Stages of follicular development include in ovulation:
Primordial follicle
Primary follicle
Secondary follicle
Vesicular follicle
Ruptured follicle
Corpus luteum
Corpus albicans
The follicular phase (i.e., follicle formation) starts on day one of a typical 28-day cycle, which is marked by the beginning of menstruation, and lasts until today (i.e., ovulation). At this point, the antral follicle is FSH-dependent and starts to compete for the hormone with other growing follicles.
Before an ovarian follicle releases its ovum, it goes through a number of unique phases. A limited number of primordial follicles emerge in the fetal ovary throughout the course of the first five months of development. The oocytes in these follicles are enclosed in a single layer of squamous follicular cells.
There are only a certain number of primordial follicles that are stimulated to form at the beginning of each menstrual cycle. The early primary follicle, which has a core oocyte surrounded by a single layer of cuboidal-shaped follicular cells, is the earliest evident histological stage.
When a follicular antrum is seen within the granulosa layer, secondary follicles can be distinguished from primary follicles. Hyaluronan and proteoglycan-rich fluid is found in the antrum.
