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MBBS QUESTION #10339
Question 1
Cyanide poisoning produces profound cellular hypoxia despite normal arterial oxygen delivery because cyanide directly inhibits:
  • Complex I (NADH dehydrogenase) of the electron transport chain
  • Cytochrome c oxidase (Complex IV), blocking the terminal transfer of electrons to molecular oxygen✔️
  • ATP synthase (Complex V) exclusively
  • Hemoglobin's oxygen-binding capacity directly
Correct Answer Explanation
Cyanide binds the ferric (Fe3+) heme iron of cytochrome c oxidase, halting the entire electron transport chain and ATP synthesis despite adequate tissue oxygen delivery — producing 'histotoxic hypoxia,' treated in part with agents (e.g., hydroxocobalamin, sodium thiosulfate) that help detoxify cyanide.