Question

Tetraiodothyronine is
A. $$T_3$$
B. $$T_4$$
C. TSH
D. TRH

Answer 1

Hint: It is a thyroid hormone which is produced by thyroid gland under regulation from the hypothalamus and the pituitary gland. It is used to treat thyroid hormone deficiency.

Complete answer:
If we look at option A which is $$T_3$$. $$T_3$$ is triiodothyronine which is an active and second thyroid hormone produced by the thyroid gland. This hormone helps in maintaining the muscle control, brain function and development, digestive functions, heart functions, etc. It is activated by TSH which is a thyroid stimulating hormone. Since $$T_3$$ is triiodothyronine and tetraiodothyronine, it is the incorrect option and it gets eliminated.
Moving to option B which is $$T_4$$. Tetra means 4 and $$T_4$$ is tetraiodothyronine and it is also known as thyroxine. This hormone is produced by thyroid gland under regulation from the hypothalamus and the pituitary gland since the TSH hormone released by the pituitary gland stimulated the thyroid gland to produce thyroid hormones. $$T_4$$ hormone regulates protein, fat and carbohydrate metabolism, along with this it stimulates vitamin metabolism too. Since $$T_4$$ is tetraiodothyronine, it is the correct option.
Moving to option C which is TSH, TSH is a thyroid stimulating hormone which is produced by the anterior lobe of the pituitary gland. It stimulates the thyroid gland to produce the thyroid hormones in the form of $$T_3$$ and $$T_4$$. $$T_3$$ is triiodothyronine and $$T_4$$ is tetraiodothyronine. So, this is the incorrect option as TSH is thyroid stimulating hormone not tetraiodothyronine and therefore it gets eliminated.
Last option D is TRH. TRH is a thyroid-releasing hormone which stimulates the thyrotrophs of the anterior pituitary in order to secrete the thyroid stimulating hormone which further stimulates the thyroid gland to produce thyroid hormones which are $$T_3$$ and $$T_4$$. Therefore, this option is also incorrect as TRH is thyroid releasing hormone.

Thus, the correct answer is option B which is $$T_4$$.

Note: TRH is the thyroid releasing hormone which stimulates the anterior lobe of pituitary gland to produce the TSH (Thyroid stimulating hormone) and then this TSH hormone released from anterior pituitary gland stimulated the thyroid gland to produce thyroid hormones which are triiodothyronine ($$T_3$$) and tetraiodothyronine ($$T_4$$). Hence, tetraiodothyronine is $$T_4$$.