Position and course
The duodenum is a part of the small intestine and is the link between the stomach and the jejunum. It has a length of approximately 30 cm and is anatomically divided into 4 different sections depending on its course. After leaving the pylorus, the chyme reaches the upper part of the duodenum (pars superior).
This section is covered by the right lobe of the liver and the gallbladder from the front (ventral). On the back (dorsal) side, the bile duct (Ductus choledochus) as well as a part of the portal vein are located. An anatomical peculiarity is that the upper part of the duodenum is the only one that lies within the peritoneum (intraperitoneal position).
The remaining sections of the duodenum are all fused with the posterior abdominal wall, their position is called secondary retroperitoneal. The pars superior duodeni is particularly susceptible to duodenal ulcers (ulci), which can be caused by the acidic food pulp from the stomach. Adjacent to the upper part of the duodenum follows the clinically important descending part (pars descendens).
This importance is mainly due to the fact that the bile duct and the pancreatic duct open into this section via a common opening (major papilla duodeni). In this way, digestive enzymes from the pancreas and bile acids from the liver enter the intestine and ensure that digestion functions properly. In addition, the acidic food pulp is neutralized by basic components of the secretions.
The third section of the duodenum is the horizontal part (pars horizontalis). It is located approximately at the level of the third lumbar vertebra and moves in front of the spine to the left side of the body. There, the horizontal part flows into the last section of the duodenum, namely the so-called ascending part (pars ascendens).
As its name suggests, this fourth segment of the duodenum takes a course towards the diaphragm, i.e. upwards (cranially). At the level of the first lumbar vertebral body, the ascending part penetrates the abdominal cavity (intraperitoneally) and merges into the following small intestine section, the jejunum. If you now visualize the course of the individual sections of the duodenum, it is approximately similar to the letter C. This is interesting in that the head of the pancreas fits exactly into this bulge.
This close positional relationship is also the reason why pancreatic cancer often grows into the duodenum and damages it. If the duodenum is ruptured (perforated), for example due to an injury to the abdominal cavity or an intestinal obstruction (ileus), food pulp can enter the abdominal cavity and lead to a life-threatening inflammation or blood poisoning (sepsis). In this case, immediate surgery is essential for survival.
