The secretion of T3 and T4 by the thyroid is controlled by an endocrine feedback system involving the pituitary gland and the hypothalamus in the brain. Calcitonin is regulated by the amount of calcium in the blood and acts in conjunction with the parathyroid gland to control calcium levels.

Since the thyroid gland is regulated by the pituitary gland and the hypothalamus, thyroid disorders may result not only from defects in the gland itself, but also from disruption of the control system. Thyroid disorders caused by overproduction of thyroid hormones are called hyperthyroidism, and underproduction of these hormones is known as hypothyroidism.

Graves' disease is the most common causes of hyperthyroidism. The production of thyroid hormone is increased resulting in many changes within the body. The cause of the disease may be related to a genetic or immune system disorder.

Other disorders of the endocrine system may be present in people with Graves' disease. The symptoms of hyperthyroidism are present and, in addition, the eyeballs may protrude (exophthalmos) causing irritation and tearing.

Risk factors are being female over 20 years old, although the disorder may occur at any age.

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