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Types of Digestion

types of digestive systems - herbivores, carnivores, omnivores 

  • sponges, unicellular organisms digest intracellularly
  • other organisms digest extracellularly, inside digestive cavity
  • gastrovascular cavity - found in cnidarians, flatworms
    • only 1 opening, no specialization
  • specialization starts w/ development of digestive tract (separate mouth/anus)
  • chemical digestion - hydrolysis reactions break down macromolecules in the food

vertebrate digestive system - has gastrointestinal tract + other digestive organs 

  • mouth >> pharynx >> esophagus >> stomach >> small intestine (absorbs nutrients in food) >> large intestine
    • in mammals, urogenital and fecal matter separated in large intestine
    • in nonmammals, waste products go into cloaca cavity
  • herbivores need longer intestines to digest plants properly (cellulose hard to break down)
    • ruminants - animals containing stomachs w/ separate chambers
    • cecum - pouch found at beginning of large intestine in some organisms for digesting cellulose
  • accessory digestive organs
    • liver - produces bile >> emulsifies fat
    • gallbladder - stores/concentrates bile
    • pancreas - produces digestive enzymes, bicarbonate buffer in pancreatic suit
  • tubular gastrointestinal tract
    • mucosa - innermost layer, circular orientation
    • lumen - inside of tract
    • submucosa - outside of mucosa, linear orientation
    • serosa - covers outside of tract
    • plexus - region where nerves concentrated

ruminant digestion - uses 4-chamber stomach 

  • rumen - 1st chamber, contains smaller reticulum
    • protists/bacteria convert cellulose into simpler compounds
    • rumination - regurgitating food to rechew after entering rumen
  • reswallowed food goes through reticulum to omasum to abomasum
  • food mixed w/ gastric juice within abomasums

cecum digestion - used by rodents, horses, deer, lagomorphs (rabbits/hares) 

  • digestion of cellulose in cecum
  • regurgitation not possible >> rodents/lagomorphs eat feces to digest a 2nd time (caprophagy)
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