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Development of the Human Embryo

Development of the Human Embryo. Developmental History of a Human. Stages of Development. 1. 2. 3. 4. 5. 6. 1. Fertilization. Fertilization. 3. 4. 5. 6. 2. Cleavage. 2. Cleavage. Begins ~ 12 hours post-fertilization Zygote divides into 2 cells (mitosis)

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Development of the Human Embryo

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  1. Development of the Human Embryo

  2. Developmental History of a Human

  3. Stages of Development 1. 2. 3. 4. 5. 6.

  4. 1. Fertilization

  5. Fertilization 3. 4. 5. 6.

  6. 2. Cleavage

  7. 2. Cleavage • Begins ~ 12 hours post-fertilization • Zygote divides into 2 cells (mitosis) • 46 chromosomes in zygote = 46 chromosomes in both daughter cells • 2 cell into 4 cell stage (24 – 36 hours) • 4 cell into 8 cell stage (36 – 72 hours) • 16 cell stage -- Morula

  8. 3. Morula Morula

  9. 3. Morula • ~ 16 cell stage • Develops ~ 72 hours (3 days) from fertilization • Morula enters the uterus ~ after 3 days in oviduct

  10. 3. Morula 72 hours post- fertilization entering uterus

  11. 4. Blastocyst

  12. 4. Blastocyst • Morula, once entering the uterine cavity, floats freely • Morula begins to accumulate fluid and forms a cavity between its cells • Once cavity appears, it is now called a blastocyst.

  13. 4. Blastocyst

  14. 4. Blastocyst • Blastocyst has fluid-filled inner cavity • Evolves from morula on day 5

  15. Day 6 • Three events happen

  16. Implantation

  17. Two Distinct Cell Types Inner cell mass trophoblasts

  18. Two Distinct Cell Types • Trophoblasts – will form the invading placenta • Inner cell mass cells – will form the embryo

  19. hCG is produced • hCG is human chorionic gonadotropin • It is produced by the trophoblasts starting on day 6 • hCG is a hormone • hCG causes endometrium of uterus to grow and proliferate • hCG prevents the menstrual cycle from occuring • This is why a female misses her periods when she is pregnant

  20. Week 2 • Implantation continues • Erosion of maternal blood vessels • Complete emersion into endometrium of uterus

  21. Weeks 3-4 • Development of CV and nervous systems

  22. Weeks 5-8 • Embryo will develop all structures that an adult has by the end of week 8

  23. Embryo/Fetus • Embryonic period is weeks 1-8 • Fetal period begins on week 9 and goes until birth at 38 weeks. • Embryonic period is characterized by development of structures (organs). • Fetal period is characterized by growth of those structures.

  24. Fetal Period 9-12 13-16 17-20 21-38

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