Final answer:
The respiratory rate is controlled by the centers in the medulla and pons of the brainstem, which are stimulated by changes in blood acidity and carbon dioxide and oxygen levels.
Step-by-step explanation:
The respiratory rate is controlled involuntarily by the centers located in the medulla and pons of the brainstem. These respiratory centers regulate the rate of breathing based on the body's needs, mainly determined by blood acidity or pH levels. They are stimulated by factors such as changes in carbon dioxide and oxygen levels in the blood.