A secondary follicle; canine.
Keywords: follicle, bitch, canine, secondary
A secondary follicle in a postpuberal canine ovary. Many layers of granulosa cells surround the zona pellucida and the oocyte within it. Some of these cells have started to split away from one another, forming an early-stage antrum. Therefore this is a secondary follicle. Outside of the basement membrane, cells from the stroma have begun to accumulate against the follicle but it is still too young to show a theca with its two zones; the theca externa (a fibrous supporting tunic) and the theca interna which is endocrinologically active. The theca interna produces androgens that are aromatized to estrogens within the follicle.