Appearance
It is marked by the formation of a fluid-filled cavity adjacent to the oocyte called the antrum. The basic structure of the mature follicle has formed and no novel cells are detectable. Granulosa and theca cells continue to undergo mitosis concomitant with an increase in antrum volume. Antral follicles can attain a tremendous size that is hampered only by the availability of follicle stimulating hormone (FSH), which it is dependent on in this stage of folliculogenesis.
By command of an oocyte-secreted morphogenic gradient, the antral follicle's granulosa cells begin to differentiate themselves into four distinct subtypes: corona radiata that surrounds the zona pellucida, membrana that's interior to the basal lamina, periantral that's adjacent to the antrum, and cumulus oophorous that connects the membrana and corona radiata granulosa cells together. Each type of cell behaves differently in response to FSH.
Read more about this topic: Antral Follicle
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