Which gas concentration is primarily monitored by peripheral chemoreceptors?

• A. O2 concentration
• B. CO2 concentration
• C. Nitrogen concentration
• D. Hydrogen concentration

Answer: (A)

Peripheral chemoreceptors predominantly monitor the concentration of oxygen (O2) in the blood. These chemoreceptors, which are located in the carotid bodies and aortic arch, are highly sensitive to changes in arterial oxygen levels. They play a crucial role in regulating respiratory drive, particularly in conditions where oxygen levels fall, such as during hypoxemia.

While carbon dioxide (CO2) levels are more closely monitored by central chemoreceptors in the brain, peripheral chemoreceptors do respond to elevated CO2 levels indirectly through the accompanying changes in blood pH, but their primary trigger remains oxygen concentration. Nitrogen concentrations do not have a significant role in respiratory control under normal physiological conditions, and while hydrogen ions (H+) are important in the regulation of acid-base balance, they are not the primary stimuli for peripheral chemoreceptors either. Thus, oxygen concentration is the crucial factor that these receptors are designed to detect, prompting appropriate adjustments in ventilation to maintain adequate oxygenation.