Read the following statements regarding the mechanism of concentration of the filtrate in human kidneys: (A) NaCl is transported by the ascending limb of Henle's loop which is exchanged with the descending limb of vasa recta. (B) NaCl is returned to the medullary interstitium by the ascending portion of vasa recta. (C) Small amounts of urea enter the thick segment of the ascending limb of Henle's loop. (D) Urea is tr

Step-by-step solution

Statements (A), (B), and (D) are correct. Statement (C) is incorrect because small amounts of urea enter the thin segment of the ascending limb of Henle's loop, not the thick segment. The urea is then transported back to the interstitium by the collecting tubule to maintain the osmolarity gradient in the inner medulla. The counter-current exchange of NaCl occurs between the loop of Henle and the vasa recta, where NaCl from the ascending limb of Henle's loop enters the descending vasa recta and is returned to the in