Question

The type of placenta found in human beings is of ………. types.
A. Diffuse.
B. Zonary.
C. Cotyledonary.
D. Discoidal.

Answer 1

Hint: In mammals like humans and rabbits, placenta is of such type in which the chorionic villi area is arranged in a circular plate. Human beings have a placenta in which part of the chorion remains smooth, and the other part interacts with the endometrium to make the placenta. The blood cells from the mother are in direct contact with the fetal chorion.

Complete answer:
Placenta is a temporary association between the foetal and maternal tissue to permit the exchange of materials between the two. In humans, the outer surface of the chorion develops a number of fingers like projections, known as chorionic villi, which grows into the tissues of the uterine mucosa.

At the time of the pregnancy, placenta forms a connection between mothers and offspring, and provides endocrine secretion and selective exchange of respiratory gases, nutrients and excretory waste with the maternal blood.

In diffuse placenta: In this type of placenta, the villi are dissipated all over the surface of the chorion. Some examples are pig, horse etc.)
In zonary placenta: In this type of placenta, the villi are formed in the form of the belt or band surrounding the middle of their blastocyst or chorionic sac. Some examples are Dogs, cats, bears etc.
In cotyledonary placenta: In this particular type of placenta, the villi are found in groups or patches, and the rest of the chorion surface remains smooth. Animals like Cattle, sheep, dear etc. have cotyledonary placenta.
In the discoidal type of placenta: Primates, including humans and rodents have this type placenta in which villi are arranged and constricted to the circular disc or a plate on the dorsal surface of the blastocyst.

Hence, the correct answer is option (D).

Note: Some other features of human placenta is allanto-chorial (i.e. when the fetal allantois is connected to the chorial placental circulation, hemo-chorial type, discoid, pseudo-cotyledon (the villi are arranged together and separated by walls between them), and decidual.

A placenta that takes part of the uterine mucosa with it, when it is expelled is called decidual type (decidua).