ABSTRACT
This chapter examines the anatomical location of the thyroid gland and its hormones. It describes the steps in thyroid hormone biosynthesis and the role of thyroid-stimulating hormone (TSH) in biosynthesis and release of thyroid hormones from the thyroid gland. The chapter discusses the mechanisms of action of tri-iodothyronine and thyroxine, and explores types, causes, symptoms and treatment of hypo- and hyperthyroidism. TSH from the anterior pituitary gland controls all important steps in thyroid hormone biosynthesis and release into the circulation. Protein binding of hormones in blood is mainly non- covalent, and there is equilibrium between bound and free hormones; only the free hormone is available to the tissues. TSH release is stimulated by hypothalamic thyrotrophin-releasing hormone. Cretinism is caused in neonates by untreated lack or severe deficiency of thyroid hormones.
