Pathophysiological and clinical aspects of the thyroid gland include after many decades of intensive studies many yet unresolved problems. The relationship with the gastrointestinal system (iodine accumulation in the stomach and salivary glands), the function of thyroxine as a prohormone (in particular the regulation of the activity of tissues deiodinases, the action of triiodothyronine similar to that of steroid hormones, a mixture of protein anabolic and protein catabolic reactions to thyroid hormones, peculiar immune features of the thyroid gland (presence of immunogenic hyperfunctional and hypofunctional syndrome), sharing of common antigens by the thyroid gland and orbital tissues, new findings on mutations of TSH receptors in the thyroid gland, biphasic dependence of the thyroid gland on iodine - all these problems call for further research. Mutation of the TSH receptor can lead to hypothyroidism (resistance to TSH) and to multinodular goitre. The gene for the iodine transporter in the thyroid gland (Na(+)I symport) was cloned. The thyroid gland is related to malignant free radicals: this is suggested also by the raised thyroxine level in rats after methylene blue administration. The increase is recorded in intact as well as carbimazole medicated animals. All this indicates that the thyroid gland must remain in the foreground of research and clinical work: 4% of the Czech population suffer from some thyroid disorder.

Keywords: Animals; Humans; Rats; Receptors, Thyroid Hormone /physiology/; Thyroid Diseases /physiopathology/; Thyroid Gland /physiology/