Hyperthyroidism is caused by conditions such as toxic adenoma, Grave's disease, thyroiditis and Plummer's disease, explains the Mayo Clinic. The thyroid gland is fairly small but produces two important hormones that directly effect an individual's metabolism.
The two hormones produced by the thyroid gland are thyroxine and triiodothyronine, which are referred to as T4 and T3, states the Mayo Clinic. These hormones affect a person's heart rate, control how the body uses fats and carbohydrates, and controls the production of protein by the body as well. These hormones even assist in regulating the body's temperature. The brain regulates how much T3 and T4 the thyroid releases. This occurs when the brain signals the pituitary gland to make a thyroid-stimulating hormone.
The amount of TSH the pituitary gland releases is directly dependant on how much T3 and T4 is present in an individual's blood, explains the Mayo Clinic. When the thyroid gland doesn't function properly, it releases or makes too much thyroid hormone, causing levels of T3 and T4 to be too low or too high. Hyperthyroidism means that the thyroid is producing too much T4 or thyroxine. This can cause weight loss, rapid heartbeat and irritability. People with hyperthyroidism may need to take anti-thyroid medications or have part or all of the thyroid removed.