Reason for hyperosmolarity is
Hyperosmolarity in the interstitium of kidney is due to activity of na+k+2cl- pump at the ascending limb of loop of henle Ref:Guyton and Hall textbook of medical physiology 12th edition,page:480,481,482
Increased glomerular capillary pressure
Decreased absorbtion of Na+ in PCT
Increased activity of Na+ K+ 2cl- ATPase in loop
Decreased activity of Na+ K+ ATPase in loop
General physiology