Calcitonin hormone, secreted by thyroid gland in response to increased blood calcium level, stimulates temporary reduction in number and activity of osteoclasts and thereby reducing the blood calcium level to normal. Hypersecretion of thyrocalcitonin causes calcium tetany; characterized by uncontrolled muscle contractions. Calcitonin deficiency (hyposecretion) causes calcium rigor characterized by higher blood calcium level and uncontrolled muscles contraction. This makes options A and B incorrect. Oversecretion of thyroid hormones (hyperthyroidism) causes Graves’s disease which is characterized by formation of exopthalamic goiter. This makes option C correct. Myxedema is caused by hypothyroidism in adults and is characterized by lethargy, hair loss, weight gain, puffed skin, lowered body temperature and slowed pulse rate. This makes option D incorrect. Correct answer is C.