Q. What is the relation between secretion of parathormone and the calcium blood level?
The parathormone increases the calcium blood level since it stimulates the resorption (remodelation) of the osseous tissue when osteoclasts remodel bones calcium is released in the circulation.
Parathormone also acts increasing the calcium absorption in the intestines by vitamin D activation in that it acts in the kidneys promoting tubular calcium resorption too.