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

• A

  Low levels of antidiuretic hormone.
• Correct answer
  B

  Maintaining hyperosmolarity towards inner medullary interstitium in the kidneys.
• C

  Secretion of erythropoietin by Juxtaglomerular complex.
• D

  Hydrostatic pressure during glomerular filtration.

Solution

A hyperosmotic renal medullary interstitium is critically important in concentrating the urine and provides the driving force for the reabsorption of water from the collecting duct.

Hence, the correct answer is option: 'B'.