1. 1 Chapter 31 Gastrointestinal Regulation and Motility

2. 2 We require:  carbohydrates (mainly glucose)  proteins (essential amino acids)  fats (but Western diet fats too high)  vitamins  minerals Nutrition Carbohydrate 50% Fat 35% Protein 15% Intake (normally 3000- 6000kcal per day & depends on Geography Occupation

3. 3 Gastrointestinal system consists of Gastrointestinal (GI) tract Accessory glandular organs

4. 4 Anatomy and functions of the GI tract GI tract mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus Accessory Glandular Organs salivary glands, liver, gallbladder, pancreas

5. 5 Histology/organization of the Gut Wall From esophagus to anus, GI tract has the same basic arrangement of tissues. There are 4 layers that can be distinguished Mucosa Submucosa Muscularis Serosa

6. 6 Layers of Alimentary Canal Serosa Submucosa Mucosa Circular muscle layer Longitudinal muscle layer

7. 7 Mucosa Serosa Submucosa Longitudinal muscle Circular muscle Layers of Alimentary Canal Myenteric plexus Submucosal plexus

8. 8 1.Digestion of food and absorption of nutrients are accomplished in a long tube connected to the external world at both ends 2.Secretion and motility of “the tube” are major themes in understanding the gut.

9. 9 1. Ingestion : process of eating 2. Propulsion : passing of food down the GI tract swallowing : voluntary peristalsis : reflex, involuntary, involves alternating contractions of muscles in body walls of GI organs 3. Mechanical digestion prepares food for chemical digestion includes chewing, mixing with saliva by tongue action, churning in stomach... Processing of food by the DS

10. 10 4. Chemical digestion catabolic steps in which food is broken down to basic building blocks accomplished by enzymes in digestive juices 5. Absorption : passage of food particles into the blood- lymph 6. Defecation: elimination of indigestible food substances Processing of food by the DS

11. 11 Gastrointestinal Motility: Movements that mix and circulate the gastrointestinal contents and propel them along the length of the tract Secretion: Process by which the glands associated with the gastrointestinal tract release water and substance into the tract Digestion: Process by which food and large molecules are chemically degraded to produce smaller molecules that can be absorbed across the wall of the gastrointestinal tract. Absorption: Process by which nutrient molecules are absorbed by cell that line the gastrointestinal tract and enter the bloodstream

12. 12 I REGULATION OF GASTROINTESTINAL TRACT FUNCTIONS

13. 13 CellHormoneSite GGastrin (G)autrumn, duodenum ICholecystokinin (CCK) duodenum 、 jejunum SSecretin duodenum 、 jejunum DSomatostatin (SS)Stamoch, duodenum, pancreas, colon LEnteroglucagonSmall intestine, colon PPPancreatic polrpeptide (PP)pancreas EC1Substance P (SP)Stamoch, intestine D1VIPStamoch, intestine, pancreas PbombesinAntrum, duodenum Nneurotensinileum Binsulinpancreas Aglucagonpancreas KGastric inhibitory polypeptide(GIP) duodenum 、 jejunum MomotilinStamoch, intestine Endocrine Cell and gut hormone

14. 14 Types of secretion

15. 15 Function of GI hormones 1. Regulate the secretion and motility of GI tract Gastrin HCl secretion, gastric empty 2. Trophic action Gastrin stomach and duodenum mucosa 3. Regulate the release of other hormones GIP insulin SS GH, gastrin

16. 16 Innervation of the GI tract 1. Central nervous system

17. 17 CNS to gut connections SPINAL CORD dorsal root ganglion Spinal afferent Vagal afferent Vagal efferent nodose ganglion BRAIN STEM

18. 18 2. The autonomic nervous system Sympathetic system: Noradrenaline Gut secretions (+) Spinal cord Pons/ medulla Mid brain Gut sphincters (-) Pancreas (+) ACTION Rectum (+)defaecation ACTION Gut wall (+) adrenaline EFFECTS Salivary glands (+) X IX VII Cranial nerves Parasympathetic system: Acetylcholine (Ach)  (+) salivary glands  (+) gut blood  2 (-) vessels  1/2 (-) gut wall,  (+) sphincters (+) secretion Adrenal medulla

19. 19 Innervation of the GI tract

20. 20 Innervation of the GI tract 3. Intrinsic (enteric) nerve plexuses Located in the submucosa (submucosal or Meissner’s plexus) and between circular and longitudinal muscle layers (myenteric or Auerbach’s plexus) Control Motility - Myenteric plexus Secretion - Submucosal plexus through release of neurotransmitters Excitatory - Acetylcholine, Substance P Inhibitory - VIP, nitric oxide Excitatory - Acetylcholine

21. 21 The enteric nervous system Deep muscular plexus Submucosal artery Muscularis mucosa Submucosal plexus MUCOSA Myenteric plexus Longitudinal muscle Circular muscle

22. 22

23. 23 The enteric nervous system coordinates digestion, secretion motility to optimize nutrient absorption. Its activity is modified by information from the CNS from local chemical and mechanical sensors.

24. 24 Myenteric plexus Submucosal plexus Enteric nervous system CNS Sympathetic ganglia Vagal nuclei Sacral spinal cord Preganglionic fibres Postganglionic fibres Preganglionic fibres Parasympathetic n.sSympathetic n.s. Smooth muscle Secretory cells Blood vessels Endocrine cells Innervation of the GI tract Postganglionic fibres

25. 25 Gastrointestinal reflex

26. 26 II GASTROINTESTINAL SMOOTH MUSCLE

27. 27 Musculature of the GI tract  All smooth muscle except:  Upper third oesophagus – striated  Middle third of oesophagus – mixed  External anal sphincter – striated  Areas of striated muscle are areas that are under conscious control

28. 28 Form hollow tubes  not contracting against skeleton Form a syncitium - electrically coupled, joined by gap junctions  contractions synchronous Actin:myosin ratio 15:1 (skeletal muscle 2:1) Contractile elements not arranged in sarcomeres  not striated Anatomical Properties of GI smooth muscle 5-10  m 200  m

29. 29 General Functional characteristics 1. Lower excitability, slower contraction and relaxation 2. Higher extensibility 3. Tonic contraction 4. Autorhythmicity 5. More sensitive to stretch, chemicals, cold and warm stimulation but not to electric stimulation

30. 30 Electrical activity of GI smooth muscle 1. Resting potential 2. Slow wave or basic electric rhythm The smooth muscle membrane slowly depolarizes and repolarizes in a cyclic fashion 3. Action potential 4. Relationship to contraction

31. 31 0 -60 Membrane potential (mV) Tension 0 -60 Tension Membrane potential (mV) Acetylcholine

32. 32  Slow waves are changes in resting membrane potential  3-12 cycles per minute depending on area of GI tract - 3/min in stomach, 12/min small intestine  Always present but do not always cause contractions  Frequency of contractions dictated by frequency of slow waves  Slow wave frequency and height modulated by – body temp & metabolic activity, intrinsic & extrinsic nerves circulating hormones Slow waves in GI smooth muscle

33. 33 Relationship to contraction

34. 34

35. 35 Contraction threshold AP threshold

36. 36 Contraction of GI smooth muscle Out In Ca 2+ (Ca 2+ ) 4. calmodulin Inactive myosin light chain kinase Active myosin light chain kinase MUSCLE CONTRACTION Myosin -(PO 4 ) 2 Calcium activates contraction Depends on influx of calcium from extracellular space through calcium channels Calcium- calmodulin complex activates myosin light chain kinase Contraction explained by sliding filament theory Out In Ca 2+ (Ca 2+ ) 4. calmodulin Inactive myosin light chain kinase Active myosin light chain kinase MUSCLE CONTRACTION Myosin -(PO 4 ) 2 Out In Ca 2+ (Ca 2+ ) 4. calmodulin Inactive myosin light chain kinase Active myosin light chain kinase MUSCLE CONTRACTION Myosin -(PO 4 ) 2

37. 37 AP in GI smooth muscle

38. 38 4. Noradrenaline release 5. Sympathetic stimulation more hyperpolarised smooth muscle,  Less excitable and fewer contractions StimulusEffect on muscle Electrical activity and muscle contraction 1. Stretch of GI tract wall 2. Acetylcholine release 3. Parasympathetic stimulation more depolarised smooth muscle,  more excitable. Leads to action potential generation and smooth muscle contraction

39. 39 GI motility There are many types of contractions in different areas of the GI tract. Some muscles contract and relax in seconds – Phasic Contractions -Peristalsis and Segmentation Some maintain contractions over minutes or hours – Tonic Contractions -Sphincter