WHEN CELLS are damaged, as often occurs during trauma and metabolic stress, the organism has to choose whether to repair the damage by promoting cell survival or remove irreparably injured cells. Cell injury occurs when an adverse stimulus reversibly disrupts the normal, complex homeostatic balance of the cellular metabolism. In this case, after injury the cells attempt to seal breaks in their membranes, chaperone the removal or refolding of altered proteins, and repair damaged DNA. On the contrary, when cell injury is too extensive to permit reparative responses, the cell reaches a “point of no return” and the irreversible injury culminates in programmed cell death (PCD). Specific properties or features of cells make them more or less vulnerable to external stimuli, thus determining the kind of cellular response. In addition, the characteristic of the injury (type of injury, exposure time, or severity) will also affect the extent of the damage.

We present a short overview of the best-known PCD pathways. We emphasize the apoptotic pathway, considered for years the hallmark of PCD, and the different stimuli that produce cell injury.

CELL INJURY

The survival of multicellular organisms depends on the function of a diverse set of differentiated cell types. After development is complete, the viability of the organism depends on the maintenance and renewal of these diverse lineages. Within each lineage homeostasis is maintained through a delicate balance between cell proliferation and cell death.