For permeant tracers, their mother substances are also accounted for in the model. The model can be used to study the physiology of the exchange process or as a tool to help analyze actual experimental data. The model provides ways to examine tracer delay and dispersion between the injection site and the target organ and the effects of flow heterogeneity on exchange within the organ. 1.1.1 shows the general layout of the model. Each of the multiple tracers flows through the common arterial vessels, the parallel pathways each containing an arteriole, an capillary-tissue unit, and an venule, and then through the common venous vessels.
Flow enters each pathway after having passed through optional large vessel components.
Each pathway includes optional small vessel components and one exchange unit. Large and small vessel components account for delay and dispersion of the input function before it reaches the exchange unit. A subscript is added to designate specific species. Vascular Components 1.2.1. Nonexchanging here means no exchange between the blood and the tissue.