Question

Plicae circulares of small intestine are permanent folds in

• A. Ruminants
• B. Horse
• C. Dog
• D. Fowl

Hint:

Ruminants rely heavily on efficient absorption of fermentation products and nutrients.
Hence, they possess permanent plicae circulares, whereas carnivores (dogs) have a rapid transit time and do not require these permanent structures.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Plicae circulares (also known as valves of Kerckring) are large, permanent, circular folds of the mucosa and submucosa that project into the lumen of the small intestine.
Unlike temporary folds (which disappear when the intestine is distended with food), permanent folds persist during distension and serve to vastly increase the absorptive surface area.

Step 2: Detailed Explanation:
There is significant species variation in the development of plicae circulares among domestic animals:
In carnivores like the dog and cat, plicae circulares are absent or highly underdeveloped; instead, their intestinal mucosa forms temporary longitudinal or transverse folds.
In horses, plicae circulares are present but are relatively temporary or disappear when the bowel is distended.
In birds (fowl), the mucosal surface is characterized by prominent villi, but it lacks true, highly developed permanent plicae circulares of the mammalian type.
In ruminants (especially sheep, goats, and cattle), the plicae circulares are highly prominent, well-developed, and represent permanent anatomical structures that do not disappear during distension or peristalsis.
These permanent folds are essential in ruminants to slow down the passage of digesta and provide maximum surface area for nutrient absorption.

Step 3: Final Answer:
Therefore, Ruminants is the correct species where plicae circulares are permanent folds. This corresponds to option (A).