Biology - Excretory Products and their Elimination Question with Solution | TestHub

The concentration of urine is primarily achieved by the counter-current mechanism, which operates between the two limbs of the loop of Henle and the vasa recta.

The proximity between the Henle's loop and vasa recta, along with the counter-current flow in them, helps in maintaining an increasing osmolarity towards the inner medullary interstitium (from $300{\text{ mOsmolL}}^{-1}$ in the cortex to about $1200{\text{ mOsmolL}}^{-1}$ in the inner medulla).

This gradient facilitates the easy passage of water from the collecting tubule, thereby concentrating the filtrate (urine). Thus, Henle's loop and vasa recta play a significant role in the concentration of urine.

Answer: Henle's loop and vasa recta