Digestion of lipids

• Lipids are digested by lipase and the action of bile salts
• Lipases are made in the pancreas and secreted into the small intestine
• Lipases are enzymes which hydrolyse the ester bonds in triglycerides to form fatty acids and monoglycerides
• Bile salts are produced by the liver and stored in the gall bladder which releases them into the small intestine
• Bile salts help to break down large fat globules by emulsifying them into smaller droplets (micelles)

  • This helps to speed up the action of lipases by increasing the surface area of lipids that can be exposed to the enzyme
• Lipid digestion, 2 stages:

  • Physical (emulsification and micelle formation)
  • Chemical (lipase)
• Physical lipid digestion:

  • Lipids are coated in bile salts to create an emulsion (split up in tiny droplets)
  • Many small droplets of lipids provides a larger surface area to enable the faster hydrolysis action by lipase
• Chemical lipid digestion:

  • Lipase hydrolyses lipids into glycerol and fatty acids (some monoglycerides)
• Once the lipid has been broken down by lipase, the monoglycerides and the fatty acids stay attached to the bile salts and form smaller structures called micelles

  • These help in the absorption of fatty acids and monoglycerides into the bloodstream
• Micelles - Water soluble vesicles formed of the fatty acids, glycerol, monoglycerides and bile salts
• Micelles:

  • Deliver the fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorption
• Micelles:

  • Tiny structures formed when monoglycerides and fatty acids remain in association with the bile salts that initially emulsified the lipid droplets.
  • They break down as they come into contact with the epithelial cells lining the villi of the ileum and release the monoglycerides and fatty acids which diffuse across the cell membrane into the epithelial cells