Identify the part of the avian digestive system that is often referred to as the mechanical stomach.
A crop
B gizzard
C proventriculus
D duodenal loop
The correct answer and explanation is:
The correct answer is: B. gizzard
Explanation:
In the avian digestive system, the gizzard is commonly referred to as the “mechanical stomach.” Here’s why:
Birds have a unique digestive system adapted to their diet and lack of teeth. Because they cannot chew food with teeth, birds rely on specialized organs to break down their food mechanically and chemically.
- Crop (Option A):
The crop is an expanded, muscular pouch near the esophagus that serves as a storage area for food. It softens and stores food temporarily but does not play a major role in mechanical digestion. - Gizzard (Option B):
The gizzard, also called the ventriculus, is a thick, muscular part of the stomach that grinds food. Birds often swallow small stones or grit, which remain in the gizzard and help pulverize hard food materials like seeds. The strong muscles of the gizzard contract to crush and grind food, effectively replacing the function of teeth. This mechanical breakdown is essential because it increases the surface area of food particles for better enzymatic digestion later on. - Proventriculus (Option C):
The proventriculus is the glandular or chemical stomach where digestive enzymes and acids are secreted to begin chemical digestion of food. Unlike the gizzard, it does not perform mechanical grinding. - Duodenal loop (Option D):
The duodenal loop is part of the small intestine, involved in nutrient absorption and further digestion after the stomach stages. It is not involved in mechanical digestion.
Summary:
The gizzard is a muscular organ specifically designed for mechanical digestion in birds. It acts like a grinding mill, breaking down food physically by contracting its thick walls and using ingested grit or stones. This compensates for the absence of teeth in birds and prepares the food for chemical digestion and absorption later in the digestive tract.
Thus, the gizzard is the correct choice as the “mechanical stomach” of birds.