Question

In which species, oesophagus is entirely made of the smooth muscles

• A. Cattle
• B. Pig
• C. Horse
• D. Poultry

Hint:

Remember the anatomical rule: Ruminants (like cattle and goats) have an entirely striated (skeletal) muscular esophagus to support active, voluntary regurgitation during rumination. Conversely, birds (poultry) have an entirely smooth muscular esophagus.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The histological structure of the esophagus varies among animal species to accommodate different feeding behaviors, anatomical requirements, and digestive processes.

Step 2: Detailed Explanation:
Let us compare the muscle fiber composition of the esophagus across the given species:

Cattle (Ruminants): In ruminants, the entire length of the esophagus is composed of striated (skeletal) muscle fibers.
This is a critical anatomical adaptation that allows for voluntary, active anti-peristalsis to regurgitate the bolus from the rumen back to the mouth during the process of rumination. Thus, option (A) is incorrect.

Pig: In swine, the muscularis layer of the cranial portion of the esophagus is striated, and it gradually transitions into smooth muscle toward the caudal portion near the stomach. Thus, option (B) is incorrect.

Horse: In horses, the cranial two-thirds of the esophagus consists of striated muscle, while the caudal one-third transitions completely to smooth muscle. Thus, option (C) is incorrect.

Poultry (Birds): Unlike mammals, the avian esophagus consists entirely of smooth muscle fibers along its entire length. This structure supports the transport of large, unchewed feed items down to the crop and gizzard. Thus, option (D) is correct.
Therefore, poultry is the species with an esophagus made entirely of smooth muscle.

Step 3: Final Answer:
The correct option is (D), representing Poultry.