Human digestion

• Digestion is the process of breaking down large molecules into smaller molecules that can be absorbed into the bloodstream
• The main biological molecules are

  • Fats - made up of glycerol and fatty acids
  • Carbohydrates - made up of simple sugars e.f starch is made from glucose molecules
  • Proteins - made up of amino acids
• Digestion Is the breakdown of large insoluble molecules of food into smaller soluble molecules

  This is important because:

  • Large molecules are too big to be absorbed across the surface of the gut wall.
  • Ensures food molecules are soluble so that they can be transported in the bloodstream.
• Digestive enzymes

  Enzymes that catalyse the breakdown of food molecules
• Main types of digestive enzymes

  • Carbohydrases
  • Proteases
  • Lipases
• Carbohydrases


  Catalyse the breakdown of carbohydrates into simple sugars
• Proteases


  Catalyse the breakdown of proteins into amino acids
• Lipases


  Catalyse the breakdown of fats into glycerol and fatty acids
• Carbohydrases


  • Location: Mouth, pancreas, small intestine
• Proteases


  • Location: Stomach, small intestine
• Lipases

  • Location: Pancreas, small intestine
• ases - enzyme

  ose - glucose any kind of sugar
• structure of the Digestive system

  Mouth -> stomach -> pancreas -> small intestines -> large intestines-> liver -> Gall bladder -> Rectum -> Anus
• Mouth

  • Food chewed and broken into smaller pieces - mechanical digestion
  • Amylase in the saliva breaks down starch into maltose
• Stomach

  • Secretes protease which breaks down proteins
  • Contains hydrochloric acid which kills any bacteria present in food
• Pancreas

  • Secretes carbohydrase and lipase (transported to small 
• Small intestine

  • Completes digestion: - Carboghydrases break down carbohydrates - Proteases break down proteins - Lipases break down lipids

  • Food molecules are absorbed into the bloodstream
• Large intestine

  • Reabsorbs water into the bloodstream
• Liver

  • produces bile
• Gall bladder

  • Stores bile prior to its release into small intestine
• Rectum

  • Stores faeces prior to egestion
• Anus

  • Where faeces are egested
• Bile

  Bile (a liquid secreted by the liver) aids the digestion of lipids in the small intestine by:

  • Neutralising acid from the stomach to provide optimum conditions for enzymes in the small 
  • intestine. Emulsifying lipids to provide a greater surface area for lipases to digest them.