Nebuliser systems make it possible to treat both the upper and the lower airways. The upper airways include the nose, the adjoining nasal cavities (sinuses), the pharynx (throat) and the larynx (voice box). The mucous membrane of the nasopharynx (the nasal portion of the pharynx) also continues downwards into the mucosa of the lower airways, the lung. The lower airways are made up of the trachea (windpipe), bronchi and alveoli (air cells) of the lung. The upper and lower respiratory tract form a functional unit. This is why the lower airways is often also affected by diseases of the upper airways, e.g with allergies.