Lipid Digestion

Lipids are hydrophobic (water ‘hating’) and hence tend to be insoluble within the aqueous environments of the body

  • Being hydrophobic, lipids will group together (coalesce) to form large globules of fats

The enzyme responsible for lipid digestion (lipase) is generally water soluble and is only hydrophobic at the active site

  • This means lipase can only bind to lipid globules at the lipid-water interface (i.e. the outer extremity of the globule)
  • As the interior of the fat globule is inaccessible to lipase, digestion of lipids in this form is normally very slow

Bile is a watery fluid that contains bile salts and pigments (bilirubin) – it is made by the liver and released from the gall bladder

  • Bile salt molecules have both a hydrophobic surface and a hydrophilic surface
  • The hydrophobic end interacts with the lipid while the hydrophilic end faces out and prevents lipids from coalescing
  • This divides the fat globule into smaller droplets (emulsification), increasing the total surface area available for enzyme activity 

Emulsification of Lipids