Histotoxic hypoxia is caused by?

Histotoxic hypoxia is caused by?

• A. Poisoning of the cytochrome oxidase enzyme system, preventing cellular use of molecular oxygen
• B. Reduction in inspired oxygen
• C. Low environmental oxygen
• D. Poor oxygen delivery due to circulation issues

Answer: (A)

Histotoxic hypoxia occurs when tissues cannot use oxygen because cellular respiration is blocked by toxins. The classic mechanism is inhibition of the mitochondrial electron transport chain, particularly the cytochrome oxidase (cytochrome c oxidase) system. When this enzyme is poisoned, oxygen reaches the tissues but cannot be utilized to produce ATP, so cellular metabolism is impaired despite adequate oxygen delivery. This is what happens with cyanide or hydrogen sulfide poisoning. The other scenarios involve problems with oxygen delivery or availability (insufficient inspired oxygen, low environmental oxygen, or circulatory issues), not an inability of cells to use oxygen at all.

Histotoxic hypoxia occurs when tissues cannot use oxygen because cellular respiration is blocked by toxins. The classic mechanism is inhibition of the mitochondrial electron transport chain, particularly the cytochrome oxidase (cytochrome c oxidase) system. When this enzyme is poisoned, oxygen reaches the tissues but cannot be utilized to produce ATP, so cellular metabolism is impaired despite adequate oxygen delivery. This is what happens with cyanide or hydrogen sulfide poisoning. The other scenarios involve problems with oxygen delivery or availability (insufficient inspired oxygen, low environmental oxygen, or circulatory issues), not an inability of cells to use oxygen at all.