The function of the ovary is to develop female germinal cells, ovocytes (also termed oocytes), and to produce hormones necessary for reproduction. The ovaries are paired organs that lie on either side of the uterus close to the lateral pelvic wall, behind the broad ligament and anterior to the rectum.
Ovaries of adult women in the reproductive age group are approximately 3 to 5 x 1.5 to 3 x 0.6-1.5 cm but their size varies considerably between individuals. The external surface is usually convoluted. Three ill-defined zones may be discerned on the cut surface: an outer cortex, a central medulla and the hilus. Follicular structures (cystic follicles, corpora lutea, white corpora albicantia) are usually visible in the cortex and medulla.
The surface epithelium (modified mesothelium) of the ovary forms a simple, focally pseudostratified layer. The cells vary from flat to cuboidal to columnar, and several types may be seen in different areas of the same ovary. The cells are separated from the underlying stroma by a basement membrane. The spindle-shaped stromal cells, which have scanty cytoplasm, are typically arranged in whorls or a storiform pattern.
The primordial follicles are comprised of a primary oocyte, 40 to 70 µm in diameter, surrounded by a single layer of mitotically inactive squamous follicular cells, resting on thin basal lamina. Women are born with approximately 400,000 primordial follicles but subsequently their numbers gradually decrease by folliculogenesis and atresia until their eventual disappearance, which marks the start of menopause. In the reproductive period, primordial follicles are scattered irregularly in clusters throughout a narrow band in the superficial cortex. During each menstrual cycle, cohorts of primordial follicles undergo maturation into primary follicles with cuboidal squamous epithelium. Each month, typically only one developing primary follicle becomes dominant, and achieves complete maturation to release the oocyte. Other developing follicles undergo atresia.