Secretory activity of normal middle ear epithelium: Scanning and transmission electron microscopic observations

The normal human middle ear epithelium and Eustachian tube are provided with numerous secretory cells. These cells can be classified by means of their morphologic characteristics. The most common cells are mucigen cells (goblet) with light granules. The less common are the dark granulated cells and mixed granulated cells (light and dark), while the rarest type is the lamellargranulated cell. In mucigen cells, the mode of secretion is through direct expulsion of a single granule by opening up limited cell membranes on contact. In the dark granulated cells, the mode is molecular diffusion, whereas in the mixed granulated cells, the secretion is carried out by the pinching off of the apical portion of the cells.