Question

What is the significance of chorion on during embryonic development?

Answer 1

Hint:Chorion is the outermost fetal membrane in mammals found inside the embryo.The chorion and amnion together forms the embryonic sac.

Complete answer:
Chorion is a double layered membrane formed from the trophoblast and the extra embryonic mesoderm, which eventually give rise to the fetal part of placenta in embryo. It has 2 layers of trophoblast on the outside and mesoderm layer on the inside. This encloses the amnion ,embryo and other membranes. It is one of the first membranes that forms during pregnancy. Chorion consists of chorionic villi which extend into the endometrium to form placenta.

It is the placenta that provides the embryo with oxygen and nutrients and also removes carbon dioxide and other wastes. During the 14 to 16 week of pregnancy the chorion and amniotic sac fuse to become chorioamniotic sac. The presence of chorion is crucial to the fetal as it provides the support for exchange of gases by making a pathway for it. It also helps in the exchange of blood and waste between the fetus and mother.

 The chorionic villi consists of genetic makeup of the fetus. So during pregnancy the doctor can take a sample of the chorionic villi to examine the chromosomal and developmental issues ,if present,in the child. Syndromes such as down syndrome and cystic fibrosis etc can be determined from this test. Chorionic villi also helps in establishing a large area of contact between mother and embryo due to its tree-like structure.

The other important function of chorion other than nurturing it and giving genetic sample is to protect the embryo from shocks and sudden movements. The chorion produces a fluid known as chorionic fluid. This lies in the cavity between amnion and chorion. This fluid will absorb the shock from forces such as movements.

Additional information: Reptiles and birds also have chorion around the embryo. In this case albumin surrounds the chorion. In insects chorion fuses with allantois and this fusion is called chorioallantoic fusion.

Note: In the primary stage of chorionic development, chorionic villi are non vascular as they do not have blood vessels,they only have trophoblast. In the secondary stage mesoderm starts to grow and chorionic villi becomes larger. In the tertiary stage chorionic villi becomes vascularised as blood vessels start to grow in them.