Porth's Essentials of Pathophysiology, 4e

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Stress and Adaptation

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health status and serves as a buffer or modifier of the physical and psychosocial effects of stress. 47 Social networks contribute in a number of ways to a person’s psychosocial and physical integrity. 20 The configuration of significant others that constitutes this network functions to mobilize resources of the person; these friends, colleagues, and family members share the person’s tasks and provide monetary support, materials, and tools, as well as guidance in improving long-term problem-solving capabilities.

Disorders of the Stress Response

Stressors can assume a number of patterns in relation to time. They may be classified as acute time limited, chronic intermittent, or chronic sustained. An acute time-limited stressor is one that occurs over a short amount of time and does not recur; a chronic inter- mittent stressor is one to which a person is chronically exposed. The frequency or chronicity of circumstances to which the body is asked to respond often determines the availability and efficiency of the stress responses. The response of the immune system, for example, is more rapid and efficient on second exposure to a pathogen than it is on first exposure, but chronic expo- sure to a stressor can fatigue the system and impair its effectiveness. Effects of Acute Stress Generally, the stress response is meant to be acute and time limited. The time-limited nature of the process renders the accompanying catabolic and immunosup- pressive effects advantageous. Reactions to acute stress are those associated with the ANS, the fight-or-flight response. Centrally, there is facilitation of neural path- ways mediating arousal, alertness, vigilance, cognition, and focused attention, as well as appropriate aggres- sion. For persons with limited coping abilities, either because of physical or mental illness, the acute stress response may be detrimental. For example, persons with preexisting heart disease who are faced with over- whelming sympathetic behaviors associated with the stress response may experience arrhythmias. In healthy individuals, the acute stress response may be detrimen- tal as well, as it can redirect attention away from behav- iors that promote health, such as attention to proper meals and getting adequate sleep. For persons with health problems, the stress response may result in inter- ruption of compliance with medication regimens and exercise programs. The acute physiologic stress associated with severe trauma, infection, and surgery can be extensive. Survival of such insults depends to a great extent upon the neuroendocrine component of the stress response, with activation of the HPA axis being one of the most important components of the response. 48–50 Cortisol, the primary glucocorticoid secreted by the adrenal cortex in response to activation of the HPA, has an important role in many of the physiologic functions during trauma and critical illness. The actions of cortisol include anti- inflammatory effects, as well as effects on blood glucose, vascular tone, endothelial integrity, and modulation of angiotensinogen synthesis. Of recent concern has been the dramatic increase in blood glucose levels that occur during the acute stress response to critical injury and illness. 49,51,52 The causes of stress-induced hyperglycemia include enhanced release of glucose from glycogen stores, increased

SUMMARY CONCEPTS

■■ Physiologic and psychological adaptation involves the ability to maintain constancy of the internal environment (homeostasis) and behavior in the face of a wide range of changes in the internal and external environments. It involves negative feedback control systems that regulate cellular function, control life’s processes, regulate behavior, and integrate functions of different body systems. ■■ The stress response involves activation of several physiologic systems: the sympathetic nervous system (SNS), hypothalamic pituitary adrenal (HPA) axis, and immune system that work in a coordinated fashion to protect the body against damage from intense demands made upon it. ■■ Selye, who referred to the stress response as the general adaptation syndrome, divided it into three stages: the alarm stage, with activation of the SNS and the HPA axis; the resistance stage, during which the body selects the most effective defenses; and the exhaustion stage, during which physiologic resources are depleted and signs of systemic damage appear. ■■ Activation and control of the stress response are mediated by combined efforts of the nervous and endocrine systems.The neuroendocrine systems integrate signals received from neurosensory pathways and circulating mediators that are carried in the bloodstream. In addition, the immune system both affects and is affected by the stress response. ■■ Adaptation implies that an individual has successfully created a new balance between the stressor and his or her ability to deal with it. Adaptation is affected by a number of factors, including experience and previous learning, the rapidity with which the need to adapt occurs, genetic endowment, age, health status, nutrition, sleep–wake cycles, hardiness, and psychosocial factors.