What is the jejunum?
The jejunum, the empty intestine, is the middle part of the small intestine, i.e. it lies between the duodenum and the ileum. There is no clear boundary to the latter. Both together (jejunum and ileum) are also called the small intestine.
The jejunum begins at the level of the second lumbar vertebra and is around two to two and a half meters long. Like the ileum, it is attached to the posterior abdominal wall by a peritoneal duplication, the so-called mesentery, and forms numerous freely movable loops.
The wall of the jejunum consists of a double layer of musculature, which is covered on the inside by mucous membrane and on the outside by peritoneum. The mucosa has many Kerckring folds and Lieberkühn glands. The Kerckring folds are transverse mucosal folds that greatly enlarge the inner surface of the rectum. This increases its absorption capacity.
The Lieberkühn glands are tubular depressions in the wall of the small intestine. Like the Kerckring folds, they serve to increase the surface area. They also secrete enzymes that are important for digestion.
Small intestinal villi (finger-shaped protrusions of the intestinal wall) and the tiny, thread-like projections on the cell surface of the wall epithelium (microvilli) further enlarge the inner surface of the jejunum.
Where does the name jejunum come from?
What is the function of the jejunum?
In the jejunum, the enzymatic breakdown of food components, which has already begun in the upper sections of the digestive tract, continues. The resulting building blocks of the main nutrients (simple sugars, amino acids, fatty acids etc.) as well as water, vitamins and electrolytes are absorbed into the blood (resorption).
In addition to the absorption function, the empty intestine also has a glandular function: the goblet cells in the intestinal mucosa produce a mucus that coats the entire inner surface and thus protects the mucosa from self-digestion by the acid from the stomach.
The muscular wall of the jejunum fulfills another important function:
- Segmentation movements divide the food pulp into smaller portions by constricting it
- pendulum movements mix the intestinal contents by moving them back and forth so that they come into even contact with the digestive juices
- peristaltic movements of the jejunum wall transport the intestinal contents further towards the ileum
What problems can the jejunum cause?
Isolated diseases of the jejunum are rare. In most cases, the entire small intestine is affected, for example in the case of inflammation of the small intestine (enteritis) or acute occlusion of the artery supplying the small intestine (mesenteric artery infarction).
In the case of genetic intolerance to gluten (gluten protein in cereals), the mucous membrane in the small intestine (also in the jejunum) is damaged by an incorrect reaction of the immune system, which impairs the absorption of nutrients.