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