Gastrointestinal Motility

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  • Created by: Becca
  • Created on: 24-12-13 01:21
What is the structure of the gastrointestinal system (deep -> superficial)?
Mucosa, submucosa, submucosal plexus, inner circular muscle, myenteric plexus, outer longitudinal muscle
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What principally happens during gut motility?
Pacemaker cells initiate a spreading basal electrical rhythm. Interstitial cells of Cajal are sensitive to stretch, stimulate GI contractility directly or by modulating local neural reflexes to control the direction of chyme movement
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Which neurotransmitters are involved in gut motility?
ACh: muscarinic receptors cause constriction of smooth muscle above chyme. VIP (vasoactive intestinal polypeptide) causes relaxation of smooth muscle. GI activity also influenced by locally produced hormones & chemicals
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How are the parasympathetic & sympathetic nervous systems involved in gut motility?
Parasympathetic: ACh, increases motility. Sympathetic: noradrenaline, decreases motility directly via B-adrenoceptors or indirectly by decreased ACh release via a2-adrenoceptors
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What are the the first stages of GI motility before a bolus reached the stomach?
Mastication & deglutition: oesophagus separated at either end by sphincters, create zone of elevated pressure, prevents transit from one region to another.
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How does a food bolus move into the oesophagus? How is this mechanism controlled?
Peristalsis: mechanoreceptors in pharynx detects bolus, initiates peristaltic wave. Controlled by vagal nerves (gravity assisted), rate proportional to viscosity of bolus, 2nd peristaltic wave initated by local vago-vagal reflexes
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What controls a peristaltic wave?
Basal electrical rhythm not always associated with peristalsis. Controlled by myogenic properties of smooth muscle, activity of intrinsic/extrinsic nerves & hormones or locally produced chemicals
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What is the neural control of gastric motility?
Vagal relaxatory fibres: induce relaxation in corpus/fundus, stimulated by oesophageal & gastric distension, mediated by VIP. Sympathetic NS: noradrenaline inhibits via inhibition of parasympathetic ganglionic transmission, activated by SI distension
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What is the hormonal control of gastric motility?
Stimulatory: gastrin (antrum) & motilin (from small intestine). Inhibitory: gastrin (proximal stomach), secretin & CCK
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Apart from gastric motility, what does the rate of chyme moving into duodenum depend on?
Meal composition, volume (greater=faster rate), fragment size (only solid, less than 1mm), osmolarity (greater/smaller than 200mOsm slows rate), acid (slows rate), fat (slows rate)
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How does motility in the small intestine happen?
Segmenting contractions occur in circular muscle, moves cyme to & fro, increases exposure to mucosal surface. Peristaltic contractions: longitudinal muscle, short distances, occassional propulsion over long distances called migrating motility complex
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How is motility in the small intestine controlled?
Myogenic mechanisms (stretch, local chemicals), myenteric plexus (local regulation) & extrinsic nerves (vagus (not very important), sympathetic: pre-synaptic inhibitor)
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What is the motility in the large intestines?
Movement is slow & non-propulsive - haustral contractions knead contents, 3/4 times/day powerful contractions drives contents to distal end, initiated by food in stomach = gastro-colic reflex. Principal function for H20 reabsorption & faecal storage
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What happens during defecation?
Arrival of faeces induces desire to defecate via sensory nerves, causes peristaltic wave in colon, internal & external sphincters relax. Defecation reflex: myenteric plexus (weak), parasympathetic reflex, voluntary effort, straining inreases pressure
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Card 2

Front

What principally happens during gut motility?

Back

Pacemaker cells initiate a spreading basal electrical rhythm. Interstitial cells of Cajal are sensitive to stretch, stimulate GI contractility directly or by modulating local neural reflexes to control the direction of chyme movement

Card 3

Front

Which neurotransmitters are involved in gut motility?

Back

Preview of the front of card 3

Card 4

Front

How are the parasympathetic & sympathetic nervous systems involved in gut motility?

Back

Preview of the front of card 4

Card 5

Front

What are the the first stages of GI motility before a bolus reached the stomach?

Back

Preview of the front of card 5
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