Question

How does the loop of Henle act as a countercurrent multiplier?

a) By allowing water reabsorption in the ascending limb.
b) By creating a concentration gradient along the length of the loop.
c) By promoting sodium secretion in the descending limb.
d) By inhibiting urea reabsorption.

Answer 1

The loop of Henle functions as a countercurrent multiplier by creating a concentration gradient along its length, with the descending limb allowing water reabsorption and the ascending limb facilitating Na+ and Cl- ion transport.

Step-by-step explanation:

The loop of Henle acts as a countercurrent multiplier which plays a critical role in concentrating urine and conserving water. The process involves a concentration gradient created along the length of the loop. The descending limb is water permeable and allows water to flow from the filtrate to the interstitial fluid, increasing the osmolality inside the limb as it descends into the renal medulla. This makes the interior of the loop more concentrated than the surrounding interstitial fluid. On the other hand, the ascending limb is impermeable to water but actively transports Na+ out of the filtrate, and Cl− follows, thereby reducing the osmolarity as the filtrate moves upwards. The countermovement of fluid and the differential permeability to water and ions create a multiplier effect that concentrates urine.