The superior part of the duodenum is the most proximal portion and extends from the pyloric opening of the stomach to the gallbladder. This part is short - only around 2 inches (5 cm) long. It lies anterolateral to the body of the first lumbar vertebra (L1) (Read more!).

The superior part of the duodenum extends laterally, superiorly and posteriorly from the pylorus (Read more!) and then makes a sharp turn inferiorly, forming the superior duodenal flexure (Read more!).

This part of the duodenum also transitions from entirely intraperitoneal to a retroperitoneal position. The first 0.8 inches (2 cm) is mobile and attached via the hepatoduodenal ligament to the liver. The first 0.8 inches (2 cm) are intraperitoneal. In contrast, the peritoneum covers only the anterior aspect of the distal 1.2 inches (3 cm) of the superior part, meaning it has a retroperitoneal position.

Clinical note: The beginning (around 0.7 - 1.2 inches or 2 - 3 cm) of the superior part is enlarged, and it is called the duodenal bulb or duodenal cap. The internal surface of the bulb is lined by smooth mucosa that lacs pronounced mucosal folds. Also, the duodenal bulb is the most common site where most duodenal ulcers develop.

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Superior part of duodenum