Hypothalamic-pituitary-adrenal axis

General Information
Latin
Greek
TA98
TA2
FMA
Details
System	Endocrine system
Artery
Vein
Nerve
Lymphatic drainage
Precursor
Function	Stress response, hormone regulation
Identifiers
Clinical significance
Notes

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 (a pea-shaped structure located below the hypothalamus), and the adrenal glands (small, conical organs on top of the kidneys).

Function

The HPA axis is 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. It is the common mechanism for interactions among glands, hormones, and parts of the midbrain that mediate the general adaptation syndrome.

Mechanism

The HPA axis involves the following sequence of events:

1. The hypothalamus releases corticotropin-releasing hormone (CRH) in response to stress.
2. CRH stimulates the anterior pituitary gland to secrete adrenocorticotropic hormone (ACTH).
3. ACTH travels through the bloodstream to the adrenal cortex, where it stimulates the release of cortisol.

Cortisol, a glucocorticoid hormone, plays a role in the body's response to stress by increasing blood sugar, suppressing the immune system, and aiding in the metabolism of fat, protein, and carbohydrates. It also provides negative feedback to the hypothalamus and pituitary to decrease the release of CRH and ACTH, thus regulating the system.

Clinical significance

Dysregulation of the HPA axis has been implicated in numerous health conditions, including depression, anxiety disorders, chronic fatigue syndrome, fibromyalgia, and post-traumatic stress disorder (PTSD). Understanding the HPA axis is crucial for developing treatments for these conditions.

See also

• Endocrine system
• Stress (biology)
• Cortisol
• Adrenal gland