Entropy where to submit6/10/2023 ![]() ![]() ![]() Although it may seem then that the dynamics of life are at odds with the second law of thermodynamics-which states that the entropy of an isolated system can only increase-this paradox is seemingly resolved by the open nature of living systems, which basically indicates that a system can exchange either heat or matter or both with its environment. A basic description of the terms we use throughout the following text is provided in Table 1.īased on the concept of association of entropy production in living systems, introduced in 1944 in Schrödinger’s outstanding work What is Life?, it is generally accepted that an increase in order within an organism is compensated for by an increase in disorder outside this organism, mainly via the loss of heat into the environment. Hence, utility of allostasis concept for stress measurement is currently limited. In addition, the theory largely relies on rather vague connection between metabolism and energy consumption. Moreover, since energy input and expenditure are both overly inconsistent and poorly understood to be used for measuring allostatic load, the entire theory is based only on indirect metabolic parameters. The primary weakness of the allostasis concept is that allostatic markers are by their very nature highly cross-sectional and thus incapable of directly reflecting the cumulative functioning of most stressors. Although McEwen and Wingfield’s allostatic model facilitates the approximation of stress response by measuring indirect parameters associated above all with HPA axis activation, it currently provides the only applicable framework for measuring stress as such, although with substantial limitations. The concept of allostasis exhibits two key strengths: i) it provides a definition of allostatic load basically as the wear and tear experienced by individuals coping with repeated stressors as well as perturbations in the given system caused by environmental stimuli, and thus ii) it provides a framework for understanding changes in physiological set points and their adaptation to external stimuli over time. The subsequently proposed allostasis model, which differentiates between two types of allostatic overload, was the first to introduce an environmental component. ![]() The introduction of the concept of allostasis by Sterling and Eyer in 1988 constitutes an important step towards a new approach to stress. Despite of this, direct measurement/calculation of stress response still isn’t possible. As a result of this, Selye’s theory is currently superseded by the novel concepts of scientific integrative medicine that integrate system biology with integrative physiology that offer more accurate and complex explanations to the biological observations. Dissatisfaction with stress as a term and with Selye’s stress theory as a whole, frequently expressed by the scientific community, is thus derived primarily from the fact that it does not allow either for the quantification of the impact of actual stressors or for any kind of evaluation of the overreaction of systems experiencing chronic stress. The practical application of the theory is thus hindered by the fact that it fails to distinguish between i) internal and external causal factors, ii) physiological and pathophysiological consequences of stress-induced processes and iii) stressor-specific and non-specific response moreover, iv) the definition of stress does not take into consideration the interpretation of the stimulus by the organism itself. The key strength of Selye’s stress theory is also its biggest weakness: it is not per se associated with any specific mechanisms of action of individual stressors. Although Selye was also the first to systemically address the crucial issue of the role of environmental influences in disease development, his theory did not provide a robust framework for the measurement of stress and was in effect criticized ever since the term’s introduction. One of the first explanations-functional, broadly conceived and still accepted-is Hans Selye’s General Adaptation Syndrome, a comprehensive stress theory proposed in 1936, which defines stress as the “nonspecific response of the body to any demand made on it”. The association between chronic environmental and intrinsic factors and the pathogenesis of disease has been extensively documented throughout the history of mankind and although many attempts at characterizing the very basis of health and disease have been made, no completely satisfactory theory capable of providing an exhausting explanation of the general pathogenic processes has thus far been proposed. Introduction to Stress, Allostasis and Entropy
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