Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The continuous flow of blood through the vasa recta washes away the dissolved solutes from the medullary interstitium, thereby destroying the concentration gradient. Reason (R): Blood flows in opposite directions in the descending and ascending limbs of the vasa recta, and NaCl is returned to the i

Step-by-step solution

Assertion (A) is false because the vasa recta actually helps in maintaining the medullary interstitial gradient rather than washing it away. It acts as a counter-current exchanger. Reason (R) is true. The counter-current flow of blood within the U-shaped vasa recta ensures that NaCl picked up by the descending limb is returned to the interstitium by the ascending limb, which prevents the washout of the concentration gradient. Answer: Assertion (A) is false but Reason (R) is true.