Summarize how the countercurrent multiplier system produces concentrated urine in juxtamedullary nephrons

What will be an ideal response?


NaCl is active transported from the filtrate in the thick ascending limb into the interstitial fluid, raising the osmolarity of the interstitial fluid. The NaCl pumped into the interstitial fluid draws water out of the filtrate in the thin descending limb into the interstitial fluid by osmosis. NaCl concentration continues to increase as filtrate reaches the bottom of the nephron loop due to the continued loss of water. Now, as the filtrate reaches the thick ascending limb, it has a high NaCl concentration. Symporters continue to pump NaCl into the interstitial fluid and thus, less NaCl is pumped into the interstitial fluid. Water is returned to the blood and less water leaves the kidney in the urine. Thus, concentrated urine is formed.

Anatomy & Physiology

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