ABSTRACT
The thyroid gland synthesizes, stores, and secretes the thyroid hormones. It is part of a balanced endocrine system involving the hypothalamus, pituitary gland, and the end organs. The thyroid hormones are vital to the metabolism, growth, and development of the organism. The thyroid gland has an active self-regulating ability aimed at maintaining a normal constant hormone level. Thyroid hormone secretion into the circulation occurs in response to thyrotropin releasing hormone produced by the hypothalamus and thyrotropin produced in the anterior pituitary gland. Thyroid hormone synthesis also depends on the availabilty of the amino acid tyrosine and inorganic iodine. Assessing true thyroid function in adults and newborns is a real challenge. The process is complicated by the presence of a multitude of thyroid function tests and misleading results of tests resulting from interference of serum protein binding, drugs, and the performance of the tests themselves.
