How is the release of corticotrophin releasing factor from the hypothalamus controlled by the steroid levels in blood?

Question

anonymous · Answer

The HPA, Hypothalamic-Pitutary-Adrenal Axis, is controlled by a positive feed back loop via the catecholamine nor-epinephrine and a negative feedback loop via cortisol. The HPA is based off the circadian rhythm, upon waking within 30-45 minutes the plasma levels of cortisol are at their highest. Cortisol is a derivative of pregnenolone to 17-alpha-hydroxypregnenolone to 17-alpha-hydroxyprogesterone to deoxycortisol to cortisol; or alternatively, pregnenolone to progesterone to 17-alpha-hydroxyprogesterone and so forth. So levels of pregnenolone and progesterone as precursors to cortisol can be detected via chemoception, when cortisol is at it's highest it suppresses the release of Corticotropin Releasing Hormone. Low levels of cortisol, or high levels or nor-epinephrine signal the release of CRH.