332 ESCH AND HAZEN 



Traditional Perspective 



Historically the word stress has been used by biomedical 

 scientists to describe a somewhat vague array of physiological, 

 morphological, and biochemical responses by an individual organism 

 to an even more vague and less defined group of etiologies. Thus 

 there is more certainty about how an individual organism manifests 

 stress than there is about what causes the response to occur. 



Selye (1950) described the response of an individual organism to 

 stressor input as a succession of physiological and biochemical 

 reactions to which he collectively referred as the general adaptation 

 syndrome (or GAS). Selye separated the GAS into three parts, the 

 alarm stage, the resistance stage, and the exhaustion stage. 



The alarm stage begins with stressor input, which promotes the 

 release of epinephrine into the blood vascular system from the 

 adrenal glands and increases the activity of the sympathetic portion 

 of the autonomic nervous system (Fig. 1). The combined action of 

 epinephrine and the autonomic nervous system then produces a wide 

 range of physiological and biochemical changes in the respondent 



STRESSOR 



RECEPTOR 



NERVOUS °SYSTEM ADRENAL MEDULLA 



RESPONSE RESPONSE 



PHYSIOLOGICAL, BIOCHEMICAL, 

 AND MORPHOLOGICAL CHANGES 



INCREASE IN LEVELS OF CIRCULATING 

 BLOOD GLUCOSE 



DILATION OF PUPILS OF THE EYE 



STIMULATION IN FREQUENCY, FORCE, 

 AND AMPLITUDE OF HEART CONTRACTIONS 



INCREASE IN VASCULAR FLOW TO 

 SKELETAL MUSCLES 



DECREASE IN BLOOD-CLOTTING TIME 



EFFECT ON PIGMENT CELLS, e.g., 

 AMONG TELEOST FISHES 



Fig. 1 Alarm stage of the general adaptation syndrome. 



