Which system enables the lungs to perform breathing?

• A. Nervous
• B. Circulatory
• C. Endocrine
• D. Respiratory

Answer: (D)

Breathing is performed by the respiratory system. This system includes the lungs, airways, and the muscles that move air in and out, such as the diaphragm and intercostal muscles. When the diaphragm contracts and moves downward, the chest cavity expands and air is drawn into the lungs; when it relaxes, air is pushed out. The lungs also enable gas exchange, taking in oxygen and releasing carbon dioxide. The nervous system helps regulate how fast and deeply you breathe, but it’s the respiratory system that actually carries out the act of breathing. The circulatory system transports the gases once they’re in the blood, and the endocrine system can influence breathing rates under certain conditions, but neither directly enables the act of breathing.