Thick keratin layer would restrict oxygen exchange ... forming the yolk sac. Yolk sac is then infiltrated with a system of blood vessels, carrying nutrients from the yolk back to the embryo. Other ...

Thick keratin layer would restrict oxygen exchange ... forming the yolk sac. Yolk sac is then infiltrated with a system of blood vessels, carrying nutrients from the yolk back to the embryo. Other ...

The fetal membranes consist of the chorion, amnion, yolk sac, and allantois. The chorion has three layers: cytotrophoblastic ... containment of the amniotic fluid, and secretion of substances ...