- Steroid production
- Paired organs on each side of the uterus
- The ovary is approximately 4x3x2cm and weighs about 10g.
- Close relation to the fallopian tubes
- Each ovary is attached to the back of the broad ligament by a peritoneal fold, the mesovarium, which carries the blood supply, lymphatic drainage and nerve supply of the ovary.
- Ovarian arteries arise from the aorta just below the renal arteries.
- Outer cortex
- Inner medulla
- Large numbers of primordial oocytes supported by a connective tissue stroma.
- Covered by a single layer of cubical germinal epithelium and the underlying fibrous capsule.
- Fibrous capsule also called tunica albuginea.
- The cortex of the ovary at menarche contains about 500000 primordial oocytes that may become follicles, cysts about 0.1mm in diameter.
- They have a single layer of granulosa cells that produce oestradiol and specially differentiated theca cells which produce androgens.
- During each menstrual cycle many primordial follicles are recruited, but usually only one develops fully to become a mature Grafian follicle and expels its oocyte. The granulosa cells multiply and secrete follicular fluid. The oocyte with its granulosa layer projects into the follicle (Fig. 1.4).
- The stroma cells outside the granulosal cell layer differentiate into (1) the theca interna (a weak androgen secretor) (2) the theca externa (no hormone-secreting function).
- Shortly before ovulation, meiosis is completed in the primary oocyte in response to the luteinizing hormone (LH) surge. The oocyte casts off the first polar body resulting in the number of chromosomes in the remaining nucleus being reduced from 46 to 23. Thus the primary oocyte and the first polar body each contain the haploid number (23) of the chromosomes.
At this stage, the ripe follicle is about 20mm in diameter.
- At ovulation the follicle ruptures, releasing the oocyte usually into the fimbriated end of the fallopian tube. The follicle in the ovary collapses, the granulosa cells become luteal cells while the theca interna forms the theca lutein cells. A corpus luteum develops and projects from the surface of the ovary. It can be recognized by the naked eye by its crinkled outline and yellow appearance. Its cells secrete oestrogen and progesterone. If the ovum is not fertilized, the corpus luteum degenerates in about 10 days. A small amount of bleeding occurs into its cavity, the cells undergo hyaline degeneration and a corpus albicans is formed. If pregnancy does occur, the corpus luteum grows and may reach 3cm in diameter. It persists for 80-120 days and then gradually degenerates
- There are about seven million primordial oocytes or germ cells in each ovary of the female fetus at 15 weeks of intrauterine life.
- This drops to two million germ cells at birth
- There are half a million at puberty.
- About 400 will be recruited during each ovulation cycle during the reproductive life
- The rest degenerate at a steady rate.