Stress and Allostasis

Abstract

The concept of homeostasis is potentially one of the most studied and understood aspects of physiology. Also well known are the effects of threats to homeostasis, known as stressors. It has long been appreciated that the body responds to stressors actively, known as an allostatic response. The classic stress response – the activation of the sympathetic nervous system and the release of glucocorticoids from the adrenal glands – has been well studied, though perhaps it has been painted in a somewhat negative light as being detrimental to health. In fact, stress responses are necessary for the survival of an organism when it faces a threat to homeostasis, and so in the acute sense, stress is beneficial. The cost of restoring normal homeostasis through active intervention is known as allostatic load. This load, be it through chronic stress, or malfunctions in the systems regulating allostasis, can lead to wear and tear on the brain and body, with significant implications for mental and physical health. This chapter will summarize how stress, and the allostatic responses that accompany stress, affects physical and psychological health. We will discuss how chronic stress and allostatic overload can contribute to disease states and affect disease progression and the role of the body’s circadian (daily) timing systems: what they mean for maintaining homeostasis and how disruption of circadian timing may lead to allostatic load and overload.