The colon (Latin colon) is the longest part of the large intestine. Its proper functioning affects our entire body. It is worth finding out how many functions it performs, what is the importance of this part of the digestive tract for our he alth and what are the most common diseases of the colon.

The colon(Latincolon ) is the longest part of the large intestine. The colon is divided into: ascending, transverse, descending and sigmoid. After passing through the ileocecal valve, the contents of the small intestine reach the cecum - the first, small section of the large intestine, and then the colon, then the remains of food go to the rectum, anal canal and are removed from the body. It takes approximately 8 hours for the contents to pass through the colon.

The colon is the final part of the digestive tract, it is primarily responsible for water absorption, its absorption capacity is up to 4.5 liters of water per day.

Interestingly, if necessary, the entire colon can be removed without serious damage to he alth, it is an extensive operation, but is often the only option for patients with severe ulcerative colitis, for example.

In this case, the final section of the small intestine transforms into the structure and function of the large intestine, a process that takes several weeks of course.

The diagnostic and therapeutic abilities in the field of many colon diseases are very large, unfortunately the most dangerous disease - colorectal cancer, still causes many deaths, mainly due to late diagnosis.

Colon - anatomical structure

The colon is about 1.5 meters long and is the longest part of the large intestine. The beginning of the colon is in the lower right abdomen, above the groin, then goes up to the right hypochondrium, this segment isascending colon .

Slightly below the liver it bends (this is the hepatic flexure) and runs below the ribs, this segment istransverse colon .

Further, at the left subcostal area, the colon changes direction again, forming a splenic flexion and descends down to the left iliac fossa, this segment isdescending colon .

It then becomes more sinuous as it descends into the pelvic cavity where it becomesrectum at the level of the third sacral vertebra.

The colon therefore runs around the entire abdominal cavity and, as it were, surrounds the small intestine. The individual sections of the colon were once called consecutively:

  • ascendant
  • cross member
  • descendant
  • esica

This terminology is slowly becoming obsolete, but you can still find it quite often.

From a clinical point of view, it is important that the transverse and sigmoid colon lie intraperitoneally and have their mesentery - the membranous structure on which the intestines hang, and in which the vessels and nerves run.

The remaining sections of the large intestine lie in the so-called retroperitoneal space, i.e. directly on the muscles of the back wall of the abdomen.

The external structure of the colon has several characteristics:

  • greater net - it is a structure made of adipose and connective tissue attached to the colon tapes. The net covers the intestines from the front in such a way that its position is sometimes compared to a curtain. The function of this structure is not certain, it is believed that its purpose is to surround and delimit possible inflammatory processes taking place in the abdominal cavity
  • the large intestine is wider than the thin intestine, with the largest diameter at the beginning and then gradually decreasing
  • colon tapes - these are clusters of smooth muscles that run along the large intestine
  • colon bumps
  • network attachments - i.e. clumps of adipose tissue located along the outer wall of the intestine

Colon - vascularization

The blood vessels reaching the colon come from the superior mesenteric artery and the inferior mesenteric artery, their branches form numerous connections, mainly through the so-called marginal artery running parallel to the large intestine, the vascularization boundary of both arteries is not tight.

It is believed that the ascending and 2/3 transverse colon are supplied mainly by the branches of the superior mesenteric artery: ileo-colonic, anterior and posterior caecum, right and middle colon. 1/3 of the transverse column, the descending and sigmoid colon are vascularized mainly by the branches of the inferior mesenteric artery: the left colon and the sigmoid arteries.

Venous flow takes place through the inferior and superior mesenteric veins, which form the portal vein. Lymph flow from the colon passes through the colonic, superior and inferior mesenteric nodes.

Colon - innervation

The colon contains autonomic nerves and its own so-called intestinal system. In terms of autonomic innervation, the colon is supplied by sensory and motor fibers.

The sympathetic system is the nervesvisceral sacral and pelvic plexus running through the visceral and interdochorial plexus, stimulation of this system slows down peristalsis.

Parasympathetic, on the other hand, the colon supplies the vagus nerve and the visceral pelvic nerves that depart from the spinal cord, the border of their innervation runs further in the transverse colon. The parasympathetic system causes the intestines to contract more, and they both affect the intestinal system.

Colon - microscopic structure of the colon

The wall of the entire digestive tract, including the colon, is made up of four layers:

  • the mucosa is the innermost, covered with cylindrical single-layer epithelium (enterocytes) and goblet cells. The mucosa, unlike the small intestine, does not have villi, but forms so-called crypts. In their structure, goblet cells are especially numerous, whose task is to produce mucus
  • submucosa
  • muscle membrane containing smooth muscles, arranged in two layers - longitudinal and circular. The muscle fibers are distributed irregularly, forming the previously mentioned tapes
  • adventitious or peritoneum - the thin outer film covering the colon

The wall of the colon contains nerve spots: the muscle membrane and the submucosa, which together form the visceral nervous system. The number of neurons that form it is estimated at 100 million. The gut is thought to contain as many nerve cells as the entire spinal cord.

Colon - contraction

The activity of the colon is an individual feature and depends on physical and chemical factors, passing the bowel contents too quickly leads to malabsorption, too slow - to putrefactive processes and constipation.

The aforementioned visceral (intestinal) nervous system is responsible for the functioning of the intestines - it regulates intestinal movements - peristalsis and segmental contractions, and the secretion of both mucus and intestinal hormones.

The perist altic wave that causes the food to move is created as a reflex - a fragment of the intestine stretched by the food stimulates the release of neurotransmitters and stimulates the cells of the intestinal plexus to activate smooth muscle contractions.

In addition, the entire digestive tract contains Cajal interstitial cells, which act as pacemakers - stimulators of the perist altic wave, which thanks to them does not disappear, even if the digestive tract is not full.

Segmental contractions and mass contractions are less important for the function of the colon. The former cause the food to mix, while the latter increase after food consumption and shift the contents of the intestine over large sections.

Bowel movements are not only regulated onby reflex and by the nervous system, but also hormonally by factors produced in the digestive system: motilin, VIP, substance P and others, but also by systemic hormones, e.g. catecholamines.

For proper intestinal perist altic function, proper nutrition is necessary, including the consumption of the right amount of fiber. If it is not enough, movements are weak and the mucous membranes are atrophied, which makes constipation easier.

Scientific reports also say that fiber has a positive effect on the prevention of colon cancer, diabetes and coronary artery disease, the mechanism of this action is unknown.

Colon - Features

The colon has several important tasks:

  • absorption of water and electrolytes
  • compaction of the intestinal contents
  • stool formation
  • slime production
  • is a habitat for gut bacteria

The adaptation to perform the first of these functions is the appropriate structure of enterocytes. They contain numerous energy-producing mitochondria, which ensure that electrolyte transporters function properly against the concentration gradient. Absorption of water occurs secondary to this process, because it "follows" sodium ions.

This process causes the contents of the intestine to thicken and form stool continuously, even from already formed stool, which can lead to solid stools and constipation, so it is important to drink enough fluids and drink regularly. defecate.

Importantly, the epithelium can be transported in both directions. In the state of he alth, it removes some electrolytes, e.g. potassium or bicarbonates, so in the case of diarrhea and acceleration of this process, electrolyte deficiencies may occur.

In the event of poisoning with osmotically active bacterial toxins, water is released into the intestinal lumen following a concentration gradient, which causes diarrhea.

Mucus production is no less important. Its secretion in large amounts is responsible for moisturizing the epithelium, its protection and allows the already concentrated intestinal contents to move.

Intestinal bacteria, dominated byEscherichia coli ,Enterobacter aerogenesand lactic acid bacteria, have several tasks: they produce B vitamins , K, folic acid and short-chain fatty acids, what is more, prevent the development of potentially pathogenic microorganisms. In addition, their metabolism causes the decomposition of undigested food residues in the fermentation process, the products of which soften the stool and, like mucus, facilitate passage.

Interesting productschanges in intestinal bacteria are responsible for both the color of the stool and its smell. Recently, scientific reports indicate a very wide influence of intestinal microorganisms on our body. They are believed to influence, among others, the concentration of cholesterol, the development of the immune system or the growth process.

Despite their positive features, intestinal bacteria are foreign organisms and their development is controlled by the immune system, but in severely weakened conditions and diseases of the digestive system, they may aggravate or develop diseases, such as peritonitis in patients with advanced cirrhosis , anemia, fatty stools or, in extreme cases, sepsis.

Colon diseases: research

Current medicine has many diagnostic tools. In diseases of the colon, both laboratory, functional and imaging tests are performed, depending on the suspected pathology.

There are no colon disease-specific markers for the first group, but the following are often helpful:

  • inflammation markers
  • blood count
  • autoantibodies in so-called inflammatory diseases
  • CEA in colorectal cancer

Functional tests are performed to assess the functioning of the colon, e.g. in the diagnosis of constipation, the time of the intestinal transit is assessed.

In terms of diagnostic imaging, you can perform:

  • X-ray of the abdominal cavity - in suspected obstruction or perforation
  • contrast examination of the gastrointestinal tract - after rectal administration of the contrast medium, a series of X-rays are taken to assess the inside of the colon and the contours of the mucosa. These tests are used in inflammatory diseases and cancers
  • computed tomography - thanks to this examination, you can see the lumen of the colon, its surroundings and neighboring organs. The indications for this test are, among others: cancer, inflammatory diseases, obstruction, perforation, diverticulitis
  • magnetic resonance imaging - less frequently used in colon diseases, mainly due to the fact that tomography better visualizes intestinal lesions
  • Abdominal ultrasound - unfortunately, in the case of colon diseases, it does not provide a reliable diagnosis, because it is very difficult to visualize its entire course. The pathologies may be evidenced by rather indirect symptoms, such as enlargement of the lymph nodes or fluid reservoirs
  • Endoscopy

The location of the colon allows for an accurate diagnosis of its interior, which is extremely important both in the diagnosis and monitoring of diseases, as well as in screening.

In terms of colon endoscopy performedare:

  • rectoscopy (rectal examination)
  • rectosigmoidoscopy (examination of the rectum and sigmoid colon)
  • colonoscopy, which allows you to see the inside of the entire colon and cecum

Due to the availability of the examination, low risk of complications, therapeutic possibilities and high diagnostic accuracy, endoscopic examinations are so common.

Such diagnostics is performed after proper preparation of the patient - emptying the entire intestine or its part with the use of oral agents and enemas.

Rectoscopy and rectosigmoidoscopy are performed in diseases of the anus and sigmoid colon, e.g. in the anal fissure or the presence of foreign bodies.

The broadest indications are for colonoscopy, including:

  • colorectal cancer screening
  • suspected cancer
  • unexplained anemia
  • diagnosis and monitoring of Crohn's disease and ulcerative colitis

Colonoscopy can also be used as a therapeutic tool for polyps or bleeding.

Colon - diseases

Symptoms of colon diseases can be:

  • stomach pains
  • nausea and vomiting
  • diarrhea
  • constipation

Irritable bowel syndrome- manifested by discomfort, abdominal pain and a change in the rhythm of bowel movements, symptomatic relief after defecation. Irritable bowel syndrome also applies to the small intestine, it is a common disease of unknown cause, so far, infectious and psychological factors are suspected. The disease, although it can be troublesome and difficult to cure, does not have serious consequences.

Hirschprung's diseaseis a congenital defect in which no nerve spots of the intestinal tract are formed, hence no perist altic wave is produced. Depending on how long the colon is damaged, newborns do not give up meconium at all, or there is a delay in defecation and bloating. Imaging studies show a narrowing of the diseased section and a significant widening of the intestine before.

Large intestine diverticulamost often refer to the sigmoid colon, they are a kind of "pockets" - a bulging of the mucosa through the muscle membrane (acquired diverticula) or the entire intestinal wall (congenital diverticula). Usually they are asymptomatic, but in 20% they cause pain and change the rhythm of bowel movements, in the case of complications (inflammation, abscess, fistulas), obstruction and haemorrhage may occur.

IBD-Crohn's diseasei ulcerative colitis . These are diseases of unexplained etiology, in their course the inflammatory process affects the wall of the colon, but it can also affect other parts of the gastrointestinal tract, the spectrum of symptoms of these diseases is very wide. Treatment is based on inhibiting inflammation and sometimes immunosuppression, and in the event of complications, surgery is often required.

Ischemic colitismost often affects the descending colon and splenic flexion, it is a disease caused by a blood flow disorder and manifests itself with pain and bleeding.

Microscopic colitisit is a histopathological diagnosis, there are no changes in the image of the intestine in imaging tests, laboratory tests and endoscopy. Ailments caused by this disease include: diarrhea, cramping abdominal pain, gas and weight loss.

Colon polyps- these are protrusions of the mucosa into the lumen of the intestine, their origin is diverse, the diagnosis is most often accidental, made during colonoscopy. Polyps most commonly found in the colon:

  • adenomas - a growth of deformed epithelial cells, they are neoplasms;
  • juvenile polyps - single, non-neoplastic protrusions of the mucosa, being a cluster of improperly located tissues;
  • inflammatory polyps - most often in inflammation of the large intestine;

In the case of numerous polyps, genetic diseases are often the cause, such as :

  • familial polyposis
  • juvenile polyposis
  • Peutz and Jeghers team

Colorectal canceris one of the most common cancers in Poland, and the mortality rate is very high - it ranks second among the causes of cancer deaths. It is most commonly located in the sigmoid colon, causing bleeding, anemia, and changes in bowel movements. The prognosis for cure depends primarily on the stage of advancement, which is why it is so important to perform screening colonoscopy after the age of 50, which enables early diagnosis.

Idiopathic constipationdoes not have a specific causative factor or pathology that causes it. The reasons may be defecation disorders, digestive tract disorders, most of them are not colon disorders. Only one of the subtypes - colon inertia, which occurs in about 25% of cases, is caused by inappropriate function of this organ - too slow passage.

Diarrheacan be caused by diseases of the small and large intestines. The role of the colon inin this case, it consists in insufficient absorption of water contained in the intestinal contents or its release into the lumen, if there are osmotically active substances, it may be due to the presence of toxins, diseases of the earlier parts of the gastrointestinal tract or the colon itself.

Bleeding from the lower gastrointestinal tractis both haemorrhage and passing stool mixed with blood, it is always a disturbing symptom, but its causes may be harmless, such as haemorrhoids . However, it should always be checked as other colon diseases causing bleeding include infections, inflammatory bowel disease, polyps, and tumors.

Gastrointestinal obstructionin the colon is most often caused by a tumor that blocks the passage or entrapment of the sigmoid in a hernia. The symptoms of this condition are stomach pain, nausea and vomiting, and stool retention. Such a condition is life threatening and requires immediate surgical treatment.

Category:

Gastrology