Which adrenal gland cell type secretes catecholamines and what is the typical proportion of epinephrine to norepinephrine?

• A. Chromaffin cells, about 80% epinephrine and 20% norepinephrine
• B. Chromaffin cells, about 50% epinephrine and 50% norepinephrine
• C. Adrenal cortex cells, 80% epinephrine and 20% norepinephrine
• D. Chromaffin cells, about 90% epinephrine and 10% norepinephrine

Answer: (A)

Catecholamines come from the adrenal medulla’s chromaffin cells, which are innervated by preganglionic sympathetic fibers and respond to sympathetic signals. These cells release mostly epinephrine, with about 80% epinephrine and 20% norepinephrine in humans. The adrenal cortex does not secrete catecholamines; it makes steroids like cortisol, aldosterone, and androgens. The higher epinephrine proportion comes from the activity of PNMT (phenylethanolamine N-methyltransferase) in chromaffin cells, which converts norepinephrine to epinephrine, and is upregulated by cortisol from the cortex. While the 80/20 distribution is typical in humans, the exact ratio can vary in different species or conditions.