I'm hungry !

How does your body know it's time for lunch ? If your stomach is quite empty, your gastric glands produce more juices and your stomach walls contract. These contractions alert your nervous system which sends messages to your brain and you begin to feel hungry.

When you have eaten, your stomach is stretched and full. Your brain receives different messages saying that all is well and the feeling of hunger goes away.

Although you cannot survive without eating, food is not as important as you might think.

Liquid is much more necessary to keep you alive. People may easily live up to 25 days without food, but cannot do without water for longer than four or five days.

About 2/3 of your body is water. During a day you will probably take in about 2 to 3 litres of water in drinks. You also take some water into your body in the food you eat.

Until recently, very little was known about how the digestive system works.

Modern science has found out much more about it by exploring inside the body. Scientists can use the endoscope, an instrument like a tube, with lights and a viewing lens to view the inside of the stomach and intestine.