Basic Terminology
Toxicology Defined
Toxicology is an evolving medical science and toxicology terminology is evolving with it. Most terms are very specific and will be defined as they appear in the tutorial. However, some terms are more general and used throughout the various sections. The most commonly used terms are introduced in this section.
Toxicant, toxin, and poison are often used interchangeably in the literature but there are subtle differences as shown below:
Toxicology Defined
Toxicology is an evolving medical science and toxicology terminology is evolving with it. Most terms are very specific and will be defined as they appear in the tutorial. However, some terms are more general and used throughout the various sections. The most commonly used terms are introduced in this section.
- Toxicology is the study of the adverse effects of chemicals or physical agents on living organisms.
- A toxicologist is a scientist who determines the harmful effects of agents and the cellular, biochemical, and molecular mechanisms responsible for the effects.
- Toxinology, a specialized area of study, looks at microbial, plant and animal venoms, poisons, and toxins.
Toxicant, toxin, and poison are often used interchangeably in the literature but there are subtle differences as shown below:
Figure 1. Pesticide chemicals are toxicants
(Image Source: iStock Photos, ©) Toxicants:
|
Figure 2. Amanita muscaria mushroom contains a neurotoxin
(Image Source: iStock Photos, ©) Toxins:
|
Figure 3. Black Widow spiders produce a poison that is a toxin
(Image Source: Texas Parks & Wildlife Department, ©) Poisons:
|
Toxic Agents
A toxic agent is anything that can produce an adverse biological effect. It may be chemical, physical, or biological in form. For example, toxic agents may be:
|
Chemical (such as cyanide)
Figure 4. Cyanide is a chemical toxic agent
(Image Source: NLM IRIS and ChemIDplus) |
Physical (such as radiation)
Figure 5. Radioactive materials are physical toxic agents
(Image Source: iStock Photos, ©) |
Biological (such as snake venom)
Figure 6. Snake venom is an example of a biological toxic agent
(Image Source: iStock Photos, ©) |
The toxicity of the agent is dependent on the dose.
A distinction is made for diseases people get from living organisms. Organisms that invade and multiply within another organism and produce their effects by biological activity are not classified as toxic agents but as biological agents. An example of this is a virus that damages cell membranes resulting in cell death.
A distinction is made for diseases people get from living organisms. Organisms that invade and multiply within another organism and produce their effects by biological activity are not classified as toxic agents but as biological agents. An example of this is a virus that damages cell membranes resulting in cell death.
Figure 7. Microscopic view of a virus
(Image Source: iStock Photos, ©)
(Image Source: iStock Photos, ©)
If the invading organisms excrete chemicals which are the basis for their toxicity, the excreted substances are known as biological toxins. In that case, the organisms are called toxic organisms. A specific example is tetanus. Tetanus is caused by a bacterium, Clostridium tetani. The bacteria C. tetani itself does not cause disease by invading and destroying cells. Rather, a toxin (neurotoxin) that the bacteria excrete travels to the nervous system and produces the disease (Figure 8).
Figure 8. Micrograph of a group of Clostridium tetani bacteria
(Image Source: CDC)
(Image Source: CDC)
Toxic Substances
|
A toxic substance is simply a material that has toxic properties. It may be a discrete toxic chemical or a mixture of toxic chemicals. For example, lead chromate, asbestos, and gasoline are all toxic substances. More specifically:
|
Figure 9. Examples of toxic substances: lead chromate (left), asbestos (center), and gasoline (right)
(Image Source: Adapted from iStock Photos, ©) |
Systemic Toxicants and Organ Toxicants
|
Toxic substances may be systemic toxicants or organ toxicants.
A systemic toxicant affects the entire body or many organs rather than a specific site. For example, potassium cyanide is a systemic toxicant in that it affects virtually every cell and organ in the body by interfering with the cells’ ability to use oxygen. Toxicants may also affect only specific tissues or organs while not producing damage to the body as a whole. These specific sites are known as the target organs or target tissues.
|
Figure 10. Systemic toxicant and organ toxicant
(Image Source: Adapted from iStock Photos, ©) |
Types of Cells
The body is composed of many types of cells, which can be classified in several ways. Table 1 shows examples of one classification of one type of cells.
The body is composed of many types of cells, which can be classified in several ways. Table 1 shows examples of one classification of one type of cells.
Germ cells are involved in reproduction and can give rise to a new organism. They have only a single set of chromosomes peculiar to a specific sex. Male germ cells give rise to sperm and female germ cells develop into ova. Toxicity to germ cells can cause effects in a developing fetus that lead to outcomes such as birth defects or miscarriage.
Somatic cells are all body cells except the reproductive germ cells. (Somatic cells include the "basic structure" and "tissue type" cells listed in Table 1). They have two sets (or pairs) of chromosomes. In an exposed individual, toxicity to somatic cells causes a variety of toxic effects, such as dermatitis, death, and cancer.
Figure 11 illustrates the differences between germ cells and somatic cells.
Somatic cells are all body cells except the reproductive germ cells. (Somatic cells include the "basic structure" and "tissue type" cells listed in Table 1). They have two sets (or pairs) of chromosomes. In an exposed individual, toxicity to somatic cells causes a variety of toxic effects, such as dermatitis, death, and cancer.
Figure 11 illustrates the differences between germ cells and somatic cells.
Figure 11. Germ cells and somatic cells
(Image Source: National Human Genome Research Institute, http://www.genome.gov)
(Image Source: National Human Genome Research Institute, http://www.genome.gov)
Natural and Man-Made Chemicals
Often, people mistakenly assume that all man-made chemicals are harmful and natural chemicals are beneficial. In reality, natural chemicals can be just as harmful to human health as man-made chemicals, and in many cases, more harmful. Figure 12 compares the toxicity of several natural and man-made chemicals.
Often, people mistakenly assume that all man-made chemicals are harmful and natural chemicals are beneficial. In reality, natural chemicals can be just as harmful to human health as man-made chemicals, and in many cases, more harmful. Figure 12 compares the toxicity of several natural and man-made chemicals.
Figure 12. Natural and man-made chemicals
(Image Source: http://pbs.twimg.com/media/CTn6HlDWwAEB1Jc.png:large, Creative Commons license)
(Image Source: http://pbs.twimg.com/media/CTn6HlDWwAEB1Jc.png:large, Creative Commons license)