The upper respiratory tract (upper airway) consists of the nose, mouth, sinuses, pharynx (upper section of the throat), and larynx (voice box). The lower respiratory tract consists of the trachea (windpipe), bronchial tubes, and lungs. The bronchial tubes carry air into the lungs and branch into smaller and smaller bronchioles. These end in alveoli (air sacs).

The main function of the respiratory system is to supply the blood with oxygen so the blood can deliver oxygen to all parts of the body. The respiratory system does this through breathing.