Enzymes in digestive system

Enzymes in digestive system

  • Three main types of digestive enzyme:
    • Protease (digests proteins)
    • Carbohydrase (digests carbohydrates)
    • Lipase (digests fats)

Digesting carbohydrates

  • Food like bread and pasta are full of large carbohydrates. They simplest carbohydrates are called sugars (glucose etc.) and they can be built up to more complex carbohydrates such as starch.
  • Carbohydrases break down carbohydrates.
  • Amylase breaks down starch into sugars (i.e. maltose). Amylase is present in saliva and secreted from the pancreas.

Digesting proteins

  • Proteases digest proteins, breaking them down into shorter chains and then amino acids.
  • Pepsin is a protease that is produced in the stomach and works best in acidic conditions e.g. pH 2-3. As the stomach walls produce acid this is the optimum place for pepsin.
  • However, the contents of the small intestine are alkaline so the proteases released into the small intestine work best around pH 8 (i.e. trypsin).

Digesting fats

  • Lipases digest fats into fatty acids and glycerol.
  • Fat and water don’t mix so at first the fats form large globules in the watery digestive juices.
  • These globules have a very small SA to volume ration so lipases can only digest the fats slowly. Bile helps by physically breaking down the large globules into tiny droplets forming an emulsion. We say bile emulsifies fats.
  • As the smaller droplets have a larger SA they can be broken down much more quickly.
  • More bile is produced after a meal.
  • Bile is alkaline when released so it helps neutralise the acidic contents of the stomach when it enters the small intestine. This is so the protease enzymes have a slightly alkaline environment to work in.


  • There is a muscular tissue all the way down the digestive system:
    • Circular muscles which surround the gut
    • Longitudinal muscles running down the length of the gut.
  • The muscles squeeze food along which is called peristalsis.
  • Waves of circular muscle contractions push food along the gut.

Waves of longitudinal muscle contractions run slightly ahead to keep food in a ball.