rectums

The rectums are the final straight portions of the large intestine, connecting the sigmoid colon to the anal canal. In humans, the rectum extends about 12 to 15 centimeters and sits within the pelvic cavity. The upper rectum is covered by peritoneum on its anterior and lateral surfaces; the middle rectum has partial peritoneal coverage; the lower rectum lies largely below the peritoneal reflection and is subperitoneal.

Anatomically, the rectum begins at the level of the third sacral vertebra (S3) and ends at the anorectal junction, where the mucosa transitions from simple columnar epithelium to stratified squamous epithelium in the anal canal. The rectum serves as a storage site for feces before defecation and contains folds and the rectal ampulla, which distends during filling.

Vascular supply arises mainly from the superior rectal artery (a branch of the inferior mesenteric artery), with smaller contributions from the middle and inferior rectal arteries (branches of the internal iliac arteries). Venous drainage mirrors this pattern: superior rectal veins drain to the portal system via the inferior mesenteric vein, while middle and inferior rectal veins drain to the systemic circulation via the internal iliac veins. Lymphatics drain to inferior mesenteric and internal iliac nodes. Innervation includes parasympathetic fibers from the pelvic splanchnic nerves and sympathetic fibers via the hypogastric plexus; the external anal sphincter, supplied by the pudendal nerve, provides somatic control.

Clinical relevance includes hemorrhoids, rectal cancer, inflammatory conditions such as proctitis, and rectal prolapse. Diagnosis commonly uses colonoscopy or sigmoidoscopy, with biopsy as indicated. Note that rectums is the common plural form in English, though recta is used in some anatomical contexts.