Blastocyst + Bilaminar Disc+ Implantation Flashcards
When does blastocyst formation occur?
Day 4
What is the cavity in the middle of an embryo?
Blastocele, result of water inflow to Morula due to Na/K ATPase pump, forms a blastocyst
What happens to zona pellucida at this stage?
It disappears to allow for implantation to occur
What mediates implantation?
Selectins and Integrins
How does blastocyst implant?
Progesterone by Corpus Luteum activates endometrial lining (decidual cells), Trophoblast cells produce hormones (Human chorionic gonadotropin hCG) that stimulate the CL to keep supplying progesterone, Cytotrophoblast enzymes break down ECM, fingerlike processes from syncytiotrophoblast pull embryo in endometrium
What day is blastocyst embedded by?
8th day
Trophoblast differentiates into 2 layers:
Cytotrophoblast (inner mononucleated cells)
Syncytiotrophoblasts (outer multinucleated cells)
Embryoblast differentiates into 2 layers:
Hypoblast layer (adjacent to blastocyst) and Epiblast layer (adjacent to amniotic cavity = amnioblasts)
How is primitive yolk sac (exocoelomic cavity) formed?
Coagulation plug seals whole where blastocyst implanted, cells from hypoblast form Heusner’s membrane lining the inner cytotrophoblast
Relevance of Lacunae in syncytiotrophoblast
They erode dilated capillaries from mother called Sinusoids and fuse with them, being filled with maternal blood (Uteroplacental circulation)
Extraembryonic mesoderm
Formed by cells in yolk sac, develop large cavities, cavities fuse, form extraembryonic/chorionic cavity, surrounding primitive Yolk sac and amniotic cavity
Extraembryonic mesoderm lining the cytotrophoblast and the amnion?
Extraembryonic somatic mesoderm
Lining covering the yolk sac?
Extraembryonic splanchnic mesoderm
What forms primary villi?
Penetration of cytotrophoblast into syncytiotrophoblast
When does secondary yolk sac form?
Day 13, from hypoblast
