Which statement about histotoxic hypoxia is correct?

• A. It results from toxins preventing cellular use of oxygen.
• B. It results from reduced oxygen content in the air.
• C. It is caused by carbon monoxide binding to hemoglobin.
• D. It results from stagnant blood flow.

Answer: (A)

Histotoxic hypoxia occurs when toxins disrupt the body's ability to use oxygen at the cellular level. Toxins such as cyanide block the enzymes of cellular respiration in mitochondria, so even though oxygen is delivered to tissues, the cells cannot metabolize it for energy. This leads to tissue hypoxia despite normal or near-normal oxygen content in the blood.

The other scenarios describe different types of hypoxia: reduced oxygen in the air points to hypoxic (or hypoxemic) hypoxia due to low ambient oxygen; carbon monoxide binding to hemoglobin impairs oxygen transport to tissues (also a delivery problem rather than utilization); and stagnant blood flow refers to circulatory (ischemic) hypoxia from poor perfusion.