NORMAL GASTRO-DUODENAL MOTILITY

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NORMAL
GASTRO-DUODENAL MOTILITY
Post-prandial phase - Gastric digestion
- Emptying
Interdigestive phase - Migrating motor complex
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POST-PRANDIAL MOTILITY
Reservoir capacity of the stomach Trituration of
food (gastric
outlet resistance) Gastric emptying of liquids
and solids Digestion and dispersion of food
Small intestinal feedback inhibition
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RESERVOIR FUNCTION OF THE STOMACH
Swallowing and oesophageal distension induce a
reflex relaxation of the fundus (adaptive
relaxation) Expansion occurs along the greater
curvature, with little change in the antrum and
the lesser curvature The reflex is responsible
for the accomodation of the stomach after
ingestion and foods
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ADAPTIVE RELAXATION OF THE STOMACH
Adaptive relaxation maintains the intraluminal
pressure within a narrow range, even
though the intragastric volume may
fluctuate Mechanisms involved
- Viscoelastic property of
the smooth muscle
- Stretch-induced
modulation of the muscle tone through intramural
/ vagovagal reflexes
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ADAPTIVE RALAXATION OF THE STOMACH

Increased volume
No changes in intraluminal pression
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TRITURATION OF FOOD
Mechanical process Propulsion of content toward
the gastric outlet by propagating ring
contractions of the corpus and
antrum Retropulsion of content by the closure
of the pylorus Fragmentation of particles occurs
as a result of the crushing of food against
the narrow and rigid distal antrum
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GASTRIC EMPTYING OF LIQUIDS AND PARTICULATE
SOLIDS
Propulsion The wave
moves over the proximal third of the antrum
Distal antrum and pylorus are relaxing
Chyme is forced
into the distal antrum All the gastric contents
are propelled into the antrum at the same time
and at same rate
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GASTRIC EMPTYING OF LIQUIDS AND PARTICULATE
SOLIDS
Evacuation Retropulsion
The wave travels over the distal part of the
antrum Chyme is evacuated through the relaxed
pylorus accompanied with retropulsion Subsequent
wave moves over the gastric body driving digesta
into the proximal antrum Only liquids and smaller
particles escape through the pylorus
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GASTRIC EMPTYING OF LIQUIDS AND PARTICULATE
SOLIDS
Retropulsion Grinding
The wave moves over the terminal antrum with
increasing velocity The contractions of terminal
antrum and pylorus enhance retropulsion and
grinding and prevent obstruction of the pyloric
opening A propagative wave starts on the duodenal
bulb
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GASTRIC EMPTYING OF LIQUIDS AND PARTICULATE SOLIDS
Liquids and suspended particles (lt 2 mm) leave
the stomach early Large particles are retained
until they are broken down and partially digested
Undigested food is retained in the stomach until
the resumption of phase III of the interdigestive
MMC
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GASTRIC EMPTYING TIME Response to food

• Determinants of the rates at which chyme is moved
  in post-prandial phase
• Caloric density
• Mixture of specific nutrients
• Physiological mechanisms
• Overall rate of contractions
• Contractile force
• Length over which contractions spread

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DIGESTION DISPERSION OF FOOD
Chemical process Splitting of starch and
carbohydrate by parotid amylase Emulsification of
fat by lipase (lingual?) Breakdown of protein by
gastric pepsin Mechanical activity allows the
digestive juice to penetrate food particles
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GASTRIC PATHOPHYSIOLOGY

• Low frequency of contractions and
  contractile force
• GASTROPARESIS
• Abnormal direction of contractions and length
  over which contractions spread
• FUNCTIONAL DYSPEPSIA

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SMALL INTESTINAL FEEDBACK INHIBITION
Duodenal chemioreceptors exert a feedback control
of gastric emptying aminoacid
receptors glucoreceptors
lipid receptors (CCK release)
osmoreceptors pH receptors
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INTERDIGESTIVE MOTILITY

• Small, cycling migrating band of intense phasic
  contractions originating from a gastric
  pace-maker and migrating slowly over the length
  of the small bowel
• As one activity front arrives at the terminal
  ileum another begins in the stomach
• The cycle continues until interrupted by food

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GASTROINTESTINAL MOTILITY Gastric myoelectrical
pace-maker
Anatomical site
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GASTROINTESTINAL MOTILITYMigrating motor complex
(MMC)

• PHASE 1 Quiescence (45-50 min)
• PHASE 2 Irregular or random contractions ( 30-45
  min)
• PHASE 3 High amplitude phasic contractions at
  the maximal frequency for the locus (5-15 min)
• PHASE 4 Decreasing contractions merging into
  phase 1

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Migrating Motor Complex (MMC)
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MMC originates in the stomach and LES and
propagates through the intestine
MMC PHASE
III
I
II
III
I
II
III
Slow waves with spikes
Gastric fundus
Gastric antrum
Duodenum
Jejunum
Proximal ileum
Distal ileum
Minutes
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GASTROINTESTINAL MOTILITY Migrating Motor
Complex (MMC)

• POTENTIAL CONTROL MECHANISMS
• Central nervous system
• Cyclic release of a chemical transmitter
• Enteric nervous system

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GASTROINTESTINAL MOTILITY MMC hormone regulation
MOTILIN
Antral phase 3
PANCREATIC POLIPEPTIDE
Antral phase 3
Motilin
Duodenal phase 3
SOMATOSTATIN
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GASTROINTESTINAL MOTILITY MMC Hormone regulation
ANTRUM Phase 2 Phase 3
MOTILIN
ANTRUM Phase 3
Phase 4 DUODENUM
Phase 1 Phase 2
Phase 3
SOMATOSTATIN
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GASTRO-DUODENAL MOTILITY MMC Central nervous
system (CNS) regulation

• It is probably not essential, since extrinsic
  denervation does not abolish cyclic activity
• This hypotesis has been tested in a variety of
  experimental transplantation models

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GASTRO-DUODENAL MOTILITYMMC hormone regulation

• MMC periodicity is related to cyclic fluctuations
  of motilin, PP, somatostatin
• Serum peaks of motilin and PP preceed
  somatostatin rise

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GASTRO-DUODENAL MOTILITY MMC Enteric Nervous
System (ENS) regulation

• It is considered to be the major control
  mechanism for interdigestive cycles of motility
• Phase 2 activity seems not influenced by ENS
  (reduction by truncal vagotomy abnormal in IBS
  patients)