Principles of Exposure to Stressful Environments*

The contributions of Bernard, Cannon, Selye, and others have been insightfully reviewed by many authors. Their publications provide a fresh perspective on several principles that are essential to a thorough understanding of the remaining chapters. For a more complete discussion, consult the suggested readings listed on page 323. Here are the basic principles you’ll need to understand now:

1. Human cells, organs, and body systems are highly organized and are capable of undergoing change.
   
2. Each of earth’s extreme environments requires a unique set of adaptive responses. But interestingly, adequate acclimitazation to virtually all of earth’s stressful environments requires about 8-14 days of exposure, and the loss of acclimatization to these stressors (e.g., heat, cold, high altitude) occurs in about 14-28 days.
   
3. Humans may lack or have insufficient hereditary abilities to adapt to all of earth’s stressful environments.
   
4. Stressful experiences result in personal growth, temporary perturbations, or permanent/deleterious effects. People vary in their capacity to respond to challenges, danger, and threats (see figure 1.1). The outcomes of stressful experiences are determined most by the factors listed in table 1.3 (page 6).
   
5. Different individuals respond to the same stressor with different outcomes. Their bodies may show no strain, illness, or injury, depending on the level of tolerance developed, immune system competence, age, level of physical fitness, and the number/intensity/type of previous exposure to this stressor.
   
6. Stressors may have positive effects that allow an individual to meet physical or psychosocial demands successfully. Among such effects are increased physical stamina and more effective coping styles.
   
7. Physical stressors (e.g., cold or heat exposure, sleep deprivation, prolonged or intense exercise) are strongly mediated by psychological factors. If these stressors are not viewed as noxious or alarming, they produce smaller or even opposite physiological responses.
   
8. Physiological responses at times can be excessive, inappropriate, inadequate, or disordered. These states are exemplified by chronic inflammatory diseases (e.g., rheumatoid arthritis), inappropriate AVP syndrome during water overconsumption (AVP also is known as ADH; it is a hormone that causes your kidneys to retain water), old age, and ventricular fibrillation, respectively.
   
9. If humans are able to prevent, avoid, control, or respond to a stressor, they usually will not become ill or injured.
   
10. Psychological strategies (e.g., coping maneuvers) may alter the amount of strain experienced by the individual when exposed to a stressful environment. This occurs because worry, fear, or panic result in strain that exceeds that from a stressful environment alone. These strategies include self-reassurance, self-deception, prayer, and seeking help from others.
    
11. Mediators are biological, social, and psychological modifiers that act on stressors to alter the level of physiological strain experienced. A genetic deficit in a metabolic enzyme (biological), peer/parental expectations (social), and personality characteristics (psychological) are examples of mediators.
    
12. Finally, physiological and behavioral changes sometimes occur before a stressor is encountered, in anticipation of and in preparation for challenges, threats, and dangers. For example, athletes experience preevent jitters because the activity of the sympathetic nervous and the endocrine systems prepare the muscular and circulatory systems for competition. Even metabolism is enhanced in anticipation of a contest, as energy-rich compounds are transported to muscles. These interactions of the nervous and endocrine systems are explained in detail below.

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