Nasal epithelium physiology

The nasal epithelium, like many other epithelia in contact with the external environment, is covered by a mucus gel. The mucus plays a number of important physiological roles ... 

The upper respiratory tract, particularly the nose, has a unique anatomy that performs normal physiologic functions as well as innate defense against inhaled toxicants. The nose extends from the nostrils to the pharynx. Inspired air enters the nose through the nostrils. The nasal cavity is divided longitudinally by a septum into two nasal compartments. In most mammalian species, each nasal cavity is divided into a dorsal, ventral, and middle (lateral) meatus by two turbinate bones, the nasoturbinate and maxilloturbinate. These turbinates project from the dorsolateral and ventrolateral wall of the cavity, respectively. In the posterior portion of the nose, the ethmoid recess contains the ethmoturbinate. The nasal cavity is lined by a vascular mucosa that consists of four distinct types of epithelia. In rodents, these epithelia are (1) the stratified squamous epithelium that lines the nasal vestibule and the floor of the ventral meatus in the anterior portion of the nose (2) the non-ciliated, pseudostratified, transitional epithelium that lies between the squamous epithelium and the respiratory epithelium and lines the lateral meatus (3) the ciliated respiratory epithelium that lines the remainder of the nasal cavity anterior and ventral to the olfactory epithelium and (4) the olfactory epithelium (neuroepithelium) that lines the dorsal meatus and ethmoturbinates in the caudal portion of the nose. The relative abundance and exact locations of these upper respiratory epithelium differ among mammalian species. 

The entire nasal cavity is lined by pseudostratilied squamous epithelium with a cover of a thin layer of mucus providing immune and mechanical protection. Cilia beat in the mucus about 1000 times per minute and surface material is moved along at a rate of 3-25 mm/min. This transport is unidirectional and moves mucus and any trapped inhaled particles back toward the nasopharynx, where it is periodically swallowed. Drug delivery to the lung is therefore likely to be markedly reduced in the presence of excess mucous seCTetion. Further details of the anatomy and physiology of the nasal cavity can be found in published reviews (24,29,30). 

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