The duodenum is part of the digestive system. It is the initial part of the small intestine, the other two parts are the jejunum and the ileum. It follows the stomach through the pylorus, the terminal part of the stomach, and ends with the jejunum at the duodenojejunal angle. The duodenum is the only fixed part of the small intestine, the other two being mobile. The excretory ducts from the pancreas and the biliary tract arrive at this segment.

The duodenum is mainly used for digestion, its function is to neutralize the strong acidity of the chyme, the food digested by the stomach. The duodenum defends itself from chemical and mechanical aggressions by the secretion of mucus, protecting the mucosa. It is in the duodenum that many nutrients are absorbed such as calcium, iron, vitamins and lipids.