Gastrin Source: - G cells (stomach antrum, duodenum) Action: - Inc: H+ secretion; gastric mucosa growth; gastric motility Regulation: - Inc: stomach distention; AAs, peptides; vagal stimulation - Dec: pH <1.5 Somatostatin Source: - D cells (pancreatic islets, GI mucosa) Action: - Dec: gastric H+ and pepsinogen secretion; pancreatic and SmI fluid secretion; gallbladder contraction; insulin and glucagon release Reguation: - Inc: acid - Dec: vagal stimulation Cholecystokinin Source: - I cells (duodenum, jejunum) Action: - Inc: pancreatic secretion; gallbladder contraction; Oddi sphincter relaxation - Dec: gastric emptying Regulation: - Inc: fatty acids, AAs Notes: - CCK acts on neural muscarinic pathways to cause pancreatic secretion Secretin Source: - S cells (duodenum) Action: - Inc: pancreatic HCO3 secretion; bile secretion - Dec: gastric acid secretion Regulation: - Inc: acid, FA in lumen of duodenum Notes: - HCO3 neutralises gastric acid in duodenum - so pancreatic enzymes can function GIP Source: - K cells (duodenum, jejunum) Action: exocrine: Dec gastric H+ secretion endocrine: Inc insulin release Regulation: - Inc FA, AA, oral glucose Notes: - Glucose-dependent insulinotropic peptide aka gastric inhibitory peptide. Motilin Source: small intestine Action: Produces migating motor complexes Regulation: - Inc: in fasting state Notes: Motilin receptor agonists used to stimulate intestinal peristalsis. VIP Source: parasympathetic ganglia in sphincters, gallbladder, small intestine Action: - Inc: intestinal water and electrolyte secretion; relaxation of intestinal smooth muscle and sphincter Regulation: - Inc: by distention and vagal stimulation - Dec: by adrenergic input Nitric oxide Action: - Inc: smooth muscle relaxation, Intrinsic factor Source: - Parietal cells (stomach) Action: - binds with VitB12 - required for uptake of VitB12 in terminal ilium Notes: Autoimmune destruction of parietal cells -> chronic gastritis and pernicious anaemia Gastric acid Source: - parietal cells (stomach) Action: - Decreases stomach pH Regulation: - Inc: histamine, gastrin, ACh - Dec: somatostatin, GIP, prostoglandin, secretin Notes: - gastrinoma: gastrin-secreting tumour that cause high levels of acid and ulcers refractory to medical therapy (PPI) Pepsin Source: chief cells (stomach) Action: protein digestion Regulation: - Inc: vagal stimulation, local acid Notes: pepsinogen is inactive form; converted to pepsin (active) by stomach HCl HCO3- Source: Mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner glands (duodenum) Action: neutralises acid Regulation: - Inc: by pancreatic and biliary secretion with secretin Notes: HCO3 is trapped in mucus that covers gastric epithelium Source