ABSTRACT
Thyroid hormones govern a host of functions of paramount importance for survival, including general cell and tissue metabolism, regulating growth, maturation and differentiation, as well as thermogenesis. Literally, every cell and tissue of the human body finds some form of interaction with thyroid hormones due to their influence on an extensive repertoire of gene expression across a broad range of organ systems. The thyroid gland is a component of the hypothalamus–pituitary–thyroid axis whose homeostatic control system is responsible for the maintenance of an optimal thyroid hormonal equilibrium termed the euthyroid state. This is achieved by a negative feedback loop which implies the existence of a stable set point analogous to a set temperature controlled by a feedback thermostat in an air-conditioned room. Such a euthyroid set point value is probably uniquely determined and programmed according to our individual genetic makeup.
