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.
