Length

The small intestine is a very motion-active organ and therefore has no fixed length. Depending on the state of contraction, the small intestine is 3.5 to 6 meters long, with the individual sections being of varying size. The smallest part of the small intestine is the duodenum, which is directly adjacent to the stomach.

It measures 24-30 cm on average. The duodenum is followed by the jejunum, which measures 2.5 meters in a relaxed state. The last section before the transition to the large intestine is the ileum, which is about 3.5 meters long. These are standard values that can vary from person to person, and there is no clear anatomical boundary between the ileum and the ileum.

Wall of the small intestine

From the inside, the small intestine wall is lined by mucous membrane (tunica mucosa), which is divided into three sublayers. The uppermost layer is a covering tissue (Lamina epithelialis mucosae). In this covering tissue, special cells (goblet cells) are embedded, which are filled with mucus, which they periodically release into the bowel, thus ensuring the gliding ability of the bowel.
The next sublayers are a connective tissue shifting layer (lamina propria mucosae), followed by a very narrow autologous muscle layer (lamina muscularis mucosae), which can change the relief of the mucosa.
This is followed by a loose shifting layer (Tela submucosa), which consists of connective tissue and in which a dense network of blood and lymph vessels runs, as well as a nerve fiber plexus called Plexus submucosus (Meissen plexus). This nerve plexus represents the so-called enteric nervous system and innervates the intestine independently of the central nervous system.In the duodenum, this layer also contains the so-called Brunner glands (Glandulae interstinales), which produce various enzymes and an alkaline mucus that is able to neutralize stomach acid. The next layer of intestinal muscle (tunica muscularis) is divided into two sublayers, whose fibers run in different directions: first an inner, strongly developed circular stratum (stratum circulare) and then an outer longitudinal stratum (stratum longitudinale).
Between this ring and longitudinal muscle layer runs a network of nerve fibers, the plexus myentericus (Auerbach plexus), which innervates (stimulates) these muscle layers. This musculature is responsible for the wave-like movement of the intestine (peristaltic movement).
This is again followed by a connective tissue displacement layer (Tela subserosa).
The end is a coating of the peritoneum which lines all organs. This coating is also called tunica serosa.