The Digestive System




  • How food enters the body
  • Chewing breaks up food and mixes it with enzymes to start digestion



  • Carries food from mouth to stomach by peristalsis
  • Peristalsis is the contraction and relaxation of muscles which pushes the food down



  • Acid and enzymes added
  • Stomach contents mixed by churning of muscular wall



  • Produces bile, which helps in the digestion of fats in small intestine
  • Converts food molecules absorbed from small intestine into other molecules


Gall bladder:

  • Where bile from the liver is stored until needed in the small intestine



  • Produces enzymes that are released into the small intestine


Small intestine:

  • Digestion of food molecules completed
  • Food molecules are absorbed into the blood by villi containing capillaries
  • Water absorbed from digested food


Large intestine:

  • Some water is absorbed
  • Undigested food forms faeces that pass out of the body through the anus


The roles of enzymes:

  • Carbohydrase digest carbohydrates, e.g. Amylase digests starch to simple sugars
  • Proteases digest proteins to amino acids
  • Lipases digest fats to fatty acids and glycerol


Bile is added in the small intestine to neutralise stomach acid. This means that the enzymes in the stomach can work at their optimum pH. Bile also emulsifies (break up large drops of fat into smaller droplets that remain mixed in a watery liquid) fats so that there is a greater surface area for lipases to work on.


Alimentary canal – a muscular tube running from the mouth to the anus.