Appearance
15.3 — Female Reproductive Anatomy
The uterus of a non-pregnant woman is about 7.5 centimetres long and weighs 60 grams. At full term it holds a baby, a placenta and a litre of fluid, and weighs around 1 kilogram — a thousandfold increase in capacity, achieved by cells enlarging rather than dividing.
It then returns to near its original size within six weeks.
No other organ does anything comparable, repeatedly, without damage.
The external structures
Collectively the vulva, and the terminology is worth getting right because it is confused constantly — including in medical settings.
The vulva is the external genitalia. The vagina is the internal canal. They are not synonyms, and using "vagina" for the whole thing obscures conditions that affect one and not the other.
Mons pubis — the fatty pad over the pubic bone.
Labia majora — the outer folds, containing fat, sweat and sebaceous glands, and hair-bearing.
Labia minora — the inner folds, hairless, richly supplied with nerves and blood vessels.
And their size and appearance vary enormously between individuals. This is worth stating because a substantial number of women believe theirs are abnormal, and requests for labiaplasty have risen sharply — driven largely by exposure to a narrow range of images. There is no standard appearance.
Clitoris — and this is where anatomy textbooks were wrong until remarkably recently.
The visible glans is a small part of the structure. The clitoris extends internally as two crura — legs — running along the pubic bones, and two bulbs flanking the vaginal opening, with a total length of around 9 to 11 centimetres.
Its full anatomy was not accurately described and published until 1998, by Helen O'Connell, and it was omitted or minimised in major anatomy texts for decades before that. It is a genuinely striking example of a gap in medical knowledge produced by whose bodies were considered worth studying.
It contains around 8,000 nerve endings in the glans alone — more than anywhere else in the human body, and roughly twice the number in the glans of the penis — and its only known function is sensation.
Vestibule — the area enclosed by the labia minora, containing the urethral and vaginal openings.
Bartholin's glands — either side of the vaginal opening, producing lubricating mucus. A blocked duct produces a Bartholin's cyst, which can become an abscess — painful, and treated by drainage with a technique that keeps the duct open.
Hymen — a thin membrane partially covering the vaginal opening, and a subject where correcting misinformation matters.
It is not a seal. It is a fold of tissue with an opening, and its shape varies widely. It stretches and can tear during first intercourse, and equally can tear during exercise, tampon use or nothing at all — and may not tear at all.
There is no reliable examination that establishes whether a person has had intercourse. "Virginity testing" has no scientific basis, is condemned by the World Health Organization, and is a human rights violation. Stating that plainly is part of the medical content, not separate from it.
Perineum — between the vaginal opening and the anus, and the site of tearing or episiotomy during childbirth (Chapter 15.7).
The internal structures
Vagina — a muscular canal about 7 to 10 centimetres long, and highly distensible in both length and width.
Its lining is stratified squamous epithelium (Chapter 4.2), thick and non-keratinised, and it has no glands at all — lubrication comes from transudation of fluid through the wall plus secretions from the cervix and Bartholin's glands.
Its pH is 3.8 to 4.5, maintained by lactobacilli metabolising glycogen in the lining cells into lactic acid.
And that acidity is the vagina's principal defence, excluding most pathogens.
Which is why disrupting it causes trouble. Douching removes the lactobacilli and raises the pH, increasing the risk of bacterial vaginosis and of sexually transmitted infection. The vagina is self-cleaning, and washing inside it is actively harmful — a point worth stating clearly given how heavily marketed such products are.
Glycogen production depends on oestrogen, which is why the vaginal pH rises before puberty and after menopause, and why atrophic vaginitis after menopause causes dryness, discomfort and increased infection (Chapter 12.6).
Cervix — the lower part of the uterus, projecting into the vagina, about 2.5 centimetres.
Its canal is narrow — a few millimetres — and it produces mucus whose properties change across the cycle (Chapter 4.3): thick and impenetrable for most of the month, thin and channelled at ovulation.
And the cervix has a specific anatomical feature that matters enormously for cancer screening.
The transformation zone is where the columnar epithelium of the cervical canal meets the squamous epithelium of the vaginal surface. Its position moves with age and hormonal state, and the cells there are actively converting from one type to another.
Essentially all cervical cancer arises in that zone, because actively dividing transitional cells are where HPV causes trouble. Which is exactly what a cervical smear samples.
Uterus — pear-shaped, with three layers.
Endometrium — the inner lining, which thickens and sheds cyclically.
Myometrium — the thick muscular wall, arranged in interlacing spirals.
And that spiral arrangement is what stops women bleeding to death after delivery. When the myometrium contracts after the placenta separates, the muscle fibres physically clamp the blood vessels running between them — "living ligatures". Uterine atony, where the muscle fails to contract, is the leading cause of postpartum haemorrhage (Chapter 15.7).
Perimetrium — the outer covering.
Position: typically anteverted and anteflexed — tipped forward over the bladder. Around 20 percent of women have a retroverted uterus, tipped backward, which is a normal variant and not a cause of infertility, though it can make some procedures and examinations more awkward.
Fallopian tubes — about 10 centimetres, extending from the upper corners of the uterus.
And they do not attach to the ovaries. The fimbriated end opens freely into the abdominal cavity, with finger-like projections that sweep over the ovary at ovulation.
Two consequences follow from that open end.
The female peritoneal cavity is in continuity with the outside world — vagina to uterus to tube to abdomen. Which is why pelvic infection can ascend and cause peritonitis, and why gonorrhoea and chlamydia can produce inflammation around the liver.
And an egg is occasionally lost into the abdomen. Abdominal pregnancy, though rare, is possible for exactly this reason.
The tube's lining is ciliated and its wall is muscular, and together they move the egg toward the uterus over 3 to 4 days. Fertilisation normally happens in the outer third (Chapter 4.3).
Damage to the cilia — from infection, most often chlamydia — is the leading cause of ectopic pregnancy and of tubal infertility.
Ovaries — almond-shaped, about 3 by 2 by 1 centimetres, and they shrink markedly after menopause.
They have two jobs: producing eggs and producing hormones (Chapter 12.6).
And their surface is unusual: it is not covered by peritoneum but by a layer of epithelium, and the egg is released by rupturing through that surface.
Which means the ovary is repeatedly wounded and repaired, roughly 400 times over a reproductive lifetime. This repeated injury-and-repair is one leading explanation for ovarian cancer risk, and it fits the observation that anything reducing the number of ovulations — pregnancy, breastfeeding, the contraceptive pill — reduces that risk substantially.
The blood supply and its consequences
The uterus is supplied by the uterine arteries, with a contribution from the ovarian arteries.
And the uterine artery crosses over the ureter about 2 centimetres from the cervix.
This is one of the most consequential anatomical relationships in surgery. The ureter is at risk during hysterectomy and during any procedure clamping the uterine artery, and the traditional teaching phrase — "water under the bridge", the ureter passing beneath the artery — exists precisely because injuring it is a recognised and serious complication.
Blood supply to the endometrium comes through spiral arteries, which are coiled and which constrict at the end of the cycle, causing the lining to become ischaemic and shed (Chapter 15.4).
The pelvic floor
Covered in Chapter 5.6, and its reproductive relevance belongs here.
A sling of muscle closing the pelvic outlet, with openings for the urethra, vagina and anus.
It supports the pelvic organs, maintains continence, and contributes to sexual function.
And it is stretched and can be torn during vaginal delivery.
The consequences — stress incontinence and prolapse — are extremely common and substantially under-reported. Around a third of women have some pelvic floor dysfunction, and most do not raise it, because it is assumed to be an inevitable consequence of childbirth or ageing.
It is not inevitable and it is treatable. Supervised pelvic floor muscle training cures or substantially improves stress incontinence in the majority, and it is first-line before any surgery.
The word "supervised" matters: a substantial proportion of women contract the wrong muscles when given only written instructions.
Breasts
Modified sweat glands, and their development is driven by oestrogen and progesterone at puberty (Chapter 15.9).
Structure: 15 to 20 lobes, each containing lobules of milk-producing alveoli, draining through ducts to the nipple, all embedded in fat and supported by fibrous ligaments.
The proportion of fat to glandular tissue varies enormously and determines breast size — and size has no relationship to milk production.
Lymphatic drainage is predominantly to the axillary nodes (Chapter 7.8), which is why those nodes are examined and sampled in breast cancer.
Cyclical changes — breasts become fuller and often tender in the second half of the cycle, from progesterone. Lumpiness that varies with the cycle is usually benign.
Breast awareness rather than formal self-examination is what is now advised. Knowing what is normal for you, and reporting change.
The changes that warrant assessment: a new lump, particularly hard, fixed or irregular; a change in the skin — dimpling, puckering, or an orange-peel texture; nipple retraction or a change in direction; any bloody or clear nipple discharge from a single duct; a persistent rash on the nipple, which can be Paget's disease of the breast; and any change persisting beyond one cycle.
Most breast lumps are benign — fibroadenomas in younger women, cysts in the 40s and 50s — and the purpose of the triple assessment (examination, imaging and needle sampling) is to establish that quickly rather than to wait.
Common conditions
Endometriosis — endometrial-type tissue growing outside the uterus, most often on the pelvic peritoneum, ovaries and the ligaments behind the uterus.
It affects around 10 percent of women of reproductive age, and it is the condition in this chapter where the medical system has performed worst.
The tissue responds to the cycle, so it bleeds each month into spaces with no outlet, causing inflammation, adhesions and scarring.
Symptoms: severe period pain, pain during or after sex, pelvic pain between periods, painful bowel movements or urination during periods, and infertility.
And the average delay from first symptom to diagnosis is 7 to 10 years.
The reasons are worth naming, because they are correctable. Severe period pain is normalised — girls are told that periods hurt. Symptoms are attributed to psychological causes. And the correlation between the amount of visible disease and the severity of pain is poor, so a normal ultrasound does not exclude it — diagnosis often requires laparoscopy.
Treatment: hormonal suppression of the cycle, pain management, and surgical excision of deposits. There is no cure, and the outcomes with specialist multidisciplinary care are substantially better than with fragmented management.
Fibroids (leiomyomas) — benign tumours of the myometrium.
Extremely common — present in up to 70 percent of women by 50, and far commoner and often more severe in women of African descent.
Most cause no symptoms. When they do: heavy periods, pelvic pressure, urinary frequency, and sometimes fertility problems depending on their position.
Position determines the effect. Fibroids distorting the uterine cavity cause heavy bleeding and can affect implantation; those on the outer surface cause pressure.
They shrink after menopause, because they are oestrogen-dependent, which is why watchful waiting is reasonable in a woman approaching it.
Treatment ranges from hormonal management to uterine artery embolisation to surgical removal, with hysterectomy reserved for those who have completed their families and have severe symptoms.
Ovarian cysts — extremely common, and most are functional: a follicle that did not rupture, or a corpus luteum that persisted. They resolve over one to three cycles.
Ovarian torsion is the emergency version — the ovary twisting on its supply, usually when enlarged by a cyst. Sudden severe one-sided pelvic pain with nausea, and it needs urgent surgery to preserve the ovary.
Pelvic inflammatory disease — infection ascending from the cervix, usually chlamydia or gonorrhoea.
And its importance is in what it leaves behind. Each episode causes tubal scarring, and the risk of infertility rises with each one — roughly 12 percent after one episode, 25 percent after two, and 50 percent after three.
Which is why it is treated promptly and with a low threshold, and why chlamydia screening in young people is a public health measure with a specific and calculable benefit (Chapter 15.13).
What the next page fixes
The anatomy is in place. Chapter 15.4 covers what it does every month — egg development from a stock laid down before birth, the hormonal cycle, ovulation, menstruation, and what a period actually is.