The carotid bodies primarily respond to changes in which parameter to control ventilation?

The carotid bodies are specialized chemoreceptors located at the bifurcation of the carotid arteries and play a crucial role in the regulation of ventilation in response to changes in arterial blood gas levels. They are particularly sensitive to partial pressure of oxygen (PaO2) in the blood. When the PaO2 falls, the carotid bodies become activated and send signals to the respiratory centers in the brain to increase ventilation, thereby improving oxygen intake.

This sensitivity to PaO2 is especially significant in situations of hypoxia, where the body needs to enhance oxygen delivery to tissues. Although the carotid bodies also monitor carbon dioxide levels and pH indirectly through their response to PaCO2 and related changes, their primary role is to detect drops in PaO2, motivating appropriate ventilatory responses to maintain oxygen homeostasis. This is why the correct choice highlights the importance of PaO2 in controlling ventilation through the action of the carotid bodies.