Oogenesis is the process of forming the female gamete, the ovum, from primordial germ cells. It begins before birth in the ovarian cortex and continues cyclically from puberty to menopause.

What are the key stages of oogenesis?

The process involves primordial germ cells forming oogonia and then primary oocytes. Primary oocytes arrest in prophase I before birth. At puberty, meiosis I resumes, producing a secondary oocyte and a first polar body. Meiosis II completes only upon fertilization, forming a mature ovum and a second polar body.

How does the ovarian follicle develop during oogenesis?

Follicles mature through stages: Primordial follicle (primary oocyte with flat cells), Primary follicle (cuboidal cells in one layer), Maturing primary follicle (multiple granulosa cell layers and zona pellucida), Secondary follicle (fluid-filled antrum with theca layers), and Graafian follicle (fully matured, ready for ovulation).

What happens during ovulation?

Ovulation is the release of a secondary oocyte from a mature Graafian follicle. The follicle ruptures at a stigma, and the oocyte, surrounded by zona pellucida and corona radiata, is picked up by the uterine tube.

What is the structure of a mature ovum?

The mature ovum (secondary oocyte) is large (~120 µm) and includes no visible nucleus (meiosis II in metaphase), surrounded by zona pellucida and corona radiata, with a perivitelline space containing the first polar body.

What is the corpus luteum and what does it do?

After ovulation, the ruptured follicle transforms into the corpus luteum under LH influence. It produces progesterone and estrogen. If no fertilization occurs, it degenerates into a corpus albicans; if fertilization occurs, it persists as the corpus luteum of pregnancy.

What are some clinical correlations related to oogenesis?

Key clinical issues include binucleated/trinucleated oocytes (often degenerate but can rarely lead to twins/triplets), aneuploidy from nondisjunction during meiosis (causing conditions like Down syndrome or Turner syndrome), and oocytes being more chromosomally stable than sperm.

Oogenesis – Ovum Formation & Follicular Development

❓ Frequently Asked Questions