Each follicle is initially made up of an immature sex cell, or primary oocyte, which is the female sex cell, and layers of theca and granulosa cells surrounding the oocyte.

每个卵泡最初是由未成熟的生殖细胞：初级卵母细胞（即女性生殖细胞）和卵母细胞外层的鞘细胞、颗粒细胞组成。