Thyroid Function
TSH (Thyroid-stimulating hormone) stimulates the thyroid gland to secrete the hormones thyroxine (T4), which has only a slight effect on metabolism. T4 is converted to triiodothyronine (T3), which is the active hormone that stimulates metabolism. Most of the thyroid hormone circulating in the blood is bound to transport proteins. Only a very small fraction of the circulating hormone is free (free T3/free T4) and biologically active, hence measuring concentrations of free thyroid hormones has an important diagnostic value.
There are many disorders related to unbalanced thyroxine levels such as Hyperthyroidism (e.g. Graves Disease), Hypothyroidism (e.g. Hashimoto’s thyroiditis), and clinical depression.
