these two gases, changes in (PO2 OR PCO2) are the most important in regulating the magnitude of ventilation. A fall in the partial pressure of this gas triggers the body to (increase OR decrease)   the magnitude of ventilation. Which of the following statements correctly describes the major mechanism by which this gas is monitored?

Central chemoreceptors in the medulla monitor changes to H⁺ levels in the extracellular fluid.

Central chemoreceptors in the medulla monitor changes to CO₂ levels in the extracellular fluid.

 Peripheral chemoreceptors in the carotid arteries monitor changes to PO2PO2 levels in the arterial blood.

 Peripheral chemoreceptors in the carotid arteries monitor changes to CO₂ levels in the arterial blood.