Question

Which endocrine gland
(a) maintain calcium in the blood
(B)regulate calcium in the body

Answer 1

Parathyroid gland maintains blood calcium levels.If blood Ca levels go down, Ca from bones is brought in to blood.That is how it maintains blood Ca levels.
Thyroid gland produces Thyrocalcitonin which helps in pumping Ca in to bones and makes bones stronger.

So together these endocrine glands maintain the Ca levels in the body.