Which cells secrete cholecystokinin in the duodenum and jejunum?

Cholecystokinin (CCK) is a peptide hormone that plays a pivotal role in digestion, particularly by stimulating the gallbladder to contract and release bile, as well as promoting the secretion of digestive enzymes from the pancreas. The cells responsible for the release of CCK are known as I cells, located primarily in the duodenum and jejunum.

I cells respond to the presence of fatty acids and certain amino acids in the lumen of the intestine, which trigger their secretion of CCK into the bloodstream. This hormone then acts on various organs, coordinating the digestive process. Understanding the role of I cells is crucial, as they are integral to nutrient digestion and absorption in the small intestine. The other cell types mentioned do not secrete CCK; for example, G cells secrete gastrin, which is involved in gastric function, while S cells produce secretin, which regulates water homeostasis in the body, and M cells are involved in immune responses rather than hormone secretion related to digestion.