Digestion
Your body needs food to build and repair itself, and to provide energy for all its processes. Before your body can make use of the food you eat, it has to be broken down into small particles, called nutrients, which can be absorbed into your blood. The process of breaking down and absorbing food is called digestion.
Digestive system
The main organ of your digestive system is a long muscular tube, called digestive tract. This is divided into four parts:
the oesophagus, the stomach, and the small and large intestines. Your pancreas, gall bladder, and liver also play a part in digestion.
Key facts:
- Digestion begins in your mouth, where your teeth break food into smaller pieces.
- Fluid called saliva softens food so it can slide down your throat.
- Your tongue shapes food into a ball and pushes it to the back of your throat, where you swallow it.
- Food enters your oesophagus and moves down into your stomach.
Inside your stomach, food is churned around by muscle contractions in the stomach wall. The lining of your stomach secretes acid and other chemicals that gradually break down the food, turning into a soupy liquid called chyme. This liquid is released in spurts into your small intestine.
Key facts:
- It takes about 10 seconds for food to travel down your oesophagus to your stomach.
- Food stays in your stomach for about four hours.
- Stomach acid is so powerful that it can dissolve metal.
- A layer of mucus lining your stomach prevents stomach acid from digesting your stomach wall.
Intestines
Your small intestine is lined with millions of tiny projections called villi, packed with blood vessels. Nutrients from the chyme pass through the walls of the villi into the blood. By the time the chyme reaches your large intestine, it is made up largely of waste and water. The water is absorbed into the bloodstream and the waste is formed into faeces in the rectum.
Key facts:
- Your small intestine is about 5 m (17 ft) long.
- Your large intestine is only 1.5 m (5 ft) long, but it is wider than your small intestine.
- Food can remain in your small intestine for up to five hours.
- Food spends up to 36 hours in your large intestine.
- Faeces reach your rectum between 20 and 45 hours after you swallowed the food.