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PHGY210- Lecture 28- Dr. Wechsler.docx

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PHGY 210
Ann Wechsler

th Lecture 27- Monday, March 15 , 2010 Vomiting involves three stages: (i)Nausea – a psychic experience (ii)Retching – abrupt, uncoordinated respiratory movements with glottis closed (iii) Emesis – actual expulsion of contents of upper GIT: individual takes deep breath, closes glottis, contracts abdominal muscles, exerting pressure on gastric contents. Emesis is completed with the reversal of thoracic pressures from –ve to +ve, as the diaphragm is displaced upwards, forcing esophageal contents to be expelled through the mouth. Upper Small Intestine 1. Neutralization 2. Osmotic Equilibration 3. Digestion 4. Absorption Motor Activites of Small Intestine Pages 603-604 1. Effective Mixing 2. Slow propulsion 2-6 hours Intestinal Contractions -governed by electrical characteristics of sm. Muscle -FREQUENCY governed by BER (ECA) -ERA (spikes)- Phase locked to BER -Amplitude of contraction- related to the number of spikes/burst of ERA (spikes) Intestinal BER (ECA) Intrinsic f of different cells is very different- it declines systematically from proximal to distal intestine Mechanism regulating intestinal motility: The BER (ECA) generated by the muscle fibres in the small intestine shows an aborally declining frequency gradient, with the highest frequency (12/min) in the duodenum and the lowest (8/min) in the terminal ileum. This gradient is determined by a series of pacemaker regions along the intestine, each with a slightly lower frequency than the preceding one. The distribution of the BER in time and space along the intestine establishes the distribution of spikes (ERA) and consequent contractions; thus, the proximal portions of the intestine exhibit more activity than the distal ones. The maximal contractile activity in the small intestine cannot exceed the BER frequency of that gut segment. Proximal vs. Distal Small Intestine 1. f of BER is greater 2. Excitability of smooth muscle is greater 3. Thickness of smooth muscle is greater Therefore both frequency and amplitude of contractions is greater in proximal small intestine. Most common type of contractile activity: -Standing rings of contraction- SEGMENTATION 1. Myogenic res
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