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Motility In The Gi Tract Notes

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Lecture 3 Motility in the GI Tract

Regulation of GI function o Transmitters
 Intrinsic NS

• Excitatory= ACh and Substance P

• Inhibitory= Vasoactive intestinal peptide (VIP) & Nitric Oxide (NO)
 Extrinsic NS

• Parasympathetic= ACh

• Sympathetic= Noradrenaline o Types
 Hormonal regulation

• Endocrine cell A

1. Circulating hormones (Endocrine)

2. Via blood

3. Act on secretory cells or even paracrine cells

• Endocrine cell B

1. Paracrine (locally) act on secretory cells
 Neural regulation


• Enteric nerves

• Act directly on smooth muscle, or endocrine cell A o Phases of GI control
 CEPHALIC phase

• Sight, smell, taste and chewing
 GASTRIC phase

• Distension, acidity etc.

• Distension, acidity, osmolarity etc. Musculature of GI tract o Motor activity of GI performs 3 functions
 Non-propulsive or Segmentation movements

• "Churning" to promote digestion

• Most frequent type of movement in small intestine

• Rhythmic contraction and relaxation of circular muscle layer

• Mixes chime & brings fresh chime into contact with mucosal surface
 Peristaltic movements

• Relatively low frequency

• Progressive contraction of successive sections circular muscle layer

• Propel chime short distance, allows time for digestion/absorption

• Contraction behind & relaxation in front of bolus of food
 Reservoir function

• Lower oesophageal sphincter (LES) & pyloric sphincter help function

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