The adrenal medulla converts norepinephrine to epinephrine using the enzyme phenylethanolamine N-methyltransferase (PNMT). What feature of adrenal anatomy allows cortical steroids to regulate this medullary enzyme?

• A A venous portal system carrying cortisol-rich blood from cortex to medulla ✓
• B Shared chromaffin and fasciculata cells arising from a common neural crest precursor
• C Direct sympathetic innervation delivering ACTH to medullary chromaffin cells
• D Countercurrent exchange between medullary capillaries and zona reticularis sinusoids

Explanation

Blood flows centripetally through the cortex and drains through a venous portal system into the medulla, exposing chromaffin cells to very high cortisol concentrations. Cortisol induces PNMT expression, which is why epinephrine is produced almost exclusively in the adrenal medulla and extra-adrenal chromaffin tissue secretes mostly norepinephrine. The medulla receives preganglionic sympathetic innervation, not ACTH delivery, and both tissues derive from separate embryologic origins.

Reference: Ganong Review of Medical Physiology, 26th ed.

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