Apoptosis, also termed programmed cell death, is a highly conserved process for deleting old, damaged cells, or deleterious cells. Its rate is coupled with the rate of mitosis, which contributes to cell homeostasis (balance proliferation/ apoptosis). Apoptosis is morphologically denned by nuclear (DNA) and cell fragmentation with the formation of membrane-bound fragments containing viable organelles referred to as apoptotic bodies. Apoptotic bodies are phago-cytosed by neighbouring cells or professional macrophages. Typically, the maintained integrity of the subcellular fragments avoids the release of potentially toxic intracellular constituents, accounting for the absence of an inflammatory response. In contrast and schematically, lethal cell injury by necrosis is characterized by cell swelling, loss of membrane integrity, cytolysis and subsequent inflammation. In the normal liver it is estimated that only < 0.1-0.5% of hepatocytes are identified as apoptotic cells. This small number is probably due to the fact that apoptosis is a rapid process (over 2-4 h) followed by immediate phagocytosis of apoptotic cells. Therefore, an apparently small rate of apoptosis can correspond with important effects on the whole liver: a rate of 3% hepatocyte apoptosis in the absence of regeneration would result in a 25% reduction in liver mass over 2-3 days.
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