101. formation of germ disk Flashcards
After the trophoblast layers become cyto + synctiotrophoblast, the embryoblasts differentiate to 2 layers: what are they
Hypoblasts - cuboidal cells
Epiblasts - columnar cells
what is the cavity that appears in the epiblast
amnniotic cavity
Epiblast cells adjacent to cytotrophoblast = amnioblasts. Epiblast cells adjacent to the cytotrophoblast are called amnioblasts
how is the primitive yolk sac/ exocoelemic cavity formed (aembryonic pole day 9)
, flattened cells form a thin membrane, which lines the inner surface of the cytotrophoblast. This membrane,
together with the hypoblast, forms the lining of
the exocoelomic cavity, or primitive yolk sac.
how is the definitive/ secondary yolk sac formed
hypoblast makes additional cells that migrate to the exocoelemic membrane. these cells proliferate and form a new cavity- this is the secondary yolk sac.
At day 9 what happens at the embryonic pole (side with inner mass)
vacuoles appear in the syntcium and fuse together to become lacunae - LACUNAR STAGE
What happens at day 12
blastocyst completely embedded in endometrial stroma of uterus
synctiotrophoblast (at embryonic pole) penetrates into the endothelial of materanl capillaries = sinusoids
lacunae become continuous with sinusoids and allow maternal blood to enter lacunar system
How is the uteroplacental circulation established
as the trophoblasts continue to erode, more of the maternal blood enters the trophoblastic system.
what forms between the cytotrophoblast and the exocoelemic cavity/primary yolk sac?
whats an extraembyonic cavity
extraembbryonic mesoderm
cavities form on this mesoderm
DAy 13 how are primary villi formed
cytotrophoblast proliferate and become synctiotrophoblasts which forms columns
what is the connecting stalk
where the extraembryonic mesoderm goes through the extraembyonic cavity (chorionic cavity)
develops blood vessels and becomes UMBILICAL CHORD
when does the trilamanar disk form and what occurs
3rd week - gastulation where 3 germ layers form
how does gastrulation start
primitive streak formed. at the end is the primitive node surrounded by primitive pits
how does the germ layers form
cells from epiblast migrate inwards = invagination
some cells displace hypoblast = endoderm
some cells lie between epiblast an hypoblast = mesoderm
some cells stay in epiblast = ectoderm
how is notochord formed
prenotochordal cells invaginate the primitive node
forms in the mesoderm
establishment of body axes- cephalic and narrow caudal
What maintains the primitave streak
the expression of NODAL
a member of the transforming growth factor-b (TGF-b)
**Baso theres lots of growth factors that determine which side organs are and formation of organs
