Abstract
The flow-reaction-absorption system is one of the fundamental physiological systems and is characterized by the following reaction processes : a compound, usually a disaccharide or a dipeptide flowing into a pipe-structured reactor is hydrolyzed by a wall-bound enzyme and the resultant products are absorbed across the wall by an active transport mechanism. The small intestine and renal proximal tubule are the typical examples. Quantitative characteristics of its processes under dynamic conditions have not been well understood because of complex interactions of multiple factors which change along the length of the system.
In this paper, a digital simulation of this particular system has been attempted in order to understand characteristics of interactions of principal factors and effects of kinetic parameters of hydrolysis and transport on the intraluminal concentration profiles for the reacting and absorbed substances. The mathematical model introduced in the simulation is composed of two ordinary differential equations for intraluminal concentrations of the hydrolyzed substance and the product and one for the solvent flow rate. The former equations are accompanied with nonlinearities coming froin Michaelis-Menten kinetics involved in hydrolytic and transport processes. The model was applied to amphibian renal proximal tubule by assuming maltose as the substance to be hydrolyzed and glucose as the product. By using available data of geometry and kinetic parameters, the standard concentration profiles for both substances were obtained, then the effects of individual changes in values of important parameters were investigated.
It was found that the changes in kinetic parameters yielded characteristic changes in the concentration profiles while the 'flow rate little affected the concentration profiles. A distinct difference between the standard and experimentally observed pattern of the product concentration suggested that the actual biological system, has an additional special device (probably the microvillous structure) for efficient linkage between hydrolytic and transport processes.
