Question

Degree of proximity of the maternal and fetal blood circulations in the placenta of animals, in increasing order is :
(A) Hemochorial
(B) Epitheliochorial
(C) Synepitheliochorial
(D) Endotheliochorial
Choose the correct answer from the options given below:

• A. (A), (B), (D), (C).
• B. (B), (C), (D), (A).
• C. (C), (D), (A), (B).
• D. (B), (A), (D), (C).

Hint:

To remember the Grosser classification based on intact maternal layers (from least to most intimate):
- Epitheliochorial: Maternal epithelium intact (6 layers total).
- Synepitheliochorial: Maternal epithelium partially modified (5 layers total).
- Endotheliochorial: Maternal endothelium intact (4 layers total).
- Hemochorial: Fetal chorion directly in maternal blood (3 layers total).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Placentas in domestic animals are classified histologically based on the Grosser system, which counts the number of tissue layers separating the maternal and fetal blood circulations.
Fewer layers mean a higher degree of proximity (intimacy) between the two circulations.

Step 2: Detailed Explanation:
Let us analyze the histological types of placentation based on Grosser's classification, from the least intimate (most tissue layers intact) to the most intimate (fewest tissue layers intact), which represents an increasing order of proximity:
1. Epitheliochorial (B):
This is the least intimate placenta, where all six tissue layers (three maternal and three fetal) remain fully intact.
The maternal uterine epithelium remains in simple contact with the fetal chorion.
Examples: Mare (horse), Sow (pig).
Therefore, (B) has the lowest proximity.
2. Synepitheliochorial Syndesmochorial (C):
In this placenta, the maternal uterine epithelium undergoes localized erosion or fusion with the fetal binucleate giant cells (forming a hybrid syncytium), reducing the barrier slightly.
Examples: Ruminants (cow, ewe, goat).
Therefore, (C) is intermediate.
3. Endotheliochorial (D):
The maternal epithelium and connective tissue layers are completely lost, meaning the chorion of the fetus is in direct contact with the endothelium of the maternal blood vessels (leaving only four layers intact).
Examples: Carnivores (bitch, queen).
Therefore, (D) has higher proximity.
4. Hemochorial (A):
This is the most intimate placenta, where all maternal tissue layers are lost.
The fetal chorion is bathed directly in maternal blood pools (leaving only the three fetal layers intact).
Examples: Primates, rodents.
Therefore, (A) has the highest proximity.
Thus, the increasing order of proximity of maternal and fetal blood circulations is:
Epitheliochorial (B) $\rightarrow$ Synepitheliochorial (C) $\rightarrow$ Endotheliochorial (D) $\rightarrow$ Hemochorial (A).

Step 3: Final Answer:
The correct option is (B), representing (B), (C), (D), (A).