Question

Throughout the gestation period, the embryo is found suspended in the fluid that acts as the shock absorber. Which of the following structures initiates the formation of the cavity that encloses the fluid?

Answer 1

The blastocyst has two types of cells- the outer trophoblast and the inner cell mass (ICM)/ embryoblast. The ICM divides further to give rise to the three germinal layers. The ICM undergoes some structural changes and gives rise to cylindrical cells. These cells begin to divide from the bottom, separating themselves from the cells at the top. The top layer thus formed is called epiblast, and the bottom layer is called hypoblast. A fluid starts accumulating in between the epiblast. This gives rise to a cavity called amniotic cavity and the fluid is called amniotic fluid.
So, the epiblast is involved in the formation of amniotic cavity. Trophoblast and hypoblast are not involved in this process.

The chorion forms the outermost membrane of the embryo. In mammals, it develops a rich supply of blood vessels and forms an intimate connection with the endometrium of the uterus. It is involved in the formation of placenta, not the amniotic cavity.