Physiology of Thyroid Hormones
Start with the big picture
Thyroid follicular cells take up iodide through the sodium–iodide symporter, and thyroid peroxidase supports the reactions that form T3 and T4 on thyroglobulin. Hormones are stored in the follicular colloid before release into blood, where most are protein-bound; the free fraction is biologically active. Peripheral deiodinases convert T4 to active T3 or inactive reverse T3. At target cells, T3 binds nuclear receptors and alters gene transcription. Thyroid hormones influence metabolism, growth and development, and cardiovascular function. The hypothalamic–pituitary–thyroid axis regulates secretion through TRH and TSH, with free T3 and T4 providing negative feedback. Iodine availability and other regulators also affect thyroid output.
What you'll learn
- Describe iodide uptake and the key steps in thyroid hormone synthesis and release.
- Explain how thyroid hormones are stored and transported in blood.
- Distinguish the roles of peripheral deiodinases in thyroid hormone metabolism.
- Summarize thyroid hormone entry into cells, receptor action, and major physiologic effects.
- Trace hypothalamic–pituitary–thyroid feedback and identify factors that regulate TSH release.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
