Hypothalamic–pituitary–adrenal

Hypothalamic–pituitary–adrenal axis (HPA axis or HTPA axis) is a complex set of direct influences and feedback interactions among three components: the hypothalamus, the pituitary gland (a pea-shaped structure located below the brain), and the adrenal (or suprarenal) glands (small, conical organs on top of the kidneys).

Function

The HPA axis is an important part of the neuroendocrine system, controlling reactions to stress, regulation of digestion, the immune system, mood and emotions, sexuality, and energy storage and expenditure. It is the common mechanism for interactions among glands, hormones, and parts of the midbrain that mediate the general adaptation syndrome (GAS).

Components and effects

The key elements of the HPA axis are:

• Corticotropin-releasing hormone (CRH)
• Adrenocorticotropic hormone (ACTH)
• Cortisol (a glucocorticoid)

CRH is released from the hypothalamus, which stimulates the release of ACTH from the pituitary gland. ACTH then stimulates the release of cortisol from the adrenal glands. Cortisol is involved in a negative feedback loop with the hypothalamus and pituitary gland, which means that cortisol levels control the release of CRH and ACTH.

Clinical significance

Dysregulation of the HPA axis is associated with numerous stress-related disorders, including Cushing's syndrome, Addison's disease, and post-traumatic stress disorder (PTSD).

See also

• Hypothalamic–pituitary–gonadal axis
• Hypothalamic–pituitary–thyroid axis

References

Hypothalamic–pituitary–adrenal Resources
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