Question

Iodine is required for synthesis of which hormone?
A. Insulin
B. Thyroxine
C. Adrenaline
D. Testosterone

Answer 1

Hint: This hormone plays a major role in the growth and development of brain and central nervous systems in humans. If iodine deficiency exists during pregnancy then it may result in derangement in the development of the brain and central nervous system.

Complete answer:
Iodine is essential for thyroid hormone synthesis and must be provided through dietary sources. Iodide is absorbed in the stomach and small intestine, and is concentrated from the bloodstream into the thyroid follicular cell through the action of the sodium/iodide symporter . The major thyroid hormone which is secreted by the thyroid gland is T4 (tetra-iodo-thyronine). T4 in circulation is taken up by the cells and is de-iodinated by the enzyme 5' prime-mono-de-iodinase in the cytoplasm to convert it into the tri-iodo-thyronine (T3). All the biological actions of T3 are mediated through its binding to the nuclear receptor, which controls the transcription of a particular gene to bring about the synthesis of a specific protein.

Additional information:
The physiologic actions of thyroid hormones can be categorised as 1) growth and development and 2) control of metabolic processes in the body. Thyroid hormones can play a major role in the growth and development of the brain and central nervous systems in humans starting from the 15th week of gestation to age 3 years.

Hence, the correct answer is option (B) i.e., Thyroxine.

Note: The daily iodine need decreases progressively with age. If iodine is not available in the diet, the thyroid gland may produce an insufficient amount of hormone. A minimum of 60 micrograms of elemental iodine per day is required to make thyroid hormone.