Question

Assertion: The final reabsorption of water from urine into blood occurs through the collecting duct of a mammalian nephron, resulting in the production of hyperosmotic urine.
Reason: The loop of Henle is responsible for the formation of a sodium gradient across the depth of the cortical intersitium of a mammalian kidney.

• A. If both Assertion and Reason are true and the Reason is a correct explanation of the Assertion
• B. If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion
• C. If Assertion is true but the Reason is false
• D. If both Assertion and Reason are false

Answer 1

Answer: (B)

The effect of collecting duct depends on the presence of vasopressin over there. This hormone increases the permeability of the collecting duct to water. Gradually the rate of reabsorption from the filtrate increases and it becomes hyperosmotic.
There is graded increase in the osmolarity of the interstitium of the pyramids. Na⁺, K⁺ and Cl^- are transported out of the thick segment of the ascending limb. The Na⁺ is actively transported out of the cells into the interstitium by Na⁺ K⁺ ATPase.