The Digestive System

1. The Digestive System

2. Nutrition • Diet = everything you eat • Proper diet 10% Protein ______________ 30% fat ____________________ 60% carbohydrates

3. Carbohydrate • Primary energy source for cells • Cereals, grains, breads, fruits, vegetables • 4 calories per gram

4. Protein • Use as building block for cell structures, enzymes, hormones, muscle, bones • Dairy products, poultry, fish, meat, grains • 4 calories per gram

5. Fat • Use to construct cell membranes & other cell structures, insulate nervous tissue, energy source, fat-soluble vitamins (A, D, E, K) • Oils, margarine, butter • 9 calories per gram

6. Rule of balancing diet & activity • Energy obtained from food – energy used by body’s cells = energy stored in fat

8. Other compounds needed • Only obtained through food eaten

9. Amino acids • 8 of 20 amino acids the body cannot produce – must be eaten

10. Vitamins • Body requires in small amounts for normal growth & activity • Used as components of cellular enzymes or coenzymes

11. Water soluble – soluble in water, body doesn’t store • ex: thiamin, niacin, ascorbic acid, folic acid

12. Fat soluble – soluble in fat • Excessive amounts accumulate in body’s fatty tissue & can reach toxic levels • A, D, E, K

13. Trace elements • minerals that are required by the body • present only in minute amounts • They are also required for plant growth so they are usually obtained by eating salads

14. Digestion • Food molecules are broken down by enzymes (amylases)

15. Fats • Insoluble in water • Aggregate into large globules consisting of many fat molecules • Not easily attacked by enzymes

16. Emulsification – breaks up fat globules into tiny fat droplets • bile salts emulsify fats • produced in liver

17. Lipases – break fat molecules into fatty acids and glycerol

18. Proteins • Folded into tight balls or wound together into tough fibers

19. Enzymes cannot break down these balls & fibers because they cannot get at the individual protein chains

20. Protein digestion – 2 steps: • Hydrochloric acid (HCl) in stomach unfolds large proteins

21. 2.Enzymes (proteases) break down single polypeptide strands

23. Starch • Broken down into sugars by enzymes (amylase) Starch-binding domain of ß-amylase

24. Structures of the Digestive System • Mouth • Teeth rip or chew food into shreds • Tongue mixes it with watery solution called saliva

25. saliva is secreted into mouth by 3 pairs of salivary glands • Moistens and lubricates food so it is swallowed easier • Contains amylase – begins breakdown of starch

26. Pharynx • Food passes through • Esophagus • Long tube that connects the mouth to the stomach • No digestion takes place • About 25 cm long

27. Food is pushed down the tube • Peristaltic contractions – successive rhythmic waves of contraction of the smooth muscle wall of the esophagus

28. Stomach • Passes from esophagus into stomach through a valve called a sphincter • Prevents acid soaked food from going back into esophagus

29. When food enters stomach, gastric juice is secreted by stomach lining • Gastric juice – HCl and acid stable proteases • Mixture of food and gastric juice is called chyme

30. Stomach mixes contents by contraction and relaxation of muscular wall

31. Small intestine • Only small amounts of chyme pass into small intestine so that acid can be neutralize

32. Some digestive enzymes secreted by cells of intestinal walls • Most digestive enzymes produced in pancreas • Sends enzymes through duct into first part of small intestine (duodenum)

33. Small intestine is around 6 m (19.8 ft) long • Complete digestion of carbohydrates, fats, and proteins in duodenum occurs in first 25 cm

34. Lining covered with fingerlike projections called villi • increase surface area for more absorption

35. Fluid absorption is about 99% • Average human consumes about 0.85 liters of solid food and 1.2 liters of water/day • With food, water, and digestive secretions, about 9 liters pass through/day

36. Only about 0.05 liters of solid and 0.1 liters of liquid leave body as waste

37. Large intestine (colon) • About 1 m long • No digestion takes place • Small amount of fluid, sodium, and vitamin K are absorbed

38. Primary function – trash compactor • Undigested food (plant fiber and cellulose) is compacted and stored • Bacteria help process into feces

39. Final segment of colon is called the rectum • Compacted material passes through by peristaltic contractions • From rectum exits body through anus

40. Nutrients delivered to cells • Blood that leaves small intestine is rich with products of digestion • Collected in portal vein and goes to liver

41. Supplies quick energy by releasing sugar into bloodstream • Builds complex carbohydrate from sugar

42. 3. Makes protein from amino acids 4. Stores vitamins and minerals

43. 5. Produces bile salts Regulates blood clotting

44. 7. Monitors cholesterol production 8. Detoxifies alcohol and poisons