Which hypoxia type results from cellular inability to utilize oxygen due to toxins?

• A. Hypoxic hypoxia.
• B. Anemic hypoxia.
• C. Stagnant hypoxia.
• D. Histotoxic hypoxia.

Answer: (D)

Histotoxic hypoxia occurs when toxins interfere with the body's ability to use oxygen at the cellular level. Even if oxygen is delivered to tissues normally, poisonous compounds—most notably cyanide—block enzymes in the mitochondria (the electron transport chain), so oxidative phosphorylation can’t proceed and cells can’t extract energy from oxygen. This is different from hypoxic hypoxia (not enough oxygen reaches the blood), anemic hypoxia (reduced carrying capacity due to low or faulty hemoglobin), or stagnant hypoxia (impaired circulation). The hallmark here is that oxygen delivery may be fine, but the cells can’t utilize it because of the toxin.