Either of two small triangular endocrine glands located on top of the kidneys. In humans, each gland weighs about 0.18 oz (5 g) and consists of an inner medulla, which produces the catecholamine hormones epinephrine and norepinephrine, and an outer cortex (about 90percnt of the gland), which secretes the steroid hormones aldosterone, cortisol, and androgens (the last two in response to ACTH from the pituitary gland). Diseases of the adrenal glands include pheochromocytoma (a tumour of the medulla) and the cortical disorders Addison disease, adrenal hypertrophy, Cushing syndrome, and primary aldosteronism.
Learn more about adrenal gland with a free trial on Britannica.com.
In mammals, the adrenal glands (also known as suprarenal glands) are the triangle-shaped endocrine glands that sit on top of the kidneys; their name indicates that position (ad-, "near" or "at" + -renes, "kidneys"; and as concerns supra-, meaning "above"). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline.
The adrenal gland is separated into two distinct structures, both of which receive regulatory input from the nervous system:
The adrenal glands and the thyroid gland are the organs that have the greatest blood supply per gram of tissue. Up to 60 arterioles may enter each adrenal gland.