Ovarian follicles are tiny sacs in the ovarian cortex, each containing one immature egg surrounded by supporting cells. A girl is born with about one to two million, falling to a few hundred thousand by puberty. Each cycle a group starts to grow, but usually only one dominant follicle matures fully and releases its egg at ovulation.
| Location | In the cortex of the ovary |
|---|---|
| Parts |
|
| Blood Supply | Ovarian artery branches |
| Venous drainage |
|
Nurture the developing egg and produce oestrogen, then release the egg at ovulation.
Follicles make oestrogen as they grow, and after ovulation the empty follicle becomes the corpus luteum, which makes progesterone. Tracking follicle growth with ultrasound and hormone tests is central to fertility treatment. The number of remaining follicles (ovarian reserve) is estimated with AMH blood levels and antral follicle counts, and their exhaustion leads to menopause.
A follicle that fails to rupture and keeps growing, usually harmless and resolving on its own.
Over-response of many follicles to fertility drugs, causing enlarged ovaries and fluid shifts that can be serious.
Loss of normal follicle function before age 40, causing irregular or absent periods and infertility.
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