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Development

Development. Chapter 29. Fertilization. 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)

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Development

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  1. Development Chapter 29

  2. Fertilization

  3. 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 woman’s urine during a pregnancy test; source of embryonic stem cells Gastrula = differentiation starts; contains three germ layers (ectoderm, endoderm, mesoderm; days 7-10)

  4. Late Gastrula Endoderm Ectoderm Mesoderm

  5. 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

  6. Pregnancy becomes established during days 10 -14: • Fluid filled amniotic cavitystarts to form • Yolk sacstarts 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

  7. Development of the Placenta

  8. 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

  9. BIRTH 3 parts: • Dilation of cervix • Expulsion of the baby • Expulsion of the placenta

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