Question

Assertion (A): Urine is hypertonic in the descending limb of loop of Henle, while urine is hypotonic in the ascending limb.
Reason (R): Ascending limb is impermeable to Na+, whereas descending limb is impermeable to water.

• A. A and R are true. R is the correct explanation for A
• B. A and R are true. But R is not the correct explanation for A
• C. A is true. But R is false
• D. A is false. But R is true

Hint:

Understanding the counter-current mechanism in the loop of Henle is crucial for comprehending how the kidneys concentrate urine and maintain water balance in the body.

Answer 1

The Correct Option is C

The assertion correctly describes the tonicity of the fluid in the limbs of the loop of Henle. The descending limb is indeed permeable to water but not to solutes, leading to increasingly hypertonic urine as water exits into the hyperosmolar medullary interstitium. Conversely, the ascending limb, while impermeable to water, actively transports Na+ and Cl- out of the urine, making it increasingly hypotonic. The reason provided is incorrect; the ascending limb is actually impermeable to water but actively transports ions.