✅ FOLICULOGÉNESIS ¿Qué son los FOLÍCULOS OVÁRICOS? | EMBRIOLOGÍA HUMANA 📚

Folliculogenesis: Understanding Ovarian Follicle Development

Overview of Folliculogenesis

• The ovarian follicle is a functional anatomical structure responsible for housing and developing the oocyte.

• Folliculogenesis is crucial for reproduction, culminating in the release of an oocyte during ovulation, starting from fetal stages to menopause.

Stages of Folliculogenesis

• The process can be divided into several stages: primordial, primary, secondary, tertiary (antral), and pre-ovulatory. Terminology may vary based on different literature.

First Stage: Primordial Follicles

• Primordial follicles develop during fetal life around the third month of gestation and remain dormant until puberty. They consist of an oocyte arrested in prophase I of meiosis surrounded by flat follicular cells.

Activation Influences

• Activation is influenced by local growth factors and autocrine/paracrine signals within the ovaries. Primordial follicles represent a woman's ovarian reserve, essential for fertility throughout reproductive life.

Second Stage: Primary Follicles

• In this stage, the oocyte enlarges while flat follicular cells transform into cuboidal granulosa cells forming a primary follicle.

• A protective layer called zona pellucida forms between the oocyte and granulosa cells containing specific receptors necessary for sperm binding.

Hormonal Regulation

• Follicle-stimulating hormone (FSH) plays a key role in stimulating granulosa cell proliferation and estrogen production during this stage.

Third Stage: Secondary Follicles

• The growing follicle becomes a secondary or mature primordial multilaminar follicle with multiple layers of granulosa cells organized around the oocyte.

Teca Layer Formation

• As follicles grow, the surrounding teca differentiates into internal (vascularized; synthesizes androgens under luteinizing hormone influence) and external layers (connective tissue providing structural support).

Fourth Stage: Antral Formation

• Small fluid-filled cavities merge to form a large cavity known as antrum; at this point, it’s referred to as tertiary or antral follicle.

Continued Growth Dynamics

• Granulosa cells continue proliferating while FSH and estrogen stimulate further growth; positive feedback increases FSH and LH secretion due to rising estrogen levels.

Fifth Stage: Pre-Ovulatory Dominance

• Among all developing follicles each cycle, only one becomes dominant—growing into a preovulatory or Graafian follicle reaching up to 25mm in diameter.

Final Preparations for Ovulation

• The oocyte resumes meiosis progressing to metaphase II; LH surge triggers events leading to rupture of the follicular wall releasing the secondary oocyte during ovulation.

Post-Ovulation Changes