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Digestive System Part II - Stomach The stomach is divided...

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Stomach The stomach is divided into four areas: Cardia, fundus, body, and pylorus. Cardia - surrounds the superior opening of the stomach near the esophagus. Fundus - the ballon-like portion above and to the left of the cardia which acts as a temporary storage area. Body - the large central portion of the stomach. Pylorus - the narrow inferior region that leads to the duodenum. The pyloric sphincter is a muscular valve that that controls the flow of food from the stomach to the duodenum and prevents the regurgitation of food from the duodenum to the stomach. Digestion in the Stomach Can be divided into two phases: mechanical and chemical. Mechanical- the muscular churning of the food contents that mixes it with the gastric juices and forms the liquid mass called chyme. The muscular movement also propels the chyme toward the duodenum, where the pyloric sphincter opens to allow small portions to enter. Digestion in the Stomach Chemical- The digestion of protein begins here with the secretion of the enzyme, pepsin. Regulation of Gastric Secretions Stimulation Parasympathetic impulses from the medulla via the vagus nerve promote peristalsis stimulate gastric glands to secrete Sight, smell, taste, and thought stimulate gastric secretions by activating parasympathetic nerves originating in the cerebral cortex. Stretching of the stomach by food stimulates receptors in the wall of the stomach that send impulses to the medulla and back to the stomach. Regulation of Gastric Secretions Partially digested protein, caffeine, and a high pH of the chyme stimulates the release of gastrin (a hormone that stimulates the secretion of gastric juices, increases parastalsis, and relaxes the pyloric sphincter. Regulation of Gastric Secretions Inhibition is controlled by sympathetic neural impulses and intestinal hormones Control of sympathetic system the presence of food in the small intestine causes the inhibition of the parasympathetic system and the stimulation of the sympathetic system.
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Negative emotions also stimulates the sympathetic system. Regulation of Gastric Secretions Intestinal hormones that regulate gastric secretions gastric inhibitory peptide (GIP)- secretion of GIP from the intestinal mucosa is stimulated by fatty acids and glucose in the small intestine. It inhibits gastric secretion and slows down gastric emptying. It also stimulates the release of insulin by the pancreas. Regulation of Gastric Secretions Secretin - secretion is stimulated by acid chyme that enters the small intestine. It inhibits secretion of gastric juice and stimulates secretion of pancreatic juices that are rich in bicarbonate ions.
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