Second week of embryonic development Flashcards
what happens in the endometrial stroma on the eighth day
blastocyst is partially embedded in it
what two layers does the trophoblast differentiate into
(1) inner layer of mononucleated cells, the cytotrophoblast,
(2) an outer multinucleated zone without distinct cell boundaries, the syncytiotrophoblast
Mitotic figures are found in the ___________ but not in the _____________
cytotrophoblast
syncytiotrophoblast
Thus, cells in the cytotrophoblast divide and migrate into the syncytiotrophoblast, where they fuse and lose their individual cell membranes.
what do Cells of the inner cell mass or embryoblast also differentiate into
(1) a layer of small cuboidal cells adjacent to the blastocyst cavity, known as the hypoblast layer
(2) a layer of high columnar cells adjacent to the amniotic cavity, the epiblast layer
what forms the flat disc
epiblast and hypoblast
how does the amniotic cavity form
a small cavity appears within the epiblast which enlarges to become the amniotic cavity
what are amnioblasts
Epiblast cells adjacent to the cytotrophoblast which line the amniotic cavity together with the rest of the epiblast cell
describe the structure of the endometrial stroma adjacent to the implantation site
edematous and highly vascular
what do the large, tortuous glands secrete
abundant glycogen and mucus
what happens to the blastocyst on day 9
blastocyst is more deeply embedded in the endometrium
what closes the penetration defect in the surface epithelium
a fibrin coagulum
where does the trophoblast develop most
at the embryonic pole, where vacuoles appear in the syncytium
what happens when the vacuoles in the syncytium fuse
they form large lacunae
what is lacunar stage
fusing of vacuoles forming lacunae
what happens at the abembryonic pole
flattened cells probably originating from the hypoblast form a thin membrane, the exocoelomic (Heuser’s) membrane that lines the inner surface of the cytotrophoblast
what forms the primitive yolk sac
exocoelomic membrane, together with the hypoblast, forms the lining of the exocoelomic cavity, or primitive yolk sac
On days 11 and 12 a new population of cells appears between the inner surface of the ____________ and the outer surface of the ______________
cytotrophoblast
exocoelomic cavity
what are the new population of cells between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity derived from
derived from yolk sac cells
what do the cells derived from yolk sac cells form
a fine, loose connective tissue, the extraembryonic mesoderm
what happens to the extraembryonic mesoderm
fills all of the space between the trophoblast externally and the amnion and exocoelomic membrane internally
how does the chorionic cavity form
large cavities develop in the extraembryonic mesoderm, and when these become confluent, they form a new space known as the extraembryonic cavity, or chorionic cavity
the chorionic cavity surrounds the primitive yolk sac and amniotic cavity, except
where the germ disc is connected to the trophoblast by the connecting stalk
what is the
a) extraembryonic mesoderm lining the cytotrophoblast and amnion called
b) lining covering the yolk sac
a) extraembryonic somatic mesoderm
b) extraembryonic splanchnic mesoderm
what does the blastocyst do in the uterus
produces a slight protrusion into the lumen of the uterus
what do the lacunar spaces in the syncytium of the trophoblast form
an intercommunicating network still evident in the embryonic pole
what happens as trophoblast continues to erode more and more sinusoids
maternal blood begins to flow through the trophoblastic system, establishing the uteroplacental circulation
growth of the ____________ is relatively slow compared with that of the trophoblast
bilaminar disc which remains small
what happens to the cells of the endometrium in the 11-12 days and what are these changes called
become polyhedral and loaded with glycogen and lipids; intercellular spaces are filled with extravasate, and the tissue is edematous changes–decidua reaction
what might cause bleeding in the implantation site
increased blood flow into the lacunar spaces
on day 13 what is the trophoblast characterized by
villous structures
Cells of the ______________ proliferate locally and penetrate into the _________________, forming cellular
columns with the syncytial covering are known as ____________
cytotrophoblast
syncytiotrophoblast
primary villi
how does the secondary yolk sac or definitive yolk sac (=Secondary umblical vesicle) form
hypoblast produces additional cells that migrate along the inside of the exocoelomic membrane, they proliferate and form the secondary yolk sac within the exocoelomic cavity
what is represented by exocolomic cysts in the chorionic cavity
large potions of the exocoelomic cavity that are pinched off during the formation of the secondary yolk sac
the extraembriyonic coelom expands and forms __________
chorionic cavity
what is the chorionic plate
extraembryonic mesoderm lining the inside of the cytotrophoblast
what is the connecting stalk
only place where extraembryonic mesoderm traverses the chrionic cavity
what happens to the connecting stalk when it develops blood vessels
it becomes the umbilical cord
