The problem of anorectal continence.

Anorectal continence depends on the rectum, the muscles of the pelvic floor, and the anorectal sphincters. The function of the rectum is to delay the passage of the intestinal contents by adapting itself to propulsive waves. A pressure gradient in an oral direction allows stool to be pushed back into the more proximal intestinal segments. The puborectalis muscle is the most important muscle of continence because of its sensitivity as well as its motor activity. In contains sensatory receptor organs which trigger off the rectal sphincter reflex mechanism and produce a feeling of fullness. From the motor point of view, its contraction which the assumption of the erect posture will cause the anorectal angle and with it the reflex and voluntary contractions of the puborectalis. The association of reflex and voluntary contractions depends on muscle fibres with different biochemical and histochemical properties. The internal anal sphincter is the most important factor in maintaining the anorectal barrier to pressure at rest. At the same time, relaxation of the internal sphincter will initiate defecation. The ambivalent properties of the internal sphincter can be explained by the different electrical, pharmacological and histological properties of this sphincter. Relaxation depends on an inhibition of electric activities initiated by stimulation of the tension receptors in the parapuborectal tissues and transmitted via the lowest rectal ganglion of the mesenteric plexus to the non-adrenergic inhibiting P-neurons of this sphincter.