Thyroxine (T4) vs. Triiodothyronine (T3): Understanding the Differences and Roles of Thyroid Hormones

In comparison to triiodothyronine (T3), the hormone thyroxine (T4)a. has greater biological activity.b. is more abundant in the circulation.c. has a shorter half-life.d. binds to nuclear receptors with greater affinity.

The correct answer is b

The correct answer is b. Thyroxine (T4) is more abundant in the circulation compared to triiodothyronine (T3).

Thyroxine (T4) and triiodothyronine (T3) are both thyroid hormones produced by the thyroid gland. They play important roles in regulating metabolism, growth, and development in the body.

T3 is the more biologically active form of thyroid hormone and is derived from T4. It is generally considered to be the more potent hormone, as it binds to nuclear receptors with greater affinity (option d). T3 has a stronger binding capacity to the receptors, allowing it to initiate gene transcription and influence various cellular processes.

However, T4 is more abundant in the circulation and is the primary form of thyroid hormone secreted by the thyroid gland. T4 is produced in greater quantities than T3, and it acts as a prohormone, serving as a reservoir of T3. T4 is converted to T3 in target tissues, such as the liver, kidney, and other peripheral tissues, through the removal of one iodine molecule. This conversion allows for tight regulation of T3 levels and ensures a constant supply of the biologically active hormone when needed.

The half-life of T4 is generally longer than T3 (option c). T4 has a half-life of about seven days, whereas T3 has a half-life of only one day. This longer half-life of T4 allows for more stable and long-lasting effects in the body.

In summary, while T3 is the more biologically active form of thyroid hormone, T4 is more abundant in the circulation, has a longer half-life, and serves as a precursor for T3 formation.

More Answers: