It is also released by the corpus luteum, which is the portion of the follicle that is left behind in the ovary. Following the release of our ovum, the mature female gaming into our Peric mule cavity and eventually into the fallopium tube. Now, what exactly is the purpose of estrogen? 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.