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The Digestive System

The Digestive System. Nutrition. Diet = everything you eat Proper diet . 10% Protein ______________. 30% fat ____________________. 60% carbohydrates. Carbohydrate Primary energy source for cells Cereals, grains, breads, fruits, vegetables

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The Digestive System

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  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

  7. Other compounds needed • Only obtained through food eaten

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

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

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

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

  12. 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

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

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

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

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

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

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

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

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

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

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

  23. 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

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

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

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

  27. 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

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

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

  30. 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)

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

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

  33. 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

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

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

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

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

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

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

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

  41. 5. Produces bile salts Regulates blood clotting

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

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