Enteroendocrine

Enteroendocrine refers to a diverse population of hormone-secreting cells interspersed among the epithelial lining of the gastrointestinal tract, and to the hormonal signaling system they comprise. These cells form part of the diffuse neuroendocrine system and originate from endodermal progenitors in the intestinal crypts. They can be classified as open-type, which extend an apical process into the lumen to sample contents, or closed-type, which do not contact the lumen.

Enteroendocrine cells produce a variety of peptide hormones and amines that regulate digestive processes and energy balance. Common hormones include gastrin (stimulates gastric acid), cholecystokinin (stimulates pancreatic enzyme secretion and gallbladder contraction), secretin (stimulates bicarbonate release), and glucose-dependent insulinotropic peptide (GIP). In the distal small intestine and colon, glucagon-like peptide-1 (GLP-1) and GLP-2 modulate insulin release and gut growth, while serotonin-secreting enterochromaffin cells influence motility and secretion. Hormones such as ghrelin, produced in the stomach, also have enteroendocrine functions. The secretions can act endocrinologically (into the bloodstream) or paracrinely, affecting neighboring cells.

Physiology and regulation: EEC activity responds to luminal nutrients, pH, and neural signals, enabling rapid coordination of digestion, absorption, and energy homeostasis. Developmentally, their differentiation involves transcription factors such as neurogenin-3 (NGN3).

Clinical relevance: abnormalities in enteroendocrine cells or their tumors can lead to gastroenteropancreatic neuroendocrine tumors (GEP-NETs). Incretin hormones from EECs underlie therapies for type 2 diabetes, illustrating the medical significance of the enteroendocrine system.