Firstly, it increases the activity rate of osteoclasts and decreases the activity of osteoblasts. So osteoblasts are those cells inside our bone that build the bone. It builds bone matrix by taking calcium from the blood and using that calcium to build the matrix. On the other hand, osteoclasts are those cells in the bone that resorb the bone. They break down the bone by breaking down the bone matrix and releasing the calcium and the phosphate ions into our blood. So what our parathyroid hormone does is it increases the activity of osteoclast, meaning it increases the rate of resorption of bone.