Urinary concentrating ability of the kidney is increased by:
A. ECF volume contraction
B. Increase in Renal blood flow
C. Reduction of medullary hyperosmolarity
D. Increase in GFR
Correct answer : A. ECF volume contraction
When there is ECF volume contraction, there is increased release of ADH from posterior pituitary. This stimulates the kidneys to reabsorb more water thereby producing concentrated urine.