Final answer:
In folliculogenesis, secondary follicles develop by forming a zona pellucida and accumulating follicular fluid, enlarging to become tertiary follicles. Most undergo atresia, with the surviving follicle reaching ovulation and possibly fertilization, leading to zygote formation.
Step-by-step explanation:
Secondary Follicle Development in Folliculogenesis
During the process of folliculogenesis, secondary follicles play a critical role. As secondary follicles develop, the primary oocyte secretes a zona pellucida, an important membrane for fertilization. Concurrently, follicular fluid accumulates between granulosa cells, forming a pool known as the antrum. Secondary follicles enlarge to form tertiary follicles, also called antral follicles. However, atresia occurs for most of these follicles, a process where they degenerate and do not proceed to ovulation. Approximately 99 percent of ovarian follicles experience atresia. The surviving follicle will continue to grow, eventually leading to ovulation, where the secondary oocyte is expelled from the ovary accompanied by several layers of granulosa cells.
The formation of the antrum and the expansion of the follicle size are due to the proliferation of granulosa cells and addition of theca cells and connective tissue, with the whole process being stimulated by hormonal signals such as FSH and LH. These hormones promote the growth of the follicles and the production of estrogen. The mature follicle will then rupture during ovulation, and if fertilization occurs, the secondary oocyte completes meiosis II to form a zygote.