HPA axis

(noun)

The body's system, comprised of the hypothalamus, pituitary gland, and adrenal gland, for stress regulation.

Related Terms

Examples of HPA axis in the following topics:

  • The Stress Response

    • The body's stress response is mediated by the sympathetic nervous system and the hypothalmic-pituitary-adrenal (HPA) axis.
    • The body's stress response is mediated by interplay between the sympathetic nervous system (SNS) and the hypothalmic-pituitary-adrenal (HPA) axis.
    • A feedback loop exists among the components of the HPA axis and the SNS.
    • The paraventricular nucleus of the hypothalmus contains neuroendocrine neurons which synthesize and release vasopressin—a hormone which acts in the HPA axis as a vasoconstrictor—and corticotropin releasing hormone (CRH).
    • Glucocorticoids of the HPA axis have many important functions, including modulation of stress reactions, but in excess they may be damaging.

  • The Endocrine System and Stress

    • In experimental studies in rats, a distinction is often made between social stress and physical stress, but both types activate the HPA axis, albeit through different pathways.
    • The hypothalamic-pituitary-adrenal (HPA or HTPA) axis is a complex set of direct influences and steroid-producing feedback interactions among the hypothalamus, the pituitary gland, and the adrenal glands.
    • Antidepressants work by reglulating the HPA axis.
    • In the process described above, the HPA axis ultimately produces cortisol.
    • Studies on people show that the HPA axis is activated in different ways during chronic stress—depending on the type of stressor, the person's response to the stressor, and other factors.

  • The Endocrine System

    • The hypothalamic-pituitary-adrenal axis (HPA or HTPA axis) is a complex set of direct influences and feedback interactions among the hypothalamus, the pituitary gland, and the adrenal glands.
    • The interactions among these glands constitute the HPA axis, a major part of the neuroendocrine system that controls reactions to stress and regulates many body processes, including digestion, the immune system, mood and emotions, sexuality, and energy storage and expenditure.
    • While steroid hormones are produced mainly in vertebrates, the physiological role of the HPA axis and corticosteroids in stress response is so fundamental that analogous systems can be found in invertebrates and monocellular organisms as well.

  • How the Body Responds to Stress

    • The main physiological structure involved in this response is known as the HPA (hypothalamic–pituitary gland–adrenal gland) axis.
    • The HPA axis coordinates all these physiological changes.
    • The hypothalamic–pituitary–adrenal axis (HPA axis) is a complex set of direct influences and feedback interactions among three endocrine glands: the hypothalamus, the pituitary gland, and the adrenal glands.
    • The HPA axis is a major part of the neuroendocrine system that, among other things, controls reactions to stress.
    • The HPA system reacts within a person's brain, and it releases the hormone cortisol from the adrenal gland when a person is exposed to a stressor.

  • Posttraumatic Stress Disorder (PTSD)

    • These findings suggest abnormality in the hypothalamic-pituitary-adrenal (HPA) axis .
    • The HPA axis is a major biological mechanism of stress and stress response

  • Stress and Disease

    • In depression, the hypothalamic-pituitary-adrenal (HPA) axis is up-regulated with a down-regulation of its negative feedback controls.
    • This leads to continual activation of the HPA axis and excess cortisol release.

  • The Resistance Reaction

    • There is also some activation of the HPA axis, producing glucocorticoids such as cortisol.

  • Regional Terms and Axes

    • The Dorsoventral axis (DV axis) is formed by the connection of the dorsal and ventral points of a region.
    • The Anterioposterior axis (AP axis) is the axis formed by the connection of the anterior (top) and posterior (bottom) ends of a region.
    • The AP axis of a region is by definition perpendicular to the DV axis and vice-versa.
    • The Left-to-right axis is the axis connecting the left and right hand sides of a region.
    • Axis (A) (in red) shows the AP axis of the tail, (B) shows the AP axis of the neck, and (C) shows the AP axis of the head.

  • Symmetry of Functions

    • Functions and relations can be symmetric about a point, a line, or an axis.  
    • The image below shows an example of a function and its symmetry over the $x$-axis (vertical reflection) and over the $y$-axis (horizontal reflection).  
    • The axis splits the U-shaped curve into two parts of the curve which are reflected over the axis of symmetry.  
    • Notice that the $x$-intercepts are reflected points over the axis of symmetry and are equidistant from the axis.
    • This type of symmetry is a translation over an axis.

  • Standard Equations of Hyperbolas

    • Consistent with the symmetry of the hyperbola, if the transverse axis is aligned with the x-axis, the slopes of the asymptotes are equal in magnitude but opposite in sign, ±b⁄a, where b=a×tan(θ) and where θ is the angle between the transverse axis and either asymptote.
    • A conjugate axis of length 2b, corresponding to the minor axis of an ellipse, is sometimes drawn on the non-transverse principal axis; its endpoints ±b lie on the minor axis at the height of the asymptotes over/under the hyperbola's vertices.
    • If the transverse axis of any hyperbola is aligned with the x-axis of a Cartesian coordinate system and is centered on the origin, the equation of the hyperbola can be written as:
    • The perpendicular thin black line through the center is the conjugate axis.
    • The two thick black lines parallel to the conjugate axis (thus, perpendicular to the transverse axis) are the two directrices, D1 and D2.