Folliculogenesis

Folliculogenesis is the maturation of ovarian follicles in the ovarian cortex, essential sites for oogenesis.

During fetal development,  a single layer of squamous pre-granulosa cells encases the primary oocyte to form primordial follicles, which pause in late prophase I until puberty.

At puberty, FSH prompts these primordial cells to mature into primary follicles.

The squamous cells in the pre-granulosa layer of the follicle become cuboidal, and the oocyte enlarges and secretes a protective glycoprotein layer called the zona pellucida.

These primary follicles mature into secondary follicles characterized by the proliferation of pre-granulosa cells into multi-layered granulosa with a thickened wall termed theca folliculi.

The secondary follicles transform into tertiary or vesicular follicles with an antrum, a fluid-filled cavity.

The tertiary follicles grow and accumulate follicular fluid as they enter the monthly ovarian cycle. One of these follicles becomes the dominant mature Graafian follicle.

This mature follicle carries the secondary oocyte arrested at metaphase II, ready for ovulation from the ovary.