What type of cells compose the adrenal medulla?

The adrenal medulla is primarily composed of neural crest-derived chromaffin cells, which are specialized neuroendocrine cells. These chromaffin cells are responsible for the production and secretion of catecholamines, such as epinephrine and norepinephrine, which play critical roles in the body's response to stress and the fight-or-flight mechanism.

During embryonic development, neural crest cells migrate to various locations in the body, including the adrenal glands. Within the adrenal medulla, these cells differentiate into chromaffin cells, which are unique in that they can release hormones directly into the bloodstream in response to sympathetic nervous system stimulation.

The other cell types listed do not compose the adrenal medulla. Endothelial cells line blood vessels, adipocytes are specialized for fat storage and are found primarily in adipose tissue, and medullary epithelial cells do not exist as a defined type in the context of the adrenal medulla. Therefore, the presence of chromaffin cells is fundamental to the adrenal medulla’s function and its role in the endocrine system.