The rectum (: rectums or recta) is the final straight portion of the large intestine in humans and some other , and the gut in others. Before expulsion through the anus or cloaca, the rectum stores the feces temporarily. The adult human rectum is about long,
Structure
The human rectum is a part of the lower gastrointestinal tract. The rectum is a continuation of the
sigmoid colon, and connects to the
human anus. The rectum follows the shape of the
sacrum and ends in an expanded section called an ampulla where
human feces is stored before its release via the
anal canal. An ampulla () is a cavity, or the dilated end of a duct, shaped like a Roman
ampulla. The rectum joins with the sigmoid colon at the level of
sacrum, and joins with the anal canal as it passes through the
pelvic floor muscles.
Unlike other portions of the colon, the rectum does not have distinct taeniae coli. The taeniae blend with one another in the sigmoid colon five centimeters above the rectum, becoming a singular longitudinal muscle that surrounds the rectum on all sides for its entire length.
Blood supply and drainage
The blood supply of the rectum changes between the top and bottom portions. The top two thirds is supplied by the superior rectal artery. The lower third is supplied by the middle and inferior rectal arteries.
The superior rectal artery is a single artery that is a continuation of the inferior mesenteric artery, when it crosses the pelvic brim. It enters the mesorectum at the level of S3, and then splits into two branches, which run at the lateral back part of the rectum, and then the sides of the rectum. These then end in branches in the submucosa, which join with () with branches of the middle and inferior rectal arteries.
Microanatomy
The microanatomy of the wall of the rectum is similar to the rest of the gastrointestinal tract; namely, that it possesses a mucosa with a lining of a single layer of column-shaped cells with mucus-secreting
interspersed, resting on a
lamina propria, with a layer of smooth muscle called muscularis mucosa. This sits on an underlying
submucosa of connective tissue, surrounded by a muscularis propria of two bands of muscle, an inner circular band and an outer longitudinal one. There are a higher concentration of goblet cells in the rectal mucosa than other parts of the gastrointestinal tract.
The lining of the rectum changes sharply at the line where the rectum meets the anus. Here, the lining changes from the column-shaped cells of the rectum to multiple layers of flat cells.
of the rectum of a dog (400×), showing a high concentration of
in amongst the column-shaped lining. Goblet cells can be seen as the circular cells with a clear inner material (
cytoplasm).]]
Function
The rectum acts as a temporary storage site for feces. The rectum receives fecal material from the
descending colon, transmitted through regular muscle contractions called
peristalsis. 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 pass feces, a process called
defecation.
An internal and external anal sphincter, and resting contraction of the puborectalis, prevent leakage of feces (fecal incontinence). As the rectum becomes more distended, the sphincters relax and a reflex expulsion of the contents of the rectum occurs. Expulsion occurs through contractions of the muscles of the rectum.
The urge to voluntarily defecate occurs after the rectal pressure increases to beyond 18 mmHg; and reflex expulsion at 55 mmHg. In voluntary defecation, in addition to contraction of the rectal muscles and relaxation of the external anal sphincter, abdominal muscle contraction, and relaxation of the puborectalis muscle occurs. This acts to make the angle between the rectum and anus straighter, and facilitate defecation.
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.
Forms of
medical imaging used to examine the rectum include CT scans and MRI scans. An ultrasound probe may be inserted into the rectum to view nearby structures such as the prostate.
Colonoscopy and sigmoidoscopy are forms of endoscopy that use a guided camera to directly view the rectum. The instruments may have the ability to take biopsy if needed, for diagnosis of diseases such as cancer. A proctoscope is another instrument that is used to visualise the rectum.
Body temperature can also be taken in the rectum. Rectal temperature can be taken by inserting a medical thermometer not more than into the rectum via the Human 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 and is about above oral (mouth) temperature and about above axilla (armpit) temperature. Availability of less invasive temperature-taking methods including tympanic (ear) and forehead thermometers has facilitated reduced use of this method.
Route of administration
Some medications are also administered via the rectum (). By their definitions, suppositories are inserted, and enemas are injected into the rectum.
Medications might be given via the rectum to relieve constipation, to treat conditions near the rectum, such as fissures or haemorrhoids, or to give medications that are systemically active when taking them by mouth is not possible.
People do not tend to like medications administered by this route because of both cultural issues, discomfort, and issues that may affect the medication working, such as leakage.
Constipation
One cause of
constipation is
faecal impaction in the rectum, in which a dry, hard
stool forms. Constipation is most commonly due to dietary and lifestyle factors such as inadequate
Drinking, immobility, and lack of dietary fibre, although there are many potential causes. Such causes may include obstruction because of narrowing, local disease (such as Crohn's disease, fissures or haemorrhoids), or diseases affecting the neurological control of the bowel, or slow bowel transit time, including spinal cord injury and multiple sclerosis; use of medications such as
opioids, and conditions such as diabetes mellitus, as well as severe illness. High calcium levels and
hypothyroidism may also cause constipation.
Testing may be carried out to investigate the cause. This may include such as biochemistry, calcium levels, thyroid function tests. A digital rectal examination may be performed to see if there is stool in the rectum, and whether there is an obstruction. When symptoms such as weight loss, bleeding through the rectum, or pain are present, additional investigations such as a CT scan may be ordered. If constipation persists despite simple treatments, testing may also include anal manometry to measure pressures in the anus and rectum, electrophysiological studies, and magnetic resonance proctography.
In general however, constipation is treated by improving factors such as hydration, exercise, and dietary fibre. Laxatives may be used. Constipation that persists may require enemas or suppositories. Sometimes, use of the fingers or hand (manual evacuation) is required. Although peristalsis in the colon delivers material to the rectum, laxatives such as bisacodyl or senna glycoside 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.
Inflammation
-
Proctitis is inflammation of the anus and the rectum.
-
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. , the cause is unknown.
Cancer
-
Rectal cancer, a subgroup of colorectal cancer specific to the rectum.
Other diseases
Other diseases of the rectum include:
-
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
-
In the context of mesenteric ischemia, the upper rectum is sometimes referred to as Sudeck'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. Sudeck'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, the rectum is an
erogenous zone and its stimulation or penetration can result in
sexual arousal.
History
Etymology
English
rectum is derived from the Latin
intestinum rectum 'straight gut',
a
calque 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 is the Latinization of ἀπευθυσμένον and
euthyenteron has a similar meaning (εὐθύς 'straight
). Much of the knowledge of the anatomy of the rectum comes from detailed descriptions provided by
Andreas Vesalius in 1543.
See also
Sources
External links
