Final answer:
A pheochromocytoma is a catecholamine-producing tumor of the adrenal medulla that can cause hypertension. The adrenal medulla is the inner part of the adrenal gland that releases catecholamines in response to sympathetic nervous system activation.
Step-by-step explanation:
A pheochromocytoma is a tumor of the adrenal medulla and sympathetic ganglion (from chromaffin cell lines) that produces catecholamines. The adrenal medulla is part of the adrenal glands situated above the kidneys and is responsible for the production of adrenaline (epinephrine) and noradrenaline (norepinephrine), which are chemically classified as catecholamines. These are neuroendocrine cells that release these hormones into the bloodstream as part of the sympathetic system activity, particularly during the fight-or-flight response. The overproduction of catecholamines by tumors such as pheochromocytomas can lead to symptoms like hypertension due to their widespread effect on various organ systems.