Tadpoles must undergo a major metamorphosis to become frogs. This change includes reabsorption of the tail, growth of limbs, calcification of the skeleton, increase in rhodopsin in the eye, development of lungs, change in hemoglobin structure, and reformation of the gut from the long gut of an herbivore to the short gut of a carnivore. Amazingly, all of these changes are induced by thyroxine. What is the most likely explanation for such a wide array of effects of thyroxine?
A) There are many different forms of thyroxine, each specific to a different tissue.
B) Different tissues have thyroxine receptors that activate different signal transduction pathways.
C) Some tissues have membrane receptors for thyroxine, while other tissues have thyroxine receptors within the nucleus.
D) Different releasing hormones release thyroxine to different tissues.

Question

Quizplus · Accepted Answer

Different tissues have thyroxine receptors that activate different signal transduction pathways. This explanation suggests that the effects of thyroxine are tissue-specific, meaning that different tissues respond differently to the same hormone. This is possible because the receptors for thyroxine are present in different amounts and in different cellular locations in different tissues. Once thyroxine binds to its receptor in a particular tissue, it activates a specific signaling pathway that leads to the desired physiological response.

Tadpoles Must Undergo a Major Metamorphosis to Become Frogs