The jejunum is the middle section of the small intestine between the duodenum and the ileum. Its most important function is the absorption of nutrients from the food pulp. Independent diseases of the jejunum are not known.
What is the jejunum?
Colloquially, the middle part of the small intestine is called the jejunum. This name comes from the fact that this section of the intestine always appears empty in deceased individuals. Its Latin name is jejunum. In humans, the jejunum is approximately 2 to 2.5 meters long. The boundary between the duodenum and jejunum is defined. It is located in the region of the second lumbar vertebra. However, there is no sharp boundary at the transition between the jejunum and the ileum. The structure and function of both intestinal segments are similar, but not identical. However, the differences can only be determined by fine tissue 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 first in the following order. Thus, the jejunum and ileum 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.
Anatomy and structure
The jejunum, placed in numerous loops, is attached to the abdominal wall via the mesentery. The following ileum is also involved in this suspension structure, which is called the radix mesenterii or small intestinal mesentery. This structure begins at the duodenum-jejunum bend and ends at the junction of the ileum and colon. Because the jejunum loops are highly motile, their location is also variable. As a very motile organ, the small intestine also does not have a constant length. It ranges from 3.5 to 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). This is followed by a double layer of smooth muscle. The final layer is a connective tissue cover (serosa cover) of the peritoneum. In addition to the ileum, appendix and ascending colon, the jejunum is supplied by the superior mesenteric artery. Starting from this artery, the jejunal arteries are specifically responsible for supplying the jejunum. To the right of the superior mesenteric artery runs the superior mesenteric vein, which drains the used 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 peristalsis and motility of the esophagus, stomach, small intestine (including jejunum), and colon.
Function and Tasks
The jejunum, along with the duodenum and ileum, has the function of absorbing nutrients from the enzymatically processed food pulp. Important substances absorbed from food are fats, proteins, carbohydrates, minerals, vitamins, salts and water. These substances then pass into the blood and reach all parts of the body. In order to effectively absorb the nutrients in the food, the small intestine must develop as large a surface area as possible. For this purpose, various structures develop, such as the Kerkig folds (plicae circulares), the villi of the small intestine (villi interstinales), the Lieberkühn crypts (glandulae interstinales) and the microvilli. The Kerkig folds form the rough relief of the small intestine. In the process, both the mucosa and the submucosa bulge out. Small intestinal villi are again finger-shaped protrusions of epithelium and lamina propria. Lieberkühn’s crypts are the tubular depressions in the valleys of the villi. The microvilli enlarge the intestinal mucosa tenfold. As a so-called brush border, they represent the micro relief of the mucosa. All three parts of the small intestine contain these structures. However, their shape and size depends on where they are located. Thus, the Kerkig folds become progressively lower from the duodenum through the jejunum to the ileum. Furthermore, the intestinal villi are longest in the jejunum with a finger-shaped structure. These subtle differences determine which nutrients are primarily absorbed. The food pulp is transported from the stomach to the colon by the peristalsis of the small intestine. In the process, its contractions become progressively slower from the duodenum through the jejunum to the ileum.
Diseases
Independent diseases of the jejunum are very rare.Most often, the jejunum is affected secondarily in the context of other diseases of the small intestine. In addition, abdominal pain often cannot be easily assigned. Thus, intensive examinations are sometimes required to determine whether the small intestine, the large intestine or even the entire intestine is affected. Many diseases of the small intestine initially cause non-specific pain in the lower abdomen. Diseases of the large intestine, the pancreas, the peritoneum or the gall bladder must then be differentiated from these. Diseases of the small intestine are often accompanied by wave-like pain 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 also cause inflammation of the small intestine. In ulcerative colitis, unlike 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-called celiac disease, for example, is triggered by an intolerance to gluten. In this disease, the intestinal villi shrink so drastically that the absorption of nutrients is severely restricted. Colorectal cancer is very rare in the small intestine and especially in the jejunum, because the rapid passage of the food pulp allows carcinogenic substances to act only for a short time.
Typical and common intestinal diseases
- Crohn’s disease (chronic inflammatory bowel disease)
- Inflammation of the intestine (enteritis)
- Intestinal polyps
- Intestinal colic
- Diverticula in the intestine (diverticulosis)
