Physiology of Stress and Anxiety Flashcards
What is Stress?
Stress is any condition that actually or potentially poses a challenge to the body’s ability to maintain homeostasis. Any chance has the potential to cause stress.
What are the two types of stress?
Eustress (good stress): Mild stress that is useful. Prepares us to meet challenges. It is helpful and improves performance e.g. revising, giving a speech, birth of baby, meeting deadlines etc.
Distress (bad stress): Unpleasant or disease producing stress e.g. death of family member, chronic pain etc. Severe stress is harmful and impairs performance.
What are the types of Stressors?
A stressor is a stimulus that produces a stress response.
External - environment, heat, life events, commuting
Internal: Lifestyle choices, caffeine etc.
Psychosocial: unemployment, marriage, divorce, new job, work problems, going for surgery, money concerns
Physiological Events: blood loss, low blood glucose, breaking an arm, catching a cold, infection, surgery, climate
What are the stages of the stress response?
What physiological areas are activated in the short-term stress response?
Short term stress response is autonomic nervous system and key to this is the adrenal medulla.
What physiological areas are activated in the long term stress response?
Describe the properties of the ‘alarm phase’ in the short term stress response
- Alarm phase if flight or fight.
- It is a rapid action to acute stress.
- It is short-lived
- It activates the sympathetic branch of the autonomic nervous system.
- Mediated by catecholamines (adrenaline, noradrenaline)
What sympathetic responses are visible after experiencing short-term stress?
- Increase in heart rate
- Increase in blood pressure
- Blood diverted to heart and skeletal muscles away from nonessential organs
- Dilation of airways (increase oxygen flow)
- Conversion of glycogen to glucose in liver
- Metabolic rate increases
- Alertness increases
- Sweating (cooling)
What occurs in the resistance and adaption phase of long-term stress, with reference to the HPA axis?
Stress activates the HPA axis (hypothalamic-pituitary-adrenal) axis:
1) Neurosecretory cells in the hypothalamus release CRH (corticotrophin releasing hormone)
2) CRH activates anterior pituitary gland
3) Anterior pituitary release ACTH
4) ACTH travels through blood to adrenal glands (kidneys)
5) ACTH stimulates cells in adrenal cortex to release cortisol (glucocorticoid)
What metabolic adjustments occur in the long-term stress response?
- Lipids released into blood
- Amino acids/proteins released from muscles into blood
- Increase in glucose in blood, through synthesis
- Aldosterone released by adrenal cortex causes retention of sodium, increased water retention, increased blood pressure.
- Immune suppression (low white blood cell count in blood)
Compare the short-term stress response with the long-term stress resposne
Short Term:
- Heartbeat and blood pressure increases
- Blood glucose levels rise
- Muscles become energised
- Adrenal medulla releases nor/adrenaline
Long Term
- Glucocorticoids release cortisol
- Protein & fat metabolism occur instead of glucose breakdown
- Inflammation is reduced, immune cells are supressed
- Mineralcorticoids (aldosterone) are released
- Sodium ions and water are reabsorbed by kidney
- Blood volume and pressure increases
What are Glucocorticoids?
- Glucocorticoids are a group of hormones in the adrenal cortex (adrenal steroids) secreted during stress.
- Main example is: Cortisol
- They increase blood glucose levels
- Maintain blood pressure
- Break down protein and convert to glucose
- Help make fats available
- Activate the CNS
- Allow the body to cope with stress
Summarise the stress response and entities produces as a result of this
What are the effects of excessive stress?
- Anxiety disorders
- Depression
- High blood pressure
- Ulcers & GI diseases
- Immune dysfunction
- Aging
- Cancer
- Stress also increases the frequency and severity of migraine headaches, asthma attacks and blood sugar fluctuations in diabetics.
- Supression of sex steroid secretion
What is the ‘Exhaustion Phase’
Comes with increasing time with stress.
- Resources in the body become so depleted that they cannot sustain the resistance phase. Exhaustion now occurs.
- Prolonged exposure to high levels of cortisol causes:
- Muscle breakdown
- Suppression of immune response
- Ulceration of GI tract
- Depression/Psychosis
- Failure of pancreatic beta cells
- Aging
- Pathological changes may persist even upon removal of the stressor
- Death likely
Identify the amygdala and hippocampus
How is the amygdala specifically involved in stress?
- Amygdala is involved in fear responses
- Activation of the central nucleus leads to stress response
Summarise how the HPA axis is regulated by the amygdala and hippocampus.
- Amygdala and hippocampus regulate CRH neurons in the hypothalamus.
- Amygdala activation stimulates HPA axis and stress response.
- Hippocampal activation supresses HPA axis = less stress.
Cortisol Feedback Mechanism:
- Circulating cortisol binds to glucocorticoid receptors in the hippocampus
- Activates hippocampus, which supresses CRH release by hypothalamus
- Reduces HPA activation - less cortisol released by adrenals.
What is the mechanism of action of Benzodiazepines?
GABA agonists
- Bind to regulatory site on the GABAa receptor to enhance the inhibitory effect of GABA
- Increases the influx of negatively charged Chloride ions (Cl-) into the neuron, causing hyperpolarisation and inhibiting action potentials
- By inference, causes supression of brain circuits in stress response
- Alcohol works in a similar fashion
