Colon

Of the Colon, also Colon called, is the middle section of the colon. It is divided into four sections, starting behind the appendix and ending at the transition to the rectum.

What is the colon?

The human colon is about one and a half meters long and has a lumen of about eight centimeters. In humans, its shape resembles a U that is upside down. This upside-down U frames the small intestine. The main task of the large intestine is the recovery of water and electrolytes and the absorption of food components that have not yet been absorbed by the small intestine.

Anatomy & structure

The colon begins after the appendix (caecum), i.e. in the right lower abdomen. In the area of ​​the appendix, the small intestine joins the large intestine. The so-called Bauhin's flap is located at the transition. It prevents the intestinal contents from flowing back from the large to the small intestine.This ensures that the different bacterial colonies in the large and small intestines do not mix. In addition, the flap ensures that the food is transported in portions. The ascending part (ascending colon) of the colon begins almost immediately after the valve.

This section is about 20-25 cm long and merges seamlessly into a horizontal part at the level of the twelfth thoracic vertebra. This section is called the transverse colon. The left bend that connects the two parts is called the right flexure or flexura coli dextra. The left flexure connects to the transverse colon (flexura coli sinistra), which merges into the descending colon, the descending large intestine. This is where the sigmoid (Colon sigmoideum), an S-shaped loop of the large intestine, connects. The colon ends with the beginning of the rectum, which in turn is bounded at its end by the anus.

The colon has a four-layer wall structure typical of the gastrointestinal tract. The innermost layer is the mucosa, a mucous membrane that is made up of three layers. The mucous membrane lies on a layer of connective tissue (tunica submucosa). The blood and lymph vessels that supply the large intestine and absorb the absorbed nutrients, electrolytes and water run in this layer. In addition, there is a plexus of nerves in the connective tissue layer, the submucosal plexus. The tunica muscularis, a muscle layer that is formed from an inner circular muscle and an outer longitudinal muscle layer, runs under the submucosa. These muscles are used to mix and transport the porridge.

Due to the peristaltic movements of the muscles and special constrictions, the muscle layer forms the tänien and house doors so typical of the large intestine. Another nerve plexus, the so-called Auerbach plexus, runs between the two muscle layers. Depending on the section of the large intestine, either loose connective tissue or the peritoneum forms the fourth and last wall layer of the colon. The transverse colon is completely covered by peritoneum, the ascending and descending parts of the colon are only covered by peritoneum on their front side.

Function & tasks

The Bauhin valve releases the chyme in portions into the appendix. The two nerve plexuses then ensure the typical peristaltic, that is, wave-shaped contractions of the colon muscles. Mixed movements can be distinguished from transport movements. The mixed movements are caused by a contraction of the circular muscles and only run over a short distance. They serve the vigorous mixing of the intestinal contents. In this way, a sufficient re-absorption of important nutrients can be guaranteed.

Mixing movements occur about 15 times per minute. Transport movements are less common. These are long peristaltic waves that carry the chyme into the rectum. The transport waves pass through the intestine about two to three times a day. This is often followed by defecation. The main function of the colon is to recover water and electrolytes. About one liter of fluid is brought back through the colon every day. In addition, an enzymatic conversion of certain food components takes place in the colon with the help of colon bacteria. The bacteria break down mainly plant-based fibers and produce vital nutrients such as vitamin K or vitamin B7.

Diseases

An inflammation of the colon is called colitis. It is usually accompanied by pain and diarrhea. Ulcerative colitis is a special form of colitis. It belongs to the group of chronic inflammatory bowel diseases and causes severe bloody diarrhea and cramps in the colon through damage to the mucous membrane with ulcer formation. Another chronic inflammatory bowel disease that can affect the colon as well as the small intestine is Crohn's disease. Here too, digestive disorders and diarrhea occur. Both diseases are autoimmune diseases.

If there are bulges in the intestinal wall, one speaks of diverticula. If food remnants accumulate in these diverticula, inflammation, known as diverticulitis, can occur. Diverticulitis most commonly occurs in the sigmoid area. The symptoms are similar to those of appendicitis, except that the pain is more likely to occur in the left lower abdomen. Diverticulitis is therefore also called left appendicitis.

Colon cancer is the second most common cancer in Germany. Carcinomas of the colon and rectum account for more than 95% of all malignant colon tumors. The symptoms of a tumor in the colon are rather uncharacteristic. Early symptoms can include blood in the stool or sudden changes in bowel movements. Other symptoms include foul-smelling gas, pencil stool (narrow shape of the stool), and alternation between constipation and diarrhea. Blood loss can also lead to anemia with symptoms such as tiredness, shivering, hair loss and paleness.

Typical & common diseases

• Ulcerative colitis
• Crohn's disease
• Diverticulitis
• Colon cancer