Which phase of the ovarian cycle is characterized by the secretion of estrogen?

The follicular phase of the ovarian cycle is marked by the maturation of ovarian follicles and a significant increase in the secretion of estrogen. During this phase, several follicles begin to develop in response to follicle-stimulating hormone (FSH), and as the primary follicle matures, it produces increasing levels of estrogen. This hormone plays a crucial role in preparing the uterine lining for potential implantation of a fertilized egg, as well as influencing the regulation of the menstrual cycle.

The surge in estrogen levels late in the follicular phase prompts a spike in luteinizing hormone (LH), which triggers ovulation. This makes the follicular phase critical not only for the preparation of the body for a potential pregnancy but also for the initiation of the physiological changes necessary for ovulation to occur.

In contrast, the luteal phase is characterized by the secretion of progesterone following ovulation, which maintains the uterine lining, while the menses phase involves the shedding of this lining in the absence of a fertilized egg. The ovulation phase is the moment of release of the egg and does not involve active secretion of hormones from the ovarian follicles as they have transitioned to the corpus luteum by this point.