Colon, Rectum and Anal Canal

The rectum and anal canal are the most terminal parts of the lower GI tract/ large intestine. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal.
The rectum and anal canal are the most terminal parts of the lower GI tract/ large intestine that form a functional unit and control defecation Fecal incontinence can occur if this function is disturbed. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Peristaltic waves within the rectal muscularis, involuntary relaxation of the internal anal sphincter (controlled by the ANS), and voluntary relaxation of the external anal sphincter (controlled by the cerebral cortex) are essential for defecation to occur. The rich plexus of veins surrounding the anal canal can develop into hemorrhoids if dilated.