If the diameter of the afferent renal arteriole is decreased and that of efferent renal arteriole is increased, the ultrafiltration will

Options

A. be faster
B. be slower
C. not takes place
D. take place with the same speed

Answer

To solve the question regarding the impact of changes in the diameters of the afferent and efferent renal arterioles on ultrafiltration, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Ultrafiltration**:
- Ultrafiltration, also known as glomerular filtration, is the first step in urine formation. It occurs in the glomerulus, where blood is filtered through the capillaries into the Bowman's capsule.

2. **Analyzing Afferent and Efferent Arterioles**:
- The afferent renal arteriole carries blood into the glomerulus, while the efferent renal 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.

3. **Effect of Decreasing Afferent Arteriole Diameter**:
- If the diameter of the afferent renal arteriole is decreased, less blood will flow into the glomerulus. This reduction in blood flow will decrease the pressure within the glomerulus.

4. **Effect of Increasing Efferent Arteriole Diameter**:
- If the diameter of the efferent renal arteriole is increased, blood will flow out of the glomerulus more easily. This can also lead to a decrease in pressure within the glomerulus.

5. **Resulting Pressure Gradient**:
- The combination of decreased blood flow into the glomerulus (due to the narrowed afferent arteriole) and increased outflow (due to the widened efferent arteriole) leads to a significant reduction in the pressure gradient necessary for ultrafiltration.

6. **Conclusion on Ultrafiltration Rate**:
- Since ultrafiltration relies on a sufficient pressure gradient to push blood components out of the glomerular capillaries, the changes described (decreased afferent diameter and increased efferent diameter) will result in slower ultrafiltration.

7. **Final Answer**:
- Therefore, the ultrafiltration will be slower. The correct option is **B (slower)**.