Mitotic indices of rat laryngeal epithelia.

The histology and mitotic indices of rat laryngeal epithelia were investigated. Five distinct types of epithelia were found: stratified squamous, squamoid (low squamous), respiratory and two cuboidal forms. Squamous epithelium was present mainly in the cranial portion of the larynx, whereas the respiratory type was mostly located in caudal regions. One type of cuboidal epithelium often formed intermediate zones between squamous and respiratory areas. Another form of cuboidal epithelium lined the ventral pouch, and the vocal folds were covered by a low squamous or squamoid type. The mitotic index for each type of epithelium was calculated using colchicine and was expressed as the percentage of total epithelial cells of that kind in mitosis. Mitotic indices for laryngeal epithelial types were: 5.6% in squamous epithelium; 2.4% in the squamoid epithelium of the vocal folds; 2.2% in the cuboidal epithelium in the ventrolateral region; 1.5% in the cuboidal epithelium of the ventral pouch, and 0.6% in respiratory epithelium, although in isolated ciliated areas in the lower epiglottis it was considerably higher (2.6%). There were no significant differences between rats examined on different occasions.