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The digestive system - powering up your body

digestion; stomach; intestines; acid; enzymes; saliva; mouth; oesophagus; liver; rectum;


Your fuel

food provides the fuel for your body to work
Machines need a power source in order to work. Your body is like a very complicated machine and it needs power to be able to work properly too. Food provides the fuel to give your body the power it needs.

Our topic Fuel for your body can tell you more about what your body needs and where it gets it from.

In your mouth

Have you noticed that when you see food which looks and smells good something starts to happen in your mouth?

  • your mouth starts to waterYour mouth starts to water as you think about eating that lovely food! The water is called saliva (or spit) and it isn't just water. One of the enzymes (en-z-eye-ms) in saliva called amylase (am-il-aze) starts to break down the food to make it all soft and easier to swallow.
  • Your teeth bite and chew to make smaller pieces of food.
  • Your tongue pushes the food towards the teeth and then pushes the food in smaller bits towards the back of your throat.
  • The food slides down the pharynx (say fa-rinks) or throat until it comes to a fork where the pharynx divides into two tubes.
  • food could go down the wrong wayOne, the oesophagus (say a-sof-a-gus) leads to the stomach and the other, the windpipe or trachea (trak-ee-a) leads to the lungs.
  • When you swallow some food a flap called the epiglottis (say ep-i-glot-is) closes over the windpipe so that the food goes down where it should into the oesophagus.
  • If you are laughing or talking at the same time as eating then you sometimes may have food going down the wrong way. This means that the epiglottis didn't move fast enough to close off the windpipe. Usually a good cough shoots the food back up into your mouth so you can swallow it down the right way next time.

The oesophagus

Once the food is in the oesophagus it is moved along by peristalsis (say pe-ri-stal-sis). This means that the walls of this tube squeeze the food along until it reaches the gateway to the stomach.

This 'gateway' is called the oesophageal sphincter (say a-sof-a-gul sfinc-ter) muscle. It opens to let food pass into the stomach then quickly closes before any food or stomach acids can come back up. (You know if this has happened if you get a nasty burning feeling in your chest and throat.)

The stomach

your stomach The stomach is a long stretchy sac which has an opening at the top end to the oesophagus, and another at the lower end to the intestines (say in-tes-tines).

  • It churns up the food using the strong muscles in the walls of the stomach. It breaks up the food into a sort of soup by adding gastric juices, including acids, which come from the stomach walls. These gastric juices also help to kill off germs which may have come into your body with your food.
  • It passes the food along to the intestines.

The intestines

The small intestine is a great team player! It works with help from the pancreas, liver and gallbladder to break down the food even more, so that all the sugars, fats, proteins, vitamins and minerals can pass through the wall of the intestine into the blood.

The blood then takes these round the body and drops them off at the places where they are needed. Different parts of the body need different foods. Your blood acts as a kind of express delivery service.

Actually, if your 'small' intestine was all straightened out it would measure nearly 6 metres!!! It is not small at all - but it is thinner than the large intestine (which is shorter).

The liver

First stop for this blood is the liver.

  • The liver sorts out the good stuff from the waste.   
  • It turns some of the waste into bile.
  • It stores some of the sugars, fats, proteins and vitamins.
  • It sends off the rest of the good stuff round the body to where it is needed. 

You can find out all the details in our topic The liver.

The large intestine

diagram of the intestines
The 'soup' now moves into the large intestine (which is called the colon (koh-lon)) where more water is taken out until the waste becomes a lot thicker. By the time it reaches that bottom part of the large intestine it is very thick indeed.

Our topic Intestines - your guts!  will give you the inside story on this.


The rectum

The last part of the 'powering up' process has been completed and it only remains to get rid of all the waste that your body cannot use.

At the bottom of the large intestine is the rectum (rek-tum.) At the bottom of the rectum there is a ring of muscle called the anus (ay-nus) which stops anything coming out of your body until you are ready for it.

your rectumWhen there is enough waste collected your brain lets you know that you 'need to go'! When you get to the toilet, lavatory, dunny or whatever you call it, the anus opens and the muscles of the rectum push out the waste as your poo. 

Some other waste water and other chemicals your body does not need come out in your wee.

Our topics Your kidneys and Your waste disposal system will tell you more about this.

Dr Kim says

Dr KimOur bodies are truly amazing aren't they?

They are sort of like really good cars which need fuel, water and regular maintenance to work well and be fuel efficient.

You can help your body be 'fuel efficient' by eating a healthy diet and putting sugary or salty foods onto the 'only sometimes' list.

Your body also needs plenty of water and daily exercise (for keeping everything 'oiled' and working well). You also need rest and sleep, especially if you are having a growth spurt.

Then your body will be able to work at maximum performance like the wonderful 'machine' that it is.

eat and drink healthy

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We've provided this information to help you to understand important things about staying healthy and happy. However, if you feel sick or unhappy, it is important to tell your mum or dad, a teacher or another grown-up.


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