Stress Physiology and the Stress Process

1. Defining Stress and Appraisal

Stress is the process of responding to demands; a stressor is the event that triggers it. Crucially, stress depends on appraisal — evaluating whether a situation matters and whether it is a threat, challenge, or manageable (primary appraisal: "Is this a threat?"; secondary appraisal: "Can I cope?"). The same stressor can thus produce very different stress. Acute stress is short-term and can even improve performance; chronic stress is prolonged and is the form most linked to health problems.

2. The Stress Response: Fight-or-Flight and the HPA Axis

The fast response runs through the sympathetic nervous system, activating the fight-or-flight response: increased heart rate, blood pressure, and respiration, plus adrenaline (epinephrine) to direct energy to muscles. The slower response runs through the HPA axis (hypothalamus–pituitary–adrenal): the hypothalamus signals the pituitary, which signals the adrenal glands to release cortisol, a hormone that sustains energy mobilization and suppresses nonessential functions over minutes to hours. Both systems should return to baseline once the threat passes.

3. General Adaptation Syndrome and Allostatic Load

Hans Selye described the general adaptation syndrome (GAS), a three-stage model of prolonged stress:

• Alarm — the body mobilizes (fight-or-flight).
• Resistance — the body tries to adapt while staying on high alert.
• Exhaustion — resources deplete, increasing vulnerability to illness.

Allostatic load is the cumulative "wear and tear" from chronic activation of these systems — the cost of repeatedly mounting, and failing to shut off, the stress response. High allostatic load is associated with cardiovascular, metabolic, and immune changes. Stress reactivity is how strongly a person's physiology responds, which varies across individuals.

How it works

1. A stressor is detected and appraised as relevant and demanding.
2. The sympathetic nervous system triggers fight-or-flight within seconds.
3. The HPA axis releases cortisol to sustain the response over minutes to hours.
4. Once the stressor resolves, the parasympathetic system helps return to baseline.
5. If stress is chronic, systems stay active and allostatic load accumulates, raising health risks.

Common confusions

Memory aids

Selye's stages: "ARE you stressed?" — Alarm, Resistance, Exhaustion. Pathways: "Sympathetic is Swift (seconds); HPA is Hormonal and slow (minutes–hours)."

Quick review

Topic Recap

Stress is a response to appraised demands. Acute stress mobilizes the sympathetic nervous system (fight-or-flight) and, over minutes to hours, the HPA axis (cortisol). Selye's general adaptation syndrome traces alarm, resistance, and exhaustion, and allostatic load captures the cumulative damage of chronic stress. Individual differences and social determinants shape who faces stress and how they respond. The stress–health link is real but largely correlational, so causation must be claimed cautiously.

Knowledge Check

1. Why does appraisal matter for the stress response?
2. Name Selye's three stages in order.
3. What is the difference between the sympathetic nervous system and the HPA axis?
4. What is allostatic load?
5. Why are most everyday stress–health findings correlational rather than causal?

Answers and Rationales

1. Because whether an event is appraised as threat or challenge (and whether we think we can cope) determines the intensity and duration of the response.
2. Alarm, resistance, exhaustion.
3. The sympathetic nervous system is the fast, seconds-long fight-or-flight response; the HPA axis is the slower hormonal cascade releasing cortisol.
4. The cumulative wear-and-tear from chronic activation of stress systems, linking stress to illness risk.
5. People who report high stress differ in many other ways (poverty, sleep, healthcare access, coping), so stress and illness may co-occur without stress being the sole cause; controlled studies are needed for causal claims.