What event marks the transition to the luteal phase in the ovarian cycle?

The luteal phase of the ovarian cycle begins after ovulation, which is the event that marks this transition. During ovulation, a mature ovarian follicle releases an oocyte (egg) into the fallopian tube. Following this release, the remnants of the follicle transform into the corpus luteum, which is responsible for producing hormones like progesterone and estrogen. These hormones are crucial for preparing the uterine lining for potential implantation of an embryo.

Understanding the phases of the ovarian cycle is crucial here. The follicular phase precedes ovulation, characterized by the growth and maturation of follicles. While fertilization can occur after ovulation if sperm is present, it does not influence the immediate transition to the luteal phase. Menstruation marks the beginning of a new cycle, occurring if fertilization does not take place. Thus, ovulation is the definitive event that signals the shift into the luteal phase and the related hormonal changes that follow.