Editing Hypothalamic–pituitary–adrenal axis (section)

{{short description|Set of physiological feedback interactions}}
[[File:HPA Axis Diagram (Brian M Sweis 2012).svg|right|thumb|350px|Schematic of the HPA axis (CRH, [[corticotropin-releasing hormone]]; ACTH, [[adrenocorticotropic hormone]])]]
[[File:HPA-axis - anterior view (with text).svg|right|thumb|Hypothalamus, pituitary gland, and adrenal cortex]]
The '''hypothalamic–pituitary–adrenal axis''' ('''HPA axis''' or '''HTPA axis''') is a complex set of direct influences and [[feedback]] interactions among three components: the [[hypothalamus]] (a part of the [[brain]] located below the [[thalamus]]), the [[pituitary gland]] (a pea-shaped structure located below the hypothalamus), and the [[adrenal]] (also called "suprarenal") [[Adrenal gland|glands]] (small, [[conical]] organs on top of the [[kidneys]]). These [[organs]] and their interactions constitute the [[HPS axis]].

The HPA axis is a major [[neuroendocrine system]]<ref name="NHM-Neuroendocrine systems">{{cite book | vauthors = Malenka RC, Nestler EJ, Hyman SE | editor = Sydor A, Brown RY | title = Molecular Neuropharmacology: A Foundation for Clinical Neuroscience | year = 2009 | publisher = McGraw-Hill Medical | location = New York | isbn = 9780071481274 | pages = 246, 248–259 | edition = 2nd | chapter = Chapter 10: Neural and Neuroendocrine Control of the Internal Milieu | quote = <br />•The hypothalamic–neurohypophyseal system secretes two peptide hormones directly into the blood, vasopressin and oxytocin.&nbsp;...<br />•The hypothalamic–pituitary–adrenal (HPA) axis. It comprises corticotropin-releasing factor (CRF), released by the hypothalamus; adrenocorticotropic hormone (ACTH), released by the anterior pituitary; and glucocorticoids, released by the adrenal cortex.<br />•The hypothalamic–pituitary–thyroid axis consists of hypothalamic thyrotropin-releasing hormone (TRH); the anterior pituitary hormone thyroid–stimulating hormone (TSH); and the thyroid hormones T<sub>3</sub> and T<sub>4</sub>.<br />•The hypothalamic–pituitary–gonadal axis comprises hypothalamic gonadotropin–releasing hormone (GnRH), the anterior pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the gonadal steroids.}}</ref> that controls reactions to [[stress (medicine)|stress]] and regulates many body processes, including [[digestion]], [[immune response]]s, [[Mood (psychology)|mood]] and [[emotion]]s, [[Human sexual activity|sexual activity]], and energy storage and expenditure. It is the common mechanism for interactions among [[gland]]s, [[hormone]]s, and parts of the [[midbrain]] that mediate the [[general adaptation syndrome]] (GAS).<ref>{{cite book |last=Selye |first=Hans |title=Stress without distress |year=1974 |publisher=Lippincott |location=Philadelphia |isbn=978-0-397-01026-4 |url-access=registration |url=https://archive.org/details/stresswithoutdis00sely}}{{page needed|date=April 2014}}</ref>

While [[steroid]] [[hormone]]s are produced mainly in [[vertebrate]]s, the [[physiological]] role of the HPA axis and [[corticosteroid]]s in stress response is so fundamental that [[analogous]] systems can be found in [[invertebrate]]s and [[Unicellular organism|monocellular]] organisms as well.

The HPA axis, [[hypothalamic–pituitary–gonadal axis|hypothalamic–pituitary–gonadal (HPG) axis]], [[hypothalamic–pituitary–thyroid axis|hypothalamic–pituitary–thyroid (HPT) axis]], and the [[hypothalamic–neurohypophyseal system]] are the four major [[Neuroendocrine cell|neuroendocrine]] systems through which the [[hypothalamus]] and [[Pituitary gland|pituitary]] direct [[Neuroendocrine cell|neuroendocrine]] function.<ref name="NHM-Neuroendocrine systems" />