These cells break down bone to release calcium into the bloodstream where it can be used by the rest of the body [20] in the above processes. In the kidneys, PTH stimulates re-absorption of calcium so it in not lost from the body through urine and returned to the bloodstream instead. Lastly, PTH acts on the intestines by indirectly promoting enzymes that activate vitamin D, a signal for the intestines to absorb more calcium, further increasing blood calcium levels.[21] This will continue until the body releases too much calcium into the bloodstream.