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Formation of morula Dr. Sherif Fahmy. Blastocyst (at 7 th day) Dr. Sherif Fahmy.

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Presentation on theme: "Formation of morula Dr. Sherif Fahmy. Blastocyst (at 7 th day) Dr. Sherif Fahmy."— Presentation transcript:

1 Formation of morula Dr. Sherif Fahmy

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

3 8 th day of pregnancy Dr. Sherif Fahmy

4 Second Week of Pregnany 8 th day: 8 th day: Blastocyt is partially implanted to the endometrium which is called decidua. 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). 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. 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. 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 9 th & 10 th days Dr. Sherif Fahmy

6 9 th day: Implantation is completed and the penetration defect in endometrium is closed by fibrin clot. 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. 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. 10 th day: 10 th day: - Lacunar spaces appear in cyncitiotrophoblast. Dr. Sherif Fahmy

7 11 th & 12 th days Dr. Sherif Fahmy

8 11 th & 12 th days: Implantation defect is covered by surface epithelium. Implantation defect is covered by surface epithelium. Blastocyst produces a slight protrusion into uterine cavity. Blastocyst produces a slight protrusion into uterine cavity. Lacunar spaces become filled with maternal blood due to deeper penetration of cyncytiotrophoblast to the endometrium. 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. 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. 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 13 th day Dr. Sherif Fahmy

10 13 th 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 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 extra-embryonic coelom and connecting stalk. Formation of primary chorionic villi. Formation of primary chorionic villi. Development of blood vessels in connecting stalk. Development of blood vessels in connecting stalk. Formation of prochordal plate in which the ectoderm and endoderm are fused together. 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: Through this week, the following structures are formed: Two cavities: amniotic and yolk. Two cavities: amniotic and yolk. Two layers of embryonic disc: ectoderm and endoderm. Two layers of embryonic disc: ectoderm and endoderm. Two layers of trophoblast: inner cytotrophoblast and outer cyncytiotrophoblast. Two layers of trophoblast: inner cytotrophoblast and outer cyncytiotrophoblast. Dr. Sherif Fahmy


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