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2. Embryology Chapter 3.pptx

  1. Second Week of Development Bilaminar Germ Disc c h a p t e r 3 By. Abiib 4/1/2023 Awdal college 1
  2. 8 cell stage Fertilization ampulla Male & female pronucleus 2 cell stage morula blastocyst
  3. BILAMINAR GERM DISC • The bilaminar embryonic disc is formed when the inner cell mass forms two layers of cells, separated by an extracellular basement membrane. • The external layer is called the epiblast and the internal layer is called the hypoblast. 4/1/2023 3
  4. DAY 8 TROPHOBLAST • At the eighth day of development, the blastocyst is partially embedded in the endometrial stroma. • The trophoblast has differentiated into two layers: – An inner layer of mononucleated cells, the cytotrophoblast, – An outer multinucleated zone without distinct cell boundaries, the syncytiotrophoblast 4/1/2023 4
  5. Day 8 Trophoblastic
  6. DAY 8 EMBRYOBLAST • Cells of the inner cell mass or embryoblast also differentiate into two layers: – A layer of small cuboidal cells adjacent to the blastocyst cavity, known as the hypoblast layer. – A layer of high columnar cells adjacent to the amniotic cavity, the epiblast layer • At the same time, a small cavity appears within the epiblast. This cavity enlarges to become the amniotic cavity. 4/1/2023 6
  8. DAY 9 • Blastocyst more deeply embedded in the endometrium, • Fibrin coagulum closes defect in surface epithelium Vacuoles appear in syncitium→fuse → lacunar stage Abembryonic pole flattened cells from hypoblast form thin exocoelomic (Heuser’s)membrane inside cytotrophoblast Hypoblast + Heuser’s membrane= primitive yolk sac 4/1/2023 8
  9. 4/1/2023 9
  10. DAY 11 AND 12 • By the 11th to 12th day of development, the surface epithelium almost entirely covers the original defect in the uterine wall • Lacunar spaces in syncytium that form an intercommunicating network - particularly embryonic pole • Synciotrophoblast erode maternal capillaries are known as sinusoids. • As maternal blood begins to flow through the trophoblastic system - the uteroplacental circulation. 4/1/2023 10
  11. DAY 11 AND 12
  12. DAY 11 AND 12 • Cells derived yolk sac fill inner surface of cytotrophoblast and outer surface of exocoelomic cavity • They form Fine, loose connective tissue- extraembryonic mesoderm • when these Cavities become confluent→extraembryonic coelom or chorionic cavity • Extraembryonic coelom surrounds primitive yolk sac and amniotic cavity except where trophoblast is connected by connecting stalk 4/1/2023 12
  13. Extraembryonic somatopleuric mesoderm Lining cytotrophoblast and amnion Extraembryoni c splanchnopleu ric mesoderm Lining yolk sac Day 11 and 12 Connecting stalk
  14. • The extraembryonic mesoderm lining the cytotrophoblast and amnion is called the extraembryonic somatopleuric mesoderm • The lining covering the yolk sac is known as the extraembryonic splanchnopleuric mesoderm • Cells of the endometrium become polyhedral and loaded with glycogen and lipids; intercellular spaces are filled with extravasate, and the tissue is edematous. These changes, known as the decidua reaction 4/1/2023 14
  15. DAY 13 • By the 13th day of development, the surface defect in the endometrium has usually healed. • Cells of cytotrophoblast proliferate and penetrate syncytiotrophoblast forming cellular columns surrounded by syncytium. • Cellular column+ syncytial covering= primary villi 4/1/2023 Dr- Ahmed Moallim Hussein MBBS 15
  16. Day 13 •Cells from hypoblast migrate inside exocoelomic membrane proloferate and form a new cavity: secondary yolk sac or definitive yolk sac •Pinched out portions of exocoelomic cavity: exocoelomic cyst
  17. Day 13 •Extraembryonic mesoderm lining inside of cytotrophoblast is chorionic plate. •Extraembryonic mesoderm and two layers of trophoblast form chorion •Chorion forms the wall of chorionic sac in which embryo, its amniotic and yolk sacs are suspended by connecting stalk.
  18. Day 13 •Extraembryonic mesoderm traverse chorionic cavity in connecting stalk→ with development of blood vessels → the stalk become umbilical cord
  19. Ectopic pregnancy • A woman with a tubal pregnancy has signs and symptoms of pregnancy (e.g., misses her menstrual period). She may also experience: Abdominal pain Abnormal bleeding, Produce human chorionic gonadotropin (HCG) at a slower rate than normal pregnancies. Some times ectopic pregnancy characterized abdominal pregnancy
  20. Placenta Previa • Implantation of a blastocyst in the inferior segment of the uterus near the internal os results in placenta previa. • A placenta partially or completely covers the os. • Placenta previa may cause bleeding because of premature separation of the placenta during pregnancy or at delivery of the fetus.
  21. Day 13 •By end of 2nd week germ disc : 2 apposed cell discs- •Epiblast: floor of amniotic cavity •Hypoblast: roof of secondary yolk sac