The HPA Axis & Stress Response

All 9 Terms & Definitions

Fight-or-flight response

Walter Cannon's term for the coordinated sympathetic nervous system response to threat: increased heart rate, bronchodilation, peripheral vasoconstriction, glucose mobilisation, and inhibition of digestion. Drives the initial alarm reaction. Complemented by the parasympathetic "rest-and-digest" system during recovery.

SAM axis (Sympatho-adrenomedullary)

The fast-acting stress axis: amygdala/hypothalamus → sympathetic preganglionic neurons → adrenal medulla → adrenaline and noradrenaline released into the bloodstream within seconds. Produces the immediate fight-or-flight response.

HPA axis

The hypothalamic–pituitary–adrenal axis: the body's primary endocrine stress system. Hypothalamus releases CRH → anterior pituitary releases ACTH → adrenal cortex releases cortisol. Operates over minutes to hours. Cortisol feeds back to hypothalamus and pituitary to dampen the response.

Cortisol

The primary glucocorticoid released by the adrenal cortex during stress. Mobilises energy (raises blood glucose via gluconeogenesis), suppresses immune and inflammatory responses, modulates memory consolidation, and elevates blood pressure. Chronically elevated cortisol is associated with immunosuppression, metabolic syndrome, hippocampal atrophy, and depression.

General Adaptation Syndrome (GAS)

Selye's (1936) three-stage model of the body's response to prolonged stress: (1) Alarm — initial fight-or-flight activation; (2) Resistance/adaptation — sustained stress hormone elevation; (3) Exhaustion — physiological resources depleted, defences fail, disease vulnerability increases. Demonstrated that diverse stressors produce the same nonspecific physiological response.

Allostatic load

McEwen & Stellar's (1993) concept: the cumulative physiological wear-and-tear on body systems resulting from repeated or chronic activation of stress-response systems. High allostatic load is associated with cardiovascular disease, metabolic syndrome, depression, cognitive decline, and accelerated biological ageing. Accumulates unevenly along socioeconomic gradients.

Cognitive appraisal (Lazarus)

Lazarus and Folkman's transactional model: stress is a transaction between person and environment, mediated by primary appraisal (Is this threatening?) and secondary appraisal (Can I cope?). Stress occurs when perceived demands exceed perceived resources. Changing appraisals (cognitive reappraisal, challenge vs threat framing) can reduce physiological stress responses.

Tend-and-befriend (Taylor)

Shelley Taylor's (2000) proposal that females respond to stress by nurturing offspring ("tending") and seeking social alliances ("befriending"), driven by oxytocin and oestrogen. An evolutionarily plausible alternative to fight-or-flight, particularly for females with dependent offspring. Social support is a key stress buffer in both sexes.

Psychoneuroimmunology

The study of bidirectional communication between the nervous system, endocrine system, and immune system. Demonstrates that psychological stress alters immune parameters: brief acute stress can enhance certain immune functions; chronic stress suppresses T-cell activity, NK cell function, and antibody production. Cohen et al. showed that stress dose-dependently increased susceptibility to experimentally induced colds.