Physiology of the Rectum and Anus

Abstract

The anorectal area is a complex area where autonomic and somatic structures coordinate to maintain continence and to regulate defecation. The fecal bolus entering the rectum is perceived, and by a reflex mechanism, the internal anal sphincter relaxes and allows the content to enter the proximal anal canal, where depending on content and situation conscious relaxation or contraction of the external anal sphincter and puborectal muscle will follow.With anal endosonography or MRI, the integrity of the sphincters and pelvic floor can be established. The physiology of the anus and rectum can be tested with anal manometry. This allows measuring of the anal resting and squeeze pressure. Furthermore, relaxation during attempted defecation and the distention reflex can be observed. The process of defecation can be observed with defecography.