Which of the following is correct pairing of the site of action and the substrate of renin

Options

A. Mouth-starch
B. Small intestine-protein
C. Stomach-casein
D. Stomach-fat

Answer

To solve the question regarding the correct pairing of the site of action and the substrate of renin, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Renin**: Renin is an enzyme that plays a crucial role in the digestion of milk proteins, specifically casein. It is primarily active in the stomach.

2. **Identifying the Substrate**: The substrate that renin acts upon is casein, which is a protein found in milk. Renin hydrolyzes casein into paracasein.

3. **Recognizing the Site of Action**: The site of action for renin is the stomach, where it works in the presence of hydrochloric acid (HCl) and calcium ions to facilitate the coagulation of milk.

4. **Evaluating the Options**:
- The first option mentions the mouth and starch, which is incorrect because starch is digested by salivary amylase in the mouth, not renin.
- The second option mentions the small intestine and protein, which is also incorrect as renin does not act in the small intestine.
- The third option mentions the stomach and casein, which is correct since renin acts on casein in the stomach.

5. **Conclusion**: Based on the understanding of renin's function and the evaluation of the options, the correct pairing is the stomach and casein.

### Final Answer:
The correct pairing of the site of action and the substrate of renin is **stomach and casein**.

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