GLOSSARY

From synthesis to tissue action

Thyroid function involves iodide handling, hormone formation in thyroglobulin, secretion, protein binding and local conversion. Transporters, deiodinases and receptor isoforms shape tissue exposure. These steps explain why circulating total hormone and intracellular thyroid action are different measurements.

Specific considerations

The gland secretes predominantly T4, while peripheral conversion contributes importantly to circulating T3.

Interpreting the axis

TSH and free thyroid hormones are interpreted together with symptoms and assay conditions. Illness, medicines and energy deficiency can alter the pattern. A change during heavy training should not automatically be treated as primary thyroid disease.