ABSTRACT
Ingested and inhaled substances are considered outside the body until they cross the cellular barriers of the gastrointestinal tract (GIT), the respiratory system, or the skin. When a xenobiotic is in the GIT, in the lungs, or on the skin, it nds itself in the physiological route of absorption-distribution-metabolism-(new distribution)–excretion (ADME). Now, its toxicity depends on many factors, including the speed and the exact way of moving along this labyrinth. Since a free toxicant or its active metabolite is at the action point (tissue) in a dynamic equilibrium with free toxicant in the plasma, in most cases, the toxic eect is proportional to the toxicant’s concentration in the blood. e intensity of the toxic eect depends on the pharmacokinetics of the xenobiotic, that is, how the compound enters the organism and the bloodstream (absorption), how and in which (original or metabolitic) form it moves along the body (distribution and metabolism), and how the xenobiotic and/or its metabolites leave the organism (excretion). e pharmacokinetics of a toxicant is substantially inuenced by the age, gender, lifestyle, nutritional condition, and dietary habits of the individual, tissue (liver, kidneys) functions and conditions, and so forth.
