HOMEOSTASIS AND ADAPTIVE RESPONSES TO STRESSORS

Chapter 2

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HOMEOSTASIS AND ALLOSTASIS

• Homeostasis: a state in which all symptoms are in balance at an ideal “set point” despite alterations within the body

• Homeostatic response: mechanistic, predictable series of orchestrated internal events

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HOMEOSTASIS AND ALLOSTASIS (CONT.)

• Allostasis: addresses complexities and variable levels of activity necessary to maintain or re-establish homeostasis

• Carried out by a superordinate set of systems that support homeostasis in light of environmental and lifestyle changes

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STRESS AS A CONCEPT• Stress: physical, chemical, or emotional

factor resulting in tension of body or mind• Or an actual state that tension produces

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GENERAL ADAPTATION SYNDROME AND ALLOSTASIS

General Adaptation Syndrome (GAS) (Selye)

• Alarm reaction: fight-or-flight response due to stressful stimulus• Allostatic state: Refers to the activity of various

systems in attempting to restore homeostasis• Stage of resistance: The activity of the

nervous and endocrine systems in returning the body to homeostasis

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GENERAL ADAPTATION SYNDROME AND ALLOSTASIS (CONT.)

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GENERAL ADAPTATION SYNDROME AND ALLOSTASIS (CONT.)

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• Stage of exhaustion: point where body can no longer return to homeostasis• Allostatic overload: “cost” of body’s organs and

tissues for an excessive or ineffectively regulated allostatic response

General Adaptation Syndrome and Allostasis (Cont.)

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STRESSORS AND RISK FACTORS• Stressors: agents or conditions that can

produce stress and endanger homeostasis• Physical, chemical, emotional, biological, social, or

cultural• Vary in scope, intensity, and duration

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STRESSORS AND RISK FACTORS (CONT.)

• Risk factors: not stressors, but conditions or situations that increase the likelihood of encountering a stressor

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NEUROHORMONAL MEDIATORS OF STRESS AND

ADAPTATION• Catecholamines: norepinephrine and

epinephrine• Play an integral role in allostasis• Sympathico-adrenal system response mediates

the flight-or-fight response• Adrenocortical steroids: cortisol and

aldosterone• Critical to maintenance of homeostasis• May synergize or antagonize effects of

catecholamines

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ENDORPHINS AND ENKEPHALINS AND IMMUNE

CYTOKINES• Endorphins and enkephalins: endogenous

opioids (body’s natural pain relievers)• Raise pain threshold; produce sedation and

euphoria• Immune cytokines (e.g., interleukin-1):

secreted by macrophages during stress response, thus enhancing immune system response

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SEX HORMONES: ESTROGEN, TESTOSTERONE, AND

DEHYDROEPIANDROSTERONE• Affect stress responses, thus influencing

allostasis

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GROWTH HORMONE, PROLACTIN, AND OXYTOCIN

• Growth hormone: can increase during stress to enhance immune function

• Prolactin: similar to structure of growth hormone; role in immune response

• Oxytocin: produced during childbirth and lactation; associated with bonding and social attachment; thought to moderate stress response

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ADAPTATION, COPING, AND ILLNESS

• Individual stress responses: change with time and circumstances

• Effects of stress response: influenced by genetics, culture, prior susceptibilities, preexisting health status, allostatic state, and ability to manage stress

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ADAPTATION, COPING, AND ILLNESS (CONT.)

• Adaptation: biopsychosocial process of change in response to new or altered circumstances, internal or external in origin

• Coping: behavioral adaptive response to a stressor using culturally based coping mechanisms

• Adaptation and coping: terms often used interchangeably

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ADAPTATION, COPING, AND ILLNESS (CONT.)

• Distress: perceived inability to cope with a stressor

• Allostatic overload: inadequate adaptation mechanisms or overwhelming allostatic load; results in inability to maintain homeostasis • Pathophysiologic states result affects all areas of

the body and emotional systems

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ADAPTATION, COPING, AND ILLNESS (CONT.)

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