What is the primary function of the respiratory system?

The primary function of the respiratory system is to facilitate the exchange of gases between the atmosphere and the bloodstream. This process is vital for delivering oxygen to the body's cells, which is essential for cellular respiration and energy production. Inhalation brings oxygen into the lungs, where it diffuses across the alveolar membranes into the blood. Conversely, carbon dioxide, a waste product of metabolism, is transported from the blood into the lungs to be exhaled. This gas exchange is crucial for maintaining proper physiological function and homeostasis.

In contrast, the other options focus on functions that are not primarily associated with the respiratory system. Circulating blood is primarily the role of the cardiovascular system, regulating body temperature involves various mechanisms including those from the integumentary and circulatory systems, and providing nutrients is largely a function of the digestive system. Thus, the correct focus on gas exchange underscores the respiratory system's critical role in supporting life.