NORMAL
GASTRO-DUODENAL MOTILITY
Post-prandial phase
- Gastric digestion
- Emptying
Interdigestive phase
- Migrating motor complex
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
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
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
ADAPTIVE RALAXATION
OF THE STOMACH
No changes
in intraluminal
pression
Increased
volume
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
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
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
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
GASTRIC EMPTYING OF LIQUIDS
AND PARTICULATE SOLIDS
Liquids and suspended particles (< 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
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
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
GASTRIC PATHOPHYSIOLOGY
• Low frequency of contractions
and contractile force
GASTROPARESIS
• Abnormal direction of contractions
and length over which contractions
spread
FUNCTIONAL DYSPEPSIA
SMALL INTESTINAL FEEDBACK
INHIBITION
Duodenal chemioreceptors exert a
feedback control of gastric emptying
aminoacid receptors
glucoreceptors
lipid receptors (CCK release)
osmoreceptors
pH receptors
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
GASTROINTESTINAL MOTILITY
Gastric myoelectrical pace-maker
Anatomical site
GASTROINTESTINAL MOTILITY
Migrating 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
Migrating Motor Complex (MMC)
MMC originates in the stomach and LES
and propagates through the intestine
MMC PHASE
III
I
II
III
% Slow waves
with spikes
Gastric fundus
Gastric antrum
Duodenum
Jejunum
Proximal ileum
Distal ileum
Minutes
I
II
III
GASTROINTESTINAL MOTILITY
Migrating Motor Complex (MMC)
POTENTIAL CONTROL MECHANISMS
• Central nervous system
• Cyclic release of a chemical transmitter
• Enteric nervous system
GASTROINTESTINAL MOTILITY
MMC: hormone regulation
MOTILIN
PANCREATIC
POLIPEPTIDE
SOMATOSTATIN
Antral phase 3
Motilin
Antral phase 3
Duodenal phase 3
GASTROINTESTINAL MOTILITY
MMC: Hormone regulation
MOTILIN
ANTRUM
Phase 3
Phase 4
DUODENUM
Phase 1
Phase 2
Phase 3
ANTRUM
Phase 2
Phase 3
SOMATOSTATIN
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
GASTRO-DUODENAL MOTILITY
MMC: hormone regulation
• MMC periodicity is related to cyclic
fluctuations of motilin, PP, somatostatin
• Serum peaks of motilin and PP preceed
somatostatin rise
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)