3: Stress Flashcards by Aoife Harkin

Define stress physiologically.

A real or threatened disruption of homeostasis
Stress responses are a non-specific adaptive response to a stressor
They optimise chances of survival but if excessive and prolonged, they can be damaging

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What are the two main classes of stressor?

Psychological
Physical

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What are the two types of psychological stressor?

Social: grief, loss, territorial defence, dominance
Fear/novelty: anxiety, predator signals

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What are the two types of physical stressor?

Physiological: pain, blood loss, fever, injury, mobility restriction, infection
Environmental: noise, temperature, pollution

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What are the two types of stressor?

Absolute (e.g. loss, injury, not subjective)
Relative (e.g. public speaking, noise, subjective)

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What are the two types of sensors?

External: eyes, ears, nose, taste-buds
Internal: baroreceptors, glucoreceptors, pain sensors, immune cells

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What are the two types of stress response?

Voluntary (specific to the stressor)
Involuntary (non-specific, lasts longer, more intense with greater stress)

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What are the two main stress hormones?

Coritsol (corticosterone)
Adrenaline (epinephrine)
Both of these are produced in the adrenal gland

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Where is adrenaline produced?

Adrenaline is a catecholamine hormone
Synthesised from Chromaffin cells in the adrenal medulla
Occurs through a variety of enzymatic reactions via tyrosine hydroxylate
Once produced, noradrenaline and adrenaline are stored in Chromaffin vesicles and ready for release
Produces 80% adrenaline and 20% noradrenaline

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What is adrenaline?

A hormone and neurotransmitter released by the adrenal glands during stress (the “fight or flight” response)
It increases heart rate, blood pressure, dilates airways, and boosts energy supply to help the body respond quickly to danger or excitement

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What is noradrenaline?

Also known as norepinephrine
A hormone and neurotransmitter released by the adrenal glands and nerve endings, especially during stress
It mainly constricts blood vessels, which raises blood pressure, and also helps increase heart rate—similar to adrenaline but with a stronger focus on blood vessel tone

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Describe what leads to adrenaline secretion.

1) Perception/anticipation of stressors via internal or external sensors
2) Input received by hypothalamus which sends impulse to SNS
3) Cholinergic preganglionic fibres send impulse to Chromaffin cells in the adrenal medulla
4) Releases adrenaline into the blood

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What is cortisol?

A steroid, glucocorticoid hormone
Formed by cholesterol in a series of enzyme-mediated conversions
Rate-limiting step is conversion to pregnenolone (a precursor molecule)
The final step only occurs in the adrenal cortex
Produced on demand, not stored

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What hormone controls cortisol secretion?

ACTH (adrenocorticotrophic hormone)
Released from the anterior pituitary into the bloodstream
Then into the adrenal cortex to stimulate cortisol release

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Compare the stress responses of adrenaline and cortisol.

Adrenaline:
Increases BP and HR
Mobilises energy
Dilates air passages
Prepares body for physical activity

Cortisol:
Increases blood sugar
Aids in fat, protein, and carb metabolism
Modulates the immune system (inhibits inflammation)
Restores homeostasis

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What are the two types of receptors that receive stress hormones?

Adrenoreceptors: used by adrenaline and noradrenaline - found on cell membrane, linked to intracellular signalling pathways using second messengers like cAMP

Cytoplasmic receptors: used by cortisol, the receptors act as transcription factors to modify gene expression

Describe the general short-term response to acute stress.

1) Stressors
2) Sensors
3) Brain
4) Voluntary responses
5) Fast hormonal + autonomic nervous responses
6) Secretion of noradrenaline, adrenaline and cortisol
7) Adjustments in bodily functions
8) Survival and adaptation to stress

What are some adjustments in body functions caused by stress?

Increased heart rate
Increased blood pressure
Increased blood sugar
Decreased immediately unnecessary activities such as digestion and reproduction
Control of immune cell defences
Increased blood flow to muscle and brain
Increased energy and oxygen supply
Increased alertness

Describe the stress responses to a relative stressor e.g. public speaking.

Increased production of catecholamines (adrenaline, noradrenaline, dopamine, etc)
Pupils dilate, peripheral vision reduced
Increased heart rate
Faster, deeper breathing
Increased blood flow to large muscle groups
Adrenal hormones released
Slowed digestion
Increased blood pressure

What causes Addison’s disease?

Under-activity of the adrenal cortex (too little cortisol produced)

What causes Cushing’s disease?

Over-activity of the adrenal cortex (too much cortisol produced)

What causes pheochromocytoma?

Over-activity of the adrenal medulla (too much adrenaline)

Describe Addison’s disease.

Results from damage to the adrenal cortex, causing under-secretion of cortisol
Damage is caused by the immune system mistakenly attacking the gland (e.g. tuberculosis, HIV, haemorrhages)
Symptoms include extreme weakness, fatigue, unintentional weight loss, skin pigmentation

Describe Cushing’s disease.

Occurs when a person’s tissues are exposed to excess cortisol
Caused by tumour in the adrenal cortex, or hyperdrive by a tumour in the anterior pituitary gland to produce excess ACTH
99% of cases result from over-treatment with synthetic glucocorticoids (Cushing’s syndrome)
Symptoms include hypertension, central obesity, type II diabetes, increased appetite, loss of tissue protein, poor wound healing, infertility

Describe pheochromoytoma.

Occurs when tumours form in the adrenal medulla, which causes excess adrenaline production Can be deadly because of the very high blood pressure caused by excess adrenaline release Without adequate treatment, the severe high blood pressure can lead to heart attack or stroke Symptoms include severe headaches, excess sweating, tachycardia, palpitations, anxiety, tremors

Describe how the hypothalamic pituitary adrenal axis generates a stress response.

PVN/Hypothalamus --> CRH --> anterior pituitary --> ACTH --> adrenal cortex --> cortisol

Describe how release of ACTH leads to cortisol release via the hypothalamic pituitary adrenal axis.

The paraventricular nucleus in the hypothalamus receives input from stressor The PVN releases CRH (corticotropin releasing hormone) CRH is received by the anterior pituitary which triggers release of ACTH ACTH is received by the adrenal cortex, which triggers cortisol release

Describe how emotional stress is received by the hypothalamic pituitary adrenal axis.

Limbic system --> PVN --> CRH --> Anterior pituitary --> ACTH --> adrenal cortex --> cortisol

What is the circadian rhythm?

The body's natural, internal process that regulates the sleep-wake cycle and other physiological processes, typically on a 24-hour cycle It's driven by an internal biological 'master clock', located in the suprachiasmatic nucleus (SCN) of the hypothalamus It responds to environmental cues like light and darkness, helping to align the body's functions (like hormone release, body temperature, and alertness) with the time of day

Describe how the circadian rhythm alters behaviour in the morning.

SCN triggers a series of hormone release to release cortisol Cortisol mobilises energy (i.e. for stress-coping behaviours) Enables fight or flight responses, and modulates immune activity

Describe how the circadian rhythm alters behaviour in the evening.

SCN does not stimulate the PVN Less cortisol released, ready for sleep Blue light in the evening is harmful as it stimulates the SCN and causes cortisol release

What is chronic stress?

Long-term exposure to stressors Leads to increase in HPA stress responses and sustained release of cortisol This decreases the body's sensitivity to cortisol Meaning cortisol feedback is less effective, making the HPA axis hyperactive

What are some physical health issues associated with sustained cortisol secretion.

Muscle wastage Fat redistribution Type II diabetes Hypertension CVD Osteoporosis Susceptibility to infection Thymus shrinks

What are some mental health issues associated with sustained cortisol secretion?

Anxiety Depression Cognitive decline Disturbed appetite Declining reproductive performance

How can stress lead to obesity?

Temporary increase in HPA activity CRH in the brain reduces appetite In the case of chronic stress, high cortisol levels act on the brain to drive desire for and satisfaction from sweet and fatty foods Intra-abdominal fat increases and signals to the brain, reducing chronic stress temporarily

What are some symptoms of depression?

Worthlessness or guilt Suicidal thoughts/actions Withdrawal, sadness, melancholy No pleasure, loss of libido and appetite Insomnia or excessive sleeping Risk factor for CVD and osteoporosis

How does chronic stress link to depression?

Chronic stress causes HPA axis overactivity, causes changes in the limbic system Leads to increased CRH, increasing anxiety Also decreases serotonin and noradrenaline secretion, which decreases mood

How can stress be controlled intrinsically?

Stress responses are normally autonomically limited by negative feedback actions of cortisol and inhibitory neural circuits

How can stress be controlled extrinsically?

Avoiding environmental stressors, minimising physical stressors, controlling diet, interfering with stressor processing in the brain (e.g. via medication which makes noradrenaline and serotonin available or blocks/limits CRH and cortisol actions)