The ovary is divided into the capsule, cortex, and medulla. The cortex contains primordial follicles, primary follicles (unilaminar and multilaminar), secondary (antral) follicles, and mature (Graafian) follicles.
T. Clark Brelje, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
Robert L. Sorenson, Ph.D.
University of Minnesota
Department of Genetics, Cell Biology and Development
6-160 Jackson Hall
321 Church St SE
Minneapolis, MN 55455
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Germinal Epithelium - the surface is covered by a simple cuboidal epithelium.
Tunica Albuginea - layer of dense irregular connective tissue that supports the epithelium.
Cortex - outer region that is the site of oocyte development.
Ovarian Follicles - oocytes surrounded by one or more layers of cells.
Primordial Follicles - oocytes arrested in development are located in the outer cortex.
Primary Oocyte - large (25 to 30 µm), round to oval cells with a vesicular nucleus.
Zona Pellucida - layer of glycoproteins between the oocyte and granulosa cells. It is visible a thin, eosinophilic band in many follicles.
Follicular Cells - single layer of flattened cells that surround each oocyte.
Primary Follicles - primary oocytes surrounded by one or more layers of cuboidal-shaped granulosa cells (which develop from follicular cells).
Unilaminar (#1, #2 and #3) - primary oocytes surrounded by a single layer of granulosa cells.
Multilaminar (#1 and #2) - primary oocytes surrounded by multiple layers of granulosa cells.
Ovary
Secondary (Antral) Follicles - characterized by the formation an antrum (a fluid-filled space) containing an oocyte. The antrum (#1, #2 and #3) increases in size as the follicle matures
Oocyte - large (50 to 100 µm), round to oval cells with a vesicular nucleus.
Zona Pellucida - layer of glycoproteins between the oocyte and granulosa cells (eosinophilic).
Granulosa Cells - continue to proliferate and form multiple structures:
Corona Radiata - several layers of cells immediately surrounding the oocyte.
Cumulus Oophorus - group of cells anchored to the follicle wall that contains the oocyte.
Stratum Granulosum - multiple layers of cells that form the follicle wall that surrounds the antrum. (It is avascular.)
Theca Folliculi - stromal cells around the follicle develop into a sheath of highly vascularized connective tissue.
Theca Interna - inner cellular layer with many blood vessels.
Secrete androgens that are converted to estrogen by granulosa cells.
Theca Externa - outer more fibrous layer.
Ovary
Mature (or Graafian) Follicles - usually only one follicle will continue to grow each cycle to form a very large, mature follicle (25 mm or more in diameter).
Note: This follicle is likely an off-center cross section of a mature follicle because of its large size and raised area on the surface (stigma).
Oocyte - not visible in most sections because of the large size of mature follicles.
Stratum Granulosum - becomes thinner as the follicle continues to grow in size. (It is avascular.).
Theca Folliculi - becomes more organized and contains many blood vessels.
Stroma - highly cellular connective tissue with fewer connective tissue fibers in which ovarian follicles are located.
