- "Rectal" redirects here. For the route of administration, see Rectal (medicine).
- For the conic sections see Latus rectum or Semi-latus rectum
The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others. The human rectum is about 12 centimetres (4.7 in) long,  and begins at the rectosigmoid junction (the end of the sigmoid colon), at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used.  Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring (the level of the puborectalis sling) or the dentate line, again depending upon which definition is used.  In humans, the rectum is followed by the anal canal, before the gut terminates at the anal verge.
Role in human defecation
The rectum intestinum acts as a temporary storage site for feces. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to defecate. If the urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed from the feces. If defecation is delayed for a prolonged period, constipation and hardened feces results.
When the rectum becomes full, the increase in intrarectal pressure forces the walls of the anal canal apart, allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincter allow the feces to be passed by muscles pulling the anus up over the exiting feces.
Supports of rectum
- Pelvic floor formed by levator ani muscles.
- Fascia of Waldeyer
- Lateral ligaments of rectum which are formed by the condensation of pelvic fascia
- Rectovesical fascia of Denonvillers, which extends from rectum behind to the seminal vesicles and prostate in front.
- Pelvic peritoneum
- Perineal body
For the diagnosis of certain ailments, a rectal exam may be done.
Suppositories may be inserted into the rectum as a route of administration for medicine.
The endoscopic procedures colonoscopy and sigmoidoscopy are performed to diagnose diseases such as cancer.
Digital Rectal Stimulation, the insertion of one finger into the rectum, is used to induce peristalsis in patients whose own peristaltic reflex is inadequate to fully empty the rectum.
Manual Evacuation is the use of a gloved finger to evacuate faeces from the rectum, and is utilised primarily in acute constipation and also the long-term management of neurogenic bowel, seen most frequently in people with a spinal cord injury or multiple sclerosis.
related article: rectal thermometry
Body temperature can also be taken in the rectum. Rectal temperature can be taken by inserting a medical thermometer not more than 25 mm (1 inch) into the rectum via the anus. A mercury thermometer should be inserted for 3 to 5 minutes; a digital thermometer should remain inserted until it beeps. Normal rectal temperature generally ranges from 36 to 38 °C (97.6 to 100.4 °F) and is about 0.5 °C (1 °F) above oral (mouth) temperature and about 1 °C (2 °F) above axilla (armpit) temperature.
Pediatricians recommend that parents take infants' and toddlers' temperature in the rectum for two reasons:
- Rectal temperature is the closest to core body temperature and in young children, accuracy is critical.
- Younger children frequently do not cooperate when having their temperature taken by mouth (oral), which is recommended for children ages 6 and above as well as adults.
In recent years, the introduction of tympanic (ear) thermometers and changing attitudes on privacy and modesty have led some parents and doctors to discontinue taking rectal temperatures.
Due to the proximity of the anterior wall of the rectum to the vagina in females or to the prostate in males and the shared nerves thereof, rectal stimulation or penetration can result in sexual arousal. For further information on this aspect, see anal sex.
Median sagittal section of male pelvis, showing arrangement of fasciæ
Arteries of the pelvis
Median sagittal section of male pelvis
Median sagittal section of female pelvis
Sagittal section of the lower part of a female trunk, right segment
Cross-section microscopic shot of the rectal wall
Section of mucous membrane of human rectum (60×)
Dog Rectum cross-section (40×)
Dog Rectum cross-section (400×)
- Henry Gray: Anatomy of the human body (Bartleby.com; Great Books Online)
- Eldra P. Solomon - Richard R. Schmidt - Peter J. Adragna : Human anatomy & physiology ed. 2nd 1990 (Sunders College Publishing, Philadelphia) ISBN 0-03-011914-6