granulosa cell

Granulosa cells are the inner lining of cells that surround and nurse the egg inside an ovarian follicle. Think of them as the egg's personal support staff: they feed the oocyte, manufacture the bulk of the follicle's estrogen, and relay the brain's hormonal commands into action.

Their signature job is aromatization. Granulosa cells carry receptors for FSH from the pituitary, and FSH switches on the enzyme aromatase inside them. They cannot make androgens themselves, so they import the androgen precursors built next door by theca cells and convert them into estradiol — the granulosa half of the two-cell, two-gonadotropin model. As the follicle matures, granulosa cells also acquire LH receptors, which prepares them to respond to the LH surge.

Granulosa cells also produce inhibin, a hormone that feeds back to the pituitary to fine-tune FSH, and they secrete anti-Mullerian hormone from small growing follicles, a marker of ovarian reserve. After ovulation, these very cells transform into the progesterone-rich cells of the corpus luteum. A caveat for clinicians: granulosa cells are the origin of granulosa cell tumors, rare ovarian tumors that can secrete estrogen and cause abnormal bleeding.