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 tubule.
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 about glomerular filtrate and urine are true, 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 formed from blood plasma during the filtration process in the kidneys. It contains water, ions, and small molecules, and its osmolarity is similar to that of plasma.
- **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 undergoes further concentration due to the reabsorption of water, making it more concentrated (hypertonic) rather than hypotonic.
- **Conclusion**: This statement is **False**.

3. **Statement III: Filtrate is isotonic in the proximal convoluted tubule.**
- **Analysis**: In the proximal convoluted tubule, the filtrate remains isotonic to plasma as it is reabsorbing solutes and water in a balanced manner.
- **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**: In the descending limb of the loop of Henle, water is reabsorbed, and solutes are not, leading to an increase in osmolarity (making it hypertonic) as it moves down.
- **Conclusion**: This statement is **False**.

### Summary of Results:
- Statement I: True
- Statement II: False
- Statement III: True
- Statement IV: False

### Correct Option:
The correct statements are I and III. Therefore, the correct option is that **the first and third statements are true**.

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