The rectum performs the function of defecation, the final function of the intestine. It is located in the posterior part of the small pelvis and ends in the perineum.
In men, the prostate gland, the posterior surface of the bladder, the seminal vesicles and the ampoules of the vas deferens are located in front of the rectum. In women, in front of the rectum are the uterus and the posterior vaginal vault. At the back, the rectum lies next to the coccyx and sacrum.
The upper border of the intestine is located at the level of the upper edge of the third sacral vertebra.
Content
Anatomy of the rectum
The rectum is the final section of the large intestine . When it is not filled, longitudinal folds form in the mucous membrane. They disappear when the intestine is distended.
The length of the rectum does not exceed 15 cm. Its upper part is surrounded by three transverse folds. The rectum ends in the anorectal region.
The rectum forms two bends. The sacral flexure is curved toward the spine, and the perineal flexure toward the abdominal wall. There are two sections of the rectum - pelvic and perineal. The border between them is the place of attachment of the levator ani muscle. The pelvic section, located in the pelvic cavity, consists of the supramullary and ampullary sections. The ampullary section has the shape of an ampulla with an expansion at the level of the sacrum. The perineal section of the rectum is also called the anal canal. It opens outward through the anus.
Muscularis
The muscular layer of the rectum is formed by outer longitudinal and inner circular layers. Transverse folds are formed by the circular muscles. The longitudinal layer contains fibers of the levator ani muscles. In the anal canal, 8-10 longitudinal folds are formed, the basis of which is smooth muscle and connective tissue.
The outlet of the rectum is ring-shaped by the muscular external sphincter of the anus (voluntary sphincter). At a distance of 3-4 cm from the anus, the thickening of the circular muscles forms another sphincter (involuntary). At a distance of 10 cm from the anus, the circular muscles form another involuntary sphincter.
Blood supply to the rectum
The blood supply to the rectum is provided by the superior and inferior rectal arteries. The superior rectal artery is a continuation of the inferior mesenteric artery, and the inferior rectal arteries are branches of the internal cava artery.
Thanks to this blood supply, the rectum is not involved in the pathological process during the development of ischemic colitis.
The outflow of blood occurs through the corresponding veins. These veins form plexuses in the wall of the rectum. In the submucosa of the anal canal, at the level of the anal valves, there is cavernous vascular tissue. Recent studies have convincingly proven that it is she who forms hemorrhoids.
The mucous membrane contains single lymphoid nodules and sebaceous glands. At the border of the intestinal mucosa and skin there are sweat glands and hair follicles. The rectal mucosa has good absorption capacity. This quality is used to administer nutritional fluids and medications through the rectum through suppositories, enemas, and irrigations.
Innervation
From the point of view of its functions, the most important part of the smooth muscles of the rectum and anal canal is the internal sphincter. It provides residual pressure in the rectal lumen. The motor activity of this sphincter is inhibited and excited by both the sympathetic and parasympathetic nervous systems.
Functions of the rectum
The rectum has two functions:
- anal continence (accumulation of feces)
- defecation (evacuation of feces).
Anal holding
Violation of the function of holding the intestinal contents of the rectum brings the greatest inconvenience to a person and creates problems of both a social and medical nature.
In its natural position, the internal anal sphincter is always contracted.
It relaxes only when the rectum is stretched. Immediately after stretching the rectum and relaxing the internal sphincter, the rectosphincteric relaxation reflex occurs.
The retention of intestinal contents is a normal condition and is regulated unconsciously.
However, volitional influence on this function is also possible. Retention depends on the interaction of many factors. Chief among them is the consistency of stool in the rectum and colon. No less important is the coordination of the activity of smooth and transverse orbicularis muscles in the area of the anal canal. Of course, the anatomical integrity of all components of this process is necessary.
The smooth muscles of the anal canal, rectum and internal anal sphincter respond to local stimuli and to reflexes transmitted by the autonomic nervous system.
The transverse muscles of the voluntary sphincter are controlled by the centers of the spinal cord and brain. This is carried out by centrifugal and centripetal nerve fibers.
So what has the greatest impact on grip function? It was assumed that this role is shared between the internal and external anal sphincters. However, cutting the internal sphincter only affects gas incontinence. And dissection of the external sphincter also leads to gas incontinence and difficulty in holding large amounts of liquid feces.
It turned out that the holding function is determined mainly by the state of the puborectalis muscle, which maintains the required anorectal angle. When this muscle is damaged, severe fecal incontinence occurs.
Defecation
Defecation is a complex process regulated reflexively. It is divided into two interrelated phases:
- afferent and
- efferent.
In the afferent phase, an urge is formed, and in the efferent phase, feces are released.
The urge to defecate occurs when feces enter the rectum from the sigmoid colon. At the same time, they put pressure on the puborectalis muscle, in which numerous receptors are located. Afferent excitations are transmitted to the cerebral cortex. Here it influences the formation of the urge to defecate; it can be both inhibitory and intensifying the process.
When the urge occurs, feces continue to be retained in the rectum due to the internal and external sphincters. Emptying occurs reflexively and is controlled by an impulse from the central nervous system. If, when the urge occurs, the situation is unfavorable for defecation, then voluntary contraction of the external sphincter causes the pelvic floor to rise, the anorectal angle increases and the feces are forced to rise upward.
Regular inhibition of the defecation process when the urge occurs (volitional inhibition) can lead to disruption of the body's regulatory functions, which in turn will lead to constipation.
The influence of the central nervous system on this process has not been fully studied. Thus, uncontrollable fecal incontinence can occur as an idiopathic phenomenon, but can occur in multiple sclerosis and other diseases of the nervous system.
In older people, constipation may occur due to weakening of the pelvic floor muscles and diaphragm.
Strong emotional stress can cause involuntary relaxation of the internal and external sphincters and lead to a violation of the act of defecation, known as “bear disease”.
An increased frequency of urges can also be caused by the effects of toxic substances on intestinal receptors. In case of various poisonings, this contributes to the accelerated removal of harmful substances from the body.
Diseases of the rectum
Like any human organ, the rectum can have functional diseases and organic lesions. In addition, functional diseases of other parts of the intestine also disrupt the normal functioning of the rectum.
- Infectious diseases and poisoning lead to diarrhea.
- Irritable bowel syndrome can cause both diarrhea and constipation.
- Sphincteritis is an inflammation of the mucous membrane of the sphincters and circular muscles.
- Proctitis is inflammation of the rectum.
- Paraproctitis is inflammation of the tissues around the rectum.
- Hemorrhoids are a disease of the blood vessels of the rectum.
- A diverticulum is a protrusion of the intestinal wall.
- Diverticulosis - multiple diverticula.
- Rectal tenesmus - multiple painful urges to defecate
- Parasitic infections - some types of worms and parasites can live in the rectum.
- Organic lesions include rectal tumors.
- Rectal prolapse.
- Rectal fissure.
What to do to keep your rectum healthy
A small set of rules significantly reduces the likelihood of rectal lesions.
- Maintain hygiene.
- Eat enough fiber, moderate amounts of meat, alcohol, and spicy seasonings.
- Don't overeat at dinner.
- Strengthen the muscles of the pelvis and diaphragm.
- Do a simple exercise every day. Squeeze and relax the muscles of the perineum as many times as you are old.
- Try not to restrain the natural urge to defecate, so as not to disrupt the body’s regulatory mechanisms.
Loading...
