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The digestive system breaks down food into nutrients.

The digestive system breaks down food into nutrients.
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Digestive system

3-minute read

Your digestive system breaks down the food you eat into nutrients such as carbohydrates, fats and proteins. They can then be absorbed into your bloodstream so your body can use them for energy, growth and repair. Unused materials are discarded as faeces (or stools).

Your digestive system starts at your mouth, then your oesophagus, stomach, small intestine, large intestine and anus. These organs are the specialised parts of a long, twisting tube called the digestive tract.

Other organs that form part of the digestive system are the pancreas, liver and gallbladder.

What is the digestive system?

Each organ of the digestive system has an important role in digestion.


When you eat, your teeth chew food into very small pieces. Glands in your cheeks and under your tongue produce saliva that coats the food, making it easier to be chewed and swallowed.

Saliva also contains enzymes that start the digestion of the carbohydrates in your food.


Your oesophagus is the muscular tube that carries food from your mouth to your stomach after you swallow. A ring of muscle at the end of the oesophagus relaxes to let food into your stomach and contracts to prevent stomach contents from escaping back up the oesophagus.


Your stomach wall produces gastric juice (hydrochloric acid and enzymes) that digests proteins. The stomach acts like a concrete mixer, churning and mixing food with gastric juice to form chyme – a thick, soupy liquid.

Small intestine

Bile from your gall bladder and enzymes in digestive juices from your pancreas empty into the upper section of your small intestine. These help break down protein into amino acids and fat into fatty acids. These smaller particles, along with sugars, vitamins and minerals, are absorbed into the bloodstream through the wall of your small intestine.

It is called small because it is about 3.5cm in diameter but it is about 5m long to provide lots of area for absorption. Most of the chemical digestion of proteins, fats and carbohydrates is completed in your small intestine.

Large intestine and anus

The lining of your large intestine absorbs water, mineral salts and vitamins. Undigested fibre is mixed with mucus and bacteria – which partly break down the fibre – to nourish the cells of the large intestine wall and so help keep your large intestine healthy. Faeces are formed and stored in the last part of the large intestine (the rectum) before being passed out of the body through the anus.

Common conditions related to the digestive system

Gastro-oesophageal reflux

Gastro-oesophageal reflux (GORD) occurs when acidic stomach contents moves from the stomach back up the oesophagus. It causes a burning sensation in the chest or throat.


Diverticulitis is a sometimes painful condition caused by inflammation or infection of abnormal pouches in the lower part of the large intestine.

Stomach ulcers

Stomach ulcers are caused by the bacterium Helicobacter pylori that can live in the stomach of about 4 in 10 Australians. They can cause long-term, low-level inflammation of the stomach lining in some people. Why they cause stomach ulcers in some people and not others is not well understood.


Haemorrhoids are itchy or painful lumps that occur in and around your anus. The lumps contain swollen blood vessels. If you find blood on the toilet paper or in the toilet, always seek medical advice.

Last reviewed: May 2017

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