Approximately 1-2 million follicles are present at birth. The oogonia develop into primary oocytes , which enter meiosis and then are arrested for years in prophase of the first meiotic division. After puberty, different stages of follicular development are observed. The following discussion stresses the histology, while Dr. Moenter's lectures will emphasize its hormonal control. A primordial follicle consists of an oocyte surrounded by 1 layer of flat follicle cells.
Primary follicles have two stages.
The oocyte grows to become a very large cell. Between the oocyte and the granulosa cells is the zona pellucida The zona appears to be the site of species restriction in fertilizing ability of sperm. Two sheaths of connective tissue develop around the follicle. FSH stimulates growth of the follicles and production of estrogens. The oocyte rests in a mound of cells known as the cumulus oophorus .