GI Motility!

GI Motility!

1. Motility

   • Grind, mix
     • easier digest
     • propel
   • Contractile
     • Smooth muscle
       • X -> Pharynx, upper 1/3 oesophagus, ext anal sphincter
       • Types
         • Multi Unit
           • Independent cells
             • own input, stimulant
         • Single
           • Linked gap junctions
             • Propagate
           • GI Tract
     • peristaltic
       • Rhythmic
         • Leading wave distention
       • Layers
         • Myenteric Plexus impt nerve supply peristalsis
         • Longitudinal
           • Outside
         • Circular
   • Mechanisim
     • Calcium
       • Bind Calmodulin -> Ca2+ - Calmodulin
         • Activate inactive Myosin Light Chain Kinase
           • Pi inactive myosin -> active phosphorylated myosin
             • Relax, opp Myosin phosphatase
     • Latch State
       • High force, low energy
         • Maintain high tension, cross-bridge binding
           • < myosin head detach
     • Slow wave potential
       • Threshold
         • Action potential
           • > frequent = more force contract
       • Interstitial cells of Cajal (ICC)
         • Initiate
         • Pacemakers
         • Myenteric Plexus lot
         • Intrinsic rate 3-12/min
           • Stomach, 3 min
           • Duodenum, 12 min
           • X affected neural, hormonal
             • Affect action potential frequency
         • Motor Neurone Effect
           • Inhibit
             • Nitric Oxide
             • Vasoactive intestinal Polypeptide
             • ATP
           • Excite
             • ACh
             • Substance P
       • Ionic
         • Voltage-gated Ca2+ open
           • Action potential
             • Ca influx -> > intracel Ca
               • Open Ca-dependent K+ channel
                 • K+ down conc gradient to outside cells
                   • Slow hyperpolarisation
                     • volt-gated Ca close
                       • Ca depend K+ close
       • Electrical Activity
         • RMP: -50 mv
         • Depolarize
           • > = > frequent AP
           • Stimulate
             • Stretch
             • ACh
             • Parasymp
         • Hyperpolarize
           • Noradrenaline
           • Symp

2. Chew

   • Mix w Saliva
     • Mucin (Glycoprotein) Lubricant
   • smaller
   • Mix enzymes
     • Salivary amylase
     • Lipase
   • Involuntary
     • reflex by food in mouth
     • Sensory
       • Mechanoreceptor -> Brainstem
       • reflex oscillatory pattern activity muscles
         • frequency
         • Extent
   • Voluntary

3. Swallow

   • Phase
     • Oral
     • Pharyngeal
     • Oesophageal
   • Voluntary initiate
     • Swallow Reflex
       • Afferent
         • Sensory from touch receptors near pharynx
       • Swallowing Centre
         • Medulla
         • Lower Pons
       • Efferent Motor
         • Cranial innervate pharynx, upper oesophagus
         • Vagal -> lower oesophagus
       • Steps
         • Upper oesophageal sphincter open -> bolus -> close
           • 1o peristalsis mediated by swallow reflex
             • coordinated contract -> high Pa behind bolus + gravity
             • Lower oeso sphincter open (peptidergic nerves in vagus release VIP)
               • Receptive relax orad region stomach
   • Achalasia
     • X relax
     • Dysphagia
       • lower oeso sphincter X relax
         • Selective loss neurons release VIP regulate LOS
       • impair peristalsis distal part