The large intestine (from the Latin intestinum, from intestine, meaning “inside”) is an organ of the digestive tract.

Location. The large intestine is an extension of the small intestine and extends to the anus (1).

Structure. The large intestine is made up of different parts (1):

• The cecum, located in the right part of the abdomen, is the initial segment of the large intestine in the continuation of the ileum, the last part of the small intestine. The cecum has an atrophied extension known as the vermicular appendix.
• The ascending colon starts from the cecum and goes up vertically to the right colic angle.
• The transverse colon starts from the right colonic angle, extends horizontally towards the left lateral aspect of the abdomen and ends at the left colonic angle.
• The descending colon starts from the left colonic angle and descends vertically to the sigmoid colon.
• The sigmoid colon is located between the descending colon and the rectum.
• The rectum descends and opens onto the anus.

Wall. The large intestine is made up of 4 envelopes (2):

• The mucous membrane is the inner layer.
• The submucosa is the intermediate layer made up in particular of vessels and nerves.
• The muscularis is the outer layer made up of muscle fibers.
• The serous mmbrane, or peritoneum, is an envelope lining the outer wall of the large intestine.

Motor skills. The wall of the large intestine, in particular at the level of the ascending colon and the transverse colon, has an increased motricity allowing the mixing, the advance, then the storage of materials (1).

Water and nutrient absorption. The large intestine is involved in the absorption of water, as well as various nutrients (1).

Protective role of the large intestine. At the level of the cecum, a sphincter helps prevent the return of material to the small intestine. This function is essential to avoid the contamination of the small intestine by the bacteria present in the colon. The large intestine also has the ability to defend itself against chemical and mechanical attacks by secreting mucus, protecting the mucous membrane (3).

Bacterial digestion. Bacteria in the colon also digest certain elements, including cellulose (3).

Tumors. Colon cancers mainly arise from a benign tumor, called an adenomatous polyp, which can develop into a malignant tumor (4) (5). These tumors can develop in particular in the cells of the inner wall of the cecum.

Chronic inflammatory bowel disease. These diseases correspond to an inflammation of the wall of part of the digestive system. They include ulcerative colitis as well as Crohn’s disease. Symptoms include severe abdominal pain and diarrhea (6).

Irritable bowel syndromeThis syndrome is manifested by hypersensitivity of the intestinal wall and irregularity in muscle contractions. It manifests itself through various symptoms associated with digestive disorders such as diarrhea, constipation, or abdominal pain. The cause of this syndrome is still unknown today.

Diverticulitis. This pathology corresponds to an inflammation of the diverticula. These are small deformities that are found quite frequently in the colon. This inflammation causes nausea, vomiting, abdominal pain and high fever.

Bowel obstruction. It indicates a stop of the functioning of the transit, causing intense pain and vomiting. Intestinal obstruction can be of mechanical origin with the presence of an obstacle during transit (gallstones, tumors, etc.) but can also be chemical by being linked to an infection of a nearby tissue such as during appendicitis or peritonitis.

Medical treatment. Depending on the pathology diagnosed, certain drugs may be prescribed such as anti-inflammatory drugs or analgesics.

Surgical treatmentthe. Depending on the pathology and its evolution, a surgical intervention may be implemented. In the most serious cases, a colostomy may be performed by removing the colon.

Chemotherapy, radiotherapy or targeted therapy. Depending on the type of tumor diagnosed and the evolution of the pathology, these treatments may be implemented to destroy cancer cells.

Physical examination. The onset of pain begins with a physical examination to assess symptoms and identify the causes of the pain.

Biological examination. Blood and stool tests may be done to make or confirm a diagnosis.

Medical imaging exam. Depending on the suspected or proven pathology, additional examinations may be performed such as an ultrasound, a CT scan or an MRI.

Review by endoscopese. A colonoscopy may be done to study the walls of the colon.

In 2010, researchers from Inserm in Nantes published their research results on the effects of Parkinson’s disease on digestive neurons in the scientific journal Plos One. They have shown that the lesions of Parkinson’s disease affect not only the cells of the central nervous system, but also those of the enteric nervous system, and more precisely that of the digestive system. This discovery could allow an early diagnosis of Parkinson’s disease (7).