Adrenal medulla: The inner portion of adrenal gland. (The outer portion is the adrenal cortex).
The adrenal medulla makes epinephrine (adrenaline) and norepinephrine (noradrenaline). Epinephrine is secreted in response to low blood levels of glucose as well as exercise and stress; it causes the breakdown of the storage product glycogen to the sugar glucose in the liver, facilitates the release of fatty acids from adipose (fat) tissue, causes dilation (widening) of the small arteries within muscle and increases the output of the heart. Norepinephrine secreted by the adrenal gland acts to narrow blood vessels and raise blood pressure.
Underfunction of the adrenal medulla is virtually unknown. However, a tumor called a pheochromocytoma produces norepinephrine and epinephrine and is equivalent to overfunction of the adrenal medulla. Pheochromocytomas arise within the adrenal medulla or elsewhere in the sympathetic nervous system. They typically cause hypertension (high blood pressure) that may be paroxysmal (sharply episodic) with attacks of headaches, feelings of apprehension, sweating, flushing of the face, nausea and vomiting, palpitations and tingling of the extremities (the arms and legs).