Experimental validation of the countercurrent model of urinary concentration.

This article focuses on a conceptual model of the countercurrent multiplication mechanism followed by the mammalian kidney to excrete concentrated urine. The concurrent model is discussed with reference to two papers by C.W. Gottschalk and M. Mylle and K.J. Ullrich. These researchers had analyzed micro-samples of interstitial fluid from the medulla and had shown that NaCl and urea were the primary contributors, in approximately equal proportion, to the medullary hypertonicity, and that concentrations of both solutes rose progressively from the corticomedullary junction to the tip of the papila.