Which of these is not a general function of the kidney?

Options

A. Regulation of blood volume
B. Regulation of vitamin-A synthesis
C. Regulation of solute concentration in the blood
D. Regulation of the pH of the extracellular fluid

Answer

To determine which of the given options is not a general function of the kidney, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Identify the Functions of the Kidney**:
- The kidneys perform several essential functions in the body, including the regulation of blood volume, solute concentration, pH levels, and the synthesis of certain vitamins.

2. **Evaluate Each Option**:
- **Option 1: Regulation of Blood Volume**:
- This is a correct function of the kidney. The kidneys help maintain blood volume by adjusting the amount of water excreted in urine.

- **Option 2: Regulation of Vitamin A Synthesis**:
- This is incorrect. The kidneys do not regulate the synthesis of vitamin A. Instead, they are involved in the regulation of vitamin D synthesis.

- **Option 3: Regulation of Solute Concentration in Blood**:
- This is a correct function of the kidney. The kidneys help maintain the balance of solutes, such as sodium and potassium, in the blood.

- **Option 4: Regulation of pH of Extracellular Fluid**:
- This is also a correct function of the kidney. The kidneys help regulate the pH of the blood and extracellular fluid by excreting hydrogen ions and reabsorbing bicarbonate.

3. **Conclusion**:
- After evaluating all options, the one that is not a general function of the kidney is **Option 2: Regulation of Vitamin A Synthesis**.

### Final Answer:
**Option 2: Regulation of Vitamin A Synthesis** is not a general function of the kidney.

---