Cell to cell communication in the GI system is mediated by ENS, modulated by hormones
Hormones and endocrine work through secretion, paracrine works through diffusion, neurocrine through action potentials
Hormones released into blood in response to changes in luminal composition
ECL cells are of a closed type
Incretins are GIP (gastric inhibitory peptide) and GLP-1 (glucagon-like peptide-1)
Gastrin family includes gastrin and cholecystokinin (CCK)
Secretins include secretin, VIP, GIP, GLP-1
Motilins are secreted between meals, and activate MMC to sweep remnants from antrum to terminal ileum to colon
Gastrin (G cells) are released by peptides in the stomach and neural reflexes and target ECL and parietal cells - they stimulate gastric acid production and are inhibited by somatostatin release
Cholecystokinin (I cells) are released by fatty acids and target the gallbladder, pancreas, stomach - they promote satiety and inhibit gastric emptying while stimulating pancreatic enzyme secretion
Secretin (S cells) is released due to acid in small intestine and targets pancreas and stomach - stimulates bicarbonate secretion to protect GI tract
Motilin (M cells) is released from fasting and targets smooth muscle to stimulate MMC - inhibited by eating
GIP (K cells) is released by glucose and targets beta cells of pancreas - stimulates insulin release
GLP-1 (L) is released by mixed meals of carbohydrates and fats and targets endocrine pancreas - stimulates insulin release, promotes satiety
Long reflexes are in CNS, short reflexes are in ENS
Ghrelin is the hunger hormone - lower in patients who've had gastric bypass surgery