Digestive system journey – enzymes, bile and absorption by villi
BiologyHuman & Animal PhysiologyAges 16–17
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Sign in to playFollow a meal from the mouth through the stomach and small intestine to the large intestine: mechanical digestion by teeth and stomach churning, chemical digestion by amylase, pepsin, trypsin and lipase, bile that emulsifies fat and neutralises acid, and villi that absorb glucose, amino acids, fatty acids and glycerol. Students change the meal, switch each enzyme and bile on or off, set the stomach and small-intestine pH and the villus surface area, then read the amount in each section, the gastric emptying time and the percentage absorbed, recording every run in a results table.
Lesson: Human nutrition and digestion: mechanical and chemical digestion, digestive enzymes and pH, the role of bile, absorption in the small intestine, gut microbiota
What it shows
Digestion breaks large, insoluble food molecules into small, soluble ones that can be absorbed. In this model a meal of starch, protein, fat and fibre moves through the mouth, stomach, small intestine and large intestine. Each enzyme works fastest near its optimum pH: amylase near 7, pepsin near 2, trypsin and lipase near 8. Bile emulsifies fat into tiny droplets, giving lipase a much larger surface area, and helps neutralise stomach acid. Villi and microvilli give the small intestine a huge surface for absorption, while gut bacteria ferment fibre in the large intestine.
How to use
Pick a meal or set Starch, Protein, Fat and Fibre, then press Start. Watch the particles move and the bars show where the meal is. Untick an enzyme or bile, change pH stomach, pH small intestine or Villi, and run the meal again. Press Record result at the same time in each run to compare conditions fairly. Choose the Advanced view to see co-transport, micelles and gut bacteria.
Parameters you can change
- Starch in the meal 0–120 g
- Protein in the meal 0–80 g
- Fat in the meal 0–60 g
- Fibre in the meal 0–40 g
- Amylase present (saliva and pancreas)
- Pepsin present (stomach)
- Trypsin present (pancreas)
- Lipase present (pancreas)
- Bile present
- Stomach pH 1–7
- Small-intestine pH (with bile) 5–9
- Villus surface area compared with normal 10–100 %
- View Basic, Advanced (villus cell, microbiota)
Questions to explore
- Why does fat absorption fall so much more than carbohydrate absorption when bile is switched off?
- Why is protein still digested when pepsin is missing, but much less when trypsin is missing?
- How does reducing the villus surface area change what reaches the large intestine?
