The Physiological Response to Stress
Stage 1: Alarm Reaction: The initial shock of the stressor triggers the SAM pathway. Resistance to stress briefly drops before the body mobilizes resources for fight-or-flight.
Stage 2: Resistance: If the stressor persists, the HPA axis takes over. The body attempts to adapt to the high demand, keeping physiological arousal high while using significant energy reserves.
Stage 3: Exhaustion: Prolonged stress eventually depletes the body's resources. The parasympathetic nervous system can no longer restore balance, leading to physical collapse or stress-related illnesses.
| Feature | SAM Pathway (Acute) | HPA Axis (Chronic) |
|---|---|---|
| Speed | Near-instantaneous (neural) | Slower (hormonal) |
| Primary Hormone | Adrenaline / Noradrenaline | Cortisol |
| Target Structure | Adrenal Medulla | Adrenal Cortex |
| Primary Goal | Immediate survival/action | Sustained energy/adaptation |
| Health Impact | Temporary arousal | Immunosuppression / Illness |
Adrenal Medulla vs. Adrenal Cortex: The medulla is the inner part of the gland responsible for rapid-fire adrenaline, while the cortex is the outer layer responsible for the slower release of cortisol.
Sympathetic vs. Parasympathetic: The sympathetic system 'revs up' the body for action, while the parasympathetic system 'calms down' the body to restore homeostasis.
Identify the Stressor Type: When analyzing a scenario, first determine if the stressor is acute (e.g., a sudden loud noise) or chronic (e.g., ongoing work pressure) to select the correct pathway.
Trace the Hormonal Chain: For the HPA axis, remember the sequence: Hypothalamus (CRF) Pituitary (ACTH) Adrenal Cortex (Cortisol). Missing one step often loses marks.
Link to Health: Always connect the 'Exhaustion' stage of GAS or high cortisol levels to specific health outcomes like immunosuppression or cardiovascular issues.
Check for Gender Bias: Be prepared to discuss how the 'Fight-or-Flight' model may be limited, as some research suggests females may exhibit a 'Tend-and-Befriend' response instead.
The 'Cortisol is Fast' Myth: Students often think cortisol is responsible for the initial 'rush' of stress. In reality, cortisol takes minutes to reach peak levels, whereas adrenaline acts in seconds.
Confusing the Adrenal Parts: A frequent error is swapping the roles of the medulla and the cortex. Remember: Medulla = Momentary (SAM), Cortex = Chronic (HPA).
Stress as Purely Negative: While chronic stress is harmful, the acute stress response is a vital survival mechanism that improves performance in short bursts (Eustress).