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Formation of morula

Formation of morula. Dr. Sherif Fahmy. Blastocyst (at 7 th day). Dr. Sherif Fahmy. 8 th day of pregnancy. Dr. Sherif Fahmy. Second Week of Pregnany. 8 th day: Blastocyt is partially implanted to the endometrium which is called decidua.

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Formation of morula

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  1. Formation of morula Dr. Sherif Fahmy

  2. Blastocyst (at 7th day) Dr. Sherif Fahmy

  3. 8th day of pregnancy Dr. Sherif Fahmy

  4. Second Week of Pregnany • 8th day: • Blastocyt is partially implanted to the endometrium which is called decidua. • Trophoblastic cells proliferate rapidly to be differentiated into 2 layers: cytotrophoblast (inner cellular layer) and outer syncytiotrophoblast (sheet of protoplasm). • Formation of amniotic cavity between epiblast and cytotrophoblast. • Cells of inner cell mass (embryoblast) become arranged into 2 layers: Hypoblast (primary endoderm) and epiblast (primary ectoderm), so forming a bilaminar germ disc. Dr. Sherif Fahmy

  5. 9th & 10th days Dr. Sherif Fahmy

  6. 9th day: • Implantation is completed and the penetration defect in endometrium is closed by fibrin clot. • Formation of primitive yolk sac (exocoelomic cavity). This occurs by proliferation of cells from hypoblast which descend to line the trophoblast at the original blastocele called Heuser’s membrane. 10th day: • Lacunar spaces appear in cyncitiotrophoblast. Dr. Sherif Fahmy

  7. 11th & 12th days Dr. Sherif Fahmy

  8. 11th & 12th days: • Implantation defect is covered by surface epithelium. • Blastocyst produces a slight protrusion into uterine cavity. • Lacunar spaces become filled with maternal blood due to deeper penetration of cyncytiotrophoblast to the endometrium. • Formation of extraembryonic mesoderm in the inner aspect of cytotrophoblast. Now trophoblasts is called chorion and blastocyst is called chorionic vesicle. • Large spaces appear in the mesoderm which communicate to form extra-embryonic coelom except at part connected to caudal end of embryo called connecting stalk. Dr. Sherif Fahmy

  9. 13th day Dr. Sherif Fahmy

  10. 13th day: • Formation of secondary yolk sac which becomes lined with endodermal cells and reduced in size due to punching off a part from it. • Formation of extra-embryonic coelom and connecting stalk. • Formation of primary chorionic villi. • Development of blood vessels in connecting stalk. • Formation of prochordal plate in which the ectoderm and endoderm are fused together. Dr. Sherif Fahmy

  11. Summary of the Second Week of Pregnancy • Through this week, the following structures are formed: • Two cavities: amniotic and yolk. • Two layers of embryonic disc: ectoderm and endoderm. • Two layers of trophoblast: inner cytotrophoblast and outer cyncytiotrophoblast. Dr. Sherif Fahmy

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