The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a wide variety of hormones. They are found on the top of the kidneys and consist of a number of different layers that directly influence the structure and function of the glands. Each gland has an outer cortex made of steroid-producing cells surrounding a core of medulla, formed by chromaffin cells in direct relationship with the sympathetic nervous system. The adrenal cortex is divided into three zones according to their functions and microscopic appearance. The adrenal cortex produces a class of steroid hormones, the corticosteroids, which are classified according to their effects. Mineralocorticoids, produced in the zona glomerulosa, help in the regulation of blood pressure and electrolyte balance. Glucocorticoids such as cortisol, are synthesized in the zona fasciculata and their functions include regulation of glycogen and lipid metabolism and immune system suppression. The innermost layer of the cortex produces androgens (steroid hormones) that are converted to fully functional sex hormones in the gonads and other target organs. The production of steroid hormones is named steroidogenesis, and involves a number of reactions and processes that take place in cortical cells. The medulla produces the catecholamines epinephrine and norepinephrine, which function to provoke a quick response on diverse organs in stress situations. Regulation of synthesis and secretion of adrenal hormones is equally varied. Mineralocorticoid production is mainly under influence of the renin–angiotensin–aldosterone system, in which specialized juxtaglomerular cells of the kidneys monitor blood volume and start a cascade of reactions that leads to the stimulation of aldosterone synthesis in the zona glomerulosa. Cortisol and androgen synthesis are under control of the hypothalamic-pituitary-adrenal (HPA) axis in a classic example of a negative feedback loop, in which the hypothalamus and pituitary gland release stimulating hormones whenever cortisol levels are low. In contrast, release of medullary catecholamines is regulated by direct innervation from the sympathetic nervous system. There are a number of endocrine diseases and disorders that can affect the normal functioning of the adrenal gland. Overproduction of corticosteroid hormones leads to Cushing’s syndrome, whereas insufficiency is commonly associated with Addison’s disease. Congenital adrenal hyperplasia is a genetic disease produced by a disregulation of endocrine control mechanisms. A variety of tumors can arise from adrenal tissue, and are commonly found in medical imaging when searching for other diseases.