Structural and Physiological Basis of the Upper Respiratory Tract

The external nose consists of paired nasal bones and upper and lower lateral cartilages. Internally, the nasal septum divides the nasal cavity into a right and left side. The lateral nasal wall consists of inferior and middle turbinates and occasionally a superior or supreme turbinate bone. The opening of the sinuses also is found under the middle turbinates on the lateral nasal wall. The lacrimal system drains into the nasal cavity below the anterior inferior aspect of the inferior turbinates. As in the rest of the upper respiratory tract, nasal membranes are composed of ciliated pseudostratified glandular columnar epithelium. Cilia beat in unison to propel mucus from the nasal cavity and paranasal sinuses toward the nasopharynx where it can be swallowed. Mucociliary transport relies on mucus production and ciliary function. Normally, the nose and paranasal sinuses produce approximately 1 quart of mucus in 24 h. The amount of mucus produced can more than double when the nose and/or sinuses are inflamed. Mucus contains IgA, immunoglobulin E, and muramidase. Blood and autonomic nerve supply control secretions and the level of congestion of nasal membranes. General innervation to the nose is from the autonomic nervous system; the parasympathetic nerves supply the resting tone and control secretions.