Implantation To Gastrulation Flashcards
Which are the three initial structures of blastocyst before implantation?
- Trophoblast or trophectoderm
- Blastocoel
- Inner cell mass or embryoblast
What happens when implantation begins?
The hatched blastocyst attaches to the endometrial layer of the uterus
At day 8 the blastocyst is partially embedded in the endometrial stroma.
In what orientation does blastocyst attach to endometrium
The embryo implants into the uterine wall with the inner cell mass towards the uterine wall
What happens to the trophoblast portion closest to the inner cell mass upon implantation?
Which structures does it give rise to?
The trophoblast over the embryoblast differentiates into two structures:
- Cytotrophoblast
- Syncytiotrophoblast
Describe syncytiotrophoblast
Multinucleated zone
No distinct cell boundaries
Distinguish between cytotrophoblast from syncytiotrophoblast in terms of cell division.
Cytotrophoblast contain mitotic figures, hence they can divide.
Mitotic figure not present in syncytiotrophoblast.
How does syncytiotrophoblast grow in the absence of mitotic figures?
Cells in the cytotrophoblast divide and migrate into syncytiotrophoblast.
Then these cells lose their individual cell membranes and fuse with the syncytiotrophoblast.
What happens to the cells of the inner cell mass upon implantation?
Cells of the inner cell mass differentiate into two structures:
- Hypoblast layer
- Epiblast layer
Hypoblast
Layer of small cuboidal cells.
Adjacent to the blastocyst cavity.
Epiblast
Layer f high columnar cells.
Adjacent to amniotic cavity (precursor area- cytotrophoblast in contact with uterine wall at the beginning of implantation)
Explain the formation of the amniotic cavity.
Formation of the amniotic cavity begins at the same time as the inner cell mass begins differentiating into epiblast and hypoblast.
A small cavity begins to appear within the epiblast, separating the epiblast from the cytotrophoblast adjacent to the uterine wall.
What happens to the conceptus as time progresses?
The conceptus invades deeper in the endometrium.
How does the epiblast contribute to formation of amniotic cavity?
Cells of the epiblast extend around the cytotrophoblast to form the amniotic cavity.
Upon formation of the amniotic cavity, the epiblast can be divided into two parts. Which are these parts?
- Epiblast- integrated into the bilaminar embryo.
2. Amniotic ectoderm- adjacent to cytotrophoblast.
Where do primordial germ cells originate from?
Primordial germ cells derive from the epiblast.
They are induced in the epiblast at the edge that will give rise to the future posterior of the embryo.
Explain the formation of the yolk sac.
The hypoblast extends to surround the cytotrophoblast, forming the yolk sac cavity.
