Microscopic structure
The different layers of the duodenum in cross-section correspond to those of the rest of the digestive tract. From the outside, the duodenum is surrounded by connective tissue (tunica adventitia), which contains both blood and lymph vessels. This is bordered by a muscle layer, the so-called tunica muscularis.
It contains an outer longitudinal and an inner ring muscle layer, which serve the peristalsis. Between the two muscle layers there is a nerve plexus (plexus myentericus), which innervates the smooth musculature and belongs to the intestinal nervous system (enteric nervous system). A further nerve plexus is found in the submucosal taenia following the tunica muscularis.
This is the submucosal plexus, which is embedded in the loose connective tissue of the submucosal layer. The innermost layer is a mucous membrane (tunica mucosa), which can be further divided into three different sublayers. The inner layer of the duodenum is lined by the lamina epithelialis mucosae.
This is followed by a thin layer of connective tissue (lamina propria mucosae), which in turn is covered by a separate muscle layer of the mucous membrane (lamina muscularis mucosae). But what is the difference between the structure of the duodenum and the other sections of the digestive tract? There are basically two different characteristics that can be used for differential diagnosis.
On the one hand, there are special Brunner glands in the tela submucosa, which only occur in the duodenum and secrete a viscous fluid.On the other hand, the mucous membrane of the duodenum already shows macroscopically conspicuous bulges, which are called plicae circulares. Together with villi and crypts, which consist of the Lamina epithelialis mucosae and the Lamina propria mucosae, these serve to increase the surface area of the lumen of the duodenum. This ensures a very efficient absorption of food particles.
Blood supply
The blood supply to the duodenum is provided by two large branches of the aorta. Approximately at the level of the twelfth thoracic vertebral body, a vascular trunk emerges from the aorta (Truncus coeliacus), which plays a major role in supplying the spleen, liver, pancreas and stomach. A branch of the Truncus coeliacus, namely the Arteria hepatica communis, also gives off a vessel (Arteria gastroduodenalis).
This artery mainly supplies the upper sections of the duodenum with blood. The lower parts of the duodenum receive their blood supply via the upper mesenteric artery (Arteria mesenterica superior). It originates directly from the aorta abdominalis at the level of the first lumbar vertebra. In addition to the duodenum, the superior mesenteric artery also provides access to the entire small intestine and the colon up to the left colon flexure.
