Apoptosis is the process of regulated cell death and removal. In some cases cell damage can trigger apoptosis, but it is usually a normal function of the cell. Apoptosis results in controlled auto digestion of the cells content. The cell membrane stays in place and the cells contents are not dispersed. When this process is near completion "eat me" signals, like phosphatidylserine, appear on the surface of the cell membrane. This in turn attracts phagocytic scavengers that complete the process of removing the dead cell without eliciting an inflammatory response. Unlike necrosis, which is a form of cell death that results from acute cellular injury, apoptosis is carried out in an ordered process that generally confers advantages during an organism's life cycle. Apoptosis Rates The rate at which cells die varies widely between different cell types of the body. Some cells, such as white blood cells, live for only a matter of hours where other cells can live an throughout the entire lifetime of the host. Homeostasis: Apoptosis is a regulated function that results in a relatively consistent number of cells in the body. This balancing act is part of the Homeostasis (see chapter 1) required by living organisms to maintain their internal states within certain limits. An example of this is that blood cells are constantly being replaced and apoptosis takes place to eliminate a simular number of older cells. Development: Apoptosis also plays a key role in growth and development. An example of how apoptosis enables development is the differentiation of human fingers in a developing embryo. Apoptosis is the function that enables the embryos fingers to separate. Disorders: Too much apoptosis causes cell-loss disorders such as osteoporosis, whereas too little apoptosis results in uncontrolled cell proliferation, namely cancer.