Consider the following statements regarding the role of Iodi

Consider the following statements regarding the role of Iodine in thyroid hormone signaling.

(i) dietary iodine is required for synthesis of functional thyroid hormone

(ii) lack of iodine can result in goiter

(iii) in iodine deficiency, one would expect to find low plasma levels of thyroid hormones, TSH, and TRH

(iv) thyroid tissue is the only tissue in the body to take up iodine in significant quantities

Of the above how many statements are true?

A. one

B. two

C. three

D. all

E. none

Solution

B. two

True statements:

(i) dietary iodine is required for synthesis of functional thyroid hormone

(ii) lack of iodine can result in goiter

(i) Functional thyroid hormone thyroxine (T4) hormone and Triiodothyronine (T3) hormone are synthesized through iodination of tyrosine in the presence of iodine.

(ii)When there is deficiency of iodine, it can lead to enlargement of the thyroid gland which is known as Goiter.

False Statements:

(iii) In iodine deficiency, one would expect to find low plasma levels of thyroid hormones, TSH, and TRH

(iv) thyroid tissue is the only tissue in the body to take up iodine in significant quantities

(iii)When T3 and T4 hormone are synthesized, there is a negative feedback mechanism which inhibits secretion of the tropic hormones, TRH (thyrotropin releasing hormone) and TSH (thyroid stimulating hormone or thyrotropin).TRH is released by hypothalamus and TSH is released by the anterior pituitary. In iodine deficiency, there is decrease in synthesis of T3 and T4 hormone which inhibits the negative feedback mechanism leading to increased secretion of TSH and TRH.

(iv)Although some quantity of iodine is taken up in thyroid tissue but nearly 70% of iodine is distributed in other body tissues also such as eyes, salivary glands, gastric mucosa etc.