What factor primarily controls respiration?

The primary factor that controls respiration is the level of carbon dioxide in the blood. This is rooted in the body’s need to maintain homeostasis and ensure that gases are exchanged efficiently. The respiratory center in the brain, particularly in the medulla oblongata and pons, responds primarily to changes in carbon dioxide levels rather than oxygen levels.

When carbon dioxide levels increase (hypercapnia), it leads to a decrease in blood pH, signaling the brain to increase the rate and depth of respiration in order to expel more carbon dioxide. Conversely, lower levels of carbon dioxide would decrease the drive to breathe.

While oxygen levels do play a role in the regulation of respiration, particularly in chronic conditions where the body is adapted to low oxygen levels, carbon dioxide levels are the most critical factor in the immediate control of the respiratory drive. The levels of nitrogen in the blood and physical activity levels also influence respiration, but they do not serve as the primary regulators in the same direct manner as carbon dioxide does.