Editing Hypothalamic–pituitary–adrenal axis (section)

==Anatomy==
The key elements of the HPA axis are:<ref>{{Cite web |date=2015-05-18 |title=Getting to know the HPA axis |url=https://www.nrdc.org/bio/kristi-pullen-fedinick/getting-know-hpa-axis |access-date=2023-08-08 |website=www.nrdc.org |language=en |archive-date=2023-08-10 |archive-url=https://web.archive.org/web/20230810072553/https://www.nrdc.org/bio/kristi-pullen-fedinick/getting-know-hpa-axis |url-status=live }}</ref>
* The [[paraventricular nucleus]] of the [[hypothalamus]]: It contains [[neuroendocrine]] [[neuron]]s which synthesize and secrete [[vasopressin]] and [[corticotropin-releasing hormone]] (CRH).
* The [[Anterior pituitary|anterior lobe]] of the [[pituitary gland]]: CRH and vasopressin stimulate the anterior lobe of pituitary gland to secrete [[adrenocorticotropic hormone]] (ACTH), once known as [[Corticotropin-releasing hormone|corticotropin]].
* The [[adrenal cortex]]: It produces [[glucocorticoid]] hormones (mainly [[cortisol]] in humans) in response to stimulation by ACTH. Glucocorticoids in turn, act back on the hypothalamus and pituitary (to suppress CRH and ACTH production) in a [[negative feedback]] cycle.

[[Corticotropin-releasing hormone|CRH]] and [[vasopressin]] are released from [[Neurosecretion|neurosecretory]] nerve terminals at the [[median eminence]]. CRH is transported to the anterior pituitary through the [[Portal venous system|portal blood vessel system]] of the [[Hypophysial stalk|hypophyseal stalk]] and vasopressin is transported by [[axon]]al transport to the [[posterior pituitary|posterior pituitary gland]]. There, CRH and vasopressin act synergistically to stimulate the secretion of stored ACTH from corticotrope cells. ACTH is transported by the [[blood]] to the [[adrenal cortex]] of the [[adrenal gland]], where it rapidly stimulates the biosynthesis of [[corticosteroid]]s such as [[cortisol]] from [[cholesterol]]. Cortisol is a major stress hormone and has effects on many tissues in the body, including the brain. In the brain, cortisol acts on two types of receptors: [[mineralocorticoid receptor]]s and [[glucocorticoid]] receptors, and these are expressed by many different types of neurons. One important target of glucocorticoids is the [[hypothalamus]], which is a major controlling centre of the HPA axis.<ref>{{Cite journal |last1=Tasker |first1=Jeffrey G. |last2=Herman |first2=James P. |date=14 July 2011 |title=Mechanisms of rapid glucocorticoid feedback inhibition of the hypothalamic–pituitary–adrenal axis |journal=Stress |volume=14 |issue=4 |pages=398–406 |doi=10.3109/10253890.2011.586446 |pmid=21663538 |pmc=4675656 }}</ref>

Vasopressin can be thought of as "water conservation hormone" and is also known as "[[antidiuretic]] hormone(ADH)". It is released when the body is [[Dehydration|dehydrated]] and has potent water-conserving effects on the kidney. It is also a potent [[vasoconstrictor]].<ref>{{Citation|last1=Cuzzo|first1=Brian|title=Vasopressin (Antidiuretic Hormone, ADH)|date=2019|url=http://www.ncbi.nlm.nih.gov/books/NBK526069/|work=StatPearls|publisher=StatPearls Publishing|pmid=30252325|access-date=2019-10-19|last2=Lappin|first2=Sarah L.|archive-date=2021-03-25|archive-url=https://web.archive.org/web/20210325180413/https://www.ncbi.nlm.nih.gov/books/NBK526069/|url-status=live}}</ref>

Important to the function of the HPA axis are some of the following feedback loops:
* [[Cortisol]] produced in the adrenal cortex will negatively feedback to inhibit both the hypothalamus and the pituitary gland. This reduces the [[secretion]] of CRH and vasopressin, and also directly reduces the cleavage of [[proopiomelanocortin]] (POMC) into ACTH and β-endorphins.
* [[Epinephrine]] and [[norepinephrine]] (E/NE) are produced by the [[adrenal medulla]] through [[Sympathetic nervous system|sympathetic]] stimulation and the local effects of cortisol (upregulation enzymes to make E/NE). E/NE will positively feedback to the pituitary and increase the breakdown of POMCs into ACTH and β-endorphins.