A Revised view of countercurrent multiplication as applied to a loop of Henle is shown, where the descending and ascending limbs are separated by the interstitium, and the descending limb fluid is concentrated by water absorption. (a) The concentrating mechanism in the outer medulla, which does not conform to the standard interpretation of the countercurrent multiplication. (b) The concentrating mechanism in the inner medulla, based on the “solute-separation, solute-mixing” mechanism. In all panels, thick lines indicate water-impermeable portions of tubules; darkening colors represent increasing osmolality. Reprinted from [31].