1. 1 DNT 200 NUTRITION FOR HEALTH SCIENCES DIGESTION AND ABSORPTION

2. 2 “I have finally cum to the konklusion that a good reliable set ov bowels iz worth more to a man than enny quantity of brains.” Josh Billings, 19th century American writer

3. 3 DIGESTION AND ABSORPTION Digestion is the process by which food is broken down into absorbable units The digestive system includes all the organs and glands associated with the ingestion and digestion of food; it is a flexible muscular tube about 26 feet long from the mouth to the anus

4. 4 DIGESTION AND ABSORPTION The Digestive Organs The Mouth –Fiber is crushed and torn –Food is moistened with saliva for swallowing –Amylase in saliva begins the digestion of starch to smaller polysaccharides and maltose –Some hard fats begin to melt as they reach body temperature

5. 5 DIGESTION AND ABSORPTION The Digestive Organs The Epiglottis –Cartilage in the throat that guards the entrance to the trachea and prevents fluid or food from entering it when a person swallows The Esophagus –The food pipe; the conduit from the mouth to the stomach –Digestion of starch continues as swallowed food moves down the esophagus

6. 6 DIGESTION AND ABSORPTION The Digestive Organs Cardiac Sphincter –The sphincter muscle at the junction between the esophagus and the stomach –Closes behind the bolus so that it cannot slip back up the esophagus

7. 7 DIGESTION AND ABSORPTION The Digestive Organs The Stomach –A muscular elastic portion of the digestive tract that grinds and churns swallowed food mixing it with acid and enzymes to form chyme –Starch digestion stops in stomach as stomach acid and enzymes digest the salivary enzymes –Sucrose and maltose begin to be hydrolyzed by stomach acid

8. 8 DIGESTION AND ABSORPTION The Digestive Organs The Stomach (continued) –Triglycerides are split into diglycerides and fatty acids (a slight action for most fats except milk) –Protein, through the action of pepsin and stomach acid is split into smaller polypeptides –Intrinsic factor attaches to Vitamin B-12 (Intrinsic factor is a substance made in the stomach and aids in the absorption of Vitamin B-12)

9. 9 DIGESTION AND ABSORPTION The Digestive Organs The Stomach (continued) –Stomach acid acts on iron to make it more absorbable –A watery fluid is secreted turning a moist chewed mass of solid food into chyme (a semi-liquid mass of partially digested food), which is then expelled into the duodenum

10. 10 DIGESTION AND ABSORPTION The Digestive Organs Pyloric Sphincter –The sphincter muscle separating the stomach from the small intestine –Is the “gate keeper” keeping chyme from going back into the stomach

11. 11 DIGESTION AND ABSORPTION The Digestive Organs The Small Intestine –Composed of three segments Duodenum (upper-most portion) Jejunum (middle- most portion) Ileum (last-most portion)

12. 12 DIGESTION AND ABSORPTION The Digestive Organs The Small Intestine (con’t) –Pancreas produces carbohydrases and releases them into the small intestine Polysaccharides are broken down into maltose (glucose + glucose) by pancreatic amylase Maltose is broken down by maltase to glucose Sucrose is broken down by sucrase to glucose and fructose

13. 13 DIGESTION AND ABSORPTION The Digestive Organs The Small Intestine (con’t) –Bile flows in from the liver and emulsifies fat –Pancreatic lipase flows in from the pancreas and breaks the emulsified fat into monoglycerides, glycerol and fatty acids, which are absorbed –Pancreatic and small intestine enzymes split polypeptides into dipeptides, tripeptides and amino acids, which are absorbed

14. 14 DIGESTION AND ABSORPTION The Digestive Organs The Small Intestine (con’t) –Bile emulsifies fat soluble vitamins and aids in their absorption with other fats –Water soluble vitamins are absorbed –Many minerals are absorbed –Water is secreted from the small intestine, pancreas, and liver

15. 15 DIGESTION AND ABSORPTION The Digestive Organs Ileocecal Valve –The sphincter muscle separating the small and large intestine –Keeps chyme from going back to the small intestine

16. 16 DIGESTION AND ABSORPTION The Digestive Organs The Large Intestine –Most fiber has passed so far intact -- bacterial enzymes break down some fiber into glucose, which is absorbed –Some fat and cholesterol, trapped in the fiber, is excreted –Bacteria produce Vitamin K, which is absorbed –More minerals and most of the water are absorbed

17. 17 DIGESTION AND ABSORPTION The Digestive Organs Rectum –The muscular terminal part of the intestine to the anus Anus –The terminal sphincter muscle of the GI tract

18. 18 DIGESTION AND ABSORPTION Involuntary Muscles and Glands Except for swallowing and defecating, the muscles and glands of the digestive tract work with no conscious effort Salivary glands secrete just enough saliva to moisten each mouthful of food Muscles of the GI tract help liquefy the bolus into chyme (i.e. chewing, in addition to saliva and the action of the tongue, reduces food into a coarse mash suitable for swallowing)

19. 19 DIGESTION AND ABSORPTION Involuntary Muscles and Glands Stomach muscles work to force the chyme downward toward the pyloric sphincter Peristalsis begins when the bolus enters the esophagus –Entire GI tract is ringed with muscles that can squeeze tightly –During peristalsis, successive waves of involuntary muscle contraction passes along the walls of the intestine Intestines segment their contents –Segmentation -- a periodic squeezing or partitioning of the intestine by its circular muscles –Allows the digestive juices and absorbing cells of the intestinal wall to make better contact

20. 20 DIGESTION AND ABSORPTION The Process of Digestion Body renders food into the basic units that make up carbohydrate, protein and fat, absorbs these units, and builds its tissues from them Five different organs secrete digestive juices –Salivary glands –Stomach –Small intestine –Liver –Pancreas

21. 21 DIGESTION AND ABSORPTION The Process of Digestion Digestion in the Mouth Digestion of carbohydrate begins in the mouth –Saliva (water, salts, and enzymes -- including salivary amylase) break the bonds in the chains of starch Enzymes in the mouth have no effect on –Fats –Proteins –Vitamins –Minerals –Fiber

22. 22 DIGESTION AND ABSORPTION The Process of Digestion Digestion in the Stomach Major event -- initial breakdown of protein Gastric juice is composed of water, enzymes, and hydrochloric acid –Acidity prevents bacteria growth –Acidity kills bacteria that enter the body with food Acid helps uncoil proteins tangled strands so that the stomach enzymes can attack the bonds Minor stomach events –Digestion of some fat by gastric lipase –Digestion of sucrose (to a small extent) by stomach acid –Attachment of a protein carrier to vitamin B-12

23. 23 DIGESTION AND ABSORPTION The Process of Digestion Digestion in the Small and Large Intestine Pancreas and liver contribute digestive juices through ducts leading into the duodenum Pancreatic juice –Contains enzymes which act on fats, proteins, and carbohydrates (glands in the intestinal wall also secrete digestive enzymes) –Also contains sodium bicarbonate (a base) which neutralizes the acid chyme as it enters the small intestine Bile –Secreted by the liver continuously –Stored in the gall bladder –Emulsifies fats and brings them into suspension with water enabling enzymes to work on them and subsequent absorption

24. 24 DIGESTION AND ABSORPTION The Process of Digestion Digestion in the Small and Large Intestine (continued) All three energy-yielding nutrients are digested in the small intestine Rate of digestion depends on the contents of the meal –High in simple sugars -- digestion proceeds rapidly –High in fat -- digestion is slower (fat increases a meal’s satiety value)

25. 25 DIGESTION AND ABSORPTION The Process of Digestion Digestion in the Small and Large Intestine (continued) Bacteria in the intestine produce a variety of vitamins (bacterial alone cannot meet the need for these vitamins) –Biotin –Vitamin K GI bacteria protect from infection –If normal intestinal flora is thriving, infections have a hard time getting established –Several types of defending cells are present and confer specific immunity against intestinal diseases

26. 26 DIGESTION AND ABSORPTION The Absorptive System The Small Intestine –Provides a surface whose extent is comparable to a quarter of a football field in area –Nutrient molecules make contact with this surface and are absorbed

27. 27 DIGESTION AND ABSORPTION The Absorptive System The Small Intestine (con’t) –A rush of blood circulation continuously bathes the underside of this surface Removes these molecules rapidly Makes room for more to be absorbed

28. 28 DIGESTION AND ABSORPTION The Absorptive System The Small Intestine (con’t) –Is a tube about 20 feet long and an inch across –Inner surface, through a microscope, is wrinkled into hundreds of folds –Each fold is covered with with thousands of finger-like projections (villi) which are in constant motion –Any nutrient molecule small enough to be absorbed is trapped in the microvilli (projections from the cells of the villi), drawn in and absorbed

29. 29 DIGESTION AND ABSORPTION The Absorptive System Release of Absorbed Nutrients Once inside the intestinal cells, the products of digestion must be released for transport to the rest of the body Water soluble nutrients are released directly into the bloodstream via the capillaries Larger fats and fat soluble vitamins –Are insoluble in blood (water) –Fats are assembled into triglycerides –These triglycerides, with fat soluble vitamins and other lipids (phospholipids, cholesterol) form with proteins into lipoproteins called chylomicrons –They are then released into the lymphatic system –Then go from the lymphatic system to the blood stream near the heart

30. 30 DIGESTION AND ABSORPTION Transport of Nutrients The Vascular System Also known as the blood circulatory system Is a closed system of vessels through which blood flows continuously in a figure eight Heart is the pump at the crossover point

31. 31 DIGESTION AND ABSORPTION Transport of Nutrients The Vascular System (con’t) Except for the digestive system, blood goes from the heart to arteries to capillaries to veins back to the heart

32. 32 DIGESTION AND ABSORPTION Transport of Nutrients The Vascular System (con’t) Digestive system –Blood gets to the digestive system (intestines) by way of arteries to capillaries –When leaving the digestive system the blood goes not back to the heart but by vein to the liver Liver has the first chance at nutrients absorbed form the GI tract Liver is the body’s major metabolic organ –Must prepare nutrients for use by the body –Performs many other jobs in this process –There capillaries give the liver access to the blood –From the liver the blood goes via vein back to the heart

33. 33 DIGESTION AND ABSORPTION Transport of Nutrients The Lymphatic System Is a one-way route for fluid from the tissue spaces to enter the blood Has no pump –Like water in a sponge, lymph is squeezed from one portion of the body to another as muscles contract and create pressure here and there

34. 34 DIGESTION AND ABSORPTION Transport of Nutrients The Lymphatic System (continued) –Ultimately collects in a large duct behind the heart –Duct terminates in a vein that conducts the lymph into the heart and thereby into the bloodstream

35. 35 DIGESTION AND ABSORPTION Review Secretion ORGAN OR GLANDTARGET ACTION ? Amylase Salivary Glands Mouth Starch ?

36. 36 DIGESTION AND ABSORPTION Review Secretion ORGAN OR GLANDTARGET ACTION Saliva Amylase Salivary Glands Mouth Starch Maltose Gastric Juice Pepsin, HCl Gastric Glands ? ? Smaller Polypeptides

37. 37 DIGESTION AND ABSORPTION Review Secretion ORGAN OR GLAND TARGET ACTION Saliva Amylase Salivary Glands Mouth Starch Maltose Gastric Juice Pepsin, HCl Gastric Glands Stomach Protein Smaller Polypeptides

38. 38 DIGESTION AND ABSORPTION Review Secretion ORGAN OR GLAND TARGET ACTION Saliva Amylase Salivary Glands Mouth Starch Maltose Gastric Juice Pepsin, HCl Gastric Glands Stomach Protein Smaller Polypeptides Intestinal Juice ? Intestinal Glands Small Intestine Carbohydrate Monosaccharides

39. 39 DIGESTION AND ABSORPTION Review Secretion ORGAN OR GLAND TARGETACTION Saliva Amylase Salivary GlandsMouth Starch Maltose Gastric Juice Pepsin, HCl Gastric Glands Stomach Protein Smaller Polypeptides Intestinal Juice Carbohydrase Intestinal GlandsSmall Intestine Carbohydrate Monosaccharides ? Juice Protease PancreasSmall Intestine Protein dipeptides, tripeptides

40. 40 DIGESTION AND ABSORPTION Review Secretion ORGAN OR GLANDTARGET ACTION Saliva Amylase Salivary GlandsMouth Starch Maltose Gastric Juice Pepsin, HCl Gastric GlandsStomach Protein Smaller Polypeptides Intestinal Juice Carbohydrase Intestinal GlandsSmall Intestine Carbohydrate Monosaccharides Pancreatic Juice Protease PancreasSmall Intestine Protein dipeptides, tripeptides and amino acids Bile Bile Bile ? Liver ?Small Intestine Fats (Emulsified fat) monoglycerides, ?, & fatty acids

41. *****41 DIGESTION AND ABSORPTION Review Secretion ORGAN OR GLANDTARGET ACTION Saliva Amylase Salivary GlandsMouth Starch Maltose Gastric Juice Pepsin, HCl Gastric GlandsStomach Protein Smaller Polypeptides Intestinal Juice Carbohydrase Intestinal GlandsSmall Intestine Carbohydrate Monosaccharides Pancreatic Juice Protease PancreasSmall Intestine Protein dipeptides, tripeptides and amino acids Bile Bile Bile Lipase Liver GallSmall Intestine Fats (Emulsified fat) Bladder monoglycerides, glycerol, & fatty acids

42. ****42 DIGESTION AND ABSORPTION Review DIGESTION IN THE MOUTH Amylase CarbohydrateStarchMaltose Fat, Protein, VitaminsNo chemical action Minerals, Fiber WaterAdded

43. ***43 DIGESTION AND ABSORPTION Review DIGESTION IN THE STOMACH Pepsin-Acid ProteinSmaller Polypeptides Carbohydrate, Fat, VitaminsMinor action Minerals, FiberNo chemical action WaterAdded

44. **44 DIGESTION AND ABSORPTION Review DIGESTION IN THE SMALL INTESTINE Carbohydrases CarbohydrateAll Carbohydrates Monosaccharides Bile FatAll FatsEmulsified fats Lipases Emulsified fatsMonoglycerides or Glycerol and Fatty Acids Proteases ProteinAll Proteins Dipeptides, Tripeptides and Amino Acids Vitamins, Minerals, No Chemical Action & Fiber WaterAdded

45. *45 DIGESTION AND ABSORPTION Review TRANSPORT OF NUTRIENTS INTO BLOOD The following are transported directly into the blood –Water Soluble Nutrients Carbohydrates –Monosaccharide s Lipids –Glycerol –Short Chain Fatty Acids –Medium Chain Fatty Acids Proteins –Amino Acids Vitamins –B Vitamins and Vitamin C Minerals

46. 46 DIGESTION AND ABSORPTION Review TRANSPORT OF NUTRIENTS INTO BLOOD (Con’t) The following are made into triglycerides –Lipids Long Chain Fatty Acids Monoglycerides These, along with Cholesterol Phospholipids Are assembled into lipoproteins and transported through the lymphatic system to the blood Vitamins A, D, E, and K are transported through the lymphatic system to the blood