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Intestines - your guts!

bowel; intestine; oesophagus; digestive system; waste; duodenum; jejunum; muscle; peristalsis; rectum; anus; appendix;


What are the intestines? (in-test-eye-ns)

eat healthy food for your digestive systemThe intestines are part of the digestive system of the body. They are sometimes called the guts or bowels.  This system deals with all the food and drink that you take into your body.

The intestines are the part of the digestive system between the stomach and the anus. They are all coiled up to fit inside your abdomen.

  • The small intestine is a tube about 6 metres long in an adult. It is greyish-purple in colour and is about 35mm wide. 
  • The large intestine is much shorter, only about 1 metre long but it is called large because it is wider. It is a reddish brown in colour. You can learn more about your large intestine in the topic 'Your waste disposal system'.

The wall of the intestines (bowel) is made up of three basic layers:

  • The serosa (se-ro-sa) is the outside lining. It is very thin, a bit like cling wrap.
  • The muscle wall is the thickest part and is made of rings of muscles, a bit like a vacuum cleaner hose. These muscles work to squeeze the food slowly along. This action is called peristalsis (say perry-stal-sis).
  • The mucosa (mew-co-sa) – the inside lining. In the duodenum and small intestine there are lots of small folds and villi (like tiny fingers) to enable your food to be taken into your body (absorbed). In your large bowel this mucosa is thinner and slippery.

This diagram gives you an idea of where everything is.

diagram of the intestines

Inside the small intestine

Food goes into the stomach where it is broken down by acid and enzymes into more manageable bits. Then it passes to the small intestine. It is pretty liquid now so it can move easily.

The small intestine (small bowel), includes the duodenum (say joo-o-deen-um), the jejunum (say jay-joo-num) and the ileum (say ill-ee-um). Inside the small intestine food continues to break down so all the nutrients which the body needs can be absorbed. Enzymes from the pancreas help break down the food.

The lining of the small intestine is not a straight slippery surface but is wavy so that there is a lot more surface on the inside than on the outside.

  • This surface is covered by villi. These are like tiny fingers.
  • All over the villi are microvilli, even tinier ‘fingers' so that the whole surface area inside the intestine is made very, very big. (It's a bit like the Tardis in Dr Who which may look small on the outside but the inside is large and filled with all sorts of useful stuff!)

As your food reaches the end of the small intestine it goes through a valve into the large intestine or lower bowel. The valve is a ring of muscle which stops the contents of the large intestine going back into the small intestine.

Inside the large intestine

The large intestine begins at the caecum (say see-kum) and ends at the rectum. It is less than 1 metre long. It includes the appendix, caecum, colon and rectum, and at the end is a muscle ring called the anus which stops your poo coming out when you don't want it to.

Inside the colon, water is absorbed through the sides so that the waste becomes more solid.

Many different types of bacteria live in the colon. Some of them produce important things like vitamin K, amino acids and growth factors which are absorbed into the body.

The waste (poo) then passes out of the body through the anus.

You can learn more about your large intestine in the topic 'Your waste disposal system'.

What happens when the intestines are not working properly?

  • maybe you have a tummy acheHave you ever had a 'tummy ache'?
  • Maybe you have felt like you really wanted to do a poo but just couldn't? You could have been constipated. This means that the waste is too hard or dry to be able to slide out when you go to the toilet.
  • Maybe you had really runny poo and needed to hang out near the loo just in case you had an accident? This is called diarrhoea (di-a-ree-a).

Sometimes, when children and adults get worried about something, they feel a pain in their tummy, and sometimes even have runny poo. This usually does not cause any harm, but it can be quite uncomfortable. Sometimes the pain is due to appendicitis.

irritable bowel syndromeUsually things get better but sometimes problems can be more serious.

  • Irritable bowel syndrome is caused by the nerves controlling the muscles of the intestines. It can cause tummy ache, diarrhoea or constipation, and a feeling like you're full of air (bloated).
  • Inflammatory bowel syndrome has similar symptoms but it is more serious and is harder to treat. One type, called Crohn's disease causes ulcers, bleeding and irritation in the bowel.
  • Cancer of the bowel is one of the more common types of cancer that people get.

Looking after your intestines

  • be activeTo keep your bowels healthy you need to be an active person. Walk, run, ride a bike and look for ways in which you can move around rather than sit. Getting into the habit of daily exercise when you are young is a great start on looking after yourself.
  • You also need to have a healthy diet with lots of fresh vegetables and fruit. Look at our topics in the 'Your food' category for some ideas.  
  • Drink plenty of water. After all your body is mostly water and you have to get it from somewhere!

Dr Kate says

Dr KateRemember to wash your hands before eating. Be careful about preparing food and check out that those leftovers in the fridge are covered up and haven't been there for days before you decide to snack on them.

If you often have tummy aches have a talk with your doctor. It's a good idea to do a bit of detective work first, like what you've been eating and where, how much exercise you're having, are you worried about something? It will help your doctor to work out what the problem is and what can be done to help you feel better. 

Isn't it amazing to think of all the stuff
That's fitted in your insides
Who'd believe there's room enough!
Hard working organs
Long lengths of tube
Collecting what your body needs
And chucking out the rough!
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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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