Figure 410

A-H, Models to demonstrate the principle of countercurrent multiplier in creating high urine concentration. The first panel illustrates the relation between urine osmolality and arginine vasopressin excretion. The long loops of Henle and their accompanying vasa recta reaching the papillae comprise only 15% of the total nephron population but are necessary for producing concentrated urine [12]. As seen, the mechanisms of countercurrent multiplication and countercurrent exchange create an increase in osmolality in the kidney from 280 mOsm at the cortex to about 1200 mOsm/kg H2O in the inner medulla and papillae. Reabsorption in the collecting ducts results in production of highly concentrated urine.

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