Hypothalamic–pituitary–adrenal axis
<p >The <b>hypothalamic-pituitary-adrenal axis</b> (<b>HPA or HTPA axis</b>), also known as the <b><a href="http://en.wikipedia.org/wiki/Limbic" title="Limbic" class="mw-redirect" >limbic</a>-hypothalamic-pituitary-adrenal axis</b> (LHPA axis) and, occasionally, as the <b>hypothalamic-pituitary-adrenal-<a href="http://en.wikipedia.org/wiki/Gonadotropic" title="Gonadotropic" class="mw-redirect" >gonadotropic</a> axis</b>, is a complex set of direct influences and <a href="http://en.wikipedia.org/wiki/Feedback" title="Feedback" >feedback</a> interactions among the<a href="http://en.wikipedia.org/wiki/Hypothalamus" title="Hypothalamus" >hypothalamus</a>, the <a href="http://en.wikipedia.org/wiki/Pituitary_gland" title="Pituitary gland" >pituitary gland</a> (a pea-shaped structure located below the hypothalamus), and the <a href="http://en.wikipedia.org/wiki/Adrenal" title="Adrenal" class="mw-redirect" >adrenal</a> (also called "suprarenal") glands (small, conical organs on top of the kidneys).</p>
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The interactions among these organs constitute the <b>HPA axis</b>, a major part of the <a href="http://en.wikipedia.org/wiki/Neuroendocrinology" title="Neuroendocrinology" >neuroendocrine system</a> that controls reactions to <a href="http://en.wikipedia.org/wiki/Stress_(medicine)" title="Stress (medicine)" class="mw-redirect" >stress</a> and regulates many body processes, including <a href="http://en.wikipedia.org/wiki/Digestion" title="Digestion" >digestion</a>, the <a href="http://en.wikipedia.org/wiki/Immune_system" title="Immune system" >immune system</a>, mood and emotions, sexuality, and energy storage and expenditure. </p>
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A wide variety of species, from the most ancient organisms to humans, share components of the HPA axis<sup class="Template-Fact" >[<i><a href="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed" >citation needed</a></i>]</sup>. It is the common mechanism for interactions among glands, hormones, and parts of the midbrain that mediate the <a href="http://en.wikipedia.org/wiki/General_adaptation_syndrome" title="General adaptation syndrome" class="mw-redirect" >general adaptation syndrome</a> (GAS)<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Hypothalamic-pituitary-adrenal_axis#cite_note-0" >[1]</a></sup>. (see "Stress")</p>