C h a p t e r 9
Stress and Adaptation
215
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.
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.
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
