| Description |
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The middle ear cavity is lined in its posterior half with a flat pavement epithelium which is similar in appearance to the mucoperiosteum of the mastoid air cells. The anterior half of the middle ear cavity is lined by a mucociliary (respiratory) type of epithelium.
This epithelium contains two types of mucus producing cells: the goblet cells which are located in the epithelial layer, and the seromucinous glands which are located in the subepithelial layer. The eustachian tube is lined with a similar type of respiratory epithelium, but contains a greater abundance of subepithelial mucous glands.
The mucus produced by these glands serves as a protecting and lubricating mantle for the mucoperiosteum which is exposed to air. It also acts as a coupler for the translation of the waving action of the beating cilia into a unidirectional mechanical clearance. The metachronous ciliary beat can only be translated into effective clearance by the interaction with and in the presence of a normal mucous blanket. The mucous blanket is pulled along the surface by the active (forward) phase of the ciliary beat, and carries with it any debris deposited upon it.
This normal ciliary action causes a layer of mucus to flow toward the tympanic opening of the eustachian tube.
It should be noted that the tympanic orifice of the eustachian tube is located above the floor of the middle ear, and consequently, the clearance of mucus from the middle ear into the tube cannot occur by gravity alone; the mucus must be carried up to the tube by active ciliary movement. |
