Stress Axis

Question 1

Describe the sympathetic adrenomedullary (SAM) axis

Answer 1

1. Neuron of sympathetic NS (splachnic) projects to adrenal medulla
2. Adrenal medulla releases adrenaline + noradrenaline into the blood (CATECHOLAMINES)
3. HR goes up, BP goes up, blood sugar goes down, GI blood flow goes down
4. FAST response

Question 2

Describe the hypothalamic-pituitary-adrenal (HPA) axis

Answer 2

1. Stressor info in hypothalamic paraventricular nucleus (PVN)
2. PVN synthesizes cortocotropin-releasing factor (CRF)
3. CRF binds to cells in anterior pituitary, stimulates ACTH synthesis
4. ACTH stimulates release of glucocorticoids (cortisol, corticosterone)
5. Provide energy to muscles, inhibit non-essential stud (immune, reproductive)
6. SLOW acting

Question 3

What is function of glucocorticoids?

Answer 3

1. Stimulate proteolysis to be converted to glucose
2. Stimulate gluconeogenesis in liver
3. Stimulate mobilization of fatty acids from adipose tissue

Question 4

How does glucocorticoids provide negative feedback in the HPA axis?

Answer 4

1. Feed back to pituitary
2. Feed back to Hypothalamus
3. Feed back to limbic structures

Question 5

Differences between MR and GR receptors

Answer 5

1. MR has high affinity for glucocorticoids; GR has low affinity
2. MR regulates HPA at trough (night-time); GR regulates HPA during peak circadian activity, actute stress
3. MR needs low levels of glucocorticoids to get activated; GR needs high levels of glucocorticoids to get activated

Question 6

What are the 3 things to look at when evaluating molecular response to stress?

Answer 6

1. Baseline level of molecule
2. Peak stress response
3. How long it takes to go back to baseline

Question 7

What projects to the Paraventricular nucleus (PVN) to cause the stress response? (

Answer 7

1. Brainstem
2. Somatosensory information
3. Cortico-limbic regions
4. Circumventricular organs
5. Hypothalamus

Question 8

What are steroid hormones secreted by adrenal cortex

Answer 8

1. Glucocorticoids (cortisol, corticosterone): increase blood glucose levels (cannot be stored in cells)
2. Mineralocorticoids: regulate electrolyte balance

Question 9

What is the method of action of steroid hormones (cortisol)

Answer 9

1. Cortisol dissociates from carrier protein
2. Enters cell via diffusion
3. Binds to low-affinity glucocorticoid receptor (GR)
4. GR oligomer changes to DNA-binding active form, forms homoDIMER.
5. GR homodimer enters nucleus, regulates transcription of genes

Question 10

Describe role of HPA axis in basal function

Answer 10

1. Has basal secretory activity that follows 24-hour rhythm
2. Cortisol levels highest during awakening, lowest during sleep.
3. Glucocorticoids stimulate metabolism so you get a booster shot in the morning
4. Pulsatile response (#of pulses can change, but not amplitude)