Explain HPA axis. Draw a transverse section of the Adrenal gland and describe the functions of its different hormones. (IAS 2018/15 Marks)

HPA Axis (Hypothalamic-Pituitary-Adrenal Axis)

• The HPA axis is a complex network involving the hypothalamus, pituitary gland, and adrenal glands. It regulates stress response, immunity, mood, and energy metabolism.
• Components:
  
  • Hypothalamus: Releases corticotropin-releasing hormone (CRH) in response to stress.
  • Pituitary Gland: Secretes adrenocorticotropic hormone (ACTH) upon stimulation by CRH.
  • Adrenal Glands: Produce glucocorticoids (e.g., cortisol) when activated by ACTH.
• Functions:
  
  • Regulates the body’s response to stress by releasing cortisol.
  • Controls metabolic processes like glucose production.
  • Maintains homeostasis during physical or emotional stress.

Transverse Section of the Adrenal Gland

Diagram:

A transverse section shows the adrenal gland with two distinct regions:

• Cortex (outer region):
  
  • Zona glomerulosa
  • Zona fasciculata
  • Zona reticularis
• Medulla (inner region): Contains chromaffin cells.

Functions of Adrenal Gland Hormones

1. Hormones from the Cortex

• Zona Glomerulosa (Mineralocorticoids):
  
  • Hormone: Aldosterone.
  • Function: Regulates sodium and potassium balance, and maintains blood pressure.
• Zona Fasciculata (Glucocorticoids):
  
  • Hormone: Cortisol.
  • Function: Controls glucose metabolism, reduces inflammation, and manages stress.
• Zona Reticularis (Androgens):
  
  • Hormone: Dehydroepiandrosterone (DHEA).
  • Function: Precursors for sex hormones, supports secondary sexual characteristics.

2. Hormones from the Medulla

• Catecholamines:
  
  • Hormones: Adrenaline (epinephrine) and Noradrenaline (norepinephrine).
  • Functions:
    
    • Prepare the body for “fight or flight” response.
    • Increase heart rate, blood flow, and glucose release.

Conclusion:

The HPA axis and the hormones produced by the adrenal gland play a crucial role in the body's response to stress and maintaining homeostasis. Understanding the functions of these hormones can help in managing stress and maintaining overall health and well-being.