Now, what happens next? Well, by about the 10th day, that entire implanting embryo is found entirely inside the endometrium, as shown in the following diagram. And notice that these cells continue to secrete these digestive enzymes that even further break down this area surrounding that implanting embryo. Notice what also happens because these digestive enzymes come in close proximity with these blood vessels, that blood vessels are also actually broken down. And what happens is this creates a temporary source of nutrition, of oxygen and nutrients such as glucose and so forth. And this eventually will develop into something called the placenta.