The function of the duodenum is to start the process of breaking food down into components the body can use. This structure is located at the top of the small intestine, at the site where the stomach dumps its contents, or chyme. It mixes secretions from the liver and pancreas with the chyme to create a semi-fluid mixture that passes through the small intestine so nutrients can be absorbed. In addition to aiding digestion, the duodenum also regulates gastric emptying and the release of pancreatic fluids and bile from the liver.
Between the stomach and the duodenum, a sphincter prevents materials from backflowing into the stomach while still permitting the release of chyme. When the duodenum is ready for a new load, it sends hormonal signals that trigger the release of material from the stomach. Contractions mix the chyme thoroughly with bile, which emulsifies fats to make them easier to process, and pancreatic juices. These secretions start breaking down complex components into things that the body can use; for example, it pulls proteins apart into their component peptides.
As material moves through the duodenum, contractions keep it mixing and make sure the mass becomes more uniform, another function of the duodenum. When it passes into the next part of the small intestine, the body can start absorbing useful nutrients through the walls of the intestine while passing waste products along. These move into the large intestine, which empties into the colon. Along the way, water is absorbed to turn the liquid mixture into a more solid mass.
The dual digestive and regulatory function of the duodenum involves considerable coordination. It needs to tell the pancreas and liver when to release more bile and pancreatic juices, signal the stomach to empty, and coordinate the contractions used to mix these secretions together. Studies on the function of the duodenum show that it plays a role in the endocrine system because of the hormones involved in stomach signaling, and errors in this process may contribute to issues like not knowing when to stop eating or being unable to fully empty the stomach for digestion.
Human survival is possible without this organ. The function of the duodenum can be replaced by other components of the small intestine, although they don’t work as efficiently. This can actually be deliberately induced with some kinds of weight loss surgery where the goal is to reduce nutrient absorption to help people lose weight. Removal of the duodenum also appears to reverse type two diabetes in some patients who have this condition.