What Goes Wrong with the Thyroid Gland and Its Hormones in Hyperthyroidism?
The thyroid gland, a butterfly shaped organ located in the lower front of the neck, normally makes precisely the right amount of its hormones, thyroxine (T4) and triiodothyronine (T3), under the exacting control of the pituitary gland, which is an extension of the brain. Specialized pituitary cells make thyroid stimulating hormone (TSH), which travels in the blood to the thyroid gland, where TSH binds to its own receptors on thyroid cells, prompting them to grow and produce more of the thyroid hormones. Normally, this system is kept in balance by the negative feedback of the thyroid hormones on TSH-secreting pituitary cells (as well as the part of the brain that controls them). When this control system is “short-circuited” or by-passed, hyperthyroidism can be the result. [See attached Hypothalamic-Pituitary-Thyroid Axis animated PowerPoint image: Hyperthyroidism Knol_HPT axis.ppt.] To understand hyperthyroidism, it is important to appreciate how thyroid hormones act and how their produ
