The respiratory system is the system by which oxygen, essential for life, is taken into the body and the waste product, carbon dioxide, is expelled from the body. The respiratory system consists of the mouth and nose, airways and lungs.

Airways

Air enters through the mouth and nose and passes down the pharynx (throat) and through the larynx (voice box). Air then continues down through the trachea (windpipe) which branches into two bronchi (singular: Bronchus ) to each of the two lungs. The inflammation of the bronchus is called bronchitis .

Bronchus

The bronchi branch many times until becoming much smaller airways called "bronchioles". At the end of each bronchiole are tiny air-filled cavities called alveoli. Each alveolus is surrounded by many blood capillaries which allow oxygen to move into the bloodstream and carbon dioxide out. This exchange of substances is the primary function of the respiratory system. See also Asthma .