So, whereas calciotonin actually decreases the concentration of calcium in our blood, the parathyroid hormone increases the concentration of calcium in our blood. Now, the remaining question is, how exactly do we control how much of our parathyroid hormone is released into our blood? Well, there is actually a negative feedback mechanism that is in place to control the amount of parathyroid hormone inside our blood. 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.