Implantation and formation of germ layers Flashcards
What happens when the blastocyst adheres to the endometrium
Implantation begins
Where does implantation occur
On the posterior wall of the uterus and nearer the fundus (top bit) than the cervix
what happens to the zone pellucida in implantation
Disappearance of it
What happens to the blastocyst in implantation
Gives rise to inner cell mass and trophoblast
What happens in the uterine lining in implantation
a ‘decimal reaction’ whereby there is increased secretory function
What does the inner cell mass form
The embryo and some membranes
What color is the primitive ectoderm
Blue
What color is the primitive endoderm
Yellow
What does the inner cell mass give rise to
primitive ectoderm
What dos the ectoderm surround
Amniotic cavity
What does the endoderm surround
Cavity of the yolk sac
How many layers does the blastocyst wall have
2
What the trophoblast form
extraembryonic embryonic mesoderm
What is the extra embryonic mesoderm
The red cells between the inner cell mass and the trophoblast (green bit)
What is the decimal reaction
Endometrium undergoes it
-GLycogen/lipid distended cells and glands swell more
What is another name for the chorionic cavity
extraembryonic coelom
What forms the chorionic cavity
Cavities in extra embryonic mesoderm coalesce (become bigger and join)
What does the extra embryonic mesoderm cover now
- amnion and yolk sac
- lines the trophoblast
What are the two layers of mesoderm joined by
connecting stlk
What happens in the second week summary
- 2 layer (ectoderm and endoderm)
- 2 cavities (amniotic and yolk sac)
- 2 trophoblast derivatives (cytotrophoblast and syncytiotrophoblast)
How is the intraembryonic mesoderm formed
Ectodermal cells begin to divide and migrate between ectoderm and endoderm in the region of the primitive streak (the bump on the blue cells where the endoderm and ectoderm meet) to form the intraembryonic mesoderm
How is the prechordal plate formed
Endoderm thickens (yellow) and becomes firmly adherent to overlying ectoderm in the region of the prochordal plate
What is the future mouth region of the foetus
Prochordal plate
How is the notochord formed
Cells from the head end of the primitive streak form the notochord
What does the notochord do
Induces overlying ectoderm to form the neuroectoderm of the neural plate
Why does the embryo lengthen
Cell production in and migration from the primitive streak
What does the primitive streak form
Mesoderm continues to be produced and migrates laterally until it joins up with the extra-embryonic mesoderm
How is the septum transversum formed
When the mesoderm migrates forwards (to the top)
What does the cloacal plate form
Anal end of gut
What is the structure that separates the endoderm and ectoderm apart from where they touch (prochordal plate)
Intraembryonic mesoderm
How is the neural tube formed
Neural plate forms neural folds which eventually fuse to form neural tube
What does the neural tube form
brain and spinal chord
What is formed in the third week summary
-3 germ layers
-3 important structures:
primitive streak
notochord
neural tube
