Rectum
|
The posterior aspect of the rectum exposed by removing the lower part of the sacrum and the coccyx. |
The
rectum (from the
Latin verb regere "to straighten, correct, rule" hence the rectum is "that which is ruled, controlled") is the final
straight portion of the
large intestine in some
mammals, and the
gut in others, terminating in the
anus.
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.
Body temperature 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 now discouraged. Normal rectal temperature generally ranges from 97.6 to 100.4 °F (36 to 38 °C) and is about 1 °F (0.5 °C) above oral (mouth) temperature and about 2 °F (1 °C) above axillary (armpit) temperature. On average, the rectal temperature is 0.7 °F (0.4 °C) higher than oral temperature. 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.
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Anatomy of the anus and rectum |
The rectum ampulla 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 is 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.
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 can result in
sexual arousal. For further information on this aspect, see
anal sex.
*
Gastrointestinal tract*
Rectal prolapse*
Latus rectum (conic section)
*
Semi-latus rectum
