We discussed progesterone and estrogen. So these two hormones are basically steroid hormones and what that means is they're lipid soluble, they cannot dissolve in the blood and so they need a protein carrier. And because they're lipid soluble, they can easily cross the plasma membrane of the target cell, which means they bind onto protein receptors found inside our cell. Now progesterone is initially produced by the corpus lutein that is found in the ovaries. Now eventually the corpus lutein begins to break down, it begins to degenerate and what happens is our placenta takes over the role of producing our progesterone. So initially it's the corpus luteum that produces our progesterone, but eventually our placenta takes over that job because the corpus luteum degenerates, it breaks down.