A theoretical note on exponential flow in the proximal part of the mammalian nephron

On the basis of the experiments of A. M. Walkeret al. (Am. J. Physiol.,134, 580–595, 1941), it is postulated that the fraction of glomerular filtrate reabsorbed up to a given point in the proximal tubule is independent of the rate of filtration. This, combined with the assumption that the proximal tubule is uniform from glomerular to distal end, implies that the volume of flow per unit of time past a given point in the proximal tubule decreases exponentially as a function of distance from the glomerulus. From this it is deduced that the rate of reabsorption of Na⁺ is proportional to the rate of formation of glomerular filtrate—a result established in clearance experiments. The analogy between a nephron and a catalytic flow reactor is indicated, and it is noted that, in both systems, reaction velocity can depend on the rate of flow.