The upper respiratory tract

The upper respiratory tract extends from the anterior nares to the larynx and comprises (1) the nose—with the main function as first-line defence against problems with incoming air, acting as a coarse particle filter and a conditioner (temperature and humidity) of the air, and with the sense of smell helping to detect noxious substances that are best avoided. (2) The pharynx—this has to act as a rigid tube when used for breathing, but during swallowing it has to be a collapsible tube capable of peristalsis, a combination of functions which is achieved by complex innervation and musculature. Subepithelial collections of lymphoid tissue in the pharynx are ideally suited to process inhaled and swallowed antigens. (3) The larynx—this has three important functions: communication, protection of the airway, and dynamic control of lung volume.