What is the primary function of the respiratory system?

What is the primary function of the respiratory system?

• A. Digestion of nutrients.
• B. Filtering blood.
• C. Gas exchange, supplying O2 to the bloodstream and removing CO2 from it.
• D. Hormone production.

Answer: (C)

Gas exchange is the primary function of the respiratory system. It supplies oxygen to the bloodstream and removes carbon dioxide from it. This happens in the lungs where tiny air sacs called alveoli provide a large surface area and very thin walls adjacent to capillaries. Oxygen diffuses from the air in the alveoli into the blood and binds to hemoglobin for transport to all body cells. Carbon dioxide, a waste product of metabolism, diffuses from the blood into the alveoli to be exhaled. The movement is driven by differences in partial pressures: O2 is higher in the alveoli than in the blood, while CO2 is higher in the blood than in the alveoli. The other options describe functions of different systems—digestion, blood filtration, and hormone production—not the lungs.

Gas exchange is the primary function of the respiratory system. It supplies oxygen to the bloodstream and removes carbon dioxide from it. This happens in the lungs where tiny air sacs called alveoli provide a large surface area and very thin walls adjacent to capillaries. Oxygen diffuses from the air in the alveoli into the blood and binds to hemoglobin for transport to all body cells. Carbon dioxide, a waste product of metabolism, diffuses from the blood into the alveoli to be exhaled. The movement is driven by differences in partial pressures: O2 is higher in the alveoli than in the blood, while CO2 is higher in the blood than in the alveoli. The other options describe functions of different systems—digestion, blood filtration, and hormone production—not the lungs.