Digestive System and Body Metabolism

1. Chapter 14 The Digestive System and Body Metabolism

2. The Digestive system takes food, breaks it down into nutrient molecules and absorbs them into the blood stream and then rids the body of indigestible remains

4. Figure 14.1

5. Organs of the Digestive System (DS) • 1. Alimentary Canal or Gastrointestinal tract(GI tract) • Digests and absorbs • Continuous muscular hollow tube

6. Mouth or Oral Cavity • Food enters – masticated (chewed) • Tonsils – located at the base of the tongue • Tongue – mixes food with saliva and initiates swallowing – taste receptors

7. Figure 14.2a

8. Figure 14.2b

9. Pharynx (air goes through too) • Peristalsis – contraction of muscles that moves food - involuntary

10. C. Esophagus (10 in) • The walls of the esophagus to the intestines – four basic tissue layers

11. Figure 14.3

12. Stomach • C shaped • 10 inches long • Full – 4 L or 1 gallon

13. Storage tank and site of food breakdown • Gastric pits – release gastric juice • Chyme – digested food – like heavy cream

14. Figure 14.4a

15. Figure 14.4c

16. E. Small Intestine • Major digestive organ • 2 meters or 6 feet • Mesentery holds in place • 3 subdivisions • Duodenum • Jejenum • Ileum

17. Chemical digestion occurs in the stomach • Bile (fats) from liver • Pancreatin from pancreas (contains 4 enzymes) • Almost all food absorption occurs in the small intestine • Villi – finger-like projections that increase the surface area for absoprtion

18. Large Intestine • Larger diameter than Small Intestine • 1.5 m or 5 ft

19. Major Functions • 1. absorbing water from undigested food • 2. eliminate residues as feces

20. 2. Accessory Digestive Organs • Assist the process of digestive breakdown

21. A. Pancreas • Produces enzymes for food breakdown • Located under the stomach

22. B. Liver and Gallbladder

23. Liver • Largest organ • Four Lobes • Very Important Organ • Produces Bile

24. Bile • Yellow to green watery solution • Not an enzyme • Bile salts emulsify (break down) fats

25. Gallbladder • Small thin walled green sac – attached to liver • Stores bile • Gallstones – bile stored too long – cholesterol crystallizes

26. C. Salivary Glands • Three pairs empty into the mouth • Product – saliva Bolus – mass of food binded by mucous • Salivary amylase – breaks down starch

27. D. Teeth • Masticate or chew • Permanent full set – 32 teeth Impacted – tooth remains embedded in the jaw

28. Figure 14.9 (1 of 2)

29. Figure 14.9 (2 of 2)

30. Tooth • Two regions – crown and root • Enamel – hardest substance in the body • Pulp – supplies nutrients to the tooth tissues

31. Figure 14.10

32. Functions of the Digestive System

33. Major Functions Digestion and Absorption

34. Six Processes of the GI Tract • Ingestion – into the mouth • Propulsion – movement from organ to organ (peristalsis)

35. Food Breakdown – Mechanical Digestion • Mixing in the mouth • Churning in the stomach • Food Breakdown – Chemical Digestion (breaking bonds) • Sequence of steps where large food molecules are broken into small ones

36. Absorption • Movement of digested end products from the GI tract to the blood • Occurs in the Small intestines • Defecation - elimination

37. Activities in the Mouth, Pharynx, and Esophagus

38. Food Ingestion and Breakdown • Chewing – physical breakdown • Mix with saliva – chemical breakdown • Pharynx and esophagus - passageways

39. Food Propulsion – Swallowing and Peristalsis • Two Phases • 1. Buccal Phase – tongue forces • food into the pharynx • 2. Pharyngeal-Esophageal Phase • involuntary • Coughing – forcing food out of the lungs • Gravity is not involved

40. Activities of the Stomach

41. Food Breakdown • Gastric juice released • HCl makes stomach acid – pH of 2 • Ulcers – stomach digests itself • Heartburn – stomach acid goes into the esophagus

42. Pepsin – digestive enzyme – activated by acid – digests protein • Only protein digestion begins in the stomach Exception – Alcohol and Aspirin absorb through stomach walls • Stomach fill – mechanical digestion continues – smashing the food

43. Food Propulsion • 3 mL of chyme squirted into small intestine – stops when the small intestine in is full • 4-6 hours for stomach to empty after a meal

44. Activities of the Small Intestine

45. Food breakdown and absorption • Food only partially digested • Carbohydrate and protein started – no fats • 3-6 hours in small intestines

46. Pancreas secretes enzymes to the small intestines. 1. Pancreatic amylase – starch 2. Trypsin – proteins 3. Lipases – fats 4. Nucleases – nucleic acids

47. Pancreatic Juice – Bicarbonate – pH of 8 – made of 4 enzymes • Liver secretes Bile • Breakdown fats and helps them be absorbed • Fat soluble vitamins (K, A, D)

48. Food absorbed a long the way • End: Water, undigested food, bacteria

49. Activities of the Large Intestine

50. Food breakdown and absorption • 12-24 hours in Large Intestine • Bacteria use some of the remaining nutrients and release gas - methane (CH4) and H2SO4 • 500mL of gas produced a day • Bacteria also make vitamins (K & B) • Absorption – water, ions and vitamins