Question

question 38
the countercurrent mechanism:
a dilutes urine
b counteracts the effects of adh
c acts within the glomerulus
d concentrates urine

Explanation:

The countercurrent mechanism in the kidneys (involving the loop of Henle) creates a concentration gradient in the medulla. This gradient allows for the reabsorption of water from the collecting duct (when ADH is present), which concentrates urine.

• Option A: Incorrect. The countercurrent mechanism is for concentration, not dilution.
• Option B: Incorrect. It works with ADH (when ADH is present, more water is reabsorbed from the collecting duct into the hypertonic medulla created by the countercurrent mechanism).
• Option C: Incorrect. It acts in the loop of Henle (part of the nephron, not the glomerulus which is involved in filtration).
• Option D: Correct as explained above.

Answer:

D. Concentrates urine