Human secretin is a gastrointestinal peptide hormone that regulates secretions in the stomach, pancreas, and liver. The hormone is produced from the enterochromaffin cells in the duodenum in response to the duodenal content with the pH less than 4.5 . The main action of secretin is to stimulate the pancreas to secrete pancreatic juice for pH regulation in the small intestines. Secretin is also responsible in body fluid homeostasis and bile production. Although it is a gastrointestinal hormone, secretin is also considered as a neuropeptide hormone since it is also expressed in the central nervous system.