A primary function of the respiratory system is to

The primary function of the respiratory system is to facilitate gas exchange, which is essential for maintaining a stable internal environment and regulating blood pH. The process of respiration allows oxygen to enter the bloodstream and carbon dioxide to be expelled from the body. When carbon dioxide levels in the blood increase, it leads to a decrease in blood pH, making it more acidic. Conversely, when carbon dioxide is removed from the blood through respiration, it helps to restore the pH balance. This regulation of blood pH is a critical homeostatic function.

Transporting nutrients is primarily the function of the circulatory system, which delivers glucose, vitamins, and minerals to tissues. Producing red blood cells is a function of the bone marrow, not the respiratory system, although the respiratory system does provide the oxygen that red blood cells carry. Absorption of calcium occurs in the digestive system, mainly in the intestines, rather than in the respiratory system. Therefore, the respiratory system's role in regulating blood pH is vital to overall metabolic stability, highlighting why this function is considered primary.