The Sphincter mechanism of the urinary bladder and the urethra

Clinical studies of continence in the female and the determination of means to correct incontinence have raised serious questions concerning existing concepts of muscular arrangements in the bladder and the urethra and the presence and action of a sphincter at the vesical neck. Previously there has been a general assumption that the urinary bladder is structured like the gastrointestinal tract with a two layer musculature having circular and longitudinal orientation. The two-part autonomic nervous system has been related to the bladder in terms of activation and inhibition, a common statement being that the parasympathetic fibers are motor to the detrusor and inhibitory to the internal sphincter and the sympathetic innervation motor to the internal sphincter and inhibitory to the detrusor. Evidence for these statements has never been good and recently the results of many diverse studies are leading to an entirely contrary concept of structure and function in these organs. Physiological evidence has not supported the assumptions noted above. In 1933, Denny-Brown and Robertson demonstrated that urination is a reflex act mediated through the centers in the sacral cord and in 1936, evidence adduced by Evans denied any part in vesical function by the sympathetic nerves. Langworthy, Kolb and Lewis ('40) also advanced the opinion that the detrusor muscle is devoid of sympathetic innervation. There is documentation for these statements in other studies and it is now certain that the emptying reflex of the urinary bladder is, like the rectum, completely under the control of the parasympathetic nerves which reach it, the parasympathetic reflex arc being completed by afferent neurons which respond to stretch receptors within the mucosa and submucosa (Langworthy and Murphy, '39). It is now generally recognized that the sympathetic innervation reaches only the representation of ureteral musculature in the trigone of the bladder. It also conducts most of the pain afferents from the bladder. It will be obvious that current concepts of structure in the urinary bladder and urethra do not harmonize with the physiological evidence and there is clearly a need for a re-examination of this area. Is the bladder composed of a nicely layered musculature? Is it equipped with a discrete and separate vesical or internal urethral sphincter and if such a sphincter exists is it antagonistic in action to the detrusor muscle? If one denies a sphincter at the vesical neck, what mechanism is available to keep the orifice closed as urine accumulates and what mechanism holds the orifice open as vesical pressure drops during micturition? To answer these and other questions a study has been conducted on the structure of the bladder and the urethra in both male and female sexes by a combination of gross and microscopic techniques using both canine and human bladders. Stimulation experiments were also conducted on the dog and embryonic specimens were studied. It is traditionally stated that the muscular coats of the bladder are arranged in layers, and inner longitudinal, middle circular, and outer longitudinal layers are frequently recognized. Observations in both dog and man on bladders from which the adventitia was stripped away and which were macerated to reduce the binding power of the connective tissue show that these three traditional layers are far from being complete nor have they been accurately described. General views of the exterior of the bladder (figs. 1, 2) show a number of longitudinal fascicles but