The structure of the digestive system

Jump to

Key points

  • The digestive system breaks down food into tiny particles which are absorbed into the blood.
  • These particles provide energy for the body to grow, repair itself and remain healthy.
  • Food that cannot be broken down is released from the body as faeces (poo).

Parts of the digestive system

The digestive system is made up of key parts, each of which has a different function. Food passes through most of these parts in a journey from the mouth to the anus.

A diagram of a human with the parts of the digestive system (as shown in the table below) labelled.
The parts of the digestive system
Part of the digestive systemFunction
MouthDigestion of food starts in the mouth. Teeth break down the food and mix it with the in saliva.
OseophagusThis is a thin tube that connects the mouth to the stomach.
LiverThis releases a chemical called bile into the intestines. Bile breaks down in the food.
StomachThis is a muscular bag which mixes food and drink with acid.
PancreasThis releases enzymes into the intestines which break down carbohydrates, protein and lipids in food.
Small intestineHere, and lipids digest. The nutrients produced are then absorbed into the blood.
Large intestineFood which cannot be broken down - mainly - passes into the large intestine. Water is absorbed into the blood.
RectumAny undigested food passes into the rectum where it is stored as faeces.
AnusThis is the opening at the very end of the digestive system through which faeces leaves the body.

Did you know?

Your mouth produces about 1.5 litres of saliva each day.

One person produces more saliva than this every week.

Video - Modelling the digestive system

How to model digestion using tights

1. In the model, what does the plastic bag represent and why is the food squeezed into it?

2. In the model, what represents the large intestine and why?

  1. It represents the stomach where food is churned up.
  1. A tea towel because it absorbs water.

Process of digestion

Mechanical and chemical digestion

Teeth break down food in the mouth mechanically, this means they grind it up. Chemical digestion occurs when enzymes digest food into nutrients.

Bile is produced by your liver and stored in the gall bladder. This is released into the small intestine to break down large molecules of lipids into smaller ones. This is not digestion because it doesn’t break down lipids into nutrients, just smaller droplets. This is called and increases the surface area for enzymes to act upon.

Moving food through the digestive system

Digested food is moved through the oesophagus, and small and large intestines by muscles in their linings that squeeze it along in a process called Squeezing a tennis ball through a pair of tights is a good model for this process.

Absorbing food and water

The intestines have lots of tiny folds in them which create a large surface area for absorbing nutrients and water. In the small intestine there are also specialised cells called villi which have a tiny hair-like structure poking into the small intestine to absorb digested food.

Villi in the intestine

Did you know?

If we stretched out all the folds in the small intestine this would be the area of a tennis court.

Test your knowledge

Quiz - Digestive system

Test questions

1. Put the parts of the digestive system in the order that food travels through them.

  • a. oesophagus
  • b. stomach
  • c. anus
  • d. large intestine
  • e. rectum
  • f. mouth
  • g. small intestine

2. Match the parts of the digestive system in the list to their function.

  • Where food that cannot be digested passes into before becoming poo
  • Connects your mouth to your stomach
  • The opening at the end of the digestive system; faeces pass out of the body here
  • Faeces is stored here
  • A muscular bag that mixes food and drink with acid
  • Where nutrients are absorbed into your blood
  • Mechanical and chemical digestion starts here
  • f. mouth
  • a. oesophagus
  • b. stomach
  • g. small intestine
  • d. large intestine
  • e. rectum
  • c. anus.
  • Mouth: mechanical and chemical digestion starts here
  • Oesophagus: connects your mouth to your stomach
  • Stomach: a muscular bag that mixes food and drink with acid
  • Small intestine: where nutrients are absorbed into your blood
  • Large intestine: where food that cannot be digested passes into before becoming poo
  • Rectum: faeces is stored here
  • Anus: the opening at the end of the digestive system; faeces pass out of the body here.