How do hormones from the thyroid and parathyroid regulate the calcium concentration of the blood?

Q. How do hormones from the thyroid and parathyroid regulate the calcium concentration of the blood?

A.            Both parathroid hormone and the three thyroid hormones function to regulate blood calcium levels

B.            Thyroxine and triiodothyronine together regulate calcium levels, as needs dictate

C.            Parathyroid hormone lowers blood calcium; calcitonin raises blood calcium

D.            Calcitonin lowers blood calcium; parathyroid hormone raises blood calcium

Answer: Calcitonin lowers blood calcium; parathyroid hormone raises blood calcium