How does a lack of parathyroid hormone cause hypocalcemia?

Calcium from bones: Most of the calcium in your body is in your bones. Parathyroid hormone releases ca from your bones to maintain a constant blood level. With most hormone deficiencies, we give back the missing hormone (eg. Diabetes, insulin). But PTH is not available as a treatment. So hypopara is treated with vit d, ca, and other meds. It is hard to regulate, and you need a doc experienced with this.