Programmed cell death

Also called apoptosis, a form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area. Apoptosis plays a crucial role in developing and maintaining health by eliminating old cells, unnecessary cells, and unhealthy cells. In contrast to the more familiar messy death known as necrosis, which is caused by an injury or attack that results in the hemorrhaging of cells and inflammation, apoptosis is a neat way to eliminate cells without leaving evidence behind. The human body replaces perhaps a million cells a second. Over the course of a year, that is roughly equal to the number of cells in the human body. Without an orderly process for getting rid of cells, we would double in size within a year. Too little or too much apoptosis plays a role in a great many diseases. When programmed cell death does not work right, cells that should be eliminated may hang around and become immortal. For example, in cancer and leukemia. When apoptosis works overly well, it kills too many cells and inflicts grave tissue damage. This is the case in strokes and neurodegenerative disorders such as Alzheimer, Huntington and Parkinson diseases. A protein called bcl-2 prevents cell suicide in normal healthy cells. Many cancer cells produce bcl-2 in abundance so they are not eliminated, as they should be, by apoptosis. Strictly speaking, the term apoptosis refers only to the structural changes cells go through, and programmed cell death refers to the complete underlying process, but the terms are often used interchangeably. "Apoptosis" is derived from the Greek apo, off, + ptosis, a falling = a falling off or dropping off.

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programmed cell death n APOPTOSIS

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the theory that particular cells are programmed to die at specific sites and during specific stages of development, often by the process of apoptosis. Although the two terms are often used synonymously, not all programmed cell death occurs by apoptosis.