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The placenta of human beings belongs to the category of:
(a) Haemo-chorialis
(b) Syndesmo-chorialis
(c) Endothelial-chorialis
(d) Epithelia-chorialis

Answer
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Hint: In human beings, the placenta is of such type where maternal blood comes in direct contact with chorionic villi.

Complete answer:Placenta is a foeto-maternal organ that develops during pregnancy. It is formed in the uterus. It helps in circulatory processes and nourishment of the growing embryo. Placenta can be of different types: Haemo-chorialis, Syndesmo-chorialis, Endothelial-chorialis and Epithelio-chorialis placenta. Although, sometimes called “placental barrier”, it does not really serve as a barrier between the Mother and baby, rather it establishes a connection between both.
In Haemo-chorialis placenta, the maternal blood comes in direct contact with the chorionic trophoblast cells. It is also known as labyrinthine placenta. It is seen in human beings.
The Syndesmo-chorialis placenta is a type of placenta in which an endometrial wall gets attached to the chorion membrane. In this, a certain amount of the endometrial epithelium gets destroyed.
In the Endothelium-chorialis placenta, the maternal vessels in the endometrium become bare and these come in contact with the chorion portion of the foetal membranes.
When the uterine epithelium of the uterus & chorion of the embryo come in contact and there is no destruction of the epithelium – this type of placenta is known as the Epithelio-chorialis placenta. It is the most primitive type of placenta.

So, the correct option is ‘Haemo-chorialis’.

Note:Chorionic villi is so called because of the finger like projections formed by it.