Cleavage. Rapid mitotic cell division of zygote

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Human Development

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  1. Human Development

  2. Fertilization • Must occur within 24hrs postovulation • Requires capacitated sperm (6-8hrs) • Secondary oocyte completes Meiosis II once sperm enters oocyte • Zygote formed with fusion of male and female pronuclei

  3. Cleavage • Rapid mitotic cell division of zygote • 2-cell stage; 36 hours • 4-cell stage; 48 hours • 8-cell stage; 72 hours • Morula - solid ball of cells (blastomeres) at 96 hours • Takes 4-5 days to travel from uterine tubes to uterine cavity

  4. Implantation • Morula develops into bastocyst, a hollow ball of cells differentiated into inner cell mass and trophoblast • Trophoblast embeds into endometrium • secretes enzymes, HCG • chorionic villi • attachment occurs 7-8 days after fertilization

  5. Embryonic Development • Extends from the 2-8th week after conception • Inner cell mass differentiates into: • Ectoderm - epidermis of skin, entire nervous system • Endoderm - functional lining of the digestive and respiratory system • Mesoderm - forms muscle, bone, blood vessels, and kidneys

  6. Fetal Membranes • Chorion - fetal part of the placenta, outermost membrane • Amnion - fluid filled sac covering embryo and later fetus • Yolk sac - source of nourishment for embryo; early site of blood formation • Allantois - developing umbilical cord and developing bladder of fetus

  7. Placenta Formation • Functions to exchange waste products and blood gases • Chorionic villi penetrate into the decidua basalis of the endometrium • Chorion - fetal portion • Decidua basalis - maternal portion • Placenta previa

  8. Hormones of Pregnancy • HCG secreted by the chorion maintains corpus luteum • FSH repressed, cycle stops • Progesterone maintains endometrial lining • Placenta secretes estrogen and progesterone • Corpus luteum degenerates • Late pregnancy: relaxin secreted

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