Stress Flashcards
STRESS
- stressor = threatening/demanding event/situation (ie. predator presence/social competition/extreme weather)
- stress response = stressors triggering coordinated physiological/psychological/beh changes
- vertebrates stress = activation of 2 neuroendocrine protection systems:
1. SAS (sympatho-adrenergic system) = rapid/short-term/catecholamine (adrenaline/noradrenaline) mediated
2. HPA (hypothalamic-pituitary-adrenal axis) = long-term/glucocorticoid (cortisol) mediated - together orchestrate response to potentially harmful/life-threatening situations
- involve bi-directional body communication
SAS (SYMPATHO-ADRENERGIC SYSTEM)
hypothalamus -> nerve impulses -> spinal cord -> adrenal medulla -> catecholamine release (epinephrine/norepinephrine)
- increased HR/BP/metabolism
- liver converts glycogen to glucose; glucose release
- bronchiole dilation
- blood flow pattern changes -> ^alertness/decreased digestive activity/decreased urine output
HPA (HYPOTHALAMIC-PITUITARY-ADRENAL AXIS)
CRH (corticotropin-releasing hormone) -> anterior pituitary corticotrope cells release ACTH -> blood target -> adrenal cortex -> mineralocorticoid/glucocorticoid release
- sodium/water retention in kidneys
- ^ blood volume/BP/gluconeogensis
- decreased insulin sensitivity/GH/T3/immune response/fat & protein mobilisation
STRESS RESPONSE STAGES
SELYE (1932)
- ALARM REACTION
- pituitary-adrenal system perceives stressor
- SAS prepares body for action/FVF
- HPA releases energy stores - RESISTANCE STAGE
- body attempts physiological balance re-establishment
- if stressor persists, stress hormones/arousal remain ^ - EXHAUSTION STAGE
- prolonged stress eventually depletes resources/exhausts body’s defences
- stress-related illnesses develop
ALARM REACTION
- prompted by sudden/unexpected stressor appearances
- startle = non-specific immediate beh response
- followed by FVF = specific beh responses
- physiological changes accompany (ie. ^BP/tachycardia (rapid HR)/tachypnoea (rapid breathing))
- above = active coping mechanisms for threat control
AR: SAS
- alarm reaction primarily linked to SAS (sympatho-adrenergic system)
- activates brainstem nuclei/vagal nerve/adrenal medulla
- adrenal medulla releases adrenaline (wide effect range)/noradrenaline (stimulates muscle alpha receptors; contraction redirects blood to essential organs/^BP)
ADRENALINE
- raises HR/muscle blood flow
- reduces blood flow to skin/intestines
- stimulates glycogenolysis via liver (glycogen broken to glucose = ^ blood sugar)
- causes adipose tissue to release fat into blood
- widens bronchioles (lung air passageways)
- dilates pupils
- assists body to escape from/deal w/stress
AR: HPA
- ACTH stimulates adrenal cortex to release cortisol/other steroids
- engages slower-acting passive coping mechanisms (useful w/FVF = ineffective)
- adaptively redirects energy:
- direct oxygen/nutrients to brain
- stimulates lipolysis (fat breakdown)/gluconeogenesis (glucose production)
- inhibits growth/reproduction
- suppresses immune system
- contains inflammatory responses
- enhances arousal/vigilance/cog
RESISTANCE STAGE
DEIZNER et al (1997)
- if stressor successfully handled, body restores homeostasis; feedback loops return stress hormones to baseline levels/recovery
- may see reduced impact of stressor w/repeated exposures BUT severe/uncontrollable/long-lasting aversive events may lead to sustained HPA activation = chronic stress response
EXHAUSTION STAGE
- stress-related illness process includes:
1. sugars mobilised; energy never stored (muscle wasting; fatigue; increased diabetes risk)
2. hypertension (^BP) maintained (blood vessel damage)
3. digestion suppressed (peptic ulcers; irritable bowel syndrome)
4. suppressed growth (psychogenic dwarfism; bone decalcification)
5. suppressed reproduction (disrupted ovulation; impotence; libido loss)
6. suppressed immunity/inflammation (long-term immunosuppression; increased disease susceptibility)
7. altered cog/sensory threshold (neural degeneration in hippocampus/pre-frontal cortex; impaired learning/memory retrieval)
STRESS TRIGGERS
- any stimulus can be stressor if perceived to threaten homeostasis & activates HPA axis
- most naturally occurring stressors involve factor combo
SYSTEMIC (“ACTUAL”) STRESSORS - visceral nociceptors
- somatic nociceptors
- inflammatory signals
- baroreceptor/osmoreceptor stimulation
NEUROGENIC (“ANTICIPATED”) STRESSORS - HPA activation in physiological challenge absence
- predator anticipation/recognition
- dangers associated w/novel environment
ST: COSPECIFICS
SAPOLSKY (2005)
- dominance interactions in baboons
- dominant male’s testosterone recovers more rapidly after stressful event
- subordinate males display ^ circulating cortisol levels
- dominance beh often subtle (threats > direct aggression)
CARLSON et al (2006)
- meerkat pup begging
- adults long-term contributions to pup feeding = + correlated w/cortisol plasma levels
- pup begging both ^ plasma cortisol levels/pup feeding via male helpers
MODERN STRESS TRIGGERS
- modern environment stressors = difficult to avoid -> high chronic stress rates:
1. job related (high pressure/long hours/inconvenient shifts)
2. financial worries
3. transport (traffic jams/dangerous driving/public transport)
4. global pandemic/environmental destruction/racial inequality
EUSTRESS VS DISTRESS
EUSTRESS
- perturbation can be dealt w/effectively
- beneficial stress response quickly terminated once homeostasis restores
DISTRESS
- chronic hypo/hyperactivation of HPA axis
- may be harmful/lead to abnormal beh
EUSTRESS/DISTRESS BALANCE
- quality/intensity tips balance
- individual characteristics challenged by stressor:
1. genetic predisposition
2. past history/experience
3. development age/stage - stimuli interpretation varies between/within individuals; may be associated w/emotional state (ie. anxiety/arousal)
