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GASTROINTESTINAL PHYSIOLOGY

GASTROINTESTINAL PHYSIOLOGY. V BS 122 2012 LUIS A BATE. TOPICS. Overall digestive tract function and regulation Regulation (motility) Secretions Digestion Absorption Fermentation. REGULATION OF GASTROINTESTINAL FUNCTION. Objectives.

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GASTROINTESTINAL PHYSIOLOGY

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  1. GASTROINTESTINAL PHYSIOLOGY V BS 122 2012 LUIS A BATE

  2. TOPICS • Overall digestive tract function and regulation • Regulation (motility) • Secretions • Digestion • Absorption • Fermentation

  3. REGULATION OF GASTROINTESTINAL FUNCTION

  4. Objectives • To understand the overall regulation of gastrointestinal function • Ingestion, mastication, deglutition, passage • To identify the main components (anatomy),substances (neurotransmitters, hormones) and processes (reflexes) involved

  5. Food ingestion • Prehension • Mastication/Chewing • Deglutition/Swallowing F1-1

  6. Prehension • Mechanisms vary greatly with species • Horses and sheep use the lips to manipulate and the teeth to rip • Cattle use the tongue to manipulate, the hard palate and lower teeth to rip • Carnivores use the incisors to cut and the canines to rip • Poultry uses the beak or bill F 1-2

  7. PREHENSION BY CATTLE • Use the tongue to manipulate food into mouth • Use mobile lower teeth and hard palate to press and tear F1-5

  8. MASTICATION • Very important in herbivores • Not important in carnivores • Non existing in avian species F1-8

  9. Mastication in hervivores • Reduce particle size • Increases surface area • Breaks cellulose membrane • Lubricate for swallowing • Mix with saliva • Exposed to digestive enzymes • Reduce excoriation of GIT F1-9

  10. Deglutition • One voluntary initial stage • Movement of bolus to back of oral cavity • A pharyngeal stage (involuntary) • Passage from oral cavity to esophagus • Oesophageal stage (involuntary) • Passage of food into stomach F1-10

  11. SOFT PALATE NASOPHARYNX GLOTTIS ESOPHAGUS EPIGLOTTIS TRACHEA F1-11

  12. Respiration F1-12

  13. Deglutition F1-13

  14. http://celiacdisease.upmc.com/Images/Sub/PhotoDigestiveTract.jpghttp://celiacdisease.upmc.com/Images/Sub/PhotoDigestiveTract.jpg

  15. www.admani.com/AllianceEquine/MotherNaturesDesign.htm

  16. http://personal.cobleskill.edu/tischda/feeds/sheepdig.htm

  17. http://www.ansi.okstate.edu/resource-room/nutrition/poultry/poultrydigestivetract.htmhttp://www.ansi.okstate.edu/resource-room/nutrition/poultry/poultrydigestivetract.htm

  18. www.extension.umn.edu/distribution/livestocksystems/components/DI0469-02.htmlwww.extension.umn.edu/distribution/livestocksystems/components/DI0469-02.html

  19. MESENTERY LONGITUDINAL MUSCLE MYENTERIC PLEXUS MUSCULARIS MUCOSA SEROSA MEISSNER’S PLEXUS MUCOSA CIRCULAR MUSCLE EPITHELIUM SUBMUCOSAL GLANDS LUMEN SUBMUCOSA F1-14

  20. Smooth muscle • Arranged in bundles containing ~ 1000 fibres • Fibres connected electrically by gap junctions • Each bundle is separated by connective tissue but they contact each other at discrete points • Function as syncytium • Electric impulses travels in all directions • Some connections between longitudinal and circular layers F1-15

  21. Electrical stimulation • Continuous slow intrinsic activity • Slow waves • Spikes • Slow waves (3 - 12/min) result by changes in resting membrane potential (range 5 to 15 mV) (from -50 to -35 mV) • Controls spike potential that initiates contraction F1-16

  22. Spike potentials • Last 10-20 msec • True action potential • Triggered when more positive than -40 mV • The higher the slow waves rise, the more frequent spike potentials occur (1-10 /sec) • Triggered by Ca++influx through calcium-sodium channels • Slower than sodium channels of nerve fibres F1-17

  23. Membrane potential F1-18

  24. Factors depolarizing membranes(membrane potential less negative) • Stretching • Acetylcholine • Parasympathetic stimulation • Mediated through acetylcholine • Specific gastrointestinal hormones F1-19

  25. Factors hyperpolarizing membranes (membrane potential more negative) • Norepinephrine or epinephrine on fibre membrane • Sympathetic stimulation • Secreting norepinephrine F1-20

  26. Enteric nervous system • Lies in the gut wall • Extends from the esophagusto anus • Has as many neurones as the spinal cord • Made of two plexuses • Myenteric or Auerbach’s plexus • Situated between long. and circ. muscle layer • Submucosal or Meissner’s plexus • Situated in the submucosal layer F1-21

  27. Enteric nervous system • Myenteric plexus controls gastrointestinal movement • Submucosal plexus controls secretions and blood flow • Innervated by sensory neurons from the epithelium • Connected to parasympathetic and sympathetic divisions F1-22

  28. VILLUS LONGITUDINAL CIRCULAR SUBMUCOSA F1-23

  29. Myenteric plexus • Controls motor activity along the gut • Increases tonic contraction or “tone” of gut wall • Increases intensity of rhythmical contractions • Increases rhythm • Increases velocity, thus more peristalsis • Has some inhibitory neurons • Secrete VIP • Controls sphincter activity F1-24

  30. Submucosal plexus • Controls the function of small sections of the intestine • Signals from epithelium to SMP control • Local secretion • Local absorption • Local contraction • Regulates folding of gastrointestinal mucosa F1-25

  31. Neurotransmitters • Acetylcholine • Mainly excites GI activity • Norepinephrine • Usually inhibits GI activity • Adenosine triphosphate (ATP) • Serotonin • Vasoactive intestinal polypeptide (VIP) • Somatostatin (SS) • Leu-enkephalin • Met-enkephalin • Bombesin F1 -26

  32. Gastrointestinal reflexes • Integrated completely within the enteric system and controls • Secretion, peristalsis, local mixing • Gut-sympathetic ganglia-gut • Gastrocolic reflex • Promotes colon evacuation • Enterogastric reflex • Prevents stomach motility and emptying • Colonoileal reflex • Inhibits ileal emptying F1-27

  33. Cont… • Gut-spinal cord / brain-gut • Uses vagus nerve • From stomach and duodenum • Controls gastric motor and secretory activity • Pain reflexes • Inhibits gastrointestinal activity • Defecation reflex • Promotes colonic rectal and abdominal contraction F1-27

  34. Endocrine control of motility • Cholecystokinin • Is secreted by I cells of the mucosa of the duodenum and jejunum • Responds to FA, monoglycerides in intestinal content • Increases contractility of the gallbladder • Secretes bile into the small intestine • Emulsifies fat • Inhibits stomach motility • Slows down transit F1-28

  35. Cont… • Gastric inhibitory polypeptide • Is secreted by mucosal of upper intestine • Responds to fat and protein • Slows down stomach emptying • Allows for proper digestion of intestinal content F1-28

  36. F1-29

  37. F1-30

  38. Functional movements of the GIT • Propulsive movements • Moves contents along the tract • Rate permitting digestion • Mixing movements • Mixes content • Facilitate enzymatic digestion • Increases exposure to epithelial wall • Facilitates digestion and absorption F1-31

  39. Propulsive movements F1-32

  40. Mixing movements (Segmentation) F1-33

  41. Summary • Reviewed the overall regulation of gastrointestinal function • Ingestion • Mastication • Deglutition • Passage • Identify the main anatomical features of the GIT • Different layers • Enteric nervous system

  42. Summary • Regulatory substances • Neurotransmitters • Hormones • Regulatory processes • Reflexes

  43. © Luis A Bate 2012 Luis A Bate by Prepared for V BS 122 MOTILITY GASTROINTESTINAL PHYSIOLOGY ☺☻☺☻ Have a good day That’s all folks

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