Osteocalcin is involved in the deposition of calcium into osteoid matrix. Vitamin D encourages the deposition of calcium.

Osteoclasts are the cells that secrete HCl and Cathepsin when signaled to increase serum calcium (osteoblasts upregulate RANKL - determined by vitamin D levels and PTH interaction).

Calcitonin is made by the thyroid C-cells to lower serum calcium