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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

4-minute read

What is the digestive system?

The digestive system is made up of the digestive tract and other organs that help the body break down and absorb food. It is a long, twisting tube that starts at the mouth and goes through the oesophagus, stomach, small intestine, large intestine and anus.

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

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

How does the digestive system work?

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


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

Saliva also contains enzymes that start to digest the carbohydrates in food.


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


The 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 the gallbladder and enzymes in digestive juices from the pancreas empty into the upper section of the small intestine and help to 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 the 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 the small intestine.

Large intestine and anus

The lining of the 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 the 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.

Illustration of the digestive system.
Illustration showing the various organs that form part of the digestive system.

What are common conditions related to the digestive system?

Gastro-oesophageal reflux

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


Diverticulitis is caused by inflammation or infection of abnormal pouches in the lower part of the large intestine. It can cause mild or severe pain on the lower left-hand side of the abdomen.

Stomach ulcers

Stomach ulcers are commonly 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. It is not well understood why they cause stomach ulcers in some people and not in others.


Haemorrhoids are itchy or painful lumps that occur in and around the anus. The lumps contain swollen blood vessels. Haemorrhoids can cause bleeding when you go to the toilet (do a poo) — you might notice bright red blood on the toilet paper or in the toilet. If you find blood on the toilet paper or in the toilet, always seek medical advice.

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Last reviewed: April 2021

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