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III GASTRIC MOTILITY

III GASTRIC MOTILITY. Major Function of Gastric Motility To serve as a reservoir To break food into small particles and mix food with gastric secretions To empty gastric contents into the duodenum at a controlled rate. 1. Anatomy and innervation of the Stomach. A. B. Fundus. Pylorus.

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III GASTRIC MOTILITY

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  1. III GASTRIC MOTILITY

  2. Major Function of Gastric Motility • To serve as a reservoir • To break food into small particles and mix food with gastric secretions • To empty gastric contents into the duodenum at a controlled rate

  3. 1. Anatomy and innervation of the Stomach

  4. A B Fundus Pylorus Antrum Gastric pump Phasiccontractions Corpus The stomach can be divided into three anatomic regions (A) and two functional regions (B) Gastric reservoir Tonic contractions

  5. Functional Anatomy of Stomach Oesophagus Fundus Lower Oesophageal Sphincter Fundus • Storage Body • Storage • Mucus • HCl • Pepsinogen • Intrinsic factor Duodenum Pylorus Body Antrum Antrum • Mixing/Grinding • Gastrin

  6. Anatomy

  7. Innervation of the GI tract

  8. 2. Responses to Gastric Filling – Receptive Relaxation

  9. Receptive relaxation During chewing and swallowing food, the stimulation of food to the receptors in mouth, pharynx, and esophagus reflexly causes the smooth muscle of the fundus and body of the stomach to relax, This process allows the stomach to accommodate a large amounts of food and fluid.

  10. 1. Receptive relaxation Mechanical stimuli in the pharynx Vagus centre Inhibitory vagal fibre (NANC-inhibition) 3. Feedback relaxation 2. Adap tive relax ation ACH NO + VIP et al. CCK Relaxation of gastric reservoir Tension receptors Nutrients Nutrients Distension The relaxation of the gastric reservoir is mainly regulated by reflexes. Three kinds of relaxation can be differentiated: the receptive, adaptive and feedback-relaxation

  11. 3.Peristalsis of the Gut and Gastric Emptying

  12. Gastric Motility • Peristaltic waves: Body  Antrum • Body • Thin muscle  weak contraction •  No mixing • Antrum • Thick muscle  powerful contraction • Mixing • Contraction of pyloric sphincter  • Only small quantity of gastric content (chyme)entering duodenum • Further mixing as antral contents forced back towards body

  13. What produces gastric peristaltic waves? • Peristaltic rhythm (~3/min) generated by pacemaker cells (longitudinal muscle layer) • Slow waves – spontaneousdepolarisation/repolarisation • Slow wave rhythm = basic electrical rhythm (BER) • Slow waves conducted through gap junctions along longitudinal muscle layer • Slow wave depolarisation sub-threshold - require further depolarisation to induce action potentials  contraction • Number of APs/wave determines strength of contraction

  14. Gastric Slow Waves and Motility

  15. peristalsis

  16. Peristalsis Figure 24.4

  17. The contraction of the gastric pump can be differentiated into three phases: A: phase of propulsion, B: phase of emptying, C: phase of retropulsion and grinding Phase of propulsion Phase of emptying Phase of retropulsion Antrum Bulge Emptying of liquids with small particles whereas large particles are retained in the buldge of the terminal antrum Rapid flow of liquids with suspended small particles and delayed flow of large particles towards pylorus Retropulsion of large particles and clearing of the terminal antrum

  18. Control of gastric motility Vagovagal reflex – fundal relaxation Myenteric plexus – slow waves – contraction Parasympathetic and Gastrin – increase contraction force and frequency Sympathetic – decrease contraction force and frequency

  19. Gastric emptying 1. Def. The process by which the chyme is expelled from the stomach into the duodenum is called the gastric emptying. 2. Control 1) stomach: stimulating factor, neuronal and hormonal 2) duodenum: inhibiting factor entero-gastric reflex, hormones

  20. Control of Gastric emptying • Stimulating factors in stomach • Presence of food • Gastrin

  21. Control of gastric emptying

  22. Balance between gastric reservoir and antral pump Gastro-gastric reflexes Enhanced and prolonged relaxation of reservoir Distension Disten- sion Inhibitoryreflex Antral pump switched on and intensified Excitatory reflex

  23. Control of Gastric emptying Inhibitory effects in duodenum and jejunum – throug refelxes and hormones Inhibitory reflexes – direct – myenteric plexus indirect – via extrinsic nerves Neural reflexes stimulated by: Distension, irritation, acidity, high osmolarity, protein/fat Fats and acids also stimulate release of humoral factors which reduce gastric emptying Cholecystokinin (CCK), stimulated by fats Secretin, stimulated by acids

  24. Enterogastric Reflex regulates the rate at which chyme leaves the stomach

  25. Vagal center Sensoric afferent fibers + Nutrients Long chain fatty acids Amino acids Dipeptids Glucose Osmolality Hydrochloric acid _ + Inhibitory vagal fibers Stimulating cholinergic vagal fibers ACH NO, VIP et al. CCK Enhanced relaxation and storage ACH Reduced opening of pyloric sphincter Backflow Reduced contraction The feedback regulation of gastric emptying is performed by entero-gastric reflexes and release of intestinal hormones It causes enhanced relaxation of the gastric reservoir, inhibition of the antral pump, and reduced opening of the pyloric sphincter. Figure 14 Figure 14 Ehrlein Ehrlein

  26. non-digestible spheres “Quality” of food regulates gastric emtying

  27. Lag phase 100 Solids 80 Viscous content 60 Gastric volume (%) 40 Liquid content 20 0 0 80 40 60 20 100 120 Time (min) Solids and liquids of the gastric chyme are emptied with different velocities. Emptying ofliquids isexponential. Emptying of largesolid particlesonly begins after sufficientgrinding(lag phase). Afterwards the viscous chymeis mainly emptied in a linear fashion

  28. 4. Vomiting • Emesis • Stretching, toxins, alcohol, spicy foods, and drugs may stimulate this. • Emetic Center of the Medulla • Diaphragm and abdominal wall contract • Cardiac sphincter relaxes. • Soft palate rises

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