Cholecystokinin.

Cholecystokinin, often abbreviated as CCK, is a peptide hormone secreted from mucosal epithelial cells in the duodenum, the first portion of the small intestine. CCK is an important facilitator of digestion in the small intestine. CCK helps deliver digestive enzymes from the pancreas and bile from the gallbladder into the small intestine. The hormone is secreted by neurons in the enteric nervous system, the localized nervous system of the digestive system. CCK is also found throughout the brain, and it is one of the most essential human brain peptides.