What is the active form of thyroid hormone?

What is the active form of thyroid hormone?

• A. Thyroglobulin
• B. T3
• C. T4
• D. TSH

Answer: (B)

The main concept is that the biologically active form of thyroid hormone is T3. The thyroid gland mainly secretes T4, which acts as a circulating reservoir and must be converted in peripheral tissues by deiodinase enzymes into T3 to exert its effects. T3 binds thyroid hormone receptors with higher affinity and greater potency, driving the metabolic actions you see with thyroid hormone. Thyroglobulin is the precursor protein stored in the thyroid follicle, and TSH stimulates production and release but is not the active hormone itself.

The main concept is that the biologically active form of thyroid hormone is T3. The thyroid gland mainly secretes T4, which acts as a circulating reservoir and must be converted in peripheral tissues by deiodinase enzymes into T3 to exert its effects. T3 binds thyroid hormone receptors with higher affinity and greater potency, driving the metabolic actions you see with thyroid hormone. Thyroglobulin is the precursor protein stored in the thyroid follicle, and TSH stimulates production and release but is not the active hormone itself.