Cholecystokinin (CCK) is a peptide hormone produced in the small intestine, primarily in response to the intake of fats and proteins. Its main functions include stimulating the gallbladder to release bile, which aids in fat digestion, and promoting the secretion of pancreatic enzymes. CCK also plays a role in regulating appetite by signaling satiety to the brain, helping to control food intake. Additionally, it may influence gastrointestinal motility and the overall digestive process.