Histotoxic hypoxia is caused by which factor?

Histotoxic hypoxia is caused by which factor?

• A. Chemical poisoning or high blood alcohol
• B. Lack of oxygen in the air
• C. Poor circulation due to cold
• D. Carbon monoxide in the blood

Answer: (A)

Histotoxic hypoxia occurs when the body's tissues cannot use oxygen even though it is being delivered. This happens when a toxin disrupts cellular respiration, stopping the cells from extracting energy from oxygen. Cyanide is the classic example because it blocks cytochrome oxidase in the mitochondria, effectively shutting down the electron transport chain. Severe chemical poisoning, including scenarios with high blood alcohol, can have a similar effect by impairing the cells’ ability to utilize oxygen. So, even with normal or adequate oxygen in the blood, the cells can’t use it, leading to tissue hypoxia. The other scenarios describe different problems. If there isn’t enough oxygen in the air, oxygen delivery to tissues is limited—this is hypoxic hypoxia. If circulation is poor due to cold, tissues aren’t adequately perfused—stagnant (or circulatory) hypoxia. Carbon monoxide binds hemoglobin and reduces the blood’s capacity to carry oxygen, which is a delivery issue as well, not a failure of cellular use.

Histotoxic hypoxia occurs when the body's tissues cannot use oxygen even though it is being delivered. This happens when a toxin disrupts cellular respiration, stopping the cells from extracting energy from oxygen. Cyanide is the classic example because it blocks cytochrome oxidase in the mitochondria, effectively shutting down the electron transport chain. Severe chemical poisoning, including scenarios with high blood alcohol, can have a similar effect by impairing the cells’ ability to utilize oxygen. So, even with normal or adequate oxygen in the blood, the cells can’t use it, leading to tissue hypoxia.

The other scenarios describe different problems. If there isn’t enough oxygen in the air, oxygen delivery to tissues is limited—this is hypoxic hypoxia. If circulation is poor due to cold, tissues aren’t adequately perfused—stagnant (or circulatory) hypoxia. Carbon monoxide binds hemoglobin and reduces the blood’s capacity to carry oxygen, which is a delivery issue as well, not a failure of cellular use.