Osmotic concentration of glomerular filtrate is the highest at the bottom of the U-shaped Henle's loop. It is about `"____________"` `mOsmL^(-1)`

Options

A. 300
B. 600
C. 900
D. 1200

Answer

To answer the question regarding the osmotic concentration of glomerular filtrate at the bottom of the U-shaped Henle's loop, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Glomerular Filtrate**: The glomerular filtrate is the fluid that is filtered from the blood in the kidneys. It initially has an osmotic concentration similar to that of blood, which is approximately 300 mOsm/L.

2. **Movement Through the Nephron**: As the glomerular filtrate moves through different parts of the nephron, its osmotic concentration changes due to the reabsorption of water and solutes.

3. **Proximal Convoluted Tubule (PCT)**: In the PCT, there is a reabsorption of solutes (like Na+, K+, and glucose) and water. However, the osmotic concentration remains around 300 mOsm/L because the reabsorption of water matches the reabsorption of solutes.

4. **Descending Loop of Henle**: As the filtrate enters the descending loop of Henle, it encounters a hyperosmotic environment in the outer medulla. Water is reabsorbed passively from the filtrate into the surrounding interstitial fluid, which has a higher osmolarity. This leads to an increase in the osmotic concentration of the filtrate.

5. **Osmotic Concentration Increase**: As water continues to be reabsorbed in the descending limb, the osmotic concentration of the filtrate increases progressively. By the time the filtrate reaches the bottom of the U-shaped loop, the osmotic concentration reaches its maximum.

6. **Maximum Osmotic Concentration**: At the bottom of the loop of Henle, the osmotic concentration of the glomerular filtrate is approximately 1200 mOsm/L. This is the highest concentration found in the nephron due to the significant loss of water.

7. **Conclusion**: Therefore, the osmotic concentration of glomerular filtrate at the bottom of the U-shaped Henle's loop is **1200 mOsm/L**.

### Final Answer:
The osmotic concentration of glomerular filtrate at the bottom of the U-shaped Henle's loop is **1200 mOsm/L**.

---