hypothalamic-pituitary-adrenal axis (redirected from HPA axis)

hypothalamic-pituitary-adrenal axis,

the combined system of neuroendocrine units that in a negative feedback network regulate the adrenal gland's hormonal activities.

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hypothalamic-pituitary-adrenal axis

A tightly-linked, interdependent endocrine unit which, with the systemic sympathetic and adrenomedullary systems, comprises a major peripheral limb of the stress system, the main function of which is to maintain basal and stress-related homeostasis; the hypothalamus and pituitary form the central part of the HPA axis, and are active even at rest, responding to blood-borne or neurosensory signals–eg, cytokines–eg, IL-1, IL-6, TNF-α; at the highest level, CRH and noradrenergic neurons innervate and stimulate each other, which is controlled by an autoregulatory, ultrashort negative-feedback loop, in which CRH and noradrenergic collateral fibers inhibit presynaptic CRH and α₂-noradrenergic receptors. Cf Hypothalamic-pituitary axis.