Peripheral factors in urinary continence.

Urinary continence is dependent upon satisfactory bladder relaxation together with adequate closure of the outflow tract. The former is mainly controlled by the interaction of the cholinergic and adrenergic mechanisms, at both central and peripheral levels. In addition, purinergic nerves, Vasoactive Intestinal Peptide (VIP), and prostaglandins may possibly play a role in the regulation of the detrusor tone. The factors responsible for closure of the outflow tract may be grouped into three local and one extrinsic mechanisms. The distal continence mechanism comprises the peri-urethral pelvic floor striated muscles, which are under somatic neural control. Their function is mainly that of active continence, produced by voluntary contraction. The proximal mechanism is that producing closure of the bladder neck, and is the consequence of the tone and arrangement of the smooth muscle fibres in this region. The intrinsic mechanism acts along the length of the female urethra (or posterior urethra in the male) and is dependent upon the functioning of several constituents of the urethral wall. The tone of both the smooth muscle (lissosphincter) and the striated muscle (rhabdosphincter) in the wall produces a centripetal force which acts upon the inner layers of the urethra, compressing them and producing a hermetic seal. These structures, the mucosa and the cushioning vascular channels in the submucosa, are of particular importance in the female, where they are hormone-sensitive. The extrinsic mechanism consists of the transference of intra-abdominal pressure rises via the wall of the intra-pelvic urethra, assisted by a simultaneous reflex contraction of the pelvic floor, so as to supplement the already existing closure pressure at the moment of stress.(ABSTRACT TRUNCATED AT 250 WORDS)