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hypothalamic-pituitary-adrenal axis (HPA),(hī'pō-thă-lam'ik-pi-tū'i-tār-ē-ad-rē'năl ak'sis),
major component of the stress system consisting of the paraventricular nucleus (PVN) of the hypothalamus, the anterior pituitary gland, and the adrenal cortices. Corticotropin-releasing hormone and vasopressin secreted by PVN neurons into the hypophysial portal system stimulate pituitary cells to produce and secrete adrenocorticotropic hormone (ACTH) into the general circulation. ACTH then stimulates cortisol secretion by the adrenal glands.
hypothalamic-pituitary-adrenal axisA 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.
hy·po·tha·lam·ic-pi·tu·i·ta·ry-a·dre·nal ax·is(HPA axis) (hī'pō-thă-lam'ik-pi-tū'i-tar-ē ă-dre'năl ak'sis)
A major component of the stress response system, consisting of the hypothalamus, anterior pituitary, cortex, and the cortex of the suprarenal gland. The HPA axis regulates secretion of cortisol from the suprarenal gland in response to stress.