Pathology
Pathology is the study of disease. The disease process has four aspects:
1. its cause (called "etiology");
2. the mechanisms of its development (called "pathogenesis");
3. changes in cells and organs (morphologic changes); and
4. functional consequences of these changes ("clinical significance").
There are two major causes of disease, genetic and acquired. They are not exclusive.
An acquired state, such as malnutrition, could affect a genetic disease, for
example. Acquired etiologies (which are sometimes called "environmental"
etiologies) might be divided into: infectious, nutritional, chemical, physical,
and so on. I catch a virus via the "environmental" route (not my genes)
so a pathologist might call my flu an "environmental disease." Further
she might go on to say that "80% of diseases are environmental in origin."
Someone who was unaware of the pathologists' definition of "environmental"
might interpret that to mean that most diseases are caused by pollution from
the environment. In toxicology we are interested in chemical etiologies.
Here's an important etiology, English.
Chemical etiologies include drugs, both therapeutic and recreational, as well as pollution and other chemicals. Toxicologists often use the word "xenobiotic" to describe chemicals introduced to the body that are "foreign" to the biological system. As with any fundamental definition, interpretations differ. Most of our fundamental biologic requirements, food, water, and oxygen, can be harmful if taken in excess or subject to deprivation. Most toxicologists would not describe the saturated fat in a McDonnell's hamburger as a "xenobiotic," although excess triglycerides are associated with disease, and may be a "chemical etiology" of heart disease. The science of toxicology is concerned with whether, or at what doses, a xenobiotic is a chemical etiology of a disease. Many toxicologists study the mechanism by which this chemical causes its harm, this often causes them to study the pathogenesis and morphological changes caused by the xenobiotic. (The term "xenobiotic chemical" is redundant). Pharmaceuticals or drugs are xenobiotics that are used to gain some beneficial (or "therapeutic") effect. The chemical is unaware of why it has been taken and it causes a variety of effects, some beneficial, some harmful, and some neither. The study of the effects of xenobiotics on organisms is called pharmacology, while the study of the harmful effects is called toxicology. Since the science is the same, often they are not separated, or slashed, as in "pharmacology/toxicology."
End of Submodule