Serum calcium levels are tightly regulated by the body, which will pull calcium from bones via increased parathyroid hormone if serum levels drop, to maintain cardiac, neuronal, and muscle function.

“that calcium level in your blood your serum calcium is tightly regulated and if your serum calcium starts to drop at all it's necessary for cardiac function neuronal function muscle function everything is calcium based that is tightly regulated your body's going to increase your pth and it's going to pull it out of bones”