From which cell type found in the gastrointestinal tract is cholecystokinin (CCK) secreted?

There are a wide range of enteroendocrine cell types (see below) but it is specifically the 'I-cells' of the duodenum that secrete CCK. CCK is responsible for modulation of bile secretion, exocrine pancreas secretion, and satiety. G-cells of the stomach secrete gastrin. Pancreatic enteroendocrine cells (found within the Islets of Langerhans) secrete insulin, glucagon, somatostatin, pancreatic polypeptide, amylin and ghrelin. Parietal cells of the stomach secrete intrinsic factor and hydrochloric acid. Chief cells of the stomach secrete pepsinogen and gastric lipase.