Colloquially, the middle part of the small intestine is called a jejunum. This name comes from the fact that in deceased this intestinal tract always appears empty. His Latin name is Jejunum. In humans, the jejunum is about 2 to 2.5 meters long. The boundary between the duodenum and the jejunum is defined. It is located in the area of the second lumbar vertebrae. However, there is no sharp boundary at the transition between the jejunum and the ileum.
The structure and function of both bowel sections are similar, but not identical. However, the differences can only be determined by histological examination. Due to the gradual change in the intestinal wall structure, there is also a gradual change in the absorbed nutrients. Thus, starting from the jejunum to the ileum, fat-soluble vitamins, proteins, water-soluble vitamins and fats are absorbed in the following order. The jejunum and the ileum thus represent a functional unit of the small intestine, so that the functions, structure and diseases of both sections are usually considered together in the medical literature.
The jejunum placed in numerous slings is attached to the abdominal wall via the mesentery. The following ileum is also involved in this hanging structure, which is referred to as a radix mesenterii or small intestinal mesentery.
This structure begins at the duodenum-jejunum curvature and ends at the junction of the ileum and the colon. Since the jejunum loops are very mobile, their location is also variable. As a very active organ, the small intestine also has no constant length. It is between 3.5 and 6 meters. The length depends on the contraction state of the small intestine. The jejunum, like all other hollow organs, has a mucous membrane (tunica mucosa). Then follows a double layer of smooth muscle. The conclusion is a connective tissue coating (serosa coating) of the peritoneum.
The jejunum is supplied with the ileum, appendix and ascending colon of the intestinal artery "superior mesenteric artery". Based on this artery, the arteriae jejunales are responsible for the supply of the jejunum. To the right of the superior mesenteric artery runs the superior mesenteric vein, which drains the spent blood from the jejunum to the portal vein. The function and movement of the jejunum is controlled by the enteric nervous system. As part of the enteric nervous system, the myenteric plexus is responsible for the peristalsis and motility of the esophagus, stomach, small intestine (including jejunum), and large intestine.
In addition to the duodenum and the ileum, the jejunum has the function of absorbing nutrients from the enzymatically processed chyme. Important substances taken from the diet are fats, proteins, carbohydrates, minerals, vitamins, salts and water. These substances then pass into the blood and thus reach all parts of the body. In order to be able to absorb the nutrients of the chyme effectively, the small intestine must form as high a surface as possible.
In addition, various structures develop, such as the Kerkig folds (Plicae circulares), the small intestine villi (Villi interstinales), the Lieberkühn crypts (Glandulae interstinales) and the Mikrovilli. The Kerkig folds form the rough relief of the small intestine. It inverts both the mucosa and the submucosa. Small intestinal villi are again finger-shaped protuberances of epithelium and lamina propria. Lieberkühn crypts are the tubular depressions in the valleys of the villi. The microvilli enlarge the intestinal mucosa tenfold. They represent the so-called brush border the micro-relief of the mucosa. All three parts of the small intestine contain these structures.
However, their shape and size depend on where they are. Thus, the Kerkig wrinkles from the duodenum via the jejunum to the ileum are getting lower. Furthermore, the villi in the jejunum are the longest with a finger-shaped structure. These histologic differences determine which nutrients are mainly absorbed. The chyme is transported by the peristalsis of the small intestine from the stomach to the colon. His contractions from the duodenum via the jejunum to the ileum become slower and slower.
Independent diseases of the jejunum are very rare. Mostly the jejunum is secondarily affected in the context of other diseases of the small intestine. In addition, abdominal pain often can not be easily attributed. It sometimes requires intensive examinations to detect whether the small intestine, the colon or even the entire intestine is affected.
Many diseases of the small intestine initially cause nonspecific pain in the lower abdomen. It should be distinguished from diseases of the colon, the pancreas, the peritoneum or the bile. Diseases of the small intestine are often associated with wave-like pains or colic. Causes include general gastrointestinal inflammation, intestinal ulcers or mesenteric infarction. Inflammation of the small intestine is called enteritis. Enteritis can be caused by infection with various bacteria or viruses.
However, autoimmune diseases, such as Crohn's disease or ulcerative colitis, can cause small intestinal inflammation. In ulcerative colitis, in contrast to Crohn's disease, usually only the large intestine is affected. In some cases, however, the small intestine may also be involved. Food intolerances produce reactions in the small intestine. So the so-called celiac disease is triggered by an intolerance to gluten. In this disease, the villi shrink so drastically that the absorption of nutrients is severely limited. Colorectal cancer is very rare in the small intestine and especially in the jejunum, because the rapid passage of the chyme can cause carcinogenic substances to act only for a short time.