Module 1
Chapter 2: Homeostasis, Allostasis, and Adaptive Responses to Stressors
Homeostasis & Allostasis
Homeostasis:
❖ Remaining stable while staying the same
❖ A state in which all systems are in balance
❖ A
...
Module 1
Chapter 2: Homeostasis, Allostasis, and Adaptive Responses to Stressors
Homeostasis & Allostasis
Homeostasis:
❖ Remaining stable while staying the same
❖ A state in which all systems are in balance
❖ A state of equilibrium
❖ An ideal “set point” despite alterations within the body
Allostasis:
❖ Ability to successfully adapt to challenges
❖ Intricate regulatory processes orchestrated by the brain
❖ A dynamic process that maintains or re-establishes homeostasis in light of environmental and lifestyle changes
Stress As A Concept
❖ Physical, chemical, or emotional factor resulting in tension of body or mind
❖ Actual physical and mental state that tension produces
❖ Real or perceived threat to homeostasis
❖ Direct consciously or indirect unconsciously sensed threat to the stability of the organism
❖ Physical, chemical, or emotional factor resulting in tension of body or mind
❖ Actual physical and mental state that tension produces
❖ Real or perceived threat to homeostasis
❖ Direct consciously or indirect unconsciously sensed threat to the stability of the organism
General Adaptation Syndrome (GAS) (Selye)
❖ Three stages: Alarm, resistance/adaption, and exhaustion
➢ Alarm stage: fight-or-flight response as the result of stressful stimulus
▪ Hypothalamic-pituitary-adrenal (HPA) axis
➢ Resistance/adaptation: activity of the nervous and endocrine systems in returning the body to homeostasis
▪ Allostatic state: activity of various systems attempting to restore homeostasis
➢ 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; effect of “wear and tear” on the body
❖ Stressors
➢ Agents or conditions that can produce stress; endanger homeostasis
▪ May be external or internal
• External examples: school, work, life event (wedding)
• Internal examples: cancer, child birth/pregnancy
▪ Physical, chemical, biological, social, cultural or psychological
• Physical: hand injury
• Social: standing in front of a class
• Cultural: acceptance/ability to practice
▪ Vary in scope, intensity, and duration
▪ Reactions to stress vary depending upon genetic constitution, gender, past experiences, cultural influences, developmental stage, and age
• Past experience: a child afraid of a playground b/c he was previously abused
there
▪ Can include both negatively and positively perceived events
➢ Risk Factors: Not stressors, but conditions or situations that increase the likelihood of encountering a stressor; there is some control over our stressors
❖ Neurohormonal Mediators of Stress & Adaption
➢ Catecholamines
▪ Play an integral role in allostasis
▪ Symphathico-adrenal system response mediates the fight or flight response
▪ Examples: Norepinephrine and epinephrine
➢ Norepinephrine
▪ Constricts blood vessels and raises blood pressure
▪ Reduces gastric secretions
➢ Epinephrine
▪ Enhances myocardial contractibility, increases heart rate, and increases cardiac output
.....................CONTINUED............................
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