Match List I with List II regarding the structures involved in the concentration of urine. List I List II A. Descending limb of Henle's loop I. Acts as a counter-current exchanger B. Ascending limb of Henle's loop II. Transports small amounts of urea into the medullary interstitium C. Vasa recta III. Permeable to water but almost impermeable to electrolytes D. Collecting duct IV. Impermeable to water but allows trans

Step-by-step solution

The correct matching is A-III, B-IV, C-I, D-II. The descending limb of Henle's loop is permeable to water but almost impermeable to electrolytes, which concentrates the filtrate as it moves down. The ascending limb of Henle's loop is impermeable to water but allows transport of electrolytes actively or passively, diluting the filtrate as it moves up. The vasa recta acts as a counter-current exchanger, maintaining the concentration gradient in the medullary interstitium. The collecting duct allows the passage of sma