Digestion and absorption

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Digestion and absorption

  1. 1.  Reduces particle size  Helps to absorb micronutrients and trace elements  Sets a physical and immunologic barrier
  2. 2. Breaks down  Carbohydrates (starch and sugar) → single sugar molecules  Proteins → amino acids  Fats → fatty acids, glycerol
  3. 3.  Proteins that break bonds
  4. 4.  Is a long tube from the mouth to the anus
  5. 5.  Mouth to anus   Barrier to invaders  Submucosal layer   Epithelium lines the lumen Muscularis Taste and smell
  6. 6.  Muscular contractions that move food along throughout GI tract
  7. 7.  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)
  8. 8.  Salivary lipase: begins fat digestion, but has minimal effect  Mucus to lubricate the food for easier swallowing  Lysozyme to kill bacteria
  9. 9. Tongue – – Taste receptors: sweet, sour, salty, bitter, savory Enzymes to help break down fatty acids
  10. 10.   Bolus is the food swallowed at one time Epiglottis blocks windpipe, prevents choking
  11. 11.  Long tube  Connects pharynx to the stomach  Peristalsis, muscle contraction  Lower esophageal sphincter  Heartburn
  12. 12.  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. 13.  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
  14. 14.  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
  15. 15.  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
  16. 16.  Activates digestive enzymes  Partially digests dietary protein  Assists in calcium absorption  Makes dietary minerals soluble for absorption
  17. 17.  Most digestion and absorption happens here  About 5-7 meters  Duodenum (.5 meters)  Jejunum (2-3 meters)  Ileum (3-4 meters)
  18. 18.  Folded walls with villi projections  Absorptive cells are located on the villi  Increases intestinal surface area 600x  Rapid cell turnover
  19. 19.  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
  20. 20. Digestion → small particles End products of digestion:  Carbohydrates → monosaccharides  Proteins → amino acids  Fats → glycerol, fatty acids
  21. 21. Through small intestine walls Absorbed into  Blood – water soluble nutrients  Lymph – fat soluble nutrients  Blood → liver → general circulation  Liver detoxifies and repackages
  22. 22.  ~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
  23. 23.  Stool remains  Stimulates elimination  Muscle contraction  Anal sphincters  Voluntary control  Opens for elimination
  24. 24.  Salivary glands  Pancreas  Gallbladder  Liver
  25. 25. Saliva  Works in mouth  Moistens  Salivary amylase  Digests starch
  26. 26.  Produces glucagon and insulin (endocrine)  Manufactures digestive enzymes→ small intestine  Secretes pancreatic juices  Bicarbonate needed to neutralize chyme when it enters small intestine
  27. 27.   Produces bile (fat digestion) Enterohepatic circulation
  28. 28. Stores bile  Concentrates it  Releases to small intestine when needed
  29. 29. The Digestive System
  30. 30. Sites of Secretion, Digestion, and Absorption
  31. 31.  Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods
  32. 32. Secretion Enzyme Substrate Action Saliva Ptyalin Starch Hydrolysis to form dextrins Gastric juice Pepsin Protein Hydrolysis of peptide bonds Gastric lipase Fats Hydrolysis into free fatty acids Final Product
  33. 33. Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Lipase Fat Hydrolysis to monoglycerides Fatty acids Cholesterol esterase Cholesterol Hydrolysis to Cholesesters of terol cholesterol and fatty acids alphaAmylase Starch, dextrins Hydrolysis Dextrin, maltose
  34. 34. Secretion Enzyme Substrate Action Final Product Pancreatic exocrine secretion Trypsin Protein Hydrolysis Polypeptides Chymotrypsin Protein Hydrolysis Polypeptides Carboxypeptidase Polypeptides Hydrolysis Amino acids Ribonuclease Ribonu-cleic Hydrolysis Monoacids nucleotides Elastase Fibrous protein Hydrolysis Amino acids
  35. 35. Secretion Enzyme Substrate Action Brush border enzymes Carboxypeptidase; aminopeptidase; dipeptidase Polypep-tides Hydrolysis Enterokinase Trypsino-gen Activates to Polypeptrypsin tidases and peptides Sucrase Sucrose Hydrolysis Final Product Amino acids Glucose, fructose
  36. 36. Secretion Enzyme Substrate Action Final Product Brush border enzymes Isomaltase Dextrin Hydrolysis Glucose Maltase Maltose Hydrolysis Glucose Lactase Lactose Hydrolysis Glucose, galactose Nucleotidases Nucleic acid Hydrolysis Nucleotides Nucleosidases and phosphorylase Nucleosidases Hydrolysis Purine and pyrimidine bases
  37. 37.  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
  38. 38. Villi of the Human Intestine
  39. 39.  GI tract compromised after starvation  Feeding results in cellular proliferation, which restores normal gastrointestinal architecture and function after a few days
  40. 40.  The major portion of fat digestion takes place in the small intestine as a result of pancreatic lipase
  41. 41. Summary of Fat Absorption
  42. 42. Transport Pathways through the Cell Membrane
  43. 43.  5 feet long  Bacterial action to produce gases and organic acids  Nutrients formed here—vitamin K, thiamin, vitamin B12, riboflavin
  44. 44. The Gradual Breakdown of Large Starch Molecules
  45. 45. Process of Digestion of Carbohydrate
  46. 46. Sites of Secretion and Absorption into Gastrointestinal Tract
  47. 47.  Alpha-aminobutyric acid: relaxes LES  Norepinephrine: decreases motility, increases contractions of sphincters, inhibits secretions  Acetylcholine: increases motility, relaxes sphincters, stimulates secretions
  48. 48.  Neurotensin: inhibits release of gastric emptying and acid secretion  Neuropeptide-Y: stimulates feeding behavior
  49. 49.  Released from gastric mucosa and duodenum in presence of peptides and amino acids; stimulates secretion of hydrochloric acid and pepsinogen; increases gastric antral motility, increases LES tone
  50. 50.  Secretin: from duodenal mucosa in presence of acid in small intestine; stimulates pancreas to secrete water and bicarb; also insulin and pancreatic enzymes
  51. 51.  Released from proximal small bowel in presence of peptices, amino acids, fat, HCL, stimulates pancreas to release pancreatic enzymes
  52. 52.  Released from small intestine in presence of glucose and fat; inhibits gastrin-stimulated release of gastric acid
  53. 53.  Released from stomach and small and large intestine in presence of biliary and pancreatic secretions; promotes gastric emptying and increases GI motility
  54. 54.  Released from stomach, pancreas, and upper small intestine in presence of acidity and products of protein and fat digestion; inhibits release of gastrin, motilin, and pancreatic secretions; decreases motility of GI tract
  55. 55.  It’s important to know the physiology and function of the GI tract in order to understand the implications of pathophysiology

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