Body and drug basics
HPA axis
Last updated
The HPA axis is the body's stress-response chain, named after the three parts it runs through: the hypothalamus in the brain, the pituitary gland below it, and the adrenal glands sitting on top of the kidneys. The hypothalamus signals the pituitary, the pituitary signals the adrenals, and the adrenals release cortisol, the main stress hormone. Cortisol then travels back and tells the chain to quieten down, so the system switches itself off.
Why it matters here
It runs on a daily rhythm, higher in the morning and lower at night, so a single measurement with no time attached says very little. Anything acting at one point in the chain also has consequences further along it, because the three parts are connected in sequence.
What it is not
One letter away from the HPG axis, which ends at the gonads and the sex hormones instead of the adrenals and cortisol, and the two are routinely swapped. Adrenal fatigue is not a finding from this system and is not what the term means. This site also carries HPA Axis as a Biological Pathway entry, which is the same chain described for filing compounds; this entry is the plain-language explanation of it.
Also called
- hpa axis
- hpa
- hpa-axis
- hypothalamic-pituitary-adrenal axis
- hypothalamic pituitary adrenal axis
- stress axis
- cortisol axis
The letters stand for hypothalamic, pituitary and adrenal, in the order the signal travels. It is often just called the stress axis.
Compounds carrying this term
None on file yet. This term is in the controlled vocabulary but no compound record currently uses it — which is a statement about our coverage, not about the term.