Graafian Follicle
கிராஃபியன் நுண்ணறை
Stop confusing the Graafian follicle with the ovum. The Graafian follicle is a complex, fluid-filled structure; the secondary oocyte is merely its cargo. If you miss this distinction, you lose marks on the ovulation mechanism every single time.
The idea
The Graafian follicle is the mature tertiary follicle. It contains the secondary oocyte arrested in metaphase II. The cavity within is the antrum, filled with follicular fluid. Upon the LH surge, this follicle ruptures to release the secondary oocyte into the fallopian tube.
Why it matters
To protect and mature the oocyte until it is ready for release into the fallopian tube for potential fertilization.
NEET lens
NEET focuses on the contents of the follicle and the hormonal trigger. Memorize that the secondary oocyte is released, not the mature ovum. Expect questions linking LH surge to the rupture of this specific stage. Do not confuse the antrum with the oocyte itself.
Clinical significance
Failure of the Graafian follicle to rupture results in anovulation, a primary cause of female infertility. If the follicle persists without releasing the oocyte, it can form follicular cysts. These cysts disrupt the hormonal feedback loop between the hypothalamus, pituitary, and ovaries.
Introduction
The Graafian follicle (mature ovarian follicle) is the final stage of follicular development — a large (18-24 mm), fluid-filled structure containing the secondary oocyte, which ruptures at ovulation to release the egg, leaving behind the corpus luteum.
Core concept
Follicular development stages: Primordial follicle → primary follicle → secondary follicle → tertiary follicle (antrum forms) → Graafian follicle (mature). Structure: Antrum: large fluid-filled cavity (follicular fluid = liquor folliculi, rich in estrogen). Granulosa cells: surround oocyte; produce estrogen (under FSH). Theca cells (outer): produce androgens (under LH) → converted to estrogen by granulosa cell aromatase. Cumulus oophorus: granulosa cells directly surrounding oocyte. Zona pellucida: glycoprotein coat around oocyte. Corona radiata: innermost granulosa cells (released with egg at ovulation). At ovulation: LH surge → follicle wall digestion → rupture → secondary oocyte + corona radiata released into peritoneal cavity → swept into fallopian tube by fimbriae.
Go deeper
Two-cell, two-gonadotropin theory: Theca cells (LH receptors) → androstenedione. Granulosa cells (FSH receptors) → aromatase converts androstenedione → estradiol. Both cell types needed for estrogen synthesis. This explains why both FSH and LH are needed for normal follicle development.
From Class 10
Inside the ovary, eggs develop within fluid-filled sacs called follicles. The mature follicle just before ovulation is called the Graafian follicle.