Answer
The four extraembryonic membranes are the amnion, yolk sac, chorion and allantois;
. The amnion develops from epiblast cells; it encloses the embryo and later is penetrated by the umbilical cord and becomes filled with fluid ( amniotic fluid). The amniotic fluid protects and serves the embryo in the following ways:
It protects embryo from trauma and infection
It facilitates movements of parts of the embryo
It promotes symmetry of development
It stimulates lung development
The yolk sac
The yolk sac develops on the ventral side of the embryo. It contributes to the following processes:
Formation the GI tract
formation of blood cells
Formation of precursors of eggs, oocytes and sperms
Work Step by Step
Chorion:
The chorio encloses all the other membranes and the embryo It grows chorionic villi many of which degenerate. However, those chorionic villi in the placental region grow many branches. They form the fetal attachment to the placenta -- chorionic villi.
Allantois
The allantois develops as an outgrowth of the tail end of the primitive gut. It forms the basis of the umbilical cord and the urinary bladder
