Toxicology with basic concepts

Toxicology can be defined as that branch of science that deals with poisons, and a poison can be defined as any substance that causes a harmful effect when administered, either by accident or by design, to a living organism. By convention, toxicology also includes the study of harmful effects caused by physical phenomena, such as radiation of various kinds, noise, and so on. In practice, however, many complications exist beyond these simple definitions, both in bringing more precise definition to the meaning of poison and to the measurement of toxic effects. Broader definitions of toxicology, such as “ the study of the detection, occurrence, properties, effects, and regulation of toxic substances, ” although more descriptive, do not resolve the difficulties. Toxicity itself can rarely, if ever, be defined as a single molecular event, but is, rather, a cascade of events starting with exposure, proceeding through distribution and metabolism, and ending with interaction with cellular macro molecules (usually DNA or protein) and the expression of a toxic end point .
 Modes of Toxic Action :This includes the consideration, at the fundamental level of organ, cell, and molecular function, of all events leading to toxicity in vivo : uptake, distribution, metabolism, mode of action, and excretion. The term mechanism of toxic action is now more generally used to describe an important molecular event in the cascade of events leading from exposure to toxicity, such as the inhibition of acetylcholinesterase in the toxicity of organophosphorus and carbamate insecticides. Important aspects include the following: 1. Biochemical and molecular toxicology consider events at the biochemical and molecular levels, including enzymes that metabolize xenobiotics, generation of reactive intermediates, interaction of xenobiotics or their metabolites with macro molecules, gene expression in metabolism and modes of action, signaling pathways in toxic action, and so on. 2. Behavioral toxicology deals with the effects of toxicants on animal and human behavior, which is the final integrated expression of nervous function in the intact animal. This involves both the peripheral and central nervous systems, as well as effects mediated by other organ systems, such as the endocrine glands. 3. Nutritional toxicology deals with the effects of diet on the expression of toxicity and with the mechanisms of these effects. 4. Carcinogenesis includes the chemical, biochemical, and molecular events that lead to the large number of effects on cell growth collectively known as cancer.
5. Teratogenesis includes the chemical, biochemical, and molecular events that lead to deleterious effects on development. 6. Mutagenesis is concerned with toxic effects on the genetic material and the inheritance of these effects. 7. Organ toxicity considers effects at the level of organ function (e.g., neurotoxicity, hepatotoxicity, and nephrotoxicity).