Secondary Follicle formation -LH stimulates, the Follicle Cells to secrete a nutritive fluid which collects into several fluid-filled cavities called Vesicles which aggregate together to form an Antrum (fluid-filled cavity). Also, a protective layer develops around the Primary Oocyte = Zona Pellucida. The Primary Oocyte plus the Antrum, multiple layers of Granulosa Cells, and the Zona Pellucida = Secondary Follicle.
With continued hormonal stimulation, the Granulosa (Follicle) Cells continue to increase in number and to secrete the nutritive fluid, and the Antrum enlarges to its maximum size. At this stage, the follicle is known as a Graafian (Mature, Vesicular) Follicle.
In the Graafian Follicle, under the influence of LH , the Primary Oocyte undergoes completion of the 1st meiotic division & begins into the 2nd meiotic division, but stops in Metaphase II = Secondary Oocyte
Once a month (at approximately day 14 of the normal 28 day cycle), under the influence of LH , the Graafian Follicle is induced to rupture = Ovulation.
A Secondary Oocyte is released, surrounded by:
1. Zona pellucida - a protective gel layer made by the granulosa cells
2. Corona radiata - two layers of granulosa cells
The remaining portion of the Graafian Follicle, under the influence of LH , is induced enlarge and to form a Corpus Luteum. It will produce Estrogen & Progesterone which thickens the stratum functionalis of the uterus.