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29 Cards in this Set
- Front
- Back
Structure of the GI tract wall
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INNERVATIONAND CONTROL OF MOTILITY
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Stretch receptors in myentericplexus (between the circular and longitudinal muscle layers) sense the passage of a bolus and stimulate neuronesto release an unknown NT which stimulate serotonergicinterneuroneswhich then stimulate motor neuronesto release AChand cause circular muscle contraction
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INNERVATIONAND CONTROL OF MOTILITY
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Stretch receptors also cause activation of Cholinergic interneuroneswhich in turn stimulate inhibitory neuronesto cause relaxation of circular muscle in front of the bolus and also behind the stretch receptors
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Define the term GI motility
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•Definition:
the spontaneous movements of the digestive tube, encompassing Contractile activity / tone Flow / transit Compliance |
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Describe four general functions of motility
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•Propulsion
•Storage •Mixing –Mechanical dispersion –Contact with digestive secretions –Contact with absorptive cells •Prevention of retrograde movement of contents to proximal organs –sphincters |
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Discuss motor functions of different gut regions
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- propulsion
- sotrage - mixing - usually more than one function to an area - all have propulsion |
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List techniques to measure gut motility
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•Radiography/fluoroscopy
•Scintigraphy •Manometry •Barostat |
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Describe major patterns of GI motility
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- oesophagus
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Describe the neural control of gut motility
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•Most activity of GI tract takes place without perception
•mouth, UOS and striated muscle of proximal oesophagus and anus - only conscious influence •other activities of gut proceed automatically and are controlled by autonomic NS and a network of cells in gut wall called the enteric nervous system (ENS) - ACTS LIKE A BRAIN |
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Sphincters
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Major patterns of digestive tract motility
•oesophagus: |
–primary peristalsis: response to swallowing
–secondary peristalsis: response to clear oesophagus |
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Major patterns of digestive tract motility
•stomach: |
–proximal stomach: tonic receptive relaxation to accommodate food- „reservoir‟; subsequent tonic contraction to facilitate emptying
–distal stomach: phasic antral contractions grind and empty contents (0.5-1.5mm)- „antral pump‟ 0.5-1.5 thus things can get stuck (eg chewing gum) |
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The Stomach is Divided into Multiple Anatomic and Only Two Functional Motor Regions
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Motility in Small Bowel
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•small bowel:
–interdigestive motor activity (migrating motor complex) –digestive motor pattern (irregular mixing contractions) |
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MMC
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rapid sequece in response to (fast irregular contraction, lumenal excluding contractions to clear the whole bowel, sweeping down th e bowel, and itgets sloer and sloer and longer and longer as it goes thorugh the bowel (it occurs spontaneusly in the stomach called the stomach brain thing)
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Interdigestive (fasting) motility of the
small bowel Phase 1, 2, 3 |
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The Migrating Motor Complex Occurs Periodically in the Interdigestive State in the Stomach and Small Intestine
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while we sleep our body is actively sweeping and clearing
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Motility in Colon & ano-rectum:
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–phasic & tonic contractions (mixing, propulsion)
–gastro-colic reflex: increased contractile activity after eating –defaecation |
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HPACs
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Scintigraphic colonic transit
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pre and post constipation Tx
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What happens when we are fasting?
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•Small intestine almost empty
•Migrating motor complex (MMC) in stomach –phase I: stomach quiescent –phase II: peristaltic contractions resume –phase III: increase force of contractions, indigestible solid leaves stomach (>1.5mm), contents swept to ileum in 1.5 hours •MMC in small bowel -“housekeeper” : prevent stasis and bacterial overgrowth; three phases |
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What happens when we eat?
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•relaxation proximal stomach
•regular peristaltic contractions in stomach •irregular small intestinal contractions •increase in colonic phasic contractions •increase in colonic tone (30%) |
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Enteric nervous system
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•Controls motility and secretory functions of the intestine
•Semi-autonomous - actions modified by parasympathetic & sympathetic nervous systems - may function independently |
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Three Main Types of Chemical Signaling Occur in the Enteric Nervous System
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The peristaltic reflex
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Autonomic control
•Parasympathetic (PSNS) |
–vagus nerve : oesophagus - ascending colon; vagus also has afferent fibres
–sacral spinal cord : pelvic splanchnic nerves - distal colon and rectum –most important neurotransmitter is acetylcholine (Ach) |
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Autonomic control
•Sympathetic |
–thoracolumbar spinal cord : sympathetic ganglia e.g. coeliac ganglia, and synapse with postganglionic nerve cells whose fibres follow mesenteric vessels and end in intramural plexus
–most important neurotransmitter is noradrenaline –also afferents: distension, ischaemia, mucosal damage |
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ENS vs Autonomic innervation
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•Isolated stomach has peristalsis! ENS
•Fasting: complex pattern, MMC cycling controlled by ENS •Sight/chewing of food: vagus - gastric acid •Accommodation of proximal stomach - vagus •Fed pattern: vagus •Tonic inhibition - sympathetic |
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Symptoms of GI tract dysmotility
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•Oesophagus - heartburn, dysphagia, regurgitation, chest pain
•Stomach - dyspepsia, nausea, vomiting, anorexia, early satiety •Small intestine - abdominal pain, bloating, abdominal distention •Colon - abdominal pain,diarrhoea, constipation •Anorectum - urgency, incomplete evacuation, incontinence, straining |