The digestive system
The digestive system
- The digestive system breaks food down.
- Food travels along one long tube — the alimentary canal.
- Five processes happen to food along the way.
The alimentary canal
- Food passes: mouth → oesophagus → stomach → small intestine → large intestine (→ anus).
- Some organs help but food does not pass through them: salivary glands, pancreas, liver, gall bladder.
Practice
Put the parts of the alimentary canal in order, from the mouth.
Food passes mouth → oesophagus → stomach → small intestine → large intestine.
Practice
Which organ helps digestion but food does NOT pass through it?
The liver, pancreas, salivary glands and gall bladder add juices but are not part of the canal.
The five processes
| Process | What it means |
|---|---|
| ingestion | taking food into the mouth |
| digestion | breaking food into small molecules |
| absorption | nutrients pass into the blood |
| assimilation | cells take in and use the nutrients |
| egestion | undigested food leaves as faeces |
Practice
Put the five processes in order.
Ingestion → digestion → absorption → assimilation → egestion.
Practice
Egestion is:
Egestion removes undigested food; excretion removes the waste products of metabolism — they are different.
You've got it
Key idea
- the alimentary canal: mouth → oesophagus → stomach → small intestine → large intestine
- liver, pancreas, salivary glands, gall bladder help but food doesn't pass through them
- five processes: ingestion → digestion → absorption → assimilation → egestion
- egestion (faeces) is not the same as excretion