Final answer:
Peripheral chemoreceptors are highly sensitive to blood oxygen levels, and they respond to significant decrements by triggering increased respiratory activity. They also respond to changes in carbon dioxide levels and pH.
Step-by-step explanation:
Peripheral chemoreceptors are most sensitive to changes in blood oxygen levels. These chemoreceptors, located in the aortic arch and carotid arteries, monitor the levels of dissolved oxygen molecules in the blood and respond to large decreases, particularly when oxygen levels fall to about 60 mm Hg or less. At this point, they stimulate an increase in respiratory activity to adjust for the deficiency. Although these chemoreceptors are primarily triggered by low oxygen levels, they are also influenced by rises in carbon dioxide levels and changes in blood pH. It is essential to note that peripheral chemoreceptors are part of a regulatory system that maintains homeostasis, particularly by influencing the respiratory rate to correct for imbalances in the body's oxygen and carbon dioxide levels, as well as pH.