So, remember earlier, I mentioned that the skin actually needs UV radiation. So certain cells in the epidermis of our skin are responsible for using UV radiation, the energy stored in UV radiation, to actually produce something called colic calcipheral. And this is basically an inactive form of vitamin D three. Now, once the skin produces Cola Calciphral, it travels into our liver, where we basically transform Cola Calcipher into calcidial. And then calcitial travels into our kidneys. And in the kidneys, that calcitial is transformed into the active form of vitamin D, calcitriol.