Summary: Chapter 11 - Stress

Read the summary and the most important questions on Chapter 11 - Stress

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• What is a stress response and which endocrine systems are involved?

  • A suite of physiological and behavioral responses that help to reestablish homeostasis. It is non-specific, many different stressors can elicit a stress response.
    
  • Endocrine systems that are involved are epinephrine (adrenaline) from the adrenal medulla and glucocorticoids from the adrenal cortex. 

• What hormones are secreted after a stressor and how is this response called?

  • Within seconds, norepinephrine is secreted, and then epinephrine.
  • A few minutes later, glucocorticoids, CRH and ACTH are secreted.

  
  
  Response is called fight-or-flight because the physiological changes in the cardiovascular and respiratory system can support both behavioral responses.

• What axis is activated after a stressor and what is the effect of the rise in hormones?

  The hypothalamus-pituitary-adrenal (HPA) axis is involved. 
  
  
  Effect of (nor)epinephrine rise:
  

  1. Sympathetic nervous system activity increased
     
  2. Oxygen delivery to tissue increased
     
  3. Glucose metabolism increased
  4. Heart output increased
     
  5. Blood pressure and flow increased

  
  Effect of CRH, ACTH and glucocorticoids:
  

  1. Release of glucose, protein and fat metabolism increased
  2. Blood flow increased
  3. Behavioral responsiveness increased
  4. Local effects on the brain

    

• Why are glucocorticoids good in mediating behevioral effects of stress?

  1. They are released in response to numerous stressors
  2. They can easily diffuse past the blood-brain barrier
  3. They have receptors in several brain regions

• What is the general adaptation syndrome (GAS) and of what 3 stages does it consist?

  The process of coping with stressors.
  

  1. The alarm reaction
  2. Resistance to the stressor
  3. Exhaustion 
     

• What is the definition of stress according to Kim and Diamond?

  1. Stress is a condition in which individuals are aroused by aversive stimuli.
  2. Because arousal can increase under both aversive and pleasurable conditions, for something to be stressful, the individual must perceive it as aversive.  
  3. The element of control in an aversive situation, as well as the element of predictability, significantly improves the long-term negative effects of the stressful experience. 

• Explain allostasis and allostatic load.

  • Allostasis is achieving homeostasis or stability through physiological or behavioral change and can be carried out via alteration in HPA axis hormones, the autonomic nervous system, cytokines, or a number of other systems. 
    
  • Allostatic load is the 'cost' made by the body during allostasis. 

• What are the 4 stages over which hormones and other mediators respond to disturbances in homeostasis?

  1. Predictive homeostasis is the response range that contains daily and seasonal variation.
  2. Reactive homeostasis is the range of mediator fluctuations necessary to respons to threats.
  3. Homeostatic overload represents values above the reactive homeostasis range.
  4. Homeostatic failure represents mediator values below the predictive homeostasis range. 

• What are the adaptive stress effects and by what hormone are they caused?

  1. Increased immediate availability of energy. Glucagon
     
  2. Increased oxygen intake. Catecholamines
     
  3. Decreased blood flow to organ systems not necessary for movement. Epinephrine
     
  4. Supplementation of energy reserves. Glucocorticoids
  5. Inhibition of energerically expensive processes that are unrelated to immediate survival (e.g. digestion, growth, reproduction). Prolactin
  6. Decreased pain perception. Endorphin
  7. Suppression of feeding behavior. 
  8. Enhancement of sensory function and memory.

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• How is CRH involved in the stress response and what other things does CRH affect?

  • CRH in the hypothalamus is mainly involved in regulation of the HPA axis.
  • CRH in the amygdala is involved in mediating anxiety responses.
  • In mice, CRH receptor antagonists decrease anxiety that is normally associated with alcohol withdrawal and social defeat.
  • High CRH levels also affect spatial learning and memory.