Question

Assertion :When urine moves through the descending limb, it becomes hypertonic and as it passes through the ascending limb of Henle's loop, it becomes hypotonic. Reason: The descending limb is permeable to sodium ions, while the ascending limb is impermeable to sodium ions.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Both Assertion and Reason are incorrect.

Answer 1

The correct option is C Assertion is correct but Reason is incorrect.

Reabsorption in the Henle's loop segment is minimum. However, this region plays a significant role in the maintenance of high osmolarity of medullary interstitial fluid. The descending limb of the loop of Henle is permeable to water but almost impermeable to electrolytes. This concentrates the filtrate as it moves down. In other words, the filtrate becomes hypertonic. The ascending limb is impermeable to water but allows transport of electrolytes actively or passively. Therefore, as the concentrated filtrate pass upward, it gets diluted or becomes hypotonic due to the passage of electrolytes to the medullary fluid.