So, an estrogen is defined as something that fits into an estrogen receptor and we tend to think of it as something that has a carbon backbone of 18 carbons but, the sort of frills may differ and the frills may gate hormone action. So, they’re really not all the same. The ones the body makes are pretty similar, one to the next, it only makes a few varieties, but what people can make in a drug company are huge and they are often not very related to what our own body makes. So they can be fairly different, and what other animals or plants make can be very different from what we make as well.