Duodenum

The duodenum is the first and shortest part of the small intestine. It is a hollow tube between 10 and 12 inches long connecting the stomach to the jejunum. This first section of the small intestine begins with the duodenal bulb and ends at the ligament of Treitz. Most of the chemical digestion and the absorption of vitamins, minerals, and other nutrients take place in the duodenum. After foods mix with stomach acid , they move into the duodenum, where they mix with bile from the gallbladder, and digestive juices from the pancreas.

The duodenum is largely responsible for the breakdown of food in the small intestine, using enzymes. Brunner's glands, which secrete mucus, are found in the duodenum. The duodenum wall is composed of a very thin layer of cells that form the muscularis mucosae. The duodenum also regulates the rate of emptying of the stomach via hormonal pathways. Secretin and cholecystokinin are released from cells in the duodenal epithelium in response to acidic and fatty stimuli present there when the pyloris opens and releases gastric chyme into the duodenum for further digestion. These cause the liver and gall bladder to release bile, and the pancreas to release bicarbonate and digestive enzymes such as trypsin, lipase and amylase into the duodenum as they are needed.