The adrenal glands are composed of two parts - the medulla and the cortex.

Addison's disease results from failure of the adrenal cortices to produce the necessary hormones. This is caused by atrophy of the cortices, usually by an autoimmune reaction although historically the cause was tuberculosis.

The result is mineralocorticoid and glucocorticoid deficiency.

Mineralocorticoid deficiency (lack of aldosterone) upsets the balance of sodium and potassium in the body and leads to a greatly reduced blood pressure.

Glucocorticoid deficiency (lack of cortisol) makes it impossible to maintain normal blood glucose and upsets other metabolic functions of the body. It also makes the body highly susceptible to the effects of different types of stress, particularly feverish illnesses and surgical operations.