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Question

Human placenta is classified as ___________

A
Haemochorial
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B
Endotheliochorial
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C
Mesoeliochorial
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D
Epitheliochorial
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Solution

The correct option is A Haemochorial

After proper implantation of the blastocyst onto the wall of the uterus, chorionic villi appear on the trophoblast, which gets surrounded by uterine tissues and maternal blood.

Integration of both these chorionic villi and uterine tissues form a structure that connects the developing embryo with the mother’s body known as the placenta. It is a structural and functional unit for the supply of oxygen, nutrients, different hormones to the growing embryo and also for the removal of CO2 and waste material produced by the growing embryo.

Just prior to placenta formation, there are six layers of tissues that separate foetal and maternal blood. Among these six layers, three are contributed by the foetus and the other three by the maternal side.

Three layers of extraembryonic membranes in the chorioallantoic placenta of all mammals are-
1.Endothelium lining allantoic capillaries
2.Connective tissue in the form of chorioallantoic mesoderm
3.Chorionic epithelium, the outermost layer of the fetal membrane derived from the trophoblast

All of these are components of a mature placenta.
There are also three layers on the maternal side, but not all of these layers are retained in the mature placenta in the process of placentation.

The three potential maternal layers are-
1.Endothelium lining endometrial blood vessels.
2.The connective tissue of the endometrium
3.Endometrial epithelial cells

On the basis of which maternal layers are retained in the placenta during the process of placentation. Placentas are classified as epitheliochorial, endotheliochorial and hemochorial.
The hemochorial placenta is a type of placenta in which the maternal blood is in direct contact with the chorion of the human placenta, chorionic epithelium is bathed in maternal blood.



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