General Adaptation Syndrome

The general adaptation syndrome (GAS), or biological stress, as it later became known, is a concept put forward by Hans Selye in 1936 based on his experimental studies. He described the triphasic nature of body adaptability when exposed chronically to intrinsic or extrinsic emotional or physical forces, referred to as stressors. The three-stage bodily response encompasses the alarm reaction and then the stages of resistance and exhaustion that are induced by the intensity and chronicity of the stressors.

The alarm reaction corresponds to the flight-or-fight response, whereby stressors convey signals to the brain, which activate the sympathetic nervous system to release catecholamines and the hypothalamic-pituitary-adrenal (HPA) axis to secrete glucocorticoids into the blood. The mobilization of these neuroendocrine systems is the hallmark of the alarm response ...