Digestive System
Digestion breaks food into small molecules that can be absorbed.
About this topic
Digestion breaks large food molecules into small soluble ones that can be absorbed into the blood. The system includes the mouth (chewing and amylase), oesophagus, stomach (acid and protease churning), small intestine (most digestion and absorption, helped by bile, and pancreatic juice), large intestine (water absorption) and rectum.
The small intestine has villi to increase surface area. Liver makes bile to emulsify fats. Undigested food leaves as faeces. Mechanical and chemical digestion work together.
Follow a cheese sandwich. In the mouth, teeth grind the bread and amylase begins breaking starch; the bolus is swallowed and pushed along the oesophagus by peristalsis, waves of muscle contraction. In the stomach, acid kills most microbes and pepsin begins on protein. In the small intestine, bile from the liver emulsifies fat and pancreatic enzymes finish digestion, while the villi absorb nutrients.
The large intestine absorbs water and houses gut bacteria that make some vitamins. The small intestine is about 6 metres long, with villi and microvilli giving it a surface area about the size of a tennis court. Undigested fibre is removed as faeces. A common misconception is that food passes through the liver; the liver makes bile and processes absorbed nutrients, but food never enters it.
Key ideas
- Mouth, stomach, small and large intestine
- Enzymes break down carbs, proteins, fats
- Villi absorb nutrients
Quick check
Use cases: where Digestive System helps
- Homework: review the key idea behind Digestive System before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Digestive System without notes.
- Visual learning: play with the interactive lab to see how Digestive System changes when you adjust its inputs.
- Teaching a friend: explain Digestive System in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Digestive System?
Digestion breaks food into small molecules that can be absorbed.
What will I learn in Digestive System?
Mouth, stomach, small and large intestine. Enzymes break down carbs, proteins, fats. Villi absorb nutrients.
Is Digestive System part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Digestive System lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Digestive System?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.