Allostasis

Allostasis is the process of achieving stability, or homeostasis, through physiological or behavioral change (Copstead & Banasik2013). This can be carried out by means of alteration in HPA axis hormones, the autonomic nervous system, cytokines, or a number of other systems, and is generally adaptive in the short term (McEwen & Wingfield 2003). Allostasis is essential in order to maintain internal viability amid changing conditions (Sterling & Eyer 1988; McEwen 1998a; McEwen 1998b; Schulkin 2003). Allostasis provides compensation for various problems, such as in compensated heart failure, compensated kidney failure, and compensated liver failure. However, such allostatic states are inherently fragile, and decompensation can occur quickly, as in acute decompensated heart failure. The concept of allostasis was proposed by Sterling and Eyer in 1988 as a process of reestablishing stability in response to a challenge. Allostasis was coined from the Greek allo, which means 'variable;' thus, 'remaining stable by being variable' (Sterling & Eyer 1988; Klein 2004). Allostatic regulation reflects, at least partly, cephalic involvement in primary regulatory events, in that it is anticipatory to systemic physiological regulation (Sterling & Eyer 1988; Schulkin 2003). This is in difference to homeostasis, which occurs in response to subtle ebb and flow. Both homeostasis and allostasis are endogenous systems responsible for maintaining the internal stability of an organism. Homeostasis, from the Greek homeo, means 'similar,' while stasis means 'stand;' thus, 'standing at about the same level.' (Sterling & Eyer 1988); The term Heterostasis (Selye 1973) is also used in place of Allostasis, particularly where state changes are finite in number and therefore discrete (e.g. computational processes).