Gastrointestinal Regulation And Motility


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  • Gastrointestinal Regulation And Motility

    1. 1. Chapter 31 Gastrointestinal Regulation and Motility
    2. 2. <ul><li>We require : </li></ul><ul><ul><li>carbohydrates (mainly glucose) </li></ul></ul><ul><ul><li>proteins (essential amino acids) </li></ul></ul><ul><ul><li>fats (but Western diet fats too high) </li></ul></ul><ul><ul><li>vitamins </li></ul></ul><ul><ul><li>minerals </li></ul></ul>Nutrition Intake (normally 3000-6000kcal per day & depends on Geography Occupation Carbohydrate 50% Fat 35% Protein 15%
    3. 3. Gastrointestinal system consists of Gastrointestinal (GI) tract Accessory glandular organs
    4. 4. Anatomy and functions of the GI tract <ul><li>GI tract </li></ul><ul><ul><li>mouth, pharynx, esophagus, </li></ul></ul><ul><ul><li>stomach, small intestine, </li></ul></ul><ul><ul><li>large intestine, anus </li></ul></ul><ul><li>Accessory Glandular Organs </li></ul><ul><li>salivary glands, liver, gallbladder, pancreas </li></ul>
    5. 5. Histology/organization of the Gut Wall <ul><li>From esophagus to anus, GI tract has the same basic arrangement of tissues. </li></ul><ul><li>There are 4 layers that can be distinguished </li></ul><ul><ul><ul><li>• Mucosa </li></ul></ul></ul><ul><ul><ul><li>• Submucosa </li></ul></ul></ul><ul><ul><ul><li>• Muscularis </li></ul></ul></ul><ul><ul><ul><li>• Serosa </li></ul></ul></ul>
    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. <ul><li>Digestion of food and absorption of nutrients are accomplished in a long tube connected to the external world at both ends </li></ul><ul><li>Secretion and motility of “the tube” are major themes in understanding the gut. </li></ul>
    9. 9. <ul><li>1. Ingestion : process of eating </li></ul><ul><li>2. Propulsion : passing of food down the GI tract </li></ul><ul><ul><li>• swallowing : voluntary </li></ul></ul><ul><ul><li>• peristalsis : reflex, involuntary, involves alternating contractions of muscles in body walls of GI organs </li></ul></ul><ul><li>3. Mechanical digestion </li></ul><ul><ul><li>• prepares food for chemical digestion </li></ul></ul><ul><ul><li>• includes chewing, mixing with saliva by tongue action, churning in stomach... </li></ul></ul>Processing of food by the DS
    10. 10. <ul><li>4. Chemical digestion </li></ul><ul><ul><li>• catabolic steps in which food is broken down to basic building blocks </li></ul></ul><ul><ul><li>• accomplished by enzymes in digestive juices </li></ul></ul><ul><li>5. Absorption : passage of food particles into the blood-lymph </li></ul><ul><li>6. Defecation : elimination of indigestible food substances </li></ul>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 lin the gastrointestinal tract and enter the bloodstream
    13. 13. Endocrine Cell and gut hormone Cell Hormone Site G Gastrin (G) autrumn, duodenum I Cholecystokinin (CCK) duodenum 、 jejunum S Secretin duodenum 、 jejunum D Somatostatin (SS) Stamoch, duodenum, pancreas, colon L Enteroglucagon Small intestine, colon PP Pancreatic polrpeptide (PP) pancreas EC1 Substance P (SP) Stamoch, intestine D1 VIP Stamoch, intestine, pancreas P bombesin Antrum, duodenum N neurotensin ileum B insulin pancreas A glucagon pancreas K Gastric inhibitory polypeptide(GIP) duodenum 、 jejunum Mo motilin Stamoch, intestine
    14. 14. Types of secretion
    15. 15. Function of GI hormones <ul><li>1. Regulate the secretion and motility of GI tract </li></ul><ul><li>Gastrin HCl secretion, gastric empty </li></ul><ul><li>2. Trophic action </li></ul><ul><li>Gastrin stomach and duodenum mucosa </li></ul><ul><li>3. Regulate the release of other hormones </li></ul><ul><li>GIP insulin </li></ul><ul><li>SS GH, gastrin </li></ul>
    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. 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 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 2. 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. 23. <ul><li>The enteric nervous system coordinates </li></ul><ul><ul><li>digestion, </li></ul></ul><ul><ul><li>secretion </li></ul></ul><ul><ul><li>motility </li></ul></ul><ul><li>to optimize nutrient absorption. </li></ul>Its activity is modified by information <ul><ul><li>from the CNS </li></ul></ul><ul><ul><li>from local chemical and mechanical sensors. </li></ul></ul>
    23. 24. CNS Preganglionic fibres Postganglionic fibres Preganglionic fibres Parasympathetic n.s Sympathetic n.s. Innervation of the GI tract Postganglionic fibres Myenteric plexus Submucosal plexus Enteric nervous system Sympathetic ganglia Vagal nuclei Sacral spinal cord Smooth muscle Secretory cells Blood vessels Endocrine cells
    24. 25. Gastrointestinal reflex
    26. 27. <ul><li>Musculature of the GI tract </li></ul><ul><li>All smooth muscle except: </li></ul><ul><ul><li>Upper third oesophagus – striated </li></ul></ul><ul><ul><li>Middle third of oesophagus – mixed </li></ul></ul><ul><ul><li>External anal sphincter – striated </li></ul></ul><ul><ul><li>Areas of striated muscle are areas that are under conscious control </li></ul></ul>
    27. 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
    28. 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
    29. 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
    30. 31. Membrane potential (mV) Acetylcholine 0 -60 Tension 0 -60 Tension Membrane potential (mV)
    31. 32. <ul><li>Slow waves are changes in resting membrane potential </li></ul><ul><li>3-12 cycles per minute depending on area of GI tract - 3/min in stomach, 12/min small intestine </li></ul><ul><li>Always present but do not always cause contractions </li></ul><ul><li>Frequency of contractions dictated by frequency of slow waves </li></ul><ul><li>Slow wave frequency and height modulated by – </li></ul><ul><ul><ul><li>body temp & metabolic activity, </li></ul></ul></ul><ul><ul><ul><li>intrinsic & extrinsic nerves </li></ul></ul></ul><ul><ul><ul><li>circulating hormones </li></ul></ul></ul>Slow waves in GI smooth muscle
    32. 33. Relationship to contraction
    33. 35. Contraction threshold AP threshold
    34. 36. Contraction of GI smooth muscle 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 Out In Ca 2+ (Ca 2+ ) 4 . calmodulin Inactive myosin light chain kinase Active myosin light chain kinase MUSCLE CONTRACTION Myosin -(PO 4 ) 2
    35. 37. AP in GI smooth muscle
    36. 38. 4. Noradrenaline release 5. Sympathetic stimulation more hyperpolarised smooth muscle,  Less excitable and fewer contractions Stimulus Effect 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
    37. 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