Figure 5.

Factors affecting cell senescence. Cells reach senescence when regions at the ends of chromosomes, telomeres, reach a critical length due to the cells’ inability to replicate them properly. The inset shows the activity of an enzyme, telomerase, that allows stem cells to extend the length of the telomeres and therefore maintain an almost indefinite capacity for self-renewal. There are many factors that also contribute to telomere shortening, which may lead to abnormal cell behavior. The accumulation of damaged cells and the inability of a depleting stem cell population to replace these cells with aging may affect tissue function. Adapted from Muller (2009).