During ________ an egg ruptures from the follicle, leaving behind the ______________ which secretes estrogen in preparation for pregnancy.

The correct answer is "ovulation" and "corpus luteum" respectively. In ovulation, the egg ruptures from the mature follicle (called the Graafian follicle). This process is preceded by the sudden rise in luteinizing hormone. The follicle now becomes the corpus luteum, actually does not secrete estrogen, it secretes progresterone which prepares the uterine lining for pregnancy.