Which of the following is correct ?

Options

A. Water reabsorption in descending limb of loop and collecting duct occur under similar conditions.
B. Sodium reabsorption in ascending limb of loop and collecting duct occur under similar conditions
C. Water reabsorption in descending limb of loop and collecting duct occur under different conditions
D. Water reabsorption in descending limb and sodium reabsorption in ascending limb of loop occur under similar conditions

Answer

To solve the question, we need to analyze the options provided regarding the nephron's structure and function, particularly focusing on the water and sodium reabsorption in different parts of the nephron.

### Step-by-Step Solution:

1. **Understand the Nephron Structure**:
- The nephron is the functional unit of the kidney and consists of several parts: the renal corpuscle, proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting duct.
- The renal corpuscle, PCT, and DCT are located in the renal cortex, while the loop of Henle and collecting duct extend into the renal medulla.

2. **Water and Sodium Reabsorption**:
- Water reabsorption occurs in the descending limb of the loop of Henle and the collecting duct. This process is influenced by the osmotic gradient established in the medulla.
- Sodium reabsorption occurs in the ascending limb of the loop of Henle, which is impermeable to water, and in the distal convoluted tubule.

3. **Evaluate the Options**:
- The question suggests that we need to determine if water absorption in the descending limb and the collecting duct occurs under similar conditions.
- The descending limb of the loop of Henle allows water to be reabsorbed due to the high osmolarity of the surrounding medullary interstitium.
- The collecting duct also reabsorbs water, but this process is regulated by the hormone ADH (antidiuretic hormone), which increases the permeability of the duct to water.

4. **Conclusion**:
- Since both the descending limb and the collecting duct are involved in water reabsorption and both operate under the influence of osmotic gradients, we can conclude that they do indeed function under similar conditions regarding water reabsorption.
- Therefore, the correct option is that water reabsorption in the descending limb of the loop and the collecting duct occurs under similar conditions.

### Final Answer:
The correct statement is that water reabsorption in the descending limb of the loop of Henle and the collecting duct occurs under similar conditions.

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