The physiology of micturition and its disorders are the subject of much confusion. While some believe that the internal sphincter is the primary urethral sphincter [l], Dixon and Gosling [2] have proved that the rhabdosphincter is the primary sphincter in both sexes. The bands of smooth muscle on either side of the bladder neck and the sympathetic nerve which supplies to the bladder play no role in micturition. Their main function is to prevent reflux of semen into the bladder during ejaculation [3,4].We present a new concept to explain the act of micturition and continence. Urinary continence depends mainly on the presence of an intact sound internal sphincter and on an acquired behavior which maintains a high sympathetic activity learned in early childhood. The internal sphincter lies at the bladder neck in the female and at the apex of the prostate in the male. It is supplied by the sympathetic nerves TlO-L2. Histopathological studies were carried out on two types of specimens, surgical and postmortem. During surgical repair l Corresponding author. of pelvic floor prolapse in 25 patients not suffering from stress incontinence 2-3 mm of tissue were taken from the bladder neck. In addition, 25 postmortem specimens of bladder, urethra, uterus and upper vagina in females, and bladder, prostate and membranous urethra in males were examined. Gross and microscopic examination showed that the internal sphincter is composed of a dense sheet of collagenous and elastic tissues extending from an inner mucosa outwards in a concentric arrangement. The mucosa lies on the lamina propria which helps keep the mucosa coapted. There is then a layer of smooth muscle fibers lying on and intermingled with the dense collagenous and elastic tissues which extend beyond the muscle layer in a concentric arrangement. The collagen and elastic tissues give the internal sphincter wall the high tension needed for the high urethral closing pressure, while the muscle layer supplied by the sympathetic nerves is the key to closure and relaxation (Fig. 1). From training early in childhood, together with fear of punishment and of embarrassment, normal subjects maintain a high sympathetic activity thus keeping the internal sphincter closed. This ac-0020-7292/96/$15.00 0 1996 International Federation of Gynecology and Obstetrics SSDI 0020-7292(95)02620-R
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