So basically, when the secondary follicle is still inside our ovary, estrogen is released by that follicle. And what it basically does is it generates our endometrium. It is responsible for generating and thickening the endometrium, which is the layer of membrane in the uterus that serves as the binding side for our zygote. The zygote is the combination of the sperm and our egg. This process of combining is known as fertilization. Now, the second purpose of estrogen is basically to promote the development of female secondary sex characteristics such as our enlargement of breasts, as well as the growth of body hair in different parts of the body.