What is digestion?

  • The digestive system is made up of a group of organs that work together to break down food.

  • During digestion larger molecules are broken down into smaller ones.

  • These molecules are transported around our body to be used for energy, growth and repair.

What is a balanced diet?

The food we eat contains carbohydrates, fats, proteins, vitamins, minerals, fibre and water. Each of these is broken down in a different part of the digestive system. These foods provide the energy our body needs to grow and repair.

The process of digestion

Stage 1 – The mouth

Digestion starts in the mouth where the food is broken down mechanically by the teeth and chemically by the enzyme amylase (contained in saliva). Amylase breaks down carbohydrates into sugars. An enzyme is a biological catalyst that speeds up chemical reactions.

Stage 2 – The stomach

The food then passes down the oesophagus and into the stomach. When it reaches the stomach, the food mixes with the stomach acid and enzymes. The stomach is a muscular bag which churns the food, breaking it down into small pieces.

Stage 3 – The intestines

The food passes through into the small intestine. Here more enzymes are released, breaking down carbohydrates, proteins and fats into smaller molecules.

The smaller molecules are then absorbed in the small intestine by the finger-like structures called villi.

Villi are very good at absorption because they have very thin walls, a large surface area and a strong network of capillaries surrounding them.

Stage 4 - The rectum

The remaining nutrients move through into the large intestine, where the water is absorbed back into the body.

The undigested food molecules that remain form our faeces.

The faeces is passed into the rectum and is excreted from the body through the anus.

Digestion quiz

Test your knowledge of digestion with this quick quiz.

Where next?

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