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What happens in the ovaries during the follicular phase?
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menstruation
Cyclical changes during a woman's normal ovulatory menstrual cycle.
During the follicular phase, which typically lasts about two weeks, the ovaries undergo significant changes to prepare for ovulation.12
- Follicular Growth: Stimulated by follicle-stimulating hormone (FSH), several immature follicles enlarge and migrate from the cortex toward the outer surface of the ovary.12
- Cellular Development: Cells lining these follicles multiply to form the zona granulosa, while surrounding stromal and interstitial cells arrange themselves to form a protective sheath called the theca.1
- Hormone Production: The theca cells produce androgens, which are converted into estrogens (such as estradiol) within the granulosa cells. These hormones are secreted into the bloodstream and accumulate in the fluid bathing the egg.12
- Maturation: One or more follicles are selected for further growth, eventually becoming mature [Graafian follicles].13
The phase concludes when a surge in luteinizing hormone (LH) triggers the rupture of the mature follicle, releasing the egg.12