What event occurs during the follicular phase of the ovarian cycle?

The follicular phase of the ovarian cycle is characterized by the maturation of the graafian follicle. During this phase, which begins on the first day of menstruation and can last until ovulation, several follicles in the ovaries begin to develop, but typically only one will mature fully into a graafian follicle. This structure is essential for the eventual release of an egg during ovulation.

As the graafian follicle matures, it produces increasing amounts of estrogen, which plays a key role in preparing the endometrium for a potential pregnancy. The hormonal changes and the increase in estrogen are critical for regulating the menstrual cycle and preparing the body for ovulation.

In contrast, other events listed do not occur during this phase. Ovulation is the release of the mature egg and occurs at the end of the follicular phase. Menstruation marks the start of the cycle and precedes the follicular phase. Implantation happens only after fertilization of the egg, which would occur after ovulation and subsequent transport of the egg to the uterus.