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Stress
Photo: http://www.lam.mus.ca.us/cats/encyclo/smilodon/
Stress: The Importance of Allostasis
The term came into being in the 1980’s as a newer more appreciative way to view the body’s rapid and efficient methods of dealing with stress.
Allostasis refers to the body’s ability to maintain stability amidst change.
M Lu, N Halfon
Allostasis: Maintain Stability through Change
McEwen BS. Protective and damaging effects of stress mediators. N Eng J Med. 1998;338:171-9.
Allostasis: Wear and Tear
There are, however, situations that ignite stress response in which neither fight nor flight is an option….the response cannot help us toward resolution. Then, deprived of its natural result, the system designed to protect us begins to cause wear and tear illness and vulnerability.
ALLOSTASIS TO ALLOSTATIC LOADFour Scenarios
McEwen B. New England J. Med. 1998
Stress and Biology: Allostatic loading
Unremitting chronic stress, or severe trauma, particularly at windows of vulnerability and opportunity in human development.
Inability to adjust. Not hearing the “all-clear” signal Feedback loops impaired.Practical leadership action: 1. Foster conditions to prevent stress
and severe trauma. 2. Strengthen capacity to deal with stress. 3. Promote healing from stress and trauma.
What we often mean by “stress” is being “stressed out”!
Feeling overwhelmed, out of control, exhausted, anxious, frustrated, angry
What happens to us?
Sleep deprivation
Eating too much of wrong things, alcohol excess, smoking, etc.
Neglecting regular, moderate exercise
All of these contribute to allostatic load Psychosocial stress is a major factor
Levels of stressful experiences:Their causes, consequences and why we experience them!
HPA Axis Hypothalamic-pituitary-adrenal axis
Initiated in the hypothalamus gland, it is the cornerstone of allostasis. Impaired HPA axis function from toxic stress leads to chronic high levels of cortisol. Prolonged high levels of cortisol suppress immune function, increase inflammation, and may lead to LBW,preterm birth, diabetes, c-v disease, etc. Toxic stress may thus result in a hyper-reactive, dysregulated HPA axis.
Two possible mechanisms: Cumulative “wear and tear” (weathering) throughout the life cycle and fetal or childhood programming.
Social environment and healthCentral Role of the Brain
McEwen B. New England J. Med. 1998
Behavioral responses (“lifestyle”) as well as stressful experiences
MacArthur Foundation Research Network on Socioeconomic Status and Health
Prenatal Programming of the Hypothalamic-Pituitary-Adrenal Axis
Welberg LAM, Seckl JR. Prenatal stress, glucocorticoids and the programming of the brain.J Neuroendocrinol 2001;13:113-28.
CRHAVP
ACTH
Cortisol
STRESS
Acute - enhances immune,Memory, energy replenishment,Cardiovascular function
Chronic - suppresses immune,Memory, promotes boneMineral loss, muscle wasting;Metabolic syndrome
Many targets for cortisol
Stress, allostasis and allostatic load
Mediators of stress and adaptationNETWORK OF ALLOSTASIS
CNS function
Cardiovascularfunction
Metabolism
Immune function
Dysregulation by Biphasic and non-linear
-unhealthy lifestyle, poor sleep, toxic chemicals -feed into network of allostasis (eg elevated inflammation, cortisol)
Positive Stress vs. Toxic Stress Positive Stress
Increased cardiac output
Increased available glucose
Enhanced immune functions
Growth of neurons in hippocampus & prefrontal cortex
Toxic Stress
Hypertension & cardiovascular diseases
Glucose intolerance & insulin resistance
Infection & inflammation
Atrophy & death of neurons in hippocampus & prefrontal cortex