Name = Rectum
GraySubject = 249
GrayPage = 1183
Caption = Anatomy of the anus and rectum
Caption2 = The posterior aspect of the rectum exposed by removing the lower part of the sacrum and the coccyx.
superior rectal artery(1st two-thirds of rectum), middle rectal artery(last third of rectum)
superior rectal veins, middle rectal veins
inferior anal nerves, inferior mesenteric ganglia[GeorgiaPhysiology|6/6ch2/s6ch2_30]
inferior mesenteric lymph nodes, pararectal lymph nodes, internal iliac lymph nodes
MeshName = Rectum
MeshNumber = A03.556.124.526.767
DorlandsPre = r_05
DorlandsSuf = 12697487
The rectum (from the Latin "rectum intestinum", meaning "straight intestine") is the final straight portion of the
large intestinein 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 systemlocated 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, constipationand hardened feces results.
When the rectum becomes full the increase in intrarectal pressure forces the walls of the
anal canalapart 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 sphincterallow the feces to be passed by muscles pulling the anus up over the exiting feces.
For the diagnosis of certain
ailments, a rectal exammay be done.
Suppositories may be inserted into the rectum as a
route of administrationfor medicine.
The endoscopic procedures
colonoscopyand sigmoidoscopyare performed to diagnose diseases such as cancer.
Body temperaturecan also be taken in the rectum. Rectal temperaturecan be taken by inserting a mercury thermometerfor 3 to 5 minutes, or a digital thermometeruntil 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( armpit) temperature.
Many pediatricians recommend that parents take
infantsand 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
privacyand modestyhave led some parents and doctors to discontinue taking rectal temperatures.
Due to the proximity of the anterior wall of the rectum to the
vaginain females or to the prostatein males and the shared nerves thereof, rectal stimulationor penetration can result in sexual arousal. For further information on this aspect, see anal sex.
* - "The Female Pelvis: The Rectum"
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