Lecture 2: What is stress? Flashcards
What is allostasis and how does it work?
It is the ability to achieve stability through change. The autonomic nervous system, the HPA axis, the cardiovascular, metabolic and immune systems respond to stressors to protect the body. Over time this leads to allostatic load which is wear and tear from chronic overactivity/underactivity of allostatic systems
What are different types of stressful experiences?
Major life events, trauma, abuse, workplace issues, home issues, neighborhood issues. Acute stress can include major life events and chronic stress is the cumulative load of minor day-to-day stresses. Can be exacerbated by environmental factors like diet and smoking
What is the link between stress and diabetes?
Exposure to repeated stress increased the incidence of diabetes in rats. Family instability increases incidence and severity of insulin-dependent diabetes. Chronic stress has been linked to insulin resistance-> non-insulin dependent diabetes. Deposition of abdominal fat is a risk factor for CHD and diabetes
Which factors determine responses to stressful situations?
- the way a person perceives a situation which includes the ability to adjust or habituate to repeated stress
- general state of physical health which can include a physiological response to stress and physical/psychological response which determines behaviour
What is the function of allostatic systems?
- they have broader ranges than homeostatic systems
- they enable us to respond to physical states
- to cope with noise, crowding, isolation, hunger, temp extremes, danger and infection
How does allostasis influence the sympathetic nervous system and the HPA axis?
- Activation releases catecholamines from ANS and glucocorticoids from adrenal cortex
- Adrenal medulla leads to the secretion of corticotropin from the pituitary
- Corticotropin results in the release of cortisol from the adrenal cortex
- The inactivates to return systems to baseline levels of cortisol and catecholamine
- If inactivation is dysfunctional, there is overexposure to stress hormones
What are the 4 situations linked to allostatic load?
- frequent stress can increase blood pressure resulting in a heart attack
- no adaptation to repeated stressors-> prolonged exposure to stress hormones
- inability to shut off allostatic responses when stress stops which can lead to a sustained increase in blood pressure (atherosclerosis)
- the lack of response in some allostatic systems can result in compensatory reactions in others, like the cytokines can increase due to lack of cortisol secretion
How can stress impact activity over time?
- age-related decline in animals and can result in signs of accelerated aging also through hippocampus unable to turn off the release of amino acids
- can cause wearing of systems-> gluco-corticoid cascade hypothesis is that wear and tear of this can lead to dysregulation of HPA axis and cognitive impairment
What have findings found about rats living in the visible-burrow system?
- stress-induced state of HPA hyporesponsiveness
- low concentrations of corticotropin releasing hormone messenger RNA in hypothalamus
What else can influence allostatic load?
- feelings of anticipation and worry as involves reflex which prevents blacking out and part of worry, anxiety etc. Can drive secretion of corticotropin, cortisol and norepinephrine
- intrusive memories of a traumatic event-> physiological responses
- smoking, alcohol, dietary choices and amount of exercise
Allostatic load in cardiovascular and metabolic systems
Those with higher levels of physical and mental functioning had low allostatic scores and lower incidence of CVD, hypertension and diabetes.
Allostatic load in the brain
- affects hippocampus which has high concentrations of cortisol receptors, glucocorticoids also involved in the context
- can affect access to info to decipher a threat
- hippocampus also involved in stress response inhibiting HPA axis
What is the mechanism for hippocampal dysfunction and memory impairment?
- acute stress increases cortisol secretion which suppresses mechanisms in hippocampus and temporal lobe short-term
- repeated stress can cause atrophy of dendrites in the hippocampus long-term
How does allostasis affect the immune system?
- responses to pathogens/antigens with own form of allostasis which has an acute-phase response and immunologic memory
- acute stress causes lymphocytes and macrophages to be redistributed through the body. These immune cells return to the blood stream if signal stops
- acute stress can exacerbate a pathologic state in the case of delated-type hypersensitivity
What are the implications of allostatic load in human society?
Hypertension found to be a sensitive index of job stress, higher fibrinogen concentrations was found in British civil service men which has been linked CHD. Obesity was also a stress-linked changed that was found.
What were the therapeutic implications found?
Important to see the relation between disease and social instability, job loss, dangerous living environments and other stressful conditions. This allostatic load can be reduced by learning coping skills, limitations.
What are the causes of allostatic load?
Isolation and lack of control in the work environment which can be used for interventions to increase social support and enhance coping and enhancing control over job.
How to prevent against Alzheimer’s disease?
Education has a protective role but unclear whether education protects against the disease or provides redundancy in the brain
Sex differences in biology of stress?
Estrogen has a protective effect so at menopause the risk increases to the same level of men. This increases HPA axis activity and linked to cognitive decline. Androgen decline can also affect HPA function but to a lesser extent.
Why do humans have more of an allostatic risk?
Large individual differences in how they respond to stress due to life experiences, personality etc.
What are the mechanisms behind immune responses to acute stress?
- redistribution of immune cells which acute stress enhances while chronic stress delays type-hypersensitivity
What does Cannon argue the function of the stress response is?
To restore homeostasis
How was the theory refuted?
The body shows anticipatory reactions during stress as during stress blood pressure increases, not restoring homeostasis.
The body has multiple set-points
Health is characterized by flexible adaptation which is allostasis
What do primary outcomes like stress hormones and secondary outcomes like metabolic perturbations lead to?
- aberrant responses
- Impaired health
