duodenum
Meaning of duodenum: Short as it is, this stretch is where most chemical digestion happens and where several other organs empty their secretions.
Definition of duodenum
The duodenum is the first and shortest section of the small intestine, a C-shaped curve running from the stomach outlet around the head of the pancreas to the jejunum. Partly digested food arrives here in small squirts, and pancreatic enzymes and bile enter through a shared opening in its wall to break down fat, protein and starch.
What happens inside it?
Stomach contents arrive strongly acidic and only coarsely broken down. Cells in the duodenal lining, together with the pancreas, release bicarbonate that neutralizes the acid so that enzymes can work, and glands in the wall add alkaline mucus for the same reason. Bile from the liver and gallbladder emulsifies fat into droplets small enough for enzymes to attack. Pancreatic enzymes then split fats, proteins and starches into pieces the intestine can absorb. Iron and calcium are taken up here more than anywhere else along the gut.
How does it control what reaches it?
| Hormone made in the lining | Released when | Effect |
|---|---|---|
| Secretin | Acid arrives from the stomach | Prompts the pancreas to release bicarbonate |
| Cholecystokinin | Fat and protein arrive | Squeezes the gallbladder, releases pancreatic enzymes, slows stomach emptying |
| Motilin | Between meals, when the gut is empty | Drives the sweeping waves that clear residue onward |
This feedback is why the duodenum is described as the pacemaker of the upper digestive system. It admits food only as fast as it can be neutralized and treated, and it signals back to the stomach to wait.
Why do problems elsewhere show up here?
Because so much converges on a few centimeters of gut. Duodenal ulcers form most often in the first part, just past the stomach, and are usually linked either to infection with Helicobacter pylori or to regular use of anti-inflammatory painkillers; they are grouped with stomach ulcers under peptic ulcer disease, though the pattern of pain differs somewhat. Gallstones, pancreatitis and tumors at the head of the pancreas can all obstruct the shared duct opening, producing jaundice or pain centered here. Celiac disease is confirmed from biopsies taken from this lining, because gluten damages it before it damages the intestine further down. Unlike the rest of the small intestine, most of the duodenum is fixed against the back wall of the abdomen rather than hanging free, which shapes both how it is reached by endoscope and how injury there behaves.
Used in a sentence
Endoscopy revealed an ulcer in the duodenum near its junction with the stomach.
Good to know
An ulcer in the duodenum is grouped with stomach ulcers under the broader term peptic ulcer, though the two differ somewhat in their typical pattern of pain.
Word origin
Where “duodenum” comes from
From Latin duodeni, meaning twelve each, reflecting an early description of the duodenum as roughly twelve finger-breadths in length.