Gulf War and Health Volume 6: Physiologic, Psychologic, and Psychosocial Effects of Deployment-Related Stress (2008) / Chapter Skim
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4 THE STRESS RESPONSE
4 THE STRESS RESPONSE
Pages 49-74
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From page 49... ...
It describes the stress response, including its basic biology and physiology, and its modifiers. The chapter also surveys some of the potential adverse consequences of the stress response that can occur in organ systems after exposure to chronic stressors.
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From page 50... ...
• Blunting of pain • Altered intestinal motility Later Phases of the Stress Response (Duration: Days to Weeks) • Enhanced immune system • Suppression of appetite and digestion • Suppression of growth • Suppression of reproduction • Persistence of increased heart rate and blood pressure in some cases • Persistence of increased cortisol in some cases • Release of stress hormones When a stressor is eliminated, the stress response may shut off quite slowly or not at all (McEwen and Lasley 2002)
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From page 51... ...
and mobilizes energy to respond to stressors. The parasympathetic nervous system does the opposite, preserving energy, putting a brake on the heart rate, increasing intestinal activity, relaxing muscles in the gastrointestinal system, and decreasing inflammation.
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From page 52... ...
The surge of epinephrine floods the brain and peripheral tissues, thereby producing the full-fledged fight or flight response: faster heartbeat, greater energy, more blood flow to skeletal and cardiac muscle, dilation of the pupils and airways, and higher blood glucose concentration and so on. With chronic stress, however, the sympathetic nervous system may 1 Catecholamines are a class of hormones and neurotransmitters that includes epinephrine and dopamine.
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From page 53... ...
For fearful memories, the hippocampus works with the amygdala and the prefrontal cortex of the brain. The prefrontal cortex modulates the actions of the amygdala, usually through inhibition, and thus can control cortisol secretion and activation of the parasympathetic and sympathetic nervous systems (Radley et al.
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From page 54... ...
In response to chronic stress, a long-term increase of glucocorticoids, such as cortisol, can dysregulate and suppress immune function, as discussed later. Allostasis The classic fight or flight response entails activation of epinephrine and cortisol with resulting increases in immune function, energy mobilization (in the form of glucose)
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From page 55... ...
Chronically Increased Heart Dysregulated Stress Response Rate, Blood Pressure, Insulin, Inflammatory Cytokines, Hyperlipidemia Adverse Health Outcomes Hypertension, Diabetes, Obesity, Coronary Heart Disease, Depression, Gastrointestinal Disorders, Fatigue, Pain FIGURE 4-2 How chronic stress can affect behavior and health. All people have some pre-existing load of stressful experiences reflected in brain and body.
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From page 56... ...
. The other two are related to chronic stressor characteristics: repeated exposure (D in the figure)
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From page 57... ...
and lack of adaptation to similar stressors (E) can lead to toxic stress and a chronic stress burden.
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From page 58... ...
and result in greater inhibition of the HPA axis after a stressful event, which in turn would lead to a less reactive HPA axis, lower cortisol concentrations, and more rapid initiation of the stress response. But the lower density of receptors in the heavily stressed offspring would be expected to reduce negative feedback and lead to greater reactivity of the HPA axis, higher cortisol concentrations, and more prolonged stress response.
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From page 59... ...
Animal studies illustrate the potential role of perception of control in the stress-response process. CHRONIC STRESS AND HEALTH Activation of the stress response ensures survival in the short term, but is maladaptive when its activation persists as a result of chronic, severe, or repeated stress.
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Memory and Cognition Memory and cognition have been studied extensively in three regions of the brain: the hippocampus, the prefrontal cortex, and the amygdala. The hippocampus, the center of explicit memory, appears be especially vulnerable to chronic stress.
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From page 61... ...
Most nerve projections from the locus coeruleus are excitatory in function and activate, for example, the sympathetic nervous system, amygdala, and HPA axis. However, some of the projections are inhibitory and act on the prefrontal cortex and the parasympathetic nervous system, the systems that normally keep the sympathetic nervous system in check.
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From page 62... ...
Greater understanding of cytokine signaling has laid the groundwork for studying the effects of chronic stress. Acute stress enhances the immune system to fight infections and to promote wound healing (Dhabhar and McEwen 1999; Viswanathan and Dhabhar 2005)
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From page 63... ...
Chronic stress induces cardiovascular abnormalities that appear to be the result of chronic inflammation; chronic inflammation might cause or contribute to early pathologic abnormalities that might progress to disease or disability. The early pathologic changes include abnormalities in heart rate and blood pressure, vascular inflammation, and atherosclerosis.
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From page 64... ...
. That hypothesis draws from evidence that during the acute stress response, cortisol, catecholamines, angiotensin, and other stress hormones induce the liver and abdominal fat tissue to release proinflammatory cytokines and other inflammatory mediators.
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From page 65... ...
As discussed earlier, CRH secretion and the HPA axis can also regulate inflammation, including that of the bowel mucosa. In IBS, however, the normal regulatory mechanisms of the brain-gut axis are dysfunctional, and there is impaired regulation of visceral pain (Naliboff et al.
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From page 66... ...
War-zone stressors might produce disruption in brain systems that mediate responses to stress and in central pain regulatory pathways that can result in greater reporting of physical and emotional symptoms. The continuation of altered physiologic states over months and years can contribute to the accumulation of a chronic stress burden that has adverse long-term health consequences.
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From page 67... ...
2005. Co-occurring mental and substance use disorders: The neurobiological effects of chronic stress.
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2000. Acute stress enhances while chronic stress suppresses skin immunity.
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2000. Chronic stress modulates the immune response to a pneumococcal pneumonia vaccine.
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2003. Chronic stress and age-related increases in the proinflammatory cytokine IL-6.
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2004. Medial prefrontal cortical integration of psychological stress in rats.
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2006. Regional differentiation of the medial prefrontal cortex in regulating adaptive responses to acute emotional stress.
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2002. Chronic stress induces mast cell-dependent bacterial adherence and initiates mucosal inflammation in rat intestine.
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From page 74... ...
2002. Chronic stress induces contrasting patterns of dendritic remodeling in hippocampal and amygdaloid neurons.
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