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Digestion and Absorption

Digestion and Absorption. Digestive System . Reduces particle size Helps to absorb micronutrients and trace elements Sets a physical and immunologic barrier. Digestion. Breaks down Carbohydrates (starch and sugar) → single sugar molecules Proteins → amino acids

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Digestion and Absorption

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  1. Digestion and Absorption

  2. Digestive System • Reduces particle size • Helps to absorb micronutrients and trace elements • Sets a physical and immunologic barrier

  3. Digestion Breaks down • Carbohydrates (starch and sugar) → single sugar molecules • Proteins → amino acids • Fats → fatty acids, glycerol

  4. Enzymes • Proteins that break bonds

  5. The Digestive System • Is a long tube from the mouth to the anus

  6. Digestive System • Mouth to anus • Epithelium lines the lumen • Barrier to invaders • Submucosal layer • Muscularis • Taste and smell

  7. Peristalsis • Muscular contractions that move food along throughout GI tract

  8. The Mouth • Mastication: chewing • Saliva • Salivary glands produce about 1.5 liters of saliva daily • Salivary amylase (ptyalin) begins to break down starch (inactivated in the stomach) • Salivary lipase: begins fat digestion, but has minimal effect • Mucus to lubricate the food for easier swallowing • Lysozyme to kill bacteria

  9. Tongue • Taste receptors: sweet, sour, salty, bitter, savory • Enzymes to help break down fatty acids

  10. Swallowing • Bolus is the food swallowed at one time • Epiglottis blocks windpipe, prevents choking

  11. The Esophagus • Long tube • Connects pharynx to the stomach • Peristalsis, muscle contraction • Lower esophageal sphincter • Heartburn http://www.gerd.com/media/grossovw.gif

  12. The Stomach • Lower esophageal sphincter and pyloric sphincter control entry and exit from stomach • Storage capacity of ~4 cups • Secretion of hydrochloric acid, enzymes, including a protease, gastric lipase; mucus, the hormone gastrin, and intrinsic factor (B12) • Stomach secretes about 2000-2500 ml of gastric juice daily

  13. Stomach • pH of stomach is low, 1 to 4; kills many bacteria and micro-organisms • Achlorhydria, gastrectomy, GI dysfunction or disease ↑ risk of bacterial overgrowth in the intestines • Protein digestion begins with pepsinogen which is converted to active pepsin in acidic stomach environment • Chief cells secrete acid-stable gastric lipase, which has minor effect on shorter-chain triglycerides

  14. Stomach • Most of a liquid meal exits in 1 to 2 hours and most of a solid meal in 2 to 3 hours • Formation of chyme • Mucus layer protects stomach from digestion • Very little absorption of nutrients

  15. Physiology of the Stomach

  16. Stomach Acid • Activates digestive enzymes • Partially digests dietary protein • Assists in calcium absorption • Makes dietary minerals soluble for absorption

  17. The Small Intestine • Most digestion and absorption happens here • About 5-7 meters • Duodenum (.5 meters) • Jejunum (2-3 meters) • Ileum (3-4 meters)

  18. The Small Intestine • Folded walls with villi projections • Absorptive cells are located on the villi • Increases intestinal surface area 600x • Rapid cell turnover

  19. The Small Intestine

  20. Nutrient Absorption • Passive diffusion: driven by concentration; fats, water, some minerals • Active absorption: uses energy; glucose and amino acids • Phagocytosis and pinocytosis: absorptive cells engulf compounds, generally larger molecules, as in immune substances in breast milk

  21. Nutrient Absorption

  22. Site of Absorption

  23. Absorption Digestion → small particles End products of digestion: • Carbohydrates → monosaccharides • Proteins → amino acids • Fats → glycerol, fatty acids

  24. Absorption Through small intestine walls Absorbed into • Blood – water soluble nutrients • Lymph – fat soluble nutrients • Blood → liver → general circulation • Liver detoxifies and repackages

  25. The Large Intestine • ~3 1/2 feet in length • No villi or enzymes present • Little digestion occurs • Absorption of water, some minerals, vitamins • Bacteria break down fiber; produce Vitamin K • Formation of feces for elimination

  26. Rectum • Stool remains • Stimulates elimination • Muscle contraction • Anal sphincters • Voluntary control • Opens for elimination

  27. Accessory Organs • Salivary glands • Pancreas • Gallbladder • Liver

  28. Salivary Glands Saliva • Works in mouth • Moistens • Salivary amylase • Digests starch

  29. The Pancreas • Produces glucagon and insulin (endocrine) • Manufactures digestive enzymes→ small intestine • Secretes pancreatic juices • Bicarbonate needed to neutralize chyme when it enters small intestine

  30. The Liver • Produces bile (fat digestion) • Enterohepatic circulation

  31. The Gallbladder Stores bile • Concentrates it • Releases to small intestine when needed

  32. The Digestive System

  33. Sites of Secretion, Digestion, and Absorption

  34. Digestion in the Stomach • Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods

  35. Summary of Enzymatic Digestion and Absorption

  36. Summary of Enzymatic Digestion and Absorption —cont’d

  37. Summary of Enzymatic Digestion and Absorption —cont’d

  38. Summary of Enzymatic Digestion and Absorption —cont’d

  39. Enzymatic Digestion and Absorption—cont’d

  40. Features of Digestion and Absorption • 92% to 97% of the diet is absorbed • Small intestine—key role in digestion and absorption • Intestines: 7 meters long —Villi and microvilli/brush border

  41. Villi of the Human Intestine

  42. Refeeding after Starvation • GI tract compromised after starvation • Feeding results in cellular proliferation, which restores normal gastrointestinal architecture and function after a few days

  43. Lipids • The major portion of fat digestion takes place in the small intestine as a result of pancreatic lipase

  44. Summary of Fat Absorption

  45. Transport Pathways through the Cell Membrane

  46. Large Intestine • 5 feet long • Bacterial action to produce gases and organic acids • Nutrients formed here—vitamin K, thiamin, vitamin B12, riboflavin

  47. The Gradual Breakdown of Large Starch Molecules

  48. Process of Digestion of Carbohydrate

  49. Sites of Secretion and Absorption into Gastrointestinal Tract

  50. Neurotransmitters • Alpha-aminobutyric acid: relaxes LES • Norepinephrine: decreases motility, increases contractions of sphincters, inhibits secretions • Acetylcholine: increases motility, relaxes sphincters, stimulates secretions • Neurotensin: inhibits release of gastric emptying and acid secretion • Neuropeptide-Y: stimulates feeding behavior

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