The human colon seen from front. The rectum (red) is near the end of the colon.
Anatomy of the anus and rectum
|Part of||Large intestine|
|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|
|Lymph||Inferior mesenteric lymph nodes, pararectal lymph nodes, internal iliac lymph nodes, Deep inguinal lymph nodes|
The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult 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 which is about 4 centimetres (1.6 in) long, before the gastrointestinal tract terminates at the anal verge. The word rectum comes from the Latin rectum intestinum, meaning straight intestine.
The rectum is a part of the lower gastrointestinal tract. The rectum is a continuation of the sigmoid colon, and connects to the anus. The rectum follows the shape of the sacrum and ends in an expanded section called the rectal ampulla, where feces are stored before their release via the anal canal. An ampulla is a cavity, or the dilated end of a duct, shaped like a Roman ampulla.
Unlike other portions of the colon, the rectum does not have distinct taeniae coli.: 397 The taeniae blend with one another in the sigmoid colon five centimeters above the rectum, giving rise to a layer of longitudinal muscle that surrounds the rectum on all sides for its entire length.
Supports of the rectum include:
- Pelvic floor formed by levator ani muscles.
- Waldeyer's fascia
- 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
Inner diameters of different sections of the large intestine, with rectum near rectal/sigmoid junction measuring on average 5.7 cm (range 4.5-7.5 cm).
The rectum 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 (if the internal and external sphincters are relaxed) 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. Although peristalsis in the colon delivers material to the rectum, laxatives such as bisacodyl or senna that induce peristalsis in the large bowel do not appear to initiate peristalsis in the rectum. They induce a sensation of rectal fullness and contraction that frequently leads to defecation, but without the distinct waves of activity characteristic of peristalsis. The anal longitudinal muscle also participates in defecation by everting the anus.
For the diagnosis of certain ailments, a rectal exam may be done. These include faecal impaction, prostatic cancer and benign prostatic hypertrophy in men, faecal incontinence, and internal haemorrhoids.: 179–180
A colonoscopy or sigmoidoscopy are forms of endoscopy that use a guided camera to view the rectum. These may have the ability to take biopsies if needed, and may be used to diagnose diseases such as cancer.
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 (96.8 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. In recent years, the introduction of non-invasive temperature taking methods including tympanic (ear) and forehead thermometers, and changing attitudes on privacy and modesty have led some parents and doctors to discontinue taking rectal temperatures.
Route of administration
By their definitions, suppositories are inserted, and enemas are injected, via the rectum. Both of these may be used for the delivery of drugs or to relieve constipation; enemas are also used for a variety of other purposes, medical and otherwise.
One cause of constipation is faecal impaction in the rectum, in which a dry, hard stool forms. Manual evacuation is the use of a gloved finger to evacuate faeces from the rectum, and, after the application of stool softeners, is utilised in acute constipation.: 914 It is also in the long-term management of neurogenic bowel, seen most frequently in people with a spinal cord injury or multiple sclerosis. Digital rectal stimulation, the insertion of one finger into the rectum, may be used to induce peristalsis in patients whose own peristaltic reflex is inadequate to fully empty the rectum.
- Proctitis is inflammation of the anus and the rectum.
- Rectal cancer, a subgroup of colorectal cancer specific to the rectum.
- Rectal prolapse, referring to the prolapse of the rectum into the anus or external area. This is commonly caused by a weakened pelvic floor after childbirth.
Other diseases of the rectum include:
- Ulcerative colitis, one form of inflammatory bowel disease that causes ulcers that affect the rectum. This may be episodic, over a person's lifetime. These may cause blood to be visible in the stool. As of 2014[update] the cause is unknown.
- In the context of mesenteric ischemia, the upper rectum is sometimes referred to as Sudak's point and is of clinical importance as a watershed region between the Inferior mesenteric artery circulation and the Internal iliac artery circulation via the Middle rectal artery, and thus prone to ischemia. Sudak's point is often referred to along with Griffith's point at the splenic flexure as a watershed region.
Society and culture
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.
English rectum is derived from the full Latin expression intestinum rectum. The English name straight gut truly expresses the literal meaning of this expression, as Latin rectum means straight, and intestinum means gut. This Latin expression is a translation of Ancient Greek ἀπευθυσμένον ἔντερον, derived from ἀπευθύνειν, to make straight, and ἔντερον, gut, attested in the writings of Greek physician Galen. During his anatomic investigations on animal corpses, Galen observed the rectum to be straight instead of curved as in humans. The expressions ἀπευθυσμένον ἔντερον and intestinum rectum are therefore not appropriate descriptions of the rectum in humans. Apeuthysmenon can be considered as Latinization of ἀπευθυσμένον ἔντερον and euthyenteron has a similar meaning (εὐθύς = straight).
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- Blue Histology
- Cross section image: pembody/body15a—Plastination Laboratory at the Medical University of Vienna
- Cross section image: pelvis/pelvis-e12-15—Plastination Laboratory at the Medical University of Vienna
- Anatomy image:7808 at the SUNY Downstate Medical Center
- Anatomy photo:43:11-0101 at the SUNY Downstate Medical Center