So let's suppose, let's begin by supposing that inside our blood plasma, we have a low concentration of calcium. In such a case, this will basically trigger the parathyroid gland to release the parathyroid hormone. So we have a positive feedback loop here, a positive feedback loop here. And so, when we increase the amount of parathyroid hormone PTH in our blood, that basically does three things. It increases bone resorption, so it increases the rate of osteoclast and decreases the rate of osteoblasts. It increases the absorption of our kidneys, as well as increases the absorption of calcium in our intestines.