CortexThe follicles at every stage lie in the cortex.
MedullaLoose tissue carrying the ovary’s blood vessels and nerves.
Primordial folliclesThe earliest stage: an oocyte with a single flat layer of cells.
Secondary follicleSeveral layers of granulosa cells have formed. Small pools of fluid begin to gather.
Mature follicleThe last stage before ovulation; also called a tertiary or Graafian follicle.
Corpus luteumIt forms from the follicle after the oocyte is released. It makes progesterone.
Ovarian ligamentIt anchors the ovary to the uterus.
A mature follicle 5
OocyteThe egg cell the follicle is raising.
Zona pellucidaA thick coat of glycoproteins around the oocyte.
Granulosa cellsThey surround the oocyte and line the antrum, and make estrogen.
AntrumFollicular fluid fills it as the follicle matures.
ThecaTheca cells work with the granulosa cells to make hormones.
How this list was compiled: Every name and detail checked on 2026-09-29 against OpenStax Anatomy and Physiology 2e, section 27.2 Anatomy and Physiology of the Ovarian Reproductive System (tunica albuginea, cortex and medulla, ovarian and suspensory ligaments, primordial, primary, secondary and tertiary follicles, oocyte, zona pellucida, granulosa and theca cells, antrum, ovulation, corpus luteum), https://openstax.org/books/anatomy-and-physiology-2e/pages/27-2-anatomy-and-physiology-of-the-ovarian-reproductive-system, and against Wikipedia, Ovary and Ovarian follicle, text only. Licence: own work
The drawing: Drawn for this site on 2026-09-29 from plain geometry; nothing traced. Licence: own work
How it works
The first drawing cuts the ovary through to show follicles at several stages in its cortex. The second enlarges one mature follicle to show the oocyte and the layers round it.
Read the full guide
The ovary, then one follicle
Numbers 1 to 3 are the ovary's layers: the tunica albuginea, the cortex and the medulla. Numbers 4 to 7 follow a follicle's life from primordial to mature, then the corpus luteum left after ovulation. Number 8 is the ovarian ligament. Numbers 9 to 13 are the parts of a mature follicle.
Follicles grow in the cortex, not the medulla; the medulla carries the blood vessels and nerves.
Questions and answers
What are the stages of an ovarian follicle?
A follicle starts as a primordial follicle, an oocyte with one flat layer of cells, then grows through primary and secondary stages into a large, fluid-filled mature (tertiary) follicle that releases its oocyte at ovulation.
What is the corpus luteum?
The structure the follicle becomes after ovulation; the name means yellowish body. Its cells make the hormone progesterone, which keeps the lining of the uterus ready for a pregnancy.
What surrounds the oocyte in a mature follicle?
A clear coat called the zona pellucida, then granulosa cells. The follicle holds a fluid-filled antrum and is wrapped in theca cells.