(biology, biogerontology) Biological aging; growing old
(cell biology) The state of a cell wherein it is no longer capable of dividing although it is still metabolically active and alive
Senescence pertains to the biological aging of a living thing. It entails the gradual deterioration of morphological features and function of a cell or of the whole organism. On the cellular level, senescence is that stage in a diploid cell’s cycle wherein it ceases to divide. For instance, a typical fibroblast cell may undergo a maximum of 50 mitotic divisions and then becomes senescent. This is referred to as the Hayflick phenomenon.1 It naturally occurs and results from the shortening of telomeres that eventuates in DNA damage. Cellular senescence is also associated with excessive exposure to reactive oxygen species, oncogene activation, and cell to cell fusion. When a cell is in senescence, it no longer divides but still remains metabolically active.
At the level of the whole organism, senescence is manifested when the organism ages, i.e. the ability to function and deal with stress deteriorates thereby increases its vulnerability to dysfunction and diseases.
Word origin: Latin senēscere (to grow old)
1 Hayflick L, Moorhead PS (December 1961). “The serial cultivation of human diploid cell strains”. Exp. Cell Res. 25: 585–621.