All of the following have inhibitory effect on secretion of gastrin, except
The gastric secretions arise from glands in the wall of the stomach that drain into its lumen, and also from the surface cells that secrete primarily mucus and bicarbonate to protect the stomach from digesting itself, as well as substances known as trefoil peptides that stabilize the mucus-bicarbonate layer The acid secreted by parietal cells serves to sterilize the meal and also to begin the hydrolysis of dietary macromolecules. Intrinsic factor is impoant for the later absorption of vitamin B12, or cobalamin (Figure 26-6). Pepsinogen is the precursor of pepsin, which initiates protein digestion. Lipase similarly begins the digestion of dietary fats. There are three primary stimuli of gastric secretion, each with a specific role to play in matching the rate of secretion to functional requirements. Gastrin is a hormone that is released by G cells in the antrum of the stomach both in response to a specific neurotransmitter released from enteric nerve endings, known as gastrin-releasing peptide (GRP, or bombesin) and also in response to the presence of oligopeptides in the gastric lumen. Gastrin is then carried through the bloodstream to the fundic glands, where it binds to receptors not only on parietal (and likely, chief cells) to activate secretion but also on so-called enterochromaffin-like cells (ECL cells) that are located in the gland and release histamine. Histamine is also a trigger of parietal cell secretion, binding to H2 histamine receptors. Finally, parietal and chief cells can also be stimulated by acetylcholine, released from enteric nerve endings in the fundus. The three agonists of the parietal cell--gastrin, histamine, and acetylcholine--each bind to distinct receptors on the basolateral membrane. Gastrin and acetylcholine promote secretion by elevating cytosolic free calcium concentrations, whereas histamine increases intracellular cyclic adenosine 3&;,5&;-monophosphate (cAMP).Stimuli that affect gastrin secretion.Stimuli that increase gastrin secretionLuminal Peptides and amino acids Distention 2 .Neural Increased vagal discharge GRP 3 Bloodborne Calcium EpinephrineStimuli that inhibit gastrin secretion 1. Luminal Acid Somatostatin 2. Bloodborne Secretin, GIP, VIP, glucagon, calcitoninREF: GANONG&;S REVIEW OF MEDICAL PHYSIOLOGY, KIM BARRETT, SCOTT BOITANO, HEDDWEN BROOKS, SUSAN BARMANTWENTY THIRD EDITIONPAGE NO:432,445
Acid in duodenum
VIP
Epinephrine
Glucagon
G.I.T