1. The GI tract is a muscular tube that begins at the mouth (oral cavity) and ends at the anus. Accessory organs Organs of the digestive system

3. Pharynx

4. Esophagus

5. Stomach

6. Small intestine

7. Large intestine

10. Pharynx Moves bolus of foods to esophagus (swallowing) Food is propelled to the esophagus by two muscle layers Longitudinal inner layer Circular outer layer Epiglottis covers the entrance to respiratory tract The epithelium lining the mouth and pharynx is stratified squamous (flattened) cells Upper GI Tract from Mouth to Stomach

12. Oropharynx – posterior to oral cavity

14. Upper GI Tract from Mouth to Stomach Esophagus: No digestive or absorption functions Connects pharynx to the stomach. Upper third contains skeletal muscle. Middle third contains a mixture of skeletal and smooth muscle. Terminal portion contains only smooth muscle.

15. Upper GI Tract from Mouth to Stomach Peristalsis: Produced by a series of localized reflexes in response to distention of wall by bolus. Wave-like muscular contractions: Circular smooth muscle contract behind, relaxes in front of the bolus. Followed by longitudinal contraction (shortening) of smooth muscle. Insert 18.4a

16. Esophagus Motility in the esophagus is peristalsis Function: propel bolus of food to the stomach

17. Stomach Functions of the stomach: Stores and digests food. Its movement mixes gastric secretion with the food Initiates digestion of proteins. Moves food (chyme) into intestine. Empties into the duodenum

18. Stomach Compose of four regions: Cardia: The region surrounding the opening through which foods enters the stomach Fundus: The dome shape part of the stomach beneath the diaphragm Body: the mid portion of the stomach Pyloric region: Funnel shaped region, contains the antrum and the pylorus Pyloric antrum is the largest part of pyloric region Pylorus is the constricted terminal portion

19. Stomach The interior of the stomach consist of folds called Rugae Consist of longitudinal, circular and oblique muscle layer Pyloric sphincter thick muscle that controls the rate of gastric emptying Strong contractions in the pyloric region are important for mixing ingested food with gastric juice and emptying chyme into the small intestine

20. Stomach Contractions and movement of the stomach: Mix chyme with gastric secretions. Push food into intestine. Insert fig. 18.5

21. Lower GI Tract includes small and large intestine Most digestion and absorption occurs in the small intestine Juices in the small intestine neutralize the acidic chyme, restore normal osmolarity and continue digestion of macromolecule Breakdown products of macromolecules are absorbed across the intestinal epithelium into blood or lymph

22. The small intestine has three regions: Duodenum Jejunum Ileum The duodenum 8 – 11 inch long The jejunum and ileum 8 – 13 feet Lower GI Tract includes small and large intestine

24. Deep folds of the mucosa and submucosa

25. Do not disappear when filled with food

29. Blood capillaries

31. Large Intestine The large intestine subdivision includes: Cecum: A blind end pouch at the beginning of the large intestine Appendix: A blind wormlike tube attached to the cecum Colon: Is the longest region of the large intestine includes, ascending, transverse, descending and sigmoid portions Rectum: The distal 5 cm of the digestive tract Anal canal: Last segment of the large intestine, consist of stratified squamous

32. Anus: Is the outlet of the GI tract The feces eliminated from the GI tract are primarily indigestible food combined with bacteria, inorganic material and sloughed off epithelial cells Large Intestine

33. Sphincters Separates the organs of the GI tract Controls the entrance of food into the tract Prevent reflux of material Control elimination of feces Such as: Upper esophageal sphincter Lower esophageal sphincter Pyloric sphincter Ileocecal sphincter Anal sphincter