The Digestive System KS2

This lesson is part of our Eating and Digestion Science scheme of work for Year 4.

What is the digestive system?

The digestive system is the group of organs that work together to break down food, absorb nutrients, and eliminate waste. It is the digestive system that helps us turn the food we eat into energy and remove the waste we don't need to keep in our bodies.

How does the digestive system work?

The digestive system starts in your mouth. Your teeth and tongue help to break down the food so you can swallow it. Saliva (spit) has enzymes which also help to break down the food. That is why it is important to chew your food properly, so the enzymes can start to work.

After you have swallowed your food, it travels down the oesophagus (food pipe). Food doesn’t just fall down your oesophagus. It has muscles which contract in waves to push food down to your stomach.

It takes about seven seconds for food to travel down your oesophagus to your stomach. The job of the stomach is to break the food down. It does this by pummelling the food with muscles in the stomach wall. It also produces acid which helps break the food down further.

Food stays in your stomach for about four hours. By this time, is it mostly liquid. It then passes into the small intestine. It is the job of the small intestine to absorb the nutrients from your food and pass it to your blood-stream.

The small intestine is helped by three other organs: the liver, the gallbladder and the pancreas. The gallbladder stores bile from the liver which helps to digest fat. The pancreas produces enzymes that help digest proteins, carbohydrates and fats. Food does not pass through these organs but they help to get the nutrients from the food out of the small intestine and into the blood-stream.

Your liver is one of the largest organs in your body and has over five hundred different functions. One of the most important is its job as a filter. Once the small intestine has absorbed nutrients into the blood stream, the liver filters the blood to make sure that toxins and any other harmful substances cannot pass through it. The liver also produces bile to break down fats.

Once the food has passed through the small intestine, it travels to the large intestine. The large intestine removes most of the water from the food to turn the food back into a solid. Here, any food that has not been digested by the small intestine is absorbed with the help of yeast and bacteria.

Any solid waste in the large intestine is passed through the anus as faeces (poo). When we go to the toilet, we get rid of all the parts of our food that our body didn’t need. The rest of it has been absorbed into our blood-stream so it can be taken to the parts of the body that need it.  

A diagram of the digestive system

How long does it take food to pass through the digestive system?

It takes between 24 hours and 72 hours for food to pass through your digestive system.

Fascinating facts about the digestive system!

• Stomach acid is strong enough to dissolve metal but our stomach lining protects us from its effects.
• The digestive system is over 9 metres long from mouth to anus.
• The small intestine isn't actually small at all. It has a surface area the size of a tennis court thanks to all the small folds and villi.
• The gurgling sound you hear when you have a hungry, empty tummy is called 'borborygmi' and is caused by gas and food moving through the digestive tract
• Your gut gut is sometimes called the "second brain" because it contains millions of neurons and can influence mood and stress levels.
• The liver is the only organ in the body that can regenerate if a part of it is removed.
• Much like fingerprints, each person’s gut bacteria community is unique, influencing digestion, immune response, and even mood.