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  1. Primary layer is made up of a single layer of Cuboidal/Columnar follicular cells whereas secondary follicles are made up of multiple layers of Cuboidal/Columnar follicular cells, which are called as “Membrana granulosa” that secretes follicular fluid.
  2. Primary follicles are developed by the formation of multiple layers around the primary oocyte.
  3. Some of the primary follicles are continued for the development and formation of secondary follicles, during which a thick layer forms in between primary oocyte and membrana granulosa that, is known as “Pellucida”.
  4. As the size of the primary follicle increases, it secretes a steroid hormone called estrogen.
  5. Around the developing secondary follicles, there is the formation of two layers of stromal cells: theca interna and theca externa.
  6. Here by comparing both layers, theca interna consist large, rounded, epithelial cells whereas theca externa consist small fibroblasts.
  7. These both layers are separated by a basement membrane from the membrana granulosa of the follicle.
  8. In human females, normally only one secondary follicle develop.


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