Linear diffusion of lead in the intestinal wall: a theoretical study.

In this paper, the authors present a diffusion model of the intestinal wall to describe the transient overall uptake of lead ions across the epithelium of gastrointestinal mucosa and their subsequent diffusion in the underlying blood capillaries. The gastrointestinal mucosa is treated as a heterogeneous two-phase medium, consisting of a continuous extracellular phase and a dispersed cellular phase. The main mode of uptake is considered to be bulk diffusion, since transport of lead across the mucosal membrane occurs mainly by a passive diffusion process. The equations give the variation with time of concentrations of lead in both the phases across the intestinal wall. The mean concentration of lead available for absorption by the blood capillaries has been studied as a function of time. It is found that a steady state is reached in 19.45 min. It has been possible to estimate the intestinal membrane permeability for the lead molecule from this analysis: it is calculated to be 3.34 X 10(-3) s-1. Finally, the rate of lead uptake by the blood for different gut concentrations has been calculated.