What is the Origin of T3 and T4 Hormones?

The names are derived from the chemical structure, specifically the number of iodine atoms attached to the thyronine molecule: T4 has four iodine atoms, and T3 has three. Their discovery and characterization in the early 20th century were foundational to modern endocrinology and the understanding of metabolic control. These hormones are synthesized from the amino acid tyrosine and iodine.

What is the Mechanism of T3 and T4 Hormones?

The thyroid's mechanism of action begins with the secretion of T4, which is largely inactive until it is peripherally converted into the potent T3, primarily in the liver and kidneys, through the action of deiodinase enzymes. Once active, T3 enters the cell nucleus and binds to its receptor, directly influencing gene expression to increase oxygen consumption and ATP production in the mitochondria. This genomic action dictates the speed and efficiency of the body's overall metabolism.

T3 and T4 Hormones ∞ Area

T3 and T4 Hormones

Meaning

T3 (triiodothyronine) and T4 (thyroxine) are the two primary thyroid hormones produced by the thyroid gland, which are absolutely essential for regulating the body’s basal metabolic rate, influencing nearly every cell and organ system. T4 is the more abundant, pro-hormone form, while T3 is the biologically active form that binds to nuclear receptors to exert its effects. Clinically, the balance and conversion of these hormones are critical indicators of metabolic health, energy levels, and thermogenesis. Dysregulation can lead to profound systemic effects, including fatigue and weight changes.