Pituitary-adrenal axis

In medicine and physiology, the Pituitary-adrenal axis, also termed the Hypothalamus-pituitary-adrenal axis, is the hormonal system of which the effector organ is the adrenal cortex.

Adrenal and pituitary
The adrenal cortex produces cortisol in response to stimulation by corticotropin (or: ACTH, adrenocorticotropic hormone). The pituitary gland, specifically the corticotroph cells, sense the blood levels of cortisol. If the levels are too low, more ACTH is secreted and the cortical activity is increased.

The hypothalamus
The hypothalamus controls the rate at which the corticotroph cells respond. In acute illness, higher cortisol levels are needed (see adrenal insufficiency). This is achieved by the hypothalamus secreting higher levels of CRH (corticotropin releasing hormone) into the portal system. This stimulates the corticotroph cells to a higher set point, leading to increased ACTH and cortisol levels.

Regulation at hypothalamus level
Now what controls the hypothalamus? This can be stress of emotional or physical nature; the CRH pulse rate (it is secreted in pulses; the rate determines its function) is increased in response to systemic inflammation, namely IL-1, IL-6 and TNF alpha.