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Implantation (General Embryology)
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- 9. Formation of blastocyst •By the end of 4th day, zona pellucida starts degeneration and disappears by the end of 5th day. • The blastomeres that remain after rupture of zona is called morula. • Fluid enters between cells and forms a cavity (blastocele) which separates cells into outer cell mass (trophoblast) and inner cell mass (embryoblast). This stage is called blastocyst which is formed at the 6th day. • Embryoblast forms embryo and then fetus while trophoblast form placenta, amniotic cavity and Dr. Sherif Fahmy
- 10. 2-cell stage 4-cellstage 8-cell stage Morula Early Blastocyst
- 11. Blastocele Inner cell mass (Embryoblast)Outer cell mass (Trophoblast) Embryonic pole Abembryonic pole Blastocyst Dr.Sherif Fahmy
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- 15. Implantation • Dif.: Itis the process by which blastocyst is embedded in the endometrium. • Timing: Starts at 7th day and completed at 11th day. • Site: usually at upper part of posterior wall of uterus near fundus. Dr. Sherif
- 16. Steps of Implantation •Blastocyst fixes its embryonic pole to site of implantation. • Syncytiotropholast erodes the compact layer of the endometrium to form implantation cavity through which the blastocyst reaches spongy layer of endometrium. Dr. Sherif Fahmy
- 17. -Endometrium of pregnancyis called decidua. -Site of penetration is closed by fibrin clot (coagulum) at 9th day. -Surface epithelium overgrows the fibrin clot at 11th day. Dr.Sherif Fahmy
- 18. Dr. Sherif Fahmy Innercell mass (embryoblast) Outer cell mass (trophoblast) Endometrial arteriol Endometrial gland Blastocyst Fixation of embryonic pole to implantation site Endometrium
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- 20. Dr. Sherif Fahmy GlandArteriol Syncytiotrophoblast Cytotrophoblast Epiblast Trophoblast Hypoblast Amniotic cavity Primary yolk sac Endometrium
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- 22. Abnormal Sites ofImplantation • 1- Ectopic pregnany: They are tubal, ovarian or omental (peritoneum). • 2- Placenta praevia: Parietalis, marginalis and centralis. Dr. Sherif Fahmy
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- 24. Placenta Praevia Dr. SherifFahmy Placenta praevia parietalis Normal implantation site Placenta praevia marginalis Placenta praevia centralis
- 25. Decidua • It isendometrium after implantation which is sheded after birth of fetus. • Character of endometrium: • Increased secretory function of uterine glands. • Decidual cells are stromal cells filled with glycogen. • Arteries become more spiral with arterio- venous anastomosis. Dr. Sherif Fahmy
- 26. Parts of decidua: •Decidua basalis: It is the part of decidua between blastocyst and myometrium. It forms the fetal part of placenta. • Decidua capsularis: It covers the blastocyst except embryonic pole and separates it from uterine cavity. • Decidua parietalis: It is the rest of endometrium that lines the rest of uterine cavity. Dr. Sherif Fahmy
- 27. Decidua basalis Decidua capsularis Deciduaparietalis Uterine cavity Dr.Sherif Fahmy
- 28. Fate of decidua: •Decidua basalis shares in the formation of placenta. • Decidua capsularis and parietalis fuse together and shedded with placenta after delivery. Dr. Sherif Fahmy
- 29. Dr. Sherif Fahmy Deciduabasalis Decidua parietalis Decidua capsularis Uterine cavity Fused decidua parietalis and capsularis Decidua basalis
- 30. Changes of Blastocyst inthe Second Week of Pregnancy
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- 32. 8TH Day of Pregnancy Endometrium Syncytiotrophoblast CytotrophoblastsHypoblasts Amniotic cavity Amnioblasts Epiblast Dr.Sherif Fahmy
- 33. • 8th day: • Blastocytis 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 amnioblasts. • Cells of inner cell mass (embryoblast) become arranged into 2 layers: Hypoblast (primary endoderm) and epiblast (primary ectoderm), so forming a bilaminar germ disc.
- 34. 9th & 10th days Fibrin clot Primaryyolk sac Heuser’s membrane Lacunar spacesSyncytio- trophoblast Endometrial arteriol Hypoblast Amniotic cavity Epiblast Amnioblast Cyto- trophoblast
- 35. 9th day: • Implantation iscompleted 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 syncytiotrophoblast. Dr. Sherif Fahmy
- 36. 11th & 12th days Blood insidelacunae Endometrial sinusoid Syncytio-trophoblast Endometrial epithelium Extraembryonic mesoderm Primary yolk sac Large spaces Amniotic cavity Cytotrophoblast Bilaminar embryonic disc
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- 38. 11th & 12th days: • Implantationdefect is covered by 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 form extra-embryonic coelom except at part connected to caudal end of embryo called connecting stalk. Dr. Sherif Fahmy
- 39. 13th day Endodermal cells Secondary yolk sac Exocoelomic cyst Somatic mesoderm Connectingstalk Somatic mesoderem Splanchnic mesoderm 1ry chorionic villi Extra- embryonic coelom Chorionic cavity) Dr.Sherif Fahmy
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- 41. 13th day: • Formation ofsecondary yolk sac which becomes lined with endodermal cells and reduced in size due to punching off a part. • 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
- 42. Summary of theSecond Week of Pregnancy • Through this week, the following structures are formed: –Two cavities: amniotic and yolk. –Two layers of embryonic disc: Primary ectoderm and primary endoderm. –Two layers of trophoblast: inner cytotrophoblast and outer cyncytiotrophoblast. Dr. Sherif Fahmy