MHS 259 Ovary

Ovary

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

• Capsule - covers the outer surface.
  • 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,#2) - primary oocytes surrounded by multiple layers of granulosa cells.

• • Secondary (Antral) Follicles - characterized by the formation an antrum (a fluid-filled space) containing an oocyte. The antrum (#1,#2,#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.

• • 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). This maybe an off-center cross section of a mature follicle because of its large size and slightly 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.
  • Stromal Cells - spindle-shaped cells.
• Medulla - inner region of fibroelastic connective tissue with many large, tortuous blood vessels, lymph vessels and nerve fibers.
  • Does not contain ovarian follicles.