upper respiratory tract (URT), one of the two divisions of the respiratory system. The URT consists of the nose, nasal cavity, ethmoidal air cells, frontal sinuses, sphenoidal sinuses, maxillary sinus, larynx, and trachea. The URT conducts air to and from the lungs and filters, moistens, and warms the air during each inspiration. Infection and irritation of the URT are common and often spread to the lower respiratory tract, where they may cause serious complications. Compare lower respiratory tract. See also larynx, nose, trachea.
