Physiological response to stress Flashcards
Summarise the stress response
- Detection (i.e. afferents from sensory systems or intrinsic sensitivity)
- Integration with top-down signals (primary limbic system)
- Output via endocrine signals (CRH → ACTH) or sympathetic/ parasympathetic balance
- Feedback regulation
How may detection occur?
The key theme is disruption of homeostasis via:
- nociception from the PNS
- alterations in blood composition as detected by CVOs (e.g. hypotension due to haemorrhage; changes in electrolyte concentrations)
- inflammation
What is a key structure involved in integration?
Paraventricular nucleus of the hypothalamus
Discuss top-down mechanisms of integration
Both psychogenic and systemic stimuli are processed in multiple limbic forebrain structures, including the amygdala, hippocampus and prefrontal cortex
These receive associational information for subcortical and cortical areas involved in higher order sensory Cprocessing and memory
Also receive ascending inputs from sites involved in attention and arousal (e.g. locus coeruleus and raphe nuclei)
STRESS MEDIATED BY EXPERIENCES, EXPECTATIONS ETC
Discuss the psychogenic stress response
arising from emotional/ mental stressors
However, not much is known about the role of hippocampus and mPFC - circuitry is complex
What is the endocrine output associated with the stress response?
HPA axis
How does HPA axis begin?
CRH release from parvoocellular neurons of the PVN into hypophysiotropic vessels
CRH induces ACTH from corticotrophs in the anterior pituitary via Gas CRH1 and CRH2
ACTH acts via Gas MC2-R on the zona fasciculata on the adrenal glands → cortisol
Effects of cortisol
- Gluconeogenesis to increase levels of blood glucose
- Lipolysis and ketogenesis
- Reduced vascular permeability to maintain plasma volume
- Immunosuppression
- Reduces ssecretion of other pituitary hormones
- Proteolysis and reduces protein synthesis
- Vasoconstriction (indirect, via upregulation of catecholamine receptors)
- Reduced sodium excretion, increases potassium excretion
Draw negative feedback loops
Essay plan
Describe symapthetic output caused by stress
PVN → connections ot both sympathetic and parasympathetic nuclei, including VLM, intermediolateral cell column and the LC (LC important as NA neurons)
The VLM, LC and PVN directly innervate the IML and initiate sympathetic response
IML has preganglionic sympathetic neurons → project to end organs and chromaffin cells of the adrenal medulla → release of adrenaline
Effects of adrenaline
- Increase in HR and force of contraction
- Vasodilation of muscle vascular beds and adrenal vasculature whereas constriction of visceral skin arteries and veins
- Dilation of respiratory tract
- Decreased secretion from GI tract + decreased motility
- Glycogenolysis occurs to reduce risk of hypoglycemia in the brain
- Stimulation of juxtaglomerular cells of the kidney, production of angiotensin II, vascular constriction and aldosterone release → Increases Na+ reabsorption and water retention, maintaining HBP
Where does the hypothalamus get inputs from?
Hippocampus & amygdala (cognition, mood, situations, perceptions and phoboas)
Arcuate nucleus - POMC and opoids (feeding)
Ascending catecholamine arousal
SCN - lgiht/dark cycle
3rd ventricle OVLT - responses to circulating hormones, osmotic changes
What is responsible for the acute stress response?
SNS
What is responsible for the chornic stress response?
HPA
What are some stres-related illnesses?
HD, peripheral vascular disease, T2D, anxiety, depression
