Mons pubis and labia majora

The mons pubis is a pad of fatty tissue overlying the symphysis pubis and covered by skin and pubic hair. The labia are folds of skin and fat which pass from the mons back to the perineum. The lateral labial surfaces are pigmented and hairy, and the inner surfaces smooth and contain many sebaceous, sweat and apocrine glands.

The substance of the labia consists of vascular fatty tissue with many lymphatics, and also vestigial remnants of the dartos muscle. (The labium is the homologue of the scrotum.)

Clitoris and labia minora

The clitoris is the vestigial homologue of the penis and is formed the same way from two corpora cavernosa and a glans of spongy erectile tissue which has a copious blood supply from the clitoral artery. The clitoris is highly innervated.

The labia minora are two cutaneous folds enclosing the urethral and vaginal orifices. Anteriorly, each divides to form a hood or prepuce, and a frenulum for the clitoris. Posteriorly, they unite in a frenulum or fourchette, which is obliterated by the delivery of a baby. The labia minora contain no fat but many sebaceous glands.

The VESTIBULE is the area between the labia minora. It is perforated by the urethral and vaginal orifices and the ducts of Bartholin’s and Skene’s glands. The fossa navicularis between the vagina and the fourchette is, like the fourchette, obliterated by childbirth. The lesser vestibular glands are mucosal glands discharging on to the surface of the vestibule.

The EXTERNAL URETHRAL ORIFICE is, in the healthy state, a small protuberance with a vertical cleft. The tiny orifices of the paraurethral (Skene’s) ducts lie just inside or outside the meatus. The paraurethral glands are homologues of the prostate and form a system of tubular glands, surrounding most of the urethra.

The VAGINAL ORIFICE is a midline aperture incompletely closed by the HYMEN. The hymen is a thin septum of tissue lined by squamous epithelium with a small hole (sometimes several) for the passage of menstrual blood. It is stretched or torn by coitus and more or less obliterated by childbirth. A few tags of skin called carunculae myrtiformes are left.

Normal virgin hymen

Hymen after coitus (or after using tampon)

Histology of bartholin’s Gland

The gland is formed of racemose glands lined with columnar or cuboid epithelium. The duct demonstrates the very intimate embryological connection between genital and urinary tracts by being lined with transitional epithelium.

Ischiocavernosus

This muscle compresses the root of the clitoris during sexual excitement, to produce erection by venous congestion.

Bulbospongiosus

This muscle conceals the vestibular bulb and Bartholin’s glands. Its function is to diminish the vaginal orifice during coitus.

Superficial transverse perineal muscle

A small muscle that helps to fix the perineal body.

External anal sphincter

Normally in a state of contraction to keep the anus closed. It also helps to fix the perineal body.

The Perineal body is a fibromuscular node between the anus and vagina with attachments to eight muscles:

The whole mass is what gynaecologists mean when they talk about ‘the perineum’. If it is damaged during childbirth and not properly repaired and healed, it will not function properly and the efficiency of the whole pelvic diaphragm may suffer, leading to urinary or faecal incontinence.

The Urogenital Diaphragm (Triangular Ligament)

This area of the perineum is more developed and surgically more important in the male. It consists of two sheets of fascia with a layer of muscle in between. It covers the pubic arch and is pierced by the urethra and, in the female, by the vagina.

(This space between the fasciae is sometimes called the ‘deep perineal pouch’.)

All the perineal muscles lie superficial to the perineal membrane, except the transversus perinei profundus, which helps to fix the perineal body.

(See page 16 on the function of the sphincter.)

The ‘sphincter urethrae’ is the system of musculature that assists the bladder muscle in closing the urethra. It is made up of the transversus perinei, the bulbospongiosus, and the levator ani; the anchoring bony points are the lower border of the symphysis pubis and the coccyx.

Boundaries

Laterally, the obturator fascia and ischial tuberosity.

Posteriorly, the sacrotuberous ligament.

Anteriorly, the urogenital diaphragm.

Medially, the sphincter ani and levator (anal) fascia.

The ischiorectal fat is traversed by the pudendal vessels and nerves and some small perineal branches of sacral nerves.

This pad of fat supports the anal canal and pelvic diaphragm.

Functions of the pelvic diaphragm

Apart from helping to fix the perineal body and assist the vaginal and anal sphincters, the main function of the pelvic diaphragm is to support the pelvic viscera.

The muscles used to be named as follows:

In the lower animals, their function is to move the tail (the coccyx). In man, they have to meet the requirements of the erect position and resist the strain imposed by any increase in intra-abdominal pressure such as when laughing, coughing, straining at stool, etc. In addition, a complete relaxation of the muscles should be possible during parturition so that the vaginal foramen may enlarge almost to the size of the bony pelvic outlet.

The pelvic fascia

Parietal Layer

The aponeuroses and fascial sheaths of the pelvic muscles (the ‘wallpaper’ of the pelvis).

Relations of the Fascia

The nerve trunks, which leave the pelvis, are ‘outside’ the fascia. The vessels are ‘inside’ and lie between the fascia and peritoneum.

These fascial prolongations on structures leaving the pelvis form points at which pus may track from a pelvic abscess to a point in the buttock or groin or above the inguinal ligament, as demonstrated in this image.

(The greater sciatic notch is not shown.)

Histology

Its length is about 9 cm along the posterior wall and 7.5 cm along the anterior. The width gradually increases from below upwards.

The vagina pierces the urogenital diaphragm and is encircled at its lower end by the voluntary bulbospongiosus, which has some sphincteric action, although the levator ani muscle is more effective.

Vaginal secretion

This is composed of alkaline cervical secretion, desquamated epithelial cells and bacteria. The epithelium is rich in glycogen which is converted by Doderlein’s bacillus into lactic acid. The vaginal pH is about 4.5 and provides a fairly effective barrier against infection.

The vaginal epithelium

This is composed of several layers of squamous cells with no keratinisation. It develops papillae, which dip into the fibrous corium. It is much thinner in the child, and the rugae are absent. This appearance recurs in old age. Cyclic changes are discussed on page 53.

Corpus and cervix

The upper two-thirds of the uterus are called the corpus or body, and the lower third is the cervix or neck. They are quite distinct in function, and therefore in structure as well, although the transition from muscle to fibrous tissue is gradual.

Corpus (uterine body)

Its function is to provide a mucous membrane (endometrium) suitable for implantation, and thereafter to contain the growing fetus until it is mature. It is composed mainly of smooth muscle.

Cervix

Its function is to provide an alkaline secretion favourable to sperm penetration, and once the uterus is gravid, to act as a sphincter. It is composed mainly of fibro-elastic tissue.

ISTHMUS UTERI This name is sometimes given to the upper few millimetres of the cervical canal below the internal os, an area to which the specific function of developing into the lower segment has been ascribed. The epithelium is intermediate between corpus and cervix; but if it were not for the importance of the lower segment in the theory of the physiology of pregnancy, it is unlikely that anatomists would have provided either an identity or a name for the isthmus uteri.

Cavity of the corpus

The anterior and posterior walls are almost in contact, but in coronal plane the cavity is triangular.

The muscle wall at each cornu is pierced by the very narrow interstitial portion of the fallopian tube.

Cervix

The external os is small before parturition and is sometimes called the os tincae (mouth of a small fish). After the birth of a child, it becomes a transverse slit – ‘the parous os’.

The cervical canal is fusiform and marked by curious folds called the ‘arbor vitae’.

The cervix is divided into supra- and infravaginal portion by the attachments of the vagina.

Relationship of uterus and ureter

The ureter is directly related to the uterine artery and the vaginal vault but is not in direct contact with the uterus.

This picture shows the ureter passing under the uterine artery on its course to the bladder.

In this picture, the bladder has been removed to show just how close the ureter is to the cervix. It also demonstrates the problems that are likely to be encountered in controlling haemorrhage and avoiding damage to the ureter during surgery in this area (see pages 288–291).

Ligaments of the uterus

The broad ligament is a fold of peritoneum passing from the uterus to the side wall of the pelvis. It contains the fallopian tube, the round and ovarian ligaments, the mesonephric remnants, the ovario-uterine anastomosis and, in its base, the ureter.

The ovarian and round ligaments are the vestigial gubernaculum. The round ligament ends in the inguinal canal and its fibres disperse in the labium majus.

The part of the broad ligament between the infundibulum and pelvic wall is called the infundibulopelvic ligament and contains the ovarian vessels and nerves. Note the proximity of external iliac vessels.

The main supports of the uterus are the fibromuscular condensations of tissue in the pelvic fascia (page 21).

The uterosacral ligaments pass from the back of the uterus to the front of the sacrum and are easily identified by the covering recto-uterine fold of peritoneum. These ligaments maintain the anteverted position of the uterus, and they are accompanied by uterine vessels and nerves.

The transverse cervical ligaments (Mackenrodt’s, cardinal ligaments) pass from the uterus and vagina to a wide insertion in the lateral pelvic wall. They lie below the broad ligament and contain vessels and nerves. The uterosacral ligament may be regarded as the posterior edge of the transverse cervical; its anterior edge is sometimes called the pubocervical, but this is not well defined.

Histology

The uterus has an incomplete peritoneal coat, which is very adherent. The anterior bare area is to allow movement of the bladder. There is a complete fascial sheath continuous with the vagina, and the body is made of smooth muscle interspersed with fibro-elastic tissue. There is a reversion of the ratio of muscle to connective tissue as the cervix is approached, and the cervix is nearly all fibrous.

The epithelium of the cavity is called the endometrium and consists of a single layer of cuboid or columnar ciliated cells on a cellular stroma. The stroma is deeply pierced by invaginations of the epithelium called uterine glands, which secrete a small amount of mucus to maintain moistness.

For cyclical changes in the endometrium see pages 49–51.

The cervix is lined by a single layer of high columnar ciliated epithelium, which covers the folds of the arbor vitae (pp. 29–30) and lines the cervical glands. The glands secrete an alkaline mucus, which is favourable to the activity of spermatozoa.

Blood vessels

There is an anastomosis between the uterine and ovarian arteries, and the fallopian tube is supplied by vessels in an arcade pattern (cf. bowel).

Vestigial structures

The epoöphoron and the paroöphoron are remnants of the mesonephros, and the duct (Gartner’s duct) is the vestige of the mesonephric duct, which passes into the uterine muscle about the level of the internal os and continues downwards in the vaginal wall.

These structures may give rise to cysts (hydatids of Morgagni, Kobelt’s tubules, fimbrial cysts) whose embryonic derivation is uncertain. They are probably mesonephric and can be grouped together as ‘vestigial cysts’.

Histology

Cross section shows the ovary to be roughly divided into a vascular medulla and a cortex.

The cortex is composed of a specialised ovarian stroma with a cuboidal surface epithelium which, like the tubal ostium, is intraperitoneal.

Note the condensed layer of stroma under the surface epithelium, called the tunica albuginea.

The hilum is characterised by the presence of paroöphoron tubules, which are of smooth muscle lined with ciliated epithelium; and by vestigial remnants of the sex cords called the rete ovarii, the analogue of the seminiferous tubules. These tissues are one reason for the extraordinary variety of ovarian tumours that can develop.

The CORPUS LUTEUM (‘yellow body’: the high lipid content required for steroid production gives the mature corpus luteum a yellow colour). During growth, the Graafian follicle gradually approaches the surface of the ovary and eventually extrudes the ovum through the stigma, into the waiting fimbriae of the tube. The follicle cells then quickly become luteinised by the retention of fluid to form the corpus luteum whose function is to secrete progesterone and prepare the endometrium for implantation of the fertilised ovum.

The growing corpus luteum is supplied with capillaries from the ovarian stromal vessels, and both theca and granulosa lutein cells secrete all the hormones. Under the influence of luteinising hormone (LH), theca cells metabolise cholesterol into androstenedione. The granulosa cells then metabolise the androstenedione produced by the theca cells into oestradiol under the control of follicle stimulating hormone (FSH). Thus, both cell types and both gonadotrophins are crucial to oestrogen synthesis.

Corpus albicans

As the physiological cycle proceeds, degeneration gradually occurs, and eventually the corpus luteum is hyalinised – a corpus albicans – and is absorbed in about a year. Consequent scarring accounts for the irregular surface of the ovary in the more mature woman.

Follicular atresia

In utero, there are 7 million ovarian follicles. Atresia of the follicles commences in utero. At birth, the ovary contains a million follicles. There is continued loss of ovarian follicles with advancing age. Only about 400 can ever become mature follicles, but at each cycle and probably during childhood several follicles may start to develop and for a time produce hormones. This abortive attempt ends in atresia and the atretic follicle is absorbed; but the process may account for anovular cycles and for the oestrogens produced by young pre-pubertal girls whose breasts are beginning to develop. The rate of follicular loss appears constant until the age of 37 and thereafter the rate of loss accelerates until the menopause.

The vulva

This is only a cleft in the perineum before puberty. Then the labia minora become more prominent and the fat of the mons and the labia majora is increased. Apart from the effects of coitus and parturition (p. 14) the most obvious sign of ageing is the gradual increase in size of the labia minora compared with the labia majora.

The vagina

The rugae are absent before puberty and gradually (over several years) disappear after the menopause. In old women, the vagina is thin, atrophic and completely smooth.

The ovary

This is at its largest during the reproductive stage and shrinks thereafter. All the oocytes are gone by the time of the menopause, and the cortex consists of fibrous tissue.

The uterus

Infantile: the cervix is longer than the corpus, and there is no flexion.

Pubertal: with the gradual increase in oestrogens, the corpus grows in relation to the cervix.

Adult: the corpus is now twice as long as the cervix and the normal degree of flexion has appeared.

After the menopause, the uterus gradually atrophies and in an old woman, the cavity may be less than 5 cm and the cervix simply an aperture in the senile vaginal vault.

Supply to uterus, vagina and bladder

This picture shows an arrangement often met with.

The vessels of the uterus and vagina are much coiled to provide extra length during pregnancy. Note the nearness of the ureter.

This picture shows the course of the pudendal artery passing behind the ischial spine and along the pudendal canal to the perineum.

In the ischiorectal fossa, the pudendal artery divides into inferior rectal and perineal branches.

Collateral blood supply

If the internal iliac artery has to be ligated, the collateral circulation should be adequate. It depends on anastomoses with the abdominal aorta, external iliac and femoral arteries.

Abdominal aorta

External iliac artery

The inferior epigastric anastomoses with the obturator; the deep circumflex iliac with the iliolumbar and lumbar arteries.

The femoral artery

The deep external pudendal anastomoses with the internal pudendal.

The superior and inferior gluteal arteries anastomose with the perforating and circumflex branches of the femoral and profunda femoris. (This is the ‘cruciate’ anastomosis.)