Chronic toxicity may lead to which adaptation?

• A. Increased sensitivity to all chemicals.
• B. No change in response.
• C. Hyperactivity with exposure.
• D. Tolerance due to metabolic detoxification.

Answer: (D)

Chronic exposure can trigger an adaptive response that makes the body better at handling a toxin, producing tolerance. This happens when detoxification pathways in the liver and other tissues are induced—enzymes involved in Phase I and Phase II metabolism (such as cytochrome P450s, glutathione S-transferases, and UDP-glucuronosyltransferases) are upregulated. The result is faster metabolism and easier elimination of the chemical, so the toxin’s effects are diminished with repeated exposure.

This is different from just reacting the same way every time, or from an immediate, heightened response to the toxin. It’s also not about becoming more sensitive; that would imply the opposite of adaptation. A hyperactive response is typically an acute reaction, not a chronic adapting process.