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. Author manuscript; available in PMC: 2015 Feb 20.
Published in final edited form as: Annu Rev Biochem. 2008;77:777–798. doi: 10.1146/annurev.biochem.77.070606.101605

Figure 2.

Figure 2

Aging of an organism is due to the decline in function of the top-level physiological systems into which the organism has been divided. This dysfunction leads to changes in system outputs that have a greater or lesser influence on the age specific mortality [P(t)], as indicated by the variable width of the arrows linking to mortality. Dysfunction of each system is in turn due to changes in either the number or function of its constituent cells. The changes to cells are caused by their metabolic history and are due to nonspecific damage and to changes in signaling pathways and gene expression. These in turn lead to effects on cell function and on cell number.