2. Nutrition and the Digestive System
Chapter 16
Nutrition and the Digestive System

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

4. General Organization

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

6. General Organization (cont’d.)

7. 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

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

10. 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

11. The Mouth or Oral Cavity (cont’d.)
Functions of tongue
Food manipulation, taste, speech
Structure of tongue
Skeletal muscle covered with mucous membrane
Lingual frenulum
Papillae
Taste buds

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

13. The Salivary Glands Pairs of salivary glands Saliva
Parotid, submandibular, sublingual
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
Needs Fig 8-1

14. The Salivary Glands (cont’d.)

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

16. Teeth (cont’d.)

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

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

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

20. The Stomach (cont’d.)

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

22. The Pancreas (cont’d.)

23. The Liver

24. The Liver 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

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

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

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

28. 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

29. The Small Intestine (cont’d.)

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

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

32. The Large Intestine (cont’d.)

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. 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
Discussed the absorption of nutrients in the small intestine and the formation of feces in the large intestine