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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