The concentration of filtrate will _____ as it moves down in the descending limb of loop of Henle

Options

A. increase
B. decrease
C. remain unchanged
D. first increase and then decrease

Answer

To solve the question regarding the concentration of filtrate as it moves down in the descending limb of the loop of Henle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Loop of Henle**: The loop of Henle consists of two limbs: the descending limb and the ascending limb. The descending limb is primarily responsible for water reabsorption.

2. **Filtrate Movement**: As the filtrate moves down the descending limb, it encounters a high osmolarity in the surrounding interstitial fluid. This osmolarity gradient is crucial for the reabsorption process.

3. **Permeability of the Descending Limb**: The descending limb of the loop of Henle is permeable to water but not to electrolytes (such as sodium and potassium ions). This means that water can exit the filtrate into the interstitium, but electrolytes cannot enter the filtrate from the interstitium.

4. **Reabsorption Process**: As water leaves the filtrate and enters the interstitial fluid, the concentration of solutes (like sodium and potassium) in the filtrate increases. However, since the electrolytes are not being reabsorbed, the overall concentration of the filtrate decreases.

5. **Conclusion**: Therefore, as the filtrate moves down the descending limb of the loop of Henle, the concentration of the filtrate will decrease.

### Final Answer:
The concentration of filtrate will **decrease** as it moves down in the descending limb of the loop of Henle.

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