Allostasis is the adaptive response of the organism to chronic or extreme strain conditions, which ensures survival in life-threatening situations. Typical examples for allostatic responses include fever, adaptation to stress by increased release of glucocorticoids and the TACITUS syndrome.
The concept of allostasis extends the theory of homeostasis. Originally defined as stability through change it comprises responses of biological feedback control systems that are mediated by changed set points or modified structure parameters. Both mechanisms back up homeostasis, thus enabling survival in extreme situations. This adaptive response requires coordinated action of all involved control mechanisms.
The penalty of allostasis, referred to as allostatic load, is wear and tear (and consecutively ageing). The term allostatic overload denotes acute pathological sequelae of allostatis.
Usually, the following types of allostasis are distinguished:
A third form of allostasis occurs in situations of rapidly decreasing strain, e.g. in the refeeding syndrome.
The concept of allostasis was first described in 1988 by Sterling and Eyer. McEwen and Stellar considerably expanded the theory in 1993 and subsequently.
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