Question

Extra embryonic membranes, chorion and amnion are formed by

• A. inner cell mass
  
• B. trophoblast
  
• C. inner cell mass and trophoblast
• D. endometrial tissues

Answer 1

The correct option is B trophoblast


The mitotic division within the zygote is known as cleavage. It results in an 8 -16 blastomere stage of the embryo called a morula. Further divisions in the morula transform it into a blastocyst by the process called blastulation. The blastomeres in the blastocyst are arranged into an outer layer called the trophoblast or trophectoderm and the inner group of cells called the inner cell mass or embryoblast. The trophoblast layer then gets attached to the endometrium. Inner cell mass gets differentiated as embryo proper, from here the future embryo will be formed. The trophoblast layer or trophectoderm layer generates the extraembryonic membranes like amnion, yolk sac, chorion and allantois.
The amnion is the innermost membrane of the embryo which surrounds the embryo and creates a fluid-filled cavity. The amniotic fluid present inside protects the embryo from mechanical stress. The yolk sac does not have a significant function in humans as the nourishment to the embryo is provided directly by the mother through the umbilical cord. Allantois collects liquid waste from the embryo, it also helps in the exchange of respiratory gases. The chorionic fluid protects the embryo from shock and the chorionic villi allows the exchange of nutrients, oxygen and waste products.
Figure: Extra embryonic layers