HPA-axis and stress Flashcards
What is the HPA axis?
- The pathway of the Hypothalamus, Pituitary gland, Adrenal gland
Explain the HPA axis
What is the role of the HPA axis in depression?
- Depressed patients show HPA hyperactivation (50%)
- If the negative feedback loop is compromise there will be overprod of cortisol
Where are the adrenal glands located?
- Small endocrine glands
- Above kidneys
- Essential for life
What is the function of the adrenal glands?
Adrenal cortex:
* Releases steroids, Glucocorticoid, mineralcorticoids (CORTISOL< ALDOSTERONE etc)
Medulla:
* Prod of catecholamines e.g. noradrenaline + adrenaline
Explain the Dual autonomic and endocrine control of drenal gland
- 2 sides to control adrenal pathways/gland
- Leads to different end production
- –(Catcholamines or steroids)
Explain the Dual autonomic and endocrine control of drenal gland
Explain the Dual autonomic and endocrine control of drenal gland WHEN affected by stress.
Summarise the effects of stress on the dual control system?
- ANS releases Noradrenaline or adrenaline via SNS - FIght or flight
(inc HR, BP, bronchodilation, blood flow to skeletal muscle) - HPA-axis releases cortisol
(INC energy metabolism, lipolysis, protein bdwon, glucogenesis)
(DEC immune and inf)
How is the circadian rhythm involved in stress?
- Enhanced glucocorticoids affect the circadian clock in the body – circadian inputs (light) into the brain affect the cascade which leads to the synchronisation of these circadian activities
- The suprachiasmatic nucleus (SCN) is affected by changes in light and regulates the timing of the circadian activities in the body
- The SCN signals via the ANS to the adrenal gland (in addition to the HPA axis)
- In the adrenal glands, the autonomous input regulates the expression of several genes, which induces a whole change of proteins
- These changes now affect the gene expression which affects glucocorticoid production
How does the circadian rhythm prepare the body for the day?
- In the morning hours, before waking, there is a strong increase in cortisol production, which is followed very closely by an increase in heart rate and blood pressure
- These changes are preparing the body for the energy demands of the day
Why is the clock gene important?
If there is a mutation to the clock gene you can have the normal process change.
- Can affect early onset of stress hormones
- Delays cortisol rise
- Rhythm now in response to activity NOT preparing for activity
What are the adaptive values of acute stress?
In the short term stress response in beneficial, improve survival. Increases attention and physiological benefit.
- Increases:
1. Anxiogenic behaviours
2. Arousal
3. Scanning attention
4. Memory
Fear-Flight-Fight
Inc:
1. Resp
2. HR
3. BP
Dec:
1. Gut function
2. Immune function
3. Repro function
What are the negative value of chronic stress?
- Although things start of good over time this develop into negative traits.
- Anxiety develops
- Sleep disturbances
- Attentional disruption
- Memory loss
The longer term fight or flight response can lead to CV disease due to long term higher blood pressure etc
- Can also develop:
1. Hyperglycemia, insulin resistance, diabetes
2. Functional bowel syndrome
3. Susceptibitlity to infection
4. Sexual disorders, prem labour
What are the 2 nuclear receptors for adrenal steroids?
MR - Mineralocorticoid receptors: Mainly limbic
* High affinity therefore occupied by low basal ganglia circulating levels of cortisol
GR - Glucocorticoid receptors: Widespread
* Low affinity therefore occupied by circadian/stress high levels of cortisol
(Mineralocorticoid always active)
(GR only at v.high stress)
What is the Locus Coeruleus?
The predominant source of NA and its role in AGing and ADs
* It is a nucleus in the brain and innervates many different brain regions and affects many different functions
- Including, memory to circadian, motion etc
