Bilaminar germ disc presentation

the process by which a bilaminar germ disc is formed within the second week of development. second week is a week of two's. development and clinical implications or correlates. the formation of the 2 fluid cavities

1. BILAMINAR DISC ( SECOND WEEK ) Presentation by Mudoogo Edgar

2. O bjectives Definition Development C linical correlates Mudoogo Edgar

3. Defination of bilaminar disc This refers to the epiblast and hypoblast evolved from the embryoblast. These two layers are sandwiched between two cavities(balloons) i.e. primitive York sac and amniotic cavity. Mudoogo Edgar

4. Development Zygote Morula Blastocyst Trophoblast Embryoblast (Formative mass- 60 cells) Embryoblast transforms into 2 distinct epithelial layers just before implantation occurs; epiblast – outer layer , has columnar cells Hypobalst - inner layer, has cuboidal cells Mudoogo Edgar

5. The second week of development is significant for: The formation of the bilaminar disc (two-layers ) – this will give rise to all the tissues and organs of the body The completion of implantation Mudoogo Edgar

6. Syncytiotrophoblast cells displace the endometrium around the implantation site The endometrium has undergone changes. Cells have become filled with glycogen and lipids The nutrients spill into the connective tissue This is called the decidua reaction Mudoogo Edgar

7. The syncytiotrophoblast is responsible for hormone production. hCG maintains the corpus luteum in the ovary, allowing it to continue to produce P+E. Produces P+ E to maintain the pregnancy Ovary Uterus hCG Mudoogo Edgar

8. The cells of the embryoblast will also differentiate into 2 layers: The epiblast - a layer of high, columnar cells adjacent to the amniotic cavity. The hypoblast - A layer of small cuboidal cells adjacent to the blastocyst cavity. Together these layers form a flat disc. Mudoogo Edgar

9. Amnioblasts (derived from the epiblast) separate and form the lining of the amniotic cavity . Cells from the hypoblast form a membrane that lines the inner surface of the cytotrophoblast . This forms the exocoelomic cavity or primitive yolk sac Mudoogo Edgar

10. The cavities allow movement of the disc The primordial uteroplacental circulation is established The yolk sac contains no yolk- the embryo is nourished from the lacunar networks- but may have a role in selective transfer of nutrients Mudoogo Edgar

11. New cells appear between the yolk sac and the cytotrophoblast They form a layer of loose connective tissue: extraembryonic mesoderm. Cavities or spaces appear in the extra-embryonic mesoderm Mudoogo Edgar

12. The cavities form a new space- the chorionic cavity The primitive yolk sac is pinched off- a secondary or definitive yolk sac is formed The cavity divides the extraembryonic mesoderm into the Extraembryonic somatic mesoderm- lining trophoblast and amnion Extraembryonic splanchnic mesoderm- lines the yolk sac Mudoogo Edgar

13. Mudoogo Edgar

14. The chorion is formed by Extraembryonic somatic mesoderm Cytotrophoblast Syncytiotropho -blast The chorion forms the wall of the chorionic cavity- the amniotic cavity and yolk sac are suspended in the chorionic cavity by the connecting stalk. 1 2 3 Mudoogo Edgar

15. By day 14 the embryo has the form of a flat, bilaminar disc, ovoid in shape. In a localized area of the hypoblast, the cells become more columnar and form a thickened circle area, the prechordal plate . Mudoogo Edgar

16. At the end of the second week: Trophoblast has had a period of growth- greater than the embryoblast. The 2 layer bilaminar disc is formed and will give rise to other tissues and structures. Mudoogo Edgar

17. Clinical correlates Human chorionic gonadotrophin (HCG) hormone produced by syncytiotrophoblast can be detected by medical test. Hydatidiform mole – little or no embryonic tissue, secrete high levels of HCG producing beneign or malignant tumor ( choriocarcinoma ). Trophoblast is well developed. Mudoogo Edgar

18. Clinical correlates ct’d Implantation sites usually posterior or anterior wall of body of uterus Abnormal implantation sites – ectopic pregnancy abdominal cavity- pouch of Douglas mesentery ampullary region of tube Mudoogo Edgar

19. Clinical correlates ct’d tubal implantation, internal os , ovarian leading to primary ovarian pregnancy interstitial implantation of narrow width of uterine tube Bleeding on the day due to increased blood with in lacunae spaces. Mudoogo Edgar

20. 2 nd week of development: The week of twos WHY? Trophoblast ↗ cytotrophoblast ↘ syncytiotrophoblast Embryoblast ↗hypoblast ↘epiblast Extraembronic mesoderm ↗ somatopleure ↘ splanchnopleure Cavities ↗amniotic ↘primitive yolk sac Mudoogo Edgar

21. Mwebare munonga “JUST BECAUSE YOU KNOW THE STUFF DOESN’T MEAN YOU ARE SMART……….. YOU HAVE TO KNOW HOW TO USE THAT INFORMATION” - JOSH KELLER- Mudoogo Edgar