Digestion 1 Higgins

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Digestion 1 Higgins

  1. 1. Gastrointestinal System:Gastrointestinal System:Smooth muscle and neuronal controlSmooth muscle and neuronal controlChapter 203rd Edition
  2. 2. Digestive Processes• Secretion• Motility• Digestion• Absorption
  3. 3. Overview: Fig 20.1
  4. 4. Digestive System: Fig 20.2
  5. 5. Gastrointestinal WallFour layers:1.Mucosa – lines the GI tract2.Submucosa – underlying layer ofconnective tissue3.Muscularis externa – smooth musclefibers4.Serosa (adventitia) – outer connectivetissue layer
  6. 6. Gastrointestinal wall structure;Gastrointestinal wall structure;Fig 20.3Fig 20.3
  7. 7. Regulation of GI tract• The GI secretions and motility must respondto the size and composition of the meal.• Certain foods require different rates ofmovement to allow for time for chemicaldigestion and absorption.• The correct enzymes and emulsifiers must besecreted to digest the different foodmolecules
  8. 8. Enervation of GI Tract• Parasympathetic• Sympathetic• Enteric–local, intrinsic neurons–cell bodies in ganglia in GI walls–integration
  9. 9. Enteric Nervous System• Sensory, motor, and interneurons• Independently regulates many functions of GItract• Two networks of nerve cells– Submucosal plexus (Meissner’s plexus)– Myenteric plexus (Auerbach’s plexus)• Receives input from autonomic NS• Sends sensory info to CNS
  10. 10. Gastrointestinal wall structure;Gastrointestinal wall structure;Fig 20.3Fig 20.3
  11. 11. Enteric Nervous System• Intrinsic neurons connected to extrinsic• > 30 NTs and neuromodulators• Glial support cells• Diffusion barrier• Integrating center
  12. 12. Enteric Nervous System: Fig 20.3• Receptors–Mechano–Chemo–Thermo• Interneurons–Reflexes & ‘motor’ programs
  13. 13. • Excitatory and Inhibitory motorneurons to–Muscles–Blood vessels–Secretory cellsEnteric Nervous System
  14. 14. Enteric Nervous System• Vagus nerve contains afferent andefferent neurons to connect entericn.s. with cns• Activity of enteric n.s. influenced by:–chemical composition–volume–Autonomic inputs
  15. 15. Interstitial Cells of Cajal, ICCs• Named for famous Spanishneuroanatomist, Santiago Ramon yCajal• Act as pacemakers for GI tract motility– Spontaneous slow waves that spread toadjacent cells via gap junctions
  16. 16. ICCs
  17. 17. ICCs
  18. 18. Sympathetic Actions• Inhibition:– decrease motility and secretion via α2and β2 receptors–decreased blood flow via α1–decreased NT release by entericsystem via α2 on presynaptic terminals
  19. 19. Parasympathetic• Excitation:–ACh on muscarinic receptors–directly onto muscle andsecretory cells–directly onto enteric nerves tocause epsp’s
  20. 20. Fig 20.2
  21. 21. Others to add:Hormone Stimulus PrimarytargetsPrimaryeffectsetc.Glucagon-like peptide 1(GLP-1)Carbs andfats inintestineEndocrinepancreasStimulatesinsulinrelease &inhibitsglucagonreleasePromotessatietyMotilin FastingperiodsGastric &intestinalsmoothmuscleStimulatesmigratingmotorcomplexInhibited byeating a meal
  22. 22. Review of Smooth MuscleReview of Smooth Muscle
  23. 23. Smooth Muscle• Small, discrete cells - 20 µm• Linked by gap junctions• Membrane invaginations - caveoli• Little SR–Most Ca++comes from outside cell• Actin & Myosin but no striations• Intermediate filaments
  24. 24. Smooth muscle structure: FigSmooth muscle structure: Fig13.2713.27
  25. 25. Smooth muscle structure: Fig 13.27Smooth muscle structure: Fig 13.27
  26. 26. Fig 13.28: Filament arrangementFig 13.28: Filament arrangementThis explains active tension curve on previous slide
  27. 27. Smooth muscle: no sarcomeres, works over largerange of muscle lengths.
  28. 28. Can you explain the active tensioncurves?http://faculty.ksu.edu.sa/15218/Medical%20Books/Medical%20Physiology%202nd%202003%20Rhoades/Medical%20Physiology%202nd%202003%20Rhoades/smch9.pdf
  29. 29. Fig 12.22:Fig 12.22: Force – velocity ofForce – velocity ofcontractioncontraction
  30. 30. And this?
  31. 31. Smooth Muscle• Oscillating Vm• High GNa+ , GCa++ ,and variable GK+• Responds to stretch• Myosin regulation of contraction
  32. 32. Smooth muscle slow waves:Fig 19.27What causes thesedepolarizations &smooth muscle tension?
  33. 33. GI Smooth Muscle - M3 receptors• Muscarininic• Gq subunit• Works via phospholipase and IP3
  34. 34. Fig 12.34: CaFig 12.34: Ca++++activation of smooth muscleactivation of smooth muscle
  35. 35. • Open membrane channels• Voltage gated membranechannels• Ligand gated membranechannels• SR and ER–Released by IP3Ca++for Contraction
  36. 36. Ca++Removal• SR, ER, & Membrane Ca++ATPase• Na+- Ca++exchange inmembrane
  37. 37. TableTable12.212.2
  38. 38. Peristalsis: Fig 20.28
  39. 39. Peristalsis• Requires only enteric n.s. for shortdistances• Enhanced by parasympatheticexcitation–duration, velocity, amplitude• Reflex relaxation ensures oral -->anal direction & sphincter opening
  40. 40. Segmentation: Fig 20.28

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