What is the countercurrent multiplier in the loop of Henle?

What is the countercurrent multiplier in the loop of Henle?

• A. Regulates glomerular filtration rate.
• B. Pumps ions across loop, altering pH.
• C. Concentrates sodium and chloride in the interstitial fluid.
• D. Produces dilute urine.

Answer: (C)

The countercurrent multiplier builds an osmotic gradient in the medullary interstitium that concentrates salts, especially sodium and chloride. As filtrate descends the loop of Henle, water moves out into the surrounding hyperosmotic interstitium, concentrating the filtrate. The ascending limb then actively pumps Na+, K+, and 2Cl− into the interstitium but remains relatively impermeable to water, which dilutes the filtrate as it rises. Repeating this arrangement along the loop amplifies (multiplies) the medullary osmotic gradient. This gradient is what allows the collecting ducts to reabsorb water and form concentrated urine under ADH control. So, the primary function described is concentrating sodium and chloride in the interstitial fluid, not regulating GFR, changing pH, or producing dilute urine.

The countercurrent multiplier builds an osmotic gradient in the medullary interstitium that concentrates salts, especially sodium and chloride. As filtrate descends the loop of Henle, water moves out into the surrounding hyperosmotic interstitium, concentrating the filtrate. The ascending limb then actively pumps Na+, K+, and 2Cl− into the interstitium but remains relatively impermeable to water, which dilutes the filtrate as it rises. Repeating this arrangement along the loop amplifies (multiplies) the medullary osmotic gradient. This gradient is what allows the collecting ducts to reabsorb water and form concentrated urine under ADH control. So, the primary function described is concentrating sodium and chloride in the interstitial fluid, not regulating GFR, changing pH, or producing dilute urine.