The duodenum is the upper portion of the small intestines in mammals. The duodenum is the section of the intestines that connects to the stomach and pancreas.It's the location where digestion takes place.he duodenum's function is to accept chyme from the stomach and complete the digestion of food. Chyme is the mixture of stomach acid and swallowed food. Bile released from the gallbladder is also delivered to the duodenum for fat digestion.