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Assertion. The final reabsorption of wat...

Assertion. The final reabsorption of water from the urine into the blood occurs through the collecting duct of a mammalian nephron resulting in the production of hyperosmotic urine.
Reason. The loop of Henle creates a sodium gradient in the interstitial fluid from the renal medulla towards the renal cortex.

A

If both A and R are true and R is the correct explanation of A.

B

If both A and R are true but R is not the correct explanation of A.

C

If A is true but R is false.

D

If both A and R are false.

Text Solution

AI Generated Solution

The correct Answer is:
### Step-by-Step Solution: 1. **Understanding the Assertion**: The assertion states that the final reabsorption of water occurs in the collecting duct of a mammalian nephron, leading to the production of hyperosmotic urine. This means that the urine becomes more concentrated than the blood due to the reabsorption of water. 2. **Role of the Collecting Duct**: In the nephron, the collecting duct is responsible for the final adjustments in water reabsorption. It is influenced by the hormone ADH (antidiuretic hormone), which increases the permeability of the duct to water, allowing more water to be reabsorbed back into the bloodstream. 3. **Understanding the Reason**: The reason states that the loop of Henle creates a sodium gradient in the interstitial fluid from the renal medulla towards the renal cortex. This gradient is essential for the counter-current multiplication mechanism, which helps in concentrating urine. 4. **Counter-Current Mechanism**: The loop of Henle consists of a descending limb and an ascending limb. The descending limb is permeable to water but not to salts, while the ascending limb is impermeable to water but actively transports sodium ions out into the interstitial fluid. This creates a high osmolarity in the medulla, which is crucial for the reabsorption of water in the collecting duct. 5. **Conclusion**: Both the assertion and the reason are true. The assertion correctly describes the role of the collecting duct in producing hyperosmotic urine, and the reason accurately explains how the loop of Henle establishes a sodium gradient that facilitates this process. Therefore, the reason is a correct explanation of the assertion. ### Final Answer: Both the assertion and the reason are true, and the reason is a correct explanation of the assertion. ---
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