Chapter 4: Human Digestion and Absorption

  1. epithelial tissue
    cells that cover surfaces inside and outside the body
  2. connective tissue
    support and protect the body by holding structure together
  3. muscle tissue
    contract and relax to permit movement
  4. nervous tissue
    transmit nerve impulses
  5. What are the parts of the GI tract?
    • mouth
    • esophagus
    • stomach
    • small intestine
    • large intestine
  6. digestion?
    mechanical/chemical processes of breaking down food into smaller components
  7. absorption?
    uptake of nutrients from the GI tract into the blood or lymph
  8. what is peristalsis?
    waves of contraction that propels material along the GI tract
  9. what is segmentation?
    back and forth action that breaks food apart
  10. what is mass movement?
    peristaltic wave that contracts over a large area of the large intestine to help eliminate waves
  11. what are the 4 parts to GI motility?
    • peristalsis
    • segmentation
    • mass movement
    • elimination
  12. what is the alimentary canal?
    • long hollow muscular canal from mouth to anus
    • nearly 15 ft
  13. What are the four layers of the alimentary canal?
    • mucosa - epithelia cells and glands, innermost
    • submucosa - CT and glands, contains blood vessels carrying nutrients to GI tract
    • smooth muscle - moves food forward, longitudinal and circular
    • serosa - outside layer that protects the tract, secretes lubricating fluid to keep it cushioned
  14. what are sphincters
    • ring link muscles that control the flow of contents in the GI tract
    • open and close valves to control flow of contents
  15. what are the 5 sphincters
    • lower esophageal sphincter
    • pyloric sphincter
    • hepatopancreatic sphincter
    • ileocecal valve
    • anal sphincter
  16. lower esophageal sphincter?
    • prevents back glow of stomach contents into the esophagus (reflux)
    • aka cardiac sphincter
  17. pyloric sphincter
    • control the flow of stomach contents into the small intestine
    • only allows 1 tsp of chyme at a time into SI to neutralize the acid and digest nutrients
  18. hepatopancreatic sphincter
    • control the flow of bile and pancreatic juice from the common bile and pancreatic ducts into the small intestine
    • aka sphincter of oddi
  19. ileocecal valve
    prevent the contents of the large intestine from reentering the small intestine
  20. anal sphincter
    prevent defecation until the person desires to do so
  21. 7 secretions that aid in digestion
    • saliva
    • mucus
    • digestive enzymes
    • hydrochloric acid
    • bile
    • bicarbonate ions
    • hormones
  22. saliva
    • dissolves taste forming compounds
    • aids in swallowing and digestion and protection of teeth
  23. mucus
    • protects GI tract cells
    • lubricates digesting food
  24. digestive enzymes
    break down carbs, fats, and proteins small enough for absorption
  25. hydrochloric acid
    • promotes digestion of protein
    • destroys microorganisms
    • increases solubility of minerals
  26. bile
    aids in fat digestion (emulsifies fat)
  27. bicarbonate ions
    neutralizes stomach acid when it reaches the small intestine
  28. hormones
    regular food intake, digestion, and absorption
  29. saliva + food =
  30. what are the 4 components of saliva
    • lysozyme - breaks down bacteria
    • mucus - lubricates and holds bolus together
    • amylase - breaks down starch, only 5%
    • lingual lipase - initiates fat digestion
  31. the 5 tastes we can taste from our taste buds
    • salty - from metal ions
    • sour - from acids
    • sweet - from organic compounds like sugar
    • bitter - from many groups, caffeine, plants
    • umami - savory tastes from amino acids and MSG
  32. what does swallowing do
    moves bolus from mouth to esophagus
  33. purpose of epiglottis
    prevents food from lodging in the trachea by covering larynx
  34. muscles that make up esophagus
    • circular muscles
    • longitudinal muscles
    • relax and contract to move food along
  35. bolus + stomach secretions =
  36. what do parietal cells secrete?
    • Hcl
    • intrinsic factor (IF)
  37. what does hydrochloric acid do? (4 things)
    • destroys bacteria and viruses
    • inactivates proteins (such as plant and animal hormones to prevent them from affecting human functions)
    • inhibits salivary amylase
    • converts pepsinogen into active form of pepsin
  38. what does IF (intrinsic factor) do?
    binds to B12 and aids in its absorption
  39. what do chief cells secrete?
    • pepsinogen (the inactive enzyme)
    • gastric lipase
  40. pepsinogen
    • turns into the enzyme pepsin by Hcl, which breaks down proteins into AA chains
    • first location of protein digestion
  41. gastric lipase
    enzyme that breaks down lipids
  42. what do mucous neck cells secrete?
  43. What does mucus do?
    protects stomach from being digested
  44. production of mucus relies on?
    presence of prostaglandins
  45. why is heavy use of aspirin/NSAIDs bad?
    inhibits prostaglandin production -> can damage the stomach
  46. what do endocrine cells secrete?
  47. Gastrin
    • stimulated by food, thoughts of food, and action potentials of autonomic nervous system
    • stimulates secretion of pepsinogen and HCl
    • stimulates contraction of lower esophageal sphincters
    • slows gastric emptying
  48. what does glucose-dependent insulinotropic peptide do?
    slows down the release of chyme into the SI
  49. what are the parts of the small intestine?
    • duodenum (10 in)- primary site of digestion
    • jejunum (4ft) - upper part of digestion, lower for absorption
    • ileum (5ft)
  50. brush border enzymes
    enzymes produced in the small intestine
  51. 3 enzymes secreted by the small intestine?
    • secretin
    • cholecystokinin (CCK)
    • gastric inhibitory peptide (GIP)
  52. Secretin
    • stimulated by presence of acidic chyme and presence of peptones in the duodenum
    • stimulates secretion of pancreatic bicarbonate which neutralizes the HCl
  53. Cholecystokinin (CCK)
    • stimulate by food, presence of fat and protein in duodenum
    • stimulates contraction of gallbladder and release of bile
    • stimulates release of enzyme rich pancreatic fluids
  54. Gastric Inhibitory Peptide (GIP)
    • stimulated by fats and protein
    • inhibits secretion of stomach acid and enzymes
    • slows gastric emptying/motility
  55. what is enterohepatic circulation
    • recycling of bile
    • bile is stored in the gallbladder until needed
    • it is release into the duodenum and then reabsorbed in the ileum to be returned to liver
  56. purpose of liver
    • produces bile to aid in digestion and absorption of fat
    • emulsifies fat
  57. purpose of gallbladder
    bile storage
  58. purpose of pancreas
    produces pancreatic juice to help break down large molecules
  59. what enzymes does pancreatic juice contain
    • sodium bicarbonate - neutralizes acidic chyme coming into SI to protect the SI from damage by the acid
    • lipase - digest fat, break down large molecules
    • proteases - digest protein, break large AA chains into smaller AA chains
    • pancreatic amylase - digest starch and carbs
  60. what do enzymes do
    speed digestion by catalyzing chemical reactions
  61. 4 types of absorption
    • passive diffusion
    • facilitate diffusion - carrier proteins allows substances through membrane into cell
    • active transport
    • endocytosis - phagocytosis and pinocytosis
  62. portal circulation - what gets absorbed and where
    • water soluble nutrients (proteins, carbs, medium chain fatty acids, B vitamins, vitamin C)
    • portal vein delivers nutrient rich blood to liver before going throughout the body
    • it gives the liver a chance to process and store nutrients before being used (liver is main processing location in the body)
  63. lymphatic circulation - what gets absorbed and where
    • fat soluble nutrients (long chain fatty acids, fat soluble vitamins, large particles
    • nutrients enter circulation at thoracic duct near the heart, far from the liver
  64. 3 main sections of the large intestine
    • colon
    • rectum
    • anas
  65. 5 parts of the colon
    • cecum
    • ascending colon
    • transverse colon
    • descending colon
    • sigmoid colon
  66. 3 main functions of the large intestine
    • houses gut microbiota to keep GI tract healthy
    • absorbs water and electrolytes
    • forms and expels feces
  67. small intestine into large intestine through?
    ileocecal valve
  68. 4 ways microbiota contribute to health
    • protect against infection by pathogens (crowd them out, produce antimicrobial substances)
    • synthesize vitamins to be absorbed in colon (especially vitamin K and biotin)
    • digest and metabolize complex carbs/fibers/starches + form short fatty chain acids
    • modulate information with metabolic products
  69. dysbiosis
    • imbalance between beneficial and pathogenic bacteria
    • can cause GI infections
  70. pro-biotic bacteria
    • live bacteria that will colonize the LI
    • found in fermented foods
  71. pre-biotic bacteria
    found in non digestible carbohydrates that promote growth of bacteria
  72. what does the large intestine absorb
    • water
    • sodium
    • potassium
    • short chain FA
    • vitamins produced by bacteria in LI
  73. ulcer
    • very small erosion of the top layer of cells in the stomach or duodenum
    • aka peptic ulcer
  74. causes of ulcers
    • hub pylori bacteria (acid resistant) - weakness mucus coating that protects stomach + duodenum -> allows HCl + acids to erode the cells
    • heavy use of aspirin, NSAIDs, alcohol, or smoking
  75. treatments for ulcers
    • antibiotics
    • antacid
    • medicines that reduce acid (pepsin)
  76. treatments for heartburn
    • smaller meals
    • less fatty meals
    • stop smoking
  77. how can meds that reduce Hcl production in stomach be bad for you?
    long term use decreases stomach acidity = Ca and Mg less well dissolved from food = decreased absorption of them = decreased bone mineralization process = increased risk of osteoporosis
  78. nonalcoholic fatty liver disease
    • liver cells store excess fat instead of metabolizing it -> swelling, inflammation, and scarring
    • gradual weight loss and daily exercise can reverse the effects
  79. Gallstones
    develop in gallbladder when cholesterol in bile forms crystal-like particles
  80. causes and treatment of constipation
    • causes - low fiber diet (bc fiber helps stimulate peristalsis and forms soft feces). Antacids, calcium, iron supplements.
    • treatment - plenty of dietary fiber and fluids, laxatives
  81. enema
    insertion of fluid into rectum -> stimulates the bowel -> liquid and feces are expelled
  82. hemorrhoids
    swollen veins of the rectum and anus
  83. crohn’s disease
    inflammation + ulceration extend through all layers of GI tract
Card Set
Chapter 4: Human Digestion and Absorption
Chapter 4