The human body can grow in several ways. The process that makes it possible is cell division.

At the beginning every human being comes from one cell. This cell divides over and over again and we soon become a mass of cells. Certain areas of these cells become our organ systems (i.e. Circulatory system, nervous system, skin, bones, and eyes). These then grow further until we are born. After that we have all the specific parts of our body and we "grow up".

Growing up happens the same way as before cell division. But the direction and magnitude of the growth is controlled very carefully by a hormone called the Human Growth Hormone or HGH for short. Most of this growth happens by the time you reach college (18-20) but it varies from person to person. Some people have genetic disorders where they never stop growing and these people end up growing very tall but often have shortened life spans.