Duodenal

Duodenal refers to the duodenum, the first segment of the small intestine. In adults it measures about 25–30 cm and forms a C-shaped curve that begins at the pylorus and ends at the duodenojejunal flexure, located in the upper abdomen. It is classically divided into four parts: the superior (bulb), descending (with the major and minor papillae), horizontal, and ascending portions.

The proximal mucosa contains Brunner glands that secrete alkaline mucus to neutralize gastric acid. The major duodenal papilla receives bile and pancreatic ducts (via the hepatopancreatic ampulla) and the minor papilla may drain an accessory duct. The duodenum continues digestion and begins significant absorption, particularly of iron, calcium, and folate, while chyme is neutralized and mixed with pancreatic juice and bile.

Arterial supply comes from the gastroduodenal and superior pancreaticoduodenal arteries, with contributions from the inferior pancreaticoduodenal arteries; venous drainage follows to the portal system. Lymphatic drainage goes to pancreaticoduodenal and celiac nodes. Innervation is parasympathetic via the vagus nerve and sympathetic via celiac and superior mesenteric plexuses.

Common duodenal pathology includes ulcers (often linked to Helicobacter pylori or NSAID use), duodenitis, and, rarely, tumors. Congenital conditions such as annular pancreas can encircle the second part of the duodenum and cause obstruction. Evaluation typically involves endoscopy and imaging, with management directed at the underlying cause.