Morphological distribution of middle-ear epithelium in the Wistar rat: a functional hypothesis.

The authors studied the overall microscopical anatomy of the middle ear and of the eustachian tube in 20 tympanic bullae of 10 Wistar rats. Large hexagonal epithelial flat cells covered the roof of the bulla, the two upper thirds of both lateral walls, the upper half of the eustachian tube, and the upper third of the tympanic orifice; ciliated and secretory cells lined the inferior thirds of both walls of the bulla while a ciliated epithelium with strong cilia, all directed towards the tubal orifice, located on the floor of the tympanic cavity together with groups of non-ciliated cells was detectable near the tubal and antral areas and on the floor of the eustachian tube. Non-ciliated cells covered by microvilli were found near the pharyngeal orifice. These observations seem to demonstrate the following: (1) the ciliated elements present a well-defined topographic distribution; (2) a preferential pathway for mucociliary clearance made up of strong ciliated cells located on the floor of the bulla is clearly detectable, and (3) the roof of the bulla seems to be mainly involved in the ventilatory function.