Blastocyst Formation; Bilaminar Embryonic Disc Flashcards
What forms in the morula to change it to its next phase?
Next phase?
When?
Whats the process called?
Blastocystic Cavity
Blastocyst
at 4 days
blastogenesis
What two types of cells differentiate initially in a blastocyst?
Where?
What do they later form?
Trophoblast - outer layer, form cyto and syncytiotrophoblast > placenta
Embryoblast - inner cell mass, form bilam disc > embryo
What happens after the blastocyst has been in the uterus ~2 days?
How?
What does it allow?
Hatching
- blastocyst growth + enzymes break the ZP
- allows further growth and implantation
What two parts does the trophoblast differentiate into?
What do they do?
cyto - outer cell ring around embryo, undergo mitosis and migrate into syncytio
syncytio - amorphous, mutlinucleate cell mass in endometrium, secretes hCG to stimulate corpus luteum production of progesterone
What cells differentiate from the embryoblast after about 7 days?
Where are they?
What cells are they continuous with? 2 names
hypoblast
facing blastocystic cavity > exocoelomic cavity
- continuous with exocoelomic membrane (or Heuser’s membrane) around cavity
What 2 layers differentiate from the embryoblast?
epiblast - thicker columnar cells on top, facing amnion
hypoblast - cuboidal cells on bottom, facing exocoelomic cavity
What is the name of the layer around the 2 cavities and their membranes?
What makes it and what is it made of?
extraembryonic mesoderm
made of CT by yolk sac endodermal cells
What spaces form between the 2 cavities and the cytotrophoblast?
What happens to them? 2 layers
extraembryonic coelomic spaces
fuse to form 2 layers of extraembryonic coelom:
- splanchnic - around primary yolk sac which pinches off to form secondary yolk sac
- somatic - around cytotrophoblast layer and amnion
What happens to some of the hypoblast cells around this time?
Where?
What does it form and eventually become?
Prechordal Plate
- columnar thickening of hypoblast cells at the cranial end of bilaminar disc
- becomes future site of mouth + major organizer of head region
-
What is the name of the 2 trophoblast layers and their adjacent extraembryonic mesoderm layer together?
And what is the name of the cavity which is now just inside them?
chorionic sac - syncytio, cytotrophoblast + somatic ex.emb. mesoderm
chorionic cavity - new name for extraembryonic coelomic cavity
What happens with the primary yolk sac towards the end of the 2nd week?
Hypoblast cells fold down and inward and create a secondary yolk sac…
…off of which the primary yolk sac pinches and travels down to the bottom of the extraembryonic coelomic cavity, eventually disappearing along with the Heuser’s membrane
What special structures form from the cytotrophoblast around this time?
What induces them?
What do they become?
