6. Stress and health Flashcards
Stress response
A non-specific response of the body to any demand that is placed upon it
(physical or psychological)
What did Selye say about stress?
All stressors evoke the same core physiological responses
- Mobilise the body for action
- sympathetic effects
- Mobilise energy resources
What are the 2 faces of stress responses?
Short term – adaptive
Longer term – maladaptive
What does psychological stress lead to?
Poor health outcomes
What is Selye’s original model of stress responses?
Initial response to stress (alarm reaction) → Adaptation stage (short term response to temporary stress) → if stress continues (chronic stress) → exhaustion phase
What are the implications of chronic stress?
Chronic stress & associated physiological changes (e.g. enlarged adrenal glands) are implicated in ill health
Acute stress
Adaptive processes; necessary to maintain homeostasis and adapt to environment
Chronic stress
Allostatic load
Negative effect on physical and mental health
Depletes energy reserves, comprises immune system
Allostatic load
Results from excessive stress or failure to achieve homeostasis, as a result of repeated stress from multiple stressors, poor adaptation and prolonged or inadequate responses to stress (McEwen, 2007)
What is the two-system view of stress and health?
Anterior-pituitary-adrenal-cortex system
sympathetic nervous system
What is the Anterior-pituitary-adrenal-cortex system of stress?
Stress → brain → anterior pituitary gland releases ACTH → adrenal cortex releases glucocorticoids (e.g. cortisol) → stimulates the effect of stress response
How is the sympathetic nervous system affected by stress?
Adrenal medulla → increases the release of adrenalin & noradrenalin
What is involved in the autonomic nervous system?
Sympathetic and parasympathetic responses
Sympathetic nervous system
- fight or flight
- enhanced heart rate, BP, RR, blood to muscles, dilate pupils, mobilised energy stores
- Adrenaline & noradrenaline (from adrenal medulla)
Parasympathetic nervous system
- decreased functions of heart rate, blood pressure
- insufficient evidence that individual emotions are characterised by different patterns of physiological response (but not al the same either)
In Selye’s original model – How do we measure stress?
The most commonly employed physiological measure of stress is the level of circulating glucocorticoids.
What is the developmental programming of the HPA axis?
Early stressful and nurturing environments – robust effects on the developing brain
The first few weeks of life represent a critical period – the HPA axis programing in rodents
As adults, offspring of “High quality maternal care” show less fearful behaviour and reduced HPA response to stress compared to offspring received “low quality maternal care”
(Liu et al., 1997; Caldji et al., 1998)
Neonatal handling vs. maternal separation experiment:
What is the handling procedure and what does it result in?
Neonatal pups received 15 minutes handling daily during postnatal days 2-14
Handling results in pups receiving increased maternal care (licking & grooming behaviour)
Thus, high maternal care (handling) lead to less stress and decreased HPA activity
Neonatal handling vs. maternal separation experiment:
What is the effect of maternal separation?
When there has maternal separation, neonatal pups are separated from the mother for prolonged period of time (several hours)
Maternal separation results in pups receiving less maternal care .
Thus, low maternal care (maternal separation) results in enhance stress and increased HPA activity
What was examined in the Romanian orphanage study?
The time of change in environment is important.
What did the Romanian orphanage study find?
Parenting affected the development of children
Children adopted before the age of 2 had better health outcomes
Early environment is important for growth and development
Seems to be a critical/golden window of opportunity during which intervention/change in environment has positive outcomes on future health of children
What was the twin murder mystery?
DNA was found on the scene of a murder
When matched to the database it revealed 2 people whom it belonged to – twins
There were no fingerprints on the scene
None of the twins could be prosecuted based on the DNA evidence initially
Recently, via a scientific breakthrough, the evidence pointed clearly towards one of the twins – HOW?
Well, through epigenetics, one of the twin was a smoker and the epigenetic analysis revealed that the DNA belonged clearly to a smoker.
What is the yin and yang of disease?
Gene x Environment interactions
i.e. epigenetics
What is the process of measuring the influence of the environment on the genome?
DNA methylation arrays (epigenetics) (DNA) → Gene-expression (RNA) → Protein → disease
What are the factors contributing the epigenetics?
Diet diurnal/seasonal correlations Disease exposure Toxic chemicals Drugs of abuse Socioeconomic status Exercise Microbiome Therapeutic drugs Alternative medicine Social interactions Psychological state
What can stress influence in relation to our genetics?
Stress can influence gene expression via the process of epigenetics
What did Meaney et al. identify with relation to epigenetic mechanisms?
Identified the molecular mechanisms underlying the long lasting effects of maternal care on stress responses. This involved DNA methylation.
What is the relationship between DNA methylation and maternal care?
Epigenetic mechanisms that influence gene expression
What is the relationship between DNA methylation and maternal care?
Increased maternal care leads to decreased methylation of a promoter site and increased hippocampal GR expression; and vice versa
How do epigenetics contribute to PTSD?
Epigenetic changes are a hallmark of stress-related disorders such as PTSD and allows us to measure the influence of stressors on our genome.
What is Mehta D et al., (2013) study on epigenetics in PTSD on African-Americans?
Looked at epigenetic changes among trauma-exposed African Americans in Atlanta.
What is Mehta D et al., (2017) study on epigenetics in PTSD on Australian Vietnam combat veterans?
Recent study in Australian Vietnam combat veterans showed many genes had epigenetic differences among veterans with versus veterans without PTSD
What is the relationship between stress and the hippocampus?
The hippocampus is highly susceptible to the effects of stress.
Why is the hippocampus so susceptible to stress?
Stress reduces dendritic branching, reduces adult neurogenesis, modifies synaptic structures, disrupts performance in tasks that rely on hippocampal function (e.g. memory).
Hippocampus contains high density of glucocorticoid receptors
Psychosomatic disorders
Psychosomatic disorders are disorders whose symptoms are primarily physical but whose development is greatly influenced by psychological factors
What is the relationship between stress and health?
Stressed individuals are more likely than unstressed individuals to report being ill. This is because they expect to be more ill; illness while stressed is more uncomfortable; and stress contributed to the cause of the illness
Gastric ulcers
Erosion of stomach lining and duodenum.
How are stress and gastric ulcers related?
Gastric ulcers were long believed to be psychosomatic. Additionally, they are almost always related to the bacterium, Helicobacter plori, or NSAIDS (e.g. aspirin). However, H.Pylori alone does not imply ulcers. Both antibiotic treatment and psychological treatments are helpful.
Psychoneuroimmunology
Began in the 1980s.
Investigates the links between: psychology, neurobiology and immunology
Immune system
System that protects the body against intruders. It requires the ability to distinguish between native and foreign cells – distinction made through antigens
Antigens
Protein molecules on cell’s surface
How are immune systems divided?
Innate immune system (1st line of defence)
Adaptive immune system (2nd line defence)
Innate immune system
Attacks foreign molecules produced by pathogens near entry points
Adaptive immune systems
Targeted process: binding with antigens on foreign cells (and destroying) or making them for destruction. This involves mechanisms of vaccinations (“immunization”)
According to meta-analyses, what are the two stress effects on the immune system?
Eustress and Distress
Eustress
Acute stressors improve immune function, primarily in the innate immune system (e.g. public speaking)
Distress
Chronic stressors have negative effects on the adaptive immune system
Cytokines
Through triggering inflammatory responses, cytokines serve an adaptive function in the short term
What are the different trajectories of stress?
- Depression, suicide, substance abuse, anxiety disorder
- PTSD
- No symptoms – resilient and/or posttraumatic growth
Genome
Pre-existing genetic risk factor
Epigenome
Environmental triggers
