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, before the gastrointestinal tract terminates at the anal verge. The word rectum comes from the Latin rectum intestinum, meaning straight intestine.
Video Rectum
Structure
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 taeniae coli.
The rectum connects with the sigmoid colon at the level of S3, and connects with the anal canal as it passes through the pelvic floor muscles.
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
Microanatomy
Maps Rectum
Function
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, 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.
Clinical significance
Examination
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.
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.
Constipation
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. 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.
Diseases
- 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
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 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
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.
History
Etymology
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 ???????????? ???????, derived from ??????????, to make straight, and ???????, 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 ???????????? ??????? and intestinum rectum are therefore not appropriate descriptions of the rectum in humans. Apeuthysmenon can be considered as Latinization of ???????????? ??????? and euthyenteron has a similar meaning (????? = straight).
See also
- Gastrointestinal tract
- Murphy drip
- Pectinate line
- Rectal prolapse
- Rectal thermometry
References
- Henry Gray: Anatomy of the human body (Bartleby.com; Great Books Online).
- Eldra P. Solomon, Richard R. Schmidt, and Peter J. Adragna: Human anatomy & physiology, 2nd ed. 1990 (Sunders College Publishing, Philadelphia). ISBN 0-03-011914-6.
External links
- 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
Source of article : Wikipedia
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