Why we digest food
Most of the food we eat is made of large molecules that are too big to pass into the blood. Digestion is the process of breaking these large molecules into small, soluble ones. It happens along a long tube called the alimentary canal, helped by digestive juices and enzymes.
The main parts
Food travels through the digestive system in order:
- Mouth — teeth chew food; saliva starts to digest starch.
- Oesophagus — a tube that pushes food down to the stomach.
- Stomach — churns food and adds acid and enzymes to digest protein.
- Small intestine — most digestion is completed here; digested food is absorbed into the blood.
- Large intestine — absorbs water; forms solid waste (faeces).
Key idea
Digestion changes large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. Enzymes speed up this process.
Enzymes and organs that help
Some organs make digestive juices but food does not pass through them:
- Liver — makes bile, which breaks fat into tiny droplets.
- Pancreas — makes enzymes that digest carbohydrate, protein and fat.
Example
When you chew rice for a while it starts to taste sweet. This is because saliva contains an enzyme that breaks starch (carbohydrate) into sugar right inside the mouth.
Remember
- Order: mouth → oesophagus → stomach → small intestine → large intestine.
- Most digestion and absorption happen in the small intestine.
- The stomach is acidic and digests protein.