Select the correct order of osmolarity changes in filtrate w.r.t. plasma in `:-`
Bowmans capsule `rarr` PCT `rarr` Descending loop of henle `rarr `Ascending loop of henle `rarr` DCT `rarr` End of collecting duct

Options

A. (a) Isotonic `rarr` Isotonic `rarr` Hypotonic `rarr` Hypertonic `rarr `Hypotonic `rarr` Hypotonic
B. (b) Isotonic `rarr` Isotonic `rarr` Hypertonic `rarr `Hypertonic `rarr ` Hypotonic `rarr `Hypertonic
C. (c) Isotonic`rarr` Hypertonic `rarr` Isotonic `rarr ` Hypertonic `rarr `Hypotonic `rarr` Hypertonic
D. (d) Hypotonic `rarr` Isotonic `rarr` Hypertonic `rarr` Isotonic `rarr` Hypotonic `rarr` Hypertonic

Answer

To determine the correct order of osmolarity changes in the filtrate with respect to plasma as it moves through various parts of the nephron, we will analyze each segment step by step.

### Step-by-Step Solution:

1. **Bowman's Capsule**:
- The filtrate in Bowman's capsule is isotonic with plasma. This means that the osmolarity is the same as that of plasma.
- **Osmolarity: Isotonic (same as plasma)**

2. **Proximal Convoluted Tubule (PCT)**:
- In the PCT, there is significant reabsorption of water and solutes. However, the osmolarity remains isotonic with plasma because the same proportion of solutes and water is reabsorbed.
- **Osmolarity: Isotonic (same as plasma)**

3. **Descending Loop of Henle**:
- In the descending loop of Henle, water is reabsorbed, but solutes are not. This leads to a decrease in the volume of filtrate and an increase in osmolarity, making it hypotonic compared to plasma.
- **Osmolarity: Hypotonic (lower than plasma)**

4. **Ascending Loop of Henle**:
- In the ascending loop of Henle, solutes are reabsorbed, but water cannot follow. This results in a decrease in osmolarity, making the filtrate hypertonic compared to plasma.
- **Osmolarity: Hypertonic (higher than plasma)**

5. **Distal Convoluted Tubule (DCT)**:
- In the DCT, further reabsorption of solutes occurs, and the filtrate becomes hypotonic again as water is not reabsorbed in this segment.
- **Osmolarity: Hypotonic (lower than plasma)**

6. **End of Collecting Duct**:
- In the collecting duct, the osmolarity can vary depending on the body's hydration status and the action of hormones like ADH. Generally, it can be hypotonic or isotonic, but it often remains hypotonic compared to plasma.
- **Osmolarity: Hypotonic (lower than plasma)**

### Summary of Osmolarity Changes:
- Bowman's Capsule: Isotonic
- PCT: Isotonic
- Descending Loop of Henle: Hypotonic
- Ascending Loop of Henle: Hypertonic
- DCT: Hypotonic
- End of Collecting Duct: Hypotonic

### Final Order of Osmolarity Changes:
**Isotonic → Isotonic → Hypotonic → Hypertonic → Hypotonic → Hypotonic**