Which of the following statement is/are true?
I. Glomerular filtrate is isotonic to plasma.
II. When the urine passes into collecting tubule, it becomes hypotonic.
III. Filtrate is isotonic in proximal convoluted tu- bule.
IV. Filtrate becomes more and more hypotonic as it passes through descending limb of Henle's loop. Choose the correct option :

Options

A. I and III
B. I, II and III
C. II and III
D. only II

Answer

To determine which statements are true regarding glomerular filtrate and urine composition, let's analyze each statement step by step:

### Step-by-Step Solution:

1. **Statement I: Glomerular filtrate is isotonic to plasma.**
- **Analysis:** Glomerular filtrate is indeed isotonic to plasma. This means that the concentration of solutes in the filtrate is the same as that in the blood plasma at the point of filtration.
- **Conclusion:** This statement is **True**.

2. **Statement II: When the urine passes into the collecting tubule, it becomes hypotonic.**
- **Analysis:** As urine passes through the collecting tubule, it can actually become more concentrated (hypertonic) due to the reabsorption of water, depending on the body's hydration status and the action of hormones like ADH (antidiuretic hormone).
- **Conclusion:** This statement is **False**.

3. **Statement III: Filtrate is isotonic in proximal convoluted tubule.**
- **Analysis:** The filtrate remains isotonic in the proximal convoluted tubule because this segment is primarily involved in the reabsorption of water, electrolytes, and nutrients, maintaining isotonicity with plasma.
- **Conclusion:** This statement is **True**.

4. **Statement IV: Filtrate becomes more and more hypotonic as it passes through the descending limb of Henle's loop.**
- **Analysis:** The descending limb of the loop of Henle is permeable to water but not to solutes. As the filtrate moves down this limb, water is reabsorbed, and the filtrate becomes more concentrated (hypertonic), not hypotonic.
- **Conclusion:** This statement is **False**.

### Final Evaluation:
- **True Statements:** I and III
- **False Statements:** II and IV

### Correct Option:
The correct answer is that statements I and III are true.

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