Integrated Response to a Meal

Integrated Response to a Meal - Dr. Kennon M. Garrett...

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Dr. Kennon M. Garrett GI-57 INTEGRATED RESPONSE TO A MEAL Learning objectives Describe the GI functions and their regulation during the Cephalic, Gastric, Intestinal and Interdigestive phases. _____________________________________________________________________________ The response to a meal can be divided into 4 Phases: Cephalic, Gastric, Intestinal and Interdigestive. I. Cephalic Phase The cephalic phase begins with presentation and ingestion of a meal. (1) The sight, smell and taste of food as well as mechanical stimulation of the oral cavity and swallowing initiate a number of "long" reflexes (2-6) which alter GI activities. (2) During this phase salivation is stimulated by cholinergic reflexes mediated by parasympathetic nerves. ( 3) Reflexes initiated during swallowing stimulate primary peristalsis in the esophagus and cause relaxation of the upper and lower esophageal sphincters. (4) Vagal reflexes inhibit contractile activity in the proximal stomach [receptive relaxation].
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Dr. Kennon M. Garrett GI-58 (5) Vagal reflexes initiated during the cephalic phase also stimulate acid secretion by parietal cells in the stomach. These "long" reflexes, acting through cholinergic neurons of the enteric nerve plexus, stimulate secretion of HCl by parietal cells and secretion of histamine by enterochromaffin-like (ECL) cells. Histamine in turn stimulates parietal cell secretion of acid. In addition, vagal reflexes to the antrum stimulate secretion of the hormone gastrin from G cells. Elevated levels of circulating gastrin increase acid secretion by direct stimulation of parietal cells and by stimulating histamine secretion from ECL cells. (6) Vagal reflexes also induce a relatively small stimulation of enzyme secretion by the exocrine pancreas. During the cephalic phase the process of digestion of complex carbohydrates is begun due to the activity of ptyalin secreted in saliva. Little absorption occurs during this phase.
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Dr. Kennon M. Garrett GI-59
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This note was uploaded on 10/01/2011 for the course PSYO 5016 taught by Professor Staff during the Fall '11 term at The University of Oklahoma.

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Integrated Response to a Meal - Dr. Kennon M. Garrett...

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