middle rectal artery (branch of internal iliac artery) supplies mid and lower rectum.
superior rectal artery (terminal branch of inferior mesenteric artery) supplies upper two thirds of the rectum.laterally: sigmoid colon, terminal ileumĪrterial supply to the rectum is formed from an anastomotic submucous plexus derived principally from superior and inferior rectal arteries, and middle rectal artery (if present).posteriorly: presacral fascia, S3-S5, coccyx, median sacral artery, superior rectal vessels, sacral sympathetic chain.female: bladder, ureter, vagina, rectovaginal septum.male: bladder, ureter, prostate, seminal vesicle.The rectum continues on as the anal canal at the level of the coccyx tip, where it takes on an acute inferior angle, the anorectal angle or perineal flexure, as it passes anterior to the sling of the puborectalis muscle where it becomes the anal canal. The lower part of the rectum is dilated and is called the rectal ampulla and there are three semilunar transverse rectal folds (valves of Houston), which project into the rectal lumen. Its upper third is covered by parietal peritoneum anteriorly and laterally, its mid third only anteriorly and its lower third is not covered by peritoneum. If demarcated from a purely gastrointestinal perspective, the rectum extends from the rectosigmoid junction to proximal anorectal sphincter. The taenia coli also flatten and fuse to form an outer longitudinal muscular layer, thus the rectum does not have the distinctive haustra nor epiploic appendages that the rest of the large intestine has. It is also sinuous with three alternating bends when viewed anteriorly. At the level of the S3 vertebral body, the sigmoid colon loses its mesentery and becomes the rectum. As the rectum passes in front of the sacrum, it takes an AP concave shape.
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