Adrenal Cortical Hormone Production and Sites of Action
Zonal Organization and Hormone Production
The adrenal cortex is anatomically and functionally divided into three distinct zones, each producing specific steroid hormones: the zona glomerulosa produces mineralocorticoids (aldosterone), the zona fasciculata produces glucocorticoids (cortisol), and the zona reticularis produces adrenal androgens (DHEA and androstenedione). 1, 2
Zona Glomerulosa (Outermost Layer)
- Hormone produced: Aldosterone (the primary and most potent mineralocorticoid)
- Primary regulators: Angiotensin II (via AT1 receptors) and elevated serum potassium (hyperkalemia) 3
- Mechanism: Angiotensin II activates two pathways: (1) Gq/11 proteins that increase intracellular calcium, and (2) β-arrestin-mediated sustained ERK activation, both upregulating StAR protein for aldosterone synthesis 3
Zona Fasciculata (Middle Layer)
- Hormone produced: Cortisol (the primary glucocorticoid)
- Primary regulator: ACTH from the pituitary gland
- Feedback mechanism: Cortisol exerts negative feedback on both hypothalamic CRH and pituitary ACTH production 4
Zona Reticularis (Innermost Layer)
- Hormones produced: DHEA and androstenedione (adrenal androgen precursors)
- Primary regulator: ACTH
- Clinical note: This zone fully develops at puberty during adrenarche 1
Sites of Action
Mineralocorticoids (Aldosterone)
- Primary target: Distal renal tubules and collecting ducts
- Action: Promotes sodium reabsorption and potassium excretion, regulating blood pressure and electrolyte balance
- Clinical monitoring: Plasma renin activity in the upper reference range indicates appropriate mineralocorticoid dosing in replacement therapy 5
Glucocorticoids (Cortisol)
- Widespread systemic effects:
- Metabolic regulation (glucose, protein, and fat metabolism)
- Immune system modulation and anti-inflammatory actions
- Cardiovascular system (blood pressure maintenance)
- Stress response coordination
- HPA axis suppression: Prolonged supraphysiologic glucocorticoid exposure causes pituitary corticotroph atrophy and adrenal cortex atrophy through negative feedback 4
Adrenal Androgens (DHEA/Androstenedione)
- Conversion sites: Peripheral tissues and gonads convert these precursors to active sex steroids
- Neurosteroidal effects: DHEA has direct actions in the brain with potential antidepressive properties 5
- Clinical significance in women: Major source of androgen production, particularly important for libido, energy, and mood 5
Important Physiological Considerations
Integrated Cortical Function
The adrenal cortex functions as an integrated whole rather than autonomous zones. The zona glomerulosa may not possess the complete enzymatic machinery for independent aldosterone biosynthesis, suggesting inter-zonal cooperation 6. Local regulatory factors including cytokines, catecholamines, and the tissue renin-angiotensin system modulate systemic trophic hormone effects throughout the cortex 6.
Steroid Hormone Characteristics
Critical caveat: Due to their high lipophilicity, no adrenal steroid hormones are stored in vesicles. They are synthesized and secreted immediately upon cellular stimulation 3. This distinguishes them from peptide hormones and has important implications for acute stress responses and replacement therapy timing.
Centripetal Cell Migration
Adrenal cortex maintenance involves peripheral Sonic hedgehog-positive progenitor cells that differentiate into zona glomerulosa cells, then transition centripetally to zona fasciculata and subsequently zona reticularis cells 1. However, proliferation can occur throughout the gland, and zonal replenishment can happen within zones themselves 6.