tkdesign,
parathyroid hormone doesn't direct calcium from the blood to the bone. The purpose of the parathyroid is to maintain adequate calcium levels in the blood to guarantee there is enough calcium for other organs, like the brain.
The way both Tymlos and Forteo work is by introducing the hormone in brief daily bursts, signaling other actors your body is losing bone. This triggers the cells that build bone rather dramatically.
While our bones store calcium, so does our blood. Only 1% of the serum calcium is said to be ionized or metabolically active. We can measure ionized calcium along with PHT levels to determine if the gland is overactive. Constant levels of high parathyroid hormone cause osteoporosis.
t