The human body contains many organs. An organ is a group of cells that performs a specific job. The cells in an organ have specialized into one or more type of tissues. The brain controls the nervous system.

The heart is the pump for the circulatory system.

The lungs are the main organ of the respiratory system.

Our bodies have many other organs such as the liver and stomach. Each one has a specific job. Sometimes when an organ is damaged or diseased, it can be replaced by one from another person. This is called an organ transplant.

Scientists believe that one day they may be able to use cloning to grow organs that could be stored and used for transplants when needed.