Cholecystokinin

Name source, action and regulation.

I cells of duodenum and jejunum

Increases pancreatic secretions

Increases gallbladder contraction

decreases gastric emptying

Upregulated by fatty acids and amino acids

Secretin

Name source, action and regulation.

Released by S cells of the duoenum

Increases pancreatic bicarbonate secretin

Decreases gastric acid secretion

Increases bile secretion

Upregulated by acid, and fatty acids in the lumen of the duodenum.

Somatostatin

Name source, action and regulation.

D cells of the pancreatic islets and GI mucosa.

Decreases gastric acid and pepsinogen secretion.

Decreases pancreatic and small intestine fluid secretion.

Decreases gall bladder contraction.

Decreases insulin and glucagon release.

Upregulated by acid, decreased by vagal stimulation.

Glucose-dependent insulinotropic peptide (GIP)

Name source, action and regulation.

K cells of the duodenum and jejunum.

Exocrine function: Decrease gastric acid secretion.

Endocrine function: increase insulin release.

Increased by fatty acids, amino acids and oral glucose.

Vasoactive intestinal polypeptide (VIP)

Name source, action and regulation.

Parasympathetic ganglia in sphincters, gall bladder and small intestine.

Increases intestinal water and electrolyte secretion

Increases relaxation of intestinal smooth muscle and sphincters.

Upregulated by distention and vagal stimulation.

Downregulated by andrenergic input.

Nitric Oxide

Name source, action and regulation.

All throughout GI.

Promotes smooth muscle relaxation; including the lower esophageal sphincter.

Parasympathetic regulation.

Motilin

Name source, action and regulation.

Small intestine.

Produces migrating motor complexes (MMCs)

Upregulated in the fasting state.

Ghrelin

Name source, action and regulation.

P/DI cells of the stomach.

Up regulates growth hormone release, ACTH, cortisol and prolactin secretion.

Upregulated before meals

Downregulated after meals