How is carbon monoxide produced in the body?

Carbon monoxide is produced in the body primarily through normal metabolic processes, particularly during the breakdown of heme, which is a component of hemoglobin in red blood cells. This process occurs in the liver and involves the enzyme heme oxygenase, which catalyzes the conversion of heme into biliverdin, yielding carbon monoxide as a byproduct. This endogenous production is important because carbon monoxide, in low concentrations, has signaling functions in various physiological processes, such as vasodilation and neurotransmission.

While pollution in the air can lead to inhalation of carbon monoxide from external sources, the question focuses specifically on production within the body. Similarly, excessive physical activity and digestion of food do not directly result in the generation of significant amounts of carbon monoxide as a metabolic byproduct. Therefore, the correct understanding of carbon monoxide's origin in the body is linked to internal metabolic processes, making normal metabolism the critical factor here.