Final answer:
The follicular phase is the initial stage of the ovarian cycle that involves the maturation of ovarian follicles and the release of estrogen, driven by the increasing levels of FSH from the pituitary gland.
Step-by-step explanation:
The follicular phase is the first phase of the ovarian cycle, typically spanning about 12 to 14 days in an average 28-day menstrual cycle. During this phase, the pituitary gland secretes follicle-stimulating hormone (FSH), which stimulates several ovarian follicles to begin maturing. While multiple follicles may start to develop, generally only one reaches full maturity to become the Graafian follicle. This dominant follicle releases an egg during ovulation.
Concurrently, the maturing follicles produce estrogen, causing its levels to rise throughout the follicular phase, which plays a key role in preparing the endometrium for potential pregnancy. If fertilization does not occur, these developing follicles stop growing and disintegrate, marking the transition into the luteal phase.