Is irritable bowel syndrome an organic disorder?

Table 1 Overview of the main endocrine cells in the gastrointestinal tract

Cell content	Localization	Source of release	Actions
Serotonin (5-HT)	EC cells in the stomach, large and small intestines	Noradrenalin; acetylcholine; acidification and intraluminal pressure	Inhibits gastric emptying and stimulates colonic motility; accelerates small- and large-intestine transit activates the submucosal sensory branch of the enteric nervous system that conveys sensation from the gut to the central nervous system
Histamine	EC-like cells in the gastric oxyntic mucosa	Vagus nerve stimulation and inhibited by somatostatin	Stimulates gastric acid secretion
Somatostatin	The stomach, and large and small intestines	Mixed meal and acidification of the stomach	Inhibits intestinal contraction; inhibits gut exocrine and neuroendocrine secretion
Ghrelin	Gastric oxyntic mucosa	Protein and fat ingestion; suppressed by carbohydrate ingestion	Increases appetite and food intake; stimulates gastric and intestinal motility
Gastrin	Gastric antral mucosa	Intraluminal peptides; amino acids; calcium; amines; low pH and prostaglandins. Somatostatin inhibits release	Stimulates gastric acid secretion and histamine release; trophic action on gastric mucosa; stimulates contraction of the LES and antrum
CCK	Small intestine, especially the duodenum	Intraluminal protein and fat and inhibited by somatostatin	Inhibits gastric emptying; stimulates gallbladder contraction and intestinal motility; stimulates pancreatic exocrine secretion and growth; regulates food intake
Secretin	Small intestine, especially the duodenum	Acidification and inhibited by somatostatin	Stimulates pancreatic bicarbonate and fluid secretion; inhibits gastric emptying; inhibits contractile activity of the small and large intestines
GIP	Small intestine, especially the duodenum	Intraluminal glucose; amino acids and fat	Incretin action; inhibits gastric acid secretion
Motilin	Small intestine, especially the jejunum	Protein and fat ingestion	Induces phase-III migrating motor complex; stimulates gastric emptying; stimulates contraction of the LES
Neurotensin	Small intestine	Fat	Stimulates pancreatic section; inhibits gastric secretion; delays gastric emptying; stimulates colon motility
PYY	Terminal ileum and large intestine	Protein-rich meals	Delays gastric emptying; inhibits gastric and pancreatic secretion, stimulates the absorption of water and electrolytes; major mediator of the ileal brake
PP	Terminal ileum and large intestine	Protein-rich meals	Inhibits pancreatic secretion; stimulates gastric acid secretion; relaxes the gallbladder; stimulates motility of the stomach and small intestine
Enteroglucagon (oxyntomodulin)	Terminal ileum and large intestine	Intraluminal carbohydrates and fat	Inhibits gastric and pancreatic secretion; reduces gastric motility; has some incretin effect
Chromogranin	All gastrointestinal tract segments	Ingestion of a meal	Induces formation, sorting, and release of secretory granules of the gut endocrine/paracrine cells; an inflammatory mediator

CCK: Cholecystokinin; EC: Enterochromaffin; GIP: Gastric inhibitory peptide; LES: Lower esophageal sphincter; PP: Pancreatic polypeptide; PYY: Peptide YY.