What hormone is exclusively secreted by the adrenal medulla (adrenal gland's inner part)?

Hormones Exclusively Secreted by the Adrenal Medulla

Adrenaline (epinephrine) is the only hormone exclusively secreted by the adrenal medulla. 1

Adrenal Gland Anatomy and Hormone Production

The adrenal gland consists of two distinct parts with different developmental origins, functions, and hormone production:

1. Adrenal Medulla (inner portion):

   • Derived from neural crest cells
   • Part of the sympathetic nervous system
   • Secretes catecholamines:
     • Epinephrine (adrenaline) - exclusively produced here 1, 2
     • Norepinephrine (noradrenaline) - also produced by sympathetic nerve endings

2. Adrenal Cortex (outer portion):

   • Derived from mesoderm
   • Divided into three zones that produce steroid hormones:
     • Zona glomerulosa: Mineralocorticoids (aldosterone)
     • Zona fasciculata: Glucocorticoids (cortisol)
     • Zona reticularis: Androgens

Why Epinephrine Is Exclusively Adrenal Medullary

Epinephrine is synthesized from norepinephrine through the action of phenylethanolamine N-methyltransferase (PNMT), an enzyme found almost exclusively in adrenal medullary chromaffin cells 1. The unique juxtaposition of the adrenal medulla to the cortex exposes the medulla to high concentrations of glucocorticoids, which induce PNMT expression and enable epinephrine synthesis 1.

Ruling Out Other Options

• Androgen (option B): Produced by the adrenal cortex (zona reticularis) and gonads, not the adrenal medulla 3

• Aldosterone (option C): Produced by the adrenal cortex (zona glomerulosa), not the adrenal medulla 3

• Antidiuretic hormone (ADH) (option D): Produced by the hypothalamus and stored/released by the posterior pituitary, not the adrenal gland 4

• Cortisol (option E): Produced by the adrenal cortex (zona fasciculata), not the adrenal medulla 3

Clinical Relevance

In the case presented (a 30-year-old man with excessive sweating and an adrenal mass), the findings suggest a possible pheochromocytoma - a tumor of the adrenal medulla that produces excessive catecholamines, including epinephrine 4. These tumors can cause symptoms related to catecholamine excess such as:

• Hypertension
• Sweating
• Headaches
• Palpitations
• Anxiety

Pheochromocytomas are rare tumors with an estimated incidence of 2-8 per million per year 4. They require careful evaluation and management due to the potential for life-threatening complications from catecholamine excess.

Diagnostic Approach for Suspected Adrenal Medullary Tumors

For suspected pheochromocytoma, diagnostic testing includes:

• Measurement of plasma-free or urinary-fractionated metanephrines 4
• Imaging studies (CT, MRI) of the adrenal glands 4
• Genetic testing for hereditary syndromes associated with pheochromocytoma 4

The distinction between adrenal medullary and cortical hormones is critical for proper diagnosis and management of adrenal pathology.