If the afferent arteriole diameter is less than efferent arteriole than what happen ?
(a) No effect
(b) Ultrafiltration reaction is slow
(c) Ultrafiltration is not possible
(d) Ultrafiltration will stop and tubular secretion will start.

Options

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

Answer

To answer the question, "If the afferent arteriole diameter is less than the efferent arteriole, what happens?" we need to analyze the roles of the afferent and efferent arterioles in the kidney's nephron, particularly in the glomerulus where ultrafiltration occurs.

### Step-by-Step Solution:

1. **Understanding the Role of Afferent and Efferent Arterioles**:
- The **afferent arteriole** carries blood into the glomerulus, while the **efferent arteriole** carries blood away from the glomerulus.
- Normally, the diameter of the afferent arteriole is greater than that of the efferent arteriole, which helps maintain a high pressure in the glomerulus necessary for ultrafiltration.

2. **Effect of Afferent Diameter Being Less**:
- If the diameter of the afferent arteriole is less than that of the efferent arteriole, this means that less blood is entering the glomerulus compared to what is leaving.
- This condition would lead to a decrease in the hydrostatic pressure within the glomerulus.

3. **Consequences on Ultrafiltration**:
- The process of ultrafiltration relies on sufficient pressure to push water and solutes from the blood into the Bowman's capsule.
- If the pressure is not adequate due to the smaller diameter of the afferent arteriole, ultrafiltration will be impaired.

4. **Conclusion**:
- Given the options:
- (a) No effect - Incorrect, as there is a clear effect on pressure.
- (b) Ultrafiltration reaction is slow - This could be partially true, but it doesn't capture the full impact.
- (c) Ultrafiltration is not possible - This is the most accurate statement given the scenario.
- (d) Ultrafiltration will stop and tubular secretion will start - This is misleading as tubular secretion is a different process that does not directly replace ultrafiltration.
- Therefore, the correct answer is **(c) Ultrafiltration is not possible**.

### Final Answer:
(c) Ultrafiltration is not possible.