High speed cinemicrographic studies on rabbit tracheal (ciliated) epithelia: determination of the beat pattern of tracheal cilia.

High speed cinemicrographs reveal that the ciliary configuration and beat pattern of rabbit tracheal cilia differ significantly from classid descriptions, although the basic forward and return pattern is still observed. The tracheal cilia are short and stout (about 6 mum in length) and are of a slightly bent original configuration bent original configuration. At the start of the forward stroke, the cilia bear about 75-90 degrees to the epithelial surface in the direction of the forward stroke. The forward stroke is planar and consists of a simple "bowing" movement, without showing any progressive bending and without changing the original ciliary configuration. The complete forward stroke sweeps through an arc of about 35-40 degrees, with the tips of the cilia penetrating the bottom of the mucous layer through an arc of about 5-8 degrees at the start of each forward stroke. The return stroke starts from close to the epithelial surface and returns to the starting position of the forward stroke by reversing the planer forward pathway at a reduced speed. The stout nature of the cilia, the original bent ciliary configuration, the near vertical starting position of the forward stroke, the extent of the angular sweeps of the strokes, the peculiar "bowing" forward stroke movement, and the nature of the return stroke all serve to enhance efficiency in moving fluid forward. It has been documented that each forward stroke of the tracheal cilia caused and maintains a swift forward movement of the intermediate serous (liquid) layer of the mucociliary system. This movement, in turn, reacts hydrodynamically with the top mucous layer, and together with the clawing action of the tips of the cilia at the start of the forward stroke, causes the mucous layer to move cephalad in the manner of a conveyor belt.