Gastrointestinal system

1. Gastrointestinal system Xiang-Yao LI, PhD Department of Physiology Zhejiang University School of Medicine Email: lixiangy@zju.edu.cn

2. Functions of the digestive system • The digestive system is response for the absorption of ingested nutrients, water, minerals and other essential factors and is central to the regulation and integration of the metabolic process throughout the body. Normal function of the digestive system is necessary for long-term whole body homeostasis.

3. Alimentary Canal Continuous, muscular digestive tube winding throughout the body Digests and absorbs food particles Contains the following organs: Mouth, Pharynx, Esophagus, Stomach, Small Intestine Large Intestine Accessory Digestive Organs Contains the following organs: Teeth, Tongue, Salivary Glands Liver, Gallbladder, Pancreas

5. The four processes carried out by the GI tract: digestion, secretion, absorption, and motility.

6. Many functions in the gut are found in specific locations along its length. Most of the absorption of nutrients occurs in the small intestine, so most of digestion is accomplished there or upstream.

8. Functions of the digestive system • Movement: propels food through the digestive system • Secretion: Release of digestive juices in response to a specific stimulus • Digestion: Breakdown of food into molecular components small enough to cross the plasma membrane • Mechanical (physical): Chew,Tear,Grind,Mash,Mix • Chemical: Enzymatic reactions to improve digestion of • Carbohydrates,Proteins,Lipids • Absorption: Passage of the molecules into the body's interior and their passage throughout the body • Elimination: Removal of undigested food and wastes

9. Fun Facts • HOW LONG ARE YOUR INTESTINES? At least 25 feet in an adult. Be glad you're not a full-grown horse -- their coiled-up intestines are 89 feet long! • Food drying up and hanging out in the large intestine can last 18 hours to 2 days! • In your lifetime, your digestive system may handle about 50 tons!!

10. Histology of the GI Tract

11. Microscopic Anatomy of the Esophagus

12. Microscopic Anatomy of the stomach

13. Microscopic Anatomy of the Small Intestine

14. Microscopic Anatomy of the Large Intestine

16. General properties of gastrointestinal smooth muscle • Low excitability • High distensibility • Tonic contraction • Autorhythmicity • High sensitivity to temperature, stretch and chemical stimulation

17. Electrophysiological properties of gastrointestinal smooth muscle • Resting membrane potential • -40~-80 mV • Ionic basis • Em (selective membrane permeability to K+, Na+, Cl- and Ca2+) • Electrogenic Na+-K+ pump

19. Slow wave (basic electrical rhythm) • The spontaneous rhythmic, subthreshold depolarizations of the cell membrane (slow wave) of the gastrointestinal tract that characterizes the underlying electrical activity of the bowel • Initiated in the interstitial cells of Cajal (ICC) (pacemaker cell)

20. Santiago Ramon Y Cajal • He and Camillo Golgi received the Nobel Prize in 1906 for introduction of the silver-chromate stain

21. Slow wave (basic electrical rhythm) • Intensity: 10~15 mV • Frequency: 3~12 cpm • Ionic mechanism • spontaneous rhythmic changes in Na+-K+ pump activity

23. Normal BER frequencies in the gastrointestinal system

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

26. The digestion and absorption Carbohydrate About 250-300g/day: Plant polysaccharides starch (2/3), Disaccharides: sucrose, lactose (1/3) Mouth(5%) + Small intestine (95%) Amylase Brush border enzymes Cellulose (fiber) Large intestine Bacteria

28. Proteins

29. Proteins

30. Fat

31. Fat

33. Neural control of gastrointestinal function • Enteric nervous system (intrinsic) • Autonomic nervous system (extrinsic)

36. Enteric (Intrinsic) nervous system • Myenteric plexus (Auerbach’s plexus) • Submucosal plexus (Meissner’s plexus) • Neurotransmitters secreted by enteric neurons • Ach, NE, ATP, serotonin, dopamine, cholecystokinin, substance P, vasoactive intestinal polypeptide, somatostatin, leu-enkephalin, met-enkephalin, bombesin, etc.

39. Autonomic nervous system • Parasympathetic nerve • Mainly ACh • Stimulatory (+) • Sympathetic nerve • NE • Inhibitory (-)

40. Afferent sensory nerve fiber from the gut • Sensory fibers with their cell bodies in the ENS terminate in the ENS • Sensory fibers with their cell bodies in the ENS send axons upward through the ANS to terminate in the prevertebral sympathetic ganglia • Sensory fibers with their cell bodies in the dorsal root ganglia or in the cranial nerve ganglia send axons to multiple area of the spinal cord or brain stem

42. Gastrointestinal reflexes • Three types • Reflexes that are integrated entirely within the enteric nervous system • Reflexes from the gut to the prevertebral sympathetic ganglia and then back to the gastrointestinal tract • Reflexes from the gut to the spinal cord or brain stem and then back to the gastrointestinal tract

43. Gastrointestinal hormones • The hormones synthesized by a large number of endocrine cells within the gastrointestinal tract • Physiological functions • Control of the digestive function • Control of the release of other hormones • Trophic action

44. Gastrointestinal hormones • Four main types • Gastrin • Secretin • Cholecystokinin (CCK) • Gastric inhibitory peptide (GIP)

47. Digestion in the stomach

48. The swallowing reflex is coordinated by the medulla oblongata, which stimulates the appropriate sequence of contraction and relaxation in the participating skeletal muscle, sphincters, and smooth muscle groups.

49. The coordinated sequence of contraction and relaxation in the upper esophageal sphincter, the esophagus, and the lower esophageal sphincter is necessary to deliver swallowed food to the stomach.

50. Now it's... QUIZ TIME!