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Structure of Ovaries and Female Accessory Ducts

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The ovaries are the female reproductive glands that produce the egg (ovum) and the hormones oestrogen and progesterone. A female has two ovaries, each about 2 to 4 cm long, oval and almond-shaped, located on either side of the uterus in the lower abdomen. They are held in place by ligaments attached to the uterus and pelvic wall.

Knowing the structure of the ovaries and the female accessory ducts explains how an egg is released, captured and transported to the uterus each month. It also clarifies where fertilisation normally happens and why blocked tubes are a major cause of infertility.

Key Concepts

  • Ovarian cortex and medulla: the outer cortex contains developing follicles; the inner medulla carries blood vessels and nerves.
  • Ovarian follicle: a structure of an oocyte surrounded by granulosa cells; it grows from primordial to primary, secondary and finally a mature Graafian follicle.
  • Ovulation: the release of the secondary oocyte from the mature follicle, around day 14 of a 28-day cycle.
  • Corpus luteum: the ruptured follicle after ovulation, which secretes progesterone.
  • Fallopian tube (oviduct): the duct with three parts — the funnel-shaped infundibulum with finger-like fimbriae, the wider ampulla, and the narrow isthmus joining the uterus. Fertilisation usually occurs in the ampulla.
  • Uterus: the muscular organ whose inner lining, the endometrium, receives the embryo.
  • Cervix and vagina: the lower neck of the uterus and the canal that receives sperm and forms the birth passage.

How It Works

  1. A follicle matures in the ovary under FSH stimulation.
  2. At ovulation the Graafian follicle ruptures and releases the secondary oocyte.
  3. The fimbriae of the infundibulum sweep over the ovary and catch the egg.
  4. Cilia lining the fallopian tube beat to move the egg towards the uterus; this journey takes about 3 to 4 days.
  5. If sperm meet the egg in the ampulla, fertilisation occurs; the resulting structure continues to the uterus for implantation.

Worked Example

Follow one egg through a 28-day cycle. Day 1 to 13: a follicle grows in the right ovary and its oocyte matures. Day 14: ovulation releases the secondary oocyte; fimbriae capture it within minutes. Days 14 to 17: cilia push it through the ampulla and isthmus, a journey of about 10 cm over roughly 3 days, averaging about 3 cm per day. Day 17 to 18: it reaches the uterus. If unfertilised, it disintegrates within about 24 hours of ovulation and is shed with the endometrium at the next period around day 28.

Common Misconceptions

  • "Fertilisation happens in the uterus." Wrong. It normally happens in the ampulla of the fallopian tube; the uterus is for implantation and growth.
  • "The egg swims to the uterus." The egg has no tail; cilia and muscular contractions of the tube move it.
  • "Both ovaries release an egg every month." Usually only one ovary ovulates in a given cycle, often alternating.

Real-World Applications

Ultrasound scans track follicle growth during fertility treatment to time egg collection for IVF. Tubectomy blocks or cuts the fallopian tubes to prevent pregnancy. An ectopic pregnancy, where the embryo implants in the tube instead of the uterus, is a medical emergency that doctors detect using knowledge of this anatomy.

The ovary produces and releases the egg, while the fallopian tube, uterus, cervix and vagina form the accessory pathway that transports the egg and supports fertilisation and pregnancy.

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