Adrenal gland

Article By:

Kemppainen, Robert J. Department of Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, Alabama.

Last reviewed:March 2021

DOI:https://doi.org/10.1036/1097-8542.011700

A complex endocrine organ in proximity to the kidney. The adrenal gland (see illustration), often called simply as the adrenal, is an important endocrine organ located on top of the kidneys. Adrenal gland tissue is present in all vertebrates from cyclostomes to placental mammals. In particular, adrenal glands occur as paired organs in mammals, most birds, and most reptiles. Structurally, the adrenal consists of two functionally distinct tissues: steroidogenic cells of mesodermal origin and neural crest–derived catecholamine-secreting cells. Whereas "adrenal" refers to the gland's proximity to the kidney, significant variation exists among vertebrates in its anatomic location and the relationship of the two endocrine tissues that make up the gland. In mammals, steroidogenic cells are separated into distinct zones that together form a cortex. This cortical tissue surrounds the catecholamine-secreting cells, constituting the medulla. In most other vertebrates, this unique anatomic cortical-medullary relationship is not present. In species of amphibians and fish, adrenal cells are found intermingling with kidney tissue, and the steroidogenic cells are often termed interrenal tissue. Malfunctions of the paired adrenal glands are most often characterized by abnormal hormone secretion. See also: Adrenal gland disorders; Endocrine mechanisms; Endocrine system (vertebrate); Endocrinology; Gland; Hormone; Kidney

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