| Abstract: | Knowledge of nasal physiology and function is necessary for a proper comprehension of nasal symptoms; a short introduction on this topic follows. It is an important task for the nose to filter, humidify and warm the inhaled air. The shape of the nasal cavity and the structure of the nasal lining seem particularly well suited for this purpose. The narrow inlet to the airway (the internal ostium), the bend of the airflow in the nasopharynx and the slit-like cavity provide for effective sedimentation of practically all particles, larger than 10μm, and also of some smaller particles (2–3 μm).1 Foreign particles deposited in the nasal filter, contact the local immune system. The airway mucosa is equipped with a secretory IgA immune system, which may help to render deposited micro-organisms harmless,2 but also IgE producing cells are found in the mucous membrane and in the regional lymph nodes.3 Therefore, the constant sedimentation in the nose of potent allergenic substances (pollen, animal dander, house dust mite) and the consequent risk of allergic rhinitis is a price which has to be paid for nasal filtration and protection of the lower airways against unconditioned ambient air. The nose is also designed for heating and humidification of the inhaled air. Again the slitlike shape of the cavity is of decisive importance, as the intimate contact between the mucosal surface and the inhaled air is necessary for rapid supply of water and heat to the air the nasal cavity. Normally the air passes the nose at a speed of 2 m/sec.4 The numerous seromucous glands,5 some anterior serous glands6 and subepithelial capillaries of the fenestrated type7 form the basis for the supply of 500 ml water a day to the inspired air.8 The venous sinusoids seem especially designed for maintenance of a slit-like nasal cavity, so important for normal function. More than half of the nasal blood flow is shunted through an abundance of arterio-venous anastomoses.9 A comparison with hot water running in a radiator illustrates the importance of this arrangement for heating of the inspired air. |
