The proteins first digested in the alimentary canal is

Options

A. Small intestine
B. Oesophagus
C. Mouth
D. Stomach

Answer

### Step-by-Step Solution:

1. **Identify the Question**: The question asks where the digestion of proteins first occurs in the alimentary canal.

2. **Understand the Alimentary Canal**: The alimentary canal consists of various parts including the mouth, esophagus, stomach, small intestine, and large intestine. Each part has specific functions in the digestion process.

3. **Locate the Starting Point for Protein Digestion**: Protein digestion begins in the stomach. This is a crucial point because it distinguishes the stomach from other parts of the alimentary canal.

4. **Identify the Enzyme Involved**: The enzyme responsible for initiating protein digestion in the stomach is pepsin. It is derived from its inactive form, pepsinogen, which is activated by hydrochloric acid (HCl) present in the stomach.

5. **Explain the Process**: When food enters the stomach, HCl activates pepsinogen to pepsin, which then starts breaking down proteins into smaller peptides.

6. **Conclude the Answer**: Therefore, the first site of protein digestion in the alimentary canal is the stomach.

### Final Answer:
The proteins first digested in the alimentary canal is the **stomach**.

---