In which of the following counter current operates

Options

A. (a) In descending limb of loop of Henle
B. (b) In ascending limb or descending limb of vasa recta
C. (c) Between the 2 limbs of Henle's loop and those of vasa recta
D. (d) In ascending limb of loop of Henle

Answer

To solve the question regarding where the counter-current mechanism operates, we will break down the information step by step.

### Step-by-Step Solution:

1. **Understanding the Counter-Current Mechanism**:
- The counter-current mechanism is a physiological process that occurs in the kidneys, specifically in the nephron, which is the functional unit of the kidney.
- It involves the flow of fluids in opposite directions, which helps to create an osmotic gradient necessary for concentrating urine.

2. **Identifying Key Structures**:
- The main structures involved in this mechanism are the **Loop of Henle** and the **Vasa Recta**.
- The Loop of Henle consists of two limbs: the **descending limb** and the **ascending limb**.
- The Vasa Recta is a series of capillaries that surround the Loop of Henle.

3. **Flow Direction**:
- In the Loop of Henle, the fluid flows in an anti-clockwise direction in the descending limb and clockwise in the ascending limb.
- In the Vasa Recta, the flow is also in a counter-current manner, with the blood flowing in the opposite direction to the filtrate in the Loop of Henle.

4. **Analyzing the Options**:
- **Option A**: "In descending limb of Loop of Henle" - This is incorrect as it does not encompass the entire counter-current mechanism.
- **Option B**: "In ascending limb or descending limb of Vasa Recta" - This is incorrect as it misidentifies the structures.
- **Option C**: "Between the two limbs of Henle's loop and those of Vasa Recta" - This is correct as it accurately describes where the counter-current mechanism operates.
- **Option D**: "In ascending limb of Loop of Henle" - This is also incorrect as it does not represent the complete mechanism.

5. **Conclusion**:
- The correct answer is **Option C**: "Between the two limbs of Henle's loop and those of Vasa Recta".