OESS - HHDGI10Neurohumoral_reg

OESS- - 1 OVERVIEW of NEUROHUMORAL REGULATION OF GI FUNCTION April Apperson UCSD SOM OESS Digestion and absorption of a meal requires neurohumoral

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1 OVERVIEW of NEUROHUMORAL REGULATION OF GI FUNCTION April Apperson, UCSD SOM OESS Digestion and absorption of a meal requires neurohumoral regulation to coordinate GI motility and GI secretions within the organs of the GI tract. The digestion and absorption of a meal can be considered in three phases that correlate with the majority of food moving through three regions of the GI tract: Phase Timing Major GI motility: Major GI secretions Cephalic phase Occurs before the majority of food reaches the stomach, so this is prior to the meal and while chewing the early portion of meal Chewing and swallowing (esophagus) Saliva Gastric phase Occurs while the majority of food is in the stomach Gastric motility – both proximal stomach (corpus and fundus) and distal stomach (antrum and pylorus) Gastric juice Intestinal phase Occurs while the majority of food is in the small intestine Gastric and duodenal motility Bile (from liver) Pancreatic juice Neurohumoral regulation involves both neural reflexes and humoral regulation and is mediated through neurocrine , endocrine and paracrine factors. •The effects of neural reflexes are mediated by the neurocrine actions of neurotransmitters released from enteric nervous system (ENS) efferent nerves. •Humoral regulation is mediated by endocrine or paracrine effects of factors secreted by cells within the GI system. Phase Neural reflexes: Humoral effects Cephalic phase Sight, smell, touch, anticipation and taste of food initiates a cephalic reflex that: •strongly stimulates saliva secretion •stimulates some gastric juice secretion and some gastric motility •stimulates a small amount of bile and pancreatic juice secretion None (Mechanical effects of chewing also stimulate saliva secretion) Gastric phase Food volume stretching the stomach wall initiates a gastric distension reflex that: •strongly stimulates gastric juice secretion •stimulates proximal stomach relaxation and distal stomach “grinding” motility •stimulates some bile and pancreatic juice secretion and some duodenal motility Peptides, amino acids and Ca ++ in the stomach acting on apical membrane receptors of gastric endocrine G cells stimulate secretion of gastrin , which stimulates secretion of gastric juice. Intestinal phase CCK activity initiates a CCK sensory reflex that: •inhibits gastric juice secretion •stimulates proximal stomach relaxation and distal stomach “grinding” motility •strongly stimulates bile and pancreatic juice secretion and duodenal motility A combination of nutrients and dietary protein in the intestinal lumen stimulate the secretion and activity of CCK , which acts endocrinely to stimulate pancreatic juice secretion and bile delivery.
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This note was uploaded on 09/14/2011 for the course PHARM gs taught by Professor Staff during the Spring '11 term at UCSD.

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OESS- - 1 OVERVIEW of NEUROHUMORAL REGULATION OF GI FUNCTION April Apperson UCSD SOM OESS Digestion and absorption of a meal requires neurohumoral

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