<Li> The gastric phase: About sixty percent of the total acid for a meal is secreted in this phase . Acid secretion is stimulated by distension of the stomach and by amino acids present in the food . </Li> <Li> The intestinal phase: The remaining 10% of acid is secreted when chyme enters the small intestine, and is stimulated by small intestine distension and by amino acids . The duodenal cells release entero - oxyntin which acts on parietal cells without affecting gastrin . </Li> <P> Gastric acid production is regulated by both the autonomic nervous system and several hormones . The parasympathetic nervous system, via 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 . </P> <P> 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 . </P>

The secretion of gastric juices in the stomach is stimulated by
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