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Rectum
Gray's Anatomy (1918) plate, public domain
The rectum is the final straight section of the large intestine, about 12 cm long, lying in the pelvis in front of the sacrum. It stores stool before defecation: as it fills, stretch receptors signal fullness to the brain. Its lower end widens into the ampulla and narrows into the anal canal. Rich veins around it and muscle slings from the pelvic floor help keep it closed at rest.
Key facts
- The rectum is normally empty until just before a bowel movement fills it from the sigmoid colon.
- Its stretch receptors distinguish gas from liquid and solid through subtle sampling by the anal canal.
- It follows the curve of the sacrum, a relation that matters for examinations and surgery.
- Absorbed medicines given as suppositories partly bypass the liver via its lower veins.
What can go wrong
The rectum is affected by inflammation (proctitis, including from ulcerative colitis), by rectal cancer — often signalled by bleeding or a feeling of incomplete emptying — and by prolapse, where its wall slides down through the anus. Bleeding from the rectum is common from haemorrhoids but any persistent bleeding or change in habit warrants examination and often camera investigation.
Related conditions
Related procedures & tests
Related symptoms
Related muscles
Watch: related videos
Frequently asked questions
What does a rectal examination involve?
A gloved, lubricated finger assesses the anal canal, prostate in men and the lower rectum for lumps, blood and stool; it is quick and gives information no scan fully replaces.
Why do doctors ask about a feeling of incomplete emptying?
Tenesmus — the sensation that the rectum is still full after passing stool — suggests rectal inflammation or a mass and is a symptom clinicians take seriously.
Educational information only. This atlas explains normal anatomy and describes conditions in general terms; it is not medical advice and does not replace assessment by a qualified clinician. If you have symptoms that worry you, seek medical care.
