The female reproductive system and the ovary

The female system

The female reproductive system is built for a harder task than the male one. It makes the ova, it receives the sperms, it is the place where the baby grows for nine months, and it feeds the baby after birth.

The ovaries

A woman has two ovaries, one on each side of the lower abdomen. They are the primary sex organs of the female. They make the ovum, the female gamete, and the female hormones, which are steroids.

• Each ovary is about 2 to 4 cm long.
• Ligaments hold it to the wall of the pelvis and to the uterus.
• A thin layer of cells covers it. Under this layer is the stroma, which has two zones: the outer cortex and the inner medulla.

The follicles that hold the developing ova lie in the cortex. We will study them below.

The oviducts

The two oviducts, also called fallopian tubes, are each about 10 to 12 cm long. Each tube runs from near an ovary to the uterus. It has three parts.

1. The infundibulum is a funnel near the ovary. Its edge has finger like fimbriae, which help to collect the ovum after it leaves the ovary.
2. The ampulla is the wider middle part. Fertilisation usually happens here.
3. The isthmus is the narrow last part. It joins the uterus.

The uterus, cervix and vagina

The uterus, or womb, is a single pear shaped organ. Ligaments hold it to the pelvic wall. It opens into the vagina through a narrow neck, the cervix. The space inside the cervix is the cervical canal. The cervical canal and the vagina together form the birth canal.

The wall of the uterus has three layers.

The endometrium goes through regular changes in the menstrual cycle. The myometrium contracts strongly when the baby is born.

The external genitalia

The parts outside the body are together called the vulva.

• The mons pubis is a cushion of fat covered by skin and hair.
• The labia majora are fleshy folds that go down from the mons pubis and surround the vaginal opening.
• The labia minora are smaller folds inside the labia majora.
• The clitoris is a tiny finger like part at the upper joining of the labia minora, above the urethral opening.
• The hymen is a thin membrane that often partly covers the vaginal opening. It can be torn by many causes, such as a fall, sports like cycling or horse riding, or the use of a tampon. In some women it stays after sexual intercourse. So the hymen is not a sign of whether a woman has had sexual experience.

The mammary glands

The mammary glands are in the breasts. They are a part of the female system because they make milk after a baby is born. Each breast has fat and glandular tissue.

The glandular tissue has 15 to 20 lobes. A lobe holds clusters of cells, the alveoli, which make the milk and store it in their central space. The alveoli open into mammary tubules. The tubules of one lobe join to form a mammary duct. Several mammary ducts join to form a wider mammary ampulla. It leads to the lactiferous duct, through which the baby sucks the milk.

The ovary from the inside

The ovum is made in a follicle. The picture shows a follicle at its different stages, going round the ovary.

• A primary follicle is a primary oocyte with one layer of cells around it, the granulosa cells.
• A secondary follicle has more layers of granulosa cells and a new outer layer, the theca.
• A tertiary follicle has a fluid filled cavity, the antrum. The theca has an inner theca interna and an outer theca externa.
• The Graafian follicle is the mature follicle. It bulges at the surface of the ovary. The secondary oocyte inside is surrounded by a new membrane, the zona pellucida.
• At ovulation the Graafian follicle bursts and releases the secondary oocyte.
• What is left of the follicle becomes the corpus luteum, a yellow body that makes hormones. If there is no pregnancy it shrinks to the corpus albicans.

The next course explains how the oocyte develops. Here, learn the order of the follicles.

You should find that the number of ova released in a lifetime is a few hundred. The ovary holds tens of thousands of follicles at puberty, so only a very small share ever releases an ovum.

Try it in Python

The program counts the ova released between the first menstruation and menopause, for a cycle of fixed length.

Practise with new numbers

Common mistakes

• Saying that fertilisation happens in the uterus. It happens in the ampulla of the oviduct.
• Mixing the layers of the uterus. The perimetrium is outside, the myometrium is the muscle and the endometrium is the lining.
• Mixing the cortex and the medulla of the ovary. The follicles lie in the cortex.
• Saying that the vagina alone is the birth canal. The cervical canal and the vagina together form it.
• Using the hymen as a test. The hymen can be torn or stay for many reasons, so it tells nothing about a woman's life.

Remember these

• The ovaries (2 to 4 cm) make ova and steroid hormones. The follicles lie in the cortex.
• Oviduct: infundibulum with fimbriae, ampulla, isthmus. Fertilisation is in the ampulla.
• Uterus: perimetrium, myometrium, endometrium. The cervical canal and the vagina form the birth canal.
• Vulva: mons pubis, labia majora, labia minora, hymen, clitoris.
• Mammary gland: 15 to 20 lobes, alveoli, mammary tubules, mammary duct, mammary ampulla, lactiferous duct.
• Follicles in order: primary, secondary, tertiary, Graafian. After ovulation: corpus luteum, then corpus albicans.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Name the three parts of the oviduct from the ovary to the uterus. Which part collects the ovum?

2. Which layer of the uterus changes with the menstrual cycle, and which one contracts during birth?

3. What forms the birth canal?

4. Name the path of the milk from an alveolus to the nipple.

5. Put these in order: Graafian follicle, primary follicle, tertiary follicle, secondary follicle.

References

• NCERT (2023). Biology, Textbook for Class XII, chapter 2, Human Reproduction.
• Betts J. G. et al. (2022). Anatomy and Physiology 2e, OpenStax, chapter 27, The Reproductive System.
• Hall J. E. and Hall M. E. (2021). Guyton and Hall Textbook of Medical Physiology, 14th edition, Elsevier, chapter 81.