Rectum

Overview

The rectum follows the sacral curve to the pelvic floor. Its outer longitudinal muscle is continuous, and typical colonic haustra and epiploic appendages are absent. Although it lacks a free sigmoid-like mesentery, surrounding mesorectal tissue contains vessels, lymphatics and nerves.

Reference facts

Location

In the posterior pelvis, conventionally from about S3 to the anorectal junction; adult length is approximately 12–15 cm, depending on definition and measurement.

Parts

An upper segment and wider distal ampulla; upper, middle and lower regions are often distinguished by changing peritoneal covering.

Blood supply

Superior rectal artery supplies most of the rectum; variable middle rectal arteries and distal inferior rectal anastomoses contribute.

Innervation

Enteric circuits receive sympathetic modulation and S2–S4 pelvic splanchnic input. Distension is a major sensory stimulus, but sensation is not restricted exclusively to stretch.

Venous/Lymphatic drainage

Superior rectal veins reach the inferior mesenteric/portal system; pelvic rectal veins communicate with systemic circulation. Lymph follows mesorectal and superior rectal routes, with internal iliac drainage from lower regions.

Relations

Sacrum and coccyx lie behind. Anterior relations include bladder base, seminal vesicles and prostate in males, or vagina and uterus in females, separated by tissue planes and peritoneal pouches.

Function

Accommodates feces, signals filling and participates in coordinated defecation.

Frequently asked questions