Читать книгу The Science of Health Disparities Research - Группа авторов - Страница 29

One of the most significant universal biological imperatives is the maintenance of homeostasis. From the Greek homeo, meaning “similar” and stasis, meaning “stand” or “state,” homeostasis refers to the body's ability to maintain internal stability. Humans and mammals have evolved numerous physiological systems to maintain homeostasis (e.g., body temperature, serum electrolytes, blood pressure, and pH). Similarly, from the Greek allo, meaning “other” or “variable,” allostasis refers to change or adaptation to maintain stability and preserve homeostasis, particularly in response to environmental challenges (Figure 2.1a). Allostasis, as initially coined by Sterling and Eyer [2] and popularized by McEwen [3], defines the central role of the brain in stress responses through the neuroendocrine and autonomic nervous system. This system is referred to as the hypothalamic‐pituitary‐adrenal (HPA) axis and, along with elements of the brain governing behavioral and physiological changes in the cardiovascular, metabolic, and autonomic nervous system, is a central component of the global stress response system [4]. Traditionally referred to as the “fight or flight” response, many components of the HPA have adapted to environmental threats or change to promote survival (Figure 2.1b) [5].

Figure 2.1 Schematic representation of the concept of Allostatic Load: (a) Graphic illustration of conceptual linkages between allostasis and environmental stress and chronic disease; (b) Graphic representation of the role and components of allostatic load over the life course illustrating influences of biological embedding, neuronal plasticity, and cumulative “wear and tear” in response to environmental stressors.

However, persistent or chronic overuse of the stress response systems leads to cumulative “wear and tear,” or cellular, physiological, cognitive, and emotional dysfunction, that eventually becomes maladaptive. Over time, this “weathering,” the disproportionate deterioration as a result of cumulative wear and tear that begins at an earlier age and is patterned by race, can result in disease [6]. The chronic conditions or diseases that result from persistent allostasis are referred to as allostatic load (Figure 2.1b) [3].

Allostatic load provides a conceptual bridge to understanding how the basic cellular and molecular biology underlying human physiology interacts with behavior and environmental exposures to affect health. Furthermore, it provides a framework to help us understand how certain aspects of human lived experience (e.g., social isolation and racism) and environmental exposure can become “embedded” or “baked in” to influence behavioral patterns and biological events across the life course [3]. The central thesis of allostatic load is that cumulative chronic stress may “get under the skin,” so that past events, occurring as distantly as early childhood or even prenatally, can have persistent effects far into adulthood [7]. These concepts form the foundation that supports how differences in societal experience can be the root cause of disparities in health outcome [8]. The concept of allostatic load enables an exploration of gene‐environment and epigenetic interactions that will ultimately provide insights into intervention.

In summary, allostasis and the influence of allostatic load occur and accumulate throughout life with consequences that ultimately result in chronic physical, emotional, and cognitive decline [3]. Understanding the forces through which societal, behavioral, and environmental determinants combine with biological susceptibility will be the subject of this chapter.