Gastrointestinal System

1. Gastrointestinal System Instructor: Ge Shun Department of Physiology Jining medical college Office: 0850 physiological sciences Email: geshun@tom.com

2. Gastrointestinal System 1. G.I. Physiology: general organization of G.I. tract 2. Mastication and deglutition 3. Gastric secretion 4. Regulation of gastric secretion 5. Pathophysiology of peptic ulcer 6. Biliary and pancreatic secretions 7. Physiology of colon 8. Pathophysiology of diarrhea disease

3. Gastrointestinal System includes GI tract plus the accessory organs.

4. Four processes carried out by the GI tract

5. Digestive secretions from the liver and the pancreas are delivered into the duodenum of the small intestine through the sphincter of Oddi.

6. Functions of small intenstine movements • Mixes the luminal contents with secretions • Brings the contents nto contact with the epithelial surface • Slowly advances the luminal material toward the large intenstine

7. Structure of the GI Tract Wall

8. Structure of the GI Tract Wall

10. (I) Physiological properties of gastrointestinal smooth muscle (1) General properties - Low excitability - High extensibility - Tonic contraction - Autorhythmicity - High sensitivity to temperature, stretch & chemical stimulation

11. (2) Electrophysiological properties • (a) Resting potential: • - between -50 and -60 Mv - Ionic basis • -Em (selective membrane permeability to K+) -Electrogenic Na+-K+ pump

12. (b) Slow wave (basic electrical rhythm,BER) • - The spontaneous rhythmic, subthreshold depolarizations of the cell membrane (slow wave) of the gastrointestinal tract • - Initiated in the interstitial cells of Cajal (ICC) (pacemaker cell)

13. Slow wave (basic electrical rhythm) - Intensity: 5~15 mV - Frequency: 3~12 cpm - Ionic mechanism spontaneous rhythmic changes in Na+-K+ pump activity

14. Frequencies: 3-12 per minute

16. (c) Spike potentials (action potentials) • only at the peaks of slow waves • Threshold: -40 mV

17. Spike potential (Action potential) -Duration: 10~20 ms -Ionic mechanism: • Depolarization: Ca2+ influx • Repolarization: K+ efflux

18. The higher the slow wave potential rises, the greater the frequency of the spike potentials

19. (II) Neural control of gastrointestinal function Enteric nervous system Extrinsic nervous system

20. Myenteric plexus : control over GI motility Submucous plexus: regulate gastrointestinal blood flow and control GI secretion

21. (III) Hormonal Regulation --GI hormones • The hormones synthesized by a large number of endocrine cells within the gastrointestinal tract • Brain-gut peptides: a number of the classical GI hormones are also synthesized in the brain

22. Four main types • Gastrin • Cholecystokinin • Secretin • Gastric inhibitory polypeptide (GIP)

23. (IV) Phases of Gastrointenstinal Control • Cephalic phase • Gastric phase • Intenstinal phase • Three phase of gastric secretion.swf

24. Summary • Terms: - Basic electrical rhythm (BER) or slow waves - Gastrointestinal (GI) hormones • Three phase of gastric secretion

25. Mouth, Pharynx, and Esophagus • Secretion of saliva The Salivary Glands • Parotid gland • Mandibular gland • Sublingual gland

26. Saliva 1000 ml/d pH 6.0~7.0 Composition of saliva -H2O -Na+, Cl-, K+, HCO3--Mucus (containing mucin) -Amylase, lysozyme, …

27. Swallowing

29. Digestion in the Stomach

30. Chief cells synthesize and secrete the protease precursor known as pepsinogen. Parietal cells synthesize and secrete the hydrochloric acid responsible for the acidic pH in the gastric lumen.

31. (I) Gastric juice • Hydrochloric acid Secreted by the parietal cells Output - Basal: 0~5 mmol/h - Maximal: 20~25 mmol/h

33. Acid production by the parietal cells in the stomach depends on the generation of carbonic acid; subsequent movement of hydrogen ions into the gastric lumen results from primary active transport.

35. Four chemical messengers regulate HCl secretion

36. Role of HCl - Acid sterilization - Activation of pepsinogen - Promotion of secretin secretion - Assisted effect of iron and calcium absorption

37. (2) Pepsinogen

38. (3) Mucus-HCO3- barrier

39. If the mucus-HCO3- barrier is weak?

40. (4) Intrinsic factor • A high molecular weight glycoprotein, synthesized and secreted by the parietal cells • •The intrinsic factor binds to Vit B12 and facilitates its absorption

41. (II) Regulation of gastric secretion (1) Basic factors that stimulate gastric secretion - Acetylcholine (+ all secretory cells) - Gastrin (+ parietal cells) - Histamine (+ parietal cells)

42. (2) Nervous regulation • ‘Short’ reflex pathways • ‘Long’ autonomic pathways

43. (3) Humoral regulation

44. (4) Phases of gastric secretion • Cephalic phase • Gastric phase • Intestinal phase

45. Motor Function of the Stomach

46. Motor Function of the Stomach • Receptive relaxation - Storage function (1.0~1.5 L) - Vago-vagal reflex • Peristalsis - BER in the stomach

47. Motor Function of the Stomach

48. Emptying of the stomach Emptying rate - Fluid > viscous - Small particle > large particle - Isosmotic > hyper- & hypo-osmotic - Carbohydrates > Protein > Fat - Regular meal 4～6 hrs

49. Summary Terms: - Receptive relaxation (Storage function of the stomach) - Mucus-HCO3- barrier - Intrinsic factor Gastric secretion (including the composition and physiological function of the gastric juice, the regulation of gastric secretion)

50. Pancreatic Secretion