Thyroid Hormone Biochemistry
- Thyroid hormones consist of two basic subtypes which differ based on the number of Iodine atoms. T3 and rT3 (reverse T3) possess three Iodine atoms whereas T4 possesses four Iodine atoms.
- In the peripheral tissues the thyroid hormone members display differential activity. T3 is the most active, T4 is somewhat active, and rT3 is completely inactive.
- Thyroid Hormones are hydrophobic and can thus cross the plasma membranes of cells. Once inside cells, they bind the Thyroid Hormone Receptor, a type of nuclear receptor, which then activates transcription of a large variety of genes (See: Basic Hormone Action).