Enzymes and digestion

• Oesophagus: carries food from the mouth to the stomach
• Stomach: muscular sac with an inner layer that produces enzymes. Breaks down food
• Ileum (small intestine): secretes enzymes to further digest food. Inner walls are folded into vili which have hairlike projections called micro-vili which further increase surface area. Absorbs products of digestion
• Large intestine: absorbs water
• Rectum: stores faeces until it is removed via egestion
• Salivary glands: release their secretions via a duct in the mouth. Secretions contain amylace that hydrolyses starch into maltose
• Pancreas: large gland below the stomach. Produces a secretion called pancreatic juice. Contains proteases, lipase and amylace
• Physical breakdown:

  • chewing by the mouth
  • churning of the food
• Chemical digestion:

  • carbohydrases: hydrolyse carbohydrates into monosaccharides
  • lipases: hydrolyse lipids into fatty acids and glycerol
  • proteases: hydrolyse proteins, ultimately into amino acids
• Carbohydrate digestion:

  • saliva contains amylace, this hydrolyses starch to maltose
  • food enters the stomach which denatures amylace , preventing further hydrolysis
  • food is passed into the small intestine, where it is mixed with pancreatic juice
  • the pancreatic juice contains pancreatic amylace which continues hydrolysis of remaining starch to maltose
  • muscles push the food down the ileum. The epithelial lining produces maltase which hydrolyses maltose into a-glucose
• Lipid digestion:

  • lipids are hydrolysed by lipases to form fatty acids and monoglycerides
  • they are split into droplets called micelles by bile salts. This is called emulsification
  • this increases the surface area of the lipid so the action of lipases are sped up
• Protein digesion:

  • endopeptidases - hydrolyses central peptide bonds between amino acids
  • exopeptidases - hydrolyse terminal peptide bonds between amino acids. Releases dipeptides and single amino acids
  • dipeptidases: hydrolyse bond between dipeptides, which line the ileum in epithelial cells