Histological comparison of external anal sphincter between normal human and rat.

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Histological and histochemical comparison was performed between normal human and rat external anal sphincters. Human external anal sphincters had 85.02 % of type 1, 6.64 % of type 2A, 8.28 of type 2B and 0.06 % of type 2C fibers. Type 1 fiber predominance was seen in all human external anal sphincters. In contrast, rat external anal sphincters had only 0.90 % of type 1 and the percentage of type 2A fibers was 98.51 %. Type 2B fibers were not seen in rat external anal sphincters. The mean diameter of type 1 fibers of the human external anal sphincter was 28.2± 9.1 μm, which was significantly smaller than that of other types (p<0.01). There were no differences of the mean diameter among each type of rat external anal shincters. Ragged-red fibers were found in human external anal sphincters, but they were not found in rats. Human external anal sphincters generate resting potentials and are always keeping tonus, but rat external anal sphincters don't, which were thougt to be one of the causes of these differences.
日本大腸肛門病学会の論文