HPA Axis: Overview and Function

Introduction:

• The hypothalamic-pituitary-adrenal (HPA) axis plays a crucial role in the body's reaction to stress.
• It includes hormone-secreting glands from both the nervous and endocrine systems:
  • Hypothalamus
  • Pituitary gland
  • Adrenal glands

Components and Functions:

Hypothalamus:

• A small neuroendocrine structure located above the brainstem.
• Controls hormone release from the pituitary gland.

Pituitary Gland:

• Sits just below the hypothalamus.
• Releases hormones into the bloodstream to reach various targets.
  • In the HPA axis, hormones influence adrenal glands.

Adrenal Glands:

• Located on top of the kidneys.
• Endocrine glands that secrete hormones as influenced by the pituitary gland.

Stress Response Regulation:

• Primary Function: Regulate the body's stress response.

Hormonal Cascade:

1. Stress Trigger:
   • Hypothalamus releases corticotropin-releasing hormone (CRH).
2. CRH Effect:
   • Signals the pituitary gland to secrete adrenocorticotropic hormone (ACTH) into the bloodstream.
3. ACTH Effect:
   • Travels to the adrenal glands.
   • Prompts the release of cortisol from the adrenal cortex.

Effects of Cortisol:

• Mobilizes energy (e.g., glucose) to cope with prolonged stressors.

Negative Feedback Mechanism:

• High cortisol levels are detected by receptors in the brain.
  • Specifically in the hypothalamus and hippocampus.
• Results in the shutting off of the stress response.

Conclusion:

• The HPA axis plays a vital role in managing stress through a well-coordinated hormonal cascade.
• The negative feedback mechanism ensures that the stress response is regulated and not excessive.