Final answer:
Peripheral chemoreceptors are primarily sensitive to carbon dioxide and hydrogen ion levels, rather than PO₂.
Step-by-step explanation:
The peripheral chemoreceptors are responsible for sensing large changes in blood oxygen levels. They are located in the aortic arch and carotid arteries and are sensitive to changes in pH, carbon dioxide, and oxygen blood levels. However, they are primarily sensitive to carbon dioxide and hydrogen ion levels, rather than PO₂. They respond to increasing carbon dioxide and hydrogen ion levels by stimulating an increase in cardiac output and constricting peripheral vessels. Therefore, at normal PCl₃ and pH, the peripheral chemoreceptors are not highly sensitive to PO₂.