Follicles which have been stimulated to develop progress through primary and secondary stages to become mature tertiary or Graafian follicles, in which a large fluid-filled cavity, the antrum, is surrounded by many layers of granulosa cells. Stromal cells around the follicle differentiate into the theca interna and the theca externa (not apparent in this image). Androgen from cells in the theca interna is processed to estrogen in granulosa cells; the estrogen then enters circulation via blood vessels which form in the theca. The cumulus oophorus, containing the oocyte, seldom appears in random sections such as this.
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Last updated: 20 May 2022 / dgk