Model of stress: GAS

• Selye’s research looked at both immediate and long-term effects of stress
• Most of his research was done on rats that were exposed to a variety of stressors such as painful tail-pulling, prolonged exposure to heat and cold, mild electric shocks, bacterial infections, strenuous exercise and forced restraint
• Physiological changes in response to stressors

  • Adrenal glands enlarged
  • Gastrointestinal ulcers developed
  • Weight loss
  • Immune system shrinkage
• Stress


  A condition that is non-specific and can only be brought on by either internal or external stressors
• Stress


  The body’s physiological response to both physical and psychological demands
• Selye: '“Stress represents the body’s generalised effort to adapt itself to new conditions” (Selye, 1936)'
• General Adaptation Syndrome (GAS)


  A three-stage physiological response to stress that occurs regardless of the stressor encountered
• GAS


  • Non-specific
  • Three stages
• Stages of General Adaptation Syndrome

  1. Alarm reaction

  2. Resistance

  3. Exhaustion
• Stage 1: Alarm reaction


  1. Initial response to stressor

  2. Shock

  3. Counter shock
• Shock


  Resistance level falls below normal, body acts as though injured
• Shock effects


  • Body temperature drops
  • Blood pressure drops
  • Muscles lose tone
  • Loss of fluid from body tissues
• Counter shock


  Sympathetic nervous system activated, body prepares to deal with stressor
• Counter shock effects


  • Adrenaline, noradrenaline, cortisol released
  • Heart and respiratory system accelerate
  • Muscles supplied with energy
• Stage 2: Resistance


  Body continues to cope and adapt to stressor
• Resistance stage effects


  • Resistance rises above normal
  • Physiological arousal remains above normal
  • Unnecessary processes shut down
• Cortisol


  Supports resistance, acts as anti-inflammatory agent
• Cortisol suppresses the immune system
• Resistance to other stressors may decline
• Everyone goes through the alarm reaction and resistance stages many times in their life
• If the effort to deal with the stressor in the resistance stage is successful

  The body will have adapted to the stressor and return to normal functioning
• Stage 3: Exhaustion


  Body cannot sustain its resistance to stressor
• Exhaustion stage effects


  • Fatigue
  • Sleep disturbances
  • Loss of concentration
  • Vulnerability to heart attacks
  • Irritability
  • Depressed mood
  • Crying spells
• High blood pressure can develop into hypertension
• Heart disease may occur
• Gastrointestinal problems may arise
• Changes to organs may be permanent
• In extreme cases, the organism may die
• Alarm reaction


  • Trembling hands and butterflies in stomach prior to an important exam
• Resistance


  • Having trouble switching gears after an exam
• Exhaustion


  • Feeling anxious and depressed after an exam
• Strengths of GAS model

  • Explains chronic stress impact on health
  • Challenges bacteria-only illness theory
• Limitations of GAS model

  • Conducted only on animals
  • Does not consider individual differences