Absorption of lipids
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of the digestion of lipids and the structure of epithelial cells in the small intestine. You can test your knowledge on these below.
What is the role of bile salts in lipid digestion?
Bile salts emulsify large lipid droplets into smaller ones, increasing the surface area for increased lipase action.
How does pancreatic lipase break down triglycerides?
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Lipase hydrolyses triglycerides into monoglycerides and free fatty acids.
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Lipase enzymes hydrolyse ester bonds by adding water.
What are micelles, and why are they important in lipid absorption?
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Micelles are tiny droplets made of bile salts, monoglycerides, and fatty acids.
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They transport monoglycerides and fatty acids to the epithelial cells of the ileum for absorption by simple diffusion.
Topic Explainer Video
Lipid Absorption in the Ileum and the Role of Bile Salts
Absorption of Lipids in the Ileum
- Lipids, mainly triglycerides, are insoluble in water, so they require emulsification and enzyme action for digestion.
- Pancreatic lipase hydrolyses triglycerides into monoglycerides and free fatty acids in the small intestine.
Role of Bile Salts in Lipid Digestion and Absorption
- Bile salts, produced by the liver and stored in the gallbladder, emulsify lipids into smaller droplets.
- This increases surface area for lipase action, making digestion more efficient.
Formation and Role of Micelles
- Monoglycerides and fatty acids remain associated with bile salts to form micelles.
- Micelles make the monoglycerides and fatty acids more soluble in water so they are able to move more easily through the digestive juices and to the epithelial cells that line the ileum.
- Micelles transport monoglycerides and fatty acids to the epithelial cells of the ileum.
- When micelles come into contact with the epithelial membrane, they release monoglycerides and fatty acids, which use simple diffusion to enter the cells.
Transport into the Bloodstream
- Inside the epithelial cells, monoglycerides and fatty acids are recombined into triglycerides in the smooth endoplasmic reticulum.
- Triglycerides are associated with cholesterol and lipoproteins forming chylomicrons. This happens in the golgi apparatus.
- Chylomicrons leave the cell via exocytosis and enter the lymphatic system (lacteals) before being transported into the bloodstream.
Key Terms
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Bile salts: Molecules that emulsify fats and aid in micelle formation.
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Emulsification: The breakdown of large lipid droplets into smaller droplets to increase surface area for lipase action.
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Lipase: An enzyme that hydrolyses triglycerides into monoglycerides and free fatty acids.
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Micelles: Small transport structures made of bile salts, monoglycerides, and fatty acids.
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Chylomicrons: Lipoprotein particles that transport reassembled triglycerides into the bloodstream via lacteals.
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Lacteals: Lymphatic capillaries in the villi of the small intestine that absorb lipids.
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Exam Tip
Common Mistake: Students often misunderstand what a micelle is. Remember:
Micelles consist of bile salts, fatty acids and monoglycerides (the products of lipid digestion).
Micelles transport monoglycerides and fatty acids to epithelial cells where they release the monoglycerides and fatty acids. They are then absorbed via simple diffusion.
No answer provided.
Describe the process by which lipids are absorbed form the ileum into the bloodstream. (6 marks)
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Monoglycerides and fatty acids are combined with bile salts to form micelles.
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Micelles make the monoglycerides and fatty acids more soluble in water
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Micelles transport monoglycerides and fatty acids to epithelial cells.
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Micelles release monoglycerides and fatty acids, which diffuse across the epithelial membrane.
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Inside the epithelial cell, monoglycerides and fatty acids are recombined into triglycerides.
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And are packaged into chylomicrons.
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Chylomicrons leave the cell by exocytosis and enter lacteals
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They are then transported via the lymphatic system into the bloodstream.
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!