(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, terminating in the anus
. The human rectum is about 12 cm long. At its commencement its caliber is similar to that of the sigmoid colon
, but near its termination it is dilated, forming the rectal ampulla
Role in human defecation
The rectum intestinum acts as a temporary storage facility 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. 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.
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.
can also be taken in the rectum. Rectal temperature
can be taken by inserting a mercury thermometer
for 3 to 5 minutes, or a digital thermometer
until it "beeps", not more than 25 mm (1 inch) into the rectum via the anus
. Due to recent concerns related to mercury poisoning
, the use of mercury thermometers is outlawed. 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 axillary
Many pediatricians recommend that parents take infants and toddler's temperature in the rectum for two reasons:
- (1) Rectal temperature is the closest to core body temperature and in children that young, accuracy is critical.
- (2) Younger children are unable to cooperate when having their temperature taken by mouth (oral) which is recommended for children, ages 6 and above and for adults.
In recent years, the introduction of ear (tympanic) 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
- - "The Female Pelvis: The Rectum"