Question

Which of the following statement(s) is/are correct?                    

(i) Maximum iodine is stored in thyroid gland

(ii) Calcitonin is non-iodinised hormone secreted by parafollicular cells of thyroid gland.

(iii) Calcitonin (TCT) regulates the blood calcium level.

(iv) TCT is hypocalcemic factor.

A) All of these
B) None of these
C) (i), (ii) and (iii)
D) Only (iv)

Answer 1

Hint Thyroid gland is the largest endocrine gland and is found on the ventral surface of the trachea below the pharynx. It consists of 2 lobes joined by an isthmus. Its dorsal surface contains 2 pairs of the parathyroid gland. 
Complete Step-by-step answer:
Parafollicular cells that release calcitonin surround the follicular cells. Calcitonin is a peptide hormone that is important for calcium metabolism.
C-cells are derived from the neural crest and migrate to the thyroid gland. It is also known as thyrocalcitonin. Its actions are antagonistic to PTH and calcitriol. CT inhibits the osteoclastic and osteolytic activity of osteoclasts. Thus, it inhibits bone resorption. It stimulates osteoblastic activity and thus promotes bone formation. These CT levels are high in children. 
Iodine in diet isan iodate form. It is converted to iodide in the stomach and is absorbed rapidly. Iodide is taken to the thyroid gland by blood. Follicular cells in the thyroid gland trap the iodide.
TCT(thyroidal calcitonin ) is a hypocalcemic hormone that plays a major role in the regulation of blood calcium by opposing PTH. 
 Hence the correct answer is option A.
Note: CT promotes excretion of calcium and phosphate via urine. It also inhibits 1-alpha-hydroxylase enzyme in the kidney. This inhibits the formation of calcitriol and its effects on calcium absorption. CT also inhibits or slows down intestinal absorption of calcium and phosphate.