The duodenum is a small part (25-30 cm) of the small intestine and is connected directly to the stomach. However, almost all of the chemical digestion that takes place in the body takes place in this part of the intestine. It contains mucous membranes that release chemicals and enzymes that assist in digestion. It is also where the bile duct (which carries bile from the gall bladder) and the pancreatic duct exit into the intestines.
Ulcers can appear in the duodenum, but the symptomology is different from a gastric ulcer in that pain decreases when a patient eats.