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Digestion

Digestion. and a bit of Absorption. Digestive System. Gastrointestinal tract (GI) Upper-jejunum and above Lower-ileum and colon Small-ileum and above Large-colon. Mechanical Digestion. Begins in mouth Chewing crushes and softens Saliva helps dissolve food

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Digestion

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  1. Digestion and a bit of Absorption

  2. Digestive System • Gastrointestinal tract (GI) • Upper-jejunum and above • Lower-ileum and colon • Small-ileum and above • Large-colon

  3. Mechanical Digestion • Begins in mouth • Chewing crushes and softens • Saliva helps dissolve food • Only particles in solution can react with taste buds

  4. Mechanical Digestion • Food called bolus • Bolus crosses epiglottis • Bypasses entrance to lungs • Moves to esophagus after swallowing

  5. Mechanical Digestion • Bolus slides down esophagus to stomach • Cardiac sphincter closes behind bolus • Stomach retains bolus & adds gastric juices

  6. Mechanical Digestion • Grinds bolus into semi-liquid mass called chyme • Bit by bit chyme pushed through pyloric sphincter into duodenum • Frequent ulcer sites-cardiac and pyloric sphincters

  7. Mechanical Digestion • In small intestine: • chyme passes by opening to common bile duct • bile is secreted to help with fat digestion • chyme continues through duodenum jejunum ileum • ~20 feet

  8. Mechanical Digestion • Chyme passes through ileocecal valve at start of colon • LRS to RS across front, down LS to back side ~5 feet to rectum • Colon reabsorbs H20 • Anus opens to pass waste out

  9. Mechanical Digestion • Involuntary muscles at work • Gastric motility and peristalsis • Peristalsis- • contraction of long muscles • propels food forward • always contracting and relaxing even if food not present

  10. Mechanical Digestion • Segmentation • only in small intestines • squeezes diameter of tube to help nutrients to be absorbed

  11. Chemical Digestion • Salvia in mouth starts process • Breaks bonds in chains of starch • Gets food in lump or bolus

  12. Chemical Digestion • Gastric juice in stomach • kills most bacteria • very strong acid • Bolus stored in upper curvature (antrum) as it enters stomach • stretches to store big meals • capacity is 1-2 liters

  13. Chemical Digestion • Bolus moves downward • pepsin breaks down large protein particles • some fat digested by gastric lipase • starch digested by gastric amylase • intrinsic factor produced to pick up B12 in ileum

  14. Chemical Digestion • Bolus reaches pyloric valve as chyme-squirted into duodenal bulb • Rate of emptying depends on • volume of meal • osmotic pressure • physical and chemical makeup • liquids pass quickly, solids slower

  15. Chemical Digestion • Antacids and simethicone-used mostly for pain relief and to help with stomach gas • New ulcer cause - H. Pylori • ulcer diets not used much any more • medications more common

  16. Chemical Digestion • Small intestine-action place • Bile emulsifies then enzymes work • Enzymes work on CHO, PRO, FAT • NabiCarb neutralizes acidic chyme • Contents of small intestine neutral or alkaline

  17. Chemical Digestion • Protein • broken into peptides • then into A2 • CHO • broken into disaccharides • then into monosaccharides

  18. Chemical Digestion • Fats • broken into glycerol and fatty acids • Intestine contains bacteria that produce small amounts of vitamins • Vitamin K and biotin • H20, vitamins, minerals absorbed complete

  19. Chemical Digestion • Fibers continue through digestive tract in semi-solid mass • retain water • carry bile acids/sterols/fat out of body • Most digestion takes place before bolus reaches colon

  20. Chemical Digestion • Colon • intestinal bacteria degrade some fibers • reabsorbs water and salts • ileocecal valve controls passage of chyme into colon • holds bolus in small intestine until adequate digestion completed

  21. Absorptive System • Small intestinal villi in constant motion • lined by thin sheet of muscle • wave and wiggle • small nutrients trapped by micovilli • drawn into cells beneath brush border

  22. Transport of Nutrients • 2 transport systems • blood stream • vascular system blood carried to digestive system by artery • leaves by vein to liver • lymphatic system • fluids travel to tissue spaces • blood lipids travel bundled with protein on lipoproteins

  23. Lipoproteins • Chylomicrons ~86% TG • formed in intestinal wall • carry fat load from recent meals • VLDL ~ 55% TG, 19% CHOL • very low density lipoproteins

  24. Lipoproteins • IDL or B VLDL ~23% TG, 38% CHOL • LDL ~6% TG, 50% CHOL • carry CHOL to cells • elevated serum levels associated with increased risk of CVD

  25. Lipoproteins • HDL ~5% TG, 22% CHOL, 40% Protein • formed in cell metabolism • carry from cells to liver for breakdown and elimination from body • has protective effect

  26. Lipoproteins • Elevated serum levels of LDL and TG associated with CVD • Normal or elevated serum levels of HDL has protective effect

  27. Food Safety • CDC reports 97% of foodborne illnesses could be prevented with basic hygiene and improved food handling • Occurrences: • 33% restaurants • 37 % unknown

  28. Food Safety • Bacteria to blame in 90% of cases • Salmonella • S. aureus • C. botulinum • C. perfringens • E. Coli • Safe handling instructions now required on packages

  29. Bacteria • Clostridium perfringens • Cafeteria germ • Foods not kept hot enough • 140° F until served • Salmonella • Raw or undercooked eggs & poultry • Cook well done • E. Coli • Undercooked beef • Cook thoroughly

  30. Countertop thawing Leftovers left on table Unclean cutting boards Room temperature marinating Store to refrigerator delay Same platter for raw & cooked meats Food Safety

  31. Shared knife for raw meat and vegetables Hide and eat Easter eggs Doggie bag delay Same stirring and tasting spoon Food Safety

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