INTRODUCTION:
Stress
is any uncomfortable “emotional experience accompanied by predictable
biochemical, physiological and behavioural changes” (Baum,
1990). In 1974 Hans Seyle defined stress as ‘‘the
non-specific response of the body to any demand imposed upon it” (Selye,
1974). This definition of stress
was later modified in 1992 by Chrousos and Gold and the term ‘‘non-specific”
replaced by the hypothesis that above a threshold intensity any stressor would elicit
the ‘‘stress syndrome” (Chrousos and Gold, 1992).
Stress is a complicated
physiological mechanism that occurs when there is a real or perceived threat to
homeostasis. While it is generally accepted that these processes are adaptive,
designed to re-establish homeostasis and allow coping, it is also apparent that
inadequate or excessive or prolonged activation of stress systems can disturb
normal physiological and behavioural function. This can result in a range of
adverse consequences such as depression, impaired cognition, cardiovascular disease,
impaired immune function with increased vulnerability to disease, impaired
growth and reproductive function, osteoporosis, diabetes, dementia and reduced
life expectancy (Charmandari
et al., 2005; Tilbrook et al., 2002; Turner 2005).
DEFINITION:
A widely accepted definition
of stress has been provided
by McEwen: ‘‘Stress may be defined
as a real or interpreted threat to the
physiological or psychological integrity of an
individual that results in physiological and/or
behavioural responses’’. Stress can affect people of all ages, genders,
circumstances and can lead to both physical and psychological health issues (McEwen,
2000).
The stress response is subserved by a
complex neuroendocrine, cellular and molecular infrastructure and the stress
system is located in both the central and peripheral nervous system. The
adaptive response of an individual to stress is determined by a multiplicity of
genetic, environmental and developmental factors. Alterations of the ability to
respond to stressors may lead to disease.
Some stress can be beneficial at times,
producing a boost that provides the drive and energy to help people get through
situations like exams or work deadlines. However, an extreme amount of stress
can have health consequences and adversely affect the immune, cardiovascular,
neuroendocrine and central nervous systems (Anderson, 1998).
In addition, an extreme amount of stress
can take a severe emotional toll. While people can overcome minor episodes of
stress by tapping into their body’s natural defences to adapt to changing
situations, excessive chronic stress, which is constant and persists over an
extended period of time, can be psychologically and physically debilitating. Unlike
everyday stressors, which can be managed with healthy stress management behaviours,
untreated chronic stress can result in serious health conditions including
anxiety, insomnia, muscle pain, high blood pressure and a weakened immune system
(Baum and Polsusnzy, 1999).
Research shows that stress can
contribute to the development of major illnesses, such as heart disease, depression
and obesity. People who suffer from depression and anxiety are at a heightened
risk for heart disease, with depression leading to a two-fold increased risk
and anxiety a doubling of increased risk (Anderson and Anderson, 2003).
TYPES OF STRESS
RESPONSE:
Stress responses include
activation of a variety of hormone and neurochemical systems throughout the
body. Two hormonal systems have received extensive attention in this regard:
(1) The sympathetic-adrenomedullary (SAM) system, which produces adrenaline in the central part of the adrenal
gland, and
(2) The hypothalamic-pituitary-adrenocortical (HPA) system, which produces cortisol in the outer shell of the adrenal gland (Sapolsky
et al., 2000).
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