Secondary follicle, a. Schematic drawing of a secondary follicle showing the fluid-filled antrum, which arises by the coalescence of small fluid-filled cavities among the granulosa cells. Note that this actively growing follicle has many dividing granulosa cells. Call-Exner bodies appear at this stage. The wedge-shaped enlargement of the shadowed area depicts the relationship of the granulosa cells, basal lamina, and the theca interna and theca externa. The theca interna cells differentiate into highly vascularized, steroid-producing cells. The theca interna is surrounded by an outer layer of stromal cells called the theca externa. The basal lamina separates the granulosa cells from the theca interna, b. Photomicrograph of a secondary follicle. The antrum (A), filled with follicular fluid, is visible within the stratum granulosum (CC). Multiple layers of theca interna cells (Tl) and theca externa cells (TE) can be seen outside the basal lamina of the secondary follicle. x85.
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