A 36-year-old woman comes to

the doctor with a usual problem. More and more often, she suffers from attacks

of tachycardia (high heart rate), accompanied by palpitations (often

irregular), and also by increased sweating and flushing, which her colleagues

at work have noticed. The doctor measures her blood pressure and it was quite

high. A blood test then reveals elevated levels of metanephrines (metabolites

of catecholamines). A subsequent CT scan confirms tumour in her right adrenal

gland. This is most likely a pheochromocytoma, a tumour of the chromaffin cells

(pheochromocytes) of the adrenal medulla from which catecholamines are released

into the body in a paroxysmal fashion. What is the origin of adrenal medulla

and how would you classify its tissue?