Peripheral chemoreceptors are most sensitive to what changes?

Peripheral chemoreceptors, primarily located in the carotid and aortic bodies, are highly sensitive to changes in the partial pressure of oxygen (PaO2) in the blood. When PaO2 levels decrease, these receptors become activated, triggering a respiratory response to increase ventilation and thus elevate oxygen levels in the bloodstream.

While changes in PaCO2 and pH are also important for respiratory regulation, the specific function of peripheral chemoreceptors is geared more towards detecting hypoxemia (low oxygen levels). Increased carbon dioxide levels (hypercapnia) primarily stimulate central chemoreceptors located in the brain, whereas significant decreases in arterial pH (acidosis) can have a more pronounced effect on central chemoreceptors too. Increased temperature, while it can have various physiological effects, does not directly influence the sensitivity of peripheral chemoreceptors in the same way that low oxygen levels do.

Thus, the primary stimulus for peripheral chemoreceptors is a decrease in PaO2, making this the correct response to the question. Understanding the roles of these chemoreceptors is crucial for grasping human respiratory physiology and its responses to hypoxemia.