adrenal gland or suprarenal gland, endocrine gland (see endocrine system) about 2 in. (5.1 cm) long situated atop each kidney. The outer yellowish layer (cortex) of the adrenal gland secretes about 30 steroid hormones, the most important of which are aldosterone and cortisol. Cortisol regulates carbohydrate, protein, and fat metabolism, and its secretion is controlled by the output of adrenocorticotropic hormone (ACTH) from the pituitary gland. Aldosterone regulates water and salt balance in the body; its secretion is only slightly influenced by the pituitary. Steroid hormones also counteract inflammation and allergies and influence the secondary sex characteristics to a limited degree. The adrenal cortex controls metabolic processes that are essential to life and if it ceases to function death ensues within a few days. 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 inner reddish portion (medulla) of the adrenal gland, which is not functionally related to the adrenal cortex, secretes epinephrine (adrenaline) and norepinephrine. 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.

or suprarenal gland

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.

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