The respiratory system performs external respiration, the exchange of gases between the body and environment, and internal respiration, the transport of oxygen from the lungs to cells and removal of carbon dioxide. Air follows a pathway from the nose through the pharynx, larynx, trachea, bronchi and bronchioles to the alveoli where gas exchange occurs. The respiratory system is susceptible to various diseases and disorders that can be diagnosed through examination, imaging and pulmonary function tests. Treatments include medications, surgery and mechanical devices.