Physiology of stress

• Physiology of stress

  • General adaptation syndrome (GAS)
  • Physiological stress response (PSR)
• General adaptation syndrome (GAS)

  • First stage = alarm reaction
  • Second stage = resistance
  • Third stage = exhaustion
• first stage = alarm reaction (GAS)

  • Selye = suggested that the stress response is initially adaptive (beneficial) - the sympathetic branch of the ANS activated by the hypothalamus
  • stimulates adrenal medulla to release adrenaline and noradrenaline to prepare the body for fight or flight
• second stage = resistance (GAS)

  • Body continues to adapt by resisting stressor
  • Body’s resources consumed at harmful rate = eg stress hormones become depleted
  • Parasympathetic branch activated to conserve energy
• third stage = exhaustion (GAS)

  • adaptation to chronic stressor fails because resources needed to resist are drained
  • Symptoms of sympathetic arousal (eg raise heart rate), adrenal glands damaged, immune system suppressed
  • Stress-related illnesses now likely =eg raised blood pressure, coronary heart disease, depression
  • Result of prolonged exposure to stress
• strength = Selye’s own research supports it (GAS)

  • Selye = subjected rates to stressors (eg extreme cold, surgical injury) - found the same collection of responses (‘syndrome’) regardless of stressor
  • The syndrome appeared after 6-48 hours = not unique to specific stressor
  • He tracked the responses through resistance and exhaustion
  • this demonstrates the same general response regardless of the particular stressor
• limitation = may not actually be a general response (GAS)

  • Mason = replicated Selye’s procedures using monkeys
  • Effects varied depending on stressor = extreme cold increased urinary cortisol, extreme heat reduced cortisol, exercise had no effect
  • These findings challenge the validity of the GAS by showing that specific stressors produce specific responses
• extra evaluation = animal research (GAS)

  • Stress research depends on using non-human mammals to study for ethical reasons and because the physiological systems in the stress response are almost identical
  • BUT stress is more complex in humans because it is affected by psychological factors (eg cognitive appraisal)
  • => animal studies may help us to understand the basic physiological of stress but their applicability to humans is limited
• Physiological stress response (PSR)

  • Acute (short-term) stress response
  • Chronic (long-term) stress response
  • Cortisol
• acute (short-term) stress response (PSR)

  • Immediate response to stressor = hypothalamus activates the sympathetic branch of the ANS
  • Stimulates the adrenal medulla to release adrenaline and noradrenaline into bloodstream = heart beats faster, muscles tense, liver converts stored glycogen into glucose to provide energy to fuel fight or flight response
  • Once stressor stops = parasympathetic nervous system activated and physiological arousal decreases = priority is noW energy conservation, rest and digest response
• Chronic (long-term) stress response (PSR)

  • If stressor continues = hypothalamic- pituitary-adrenal system (HPA) now activated
  • Hypothalamus produces corticotropin releasing factor (CRF)
  • Detected by anterior lobe of pituitary gland and causes release of adrenocorticotropic hormone (ACTH)
  • ACTH detected by adrenal cortex which secretes cortisol
• role of cortisol in chronic stress response (PSR)

  • Cortisol = major stress hormone, strops non-essential functions (eg digestion)
  • It affects glucose metabolism and restores energy y
  • Other effects include suppressing the immune system
  • HPS is self-regulating via negative feedback loop = cortisol in bloodstream monitored by pituitary and hypothalamus
  • High levels of cortisol trigger reduction in both CRF and ACTH = resulting in corresponding reduction in cortisol
• strength = knowledge of physiology has real-world value (PSR)

  • People with Addison’s disease (disease of adrenal glands) cannot produce cortisol - so in stressful situations they don’t mobilise energy to deal with stressor
  • This triggers an Addisonian crisis = mental confusion, low blood pressure etc
  • Individuals self-administer cortisol replacement therapy and must be aware of dangers of stress
  • => a better understand of stress physiology has improved the lives of people
• limitation = physiological explanations ignore psychological factors (PSR)

  • Cognitive appraisal was demonstrated in one study where students watched a gruesome medical procedure
  • Heart rates increased in those who perceived the procedure as traumatic
  • BUT heart rates decreased in those told the procedure was voluntary initiation rite
  • This finding cannot be explained by a purely physiological theory
• extra evaluation = gender bias (androcentrism)

  • Fight or flight is a universal physiological response to an acute stressor = based on male animals (avoided females because of hormone fluctuations)
  • BUT = Taylor et al argued that females ‘tend and befriend’ instead = tend offspring, befriend other females for cooperation
  • Oxytocin inhibits fight or flight response in females
  • => there is no single baseline stress response = it varies depending on gender and circumstances