BIOL40C Ch. 24 Digestive System

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BIOL40C Ch. 24 Digestive System
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2012-05-05 09:03:22
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Digestive System
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Digestive System
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  1. 6 components of the GI tract
    mouth, pharynx, esophagus, stomach, small intestine, large intestine

    (MPESSL)
  2. 6 accessory digestive organs
    teeth, tongue, salivary glands, liver, pancreas, gall bladder

    (TTSLPG)
  3. Are accessory organs classified as part of the digestive system?
    yes, although most do not come into contact with food
  4. major functions of accessory organs
    secrete or store secretions needed for digestion
  5. 6 major functions of the digestive system
    • 1) ingestion
    • 2) secretion of substances to aide in digestion
    • 3) mixing & propulsion
    • 4) digestion (mechanical, chemical)
    • 5) absorption
    • 6) disposal of wastes
  6. definition of absorption in terms of the digestive system
    process of digested food, fluids, ions crossing the gut wall to enter blood or lymph
  7. How is selective absorption facilitated?
    by properties of epithelial cells
  8. layers of the GI tract
    mucosa, submucosa, muscularis, serosa
  9. components of mucosa
    epithelium, connective tissue layer (lamina propria), smooth muscle
  10. mucosa epithelium in the mouth
    non-keratinized stratified squamous
  11. mucosa epithelium in the pharynx
    non-keratinized stratified squamous
  12. mucosa epithelium in the esophagus
    non-keratinized stratified squamous
  13. mucosa epithelium in the anal canal
    non-keratinized stratified squamous
  14. mucosa epithelium in the stomach and intestines
    simple columnar
  15. MALT
    mucosa-associated lymphatic tissue

    immune cell clusters in lamina propria
  16. Where is most MALT found?
    tonsils, small intestines, appendix, large intestine
  17. 2 plexuses of the GI tract
    • 1) myenteric plexus
    • 2) submucosal plexus
  18. location of myenteric plexus
    between circular and longitudinal muscle layers of muscularis
  19. location of submucosal plexus
    in submucosa
  20. How are the 2 plexuses interconnected?
    by interneurons
  21. function of myenteric plexus
    controls gut motility
  22. function of submucosal plexus
    control secretion
  23. role of autonomic nervous system in the gut
    parasympathetic: increase GI secretion/motility

    sympathetic: decrease GI secretion/motility
  24. Where do parasympathetic nerves enter the GI tract?
    via cranial nerve X (vagus)

    EXCEPT large intestine, which is supplied by PS fibers from sacral spinal cord
  25. Where do sympathetic nerves enter the GI tract?
    from thoracic & lumbar regions of spinal cord
  26. peritoneal cavity
    space containing lubricating serous fluid between parietal and visceral portions of peritoneum
  27. location of parietal peritoneum
    lines outside of abdominopelvic cavity
  28. location of visceral peritoneum
    covers some organs of abdominopelvic cavity
  29. peritoneum
    largest serous membrane in the body

    consists of mesothelium (simple squamous), w/ underlying layer of areolar CT
  30. peritonitis
    acute inflammation of the peritoneum

    caused by infectious microbes
  31. ascites fluid
    fluid accumulated in the peritoneal cavity in some diseases
  32. location of mouth
    between teeth, hard palate, soft palate, and tongue
  33. location of parotid glands
    inferior/anterior to the ears, between skin & masseter muscle
  34. location of submandibular glands
    floor of the mouth, medial/partly inferior to body of the mandible
  35. location of sublingual glands
    beneath tongue, superior to submandibular glands
  36. components of saliva
    • 99.5% water
    • ions, enzymes, mucous
  37. mumps
    inflamed parotid glans due to paramyxovirus

    also inflammation of testes in adult men
  38. GERD
    gastrointestinal reflux disease

    lower esophageal sphincter doesn't close completely, resulting in reflux

    can lead to esophageal cancer
  39. deglutition
    swallowing
  40. 5 cell types of the stomach
    • 1) chief cells
    • 2) parietal cells
    • 3) surface mucous cells
    • 4) mucous neck cells
    • 5) G cells
  41. chief cells
    secrete pepsinogen, gastric lipase

    breaks down proteins/peptides, triglycerides
  42. parietal cells
    secrete HCl, intrinsic factor
  43. intrinsic factor
    needed for vitamin B12 absorption, which is used in RBC formation
  44. surface mucous & mucous neck cells
    secrete mucous as protective barrier

    some absorption
  45. G cells
    secrete gastrin

    stimulates parietal cells to secrete HCl, and chief cells to secrete pepsinogen

    contracts lower esophageal sphincter, increases motility of stomach, relaxes pyloric sphincter
  46. 7 functions of the stomach
    • 1) make chyme
    • 2) hold food until room in small intestine
    • 3-7) secrete HCl, pepsin, intrinsic factor, lipase, gastrin
  47. chyme
    mixture of saliva, food, gastric juices
  48. 3 types of exocrine cells of the stomach
    • 1) mucous neck cells
    • 2) parietal cells
    • 3) chief cells
  49. endocrine cell of the stomach
    G cells
  50. mechanism of secretion of HCl by parietal cells
    • 1) carbonic anhydrase (CA) forms carbonic acid (H2CO3) from water & CO2
    • 2) H2CO3 dissociates to form H+ & bicarbonate (HCO3-)
    • 3) H+ secreted into lumen by H+/K+ pump
    • 4) HCO3- exchanged for Cl- by Cl-/HCO3- antiporter
    • 5) Cl- secreted by Cl- channel
  51. HCl secretion increased by:
    • 1) ACh from PS neurons
    • 2) gastrin from G cells
    • 3) histamine from mast cells
  52. exocrine portion of pancreas
    acini (99%)
  53. endocrine portion of pancreas
    islets (1%)
  54. enzymes produced by acini
    amylase, trypsin, carboxypeptidase, elastase, lipase, RNase, DNase
  55. amylase
    digests starch
  56. function of trypsin, chymotrypsin, carboxypeptidase, elastase
    digest proteins
  57. hormones produced by islets
    insulin, glucagon, somatostatin, pancreatic polypeptide
  58. organization of liver lobule
    • - hexagonal
    • - central vein in center
    • - portal triad at 3 corners
  59. portal triad
    bile duct, hepatic artery, portal vein
  60. flow of blood in liver lobules
    from GI -> portal vein -> sinusoids -> central vein -> hepatic veins -> inferior vena cava

    (TOWARD central vein)
  61. 3 types of cells in liver
    • 1) hepatocytes
    • 2) bile duct cells
    • 3) Kupffer cells (phagocytes)
  62. 7 functions of the liver
    • 1) carb, fat, protein metabolism
    • 2) hormone, drug processing
    • 3) excrete bilurubin
    • 4) synthesize bile salts
    • 5) vitamin, mineral storage
    • 6) phagocytosis
    • 7) vitamin D activation
  63. gall bladder
    stores/concentrates bile

    pear-shaped sac in depression of liver
  64. bile
    • - secreted by hepatocytes, stored in gall bladder
    • - partial excretory product, partially digestive secretion
    • - bile salts break down large lipid globules
  65. bilirubin
    principal bile pigment

    derived from heme, by-product of RBC phagocytosis
  66. 3 components of small intestine
    • 1) duodenum
    • 2) jejunum
    • 3) ileum
  67. brush border
    microvilli lining small intestine

    increases surface area of plasma membrane of absorptive cells -> larger amounts of digested nutrients can diffuse into cells
  68. 4 enzymes responsible for carb digestion in small intestine
    • 1) a-dextrase
    • 2) sucrase
    • 3) lactase
    • 4) maltase
  69. enzymes responsible for protein digestion
    • 1) pepsin (stomach)
    • 2) trypsin, chymotrypsin, carboxypeptidase, elastase
    • 3) aminopeptidase, dipeptidase (brush border)
  70. end product of carb digestion
    monosaccharides (glucose, fructose, galactose)
  71. end product of protein digestion
    amino acids

    (and some di-/tri-peptides)
  72. end product of lipid digestion
    fatty acids and glycerol
  73. How are sugars and amino acids absorbed?
    • - secondary active transport
    • - facilitated diffusion
    • - active transport

    most sugars transported by cotransport with Na+ ions
  74. How are lipids absorbed?
    • - short chain FAs absorbed by simple diffusion
    • - long chain FAs & monoglycerides form micelles with bile salts
  75. chylomicrons
    large aggregates of long chain FAs in the cell (entered by transport to brush border as micelles)

    leave cell by exocytosis, transported via lacteals
  76. total fluid volume ingested/secreted:
    9.3L
  77. total fluid volume absorbed:
    9.2L
  78. fluids contributing to digestion
    • 1) saliva
    • 2) ingested liquids
    • 3) gastric juice
    • 4) pancreatic juice
    • 5) intestinal juice
  79. 4 functions of large intestine
    • 1) completion of absorption (particularly water)
    • 2) production of some B vitamins and vitamin K
    • 3) formation of feces
    • 4) expulsion of feces

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