(ii)Hypothalamic-pituitary-adrenocortical (HPA) activation: In addition to the above
sympathetic activation, stress also triggers changes in the HPA system. This results
in the production of increased levels of corticosteroids the most important of which is
cortisol which results in more diffuse changes such as the management of carbo-
hydrate stores and inflammation. These changes constitute the background effect
of stress and cannot be detected by the individual. They are similar to the alarm,
resistance and exhaustion stages of stress described by Seyle (1956). In addition,
raised levels of the brain opiods beta endorphin and enkaphalin have been found
following stress which are involved in immune-related problems.The physiological aspects of the stress response are linked to stress reactivity, stress
recovery, the allostatic load and stress resistance.Stress reactivity
Changes in physiology are known as ‘stress reactivity’ and vary enormously between
people. For example, some individuals respond to stressful events with high levels of
sweating, raised blood pressure and heart rate whilst others show only a minimal
response. This, in part, is due to whether the stressor is appraised as stressful (primary
appraisal) and how the individual appraises their own coping resources (secondary
appraisal). However, research also shows that some people are simply more reactive to
stress than others, regardless of appraisal. Two people may show similar psychological
reactions to stress but different physiological reactions. In particular, there is some
evidence for gender differences in stress reactivity with men responding more strenu-
ously to stressors than women and women showing smaller increases in blood pressure
during stressful tasks than men (Stoney et al. 1987, 1990). This indicates that gender
may determine the stress response to a stressful event and consequently the effect of thisFig. 10-3 Stress and changes in physiology242 HEALTH PSYCHOLOGY