chromaffin cells
Summary
Chromaffin cells are neuroendocrine cells located primarily in the adrenal medulla that synthesize, store, and secrete catecholamines (epinephrine and norepinephrine) in response to sympathetic stimulation. They are derived from neural crest cells and function as modified postganglionic sympathetic neurons. They stain brown with chromium salts (chromaffin reaction), hence their name.
Detail
Chromaffin cells are specialized neuroendocrine cells found mainly in the adrenal medulla, with smaller collections in extra-adrenal paraganglia (organ of Zuckerkandl). Embryologically derived from neural crest cells, they are essentially modified postganglionic sympathetic neurons that have lost their axons and dendrites, instead secreting neurotransmitters directly into the bloodstream as hormones. They are innervated by preganglionic sympathetic fibers (cholinergic, via nicotinic ACh receptors), representing a unique exception where only one neuron separates the CNS from the effector organ (unlike typical two-neuron sympathetic pathways). Upon stimulation, chromaffin cells release epinephrine (~80%) and norepinephrine (~20%) from storage granules via calcium-dependent exocytosis. These catecholamines mediate the 'fight-or-flight' response—increasing heart rate, blood pressure, glycogenolysis, lipolysis, and bronchodilation while decreasing GI motility. Clinically, chromaffin cells are the origin of pheochromocytoma, a catecholamine-secreting tumor causing episodic hypertension, headache, palpitations, and diaphoresis (classic triad). Pheochromocytomas follow the 'rule of 10s' and are associated with MEN 2A/2B, von Hippel-Lindau disease, and neurofibromatosis type 1. Diagnosis involves measuring plasma free metanephrines or 24-hour urine metanephrines/catecholamines. The chromaffin reaction (brown-black staining with potassium dichromate) reflects oxidation of catecholamines and is used histologically to identify these cells. Extra-adrenal paragangliomas can also arise from chromaffin-like cells in sympathetic ganglia.
Sources
- First Aid for the USMLE Step 1
- Guyton and Hall Textbook of Medical Physiology
- Robbins and Cotran Pathologic Basis of Disease
- Junqueira's Basic Histology
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