<prompt> Renal medullary hyperosmolarity is due to:Increased NaIncreased Na contentIncreased GlucoseAll  <response>: A i.e. Increased NaThe Counter current mechanism at the loop of henle is responsible for development of hyper osmolarity of medullary interstitial fluid and medullary gradient. Hyperosmolarity is due to high Na conc. of the filtrate in renal medullaQMaintenance of osmolarityMedullary gradientThe osmolarity of coicalinterstitium is same as that of plasma 300 mosmL. However osmolality of medullary interstitium is very high 1200 mosmLGradual increase in the osmolarity from 300 to 1200 mosmL of medullary interstitium is called medullary gradientCounter - current mechanism isresponsible for maintenance of medullary gradient. 