Which of the following inhibits gastric phase of gastric secretion: March 2011
Ans. D: Low gastric pHFood in the stomach increase gastric acid secretion by stretching the receptors in the wall of the stomach (mechanical stimulus) The fibers from the receptor enter Meissner's plexus (site of ganglion cells of vagus nerve)Products of digestion (specially amino acids) in the stomach also stimulates gastric mucosa (chemical stimulus)Gastric secretionGastric acid is produced by parietal cells (also called oxyntic cells) in the stomach. There are three phases in the secretion of gastric acid:The cephalic phase: Thiy percent of the total gastric acid secretions to be produced is stimulated by anticipation of eating and the smell or taste of foodThe gastric phase: Sixty percent of the acid secreted is stimulated by the distention of the stomach with food. Plus, digestion produces proteins, which causes even more gastrin productionThe intestinal phase: The remaining 10% of acid is secreted when chyme enters the small intestine, and is stimulated by small intestine distention.Regulation of secretionGastric acid production is regulated by both the autonomic nervous system and several hormones.The parasympathetic nervous system, the vagus nerve, and the hormone gastrin stimulate the parietal cell to produce gastric acid, both directly acting on parietal cells and indirectly, through the stimulation of the secretion of the hormone histamine from enterochromaffine-like cells (ECL).Vasoactive intestinal peptide, cholecystokinin, and secretin all inhibit production.The production of gastric acid in the stomach is tightly regulated by positive regulators and negative feedback mechanisms.Four types of cells are involved in this process: parietal cells, G cells, D cells and enterochromaffine-like cells.Besides this, the endings of the vagus nerve (CN X) and the intramural nervous plexus in the digestive tract influence the secretion significantly.Nerve endings in the stomach secrete two stimulatory neurotransmitters: acetylcholine and gastrin-releasing peptide. Their action is both direct on parietal cells and mediated through the secretion of gastrin from G cells and histamine from enterochromaffine-like cells.Gastrin acts on parietal cells directly and indirectly too, by stimulating the release of histamine.The release of histamine is the most impoant positive regulation mechanism of the secretion of gastric acid in the stomach.Its release is stimulated by gastrin and acetylcholine and inhibited by somatostatin.
Amino acids in stomach
Vagus effect
Distension of the stomach
Low gastric pH