PSYC 132: Chapter 11

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Stress

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22 Terms

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Stress

Any significant disturbance of homeostasis

  • e.g. as by extreme temperatures or physiological factors

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Stressor

Condition, agent, or other stimulus that causes stress to an organism

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Stress Response

Suite of physiological and behavioral responses that help to reestablish homeostasis

  • Relatively nonspecific, i.e., many different stressors elicit a similar stress response

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Allostasis

Physiological/behavioral process of getting back to homeostasis

  • e.g. being cold → shivering, putting on a sweater, changes in hormones and stored energy, etc.

  • Total cost of this is called allostatic load

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Fight-or-flight response

Automatic and endocrine responses that prepare an individual to battle or flee from real or perceived attack, harm, or threats to survival

  • Coined by Walter Cannon

<p>Automatic and endocrine responses that prepare an individual to battle or flee from real or perceived attack, harm, or threats to survival</p><ul><li><p>Coined by Walter Cannon</p></li></ul><p></p>
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Fight-or-flight: hormones

  • Epinephrine and norepinephrine increase blood glucose, oxygen, and alertness

  • Epinephrine usually acts first

    • A doubling of epinephrine can have substantial effects

    • Causes blood to be routed away from digestion and non-essential functions and routes it to the muscles

  • NE

    • must increase fivefold to have the same effects as epinephrine

  • Glucocorticoids

    • Don’t get released until minutes after a fight-or-flight response and increase blood glucose levels

    • Corticosterone in most rodents, birds, reptiles, and fish

    • Cortisol in most primates, large mammals, and carnivores

  • Epinephrine and glucocorticoids are known as the primary stress hormones and are released in response to almost any stressor

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HPA (Hypothalamic-pituitary-adrenal) Axis

Complex and interactive system comprised of the hypothalamus, pituitary gland, and adrenal gland

  • Regulates stress responses

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HPA function

  • Stress → stimulates release of epinephrine (E) from adrenal medulla and norepinephrine (NE) from the sympathetic nervous system

  • N and NE → stimulate hypothalamus to release corticotropin-releasing hormone (CRH)

    • Positive feedback

  • CRH → stimulate anterior pituitary to release adrenocorticotropic hormone (ACTH) and beta-endorphin

  • ACTH → stimulates adrenal cortex to release glucocorticoids

  • Glucocorticoids signal the hypothalamus and the pituitary to decrease CRH and ACTH release

    • Negative feedback

    • In all, the HPA axis has a negative feedback cycle

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GAS (General Adaptation Syndrome)

Three-stage reaction to stress

  • Include alarm, adaptation (resistance), and exhaustion stages

  • Proposed by Hans Selye

    • Considered the founder of modern stress research

    • Believed that exhaustion phase was due to termination of the stress response but currently it’s believed that the exhaustion stage is the result of prolonged exposure to stress hormones

<p>Three-stage reaction to stress</p><ul><li><p>Include alarm, adaptation (resistance), and exhaustion stages</p></li><li><p>Proposed by Hans Selye</p><ul><li><p>Considered the founder of modern stress research</p></li><li><p>Believed that exhaustion phase was due to termination of the stress response but currently it’s believed that the exhaustion stage is the result of prolonged exposure to stress hormones</p></li></ul></li></ul><p></p>
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<p>Fig. 11.8 GAS</p>

Fig. 11.8 GAS

Stage 1) Alarm

  • Decreased resistance to stress

  • Physiological systems may suffer

Stage 2) Resistance

  • Increased resistance to stress due to increased adrenal function

  • Resistance to other stressors decrease

Stage 3) Exhaustion

  • If stress is prolonged, physiological and behavioral coping mechanisms fail

    • Ultimately survival may be compromised

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Adaptive (positive) features of acute stress response

  • Immediate availability of acute stress response

  • An increase in oxygen uptake

  • A decrease in blood flow in areas not needed for movement

  • Inhibition of digestion, growth, immune function, reproductive function, pain perception

  • Enhancement of memory and perception

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<p>Fig. 11.13: Optimal levels of stressors </p>

Fig. 11.13: Optimal levels of stressors

  • Maintain neurogenesis and cognitive function

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Pathological (negative) features of chronic stress

  • Fatigue

  • Myopathy (i.e. muscle disorders)

  • Cardiovascular disease

  • Gastric ulcers (i.e. stomach ulcers)

  • Psychosocial dwarfism

  • Impotence

  • Anovulation

  • Compromised immune function

  • Potentially accelerated neural degeneration during aging

  • Where the dividing lines between efficient and excessive acute stress, and between acute and chronic stress is unclear

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Status and stress

  • In some species, high-ranked individuals display pronounced stress response

  • In others, low-ranked individuals display pronounced stress responses

  • In a social hierarchy, indicators of stress tend to be state dependent rather than trait dependent

    • i.e. the relationship reflects an animal’s current position rather than future position

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<p>Fig. 11.17 Corticosterone concentrations in dominant wild dogs and mongooses</p>

Fig. 11.17 Corticosterone concentrations in dominant wild dogs and mongooses

  • Dominant individuals appear to be more stressed than subordinate individuals in these two species

  • Fig. 11.31: African wild dogs

    • Only the alpha pair of each pack breeds

<ul><li><p>Dominant individuals appear to be more stressed than subordinate individuals in these two species</p></li></ul><ul><li><p>Fig. 11.31: African wild dogs</p><ul><li><p>Only the alpha pair of each pack breeds</p></li></ul></li></ul><p></p>
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Development and Stress

  • Glucocorticoids have O/A effects on brain and behavior

    • E.g. Organizational effect

      • Stressed pregnant rats have offspring with permanently altered brain morphology (i.e. lack of sexual brain dimorphism) and behavior (i.e. failure to ejaculate even with normal levels of testosterone and LH)

  • Stressed human mothers, i.e. with elevated glucocorticoids, had children with reduced birth weights, developmental delays, social deficits, etc.

    • Also observed in rhesus monkeys

  • Post-natal exposure to mild stressors decreased the negative impact in adult rodents

    • Moderate or high stressors had opposite effect.

  • Contact comfort can serve as a powerful buffer against stress in nonhuman primate infants

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<p>Fig. 11.23: Cortisol concentrations increase as a function of time in an orphanage</p>

Fig. 11.23: Cortisol concentrations increase as a function of time in an orphanage

  • Children who spent any time are orphanages had higher cortisol levels than children who stayed with their birth family

  • The longer the children remained institutionalized, the higher their cortisol concentrations were 6 or more years later

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Psychosocial dwarfism

Grouping of disorders of retarded growth caused by neglect and abuse; this syndrome is also termed failure to thrive

  • Characterized by:

    • lack of growth despite adequate nutrition

    • disruption of sleep cycles and GH secretion

    • absence of tissue responsiveness to exogenous GH

      • Distinguishes from hypopituitary dwarfism (treatment with GH restores normal growth

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<p>Fig. 11. 24: Psychosocial dwarfism</p>

Fig. 11. 24: Psychosocial dwarfism

  • Left panel

    • 15.3 years old

    • Height normal for a 9 year old

    • Displayed abnormal GH release, undetectable LH and FSH

  • Middle panel

    • 16 years old

    • Living in foster care

    • Displayed significant GH release

  • Right panel

    • 16.9 years old

    • Grown 27.5 cm

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Reproduction and Stress

  • Stress impairs male sexual behavior (motivation and performance) by suppressing testosterone

    • Glucocorticoids can inhibit GnRH → lower LH and FSH release → lower testosterone release and spermatogenesis

    • Cortisol inhibits testosterone secretion in men by impairing testicular LH receptors

  • Stress impairs female sexual behavior by interrupting timing of neuroendocrine events for ovulation and sexual behavior

    • Can interrupt pregnancy or lactation

  • In sum, when resources are limited, reproduction is put on hold

  • Figure 11.29

    • LH pulses are less frequent in women who are long-distance runners

<ul><li><p>Stress impairs male sexual behavior (motivation and performance) by suppressing testosterone</p><ul><li><p>Glucocorticoids can inhibit GnRH →  lower LH and FSH release → lower testosterone release and spermatogenesis </p></li><li><p><strong>Cortisol inhibits testosterone secretion in men by impairing testicular LH receptors</strong></p></li></ul></li><li><p>Stress impairs female sexual behavior by interrupting timing of neuroendocrine events for ovulation and sexual behavior</p><ul><li><p>Can interrupt pregnancy or lactation</p></li></ul></li><li><p>In sum, when resources are limited, reproduction is put on hold</p></li><li><p>Figure 11.29</p><ul><li><p>LH pulses are less frequent in women who are long-distance runners</p></li></ul></li></ul><p></p>
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Crowding and Stress

  • Rodents confined to a cage and left to breed

    • Population increases quickly and significantly

    • Later, population crashed likely due to enlarged adrenal glands and likely died of excessive glucocorticoid concentrations

  • When caged alone with the same amount of space, rodent did not show the same stress effects

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Psychological Factors

1) Control

  • Fewer stress-related pathologies if conditions can be controlled

2) Predictability

  • Stress that is predictable influences the stress response

  • (See image) Rats that heard warning bells before a shock had decreased lengths of gastric ulcerations

3) Coping

  • Therapies, hobbies, exercise

4) Habituation

  • Learning that a stressor is not as bad as it seems

<p>1) Control</p><ul><li><p>Fewer stress-related pathologies if conditions can be controlled</p></li></ul><p>2) Predictability</p><ul><li><p>Stress that is predictable influences the stress response </p></li><li><p>(See image) Rats that heard warning bells before a shock had decreased lengths of gastric ulcerations</p></li></ul><p>3) Coping</p><ul><li><p>Therapies, hobbies, exercise</p></li></ul><p>4) Habituation</p><ul><li><p>Learning that a stressor is not as bad as it seems</p></li></ul><p></p>