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Gastric and intestinal motility

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Western University
Physiology 3120
Tom Stavraky

Human Physiology Wednesday, March 31, 2010 “Gastrointestinal VI” Gastric Motility (cont’d) • The tracing shown last class deals with slow waves only; doesn’t deal with mechanical activity; need to induce APs at the blips to produce mechanical activity; orientation of slow waves dictates the sequence of contractile waves (wave of propulsion is a result of sequential contractions at progressively distal gastric segments) • If you make cuts between the segments, each segment goes to its own intrinsic frequency, with the most proximal part having the highest frequency; in an intact stomach, the frequencies are the same, but the most proximal part of the stomach is the most dominant oscillator (i.e. the pacemaker); the importance of this property is to ensure a wave of contraction to push stuff into the intestine, and a system that moves material faster as you move towards the pylorus • Vagus has very few branches to the stomach  Vagal information stimulates the enteric nervous system, which projects to smooth muscle, as well as secretory cells; placing a balloon into the stomach and inflating it will cause motility because it activates stretch receptors, which activates the ENS to release ACh, which works on the slow wave to induce mechanical activity Gastric Emptying • Absorptive and digestion capacity of the duodenum is limited; so don’t want to overwhelm it by pumping all the material into the duodenum at once; want to regulate how quickly food gets from distal stomach to duodenum; not to mention the acidity of the stomach fluid that must be neutralized by the pancreas • Can either increase or decrease the rate of emptying  Increase rate  Increase volume  Decrease rate  Increase acidity  Increase fat  Increase protein
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