Ninety percent of medullary cells are the epinephrine-secreting type, and 10% are the norepinephrine-secreting type. These cells are innervated by preganglionic autonomic nerve fibers from the central nervous system. Separate dopamine-secreting cells have not been identified. The adrenal medulla contains large, irregularly shaped cells that are closely associated with blood vessels. Morphologically, two types of medullary cells can be distinguished: epinephrine-secreting cells, which have larger, less dense granules, and norepinephrine-secreting cells, which have smaller, very dense granules. It is divided into three separate zones: zona glomerulosa, zona fasciculata and zona reticularis.

The granules contain the catecholamines epinephrine and norepinephrine. The adrenal cortex is the outer region and also the largest part of an adrenal gland. It does so via excitation of the intermediolateral cell column (IML) in the spinal cord, which stimulates the adrenal medulla to release epinephrine and. Histologically, these cells and granules have a high affinity for chromium salts ( chromaffin reaction) and thus are called chromaffin cells and contain chromaffin granules. Medullary parenchymal cells accumulate and store their hormone products in prominent, dense secretory granules, 150–350 nm in diameter. This relationship is analogous to the other sympathetic ganglia, which connect preganglionic cholinergic sympathetic nerve fibers with postganglionic fibers using catecholamines (mainly norepinephrine) as neurotransmitters. The adrenal medulla can be regarded as a specialized sympathetic ganglion, in which preganglionic sympathetic nerve fibers (using acetylcholine as a neurotransmitter) directly make contact with postganglionic cells, which secrete catecholamines (mainly epinephrine) directly into the circulation. The adrenal medulla is mainly responsible for the synthesis of the catecholamines, adrenaline and noradrenaline, but also has other secretory functions such. Medullary cells are innervated by cholinergic preganglionic nerve fibers that reach the gland via the splanchnic nerves.

Embryologically, the adrenal medullary cells derive from neural crest cells. The adrenal medulla is made up of polyhedral cells arranged in cords or clumps.

Secretion of adrenal medulla