What is the primary function of the respiratory system?

What is the primary function of the respiratory system?

• A. Gas exchange between the external environment and the blood
• B. Detoxification of blood
• C. Nutrient processing
• D. Hormone regulation

Answer: (A)

Gas exchange between the air in the lungs and the blood is the main job of the respiratory system. Oxygen from inhaled air diffuses across the thin walls of the alveoli into the surrounding capillaries, where it binds to hemoglobin and travels to tissues. At the same time, carbon dioxide, a waste product from cellular metabolism, diffuses from the blood into the alveolar air to be exhaled. This exchange is driven by differences in partial pressures: high O2 in the alveolar air and higher CO2 in the blood, with a huge surface area and a very thin respiratory membrane that maximize diffusion. Breathing (ventilation) and blood flow (perfusion) keep these gradients working. The other options relate to functions of different systems—detoxifying blood is a liver job, nutrient processing is digestive system work, and hormone regulation is endocrine system work—so they aren’t the primary role of the respiratory system.