Effectiveness of a salt transport cascade in the renal medulla: computer simulations.

Based on morphological observations, it has been concluded that the upper parts of the long descending limbs of Henle's loops should be able to secrete salts into the tubular fluid (Kriz, W. Federation Proc. 42:2379-2385, 1983). In the same article, a hypothesis is given depicting how this active transport in concert with certain characteristics of the medullary architecture might produce a transport cascade toward the papillary tip, thus supporting the accumulation of salts in this region. The effectiveness of the proposed mechanism can be judged by a mathematical model only. The computer simulations of the present study demonstrate that this mechanism indeed leads to an increase of the concentrating capability of the renal countercurrent system.