HPA Axis
The Hypothalamic–Pituitary–Adrenal (HPA) axis is a complex neuroendocrine system that regulates the body’s response to stress and maintains physiological homeostasis by controlling hormone release and feedback among three key components: the hypothalamus, the pituitary gland, and the adrenal glands123.
Components and Function
- Hypothalamus: Located below the thalamus in the brain, it produces corticotropin-releasing hormone (CRH) and vasopressin in response to stress signals13. CRH is released into the hypophyseal portal system to stimulate the pituitary.
- Pituitary Gland: The anterior pituitary responds to CRH and vasopressin by secreting adrenocorticotropic hormone (ACTH) into the bloodstream13.
- Adrenal Glands: Situated atop the kidneys, the adrenal cortex responds to ACTH by producing glucocorticoids, primarily cortisol in humans13. Cortisol mobilizes energy by increasing glucose availability and modulates many body systems including immune responses, mood, digestion, and cardiovascular function.
Regulation and Feedback
- Cortisol exerts negative feedback on both the hypothalamus and pituitary to suppress further CRH and ACTH release, thus regulating the stress response and maintaining balance16.
- Cortisol acts on mineralocorticoid and glucocorticoid receptors widely expressed in the brain and peripheral tissues1.
Physiological Roles
- Mediates the stress response, enabling the body to adapt to physical and psychological stressors.
- Regulates metabolism, immune function, mood, energy storage and expenditure, digestion, and sexual function123.
- Involved in the general adaptation syndrome (GAS), the body’s overall response to stress1.
Clinical Relevance
- Dysregulation of the HPA axis is implicated in various disorders including depression, anxiety, PTSD, metabolic syndrome, and immune dysfunction28.
- Abnormal development or chronic disruption during fetal life can predispose to neurodevelopmental and psychiatric conditions later in life2.
Summary Table
| Component | Role |
|---|---|
| Hypothalamus | Releases CRH and vasopressin to stimulate pituitary |
| Pituitary Gland | Secretes ACTH in response to CRH and vasopressin |
| Adrenal Glands | Produce cortisol, which mobilizes energy and regulates body functions |
| Feedback Mechanism | Cortisol inhibits hypothalamus and pituitary to regulate hormone levels |
| Main Function | Regulates stress response and maintains homeostasis |
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References
- Wikipedia: Hypothalamic–pituitary–adrenal axis
https://en.wikipedia.org/wiki/Hypothalamic%E2%80%93pituitary%E2%80%93adrenal_axis - Pariante CM. The Hypothalamic-Pituitary-Adrenal Axis – PubMed Central
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7838595/ - Verywell Health: Hypothalamic-Pituitary-Adrenal (HPA) Axis
https://www.verywellhealth.com/hypothalamic-pituitary-adrenal-hpa-axis-5222557 - 2-Minute Neuroscience: HPA Axis – YouTube
https://www.youtube.com/watch?v=QAeBKRaNri0 - Introduction to the Hypothalamic-Pituitary-Adrenal Axis: Healthy and … – PMC
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6057754/
The HPA axis is a critical regulatory system integrating neural and endocrine signals to coordinate the body’s response to stress and maintain internal balance.
