NORMAL GASTRO-DUODENAL MOTILITY

Interdigestive phase

- Migrating motor complex

Post-prandial phase

- Gastric digestion - Emptying

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 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

Migrating Motor Complex (MMC)

MMC originates in the stomach and LES and propagates through the intestine

Gastric fundus

Gastric antrum

Duodenum

Jejunum

Proximal ileum

Distal ileum

Minutes

MMC PHASE% Slow waves with spikes

III I II III 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

Antral phase 3

Duodenal phase 3

Motilin

GASTROINTESTINAL MOTILITY MMC: Hormone regulation

MOTILINANTRUM Phase 2 Phase 3

ANTRUM Phase 3 Phase 4 DUODENUM Phase 1

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 MOTILITYMMC: 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)