Gray's Anatomy Chapter 77. Female reproductive system. Lower genital tract

 Female reproductive system

BS. Nguyễn Hồng Anh

The female reproductive system consists of the lower genital tract (vulva and vagina) and the upper tract (uterus and cervix with associated uterine (Fallopian) tubes and ovaries).

LOWER GENITAL TRACT

VULVA

The female external genitalia or vulva include the mons pubis, labia majora, labia minora, clitoris, vestibule, vestibular bulb and the greater vestibular glands (Fig. 77.1).

Mons pubis

The mons pubis is the rounded, hair-bearing area of skin and adipose tissue over the pubic symphysis and adjacent pubic bone. Before puberty, the mons pubis is relatively flat and hairless, and the labia minora are poorly formed. Through adolescence and into adult life, the mons becomes prominent with coarse hair and atrophies slightly after menopause.

Labia majora

The labia majora are two prominent, longitudinal folds of skin that extend back from the mons pubis to the perineum (Fig. 77.1B). They form the lateral boundaries of the vulva. Each labium has an external, pigmented surface covered with hairs and a smooth, pink internal surface with large sebaceous follicles. Between these surfaces there is loose connective and adipose tissue, intermixed with smooth muscle (resembling the scrotal dartos muscle), vessels, nerves and glands. The subcutaneous layer consists of a superficial fatty layer similar to Camper’s fascia, and a deep membranous layer – Colles’ fascia – continuous with Scarpa’s fascia of the anterior abdominal wall (p. 1069). The uterine round ligament may end in the adipose tissue and skin in the anterior part of the labium. A patent processus vaginalis may also reach a labium. The labia join anteriorly to form the anterior commissure.

Posteriorly, they do not join, but instead merge into neighbouring skin ending near and almost parallel to each other. The connecting skin between them posteriorly forms a ridge, the posterior commissure, which overlies the perineal body and is the posterior limit of the vulva.

The distance between the posterior vulva and the anus is 2.5–3 cm and is termed the ‘gynaecological’ perineum.

Fig. 77.1 A, The superficial features of the perineum. B, The labia majora and surrounding external genitalia. C, The labia minora. D, An inferior view of the vestibule with the left labium minus pulled to one side to show the regions of the vestibule into which the greater vestibular and para-urethral glands open. (A, With permission from Drake RL, Vogl AW, Mitchell A, Tibbitts R, Richardson P (eds), Gray’s Atlas of Anatomy, Elsevier, Churchill Livingstone. Copyright 2008. B–D, With permission from Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright 2010.)

Labia minora

The labia minora are two small cutaneous folds, devoid of fat, that lie between the labia majora. They extend from the clitoris obliquely down, laterally and back, flanking the vaginal orifice. Anteriorly, each labium minus bifurcates. The upper layer of each side passes above the clitoris to form the hood or prepuce, while the lower layer passes below the clitoris to form the frenulum of the clitoris (Fig. 77.1A–C). Sebaceous follicles are numerous on the medial surfaces. Sometimes, an extra labial fold (labium tertium) is found on one or both sides between the labia minora and majora. Adhesions between the labia minora are common in prepubertal girls and may predispose to urinary infections

(Leung and Robson 1992).

Vestibule

The vestibule is the cavity that lies between the labia minora. It contains the vaginal and external urethral orifices and the openings of the two greater vestibular (Bartholin’s) glands and of numerous mucous, lesser vestibular glands. There is a shallow vestibular fossa between the vaginal orifice and the frenulum of the labia minora. The posterior part of the vestibule is a classic site where a fistulous opening of the rectum may be located in girls born with an imperforate anus (Bill et al 1975).

Urethra

The urethra opens into the vestibule about 2.5 cm below the clitoris and above the vaginal opening via a short, sagittal cleft with slightly raised margins: the urethral meatus. The meatus is very distensible and varies in shape; the aperture may be rounded, slit-like, crescentic or stellate. The ducts of the para-urethral glands (Skene’s glands) open on each side of the lateral margins of the urethra.

Bulbs of the vestibule

The bulbs of the vestibule lie on each side of the vestibule (Fig. 77.2B). They are two elongated masses of erectile tissue, 3 cm long, which flank the vaginal orifice and unite anterior to it by a narrow commissura bulborum (pars intermedia). Their posterior ends are expanded and are in contact with the greater vestibular glands. Their anterior ends taper and are joined by a commissure, and also to the clitoris by two slender bands of erectile tissue. Their deep surfaces contact the inferior aspect of the perineal membrane; superficially, each is covered posteriorly by bulbospongiosus (Fig. 77.2A) (Delancey 2011).

Greater vestibular glands

(Bartholin’s glands)

The greater vestibular glands are homologues of the male bulbourethral glands. They consist of two small, round or oval, reddish-yellow bodies that flank the vaginal orifice, in contact with, and often overlapped by, the posterior end of the vestibular bulb. Each opens into the vestibule by a 2 cm duct, situated in the groove between the hymen and the labium minus at approximately the 5 and 7 o’clock positions (Corton 2012) (see Fig. 77.1D). The glands are composed of tubulo-acinar tissue; the secretory cells are columnar and secrete a clear or whitish mucus for lubrication during sexual arousal.

Clitoris

The clitoris is an erectile structure, partially enclosed by the anterior bifurcated ends of the labia minora. It has a root, a body and a glans (see Fig. 77.2). The body can be palpated through the skin. It contains two corpora cavernosa, composed of erectile tissue and enclosed in dense fibrous tissue, and separated medially by an incomplete fibrous pectiniform septum. The fibrous tissue forms a suspensory ligament that is attached superiorly to the pubic symphysis. Each corpus cavernosum is attached to its ischiopubic ramus by a crus that extends from the root of the clitoris. The glans clitoris is a small, round tubercle of spongy erectile tissue at the end of the body, connected to the bulbs of the vestibule by thin bands of erectile tissue. It is exposed between the anterior ends of the labia minora. Its epithelium has high cutaneous sensitivity, important in sexual responses. Congenital absence of the clitoris is very rare.

Vascular supply and lymphatic drainage of the vulva

Arteries

The arterial blood supply of the female external genitalia is derived from the superficial and deep external pudendal branches of the femoral artery superiorly and the internal pudendal artery inferiorly on each side (Figs 77.3A, 77.4)

Fig. 77.3 A, The vessels of the female pelvis: sagittal view. B, The nerves and lymphatics of the female pelvis: sagittal view. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)

Fig. 77.4 The muscles, vessels and nerves of the female perineum: inferior view. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)

This blood supply to the labial fat must be carefully preserved during vaginal surgery, e.g. in creating a Martius fat pad flap to repair a vesicovaginal fistula where blood supply has already been compromised by radiation or fibrosis (Delancey 2011).

Veins

Venous drainage of the vulval skin is via external pudendal veins to the long saphenous vein. Venous drainage of the clitoris is via deep dorsal veins to the internal pudendal vein, and via superficial dorsal veins to the external pudendal and long saphenous veins.

Lymphatic drainage

A meshwork of connecting vessels from the skin of the labia, clitoris and perineum join to form three or four collecting trunks that drain to superficial inguinal nodes lying on the cribriform fascia covering the femoral artery and vein; these nodes drain through the cribriform fascia to the deep inguinal nodes lying medial to the femoral vein (Corton 2012). The deep inguinal nodes drain via the femoral canal to the pelvic nodes (Table 77.1). The last of the deep inguinal nodes lies under the inguinal ligament within the femoral canal and is often called Cloquet’s node. Lymph vessels from the clitoris drain directly to the deep inguinal nodes, and direct clitoral lymphatics may pass to the internal iliac nodes (Fig. 77.3B). Lymph vessels in the perineum and lower part of the labia majora drain to the rectal lymphatic plexus.

Innervation

The main nerve supply of the vulva is the pudendal nerve (S2, 3 and 4) through its inferior rectal and perineal branches and the dorsal nerve of the clitoris (Table 77.2; Figs 77.4, 77.5). Shoja et al 2013). The sensory innervation of the anterior and posterior parts of the labium majus differs. The anterior third of the labium majus is supplied by the ilioinguinal nerve (L1), the posterior two-thirds are supplied by the pudendal nerve through the posterior labial branches of the perineal nerve (S3), and the lateral aspect is also innervated by the perineal branch of the posterior cutaneous nerve of the thigh (S2). Vulvar nerves are susceptible to trauma and inflammation, leading to vulvar pain syndromes or vulvodynia (Shoja et al 2013).

VAGINA

The vagina is a fibromuscular tube lined by non-keratinized stratified epithelium. It extends from the vestibule (the opening between the labia minora) to the uterus. The upper end of the vagina surrounds the vaginal projection of the uterine cervix. The anular recess between the cervix and vagina is the fornix; the different parts of the fornix are given separate names, i.e. anterior, posterior and right and left lateral, but they are continuous (Fig. 77.6).

In the standing position, the vagina ascends posteriorly and superiorly, forming an angle of 60–70° with the horizontal plane (Corton 2012). The vagina forms an angle of over 90° to the uterine axis (see Fig. 77.12); this angle varies with the contents of the bladder and rectum. The apex of the vagina is directed posteriorly towards the ischial spines. The width of the vagina increases as it ascends. The inner surfaces of the anterior and posterior vaginal walls are in contact with each other, forming a transverse slit. The vaginal mucosa is attached to the uterine cervix higher on the posterior cervical wall than on the anterior; the anterior wall is approximately 7.5 cm long and the posterior wall is approximately 9 cm long. The fibromuscular anterior wall of the vagina supports the base of the bladder in its middle and upper portions, and the urethra (which is embedded in it) inferiorly. The fibromuscular posterior wall of the vagina supports the rectum. The upper quarter of the posterior vagina is separated from the rectum by the peritoneum of the recto-uterine pouch, and by moderately dense fibromuscular tissue (Denonvilliers’s fascia) in its middle half (Delancey 2011). In its lower quarter, it is separated from the anal canal by the fibromuscular perineal body. The upper part of the vagina is supported laterally by levator ani, together with the transverse cervical, pubocervical and uterosacral ligaments. Pubovaginalis provides a U-shaped muscular sling around the mid-vagina. The lower vagina is surrounded by the skeletal muscle fibres of bulbospongiosus (see Fig. 77.4). As the ureters pass anteromedially to reach the fundus of the bladder, they pass close to the lateral fornices, where care must be taken to avoid damage during hysterectomy (Fig. 77.7). As they enter the bladder, the ureters are usually anterior to the vagina; at this point, each ureter is crossed transversely by a uterine artery (Fig. 77.8).

Fig. 77.5 The autonomic innervation of the female reproductive system. (Based on Barucha AE 2006 Pelvic floor: anatomy and function. Neurogastroenterol Motil 18:507–19.)

The vagina opens externally via a sagittal introitus positioned below the urethral meatus (see Fig. 77.1C). The size of the introitus varies; it is capable of great distension during childbirth and, to a lesser degree, during sexual intercourse. The hymen is a thin fold of mucous membrane situated just within the vaginal orifice. The internal surfaces of the folds are normally in contact with each other and the vaginal opening appears as a cleft between them. The hymen varies greatly in shape and dimensions. When stretched, it is anular and widest posteriorly; it may also be semilunar and concave towards the mons pubis, cribriform, fringed, absent or complete and imperforate. The hymenal ring normally ruptures after first sexual intercourse, but can rupture earlier during non-sexual physical activity. Small round carunculae hymenales (also known as carunculae myrtiformis) are its remnants after it has been ruptured. It has no established function. The hymen may be imperforate; this is usually detected in adolescence.

Remnants of the duct of Gartner (embryologically, the caudal end of the mesonephric duct) (see Figs 72.13, 72.19) are occasionally seen protruding through the lateral fornices or lateral parts of the vagina and may cause cysts (Gartner’s cysts). Prepubertal distal longitudinal folds are common within the vagina and they disappear during puberty (Altchek et al 2008).

Vascular supply and lymphatic drainage

Arteries

The arterial supply of the vagina is derived from the internal iliac arteries by two median longitudinal vessels, the azygos arteries of the vagina, which descend anterior and posterior to the vagina; they also supply the vestibular bulb, fundus of the bladder, and adjacent part of the rectum (see Fig. 77.3A). The uterine, internal pudendal and middle rectal branches of the internal iliac artery may contribute to the blood supply of the vagina.

Veins

The vaginal veins, one on each side, arise from lateral plexuses that connect with uterine, vesical and rectal plexuses and drain to the internal iliac veins. The uterine and vaginal plexuses may provide collateral venous drainage to the lower limb.

Lymphatic drainage

Vaginal lymphatic vessels link with those of the cervix, rectum and vulva. They form three groups but the regions drained are not sharply demarcated. Upper vessels accompany the uterine artery to the internal and external iliac nodes; intermediate vessels accompany the vaginal artery to the internal iliac nodes; and vessels draining the vagina below the hymen, and from the vulva and perineal skin, pass to the superficial inguinal nodes (see Table 77.1).

Fig. 77.7 The most common sites of ureteric injury during hysterectomy. Key: 1, distal ureter at the level of the uterine artery; 2, dorsal to the infundibulopelvic ligament, near the pelvic bone; 3, intramural portion of ureter at the angle of the vaginal cuff.

Fig. 77.8 The relationship of the ureter to the uterine and vaginal arteries. (With permission from Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright 2010.)

Innervation

The lower vagina is supplied by the pudendal nerve (S2, S3 and S4). The upper vagina is supplied by the pelvic splanchnic nerves (S2, S3 and, sometimes, S4) (see Fig. 77.5 and Table 77.2).

Developmental anomalies of the vagina 

Congenital anomalies of the vagina are vaginal agenesis, absent hymen, transverse vaginal septum and persistent cloaca. Vaginal agenesis, in the presence of other Müllerian duct anomalies and renal agenesis, is termed Mayer–Rokistansky–Kuster–Hauser syndrome. An absent hymen in patients with vaginal agenesis is associated with renal agenesis (Kimberley et al 2012). A congenital transverse septum may be present within the vagina and manifests clinically in adolescence with primary amenorrhoea and haematocolpos. Children with a persistent cloaca have a congenital defect characterized by fusion of the rectum, vagina and urethra into a single common channel that varies in length from 1 to 7 cm.

Microstructure

The vagina has an inner mucosal and an external muscular layer. The mucosa adheres firmly to the muscular layer. There are two median longitudinal ridges on its epithelial surface: one anterior and the other posterior. Numerous transverse bilateral rugae extend from these vaginal columns, divided by sulci of variable depth, giving an appearance of conical papillae. These transverse rugosities are most numerous on the posterior wall and near the orifice; they increase under the influence of oestrogen during puberty and pregnancy, are especially well developed before parturition, and decrease after the menopause (Corton 2012). The epithelium is non-keratinized, stratified, squamous similar to, and continuous with, that of the ectocervix. After puberty, it thickens and its superficial cells accumulate glycogen, which gives them a clear appearance in histological preparations.

The vaginal epithelium does not change markedly during the menstrual cycle, but its glycogen content increases after ovulation and then diminishes towards the end of the cycle. Natural vaginal bacteria, particularly Lactobacillus acidophilus, break down glycogen in the desquamated cellular debris to lactic acid. This produces a highly acidic (pH 3) environment that inhibits the growth of most other microorganisms.

The amount of glycogen is less before puberty and after the menopause, when vaginal infections are more common. There are no mucous glands, but a fluid transudate from the lamina propria and mucus from the cervical glands lubricate the vagina (Fig. 77.9). The muscular layers are composed of smooth muscle and consist of a thick outer longitudinal and an inner circular layer; the  two layers are not distinct but are connected by oblique interlacing fibres. The longitudinal fibres are continuous with the superficial muscle fibres of the uterus. A layer of loose connective tissue, containing extensive vascular plexuses, surrounds the muscle layers.

Fig. 77.9 Stratified squamous non-keratinizing epithelium (E) covering the ectocervix and vagina. The cells of the middle and upper layers appear clear due to their glycogen content. (Courtesy of Mr Peter Helliwell and the late Dr Joseph Mathew, Department of Histopathology, Royal Cornwall Hospitals Trust, UK.)

Fig. 77.10 T2-weighted magnetic resonance images through the pelvis, demonstrating the normal female anatomy. A, Sagittal view. Abbreviations: A, anus; B, bladder; C, cervix; R, rectum; S, pubic symphysis; V, vagina; *, endometrium; **, inner myometrium of uterus (also known as the junctional zone); ***, outer myometrium of uterus. B–D, Axial views. B, Abbreviations: O, ovaries; R, rectum; *, endometrium, **, inner myometrium of uterus (junctional zone); ***, outer myometrium of uterus. C, Abbreviations: B, bladder; C, cervix (which, from external to internal, has several layers, as seen on T2 weighted images: a high-signal-intensity outer cervical stroma (contiguous with the outer myometrium); a low-signal-intensity inner cervical stroma (contiguous with the inner myometrium); high-signal-intensity endocervical glands (contiguous with endometrium); and a very high-signal intensity endocervical canal (contiguous with the endometrial canal)); R, rectum. D, Abbreviations: A, anus; I, ischio-anal fossa; S, pubic symphysis; U, urethra; V, vagina.