Large intestine – structure, functions, the most common diseases. How to care for the large intestine?

The large intestine is a long organ connected to the small intestine on one side and to the anus on the other. It is divided into three parts: caecum, colon and rectum. The partially digested food passes through the cecum to the colon, where water, some nutrients and electrolytes are removed. The remaining material, a solid waste called stool, travels through the colon, is collected in the rectum, and leaves the body through the anal canal and anus.

Large intestine – structure

Large intestine (lat. intestine) is the last part of the gastrointestinal tract, the long, tube-like path that food travels through the digestive system. It starts in the small intestine and ends in the anal canal where food debris leaves the body. The large intestine is where food waste is formed into stools, stored and eventually excreted. The large intestine includes the caecum, colon and rectum.

The large intestine is one long tube, but slightly different things happen in different parts of it, and this is how the large intestine is divided into:

1. cecum (lat. cecum, blind man) also known as the cecum, it is the widest part of the large intestine. This is the reservoir where food reaches the small intestine. When the cecum is full, the muscles of the colon begin to move. Takes part in the absorption of water and electrolytes.
2. colon (lat. colon) consisting of several parts. First, the food reaches the ascending colon (Latin. ascending colon), it moves up and eventually sideways through the transverse colon (lat. transverse colon). These segments surround the small intestine, which coils inside. The remaining water and electrolytes are absorbed in the ascending colon (Latin. descending colon) and transverse, so that the food debris that reaches the descending colon is mostly solid. The colon secretes mucus to bind and lubricate food debris to help them move through dehydration smoothly. Eventually, the food debris ends up in the sigmoid colon (Latin sigmoideum) before they travel further and are excreted from the body.
3. rectum (lat. right) also known as the rectum or the rectum, which receives undigested food material from the colon. The rectum holds the stool until it cannot be removed from the body. Stool consists of indigestible matter and dead cells shed from the intestinal lining, along with small amounts of mucus and water. If approximately 500 ml of liquid food enters the colon, approximately 150 ml will remain as stool. When the stool enters the anus, it triggers the urge to have a bowel movement. It is a natural continuation of the colon’s muscle movements.

When it comes to the structure of the large intestine, we cannot forget about the anus. The large intestine opens out through a single opening called the anus (Latin. anus). The anus is the channel through which the stool passes to leave our body. It is closed on each side by a muscle sphincter. Inside, the sphincter opens automatically to let the poo pass through. The external sphincter is the one we control to defecate when we’re ready. When the stool in the rectum triggers the urge to have a bowel movement, nerve signals cause the internal sphincter to relax. This is a tip to find a toilet in time.

The large intestine is separated from the small intestine by an ileocecal valve (Latin. ileocecal valve, Bauhini valve).

The large intestine is assumed to be about 1,5 meters long, and the colon is its longest part. The remaining parts, i.e. the cecum, rectum and anus, are much shorter, only a few centimeters long. As for the diameter of the large intestine, it is larger than the diameter of the small intestine and is approximately 7,6 centimeters wide.

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What tissues make up the large intestine?

The large intestine is made up of four layers of tissue, like other parts of the digestive tract. They include:

1. mucosa (gr. mucous membrane) or the mucosa is the innermost layer and is made of straight, cylindrical epithelial tissue which makes it smooth (compared to the small intestine, which has villi, small finger-like projections). Many glands secrete mucus into the inner lumen of the large intestine, which lubricates its surface and protects it from abrasive food particles.
2. the submucosa (Latin. tunica submucosa) the so-called The submucosa is the layer of blood vessels, nerves, and connective tissue that supports the other layers of your colon. It surrounds the mucosa.
3. the muscle membrane (lat. muscular plate) also known as the myositis, it surrounds the submucosa and contains many layers of visceral muscle cells that contract and carry waste products through the colon in a process known as peristalsis.
4. the serosa (Latin. silky tunic) it is a thin layer of straight, squamous tissue. It secretes a watery fluid that lubricates the surface of the colon, which protects it from damage from contact with other abdominal organs, as well as with the muscles and bones of the lower torso that surround it.

Large intestine – functions

Functions of the large intestine – absorption of water and electrolytes

The presence of food debris in the colon stimulates contractions that occur approximately every 30 minutes, each lasting approximately one minute. With each such contraction, food debris shifts and mixes, which in turn facilitates water absorption. The large intestine also absorbs electrolytes. Sodium ions are actively absorbed by the action of the sodium-potassium pump, which shifts sodium and potassium ions in opposite directions across cell membranes, promoting sodium absorption and loss of potassium through the release of the hormone aldosterone.

Antipersistaltic contractions move food debris back towards the ileocecal valve, slowing transit and allowing more time for the colon to absorb water and electrolytes.

Functions of the large intestine – the formation and transport of feces

It is assumed that for every 500 ml of food scraps that enter the cecum each day, approximately 150 ml becomes faeces. They mainly contain bacteria, old epithelial cells from the intestinal mucosa, inorganic waste, undigested food debris and fiber, as well as water to help smoothly pass through the digestive tract. They also contain small amounts of fats and proteins. Their characteristic brown color is due to the presence of stercobilin and urobilin, hemoglobin breakdown products from old red blood cells.

As food remains in the large intestine for 12-24 hours, most of the 1,5 liters of fluid entering the colon each day is absorbed, leaving less than 100 ml for excretion in the faeces. This small amount of liquid gives the faeces a semi-solid texture. The stool is also softened by dietary fiber. The mucus secreted by the goblet cells that line the entire colon helps to bind dehydrated chyme and lubricate the fecal passage.

Peristalsis in the ileum forces the transport of food to the cecum. Stimulated by gastric distension and irritation in the colon, movements usually occur three or four times a day, often with or immediately after meals. These strong waves, which can last up to 30 minutes, begin in the middle of the transverse colon. With the help of abdominal contractions, they now push the largely dehydrated contents along the colon towards the rectum. Dietary fiber increases the force of the contractions of the colon to drive feces into the anus. Movements in the colon fill the rectum, creating a need for a bowel movement.

It is important to act in accordance with this desire, because once the movements have passed, the desire also ceases. If the urge to have a bowel movement is neglected for a long time, the rectum overflows, the large intestine absorbs more water, and the stool becomes harder and drier. This can cause constipation.

See also: Why is the poop brown? [WE EXPLAIN]

The functions of the large intestine – digestion

The large intestine does not produce its own digestive enzymes: in this part of the digestive tract, chemical digestion is only due to the action of millions of bacteria in the colon. By fermenting, these bacteria break down some of the remaining carbohydrates, which release hydrogen, carbon dioxide, and methane, which create gas. Colon bacteria also protect the gut from potentially harmful bacteria that come from the external environment and can synthesize some vitamins.

Colon functions – defecation

As feces begin filling the rectum, the rectal wall stretches, which sends an impulse to the nerve centers in the spinal cord. This causes the internal anal sphincter to relax, allowing a small amount of stool to enter the anus. The anus detects whether the material is gaseous or solid and works accordingly. If the material is solid, the external anal sphincter opens and defecation occurs. However, the external anal sphincter is controlled by muscles that are subject to our will, so it can be consciously stopped to delay bowel movements to a more convenient time.

Children usually learn this behavior by the age of two or three. People with severe dementia may not know how to do this anymore. If the nerves between the external anal sphincter and the bowel movement of the spine are damaged (for example, after a stroke or spinal injury), the ability to suppress bowel movements may be lost, resulting in faecal incontinence. In addition, with age, the ability of the anus to detect whether it contains gas or feces may deteriorate and feces may become treated as gas, causing fecal incontinence.

Also read: Is frequent bowel movement a symptom of an illness?

Large intestine – diagnosis

Medical history and physical examination play a key role in the correct diagnosis of colon disorders. Other tests may also be used to help develop a treatment plan for colon conditions.

1. Rectal infusion with barium contrast. A barium solution is placed in the colon and x-rays are taken.
2. Blood tests.
3. Hydrogen breath test. Safe, simple and non-invasive absorption assessment method. The test uses a nutrient containing radioactive material that is measured in the exhaled air.
4. Colonoscopy. A thin, flexible tube called a colonoscope is used to examine the inner lining of your colon. The test helps find ulcers, colon polyps, tumors, and areas of inflammation or bleeding. Tissue samples can be taken (biopsy) and abnormal growths removed. Colonoscopy can also be used as a screening test for cancer or precancerous growths (polyps) in the colon or rectum.
5. Less invasive research. Blood tests are available to help make a diagnosis. The fecal immunochemical test (FIT) is a newer version of the fecal occult blood test (FOBT) that detects small traces of blood in the stool.
6. Capsule endoscopy. Provides a better view of the lower GI tract that might not be visible with traditional colonoscopy.
7. Sigmoidoscopy. A procedure used to look inside the rectum and the area of ​​the large intestine closest to the rectum.
8. Imaging studies. X-ray, computed tomography (CT), MRI, PET.
9. Ultrasounds. They are used to detect colon tumors.

Large intestine – diseases

There are many medical conditions that can affect the large intestine. Some of them are:

Colon diseases – diarrhea

Diarrhea is most commonly caused by gastroenteritis, norovirus, or food poisoning, but it can also be caused by food intolerance or allergies, irritable bowel syndrome, inflammatory bowel disease, celiac disease, and diverticular disease. If the gut does not absorb fluid, the body may lose several liters of fluid per day. The consequences are dehydration, loss of electrolytes (potassium and sodium ions) and an increased risk of blood clotting.

Diarrhea can lead to serious consequences as large losses of potassium ions can cause cardiac arrest. In the case of diarrhea, it is necessary to quickly replace the fluid and electrolytes by administering a solution containing the appropriate balance of glucose and electrolytes.

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Colon diseases – lactose intolerance

People who are lactose intolerant cannot digest lactose in their diet. Undigested lactose ferments in the large intestine, producing gas, abdominal cramps, gas and diarrhea. Symptoms range from mild discomfort to severe pain. One of the gases produced by bacterial fermentation of lactose in the colon is hydrogen, so people who are lactose intolerant exhale hydrogen, so in the case of lactose intolerance, a hydrogen breath test is used.

Colon diseases – celiac disease

Celiac disease is an intolerance to gluten, which is a protein derived from wheat, barley and rye. When people with celiac disease eat gluten, intestinal immune cells (T lymphocytes) release inflammatory mediators that flatten the lining of the gut, impairing the ability to digest and absorb food. Symptoms range from mild to severe and include diarrhea, abdominal pain, gas, indigestion, and constipation; in severe cases, celikia can lead to malnutrition.

Colon diseases – constipation

Constipation is the rare and painful passing of stools caused by the slow movement of hard, dry stools. It can lead to bloating and abdominal pain and, if left untreated, can lead to stool clogging and obstruction of the digestive tract. It can be caused by irregular bowel movements, a low-fiber diet, and immobility. Certain medications, eating disorders, and overuse of laxatives can also cause constipation. It is believed that including 20-60 grams of fiber per day in your diet and drinking one or two glasses of fluid with each meal can help prevent constipation.

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Colon Diseases – Intestinal obstruction

Lumps, adhesions in the intestinal walls, foreign bodies, or stool wedges can cause partial or complete blockage of the intestines and the retraction of intestinal contents. This can cause abdominal swelling, pain, cramps, vomiting, and severe constipation or diarrhea. In the case of intestinal obstruction, sometimes you can talk about the so-called. paralytic ileus, which is a dramatic slowdown in the normal peristaltic movement of the intestines. Paralytic ileus can be caused by bacterial or fungal infections, mesenteric embolism, appendicitis, abdominal surgery, and some medications.

Colon diseases – diverticulitis

Small bumps (called diverticula) sometimes form over weak areas of the intestinal walls as a result of increased pressure; for example, when straining to defecate. They are most common in the sigmoid colon, but both the location and frequency of occurrence vary with age. For people who have diverticula, but also have mild or no symptoms, we are talking about mild diverticulosis.

Complications may occur in about 20% of people with diverticulosis who develop diverticulitis – inflammation and infection of diverticula. This usually happens when bacteria have built up in the diverticula blocked by waste. Bleeding may occur, as well as chronic damage to small blood vessels in diverticula and colonic obstruction.

Colon Diseases – Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is an uncontrolled inflammation and damage to the large intestine that causes severe discomfort, with symptoms such as abdominal cramps, gas, fluid and diarrhea. There is often an urgent need to have a bowel movement and there may be discharge from the rectum or bleeding. Severe IBD can result in loss of appetite, weight loss, and iron deficiency anemia.

The two types of IBD are Crohn’s disease and ulcerative colitis. While ulcerative colitis often presents with persistent inflammation and can usually be cured by removing the affected areas, Crohn’s disease tends to have an uneven distribution of inflammatory ulcers that can affect any part of the digestive tract but most commonly affects the terminal ileum or colon, which makes treatment and surgery difficult.

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Colon diseases – Crohn’s disease

Until recently, Crohn’s disease was thought to be an autoimmune disease in which the immune system attacks the lining of the gut. There is now evidence to suggest that the immune system over-attacks the microbial antigen on the lining of the gut. Most people with Crohn’s disease are diagnosed before the age of 30. A common complication is intestinal obstruction, caused by swelling and scarring, thickening of the intestinal wall and narrowing of the gastrointestinal tract. Bowel perforation can occur as a result of an abscess or fistula.

Also check: How does the immune system work?

Colon diseases – ulcerative colitis

Ulcerative colitis is characterized by inflammation and ulceration in the lining of the colon and rectum and an urge to the anus, which can cause painful, bloody diarrhea up to 20 times a day. Perforation is a potential complication as chronic inflammation and ulceration can weaken the intestinal wall to the point where a hole can form. It is generally associated with an acute distension of the colon, an emergency in which the colon loses all contractile function and gas accumulates in it. The perforation can cause life-threatening peritonitis.

Colon diseases – appendicitis

If the appendix gets blocked, it becomes inflamed, causing appendicitis. The obstruction causes an increase in pressure, which can reduce blood flow to the intestinal wall, causing ischemic injury and bacterial infection. The classic symptom is acute pain that starts at the navel and spreads to the right iliac fossa. Nausea, vomiting and possibly fever may occur.

If the condition is left untreated, the appendix can rupture, causing dangerous peritonitis and allowing the bacterial infection to spread rapidly through the peritoneal cavity, potentially leading to death within hours. Appendicitis is one of the most common causes of acute abdominal pain.

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Colon Diseases – Colorectal Cancer

Colorectal cancer has been associated with symptoms such as constipation or diarrhea, cramps, abdominal pain, and rectal bleeding. Smoking, excessive alcohol consumption, and a diet high in animal fats and proteins are believed to be associated with an increased risk of colorectal cancer. Since most colon cancers arise from benign growths in the mucosa called polyps, prophylaxis focuses on identifying these polyps.

Large intestine – treatment

In some cases, your doctor may suggest some simple measures to determine if your symptoms go away, such as:

1. avoiding smoking;
2. avoiding foods that cause unwanted symptoms;
3. exercise;
4. increasing the consumption of dietary fiber;
5. maintaining a healthy weight;
6. medications (i.e. over-the-counter or prescription medications).

As an advanced treatment measure, a specialist may also recommend surgery. The procedures performed in the treatment of the large intestine include:

1. colon and rectal surgery;
2. polypectomies (surgical removal of polyps);
3. sacral nerve stimulation (in case of accidental stool leakage).

Large intestine – prevention

To keep the colon as healthy as possible, you should follow these few rules.

1. Eat more fiber. Fiber causes muscle contractions that move food through the colon and helps remove debris that can slow the process down. The best way to do this is by eating plant-based foods.
2. Eating fats. Saturated fats, such as those found in red meat, are associated with higher rates of colon disease. On the other hand, healthy fats, such as the omega-3 fatty acids found especially in oily fish, support the friendly bacteria in our gut.
3. Drinking more water. The gut uses a lot of water to cleanse, moisturize, and absorb nutrients, and most of us don’t drink enough of it.
4. Regular examinations. Colon cancer is common and can be prevented. Anyone with a colon can get it, and it may be too late for treatment by the time symptoms appear. Regular screening is the best way to prevent and treat it on time.