FINALS

• Toxicology


  Science of poisons
• Poison/Toxicant


  Substance that is harmful to living organisms because of its detrimental effects on tissues, organs, biological processes
• Effects of toxicants


  • Destruction of cells
  • Mutation of DNA leading to cancer
  • Disruption of the signaling mechanisms by which cell development and function are controlled

  
• Toxicants


  Undergo metabolism to produce an active species that causes poisoning
• Physical forms of exposure

  • Gasses
  • Vapors
  • Dusts
  • Fumes
  • Mists
• Matrix


  Substance with which a toxicant is associated (the solvent in which it is dissolved or the solid medium in which it is dispersed)
• Matrix may have a strong effect on the toxicity of the toxicant
• Variables affecting toxicity


  • Dose
  • Toxicant concentration
  • Duration of exposure per exposure incident
  • Frequency of exposure
  • Rate of exposure
  • Total time period over which the organism is exposed
  • Exposure site
  • Route

  
• Categories of exposure


  • Acute Local
  • Chronic Local
  • Acute Systemic
  • Chronic Systemic
• Major routes of exposure

  • Skin (percutaneous or dermal route)
  • Lungs (inhalation, respiration, pulmonary route)
  • Mouth (oral route)
• Minor routes of exposure

  • Rectal
  • Vaginal
  • Parental (intravenous or intramuscular)
• The way that a toxic substance is introduced into the complex system of an organism is strongly dependent on the physical and chemical properties of the substance
• The defensive barriers that a toxicant may encounter vary with the route of exposure
• Intestinal epithelium


  Where toxic substances are ingested orally and is absorbed
• Stratum/horny layer


  Major barrier to dermal absorption of toxicants
• The permeability of skin is inversely proportional to the thickness of the stratum/horny layer
• Biomonitors


  • Higher plants
  • Fungi
  • Lichens
  • Mosses
• Biomonitors


  Serve as indicators of various kinds of pollutants
• Types of interactions between substances

  • Additive/synergistic
  • Potentiation
  • Antagonism
• Additive/synergistic


  When both substances have the same physiologic functions, the total effect is greater than the sum of the effects of each separately
• Potentiation


  Inactive substance enhances the action of an active one
• Antagonism


  Active substances decreases the effect of another active one
• Dose


  Amount, usually per unit body mass, of a toxicant to which an organism is exposed
• Response


  Effect of an organism resulting from exposure to toxicant
• Dose-response relationships differ among different kinds and strains of organisms, types of tissues, and population of cells
• LD50


  The dose corresponding to the midpoint (inflection point) of the resulting S-shaped curve, which is the statistical estimate of the dose that would kill 50% of the subjects

  
• Larger LD50, lower toxicity
• Relative toxicities


  • Drops of super toxic substances is fatal
  • Teaspoonful of a very toxic substance is fatal
  • Quart of a slightly toxic substance is fatal
• Low slope for the nonlethal effects curve indicates a wide range of effective dose and a wide margin of safety
• Reversible


  No lasting effect from the exposure
• Irreversible


  Effect is permanent, remain after the toxic substance is eliminated from the organism
• Hypersensitivity


  Very sensitive to a particular poison, induced after one or more doses of a chemical
• Hyposensitivity


  Very resistant to the same substance
• Xenobiotic


  Substances that are foreign to a living system
• Endogenous


  Substances that occur naturally in a biologic system, fill an essential function, and their levels must usually fall within a particular concentration range in order for metabolic processes to occur normally
• Below a normal range of endogenous substances - deficiency response/death (hypocalcemia)
• Above normal range of endogenous substances - adverse effects may occur (Hypercalcemia (kidney malfunction))
• Xenobiotic chemical species


  Found in an organism that is not produced by the organism or part of a normal diet of that organism

  
• Examples of environmental xenobiotics

  • Formaldehyde in inhaled polluted air
  • Synthetic chemicals from the anthrosphere
  • Chemicals produced biologically by some organisms as defense against predators

  
• Biological effect of an endogenous substance in an organism showing optimum level, deficiency, and excess