Formation of hypertonic urine is mediated through

Options

A. eating salt free diet
B. counter-current system
C. increased water intake
D. having small loop of Henle

Answer

### Step-by-Step Solution:

1. **Understanding Hypertonic Urine**:
- Hypertonic urine is urine that has a higher concentration of solutes compared to the blood plasma. This means it has less water relative to solutes, which is important for the body to conserve water, especially in conditions of dehydration.

2. **Identifying the Mechanism**:
- The formation of hypertonic urine is primarily mediated by the counter current multiplication system in the kidneys. This system allows for the reabsorption of water and the concentration of urine.

3. **Role of the Loop of Henle**:
- The Loop of Henle, which is part of the nephron in the kidney, plays a crucial role in this process. It consists of a descending limb and an ascending limb, which work together to create a concentration gradient in the renal medulla.

4. **Counter Current Mechanism**:
- The counter current mechanism occurs between the Loop of Henle and the vasa recta (the blood vessels that run alongside the Loop of Henle). This arrangement allows for the efficient exchange of water and solutes, facilitating the concentration of urine.

5. **Length of the Loop of Henle**:
- The longer the Loop of Henle, the more concentrated the urine can become. This is because a longer Loop allows for a greater gradient to be established in the renal medulla, enhancing water reabsorption.

6. **Conclusion**:
- Therefore, the correct answer to the question is that the formation of hypertonic urine is mediated through the counter current system.

### Final Answer:
- **Counter Current System**