Histotoxic hypoxia is classically caused by which toxin?

Histotoxic hypoxia is classically caused by which toxin?

• A. Carbon monoxide
• B. Cyanide poisoning
• C. Nitrogen dioxide
• D. Oxygen toxicity

Answer: (B)

Histotoxic hypoxia happens when tissues can’t use oxygen because a toxin disrupts cellular respiration. The classic culprit is cyanide, which blocks cytochrome c oxidase in the mitochondria. That stops oxidative phosphorylation, so even though oxygen is delivered to tissues, it can’t be used to produce ATP. Venous oxygen content remains high, and cells shift to anaerobic metabolism, leading to metabolic acidosis. Other options differ in mechanism: carbon monoxide reduces oxygen delivery by forming carboxyhemoglobin; nitrogen dioxide is mainly a pulmonary irritant with different effects; oxygen toxicity involves damage from high oxygen levels, not a failure of cellular oxygen use.

Histotoxic hypoxia happens when tissues can’t use oxygen because a toxin disrupts cellular respiration. The classic culprit is cyanide, which blocks cytochrome c oxidase in the mitochondria. That stops oxidative phosphorylation, so even though oxygen is delivered to tissues, it can’t be used to produce ATP. Venous oxygen content remains high, and cells shift to anaerobic metabolism, leading to metabolic acidosis.

Other options differ in mechanism: carbon monoxide reduces oxygen delivery by forming carboxyhemoglobin; nitrogen dioxide is mainly a pulmonary irritant with different effects; oxygen toxicity involves damage from high oxygen levels, not a failure of cellular oxygen use.