Stress Flashcards
What is stress in physiology and what are stress responses?
A real or threatened disruption of the homeostasis
Responses = the body’s non-specific adaptive responses to a stressor
What is an absolute stressor and what is a relative stressor?
Absolute = stressor that everyone would find stressful (e.g. injury, loss)
Relative = stressor that NOT everyone would find stressful (e.g. public speaking, noise)
What parts of the brain do stressor inputs converge onto and what are those parts of the brain responsible for?
Cerebral cortex - decision making + learning/memory
Limbic system - learning/memory + emotion/behaviour
Hypothalamus - emotion/behaviour, neuroendocrine reactions, and autonomic responses
Brainstem - autonomic responses
What are the 2 types of stressor responses produced by the brain and what are the differences between them?
Voluntary = specific to the type of stressor e.g. needing to run to get out of harms way
Involuntary = non-specific to the type of stressor, lasts longer, more intense with greater stress
What are the 2 hormones associated with stress, where exactly are they produced (for both)?
Cortisol and adrenaline, both produced in the adrenal gland
Adrenaline = produced in the medulla (middle) of the adrenal gland
Cortisol = produced in the cortex (outside) of the adrenal gland
What type of hormone is adrenaline and how is it synthesised?
What type of hormone is cortisol and how is it synthesised?
Adrenaline = Catecholamine hormone, produced in modified nerve cells called chromaffin cells
Cortisol = Glucocorticoid (steroid) hormone, produced from cholesterol through enzymes
How does Adrenaline effect the body in response to stress? (3)
Prepares the body for physical activity by:
- Increasing blood pressure and heart rate
- Mobilising energy (increasing blood glucose)
- Dilating air passages
How does Cortisol effect the body in response to stress? (3)
Helps to restore the body’s homeostasis by:
- Increasing blood sugar (glucose)
- aids in metabolism (of fat, protein and carbohydrates)
- modulates the immune system (inhibits inflammation)
How do stress hormones mediate stress responses, and to which type receptors do they bind to?
Act via binding to a specific receptor on the target tissue
Adrenaline = via membrane receptors that are linked to intracellular pathways using secondary messengers
Cortisol = via cytoplasmic receptors (within the cell) that are transcription factors (inhibit/promote gene expression)
What are the adjustments to body functions caused by the release of Cortisol and Adrenaline, and which adjustments are controlled by which hormone(s)? (4)
What is the fight or flight response changes gained by these adjustments? (3)
Increased heart rate (Both)
Increased blood sugar (Both)
Decreased immediately unnecessary activity (e.g. reproduction, digestion) - Adrenaline
Control of immune cell defences - Cortisol
Increased blood flow to muscles and brain
Increased energy and oxygen supply
Increased alertness
What are the 3 examples of diseases associated with dysfunction of stress responses, where does the disease affect, and which hormones do they involve?
- Addison’s disease = in the adrenal cortex causes underactivity, producing too little cortisol
- Cushing’s disease = in the adrenal cortex causes over activity, producing too much cortisol
- Phaeochromocytoma = in the adrenal medulla causes over activity, producing too much adrenaline
What is Cushing’s disease and Cushing’s syndrome caused by?
Disease = Hyperdrive by a tumour in the anterior pituitary gland producing too much ACTH (affects the HPA axis)
Syndrome = over-treatment with synthetic glucocorticoids
What is Phaeochromocytoma caused by, and what does this result in?
Tumours in the medulla of the adrenal gland which produce excess adrenaline. Causes severe high blood pressure
What is the HPA axis?
Stress triggers the hypothalamus to release CRH, which triggers the Anterior Pituitary gland to release ACTH, which triggers the Adrenal cortex to release Cortisol, which acts to trigger stress coping behaviours and flight/fight responses
How do different types of stress converge to produce common responses in the brain? (where in the brain and how is this modulated?)
PVN in the hypothalamus receives inputs from different parts of the brain that receive different types of stressors.
The CRH neurons in the PVN receive these signals and release CRH which acts on the anterior pituitary.
CRH neurons are mediated by neurotransmitters released from neurons of other brain regions (Inhibit/excite the neurons)
Which part of the brain does physical stress target and what does this lead to?
The brainstem (bottom of brain), leads to activation of the HPA axis.
Cortisol works to modulate immune activity and cause inflammation
Which part of the brain does emotional stress target, and how does the reaction to this differ from physical stress?
The limbic system (Amygdala) (front of the brain)
Still activates the HPA axis, but cortisol doesn’t result in inflammation
How does the brain’s biological clock work? (sleeping and waking up)
The SCN in the hypothalamus controls the HPA axis circadian rhythm.
During the day, the SCN stimulates the PVN in the hypothalamus to release CRH and increase cortisol levels.
At night the SCN stops stimulating the PVN releasing CRH, to prevent the release of ACTH and cortisol at night, to prepare the body for sleep
ACTH and cortisol levels peak just before we wake up to prepare our body for stress again (SCN starts activating PVN again just before we wake up)
How does Addison’s disease affect the HPA axis?
The adrenal cortex is damaged, leading to a very low conc. of cortisol secreted and therefore poor response to stress. Since there is very little cortisol secreted, there is a very weak negative feedback on the HPA axis. This means that there is a very high conc. of ACTH being secreted from the anterior pituitary, but low cortisol secreted from the adrenal cortex, as it’s damaged. (diagram on summary sheet)
How does treating patients with synthetic glucocorticoids for too long affect the HPA axis?
Reduces the HPA axis activity. Synthetic glucocorticoids have very strong negative feedback on the PVN and anterior pituitary, leading to low conc. of ACTH being secreted from the anterior pituitary. This low conc. of ACTH means that the Adrenal cortex can only secrete a low conc. of cortisol, meaning it is underactive and leading to poor response to stress (see diagram in summary sheet)
How does chronic stress affect the HPA axis? (cycle)
- Chronic stress causes HPA stress responses to become increased and prolonged, causing hyperactivity of the HPA axis
- This results in a sustained secretion of cortisol
- The sustained secretion of cortisol results in a reduced sensitivity to cortisol
- This results in cortisol negative feedback becoming less effective, leading to hyperactivity of the HPA axis
What are the 7 physical health impairments that chronic stress can lead to?
- Muscle wasting
- Fat redistribution
- Diabetes mellitus
- Hypertension and cardiovascular disease
- Osteoporosis (bone disease)
- Susceptibility to infection
- Thymus shrinks
What are the 5 mental health impairments that chronic stress can lead to?
- Anxiety
- Depression
- Cognitive decline (e.g. memory worsens)
- Appetite increase/decrease
- Reproductive performance declines
How can chronic stress cause obesity?
Chronic stress causes high cortisol levels to act on the brain, which drives the desire for sweet and fatty foods. When fatty foods have been consumed, abdominal fat increases, and signals are sent to the brain which reduces the chronic stress
How can chronic stress cause mental illnesses? (anxiety and depression)
Chronic stress causes HPA axis hyperactivity which increases the conc. of CRH and changes in the limbic system activity, causing increase in anxiety levels and a decrease in mood which can lead to depression.
How are stress responses measured? (4 ways)
- Verbal interviews = showing signs of anxiety, depression, or sleep disturbance
- By physical measures
- Measuring autonomic nervous activity e.g. heart rate
- Measure the levels of secretion of “stress” hormones - high levels of cortisol can be found in the saliva, blood, urine, and earwax
