Anatomy of the female reproductive system

The female reproductive system has external genitalia (the vulva) and internal genitalia (the vagina, cervix, uterus, uterine tubes and ovaries). The vagina and cervix form the lower canal, the uterus holds the pregnancy, the tubes carry the ovum to the uterus, and the ovaries produce the gametes and the sex steroids. The internal organs lie in the pelvis, held by peritoneal folds and ligaments. Each organ has a characteristic wall, lining and normal size, which this topic sets out with the blood and nerve supply.

The female reproductive system is made up of the external genitalia, which together form the vulva, and the internal genitalia, which are the vagina, cervix, uterus, uterine (fallopian) tubes and ovaries. The vagina and cervix form a canal between the outside of the body and the uterus. The uterus lies between the bladder in front and the rectum behind. The uterine tubes run out from its upper corners, and the ovaries lie on the posterior surface of the broad ligament beside the uterus.

Functions of the internal genitalia

• The vagina receives the penis and the ejaculate, provides the birth canal, and is the channel through which menstrual fluid leaves the body.
• The cervix allows sperm to pass into the uterine cavity and helps keep the upper female genital tract sterile.
• The uterus accommodates the growing fetus and is the site of implantation and of the menstrual shedding of the endometrium.
• The uterine tubes transport the ovum from the ovary to the uterus and are the normal site of fertilisation.
• The ovaries produce the oocytes, and they produce oestrogen and progesterone in response to LH and FSH.

Relations in the pelvis

In the median sagittal section below, the uterus lies above the bladder and urethra in front and above the rectum and anal canal behind. The vagina runs between the urethra and the rectum.

The vulva is the external female genitalia. It consists of the mons pubis, the labia majora, the labia minora, the clitoris, the vestibule with its glands and openings, and the vestibular bulbs. The vulva rests on the triangular urogenital diaphragm in the anterior part of the pelvis. The perineum is the area of the surface of the trunk between the thighs and the buttocks, extending from the coccyx to the pubis. The labia majora extend from the mons pubis to the posterior commissure, and the labia minora lie deep within them.

Mons pubis and labia

• The mons pubis is a pad of subcutaneous adipose and connective tissue in front of the pubic bone. In the adult woman it is covered with hair.
• The labia majora are folds of skin with underlying adipose tissue. They fuse anteriorly with the mons pubis and posteriorly at the perineum. They contain hair follicles, sebaceous glands and sweat glands.
• The labia minora are narrow skin folds inside the labia majora. Anteriorly they fuse to form the clitoral hood (prepuce) and frenulum of the clitoris, and posteriorly with the labia majora and the perineum. They contain sebaceous and sweat glands, but no hair follicles and no underlying adipose tissue. They also contain connective tissue, many vessels and nerve endings. Posteriorly they form a fold of skin called the fourchette at the back of the vaginal introitus. They are poorly developed before puberty and atrophy after the menopause. Both the labia minora and the labia majora become engorged during sexual arousal.

Clitoris

The clitoris is a cylindrical erectile body about 2.5 cm long, with a range of about 0.5 to 3.5 cm between women. It is the embryological homologue of the penis. It consists of two crura, which correspond to the corpora cavernosa of the male, a body, and a glans. The frenulum is found on the ventral surface of the glans and is the fused junction of the labia minora.

Vestibule and its openings

The vestibule lies between the labia minora. It is bounded anteriorly by the clitoris and posteriorly by the perineum.

• The urethral opening lies in the midline just in front of the vaginal orifice, about 1 to 1.5 cm below the pubic arch. The ducts of the paraurethral (Skene) glands open into the vestibule.
• The vaginal opening lies at the posterior end of the vestibule. It is closed by a thin fold of mucous membrane, the hymen, which is usually perforated so that menstrual blood can leave the body. The hymen is ruptured by sexual activity and by childbirth, and any remaining tags are called the carunculae myrtiformes.

Greater vestibular (Bartholin) glands

The greater vestibular glands lie close to the posterior end of the vestibular bulb. They correspond to the bulbourethral glands of the male. They secrete an alkaline mucus that lubricates the vestibule during sexual stimulation. The glands are about the size of a pea, and each opens through a duct about 2 cm long. Each gland has a duct that opens into the vestibule. The ducts are lined by columnar epithelium, but near their opening they are lined by stratified squamous epithelium.

Vestibular bulbs

The vestibular bulbs are two elongated masses of erectile tissue beneath the mucosa of the vestibule. Each bulb lies on one side of the vaginal orifice, in front of the greater vestibular glands. The bulbs are traditionally named the bulbs of the vaginal vestibule. They almost completely cover the distal vaginal wall, and their function is not fully known. They probably support the distal vaginal wall and add to its rigidity during penetration. Some recent work suggests they may be part of the clitoris.

Muscles of the vulva

The muscles of the vulva are the bulbocavernosus, the ischiocavernosus and the superficial transverse perineal muscle. They lie superficial to the fascia of the urogenital diaphragm.

Blood supply of the vulva

• Branches of the internal pudendal artery supply the vulva. The labial artery supplies the vestibular bulb, and the deep and dorsal arteries supply the clitoris.
• Branches of the femoral artery, the superficial and deep external pudendal arteries, also supply the vulva.

Nerve supply of the vulva

• The anterosuperior part is supplied by the cutaneous branches of the ilioinguinal nerve and the genital branch of the genitofemoral nerve (L1 to L2).
• The posteroinferior part is supplied by the pudendal branches of the posterior cutaneous nerve of the thigh (S2 to S4).
• The labial and perineal branches of the pudendal nerve (S2 to S4) supply the remainder.

The vagina is a distensible muscular tube. It extends posterosuperiorly from the external vaginal orifice to the cervix. It is a fibromusculomembranous sheath. It is the excretory channel for the uterine secretions and menstrual blood, the organ of copulation, and the lower part of the birth canal. It is about 10 cm long, with the anterior wall about 7 cm and the posterior wall about 9 cm.

Structure and layers

The vagina is lined by stratified squamous epithelium that is not keratinised. The wall has three layers of smooth muscle. Beneath the muscle layers is a submucosal layer of connective tissue that contains a rich supply of veins and lymphatic vessels. Histologically, working from the inside outwards, the wall has the stratified squamous epithelium, an elastic lamina propria, a fibromuscular layer and an adventitia.

The anterior and posterior walls are normally collapsed, so they lie in contact with one another. The mucosa has transverse folds called rugae. In children and young women the rugae are present in the submucosa, and they connect to the tendinous arch of the pelvic fascia. That connection is the main support of the vaginal walls. With age and childbirth the connection between the vaginal walls and the muscular pelvis may weaken, which makes the pelvic floor less stable.

Relations

• Anteriorly lie the bladder and the urethra.
• Posteriorly lie the rectouterine pouch, the rectum and the anal canal.
• Laterally lie the ureters and the levator ani muscle. At the fornices the cardinal ligaments lie laterally, and below them lie the levator ani muscles and the ischiorectal fossae.
• The upper posterior wall forms the anterior reflection of the peritoneum of the pouch of Douglas. The middle third is separated from the rectum by pelvic fascia, and the lower third abuts the perineal body.
• The urethra runs down the lower half of the anterior wall in the midline to open into the vestibule.

Fornices

The upper end of the vagina surrounds the cervix and creates the fornices. There are four of them: an anterior fornix, a posterior fornix, and two lateral fornices. The posterior fornix is the deepest. It is close to the peritoneum that forms the floor of the pouch of Douglas. After intravaginal ejaculation the posterior fornix acts as a reservoir for semen, which then passes through the cervical canal.

Lower end and the urogenital diaphragm

At its lower end the vagina passes through the urogenital diaphragm and is surrounded by the bulbocavernosus muscles of the vulva, which act as a sphincter. The hymen is a fold of mucous membrane-covered connective tissue.

Blood and nerve supply of the vagina

• The vaginal artery, a branch of the internal iliac (hypogastric) artery, is the major supply. The cervicovaginal branch of the uterine artery also supplies the vagina.
• Innervation is autonomic, from the uterovaginal nerve plexus.

Epithelium and age changes

• At birth and for the first 10 to 14 days of life, the epithelium is stratified under the influence of maternal oestrogen circulating in the newborn.
• Before puberty and after the menopause, the epithelium becomes thin, with only a few layers of cells.
• From puberty to the menopause the vaginal epithelium is stratified squamous, has no glands, and has three distinct layers of cells: basal cells, intermediate cells and superficial cells.

Vaginal secretions and flora

Vaginal secretions come mainly from the cervical glands. They also come from transudation through the vaginal epithelium and from the greater vestibular glands. The secretion is made of tissue fluid, epithelial debris, electrolytes, proteins and lactic acid.

The Döderlein bacillus (a Gram-positive rod, now generally identified with lactobacilli) appears in the vagina 3 to 4 days after birth and disappears after 10 to 14 days. It reappears at puberty and disappears after the menopause. It converts the glycogen in the vaginal mucosa to lactic acid. This keeps the vaginal pH acidic, at about pH 4.5, which prevents the growth of other pathogenic organisms.

The cervix is the lowest part of the uterus. It connects the uterine body with the vagina and acts as a gateway between them. It is about 2.5 cm long (2 to 3 cm in some descriptions). It joins the vagina at an angle of between 45 and 90 degrees. Its external opening into the vagina is the external os, and its opening into the uterine cavity is the internal os.

Parts and epithelium

• The ectocervix is the part that projects into the vagina. It is covered by stratified squamous non-keratinised epithelium.
• The endocervical canal is the more proximal part. It is lined by simple columnar epithelium.
• The cervix allows sperm to pass into the uterine cavity and helps keep the upper female genital tract sterile, because all the structures above the cervix are sterile.
• Before puberty the lengths of the body and the cervix are equal. After puberty, under the influence of oestrogen, the ratio of body to cervix changes to about 2:1 or 3:1.

Transformation zone

The stratified squamous epithelium of the ectocervix changes to simple columnar epithelium at the transformation zone (the squamocolumnar junction), which lies at about the level of the external os. The external os is round to oval in a woman who has not had children, and it is often a transverse slit after childbirth.

Cervical glands and mucus

The cervical glands secrete an alkaline mucus that is rich in fructose, glycoprotein and mucopolysaccharides. The cervical mucus contributes to the normal vaginal discharge. The fructose has a nutritive function for spermatozoa.

Relations and blood supply of the cervix

• The uterine artery supplies the cervix. Its cervicovaginal branch also supplies the upper vagina.
• The ureter runs about 1 cm lateral to the supravaginal cervix, within the parametrium. Where the uterine arteries reach the uterus they overlie the ureter, so the ureter can be injured inadvertently during pelvic surgery.

The uterus is a hollow muscular organ that lies between the rectum and the bladder. It can expand to accommodate the growing fetus. In a woman who has not had children it is about 7 to 8 cm long and 4 to 5 cm wide at its widest point. The maximum external dimensions of a non-pregnant uterus are about 7.5 cm long, 5 cm wide and 3 cm thick, and an adult uterus weighs about 70 g. The uterus connects distally to the vagina through the cervix and laterally to the uterine tubes.

Parts of the uterus

• The fundus is the part above the openings of the uterine tubes.
• The body (corpus) is the main part. The body is where the blastocyst should implant. The two uterine tubes enter at the upper corners, called the cornua.
• The isthmus is the narrowed part between the body and the cervix.
• The cervix is the lowest part, about 2.5 cm long.

Position of the uterus

The uterus can lie in several positions in relation to the vagina. The normal position is anteversion with anteflexion. In anteversion the long axis of the cervix lies at about 90 degrees to the long axis of the vagina. In anteflexion the long axis of the body lies at about 120 degrees to the long axis of the cervix. Other combinations are possible and are clinically important. In about one woman in five the uterus is tilted backwards (retroversion and retroflexion). This usually has no pathological significance, but a retroversion that is fixed and immobile may be associated with endometriosis.

• Antevertedthe uterus is pushed forward on top of the bladder.
• Anteverted and anteflexedthe uterus has an additional flexion at its most proximal part.
• Retrovertedthe uterus is pushed back towards the rectum.
• Retroverted and retroflexedthe uterus has an additional posterior flexion towards the rectum.

A retroflexed or anteflexed uterus carries a greater risk of uterine perforation during certain procedures, and the risk of intrauterine device insertion is higher in these women.

Layers of the uterus

• The endometrium is the inner mucosa. It is simple columnar epithelium with an underlying connective tissue. It has a deep and a superficial layer, and it changes in structure during the menstrual cycle.
• The myometrium is the middle layer of smooth muscle. It becomes distensible during pregnancy, and during labour the smooth muscle contracts in response to hormonal stimulation.
• The perimetrium is the outer serous layer, formed of peritoneum over a thin connective tissue layer.

Blood supply of the uterus

The uterine arteries, branches of the internal iliac (hypogastric) arteries, are the main supply. The ovarian arteries contribute a further supply. Where the uterine arteries meet the uterus they overlie the ureter.

The uterus, tubes and ovaries are held in place by peritoneal folds and ligaments, which are attached to the pelvic walls and the sacrum.

The sacrospinous ligament connects the sacrum to the ischial spine and is not attached to the uterus.

The uterine tubes are muscular, J-shaped tubes. They lie in the upper border of the broad ligament and extend laterally from the horns of the uterus to open into the abdominal cavity near the ovaries. Each tube is about 7 to 14 cm long.

Parts of the tube

• The intramural (interstitial) part lies within the wall of the uterus.
• The isthmus is the narrow, straight part that joins the uterus.
• The ampulla is the widest part of the tube. Fertilisation usually occurs here.
• The infundibulum is the funnel-shaped end near the ovary. It is fringed by finger-like fimbriae, which capture the ovulated ovum from the surface of the ovary. One fimbria is longer than the others and reaches the ovary.

Function

The tube transports gametes, facilitates fertilisation, and supports the survival of the zygote through its secretions. The mucosa is lined by ciliated columnar epithelium, and the cilia beat towards the uterus to help move the oocyte. The smooth muscle layer contracts to propel the ovum. The tube contains ciliated cells, which produce a steady current of fluid towards the uterus, and secretory cells, which add to the volume of tubal fluid. The tube has no submucosa and no glands. Its mucosa forms branched longitudinal folds (plicae), and the lumen of the ampulla is almost filled with these folds. The folds have a cellular stroma. Their epithelium changes with the menstrual cycle, but the tube does not shed cells at menstruation.

Blood and nerve supply of the tube

• Arterial supply is from the uterine and ovarian arteries.
• Venous drainage is through the pampiniform plexus into the ovarian veins.
• Innervation is autonomic (sympathetic and parasympathetic) from the ovarian and uterine plexuses.

Relations

The tube runs in the upper margin of the broad ligament, which is called the mesosalpinx. The tube is covered by peritoneum, except along a narrow strip on its inferior aspect. The abdominal opening of the tube opens into the peritoneal cavity, which is therefore in communication with the exterior through the uterus and the vagina.

The ovaries are the paired female gonads. Each ovary is oval, almond-shaped and lies on the posterior surface of the broad ligament. The ovary is the only intra-abdominal organ that is not covered by peritoneum. Its surface is covered by a single layer of cuboidal cells, known as germinal epithelium. The ovary develops from the medial aspect of the mesonephric ridge and descends through the abdomen. In the young adult the ovary is almond-shaped.

Structure of the ovary

• The cortex is the outer part. It is made of a connective tissue stroma, and it supports the follicles. Each follicle contains an oocyte surrounded by follicular cells.
• The medulla is the inner part. It contains smooth muscle fibres, blood vessels, nerves, lymphatics and loose connective tissue. Its neurovascular network enters the ovary at the hilum from the mesovarium.

Follicles and corpora

Ovarian follicles include primordial follicles, maturing (primary and secondary) follicles, Graafian (mature) follicles and the corpus luteum. The follicles are related to sex hormone production and to ovulation. Each primordial follicle contains an oocyte arrested in prophase, surrounded by granulosa cells. The maximum number of primordial follicles is reached at about 20 weeks of gestation, and they are reduced by atresia throughout childhood and adult life. Atresia of these structures leaves a corpus albicans.

Function

The ovaries produce the female gametes (oocytes), store them and release them at ovulation, and produce oestrogen and progesterone in response to LH and FSH. The ovaries are concerned with germ cell maturation, storage and release, and with steroidogenesis.

Attachments

• The mesovarium attaches the ovary to the posterior surface of the broad ligament and carries its nerves and blood vessels.
• The ovarian ligament attaches the ovary to the uterus.
• The suspensory ligament of the ovary, also called the infundibulopelvic ligament, attaches the ovary to the lateral pelvic wall. It is the lateral margin of the broad ligament and contains the ovarian vessels.

Blood and nerve supply of the ovary

• The ovarian arteries are direct branches of the abdominal aorta. The uterine artery also supplies the ovary.
• The right ovarian vein drains directly into the inferior vena cava. The left ovarian vein drains into the left renal vein.
• Innervation is autonomic, from the ovarian and uterine plexuses.

• Childhoodthe uterus grows slowly in length, in parallel with height and age. The average longitudinal diameter is about 2.5 cm at 2 years and about 3.5 cm at 10 years. The ovaries are small, about 1.5 cm long, until puberty.
• Newbornmaternal oestrogen circulating in the newborn stratifies the vaginal epithelium for the first 10 to 14 days. When the oestrogen disappears, the vaginal pH rises towards 7 and the epithelium atrophies again. After birth the uterus decreases in length by about one-third and in weight by about one-half as the maternal oestrogen disappears.
• Pubertythe anteroposterior and transverse diameters of the uterus start to increase, and the uterine volume rises sharply. The uterus reaches adult size and shape by the late teens. The ovaries reach adult size, with stromal proliferation and the start of follicular maturation.
• Reproductive yearsthe cervix is about one-third to one-half the length of the body of the uterus. The vaginal epithelium is thick and stratified.
• After the menopauseno active follicles remain and the ovary becomes smaller, with a wrinkled surface. The uterus atrophies, the endometrium becomes very thin, the glands almost disappear, and the wall becomes less muscular. The vaginal epithelium becomes thin again.