What is the duodenum?
The duodenum is the beginning of the intestinal system and the first section of the small intestine. It is sharply separated from the stomach outlet (pylorus), about 25 to 30 centimetres long and has the shape of a C with the head of the pancreas in the round side.
The sections of the duodenum
The initial section of the duodenum is the approximately five centimetre long and horizontally running limb (pars superior). It has a widened beginning and an almost smooth inner surface.
This is followed by the descending limb (pars descendens) of the duodenum, whose inner surface is enlarged by numerous folds (Kerck ring folds) and contains the so-called Brunner glands (duodenal glands). The ducts of the large digestive glands also open into the duodenum in this area: the main bile duct (which transports bile from the liver or gallbladder to the duodenum) and the pancreatic duct, which transports pancreatic secretions.
In many people, the bile duct merges with the pancreatic duct before the duodenum so that they then flow into it together.
What is the function of the duodenum?
The function of the duodenum is to continue the digestive process begun in the mouth and stomach and to produce certain hormones.
Involvement in digestion
The digestive enzymes that work in the duodenum originate from the pancreas and the duodenal glands.
In addition to digestive enzymes, both glandular secretions also contain bicarbonate: it increases the pH value of the chyme, which – when it enters the duodenum from the stomach – is highly acidic. In order for the enzymes to become active, the acidity must be reduced by bicarbonate.
The bile introduced into the duodenum is also important for digestion: the bile acids it contains are necessary for the digestion of fat.
Hormone production
Various enterohormones (= hormones produced in the digestive tract) are also formed and secreted in the duodenum:
- Gastrin: This hormone, which is also produced in the stomach, stimulates the formation and secretion of gastric acid and pancreatic secretions.
- Secretin: It is produced in the duodenum and the subsequent jejunum and stimulates the production of bicarbonate.
- Cholecystokinin: This hormone is also produced in the first two sections of the small intestine (duodenum and jejunum). It promotes the release of pancreatic enzymes and bile acids for fat digestion.
Doctors refer to a permanent enlargement of the duodenum as a megaduodenum, which can be congenital or acquired.
Duodenal diverticula are protrusions of the intestinal wall in the area of the duodenum. They are almost always found on the inner side of the curvature and rarely cause symptoms.
Inflammation of the duodenum (duodenitis) can lead to a duodenal ulcer (duodenal ulcer).
The passage through the duodenum can be impaired by a congenital or acquired narrowing. Doctors refer to this as duodenal stenosis.
