Homestasis and Stress Flashcards
Homeostasis is______
feature of a system ( human body) that regulates a specific parameter to maintain stable condition
Homeostasis is ___________ regulated.
highly
Allostasis is________
mechanisms that let an organism maintain long-term stability and viability by coordinating body-wide (brain controlled) responses via overriding homeostatic setpoints to meet predicted needs
4 keys points of Allostasis
- achieves long term stability through change
- a series of coordinated changes in multiple systems
- override homeostatic mechanisms
- is preemptive and predictive ( zebra being chase by a lion)
Allostatic state
a period when there is an override of homeostatic setpoints
Allostatic load
short term burden caused by allostatic states
Allostatic overlaod
long term, maladpative allostatic load that causes damage to system
A stressor is__________
a positive or negative experiences that changes homestasis
What is a stress response?
a response to changes in allostatic or homeostatic balance
or
response to stressor
What is stress?
anything that changes the allostatic or homeostatic balance of a living organism
Sella Turcica
Where pituitary gland is encased
What is the purpose of releasing hormones/factors released by hypothalamus
Releasing hormones tell pituitary to release hormones found in pituitary into blood
2 types of neurons found in the paraventricular nucleus (PVN) of hypothalamus
- medial parvocellular ( parvo=small) neurons -secrete releasing factors into smaller, special circurlation via media eminence
- magnocellular ( magno=large) neurons -secrete oxycotin and vasopressin directly into general circulation
HPA axis and stress hormone release
- medial parvocellular neurons make and secrete CRH/F
- CRH/F is released in capillary bed called median eminence and carried down to anterior pituitary via superior hypophyseal artery ( a special portal circulation)
- CRH/F binds to CRH/F receptors on corticotrophs, cell type found in anterior pituitary
- Corticotroph are activated/stimulated by CRH/F to release ACTH in general blood circulation
- ACTH travels in blood to effector organ, adrenal cortex
- ACTH binds on receptor in adrenal cortex and stimulates release of cortisol
Hormones released by Posterior Pituitary
- ADH/vasopressin
2. Oxytocin
Adenohypopsis
the anterior pituitary
adeno=gland
a lot of blood vessels
Neurohypopsis
posterior pituitary
neuro=neurons
contain alot of neuronal axons
Cortisol/corticorsterone
main stress hormone in humans/rodents
hormones differ by one hydroxyl group
biosynthesis of steroid hormones
precursor of all steroids is cholesterol
aldosterone, progesterone, testoterone, estrogen, cortisol
How is stress response terminated
- removal of stressor
2. Negative feedback along the Hypothalamus, Pituitary, Effector Organ Axis
What evidence shows that hippocampus is invovlved in stress response?
There is a dense concentration of cortisol/corticosterone receptors in the hippocampus
3 types of effects caused by stress response
- CRFergic central effects ( hypothalamus)
- Glucocorticoid peripheral effects ( increase GC receptors)
- SNS mediated peripheral effects
Effect of Stress on Reproduction
A CRFergic central effect
Stress inhibits reproduction
Effect of stress on SNS
A SNS peripheral effect
Stress activates SNS system
Effect of stress on GC control
A GC peripheral effect
stress increase stress hormone release and results in
- Increase metabolism ( protein production)
- Decreased immune response (immuno-suppression)
Mechanism of glucocorticoid effect during stress response
- Cortisol can freely enter cell vis passing through cell membrane
- Cortisol binds to glucocorticoid receptor inside cell
- Glucocorticoid receptors are normally held in cytsol of cell by chaperone proteins like heat shock protein so the receptors can’t enter into nucleus of cell
- Glucocorticoid displaces the chaperone protein and enters into nucleus as a glucocorticoid-glucocorticoid receptor complex
- G-GC complex binds to glucocorticoid responsive element in nucleus and this recruits transcription factors
- Transcription factors are start transcription of genes with glucose responsive elements; mRNA is translated to protein
- Newly produced protein increases cellular function
Rate of change and Stress Response
Stress response occurs at molecular, cellular, and behavioral levels
slow change-protein synthesis
faster change-SNS
Effect of cortisol on neuron activity
hippocampal neurons fire more frequency
Brain structures that inhibit stress response
Hippocampus
Pre-frontal cortex
Brain structures that increase stress response
Amygdala
What happens to key brain structures during chronic stress?
Amygdala hypertrophies and then atrophies
Hippocampus and prefrontal cortex atrophy
Net effect of Hypothalamus-Pituitary-Adrenal Cortex Axis in Chronic Stress Brain remodeling?
Stress response is lengthened because negative feedback mechanism are decreased and pro-stress mechanism are increased
Hippocampus activity and stress response
Acute stress: Hippocampus is healthy and decreases effects of stress
Chronic stress: hippocampus is damaged and there is an increase in negative effects of prolonged stress response
Stress and Learning/memory
Acute stress: increase stress, increase learning and memory
chronic stress:
increase stress, decrease learning and memory
Why is stress an vital physiological feature?
Acute Stress and stress response has evoluntionary benefit;
stress hormones help us survive stressful situations!
Describe the epigenetic nature of early life stress on organism
Stress during early development has negative long-lasting effects on brain and behavior
Stress is not only mediated by genetic effects but also environment
What did low/high grooming rodent study reveal about epigenetic affects of stress
rats who had low stress/high groom enviroment had more demethlyaltion of
the promoter NR3C1, the glucocorticoid receptor responsible for increased glucocorticoid receptor expression ( a good thing!) than rats that had high stress/low groom environment
