Secondary follicle with antrum.

As the secondary follicle grows under the influence of FSH and increases in size, fluid (follicular liquor) accumulates between the granulosa cells. The fluid-filled spaces become confluent and form one large space known as the antrum. Protein in the follicular liquid sometimes is preserved in tissue processing and will give a background stain. The oocyte is surrounded by several layers of granulosa cells and is attached to the “wall” of the follicle by a clump of granulosa cells known as cumulus oophorus. In this micrograph the oocyte has detached from the mural cells and appears to be floating free in the antrum, still surrounded by the granulosa cells (corona radiata). The thecal cells outside the basal lamina of the granulosa cells have differentiated into an inner theca interna (paler, larger cells) and a theca externa (looks like the regular stroma). PK1460. Original mag. 50x H&E Secondary follicle. Cortex. Ovary. Female Reproductive System. Cat