Essential Guide to the Digestive System

1. Chapter 16 Nutrition and Digestive System

2. Introduction • Digestion: breakdown of food into smaller, usable form • Ingestion • Peristalsis • Digestion • Absorption • Defecation

3. General Organization

4. General Organization (cont’d) • Gastrointestinal tract • Mouth, pharynx, esophagus, stomach, small intestine, large intestine • Accessory organs • Teeth, tongue, salivary glands, liver, gallbladder, pancreas

5. General Organization (cont’d)

6. Histology • Tunics (from the inside out) • Mucosa: mucous membrane attached to thin layer of visceral muscle • Submucosa: loose connective tissue • Muscularis: skeletal or smooth muscle • Adventitia: serous membrane made of connective and epithelial tissue • Also called visceral peritoneum

7. Histology (cont’d)

8. The Mouth or Oral Cavity • Functions • Taste • Mechanical breakdown of food • Chemical digestion of carbohydrates • Amylase

9. The Mouth or Oral Cavity (cont’d.) • Structure • Cavity lined with mucous membrane • Cavity floor formed by tongue • Cavity roof formed by hard and soft palate • Cavity sides formed by cheeks • Cavity opening guarded by lips

10. The Mouth or Oral Cavity (cont’d.) • Functions of tongue • Food manipulation, taste, speech • Structure of tongue • Skeletal muscle covered with mucous membrane

11. The Mouth or Oral Cavity (cont’d.) • Structure of tongue • Lingual frenulum • Papillae • Taste buds

12. The Mouth or Oral Cavity (cont’d.)

13. The Salivary Glands • Pairs of salivary glands • Parotid, submandibular, sublingual

14. The Salivary Glands (cont’d.) • Saliva • Is 99.5% water • Has amylase which digests carbohydrates • Is buffered by bicarbonates and phosphates • Has mucin to lubricate food • Has lysozyme to destroy bacteria

15. The Salivary Glands (cont’d.)

16. Teeth • Structure: crown, neck, root • Crown covered in enamel • Dentin: bonelike substance enclosing pulp cavity • Cementum: covers root • Periodontal ligament: anchors tooth

17. Teeth (cont’d.)

18. The Pharynx • Common passageway for food and air • Divisions • Nasopharynx, oropharynx, laryngopharynx • Function: begins swallowing (deglutition) • Forms food bolus • Air passageways close

19. The Esophagus • Function • Secrete mucus • Transport food • Peristalsis: smooth muscle contractions push food • Lower esophageal sphincter • Controls passage of food into stomach

20. The Stomach • Functions: chemical and mechanical breakdown of food • Parts • Cardia, fundus, body, pylorus • Gastric glands: secretory cells • Zymogenic, parietal, mucous

21. The Stomach (cont’d.)

22. The Pancreas • Functions • Acini: digestive enzymes • Islets of Langerhans: insulin and glucagon • Divisions • Head, body, tail

23. The Pancreas (cont’d.)

24. Animation – The Pancreas Click Here to Play Pancreas Animation

25. The Liver

26. Introduction • Functions • Produces heparin, prothrombin, thrombin • Phagocytosis of bacteria and old blood cells • Stores excess carbohydrates, minerals, and vitamins • Converts toxins into less harmful substances • Produces bile salts

27. The Gallbladder • Pear-shaped sac • Located in depression on surface of liver • Stores and concentrates bile until needed • Enters duodenum through common bile duct

28. The Small Intestine • Function: absorption of digested food • Divisions • Duodenum: 10 inches • Jejunum: 8 feet • Ileum: 12 feet

29. The Small Intestine (cont’d.) • Crypts of Lieberkuhn: secrete digestive enzymes • Brunner’s glands: secrete alkaline mucus • Chyme: digested contents of small intestine

30. The Small Intestine (cont’d.) • Plicae: folds in the small intestine • Villi: site of nutrient absorption • Each villus is covered by microvilli • Microvilli increase absorption area • Villus contains arteriole, venule, capillary network and lacteal

31. The Large Intestine • Reabsorption of water • Manufacture and absorption of vitamins • Formation and expulsion of feces

32. The Large Intestine (cont’d.) • Cecum: pouchlike area • Colon: ascending, transverse, descending • Pouches called haustra • Rectum: terminates at the anus • Anus: controlled by internal and external sphincter

33. The Large Intestine (cont’d.) • Mechanical movements • Haustral churning • Peristalsis: 3 to 12 contractions per minute • Mass peristalsis

34. The Formation of the Feces • Feces: semisolid mass originating from chyme • Contain water, inorganic salts, epithelial cells, Escherichia coli • Rectal distention initiates defecation reflex

35. Animation – Digestion • This animation illustrates the various actions that take place throughout the digestive system after food is consumed Click Here to Play Digestion Animation

36. Summary • Described the major activities of the digestive system • Discussed the major organs that are part of the digestive system • Explained the functions of the liver

37. Summary (cont’d.) • Discussed the absorption of nutrients in the small intestine and the formation of feces in the large intestine