The duodenum lies at the beginning of the small intestine. Together with the jejunum, and the ileum it forms the small intestine. It is connected to the stomach above and the jejunum below it. When food enters the duodenum, there are multiple feed-back pathways and nervous reflexes that will affect how fast the stomach empties as well as the secretion of other hormones.

Digestion is a complex process and the objective of the entire process is to provide energy for sustenance of the human body. The human digestive system consists of the digestive tract and other organs that are necessary for the digestion of food, absorption of nutrients, and elimination of waste.