In the countercurrent mechanism for the concentration of urine, NaCl is transported out of the ascending limb of Henle's loop into the medullary interstitium. Which of the following structures directly takes up this NaCl from the interstitium to help maintain the osmolarity gradient?

Step-by-step solution

According to the NCERT Biology textbook, the countercurrent mechanism operates between the Henle's loop and the vasa recta to maintain a concentration gradient in the medullary interstitium. NaCl is transported out of the filtrate by the ascending limb of Henle's loop into the medullary interstitium. From the interstitium, this NaCl is exchanged with (taken up by) the descending limb of the vasa recta. The NaCl is later returned to the interstitium by the ascending portion of the vasa recta. The descending limb of