15 - Stress response Flashcards
stress response (2)
- coordinated by brain regions such as the hypothalamus
- signals stress to the body via autonomic and endocrine routes
low arousal
low activation of nervous system characterised by fatigue, cognitive dullness and sleepiness
high arousal
heightened activation of the nervous system, leading to anxiety and stress
moderate arousal
may include some level of stress, can benefit performance
allostasis
change in set point of one/more physiological variables outside normal homeostatic range (can involve physiological and/or behavioural changes)
why is allostasis important?
allows organisms to respond adaptively to change in internal/external conditions
acute stress (3)
- lasts for short period of time
- sympathetic activation due to stressor, fades quickly
- parasympathetic dominance restored
chronic stress (2)
- occurs if stress response becomes elevated over prolonged period
- sympathetic activation maintained long after initial stressor
allostatic load
with chronic stress, homeostatic regulation cannot return to set point, set point remains elevated
2 main systems that coordinate physiological stress responses (2)
- sympathetic nervous system
- hypothalamic-pituitary-adrenal
sympathetic nervous system stress response (3)
- fast stress response
- mediated by autonomic sympathetic nervous system
- including by specialised direct neuroendocrine route via adrenal medulla (the sympatho-adrenomedullary axis)
hypothalamic-pituitary-adrenal stress response (2)
- slower stress response
- mediated by endocrine interactions between the hypothalamus, pituitary gland and adrenal cortex
how does the sympatho-adrenomedullary axis trigger a fast stress response? (3)
- stress signals from brain sent directly via sympathetic preganglionic neurons
- these pass through spinal cord and thoracic splanchnic nerves to adrenal medulla
- release acetylcholine in adrenal medulla to activate chromaffin cells
role of chromaffin cells in adrenal medulla
release adrenaline and noradrenaline to trigger effector organs
adrenaline and noradrenaline (3)
- catecholamines
- synthesised from tyrosine by chromaffin cells in adrenal medulla
- chromaffin cells mainly release adrenaline (80%)
how does adrenaline exert itself on multiple organs?
via alpha and beta adrenergic receptors on organs
adrenaline effect on heart
increases heart rate and force of contraction
adrenaline effect on lungs
increases bronchodilation (relaxes muscles in bronchi to widen airways)
adrenaline effect on liver
increases glycogenolysis to increase blood glucose level
adrenaline effect on digestive system
triggers vasoconstriction to reduce blood flow to gut
most common cause of adrenaline overproduction
tumour in adrenal medulla
corticotropin-releasing hormone (CRH)
hormone that activates stress response as part of the hypothalamic-pituitary adrenal (HPA) axis
components of HPA axis (4)
- hypothalamus
- anterior pituitary gland
- adrenal glands
- adrenal cortex
hypothalamus role in HPA axis (2)
- neurosecretory cells in paraventricular nucleus (PVN) secrete corticotropin-releasing hormone (CRH)
- diffuses via portal vein to trigger anterior pituitary gland
anterior pituitary gland role in HPA axis
binding of CRH triggers release of adrenocorticotropic hormone (ACTH) from endocrine cells
adrenal glands role in HPA axis
located on top of each kidnet and are made up of adrenal medulla (inner) and adrenal cortex (outer)
adrenal cortex role in HPA axis (2)
- ACTH (adrenocorticotropin hormone) binding triggers release of cortisol from cells in adrenal cortex
- cortisol triggers stress response via effector organs (e.g. heart, lungs)
negative feedback mechanisms in HPA axis (2)
- ACTH secreted by anterior pituitary -> inhibits CRH release
- cortisol secreted by adrenal cortex -> inhibits both ACTH and CRH release
how can chronic stress effect HPA axis?
can cause sensitisation of neural responses -> leading to HPA axis hyperactivation
cortisol (3)
- glucocorticoid hormone (form of steroid hormone)
- lipid soluble (like all steroid hormones) - can cross plasma membranes
- synthesised from cholesterol in adrenal cortex
endocrine effect of cortisol (3)
- lipid soluble - can cross plasma membrane of target cells to bind to intracellular receptor
- cortisol receptor complex enters nucleus
- acts as transcription factor, altering gene expression
cortisol effect on liver
increases gluconeogenesis and glycogenolysis
cortisol effect on pancreas
decreases insulin secretion
cortisol effect on adipose tissue
increases lipolysis in peripheral fat stores to yield fatty acids
cortisol effects on skeletal muscle (2)
- increases breakdown of muscle proteins (proteolysis) to yield amino acids
- also has numerous other effects e.g. increasing blood pressure by enhancing vasoconstriction caused by adrenaline/noradrenaline
