|Anatomical terms of microanatomy|
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.
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.
Main article: G cell
Stomach enteroendocrine cells, which release gastrin, and stimulate gastric acid secretion.
Enterochromaffin cells are enteroendocrine and neuroendocrine cells with a close similarity to adrenomedullary chromaffin cells secreting serotonin.
Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell secreting histamine.
Located in the jejunum, N cells release neurotensin, and control smooth muscle contraction.
Main article: S cell
S cells secrete secretin from the duodenum and jejunum, and stimulate exocrine pancreatic secretion.
Main article: Delta cell
Also called Delta cells, D cells secrete somatostatin.
Gastric enteroendocrine cells are found in the gastric glands, mostly at their base. The G cells secrete gastrin, post-ganglionic fibers of the vagus nerve can release gastrin-releasing peptide during parasympathetic stimulation to stimulate secretion. Enterochromaffin-like cells are enteroendocrine and neuroendocrine cells also known for their similarity to chromaffin cells secreting histamine, which stimulates G cells to secrete gastrin.
Other hormones produced include cholecystokinin, somatostatin, vasoactive intestinal peptide, substance P, alpha and gamma-endorphin.
Pancreatic enteroendocrine cells are located in the islets of Langerhans and produce most importantly the hormones insulin and glucagon. The autonomous nervous system strongly regulates their secretion, with parasympathetic stimulation stimulating insulin secretion and inhibiting glucagon secretion and sympathetic stimulation having opposite effect.
Other hormones produced include somatostatin, pancreatic polypeptide, amylin and ghrelin.
Rare and slow growing carcinoid and non-carcinoid tumors develop from these cells. When a tumor arises it has the capacity to secrete large volumes of hormones.
The very discovery of hormones occurred during studies of how the digestive system regulates its activities, as explained at Secretin § Discovery.