Extra embryonic structures Flashcards
What with the decidua basalis, forms the placenta?
The chorion
What 3 extra-embryonic tissues is the chorion formed from?
i) Outer syncytial trophoblast 2) middle cellular trophoblast 3) inner extraembryonic mesoderm
Why is the yolk sac important in mammals?
It produces the cells that will form the embyo’s primordial germ line that will migrate into the developing reproductive system to form sperm and egg mother cells.
Also, the yolk sac contains precursors for blood cells.
Why is the yolk sac not needed in development?
The embryos of placental mammals can obtain nutrients directly from the mother and the yolk sac no longer is needed as a food supply during development once the placenta has formed.
How is the yolk sac formed?
When the cells of the hypoblast migrate to cover the inner walls of the blastocyst cavity.
What is the role of the yolk sac in reptiles and birds?
fILLED WITH NUTRIENTS THAT ALLOW THE EMBRYO TO DEVELOP INSIDE THE ISOLATED EGG
What of the foetus and the mother forms the placenta?
Embryo’s chorion and the mother’s decidua.
What is it called when the blastocyst attaches to the endometrium?
The decidua y’all
What is the decidua split up into? Hint: it’s split up into the 3 parts.
The decidua basalis, the decidua parietalis, the decidua capsularis
What does the embryo contribute to in its chorion?
Syncytial trophoblast, cellular trophoblast, and extraembryonic mesoderm.
How is the lacunae formed in the endometrium/basalis?
Enzymes are secreted by the syncytial trophoblast which erode the connective tissue and some of the blood vessels in the uterine wall giving rise to large spaces that are filled with blood called lacunae (blood lakes, man.)
What happens in the 2nd week of development?
The syncytial an cellular trophoblast begin to form finger like projections called CHORIONIC VILLI that come in contact with the lacunae.
Wht is the purpose of the chorionic villi?
it increases the surface area that is exposed to maternal blood in the lacunae helping maximise exchange between the maternal and foetal blood.
Although vestigial, the allantoic sac is still important in mammals. Why is that?
It becomes surrounded by the stalk of the extraembryonic mesoderm and contributes to the formation of the umbilical cord.
What are the features of the allantois walls?
They are well vascularised.
What will become of these blood vessels?
They become the umbilical arteries and veins that transport blood between the foetus and the placenta.
What are the features of the umbilical cord?
It has 2 ARTERIES that go to the placenta and ONE VEIN that carries OXYGENATED blood from the placenta to the foetal heart (via the liver)
What processes does the chorionic vill facilitate?
It is where the gas exchange and the exchange of nutrients and nitrogenous waste between mother and foetus take place.
Where is the allantois sac positioned in mammals?
Vestigially.
