Anatomic basis of micturition and urinary continence. Muscle systems in urinary bladder neck during ageing.

Dorschner et al have described the unique function and form of several different muscle systems of the urinary bladder neck. If these systems have different functional responsibilities, then the muscles must undergo different ageing processes, as stated in the theory of function-dependent ageing. One characteristic of histologic ageing is the change over time in the proportion of muscle cells to connective tissue, a phenomenon we have demonstrated in both the ciliary muscle and in the two muscle systems of the small intestine. Using an SIS-Image Analysing System, we have now measured automatically the ratios of muscle cells to connective tissue in sections from several regions of the urinary bladder neck, taken from 50 male and 15 female cadavers. Our results confirm new functional explanations of the different muscle systems in the bladder neck. The relative volume of muscle cells in both the sphincter trigonalis m. and the dilator urethrae m. diminishes continuously with age. In the ejaculatorius m., however, the volume of muscle cells first increases until beginning at the end of the third decade, it decreases until senescence. As was presumed, the proportion of muscle cells in the detrusor vesicae m. does not decline during the later decades. The volume of muscle cells and fibers in both urethral sphincter muscles, however, decreases with age, beginning in early childhood.