The term apoptosis describes the regulated and gradual death of a cell. In contrast to uncontrolled necrosis, apoptosis is limited to one or a few cells and is not accompanied by inflammation. Through apoptosis, the organism can get rid of cells, which are non-functional or which are harmful, such as virus infected or tumor cells. The apoptotic process goes through the three different phases of initiation, execution and phagocytosis. Initiation can be mediated by internal signals such as DNA damage or by external factors like TNFa. Execution involves the proteolytic cleavage of many different proteins by caspases, which are proteases activated during apoptosis. At the end of the execution phase, the DNA packaging histones, cytoskeletal proteins and many other intracellular proteins are degraded. In the last phase, the cell dissolves into apoptotic vesicles, which are internalized by other cells like macrophages.