ABSTRACT
The genesis of toxicological effects, or biological effects, is an inordinately complex process involving many parts or steps. It is useful to categorize toxicological effects into three phases (Figure 2.1): (1) the exposure phase, which covers those factors that are responsible for determining the concentration of a toxic substance that effectively comes in contact with an organism; (2) the toxicokinetic phase, which includes the physiological processes that influence the concentration of the toxic substance or its active metabolite at the active site or receptors in the organism; and (3) the toxicodynamic phase, which includes interactions of the toxic substance with its molecular site of action and the biochemical or biophysical events that finally lead to the toxic effects observed. The details of each phase are discussed in this chapter.
