1. NORMAL GASTRO-DUODENAL MOTILITY Interdigestive phase - Migrating motor complex Post-prandial phase - Gastric digestion - Emptying

2. 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

3. 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

4. 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

5. ADAPTIVE RALAXATION OF THE STOMACH No changes in intraluminal pression Increased volume

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. GASTRIC PATHOPHYSIOLOGY Low frequency of contractions and contractile force GASTROPARESIS Abnormal direction of contractions and length over which contractions spread FUNCTIONAL DYSPEPSIA

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

15. 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

16. GASTROINTESTINAL MOTILITY Gastric myoelectrical pace-maker Anatomical site

17. 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

18. Migrating Motor Complex (MMC)

19. 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 IIIIIIIIIIIIIII

20. GASTROINTESTINAL MOTILITY Migrating Motor Complex (MMC) POTENTIAL CONTROL MECHANISMS Central nervous system Cyclic release of a chemical transmitter Enteric nervous system

21. GASTROINTESTINAL MOTILITY MMC: hormone regulation MOTILIN PANCREATIC POLIPEPTIDE SOMATOSTATIN Antral phase 3 Duodenal phase 3 Motilin

22. GASTROINTESTINAL MOTILITY MMC: Hormone regulation MOTILIN ANTRUM Phase 2 Phase 3 ANTRUM Phase 3 Phase 4 DUODENUM Phase 1 Phase 2 Phase 3 SOMATOSTATIN

23. 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

24. 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

25. 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)