Many types, but not all cells, are dividing constantly in the body at any given time. For example, most mature and differentiated cells such as cardiac cells and neurons lose their ability to divide. However, cells such as epidermal or blood cells are continually dividing. When cells become damaged or die the body forms new cells to replace them. Essentially, the body knows which cells are responsible for constantly dividing and which cells are programmed to stop dividing in order to maintain proper functioning. Additionally, hormones play a role in cell cycling by binding to receptors on target cells. The number of receptors on a target cell may increase or decrease in response to hormone activity and as a result cause cellular changes.