Duodenum

At a glance

English

Duodenum

Latin (TA2)

Duodenum

System

Digestive

Region

Abdomen

Side

Single, on the midline

About the duodenum

The duodenum runs from the pylorus of the stomach to the duodenojejunal flexure, a length of roughly 25 cm. It forms a C open to the left, wrapping round the head of the pancreas; it lies high on the posterior abdominal wall at the level of the first to third lumbar vertebrae. Apart from its first couple of centimetres it is retroperitoneal, fixed behind the peritoneum and so not freely movable.

It is described in four parts. The superior (first) part runs back and to the right from the pylorus; its widened, mobile start is the duodenal bulb or ampulla, and the gallbladder and liver lie above it. The descending (second) part drops down beside the pancreatic head, in front of the right kidney; on its inner wall the bile duct and pancreatic duct open on the major duodenal papilla, with the minor papilla a little higher. The horizontal (third) part crosses from right to left over the inferior vena cava and aorta, with the superior mesenteric vessels passing over it. The ascending (fourth) part climbs just left of the aorta to the duodenojejunal flexure, which is held up by the suspensory muscle of the duodenum.

The duodenum receives acidic chyme from the stomach and mixes it with bile and pancreatic juice. Submucosal duodenal (Brunner's) glands secrete an alkaline mucus that helps neutralise the acid. Beyond the bulb the lining is folded into circular folds covered with villi, which begin absorption; iron and calcium are absorbed largely here. Cells in the wall release hormones such as secretin and cholecystokinin that prompt the pancreas and gallbladder to release their secretions.

The first part is the commonest site of peptic ulcers. An ulcer on its back wall can erode the gastroduodenal artery, causing major bleeding, while one on the front wall may perforate into the peritoneal cavity. Because the third part is squeezed between the superior mesenteric artery and the aorta, rapid weight loss can occasionally compress it. The duodenum is the region of the gut where the territory of the coeliac trunk meets that of the superior mesenteric artery.

Function and supply

Function

Receives chyme from the stomach, neutralises its acid, mixes it with bile and pancreatic juice, begins absorption and releases hormones that coordinate digestion.

Nerve supply

Parasympathetic fibres from the vagus and sympathetic fibres from the coeliac and superior mesenteric plexuses.

Blood supply

The superior pancreaticoduodenal arteries, which branch from the gastroduodenal artery (coeliac territory) and the inferior pancreaticoduodenal artery from the superior mesenteric artery; supraduodenal branches for the first part.