The digestive system · Year 7
The food we eat is mostly made of big molecules that cannot get into our blood. Digestion breaks them down into small, soluble molecules that can be absorbed and carried to every cell. It starts with your teeth and ends about 30 hours later, after a 9-metre journey through the digestive system.
Key facts
- Food goes: mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus. The liver, gall bladder and pancreas help along the way.
- Teeth: incisors cut and bite, canines tear and grip, molars and premolars crush and grind. Children have 20 milk teeth; adults have 32 teeth.
- The stomach churns food with hydrochloric acid (which kills bacteria) and a protease enzyme.
- Digestion finishes in the small intestine, and the small molecules are absorbed into the blood through millions of villi. The large intestine absorbs water.
- Enzymes speed up digestion: amylase breaks starch into sugars, protease breaks proteins into amino acids, and lipase breaks lipids (fats and oils) into fatty acids and glycerol.
- Bile is made in the liver and stored in the gall bladder. It neutralises stomach acid and breaks fat into small droplets, so lipase works faster.
- Villi have a large surface area, a wall only one cell thick and a good blood supply, so food molecules are absorbed quickly.