Ovary

Ovaries produce female gametes (oocytes) and steroid hormones (estrogen and progesterone).

This specimen has few primordial and primary follicles, but contains several secondary (antral) follicles and many corpus albicans.

• Cortex - outer region that is the site of oocyte development. This specimen is mostly cortex.
• Ovarian Follicles - oocytes surrounded by one or more layers of cells.
• Primordial Follicles - oocytes arrested in development. There are very few of them in this specimen.
• Primary Oocyte - large (25 to 30 µm), round to oval cells with a vesicular nucleus.
• 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). There are few of them in this specimen.
• Unilaminar - primary oocytes surrounded by a single layer of granulosa cells.
• Multilaminar - primary oocytes surrounded by multiple layers of granulosa cells. (Note the poor fixation and preservation of this follicle.)

• Secondary (Antral) Follicles - characterized by the formation an antrum (a fluid-filled space) containing an oocyte.
• Oocyte - large (50 to 100 µm), round to oval cells with a vesicular nucleus. (Nucleus is not visible.)
• 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.

• 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).
• Because of its large size, the oocyte is usually not visible in most sections of a mature follicle.
• 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.
• Stigma - raised area of the ovarian surface where a mature follicle will burst through to release the ovum during ovulation.
• Corpus Albicans - after a corpus luteum ceases to function it degrades into a fibrous scar that is eventually removed. There are many of them in this specimen.
• Stroma - highly cellular connective tissue with fewer connective tissue fibers in which ovarian follicles are located.
• Stromal Cells - spindle-shaped cells.
• Medulla - inner region of fibro-elastic connective tissue with many large, tortuous blood vessels, lymph vessels and nerve fibers.
• Does not contain ovarian follicles.