Question

In the nephron, the osmolarity of the medulla is the cortex.

• A. the same as of
• B. lower than that of
• C. higher than that of
• D. negligible, like in

Answer 1

The correct option is C higher than that of

The osmolarity towards the inner medullary interstitium increases, i.e., from the cortex to the inner medulla. This gradient is mainly caused by NaCl and urea. NaCl is transported by the ascending limb of Henle’s loop which is exchanged with the descending limb of vasa recta. NaCl is returned to the interstitium by the ascending portion of vasa recta. Similarly, small amounts of urea enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the collecting tubule. The above described transport of substances facilitated by the special arrangement of Henle’s loop and vasa recta is called the counter current mechanism. This mechanism helps to maintain a concentration gradient in the medullary interstitium. Presence of such interstitial gradient helps in an easy passage of water from the collecting tubule thereby concentrating the filtrate.