Urine concentrating ability of the kidney is increased by: (A) Increased medullary hyperosmolarity, (B) Increase in RBF, (C) Reduction of medullary hyperosmolarity, (D) Increase in GFR
Answer is A. Countercurrent mechanism is a system in the renal medulla that facilitates concentration of the urine as it passes through the renal tubules.Ref: Ganong&;s review of medical physiology; 24th edition; page no: 687