AJP - Renal Physiology, Vol 260, Issue 3 384-F394, Copyright © 1991 by American Physiological Society
Three-dimensional anatomy and renal concentrating mechanism. II. Sensitivity results
A. S. Wexler, R. E. Kalaba and D. J. Marsh
Department of Physiology and Biophysics, School of Medicine, University of Southern California, Los Angeles 90033.
A mathematical model has been developed to simulate hypertonic urine
formation in the renal medulla. The model uses published values of membrane
transport parameters, as have other models, but is unique in its
representation of the three-dimensional anatomy of the medulla. The model
successfully predicts measured fluid flows, osmolarities, and NaCl and urea
concentrations. The model results are presented in the companion to this
paper [A. S. Wexler, R. E. Kalaba, D. J. Marsh. Am. J. Physiol. 260 (Renal
Fluid Electrolyte Physiol. 29): F368-F383, 1991.]. In this paper we provide
tests of the sensitivity of model performance to variations in the
description of the anatomy and in membrane transport parameters. From these
studies we conclude that 1) strict counterflow arrangements are required in
the outer stripe to prevent loss of NaCl to the systemic circulation, 2)
the radial organization in the inner stripe materially improves performance
of the inner medulla, 3) radial organization of the inner medulla is
essential to hypertonic urine formation there, 4) the model is most
sensitive to variation in collecting duct parameters, and 5) reabsorption
of urea in the distal tubule improves system performance. The results
support the claim that the three-dimensional structure, as captured in the
model, provides a crucial framework for the production of hypertonic urine.
