The human digestive system

• What is digestion?


  Digestion is the breakdown of food from large, insoluble molecules, to small, soluble molecules.
• What are enzymes?


  Biological catalysts - they speed up chemical reactions.
• What is the lock and key theory?


  The active site of each enzyme has a unique shape and is complementary to the substrates. For the enzyme to work, the substrate has to fit into its active site.
• Digestive enzymes


  Carbohydrases breaks down carbohydates into simple sugars. Amylase is a carbohydrase which breaks down starch into glucose. Proteases breaks down proteins into amino acids. Lipases breaks down lipids into fatty acids and glycerol.
• Where is amylase produced?


  The salivary glands, small intestine and pancreas.
• Where is lipase produced?


  The pancreas and small intestine.
• Where is protease produced?


  The stomach, pancreas and the small intestine.
• What factors effect enzyme action?

  Temperature and pH.
• What is bile?


  Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area.
• Food tests.

  • Benedict's test - sugars. Blue to brick-red.
  • Iodine test - starch. Brown/orange to blue-black.
  • Biuret's test - protein. Blue to purple.
  • Ethanol test - lipids. Clear to cloudy white.
• Liver


  Where bile is produced.
• Large intestine


  Absorbs excess water from food.
• Stomach

  • Pummels food with muscular walls.
  • Produces protease enzyme, pepsin.
  • Produces hydrochloric acid to kill bacteria and give the right pH for the protease enzyme to work.
• Rectum


  Where the faeces are stored.
• Small intestine


  Where the digested food is absorbed out of the digestive system and into the blood.
• Gall bladder


  Where bile is stored before it is released into the small intestine.
• What are villi?


  Tiny little projections inside the small intestine.