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  1. 1. The GI tract is a muscular tube that begins at the mouth (oral cavity) and ends at the anus.<br />Accessory organs<br />Organs of the digestive system<br />
  2. 2. Organs of the Alimentary Canal<br /><ul><li>Mouth
  3. 3. Pharynx
  4. 4. Esophagus
  5. 5. Stomach
  6. 6. Small intestine
  7. 7. Large intestine
  8. 8. Anus</li></li></ul><li>Accessory organs includes:<br />Teeth<br />Tongue<br />Gallbladder<br />Digestive glands<br />Organs of the digestive system<br />
  9. 9. Upper GI Tract from Mouth to Stomach<br />Mouth:<br />Receive food<br />Mechanical action of teeth and tongue (Chewing) breaks the foods and mix it with saliva which contains salivary amylase.<br />Enzyme that can catalyze the partial digestion of starch.<br /><ul><li>Initiation of swallowing by the tongue</li></li></ul><li>Motility in the mouth is chewing<br />Function<br />Mechanical breakdown of food particles<br />Mixing food with saliva<br />
  10. 10. Pharynx<br />Moves bolus of foods to esophagus (swallowing)<br />Food is propelled to the esophagus by two muscle layers<br />Longitudinal inner layer<br />Circular outer layer<br />Epiglottis covers the entrance to respiratory tract<br />The epithelium lining the mouth and pharynx is stratified squamous (flattened) cells<br />Upper GI Tract from Mouth to Stomach <br />
  11. 11. Pharynx Anatomy<br /><ul><li>Nasopharynx – not part of the digestive system
  12. 12. Oropharynx – posterior to oral cavity
  13. 13. Laryngopharynx – below the oropharynx and connected to the esophagus</li></li></ul><li>
  14. 14. Upper GI Tract from Mouth to Stomach <br />Esophagus:<br />No digestive or absorption functions<br />Connects pharynx to the stomach.<br />Upper third contains skeletal muscle.<br />Middle third contains a mixture of skeletal and smooth muscle.<br />Terminal portion contains only smooth muscle.<br />
  15. 15. Upper GI Tract from Mouth to Stomach <br />Peristalsis: <br />Produced by a series of localized reflexes in response to distention of wall by bolus.<br />Wave-like muscular contractions:<br />Circular smooth muscle contract behind, relaxes in front of the bolus.<br />Followed by longitudinal contraction (shortening) of smooth muscle.<br />Insert 18.4a<br />
  16. 16. Esophagus<br />Motility in the esophagus is peristalsis<br />Function: propel bolus of food to the stomach<br />
  17. 17. Stomach<br />Functions of the stomach:<br />Stores and digests food.<br />Its movement mixes gastric secretion with the food<br />Initiates digestion of proteins.<br />Moves food (chyme) into intestine.<br />Empties into the duodenum<br />
  18. 18. Stomach<br />Compose of four regions:<br />Cardia: The region surrounding the opening through which foods enters the stomach<br />Fundus: The dome shape part of the stomach beneath the diaphragm<br />Body: the mid portion of the stomach <br />Pyloric region: Funnel shaped region, contains the antrum and the pylorus <br />Pyloric antrum is the largest part of pyloric region<br />Pylorus is the constricted terminal portion <br />
  19. 19. Stomach<br />The interior of the stomach consist of folds called Rugae<br />Consist of longitudinal, circular and oblique muscle layer<br />Pyloric sphincter thick muscle that controls the rate of gastric emptying<br />Strong contractions in the pyloric region are important for mixing ingested food with gastric juice and emptying chyme into the small intestine<br />
  20. 20. Stomach <br />Contractions and movement of the stomach: <br />Mix chyme with gastric secretions.<br />Push food into intestine.<br />Insert fig. 18.5<br />
  21. 21. Lower GI Tract includes small and large intestine<br />Most digestion and absorption occurs in the small intestine<br />Juices in the small intestine neutralize the acidic chyme, restore normal osmolarity and continue digestion of macromolecule<br />Breakdown products of macromolecules are absorbed across the intestinal epithelium into blood or lymph<br />
  22. 22. The small intestine has three regions:<br />Duodenum <br />Jejunum <br />Ileum<br />The duodenum 8 – 11 inch long<br />The jejunum and ileum 8 – 13 feet<br />Lower GI Tract includes small and large intestine<br />
  23. 23. Folds of the Small Intestine<br /><ul><li>The interior of the small intestine contains many circular folds called plicae circulares
  24. 24. Deep folds of the mucosa and submucosa
  25. 25. Do not disappear when filled with food
  26. 26. The submucosa has Peyer’s patches (collections of lymphatic tissue)</li></li></ul><li>Villi of the Small Intestine<br /><ul><li>Fingerlike structures formed by the mucosa
  27. 27. Give the small intestine more surface area</li></li></ul><li>Microvilli of the Small Intestine<br /><ul><li>Small projections of the plasma membrane
  28. 28. Found on absorptive cells</li></li></ul><li>Structures Involved in Absorption of Nutrients<br /><ul><li>Absorptive cells
  29. 29. Blood capillaries
  30. 30. Lacteals (specialized lymphatic capillaries)</li></li></ul><li>Large Intestine<br />Small intestine delivers chyme to the large intestine<br />Water and electrolyte absorbed from the chyme<br />
  31. 31. Large Intestine<br />The large intestine subdivision includes:<br />Cecum: A blind end pouch at the beginning of the large intestine<br />Appendix: A blind wormlike tube attached to the cecum<br />Colon: Is the longest region of the large intestine includes, ascending, transverse, descending and sigmoid portions<br />Rectum: The distal 5 cm of the digestive tract<br />Anal canal: Last segment of the large intestine, consist of stratified squamous<br />
  32. 32. Anus: Is the outlet of the GI tract<br />The feces eliminated from the GI tract are primarily indigestible food combined with bacteria, inorganic material and sloughed off epithelial cells <br />Large Intestine<br />
  33. 33. Sphincters<br />Separates the organs of the GI tract<br />Controls the entrance of food into the tract<br />Prevent reflux of material<br />Control elimination of feces <br />Such as:<br />Upper esophageal sphincter<br />Lower esophageal sphincter<br />Pyloric sphincter<br />Ileocecal sphincter<br />Anal sphincter<br />