Assertion(A): Excess amount of calcium is regulated by calcitonin.
Reason(R): Calcitonin deposits excess calcium in the blood in bones.

The correct option is A

Both A and R are true and R is the correct explanation of A

When the calcium in blood increases, thyroid gland secretes a hormone called calcitonin. This hormone helps in maintaining the level of calcium in blood by depositing excess calcium into the matrix of bones and by preventing the mixing of calcium with blood from the bones.