Vet Clin North Am Small Anim Pract, 1984. 14(4): p.809-26.
Hyperthyroidism is a disorder resulting from excessive circulating concentrations of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3) . Normally, circulating concentrations of these hormones lie within a narrow range; increased production and sustained high concentrations of T4, and T3, circulated in excessive amounts to all body tissues, cause the clinical and biochemical state of hyperthyroidism. Thyroid hormones act in many tissues, and hyperthyroidism can produce abnormalities involving virtually every organ system.