All of the following help to maintain a concentration gradient in the medullary interstitium, except

The flow of filtrate in the two limbs of Henle’s loop is in opposite directions and thus forms a counter-current. The flow of blood through the two limbs of the vasa recta is also in a counter-current pattern. The proximity between the Henle’s loop and the vasa recta, as well as the counter-current in them help in maintaining an increasing osmolarity towards the inner medullary interstitium, i.e., from 300 mOsmolL–1 in the cortex to about 1200 mOsmolL–1 in the inner medulla.