Which system is primarily responsible for gas exchange in the body?

• A. Digestive system
• B. Nervous system
• C. Respiratory system
• D. Integumentary system

Answer: (C)

Gas exchange with the environment happens mainly through the respiratory system. In the lungs, tiny air sacs called alveoli provide a huge surface area with very thin walls that are close to capillaries. Oxygen in the inhaled air diffuses across the alveolar wall into the blood, while carbon dioxide in the blood diffuses into the alveolar air to be exhaled. This process is driven by diffusion along concentration gradients across the respiratory membrane, aided by the moist surface and good blood supply.

The oxygen-rich blood is then circulated to tissues, and carbon dioxide produced by metabolism is carried back to the lungs to be expelled. While other systems support life—nutrients from the digestive system, neural control of breathing, and minor diffusion through the skin—the primary system responsible for the actual gas exchange is the respiratory system.