If the afferent arteriole diameter is less than efferent arteriole than what happen ?

Options

A. No effect
B. Ultrafiltration reaction is slow.
C. Ultrafiltration is not possible.
D. Ultrafiltration will stop & tubular secretion is start.

Answer

### Step-by-Step Solution:

1. **Understanding the Afferent and Efferent Arterioles**:
- The afferent arteriole carries blood into the glomerulus, while the efferent arteriole carries blood away from the glomerulus.
- The diameter of these arterioles plays a crucial role in regulating blood flow and pressure within the glomerulus.

2. **Role of Hydrostatic Pressure in Ultrafiltration**:
- Ultrafiltration is the process where blood is filtered in the kidneys, specifically in the glomerulus.
- This process relies on hydrostatic pressure, which is generated when the afferent arteriole is wider than the efferent arteriole.

3. **Effect of Afferent Arteriole Being Smaller than Efferent Arteriole**:
- If the diameter of the afferent arteriole is less than that of the efferent arteriole, it will lead to a decrease in hydrostatic pressure within the glomerulus.
- A lower hydrostatic pressure means that the force required to push the fluid and small molecules through the filtration barrier (the glomerular capsule) is insufficient.

4. **Conclusion**:
- As a result, ultrafiltration will not occur effectively, and the process of filtering blood to form urine will be compromised.
- Therefore, if the afferent arteriole diameter is less than the efferent arteriole, ultrafiltration is not possible.

### Final Answer:
The correct answer is that ultrafiltration is not possible (Option 3).

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