The role of bile in lipid digestion
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of the function of organs in the digestive system (especially the liver and stomach), and the action of digestive enzymes such as lipase.
What is the function of the liver in the digestive system?
The liver produces bile which helps in the digestion of lipids (fats).
What type of molecule does lipase break down?
Lipase breaks down lipids (fats) into fatty acids and glycerol.
What is the pH of the contents coming out of the stomach?
The contents are acidic due to the presence of hydrochloric acid in the stomach.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains the role of bile in lipid digestion, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
What is Bile?
- Bile is a yellow-green fluid made in the liver and stored in the gall bladder.
- It is released into the small intestine through the bile duct when food (especially fat) is present.
Functions of Bile in Digestion
1. Neutralising Stomach Acid
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Stomach contents entering the small intestine are acidic due to hydrochloric acid.
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Bile is alkaline, so it neutralises the acid to create the optimum pH (around 7-8) for enzymes in the small intestine (especially lipase) to work efficiently.
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If the stomach acid was not neutralised the lipase enzymes would be denatured.
2. Emulsifying Fats
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Fats are insoluble and form large globules.
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Bile emulsifies fats, breaking them into smaller droplets.
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This increases the surface area of the fat, giving lipase enzymes more area to work on.
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This increases the rate at which lipase enzymes can digest lipids into fatty acids and glycerol..
Key Terms
- Bile – an alkaline digestive fluid produced by the liver.
- Emulsify – to break up large fat globules into smaller droplets with a larger surface area.
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Exam Tip
- Don't say “bile digests fats” – bile does not contain enzymes. It helps lipase work faster by neutralising stomach acid and emulsifying fats to increase the surface area.
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Practice Question
Explain how bile helps in the digestion of fat. (4 marks)
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Bile is produced by the liver and stored in the gall bladder.
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It is alkaline, so it neutralises hydrochloric acid from the stomach, providing the optimum pH for lipase enzymes.
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It emulsifies fats into smaller droplets, increasing their surface area.
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This increases the rate at which lipase enzymes can break down fats.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!