A 12 cm curved tube in the hollow of the sacrum, ending at the pelvic floor where it becomes the anal canal
Rectum — the last part of the large intestine before the anal canal.
Anatomy · Organs & viscera
Rectum
About 12 cm long
Pelvis · large intestine
The rectum is the final straight-looking segment of the large intestine, about 12 cm long, running from the sigmoid colon at about the level of the third sacral vertebra to the anal canal at the pelvic floor. Despite its name, it is not straight: it follows the curve of the sacrum and has three side-to-side bends that form internal folds. It stores faeces until defaecation, and its lower part widens into the ampulla.
How to spot them
- ▸Follows the curve of the sacrum and coccyx in the back of the pelvis, in front of the lower sacrum
- ▸Three lateral curves, giving three internal transverse folds (valves of Houston), the middle one on the right
- ▸Lacks taeniae coli, haustra and appendices epiploicae; the longitudinal muscle forms a continuous coat
- ▸Peritoneum covers the upper third on the front and sides, the middle third on the front only, and the lower third not at all
What to know
Its interior has three crescentic shelves, the middle one, on the right, being the largest, at the level of the peritoneal reflection
The transverse rectal folds (valves of Houston) of the rectum.
The lower widened portion above the pelvic floor, in which faeces are stored
The rectal ampulla.
In the female the peritoneal pouch in front of it is the lowest part of the peritoneal cavity, named after a Scottish anatomist
The rectouterine pouch (pouch of Douglas), in front of the rectum.
A digital examination can feel, in a man, the prostate in front, and in a woman the cervix
Digital rectal examination — the rectum's anterior relations.
Surgery that removes the fatty package of tissue enveloping it, described by Bill Heald, improved cancer outcomes
Total mesorectal excision for rectal cancer.
Its blood supply from three arteries, and its veins draining to both the portal and systemic circulations, explains haemorrhoids
The superior, middle and inferior rectal vessels — a portosystemic anastomosis at the rectum.
Key ideas
- Its two curves in the sagittal plane, the sacral flexure and the anorectal flexure, and its lateral curves help support the weight of faeces.
- The puborectalis muscle of the pelvic floor pulls the anorectal junction forwards, maintaining the anorectal angle that is important for continence.
Quick-fire facts
- •It is about 12 cm long and begins at the rectosigmoid junction, at about S3.
- •Three lateral curves (the upper and lower convex to the right, the middle convex to the left) give three internal folds: upper and lower on the left wall, middle on the right; a separate front-to-back curve follows the sacrum.
- •In men the rectovesical pouch lies in front; in women the rectouterine pouch (of Douglas), a common site for fluid or pus to collect.
- •The mesorectum is a fatty envelope containing lymph nodes and vessels; total mesorectal excision was popularised by Bill Heald in the 1980s.
- •It has no taeniae coli; the outer longitudinal muscle spreads out to form a continuous layer.
- •The superior rectal artery is a branch of the inferior mesenteric; the middle rectal from the internal iliac; the inferior rectal from the internal pudendal.
- •Waldeyer's fascia attaches the lower rectum to the sacrum.
- •Its lower end joins the anal canal at the anorectal junction, where the puborectalis muscle forms a sling.
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