The human respiratory system is responsible for the exchange of gases between the body and the environment. It supplies oxygen needed for energy production and removes carbon dioxide, a waste product of metabolism. The system includes the nose, pharynx, larynx, trachea, bronchi, and lungs. Inside the lungs, tiny air sacs called alveoli allow oxygen to pass into the blood and carbon dioxide to be expelled. Breathing involves inhalation (taking in oxygen-rich air) and exhalation (releasing carbon