Which system is primarily involved in gas exchange between the air and the blood?

Which system is primarily involved in gas exchange between the air and the blood?

• A. Respiratory
• B. Circulatory
• C. Digestive
• D. Immune

Answer: (A)

Gas exchange between air and blood happens where the respiratory system does the work—in the lungs, specifically at the alveoli. Oxygen in the air diffuses across the very thin alveolar and capillary walls into the blood, while carbon dioxide diffuses the opposite direction to be exhaled. This relies on the partial pressure differences: oxygen is higher in inhaled air than in blood, and carbon dioxide is higher in blood than in the air inside the alveoli. The diffusion distance is short and the barrier is moist and thin, with a rich network of capillaries to maximize exchange. The circulatory system then transports the gases once loaded, but it is the respiratory structures that enable the actual exchange with the atmosphere. The digestive system handles nutrients, and the immune system focuses on defending the body, not directly exchanging gases.

Gas exchange between air and blood happens where the respiratory system does the work—in the lungs, specifically at the alveoli. Oxygen in the air diffuses across the very thin alveolar and capillary walls into the blood, while carbon dioxide diffuses the opposite direction to be exhaled. This relies on the partial pressure differences: oxygen is higher in inhaled air than in blood, and carbon dioxide is higher in blood than in the air inside the alveoli. The diffusion distance is short and the barrier is moist and thin, with a rich network of capillaries to maximize exchange. The circulatory system then transports the gases once loaded, but it is the respiratory structures that enable the actual exchange with the atmosphere. The digestive system handles nutrients, and the immune system focuses on defending the body, not directly exchanging gases.