The Physiology of Stress - stress pathways (SAM & HPA axis) Flashcards
what is stress
The subjective experience of a lack of fit between a person and his or her environment (e.g. where the perceived demands of a situation are greater than a person’s perceived ability to cope).
what is the Sympathomedullary Pathway
The sympathomedullary pathway (fight or flight response) is thought to be an innate, evolutionary-determined response to threatening situations
what is the hypothalamus
The hypothalamus lies at the base of the brain.
It is involved in many of the body’s physiological functions, such as stress-related arousal, hunger, thirst and sexual and reproductive behaviours.
It regulates many of these functions automatically.
If the cortex and limbic system identify a stressful situation of threat or danger, then the hypothalamus is stimulated to activate one of the stress pathways.
Acute (short-term) stress and the Sympathomedullary pathway
Immediate (acute) stressors arouse the autonomic nervous system (ANS) – the response is fast!
It is called autonomic because it governs itself i.e. heart beat, blood pressure, body temperature.
The ANS governs the release of hormones (chemical substances which circulate in the blood).
The Autonomic Nervous System (ANS)
ANS centres are located in the brainstem. Pathways run down the spinal cord and are distributed throughout the body by spinal nerves.
It has two separate divisions: the sympathetic branch and the parasympathetic branch.
Nerve fibres from both branches connect with internal structures such as various glands e.g. the adrenal medulla.
The SYMPATHOMEDULLARY (SAM) PATHWAY
1)Hypothalamus detects stressor/threat
2)Arousal of the Autonomic Nervous System (ANS) (Sympathetic branch)
3)SNS stimulates the Adrenal Medulla…
4)…which releases Adrenaline and Noradrenaline
Release of adrenaline results in…..
Sweatiness
Increased heart rate and raised blood pressure
Diverts blood away from the skin
Breathing quickens and becomes shallower
Increases blood supply/oxygen to the brain (for rapid response planning) and skeletal muscles (for physical action)
Pupil dilation
Digestion slows down, to conserve resources for fight/flight.
what does adrenaline also trigger
Adrenaline also triggers the release of blood sugar (glucose) and fats into the bloodstream, supplying energy to the muscles to enable the individual to fight or flee the threatening situation.
what is the parasympathetic branch of the ANS
The parasympathetic branch of the ANS returns heart rate and blood pressure to normal, as well as speeding up digestion, helping the body to relax.
Chronic (persistent) Stress and the Hypothalamic Pituitary-Adrenal (HPA) System
1)Hypothalamus (part of the brain)
stimulates the release of corticotropin-releasing factor (CRF),
which travels to….
2)the Pituitary Gland
(master gland, resistance to stress and
disease, bodily growth)
- secretes adrenocorticotropic hormone (ACTH)
3)Adrenal Cortex
4)Release of Corticosteroids/Cortisol
Evaluation of the Stress Pathways
:)This biological explanation of stress allows accurate, objective measures to be made.
- For example, stress hormones can be measured in urine samples.
:)People who have had their adrenal glands removed have to be given hormone supplements to help them cope with stressors, highlighting the importance of the SMP, HPA system and stress hormones in responding to stress.
Briefly outline what is meant by the ‘tend-and-befriend’ response observed in females.
During our evolutionary past this would have involved protecting themselves and their young through nurturing behaviours (tending) and forming protective alliances with other women (befriending)
Why might females have evolved to have a different system for coping with stress?
This may be because their responses evolved in the context of being the primary caregiver of their children.
Fleeing too readily at any sign of danger would put a female’s offspring at risk – they would be left defenceless, reducing reproductive success.
What is the name of the hormone thought to inhibit a fight-or-flight response in females?
Oxytocin
What effect is oxytocin thought to have on behaviour?
Oxytocin is thought to increase relaxation and nurturing, reduces fearfulness and decreases the stress response characteristics of the fight or flight response.
what did Taylor(2000) suggest
research by Taylor (2000) suggests that males and females respond in different ways to stress, with acute stress producing the ‘fight-or-flight’ response in males and the ‘tend-and-befriend’ response in females.
why are the HPA and SAM systems gender-bias
the standard descriptions of the HPA and SAM systems are arguably gender-biased (towards how males respond to stress) and not applicable to females, particularly as studies on human stress responses have mainly been conducted on males - researchers were concerned that fluctuations in hormone levels as a result of the menstrual cycle could act as a confounding variable, leading to varied stress responses, thus reducing the validity of the data.
Furthermore, most of the research into the sympathomedullary pathway is animal-based.
This presents extrapolation issues.
Why might the stress responses observed in animals fail to represent how humans respond to stress? Are there any specific factors that you can identify that set animals and humans apart in terms of how they respond to stressful situations?
Humans are more likely to have a cognitive element to their stress responses i.e. an individual’s thoughts and their interpretation of the situation determine whether there is a physiological response or not.
research suggests that cognitive appraisal of a situation is crucial in terms of how the individual responds and determines how the body responds, which neither of the stress pathways acknowledge
why?
the individual’s thoughts (cognitions) and their interpretation of the situation determine whether there is a physiological response or not.
what did Lazarus and Folkman (1984)
Lazarus and Folkman (1984) developed the transactional model to explain the role of cognitive appraisal in stress responses, explaining how an individual’s assessment of the demands of the situation (‘perceived demands’) and their perceived ability to cope determine whether or not the sympathomeduallary pathway is activated.
If there is a mismatch between the perceived demands and the individual’s perceived ability to cope, then the sympathomedullary pathway is more likely to be activated.
Explain the type of stress that leads to the secretion of the stress hormone cortisol
Chronic or persistent stress e.g. workplace stress
What is the name of the stress system that is activated when this type of stress is experienced?
The Hypothalamic Pituitary-Adrenal (HPA) System
How does cortisol help your body to deal with this type of stress and why wouldn’t adrenaline be sufficient enough?
Cortisol is a glucocorticoid hormone, permitting a steady supply of blood sugar, providing individuals with a constant source of energy, allowing the body to deal with more persistent stressors.
Adrenaline, on the other hand, just provides an immediate source of energy.
What are some of the known positive effects of the hormone cortisol?
Helps the body to cope with a stressor
Lower sensitivity to pain
