The sigmoid colon is the last section of the large intestine and is located immediately before the rectum. It is primarily responsible for the final digestion and portioning of digestive debris before it enters the rectum.
What is the sigmoid colon?
The fourth and final section of the large intestine (colon) is called the sigmoid colon. It is located near the pelvis. The name sigmoid colon developed from the Greek and describes the appearance of this section of the intestine. It has a similar shape to the Greek lowercase letter sigma, which is the predecessor of the Latin S. Simplified, this section of the intestine is then also referred to as the sigma. As part of the large intestine, the sigmoid colon is primarily responsible for the further digestion and proportioning of the last digestive residues before they are excreted as faeces via the rectum. However, due to anatomical peculiarities, the sigmoid colon is also prone to certain intestinal diseases, such as diverticulitis, diverticulosis, or colorectal cancer.
Anatomy and structure
The sigmoid colon is an inseparable part of the large intestine (colon). Thus, the colon is divided into four sections. The first section is called the ascending colon because of its ascending course on the right side of the abdomen. This is followed by the transverse colon (colon transversum). The third section of the colon is the descending colon. This is followed by the sigmoid colon, which finally merges into the rectum (rectum). rectum (rectum). The course of the sigmoid colon looks like an inverted S-curve. Starting from the descending colon, the sigmoid rises again slightly near the left iliac crest before it flows downward into the rectum according to the course of a twisted curve. In this process, the sigmoid colon always runs within the peritoneum. Its uppermost third is attached to the posterior peritoneum by delicate adhesions. The sigmoid colon does not have a uniform length. The sigmoid colon is supplied by the sigmoid arteries, which originate from the inferior mesenteric artery. The arteriae sigmoideae (sigmoid arteries) are arteries that supply fresh blood to the sigmoid. However, within the so-called mesentery, there are cross connections of the sigmoid to other parts of the intestine, so that its blood supply can also be ensured in case of occlusion of the sigmoid arteries. Full bowel function can also be restored after surgical removal of the sigmoid colon.
Function and Tasks
The function of the sigmoid colon is to further digest and proportion digestive residue before it enters the rectum for excretion. In the rectum, further dehydration then occurs from the remaining residues until they are excreted as faeces via the anus. The processes that occur in the sigmoid are similar to those that occur throughout the colon. The major function of the colon is to further thicken the intestinal contents by removing water. It also continues digestion of the food pulp entering from the small intestine. A large number of intestinal bacteria are available for this purpose. On the one hand, these bacteria benefit from the nutrient content of the food pulp. On the other hand, they also supply the organism with valuable vitamins, such as vitamin K. In this process, a vital symbiosis has developed between host and bacteria. These processes occur similarly in all sections of the colon, with the food pulp thickening considerably towards the sigmoid colon. However, the length of the colon helps to ensure that digestive residues can still be used effectively by the body. This is true both for valuable nutrients and for the recovery of important electrolytes and water. During the passage through the colon, approximately 1.5 liters of water are removed from the food pulp. However, the special feature of the function of the sigmoid colon is that, in addition to the further digestive process, it controls the release of the food residues into the rectum by proportioning. Only after the rectum has been emptied do further digestive residues from the sigmoid colon move back in.
Diseases
The sigmoid colon, as the last section of the large intestine, is subject to strong pressure due to increased muscle tension. As a result, the s-shaped portion of the colon appears more constricted and spastic than other bowel segments.Due to pressure, intestinal protrusions often form here, which are called diverticula. Fecal debris can collect in these diverticula, which may lead to their inflammation. The inflammation of diverticula is called diverticulitis. Due to low-fiber diets, this condition has become very common in industrialized countries. Diverticulitis is manifested by pain in the left upper abdomen, which often radiates to the back. Furthermore, fever, nausea and vomiting occur. In extreme cases, life-threatening complications such as peritonitis can occur. Diverticulitis is treated with antibiotics and in severe cases even by surgery. Diverticulosis is another disease of the sigmoid colon. In diverticulosis, in contrast to diverticula, only the intestinal mucosa is distended. The diagnosis of this disease is often made only by chance, since there are usually no symptoms. However, diverticulitis can also occur as a complication in this case. In colorectal cancer, the sigmoid colon together with the rectum is most frequently affected. Colorectal cancer develops especially when digestive debris remains in the intestine for too long. Another disease specific to the colon is the chronic autoimmune disease ulcerative colitis, which occurs in constant episodes. However, there are also a number of intestinal diseases that affect all other intestinal segments equally in addition to the sigmoid colon.
Typical and common colon diseases
- Diverticula in the intestine (diverticulosis).
- Intestinal colic
- Appendicitis
- Colon cancer