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Chapter 3. Mechanisms of Toxicity

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The severity of a toxin depends, in large part, on the concentration of the toxin at its site of action. Which of the following will decrease the amount of toxin reaching its site of action?

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a. absorption across the skin.

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b. excretion via the kidneys.

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c. toxication.

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d. reabsorption across the intestinal mucosa.

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e. discontinuous endothelial cells of hepatic sinusoids.

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Toxication (or metabolic activation) is the biotransformation of a toxin to a more toxic and reactive species. Which of the following is not a reactive chemical species commonly formed by toxication?

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a. electrophiles.

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b. nucleophiles.

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c. superoxide anions.

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d. hydroxy radicals.

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e. hydrophilic organic acids.

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Which of the following is not an important step in detoxication of chemicals?

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a. formation of redox-active reactants.

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b. reduction of hydrogen peroxide by glutathione peroxidase.

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c. formation of hydrogen peroxide by superoxide dismutase.

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d. reduction of glutathione disulfide (GSSG) by glutathione reductase (GR).

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e. conversion of hydrogen peroxide to water and molecular oxygen by catalase.

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Regarding the interaction of the ultimate toxicant with its target molecule, which of the following is false?

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a. Toxins often oxidize or reduce their target molecules, resulting in the formation of a harmful by-product.

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b. The covalent binding of a toxin with its target molecule permanently alters the target’s function.

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c. The noncovalent binding of a toxin to an ion channel irreversibly inhibits ion flux through the channel.

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d. Abstraction of hydrogen atoms from endogenous compounds by free radicals can result in the formation of DNA adducts.

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e. Several toxins can act enzymatically on their specific target proteins.

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All of the following are common effects of toxicants on target molecules EXCEPT:

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a. blockage of neurotransmitter receptors.

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b. interference with DNA replication due to adduct formation.

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c. cross-linking of endogenous molecules.

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d. opening of ion channels.

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e. mounting of an immune response.

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