Mature Follicle

The antrum of a tertiary follicle will enlarge tremendously, so that the entire follicle starts to bulge from the ovarian surface, similar to a blister. The follicle is then called a mature or Graafian follicle. This is the preovulatory state. During this time, the primary oocyte will finally undergo the first meiotic division giving rise to a secondary oocyte, which represents the egg cell and can become fertilized, and a polar body.

A mature follicle bulges from the ovarian surface and consists of:

1. A secondary oocyte and polar body surrounded by the zona pellucida and granulosa cells

2. Multiple layers of granulosa cells

3. Antrum

Figure 1: Illustration of a mature follicle inside an ovary.