The duodenum is the most proximal portion of the small intestine. It receives partially digested food from the stomach and begins intensive absorption of nutrients. It is positioned inferior to the stomach and is directly connected to its pyloric part.

The Latin word duodenum means "twelve," and it comes from the Latin duodenum digitorum meaning "12 finger breadths in length." The duodenum is approximately 10 to 12 inches (25 - 30 cm) long tubular organ, and it is the initial part of the small intestine. 

The duodenum is located in the abdominal cavity at the level of the first to third lumbar vertebrae (L1 - L3). The shape of the duodenum resembles the letter "C," or simply it is horseshoe-shaped.

The duodenum wraps around the head of the pancreas (Read more!) and surrounds it from three sides. It ends at the duodenojejunal flexure at the level of the second lumbar vertebra (L2), approximately 0.8 to 1.2 inches (2 - 3 cm) from the midline. Further, it continuous as the next part of the small intestine - the jejunum (Read more!). 

Most of the duodenum is located retroperitoneally, and the duodenum is situated behind the peritoneum. However, the first few centimeters of the duodenum (its superior part) lie intraperitoneally, as they are covered posteriorly and anteriorly by the visceral layer of the peritoneum.