Tricky Topics: Stress Response

Stress is an internal state triggered by situations that overwhelm our perceived ability to meet demands. Stressors are events that trigger a stress response, ranging from physical threats (systemic stressors) to psychological challenges (processive stressors) like public speaking or traffic. Most everyday stressors are processive.

Hans Selye's research in the 1930s established the biological link between psychological stress and physical illness. He observed that rats exposed to prolonged unpleasant events developed similar symptoms like stomach ulcers and enlarged adrenal glands, regardless of the specific stressor. Selye concluded that the stress response is universal across various negative experiences and species, and that chronic stress, not acute stress, makes us susceptible to illness.

The adrenal glands, located on top of the kidneys, have two main parts: the adrenal cortex and the adrenal medulla. The cortex releases cortisol, while the medulla releases epinephrine and norepinephrine (adrenaline and noradrenaline). These hormones are key to the body's physiological stress response.

The physiological stress response involves two systems. The adrenal medullary system is a fast response where the hypothalamus activates sympathetic nerves, leading to the release of norepinephrine and epinephrine from the adrenal medulla. This increases heart rate and blood pressure for a 'fight or flight' response. The hypothalamic-pituitary-adrenal (HPA) axis is a slower response; the hypothalamus releases CRF, which signals the pituitary gland to release ACTH, which then stimulates the adrenal cortex to release cortisol. Cortisol frees up energy reserves and inhibits the immune system, preparing the body for a perceived threat.

Selye proposed the General Adaptation Syndrome to explain how repeated stress leads to illness, consisting of three stages: alarm, resistance, and exhaustion. In the alarm stage, resources are mobilized. In the resistance stage, the body copes, and cortisol levels remain high. In the exhaustion stage, resources become depleted, leading to heightened susceptibility to illness. While some details of Selye's model have been refined, its core idea of the link between stress and illness remains influential.

According to Robert Sapolsky's 'Why Zebras Don't Get Ulcers,' stress-related illnesses are rare in wild animals because their stress responses are short-lived, activated only for life-threatening events. Humans, however, frequently activate their stress responses for non-life-threatening, chronic stressors like crashing computers or slow Wi-Fi. This constant activation leads to prolonged elevated cortisol levels, causing illness. Sapolsky suggests this overuse of our stress response is biologically inappropriate in the modern world and that our continued response to non-critical, prolonged stress is the problem.