How does thyroxine trigger metamorphosis in frog tadpoles?

In the metamorphosis of a tadpole into a frog, the process is initiated by the hypophysis, which releases thyrotropic hormone. This hormone stimulates the thyroid gland to produce and secrete thyroxine into the bloodstream.1

Thyroxine acts as a systemic signal that coordinates the transformation by interacting with various tissues. The specific effect of the hormone depends on the "competence" of the target cells—meaning different tissues respond to the same chemical signal in distinct ways. For example, thyroxine triggers the synthesis of enzymes that lead to the degeneration of the tadpole's tail, while simultaneously stimulating the growth and development of the limbs.12

Ultimately, this hormonal regulation ensures that diverse morphological and biochemical changes occur in a synchronized manner, allowing the larval form to successfully transition into an adult.12