Structure and Location

The adrenal glands (also called suprarenal glands) are triangular-shaped endocrine organs situated atop each kidney. Each gland consists of two distinct structures:

• The outer adrenal cortex
• The inner adrenal medulla

Adrenal Cortex

The cortex comprises three layers, each producing different hormones:

1. Zona Glomerulosa

   • Produces mineralocorticoids, primarily aldosterone
   • Regulates sodium and potassium balance
   • Influences blood pressure

2. Zona Fasciculata

   • Secretes glucocorticoids, mainly cortisol
   • Essential for stress response
   • Regulates metabolism

3. Zona Reticularis

   • Produces androgens
   • Contributes to secondary sexual characteristics

Adrenal Medulla

The medulla produces catecholamines, primarily:

• epinephrine (adrenaline)
• norepinephrine (noradrenaline)

These hormones are crucial for the "fight-or-flight" response, working with the sympathetic nervous system.

Clinical Significance

Several conditions can affect adrenal function:

• Addison's disease (adrenal insufficiency)
• Cushing's syndrome (excess cortisol)
• Pheochromocytoma (tumor of the adrenal medulla)

Regulation

The adrenal glands are primarily regulated by:

• hypothalamus
• pituitary gland
• renin-angiotensin system

Through complex feedback loops, these systems maintain precise hormone levels essential for homeostasis.

Evolutionary Perspective

The adrenal glands demonstrate remarkable conservation across vertebrate species, highlighting their fundamental role in survival and stress response. Their development is closely tied to the evolution of the vertebrate endocrine system.