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Digestion and absorption
- 3. Reduces particle size Helps to absorb micronutrients and trace elements Sets a physical and immunologic barrier
- 4. Breaks down Carbohydrates (starch and sugar) → single sugar molecules Proteins → amino acids Fats → fatty acids, glycerol
- 6. Is a long tube from the mouth to the anus
- 7. Mouth to anus Barrier to invaders Submucosal layer Epithelium lines the lumen Muscularis Taste and smell
- 9. Muscular contractions that move food along throughout GI tract
- 10. 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)
- 11. Salivary lipase: begins fat digestion, but has minimal effect Mucus to lubricate the food for easier swallowing Lysozyme to kill bacteria
- 12. Tongue – – Taste receptors: sweet, sour, salty, bitter, savory Enzymes to help break down fatty acids
- 13. Bolus is the food swallowed at one time Epiglottis blocks windpipe, prevents choking
- 14. Long tube Connects pharynx to the stomach Peristalsis, muscle contraction Lower esophageal sphincter Heartburn
- 15. 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
- 16. 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
- 17. 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
- 18. 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
- 20. Activates digestive enzymes Partially digests dietary protein Assists in calcium absorption Makes dietary minerals soluble for absorption
- 21. Most digestion and absorption happens here About 5-7 meters Duodenum (.5 meters) Jejunum (2-3 meters) Ileum (3-4 meters)
- 22. Folded walls with villi projections Absorptive cells are located on the villi Increases intestinal surface area 600x Rapid cell turnover
- 25. 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
- 28. Digestion → small particles End products of digestion: Carbohydrates → monosaccharides Proteins → amino acids Fats → glycerol, fatty acids
- 29. Through small intestine walls Absorbed into Blood – water soluble nutrients Lymph – fat soluble nutrients Blood → liver → general circulation Liver detoxifies and repackages
- 30. ~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
- 31. Stool remains Stimulates elimination Muscle contraction Anal sphincters Voluntary control Opens for elimination
- 34. Saliva Works in mouth Moistens Salivary amylase Digests starch
- 35. Produces glucagon and insulin (endocrine) Manufactures digestive enzymes→ small intestine Secretes pancreatic juices Bicarbonate needed to neutralize chyme when it enters small intestine
- 36. Produces bile (fat digestion) Enterohepatic circulation
- 37. Stores bile Concentrates it Releases to small intestine when needed
- 41. Different nutrients leave the stomach at different rates: —Carbohydrates first, followed by protein, fat, and fibrous foods
- 42. 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
- 43. 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
- 44. 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
- 45. 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
- 46. 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
- 47. 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
- 48. Villi of the Human Intestine
- 49. GI tract compromised after starvation Feeding results in cellular proliferation, which restores normal gastrointestinal architecture and function after a few days
- 50. The major portion of fat digestion takes place in the small intestine as a result of pancreatic lipase
- 52. Transport Pathways through the Cell Membrane
- 53. 5 feet long Bacterial action to produce gases and organic acids Nutrients formed here—vitamin K, thiamin, vitamin B12, riboflavin
- 54. The Gradual Breakdown of Large Starch Molecules
- 55. Process of Digestion of Carbohydrate
- 56. Sites of Secretion and Absorption into Gastrointestinal Tract
- 57. Alpha-aminobutyric acid: relaxes LES Norepinephrine: decreases motility, increases contractions of sphincters, inhibits secretions Acetylcholine: increases motility, relaxes sphincters, stimulates secretions
- 58. Neurotensin: inhibits release of gastric emptying and acid secretion Neuropeptide-Y: stimulates feeding behavior
- 59. 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
- 60. Secretin: from duodenal mucosa in presence of acid in small intestine; stimulates pancreas to secrete water and bicarb; also insulin and pancreatic enzymes
- 61. Released from proximal small bowel in presence of peptices, amino acids, fat, HCL, stimulates pancreas to release pancreatic enzymes
- 62. Released from small intestine in presence of glucose and fat; inhibits gastrin-stimulated release of gastric acid
- 63. Released from stomach and small and large intestine in presence of biliary and pancreatic secretions; promotes gastric emptying and increases GI motility
- 64. 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
- 65. It’s important to know the physiology and function of the GI tract in order to understand the implications of pathophysiology