Secondary follicle in the ovary of a cat.

As the follicle develops, the oocyte becomes larger. The follicular cells proliferate and the oocyte is surrounded by stratified polyhedral cells called granulosa cells. At the interface between the oocyte and the granulosa cells a glycoprotein layer, the zona pellucida, appears. Tiny microvilli (not discernible here) from the oocyte penetrate the zona and form gap junctions with the granulosa cells. Through these contacts nutrients, hormones and signal molecules can be passed. The nucleus of the oocyte is out of the plane of section. As the follicle becomes larger, little fluid-filled spaces appear between the granulosa cells. The granulosa cells are enclosed by a distinct basal lamina. The stromal cells immediately around the follicle differentiate into plump theca cells. Although blood vessels may be found among the thecal cells, they do not penetrate the basal lamina. PK4892-25.Original mag. 80x. H&E. Secondary follicle. Cortex. Ovary. Female Reproductive System. Cat.