Final answer:
In the ovarian cycle, the follicular phase leads to ovulation, initiated by FSH and regulated by rising estrogen levels. The LH surge causes the follicle to release the egg, and after ovulation, the corpus luteum forms and secretes progesterone unless fertilization occurs.
Step-by-step explanation:
Events Leading Up to Ovulation in the Ovarian Cycle
The ovarian cycle involves a series of events that occur in the ovaries in preparation for ovulation and is regulated by fluctuating hormone levels. The cycle is composed of three major phases: the follicular phase, ovulation, and the luteal phase.
During the follicular phase, levels of Follicle-stimulating hormone (FSH) rise, stimulating the growth of follicles on the ovarian surface. One of these follicles will become dominant, and as it grows, it begins to secrete increased levels of estrogen. Rising estrogen levels signal the thickening of the endometrium, supporting potential pregnancy.
The transition to ovulation is marked by a surge in Luteinizing Hormone (LH). The LH surge is a response to high estrogen levels from the dominant follicle. This sudden increase in LH leads to the maturation of the oocyte and weakens the follicle wall, culminating in the release of the egg during ovulation.
Post-ovulation, the luteal phase begins with the transformation of the ruptured follicle into the corpus luteum, which secretes prolactin to sustain the endometrium. If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone and eventually menstruation.