rectum

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For the conic sections see Latus rectum or Semi-latus rectum

Rectum
Anatomy of the anus and rectum
Posterior aspect of rectum exposed by removing lower part of sacrum and coccyx
Gray's	subject #249 1183
Artery	superior rectal artery (first two-thirds of rectum), middle rectal artery (last third of rectum)
Vein	superior rectal veins, middle rectal veins
Nerve	inferior anal nerves, inferior mesenteric ganglia[1]
Lymph	inferior mesenteric lymph nodes, pararectal lymph nodes, internal iliac lymph nodes
Precursor	Hindgut
MeSH	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, terminating in the anus. The human rectum is about 12 cm long.^{[citation needed]} Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, 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.^{[citation needed]}

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.

Medical procedures

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.

Temperature taking

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. 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 axilla (armpit) temperature.^{[citation needed]}

Many^[who?] pediatricians recommend that parents take infants' and toddlers' temperature in the rectum for two reasons:

1. Rectal temperature is the closest to core body temperature and in young children, 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 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.^{[citation needed]}

Sexual stimulation

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.

Additional images

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  Blood vessels of the rectum and anus  Organs of the female reproductive system  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×)

See also

• Gastrointestinal tract
• Murphy drip
• Pectinate line
• Rectal prolapse

References

External links

• Cross section at UV pembody/body15a
• Cross section at UV pelvis/pelvis-e12-15
• SUNY Anatomy Image 7808
• SUNY Labs 43:11-0101

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