ABSTRACT
The rectum commences at a point roughly corresponding to the confluence of the tenia coli, at the distal end of the sigmoid mesocolon, usually opposite the third sacral vertebral body. The outer muscular coat of the rectum is composed of longitudinal fibers which thin into a fibromuscular layer at the anus and separates the internal and external sphincters. The rectum is lined by a single layer of columnar epithelium with an abundance of goblet cells and few argentaffin cells. The nerve supply to the upper rectum is via postganglionic sympathetic fibers which run with the inferior mesenteric artery. The lower rectum and anus are supplied by sympathetic fibers from the hypogastric nerves, leaving the pelvic plexus on the lateral pelvic walls. The rectum is insensitive to stimuli producing pain and other somatic sensations, but is sensitive to distension. The anal canal is a short segment extending from the rectum to the anal verge.
