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Parts of Digestive System

mouth/teeth - for chewing (mastication) 

  • sharp teeth in carnivores for cutting
  • flat teeth in herbivores for grinding
  • both types in omnivore
  • saliva - mucous solution
    • makes food easier to swallow
    • contains amylase >> breaks down starch into disaccharide
  • epiglottis prevents food from entering respiratory tract

esophagus - 1/3 skeletal muscle, 2/3 smooth muscle 

  • peristalsis - rhythmic waves of muscle contraction
  • cardiac sphincter - ring of smooth muscle preventing food in stomach from coming back into esophagus

stomach - sac part of digestive tract 

  • can expand due to folds on interior
  • extra layer of smooth muscle for churning food, mixing w/ gastric juice
    • parietal cells - secrete hydrochloric acid, intrinsic factor (for red blood cells)
    • chief cells - secrete pepsinogen (weak protease)
  • only proteins digested in stomach
  • kills most of bacteria w/ acid, survivors go on to live in large intestine
  • ulcer - acid eating hole through stomach wall
  • pyloric sphincter - leads to small intestine

small intestine - limited capacity >> digestion takes time 

  • duodenum - 1st 25 cm of small intestine
    • receives chyme from stomach, digestive enzymes from pancreas, bile from liver
    • digests larger food molecules
  • villi - fingerlike projections w/ microvilli on plasma membrane
    • greatly increases surface area >> better absorption
    • brush border enzymes in epithelial membrane
  • nutrients go into capillaries, to hepatic portal vein

pancreas - secretes fluid to duodenum through pancreatic duct 

  • exocrine gland
  • sends enzymes that are activated by brush border enzymes in intestine
  • islets of Langerhans - produces insulin, glucagon for glucose level in blood

liver/gallbladder - largest internal organ 

  • bile - contains bile pigments, bile salts
    • bile pigments from destruction of red blood cells
    • jaundice - when bile pigments can’t leave liver
    • bile salts - break down fat droplets in duodenum
    • gallstone - formed by hardened cholesterol, blocks bile duct
  • 1st organ to receive digestion products

large intestine (colon) - connects to small intestine at cecum, appendix 

  • no digestion, only limited absorption
  • no villi in inner surface
  • purpose = concentrate waste material
    • waste gets compacted/stored
  • feces - waste material, exit through rectum to anus
  • undigested fiber >> bacterial fermentation produces more gas
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