[Electron microscopic observations of the porcine middle ear--normal cases]

Pigs are frequently used in basic studies of the middle ear because they have a middle ear air cell system which resembles the human mastoid air cell system. However, the morphology of epithelial cells of the middle ear of pigs has not been thoroughly studied. In this study, the morphological features of the mucosal epithelium of the normal porcine middle ear from juveniles to adults were investigated by scanning and transmission electron microscopy. The features were compared with the mucosal epithelium of the human middle ear. Macroscopic observation of the resected middle ears showed all normal. The mucoepithelial cells of the normal porcine middle ear consisted of ciliated cells, non-ciliated cells, secretory cells and basal cells. Ciliated cells were distributed most densely in the Eustachian tube and tube orifice of the middle ear cleft, decreasing in number towards the air cell system, where no ciliated cells were found. The distribution of secretory cells was similar to that of ciliated cells, while non-ciliated cells distributed conversely. Ciliated cells of juvenile pigs had 40 to 100 cilia 5 to 6 mu in length and 0.2 to 0.3 mu in thickness and microvilli on the cell surface. On the other hand, pigs 4 weeks old or older, had ciliated cells with 80 to 100 cilia 5 to 8 mu in length and 0.3 to 0.4 mu in thickness. Younger pigs had a smaller range of ciliated cell distribution. The range increased with growth, and rapidly expanded by 2 weeks after birth; then the expansion slowed down to 4 weeks, when the distribution was similar that in maturity.(ABSTRACT TRUNCATED AT 250 WORDS)