The normal protective mechanism of the lower respiratory tract consists of the (1) mucous secretion, (2) ciliary action, (3) cough reflex and (4) phagocytosis.
PROTECTIVE MECHANISM OF THE TRACHEA AND BRONCHI
Mucous Secretion.—There are two sets of glands producing mucus in the trachea and bronchi: (a) the goblet cells which are distributed in the mucosa, being more numerous in the larger bronchi than in the trachea, but diminishing in number as the bronchi diminish in diameter and finally disappearing in the bronchioli 0.4 mm. in diameter1 and (b) the acini of the secretory glands within the tunica propria, which are serous, mucous or mixed. The rate, quality and quantity of secretion appear to be vastly different under varying conditions. Hill2 showed, on the excised trachea, that mucous secretion evidences a remarkable power to enmesh small foreign bodies. Larsell3 noted that the stimulation
HARA HJ. ORGANIC FOREIGN BODIES IN THE BRONCHI: REACTION OF LUNG TISSUE IN RABBITS. Arch Otolaryngol. 1934;20(4):549–569. doi:10.1001/archotol.1934.03600040105008
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