Enteroendocrine cells are specialized cells of the gastrointestinal tract and pancreas with endocrine function. They produce gastrointestinal hormones or peptides in response to various stimuli and release them into the bloodstream for systemic effect, diffuse them as local messengers, or transmit them to the enteric nervous system to activate nervous responses. Enteroendocrine cells of the intestine are the most numerous endocrine cells of the body. They constitute an enteric endocrine system as a subset of the endocrine system just as the enteric nervous system is a subset of the nervous system. In a sense they are known to act as chemoreceptors, initiating digestive actions and detecting harmful substances and initiating protective responses. Enteroendocrine cells are located in the stomach, in the intestine and in the pancreas. Microbiota plays key roles in the intestinal immune and metabolic responses in these enteroendocrine cells via their fermentation product (short chain fatty acid), acetate.
Intestinal enteroendocrine cells are not clustered together but spread as single cells throughout the intestinal tract.
Hormones secreted include somatostatin, motilin, cholecystokinin, neurotensin, vasoactive intestinal peptide, and enteroglucagon. The enteroendocrine cells sense the metabolites from intestinal commensal microbiota and, in turn, coordinate antibacterial, mechanical, and metabolic branches of the host intestinal innate immune response to the commensal microbiota.
K cells secrete gastric inhibitory peptide, an incretin, which also promotes triglyceride storage. K cells are mostly found in the duodenum.
L cells secrete glucagon-like peptide-1, an incretin, peptide YY3-36, oxyntomodulin and glucagon-like peptide-2. L cells are primarily found in the ileum and large intestine (colon), but some are also found in the duodenum and jejunum.
I cells secrete cholecystokinin (CCK), and are located in the duodenum and jejunum. They modulate bile secretion, exocrine pancreas secretion, and satiety.