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During embryogenesis, primordial germ cells develop from mesoderm
in the allantois, migrate to the ovary, and then proliferate
and differentiate into primordial follicles. Primordial follicles
are arrested in growth until menarche, and some remain so until
menopause. At the beginning of each menstrual cycle, between
15 and 20 primordial follicles develop into primary follicles.
Under the influence of gonadotropins and ovarian hormones, primary
follicles grow; ultimately, however, only one primary follicle
develops into a Graafian follicle and the remaining follicles
undergo atresia. The Graafian follicle is ovulated, expelling
the oocyte and corona radiate into the peritoneum while the zona
granulosa cells remain in the ovary. The zona granulosa and surrounding
theca cells develop into the corpus luteum, which in turn becomes
atretic after 14 days. After several months, the corpus luteum
has fully devolved into the corpus albicans. Follicular development
from primary follicle to the last stage of corpus luteum requires
approximately three complete menstrual cycles.
The diagram below outlines follicular
development. Click on any stage to learn more details and view
a histological slide, if available.
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