So what our parathyroid hormone does is it activates vitamin D, produces the active form of vitamin D in the kidneys, and then this vitamin D basically helps to absorb more calcium in our intestines. So notice these three things that we just mentioned are the opposite of what our calcitonin does released by the thyroid gland. So notice that the parathyroid hormone reverses the effects of calcitonin. 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.