Question

Which of the following factors is responsible for the formation of concentrated urine? 

(1) Low levels of antidiuretic hormone 

(2) Maintaining hyperosmolarity towards inner medullary interstitium in the kidneys. 

(3) Secretion of erythropoietin by Juxtaglomerular complex 

(4) Hydrostatic pressure during glomerular filtration

Answer 1

Correct option: (2) Maintaining hyperosmolarity towards inner medullary interstitium in the kidneys.

Explanation: 

The proximity between loop of henle and vasa recta as well as counter current in them help in maintaining an increasing osmolalrity towards the inner medullary interstitium. This mechanism help to maintain a concentration gradient in medullary interstitium so human urine is nearly four times concentrated than initial filtrate formed.