ABSTRACT
Physiological models are sets of mathematical descriptions of biological processes,
which have been shown to be useful for prediction in pharmacology and toxicology.
The anatomical, biological, and biochemical basis of these models provide excellent
potential for dose, surface area, duration, and species extrapolation. These same
strengths furnish a tool to predict efficacy and toxicity as well as a tool for risk
assessment. Most of these models use simultaneous differential equations to
describe changes in mass of a specific chemical as it undergoes absorption,
distribution, elimination, and metabolism in a living system. A physiological
model employs a “chemical engineering approach” to describe the animal or
human in terms of well-stirred vats connected by flows. In these models, the vats
are equivalent to lumped sets of organs that have similar affinity for the chemical
and similar blood flows. These lumped compartments have a total volume equal to
the sum of the perfused tissues in the organism, and are connected by blood flows
equivalent to the sum of the blood flows leaving the heart. Organs are frequently
treated separately (rather than being lumped with other organs) when absorption,
elimination, or metabolism of the chemical occurs.
