The traditional definition of TOXICOLOGY "is the science of poisons" or study of poisons". As our understanding of how various agents can cause harm to humans and other organisms; a more descriptive of Toxicology is "the study of the adverse effects of chemical or physical agents on living organisms".
Poison refering to any substance that causes a harmful effect. The concept that any substance has the potential to cause harm if given at the correct dosage is a central theme in toxicology.
There are four major disciplines within Toxicology:
*Mechanistic Toxicology elucidates the cellular and biochemical effects of toxins. These studies provide a basis for rational therapy design and the development of test to asses the degree of exposure of poisonned individuals.
*Descriptive Toxicology uses the results from animal experiments to predict what level of exposure will cause ham in humans.
*Forensic Toxicolgy is primarily concerened with the medicolegal consequences of toxin exposure.Evaluation of analytical chemistry techniques and measurement,and testimony of conclusions and opinions in courts of law encompass the activity of this specialized field of toxicology.
*Clinical Toxicology is the study of interrelationship between cause toxin exposure and disease states. Involves the application of toxicological principles within a diagnostic setting, usually to determine whether a presenting adverse effect or disease or injury is due to some type of chemical exposure. This area of toxicology is typically practiced by a physician, nurse or other clinician, often times in consultation with the experimental toxicologist, who is in a position to better explain certain published experimental findings and whether they would be applicable to the case at hand.
Dose is the amount of a substance administered at one time. There are four types of dose it shown in a table form:
The Dose-response relationship is a fundamental and essential concept in toxicology. It correlates exposures and the spectrum of induced effects.In general, the higher the dose, the more severe the response. The dose-response relationship is based on observed data from experimental animal, human clinical, or cell studies.
Knowledge of the dose-response relationship:
Knowledge of the dose-response relationship:
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 | establishes causality that the chemical has in fact induced the observed effects | |
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| establishes the lowest dose where an induced effect occurs - the threshold effect | |
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| determines the rate at which injury builds up - the slope for the dose response. | |
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Toxicity is complex with many influencing factors; dosage is the most important. Xenobiotics cause many types of toxicity by a variety of mechanisms. Some chemicals are themselves toxic. Others must be metabolized (chemically changed within the body) before they cause toxicity.
Many xenobiotics distribute in the body and often affect only specific target organs.
Toxicity can be generally broken down into two categories:
chronic toxicity is the harmful effects of long-term exposure to relatively low doses of toxicant. This would include traces of pesticides in foods, air pollution, etc.
Toxicity can result from adverse cellular, biochemical, or macromolecular changes. Examples are:
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| cell replacement, such as fibrosis | |
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| damage to an enzyme system | |
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| disruption of protein synthesis | |
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| production of reactive chemicals in cells | |
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| DNA damage | |
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Some xenobiotics may also act indirectly by:
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Factors Influencing Toxicity The toxicity of a substance depends on the following:
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