Rectum

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Rectum
Retto(anatomia).png
The human colon seen from front. The rectum (red) is near the end of the colon.
Rectum anatomy en.svg
Anatomy of the anus and rectum
Details
Precursor Hindgut
Part of Large intestine
System Gastrointestinal system
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, Deep inguinal lymph nodes
FunctionStore feces prior to defecation
Identifiers
Latin rectum intestinum
MeSH D012007
TA A05.7.04.001
FMA 14544
Anatomical terminology

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, [2] 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. [3] 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. [3] 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.

Contents

Structure

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The rectum lies in front of the sacrum. It lies behind the bladder in males (left), and the vagina and uterus in females (right).

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 an ampulla where feces are stored before their release via the anal canal. An ampulla (from Latin bottle) is a cavity, or the dilated end of a duct, shaped like a Roman ampulla. [4] The rectum joins with the sigmoid colon at the level of S3, and joins with the anal canal as it passes through the pelvic floor muscles. [4]

Unlike other portions of the colon, the rectum does not have distinct taeniae coli. [5] 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. [6] [5]

Blood supply and drainage

The blood supply of the rectum changes between the top and bottom portions. [7] The top two thirds is supplied by the superior rectal artery. The lower third is supplied by the middle and inferior rectal arteries. [7]

The superior rectal artery is a single artery that is a continuation of the inferior mesenteric artery, when it crosses the pelvic brim. [7] 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 (anastamose) with branches of the middle and inferior rectal arteries. [7]


Microanatomy

The microanatomy of the wall of the rectum is similar to the rest of the gastrointestinal tract; [8] namely, that it possesses a mucosa with a lining of a single layer of column-shaped cells with mucous-secreting goblet cells 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. [9] There are a higher concentration of goblet cells in the rectal mucosa than other parts of the gastrointestinal tract. [8]

The lining of the rectum changes sharply at the point where the rectum meets the anus. Here, the lining changes from the column-shaped cells of the rectum to multiple layers of flat cells. [8]

Function

The rectum acts as a temporary storage site for feces. The rectum receives faecal material from the descending colon, transmitted through regular muscle contractions called peristalsis. [10] 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. [10]

An internal and external anal sphincter, and resting contraction of the puborectalis, prevent leakage of faeces (faecal 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. [10]

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. [10]

Clinical significance

The inside of a normal human rectum in a 70-year-old, seen during colonoscopy Rectum-2016-12.jpg
The inside of a normal human rectum in a 70-year-old, seen during colonoscopy
Retroflexed view of the human rectum seen at colonoscopy showing anal verge Rectum-2016-12-hemo.jpg
Retroflexed view of the human rectum seen at colonoscopy showing anal verge
A digital rectal exam is conducted to investigate or diagnose conditions including of the prostate. Digital rectal exam nci-vol-7136-300.jpg
A digital rectal exam is conducted to investigate or diagnose conditions including of the prostate.

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. [11]

Colonoscopy and sigmoidoscopy are forms of endoscopy that use a guided camera to view the rectum. The instruments may have the ability to take biopsies 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 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.[ citation needed ] 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. [12] 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. [13] : 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.

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.[ citation needed ]

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. [14] The anal longitudinal muscle also participates in defecation by everting the anus. [15]

Diseases

Other diseases

Other diseases of the rectum include:

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. [16] The English name straight gut [17] truly expresses the literal meaning of this expression, as Latin rectum means straight, [18] and intestinum means gut. [18] This Latin expression is a translation [19] [20] of Ancient Greek ἀπευθυσμένον ἔντερον, derived from ἀπευθύνειν, to make straight, [21] and ἔντερον, gut, [21] attested in the writings of Greek physician Galen. [19] [20] During his anatomic investigations on animal corpses, Galen observed the rectum to be straight instead of curved as in humans. [19] [20] The expressions ἀπευθυσμένον ἔντερον and intestinum rectum are therefore not appropriate descriptions of the rectum in humans. Apeuthysmenon [22] can be considered as Latinization of ἀπευθυσμένον ἔντερον and euthyenteron [23] has a similar meaning (εὐθύς = straight [21] ). Much of the knowledge of the anatomy of the rectum comes from detailed descriptions provided byn Andreus Vesalius in 1543. [24]

See also

Notes

    Related Research Articles

    Large intestine Last part of the digestive system in vertebrates

    The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored as feces before being removed by defecation.

    Defecation Expulsion of feces from the digestive tract via the anus

    Defecation is the final act of digestion, by which organisms eliminate solid, semisolid, or liquid waste material from the digestive tract via the anus.

    Fecal incontinence Inability to refrain from defecation

    Fecal incontinence (FI), or in some forms encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents both liquid stool elements and mucus, or solid feces. When this loss includes flatus (gas) it is referred to as anal incontinence. FI is a sign or a symptom, not a diagnosis. Incontinence can result from different causes and might occur with either constipation or diarrhea. Continence is maintained by several interrelated factors, including the anal sampling mechanism, and usually there is more than one deficiency of these mechanisms for incontinence to develop. The most common causes are thought to be immediate or delayed damage from childbirth, complications from prior anorectal surgery, altered bowel habits, and receptive anal sex. An estimated 2.2% of community dwelling adults are affected.

    Levator ani Broad, thin muscle, situated on either side of the pelvis

    The levator ani is a broad, thin muscle, situated on either side of the pelvis. It is formed from three muscle components: the pubococcygeus, the iliococcygeus, and the puborectalis.

    Rectal prolapse Medical condition

    Rectal prolapse is when the rectal walls have prolapsed to a degree where they protrude out the anus and are visible outside the body. However, most researchers agree that there are 3 to 5 different types of rectal prolapse, depending on if the prolapsed section is visible externally, and if the full or only partial thickness of the rectal wall is involved.

    Fecal impaction medical condition

    A fecal impaction is a solid, immobile bulk of feces that can develop in the rectum as a result of chronic constipation. A related term is fecal loading which refers to a large volume of stool in the rectum of any consistency.

    Anal canal part of large intestine

    The anal canal is the terminal segment of the large intestine between the rectum and anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of perineum, between the right and left ischioanal fossa. As the final functional segment of the bowel, it functions to regulate release of excrement by two muscular sphincter complexes. The aperture at the terminal portion of the anal canal is known as the anus.

    External anal sphincter

    The external anal sphincter is a flat plane of skeletal muscle fibers, elliptical in shape and intimately adherent to the skin surrounding the margin of the anus.

    Internal anal sphincter Detailed B&W medical cross-section diagram of both internal anal sphincter/rectum tissues.

    The internal anal sphincter, IAS, is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal; its inferior border is in contact with, but quite separate from, the external anal sphincter.

    Proctalgia fugax, a variant of levator ani syndrome, is a severe, episodic pain in the regions of the rectum and anus. It can be caused by cramping of the levator ani muscle, particularly in the pubococcygeal part.

    Superior rectal artery

    The superior rectal artery is an artery that descends into the pelvis to supply blood to the rectum.

    Defecography is a type of medical radiological imaging in which the mechanics of a patient's defecation are visualized in real time using a fluoroscope. The anatomy and function of the anorectum and pelvic floor can be dynamically studied at various stages during defecation.

    Human anus external opening of the rectum

    In humans, the anus is the external opening of the rectum. Two sphincters control the exit of feces from the body during an act of defecation, which is the primary function of the anus. These are the internal anal sphincter and the external anal sphincter, which are circular muscles that normally maintain constriction of the orifice and which relaxes as required by normal physiological functioning. The inner sphincter is involuntary and the outer is voluntary. It is located behind the perineum which is located behind the vagina or scrotum.

    Anismus failure of the normal relaxation of pelvic floor muscles during attempted defecation

    Anismus is the failure of normal relaxation of pelvic floor muscles during attempted defecation. It can occur in both children and adults, and in both men and women. It can be caused by physical defects or it can occur for other reasons or unknown reasons. Anismus that has a behavioral cause could be viewed as having similarities with parcopresis, or psychogenic fecal retention.

    Dyssynergia is any disturbance of muscular coordination, resulting in uncoordinated and abrupt movements. This is also an aspect of ataxia. It is typical for dyssynergic patients to split a movement into several smaller movements. Types of dyssynergia include Ramsay Hunt syndrome type 1, bladder sphincter dyssynergia, and anal sphincter dyssynergia.

    In fecal incontinence (FI), surgery may be carried out if conservative measures alone are not sufficient to control symptoms. There are many surgical options described for FI, and they can be considered in 4 general groups.

    Gastrointestinal wall

    The gastrointestinal wall surrounding the lumen of the gastrointestinal tract is made up of four layers of specialised tissue – from the lumen outwards:

    Human digestive system combination of anatomical organs that are responsible for digestive function

    The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion. Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages. The first stage is the cephalic phase of digestion which begins with gastric secretions in response to the sight and smell of food. This stage includes the mechanical breakdown of food by chewing, and the chemical breakdown by digestive enzymes, that takes place in the mouth.

    Constipation in children refers to the medical condition of constipation in children. It is a functional gastrointestinal disorder.

    Neurogenic bowel dysfunction Human disease involving inability to control defecation

    Neurogenic bowel dysfunction (NBD) is the inability to control defecation due to a nervous system problem, resulting in faecal incontinence or constipation. It is common in people with spinal cord injury (SCI), multiple sclerosis (MS) or spina bifida.

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