In higher vertebrates, mesenchymal cells originating from the coelomic cavity near the genital ridge proliferate to form a cluster of cells destined to be the adrenal cortex. The adrenal gland forms from two primordia: cells of mesodermal origin which give rise to the steroid-secreting cells, and neural cells of ectodermal origin which develop into the catecholamine-secreting tissue (also known as chromaffin tissue). In species of amphibians and fish, adrenal cells are found intermingling with kidney tissue, and the steroidogenic cells are often termed interrenal tissue.

In most other vertebrates, this unique anatomic cortical-medullary relationship is not present. This cortical tissue surrounds the catecholamine-secreting cells, constituting the medulla. In mammals, steroidogenic cells are separated into distinct zones that together form a cortex. While “adrenal” refers to the gland's proximity to the kidney, significant variation exists among vertebrates in its anatomic location as well as the relationship of the two endocrine tissues which make up the gland. The adrenal consists of two functionally distinct tissues: steroidogenic cells and catecholamine-secreting cells. Adrenal gland tissue is present in all vertebrates. Adrenal glandĪ complex endocrine organ in proximity to the kidney. The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. The release of these hormones is stimulated when an animal is excited or frightened, causing increased heart rate, increased blood flow to the muscles, elevated blood sugar, dilation of the pupils of the eyes, and other changes that increase the body's ability to meet sudden emergencies.

The inner reddish portion (medulla) of the adrenal gland, which is not functionally related to the adrenal cortex, secretes epinephrine (adrenaline) and norepinephrine.

Artificial synthesis of the steroid hormones has made it possible to treat many conditions related to underactivity of the adrenal cortex, e.g., Addison's disease. The adrenal cortex controls metabolic processes that are essential to life and if it ceases to function death ensues within a few days. Steroid hormones also counteract inflammation and allergies and influence the secondary sex characteristics to a limited degree. Aldosterone regulates water and salt balance in the body its secretion is only slightly influenced by the pituitary. Cortisol regulates carbohydrate, protein, and fat metabolism, and its secretion is controlled by the output of adrenocorticotropic hormone (ACTH) from the pituitary gland. The outer yellowish layer (cortex) of the adrenal gland secretes about 30 steroid hormones, the most important of which are aldosterone and cortisol. Adrenal gland (ədrēnˈəl) or suprarenal gland (so͞oprərēnˈəl), endocrine gland (see endocrine system) about 2 in.

Medulla of adrenal gland secretes