MCAT topics → Emotion, Stress, and Physiological Response → General Adaptation Syndrome (Selye)

General Adaptation Syndrome (Selye)

MCAT trap: Mistakes the resistance stage for recovery rather than sustained, resource-depleting adaptation. During the resistance stage, the body maintains elevated cortisol and sympathetic activation to cope with the ongoing stressor; resources are depleted but the response is sustained.

General Adaptation Syndrome (GAS), developed by Hans Selye, is the body's stereotyped, three-stage physiological response to any stressor — biological, psychological, or environmental. The MCAT tests this framework primarily through passage-based questions that describe a patient or research subject under chronic stress, then ask you to identify which stage they're in or predict downstream physiological consequences. One misconception that wrecks students on these questions: the resistance stage looks like recovery, but the body is absolutely not back to baseline — cortisol and sympathetic tone are still elevated, resources are being depleted, and the organism is quietly setting up for exhaustion.

The tricky part is that GAS isn't just a list to memorize — it's a mechanistic story. The alarm stage fires the sympathetic nervous system and HPA axis. The resistance stage looks like the body is 'handling it,' but that's deceptive: cortisol and sympathetic tone are still elevated, and resources are quietly being depleted. The exhaustion stage is when the body's adaptive reserves give out, leading to immune suppression, organ damage, and psychological breakdown. Students who memorize stage names without understanding the underlying physiology get destroyed on application questions.

Two misconceptions show up constantly. First, students confuse the resistance stage with recovery — the body is NOT back to baseline; it's burning through reserves to maintain a stress response. Second, students assume cortisol is uniformly 'protective' because it's a stress hormone. Chronically, cortisol suppresses the immune system, and the MCAT loves testing this counterintuitive consequence in passages about chronic disease and infection risk.

Common misconceptions

Common mistake
Wrong: During the resistance stage of GAS, the body returns to baseline and stress hormones normalize.
Right: During the resistance stage, the body maintains elevated cortisol and sympathetic activation to cope with the ongoing stressor; resources are depleted but the response is sustained.
The resistance stage looks stable from the outside — the acute panic of the alarm reaction fades — but internally the body is still running a stress response at full cost. Cortisol remains elevated and sympathetic tone is sustained so the organism can keep coping with the stressor. The key insight is that this sustained effort depletes energy stores, suppresses repair processes, and sets the stage for exhaustion; it is absolutely not a return to homeostasis. Think of it like running an engine at high RPM continuously — it 'works,' but it's wearing out.
Common mistake
Wrong: Chronic cortisol elevation enhances immune function because cortisol is a stress-response hormone that prepares the body to fight threats.
Right: Chronic cortisol elevation suppresses immune function by inhibiting cytokine production and lymphocyte activity, increasing susceptibility to infection and disease.
Cortisol is anti-inflammatory and immunosuppressive, not immunoenhancing — this is actually why synthetic glucocorticoids like prednisone are prescribed to treat autoimmune diseases. Acutely, suppressing inflammation makes sense during a stressor, but chronically, this means the immune system can't mount effective defenses against pathogens. Chronic cortisol elevation specifically inhibits cytokine production (including IL-2 and interferon) and reduces lymphocyte proliferation, which is why chronically stressed individuals get sick more often.
Common mistake
Wrong: The alarm stage of GAS is characterized by parasympathetic activation to conserve energy for the stressor.
Right: The alarm stage is characterized by sympathetic nervous system activation (fight-or-flight) with epinephrine and norepinephrine release, not parasympathetic activity.
The alarm stage is textbook fight-or-flight: the sympathetic nervous system fires, releasing epinephrine and norepinephrine from the adrenal medulla, driving increased heart rate, elevated blood pressure, dilated airways, and redirected blood flow to muscles. The parasympathetic system does the opposite — it slows the heart, promotes digestion, and conserves energy — which is exactly what you do NOT want when facing a threat. Parasympathetic dominance is the 'rest and digest' state; it has no role in initiating the GAS alarm reaction.
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What the exam tests

  1. Know all three GAS stages — alarm, resistance, and exhaustion — and be able to describe the specific physiology of each, including which hormones are elevated and what organ systems are active or failing.
  2. Understand the HPA axis mechanism: stressor → hypothalamus releases CRH → anterior pituitary releases ACTH → adrenal cortex releases cortisol; know why chronic activation of this pathway is harmful, including metabolic, cardiovascular, and immune consequences.
  3. Apply the GAS framework to passage scenarios involving chronic stress — identify which stage a described individual is in based on physiological or behavioral clues, and predict outcomes like immune suppression, hypertension, or burnout.
  4. Connect chronic stress physiology to immune suppression (cortisol inhibits cytokines and lymphocytes), cardiovascular disease (chronic sympathetic activation raises blood pressure and damages vessels), and metabolic dysregulation (cortisol promotes gluconeogenesis and fat redistribution).

Can you avoid these mistakes?

A researcher notices that long-distance runners training for months show elevated resting cortisol, frequent upper respiratory infections, and chronic fatigue despite adequate sleep. Which stage of GAS best describes their condition, and what physiological mechanism explains their immune vulnerability?
During the resistance stage of GAS, a patient's cortisol levels are measured and found to be significantly above baseline. Is this expected or unexpected? What would you predict happens to their lymphocyte count and why?
Trace the complete HPA axis pathway from perception of a stressor to cortisol release. At each step, name the structure and hormone involved. Then explain why this pathway being chronically activated leads to cardiovascular disease.
A passage describes a medical student during exam season who has elevated blood pressure, disrupted sleep, frequent colds, and feels constantly on edge but is still functioning. Distinguish whether this student is more likely in the resistance or exhaustion stage of GAS, and identify two specific physiological markers you would look for to confirm your answer.

Related topics

Adrenal Cortex and Medulla Hormones Theories of Emotion (James-Lange, Cannon-Bard, Schachter-Singer, Lazarus) Universal Emotions and Display Rules Limbic System Role in Emotion (Amygdala, Hippocampus) Stress and Cognitive Appraisal (Lazarus)

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