The effect of restricted convection-diffusion on bolus concentration along an exchange vessel.

If a sudden rise in solute concentration travels through a capillary system, a diffusible neutral solute passes the walls of the exchange vessels. If then the rate of passage depends on a chemical potential gradient (diffusion) and a hydrodynamical potential gradient (convection) and is sterically restricted (restricted convection-diffusion), water and low molecular weight solvents leave the filtering part of the capillary at a higher rate than the solute, causing a relative increase in its concentration. This phenomenon and the effect of an increasing pore size along the capillary is investigated in a model for an impermeable solute and two diffusible solutes, corresponding to glucose and raffinose. It is shown that in the model, the concentration fall along the capillary tends to become rectilinear.