Which is a function of the thyroid gland? a. it secretes melatonin to regulate sleep. b. it increases blood levels of glucose. c. it regulates calcium in the blood. d. it maintains water and salt balance

Option C, It regulates calcium in the blood

Explanation:

Thyroid releases hormone known as calcitonin which is responsible for  regulating calcium  through involvement in calcium metabolism.  The parafollicular cells (also known as C- cells) of the thyroid gland produces calcitonin hormone which regulate the level of both calcium and phosphate with in the blood.  

Calcitonin  increase the level of calcium in blood by opposing  the effect of parathyroid hormone  (PTH)

Hence, option C is the correct answer

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