Introduction to toxicology & Toxicokinetics Flashcards
(17 cards)
What are the three types of toxic substances?
Chemical (defined by a threshold for the substance to work), biological, and physiological
What is the difference between toxins and xenobiotics?
Toxins are poisons that originate from plants and microbial organisms, and include venoms released by animals in order to injure predators.
Xenobiotics include a variety of synthetic chemicals with different intended purposes.
By what terms are toxic chemicals classified?
They are classified in terms of physical state, chemical stability or reactivity, general chemical structure, ability to cause significant toxicity, and by their biochemical mechanisms of action.
What is a chemical allergy?
A chemical allergy is an adverse reaction of the immune system to a chemical in response to a previous exposure to that chemical or to a structurally similar one.
Allergic reaction and sensitization reaction mat also describe the situation when a prior exposure (sensitization) to the chemical is required to produce its subsequent toxic effect.
What is the difference between reversible and irreversible toxic effects?
Some toxic effects of chemicals are reversible, whereas others are irreversible. The likelihood of a toxic response to be reversed largely depends on the ability of an injured tissue to adapt, repair, and regenerate. For tissues such as the liver and gastrointestinal tract that have a high ability to regenerate, many injuries are reversible. By comparison, the CNS has a much more limited ability to divide and replace damage neurons making damage largely irreversible.
What is the difference between local and systemic toxicity?
Toxic responses are also characterized by the proximity between the site of chemical exposure and the site(s) of molecular action. Local effects are those that occur where contact is first made by the toxicant and the biological system. Such effects are produced by the ingestion of toxic substances or the inhalation of irritant materials.
Systemic effects require the absorption and distribution of a toxicant from its entry point to a distant site where the deleterious effects are produced. Most chemicals usually elicit their major toxicity in only one or two organs.
When does an additive effect occurs?
An additive effect occurs when the combined responses of two chemicals are equal to the sum of the responses to each chemical given alone (ex. 2+3=5).
When does a synergistic effect occurs?
A synergistic effect is observed when the combined responses of two chemicals are much greater than the sum of the response to each chemical when given alone (ex. 2+2=20)
When does potentiation occurs?
Potentiation occurs then one substance does not produce any toxicity on a particular tissue or system but when added to another chemical it makes that chemical much more toxic (ex. 0+2=10)
When does antagonism occurs?
Antagonism occurs when two chemicals administered together interfere with each other´s actions or one interferes with the action of the other (ex. 4+6=8; 4+(-4)=0; 4+0=1).
There are four major types of antagonism: receptor, chemical, dispositional, and functional.
What is tolerance?
Repeated exposure to a chemical can reduce its pharmacologic and/or toxicologic actions, a prosess called tolerance.
The duration and frequency for exposure of experimental animals to chemicals is classified according to what four categories?
1) Acute exposure refers to exposure to a chemical for less than 24 hours, and usually refers to a single administration.
2) Subacute exposure refers to repeated exposure to a chemical for 1 month or less.
3) Subchronic exposure refers to repeated exposure to a chemical for 1 to 3 months.
4) Chronic exposure refers to repeated exposure for more than 3 months, although usually this refers to studies with at least 1 year of repeated dosing.
What is the difference between the external and the internal dose?
The external dose is the dose of the chemical administered or measured in the environment.
The internal dose is the amount of chemical absorbed and found at the site of biological activity.
What is the dose-response relationship?
Dose-response relationships ae defined as the association between the amount of a toxicant administered and the extent to which changes are observed in a biological system.
Which two types are the dose-response relationship routinely divided into?
1) The individual dose-response relationship, which describes the response of an individual organism to increasing doses of a chemical, often referred to as a “graded” response because the measured effect is continuous over a range of doses.
2) A quantal dose-response relationship, which characterizes the distribution of individual responses to different doses in a population of organisms.
What is a widely used approach for estimating the response of a population to a toxic exposure?
The “effective dose” (ED).
What is the factors behind selective toxicity?
1) The chemical is equelly toxic to both organisms but accumulates preferentially in the target, and 2) alters a unique cellular or a biochemical feature that is absent or irrelevant in the unaffected species. Differences in the absorption, biotransformation, or excretion of the toxicant, or intracellular metabolism or transport may dictate accumulation of the ultimate toxic compound in affected tissues.
