The intestine is a large and important organ of the digestive tract. In interaction with the stomach, it performs digestion and absorption of nutrients, as well as storage and elimination of food residues. In addition, the intestine plays an important role in the immune system.
What is the intestine?
Schmatic diagram on the types of intestinal diseases (ulcerative colitis, diverticulitis, diverticulosis and intestinal polyps. Click to enlarge. The intestine is an elongated hollow organ of the gastrointestinal tract. It extends from the pylorus to the anus. Its total length is approximately 8 m.
The intestine is divided into several sections according to functional and anatomical aspects: After passing through the stomach, food first enters the small intestine, consisting of the duodenum, jejunum and ileum. The large intestine, consisting of the “true” appendix (caecum) with the vermiform appendix (appendix vermiformis; colloquially “appendix”), the colon (grimmdarm), and the rectum (rectum), joins the scum.
Anatomy and structure
The intestine is essentially a muscular tube lined with mucosa. Its wall structure is three-layered: inside is a mucous membrane (mucosa), the shape of which varies considerably in different sections of the intestine. The middle layer is the tunica muscularis, which in turn is composed of an inner annular muscle layer and an outer longitudinal muscle layer. Externally, the intestine is closed by a membranous tunica serosa or a connective tissue tunica adventitia. The intestinal mucosa shows a considerable increase in surface area in the small intestine:
It is not only folded, but bulged out into a total of about 4 million intestinal villi. These intestinal villi are additionally covered by a brush border of microvilli. Thus, the intestinal mucosa reaches a total surface area of about 500 square meters.
Functions and tasks
The different sections of the intestine perform different tasks. The small intestine is mainly responsible for nutrient absorption. Before absorption, enzymatic cleavage of nutrients must occur in the small intestine:
For carbohydrates, the lining cells of the intestinal mucosa themselves have the appropriate enzymes ready. For protein and fat digestion, the small intestine needs the support of the pancreas and gall bladder, whose secretions flow into the duodenum. Salts, vitamins and water are also absorbed in the small intestine. The intestinal villi are well supplied with blood so that the nutrients obtained can be transported away with the blood. In the large intestine, only minerals and water are predominantly absorbed. Finally, the rectum stores the feces until the next time it is emptied. Beyond nutrient absorption, the intestine is of great importance for the immune system: The intestinal flora not only has a physiological bacterial colonization, but is also confronted daily with countless pathogens through food. The intestine thus fulfills an important barrier and protective function. For immune defense, lymphocytes are distributed diffusely or in clusters as lymphoid follicles throughout the intestine. They are grouped together as GALT (“gut associated lymphoid tissue”). In total, about 75% of all antibody-producing cells are located in the intestine. The muscular layer of the intestine enables intestinal peristalsis, which is critical for grinding and propelling food. Intestinal peristalsis and glandular secretion are regulated by the vast intestinal nervous system (enteric nervous system, or ENS). The ENS is part of the autonomic nervous system, has about 4 times more neurons than the spinal cord, and is nicknamed the “gut brain.”
Diseases
The most common intestinal diseases include intestinal infections, which typically manifest as diarrhea, vomiting, bloating, or abdominal pain. If an infection affects the appendix, surgical removal may be necessary. If certain enzymes in the intestine are defective or insufficiently present, food intolerances occur, e.g. the widespread lactose intolerance. Undetected, these intolerances can cause irritable bowel syndrome, as can bacterial overgrowth. Chronic inflammatory bowel diseases are Crohn’s disease and ulcerative colitis. Colorectal cancer is the second most common malignant tumor disease in Germany. Almost 90% of all colorectal cancers are adenocarcinomas of the colon arising from glands. Polyps – benign growths that can degenerate into malignant tumors – are considered a precursor of colorectal cancer.Intestinal infarctions are also particularly dangerous, as they are often detected too late and intestinal tissue dies quickly. Overall, there are many other intestinal disorders. Initial symptoms of intestinal disease are usually stool changes and/ or pain.
Typical and common disorders
- Crohn’s disease (chronic inflammation of the intestine).
- Inflammation of the intestine (enteritis)
- Intestinal polyps
- Intestinal colic
- Diverticula in the intestine (diverticulosis)