Toxicology: Nlom: Introduction

Front 1

What is Toxicology?

Back 1

The traditional definition of toxicology is "the science of poisons." As our understanding of how various agents can cause harm to humans and other organisms, a more descriptive definition of toxicology is "the study of the adverse effects of chemicals or physical agents on living organisms".

Front 2

Adverse effects may occur in many forms, ranging from what to what?

Back 2

Adverse effects may occur in many forms, ranging from immediate death to subtle changes not realized until months or years later.

Front 3

Adverse effects may occur at various levels within the body. List three.

Back 3

adverse effects may occur at various levels within the body, such as an organ, a type of cell, or a specific biochemical.

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Knowledge of how toxic agents damage the body has progressed along with what?

Back 4

Knowledge of how toxic agents damage the body has progressed along with medical knowledge.

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It is now known that various observable changes in anatomy or body functions actually result from what?

Back 5

It is now known that various observable changes in anatomy or body functions actually result from previously unrecognized changes in specific biochemicals in the body.

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The historical development of toxicology began with who?

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The historical development of toxicology began with early cave dwellers who recognized poisonous plants and animals and used their extracts for hunting or in warfare. By 1500 BC, written recordings indicated that hemlock, opium, arrow poisons, and certain metals were used to poison enemies or for state executions.

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What did Paracelsus determine?

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Paracelsus determined that specific chemicals were actually responsible for the toxicity of a plant or animal poison. He also documented that the body's response to those chemicals depended on the dose received. His studies revealed that small doses of a substance might be harmless or beneficial whereas larger doses could be toxic. This is now known as the dose-response relationship, a major concept of toxicology. Paracelsus is often quoted for his statement: "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."

Front 8

Who is often referred to as the founder of toxicology?

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Orfila, a Spanish physician, is often referred to as the founder of toxicology.

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The 20th century is marked by what?

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The 20th century is marked by an advanced level of understanding of toxicology. DNA (the molecule of life) and various biochemicals that maintain body functions were discovered. Our level of knowledge of toxic effects on organs and cells is now being revealed at the molecular level. It is recognized that virtually all toxic effects are caused by changes in specific cellular molecules and biochemicals.

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What is a Xenobiotic?

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Xenobiotic is the general term that is used for a foreign substance taken into the body. It is derived from the Greek term xeno which means "foreigner." Xenobiotics may produce beneficial effects (such as a pharmaceuticals) or they may be toxic (such as lead)

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Toxicology is the study of what?

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Toxicology is the study of the adverse effects of chemicals or physical agents on living organisms.

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A toxicologist is a scientist that determines what?

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A toxicologist is a scientist that determines the harmful effects of agents and the cellular, biochemical, and molecular mechanisms responsible for the effects.

Front 13

Define Toxicant?

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Substances that produce adverse biological effects of any nature.

May be chemical or physical in nature.

Effects may be of various types (acute, chronic, etc)

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Define Toxin?

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Specific proteins produced by living organisms (mushroom toxin or tetanus toxin)

Most exhibit immediate effects.

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Define Poisons?

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Toxicants that cause immediate death or illness when experienced in very small amounts.

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What is a toxic agent?

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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), physical (such as radiation) and biological (such as snake venom).

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A distinction is made for diseases due to ?. Give an example.

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A distinction is made for diseases due to biological organisms. Those organisms that invade and multiply within the organism and produce their effects by biological activity are not classified as toxic agents. An example of this is a virus that damages cell membranes resulting in cell death.

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If the invading organisms excrete chemicals which is the basis for toxicity, the excreted substances are known as ?. The organisms in this case are referred to as ?. Give an example.

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If the invading organisms excrete chemicals which is the basis for toxicity, the excreted substances are known as biological toxins. The organisms in this case are referred to as toxic organisms. An example of this 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, it is a toxin that is excreted by the bacteria that travels to the nervous system (a neurotoxin) that produces the disease.

Front 19

What is a toxic substance?

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A toxic substance is simply a material which has toxic properties. It may be a discrete toxic chemical or a mixture of toxic chemicals.

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Give some examples of toxic substances.

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Lead chromate, asbestos, and gasoline are all toxic substances.

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Lead chromate is a discrete what?

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Lead chromate is a discrete toxic chemical.

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Asbestos is a what?

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Asbestos is a toxic material that does not consist of an exact chemical composition but a variety of fibers and minerals

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Gasoline is a ? rather than a ? in that it contains a mixture of many chemicals.

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Gasoline is also a toxic substance rather than a toxic chemical in that it contains a mixture of many chemicals.

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Toxic substances may not always have a what?

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Toxic substances may not always have a constant composition. For example, the composition of gasoline varies with octane level, manufacturer, time of season, etc.

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Toxic substances may be what in composition?

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Toxic substances may be organic or inorganic in composition.

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Define organic toxins.

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Substances that were originally derived from living organisms. (thus named organic)

Contain carbon and often are large molecules can be synthesized (that is man-made) as well as obtained from natural sources.

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Define inorganic toxins.

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Specific chemicals that are not derived from living organisms (minerals)

Generally small molecules consisting of only a few atoms. (such as nitrogen dioxide)

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Toxic substances may be ? toxins or ? toxins.

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Toxic substances may be systemic toxins or organ toxins.

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What is a systemic toxin? Give an example.

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A systemic toxin is one that 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 cell's ability to utilize oxygen.

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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 what?

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These specific sites are known as the target organs or target tissues.

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Benzene is primarily toxic to the blood-forming tissues. What does this make it?

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Benzene is a specific organ toxin in that it is primarily toxic to the blood-forming tissues.

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Lead is a specific organ toxin; however, it has what?

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Lead is also a specific organ toxin; however, it has three target organs (central nervous system, kidney, and hematopoietic system).

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When is a toxic site referred to as the target tissue?

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A toxicant may affect a specific type of tissue (such as connective tissue) that is present in several organs. The toxic site is then referred to as the target tissue.

Front 34

There are many types of cells in the body. List some of the ways that they can be classified.

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There are many types of cells in the body and they can be classified in several ways.


1. basic structure (e.g., cuboidal cells)



2. tissue type (e.g., hepatocytes of the liver)



3. germinal cells (e.g., ova and sperm)



4. somatic cells (e.g., non-reproductive cells of the body)

Front 35

Describe germ cells.

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Germ cells are those cells that are involved in the reproductive process 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 on the developing fetus (such as birth defects, abortions).

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Describe somatic cells.

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Somatic cells are all body cells except the reproductive germ cells. They have two sets (or pairs) of chromosomes. Toxicity to somatic cells causes a variety of toxic effects to the exposed individual (such as dermatitis, death, and cancer).