8.4 Digestive Part II

• amylases (carbohydrases) work on carbohydrates

  e.g. starch --> maltose
• proteases work on proteins

  e.g. protein --> peptides --> amino acid (by pepsin)
• lipases work on fats

  e.g. fats --> 3 fatty acids + 1 glycerol (by lipase)
• enzymes are classified according to which molecule they break down
• small intestines are slightly alkaline - neutral pH
• inside small intestine, are many tiny structures called villi
• small intestines: absorbs nutrients from food & secretes bile
• each villi has a capillary network to absorb carbohydrates & amino acids
• villi have a lacteal to absorb fats
• duodenum: the first part of SI; digesting
• jejunum: second part of SI, majority of absorption happens here
• ileum: last part of SI, some digestion & some absorption
• acidic chyme enters SI, trigger hormone called prosecretin; later converted to secretin
• secretin absorbed by bloodstream, carried to pancreas; signal bicarbonate ions to neutralize HCL (pH ~9)
• SI: alkaline environment deactivates pepsin from stomach
• SI enzymes: lactase, sucrase, maltase
• monosaccharides & amino acids absorbed into capillaries of villi
• fatty acids absorbed into lacteals of villi
• appendix: small pouch at junction of SI & LI
• large intestine: mostly water absorption; absorb back into body (vitamin B & K)
• large intestine: with peristalsis leftover material is moved
• rectum & anus: rectum = storage, anus = exit
• accessory structures: pancreas, liver, gall bladder
• pancreas: secretions go down pancreatic duct & merge w/ bile duct, then enter duodenum of SI
• pancreas: secretes alkaline substance into SI (bicarbonate)
• pancreas: neutralize acidic chyme in SI
• pancreas enzymes: pancreatic amylase, lipase, protease
• pancreas: break down proteins called peptones --> trypsin (inactive form: trypsinogen) & chymotrypsin (chymotrysinogen)
• pancreas: once in SI, trypsin & chymotrypsin convert to active form by the enzyme enterokinase
• order: pepsin, trypsin, chymotrypsin, erepsin
• pancreas: erepsin complete digestion of peptones into amino acids
• liver: process & store some nutrients & produces bile salts
• liver: bile salts --> emulsify fats & increase SA to speed up chem digestion; stored in gall bladder
• liver: store glycogen, vitamin (A, B12, D)
• liver: detox harmful chem, pee out
• liver: damaged cells are replaced by connective tissue; cannot carry out necessary cell functions & liver function is impaired
• gall bladder: store bile salts & empties into SI
• bile: breaks down into smaller pieces so lipases (enzyme) can work better NOT digest
• emulsification: turn fat into small pieces so enzyme have more SA to work on