Children, and young adults, grow because they have a chemical signaller in their body, a hormone, that tells the body to grow. This hormone circulates around the body and attaches onto specific cells that help to co-ordinate growth for a particular set of tissues. These cells in turn may signal other tissues to make sure that growth is controlled at the same time. There are certain types of cells, stem cells, that can turn into lots of different types of cells. These are involved in making the new cells that we need for growing body tissues.
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