CHAPTER OUTLINE
- ⋄ External Genitalai
- ▸ Mons Veneris
- ▸ Labia Majora
- ▸ Labia Minora
- ▸ Clitoris
- ▸ Vestibule
- ▸ Perineum
- ⋄ Internal Genitalia
- ▸ Vagina
- ▸ Uterus
- ▸ Fallopian Tube
- ▸ Ovary
- ⋄ Muscles and Fascia in Relation to the Pelvic Organs
- ▸ Pelvic Floor
- ▸ Perineum
- ▸ Pelvic Fascia
- ⋄ Pelvic Cellular Tissue
- ⋄ Female Urethra
- ⋄ Urinary Bladder
- ⋄ Pelvic Ureter
- ⋄ Breasts
The reproductive organs in female are those which are concerned with copulation, fertilization, growth and development of the fetus and its subsequent exit to the outer world. The organs are broadly divided into:
- External genitalia
- Internal genitalia
- Accessory reproductive organs
EXTERNAL GENITALIA (Synonyms: Vulva, Pudendum)
The vulva or pudendum includes all the visible external genital organs in the perineum. Vulva consists of the following: the mons pubis, labia majora, labia minora, hymen, clitoris, vestibule, urethra and Skene's glands, Bartholin glands and vestibular bulbs (Fig. 1.1).
2It is therefore bounded anteriorly by mons pubis, posteriorly by the rectum, laterally by the genitocrural fold. The vulvar area is covered by keratinized stratified squamous epithelium.
MONS VENERIS (MONS PUBIS)
It is the pad of subcutaneous adipose connective tissue lying in front of the pubis and in the adult female is covered by hair. The hair pattern (escutcheon) of most women is triangular with the base directed upwards.
LABIA MAJORA
The vulva is bounded on each side by the elevation of skin and subcutaneous tissue which form the labia majora. They are continuous where they join medially to form the posterior commissure in front of the anus. The skin on the outer convex surface is pigmented and covered with hair follicle. The thin skin on the inner surface has sebaceous glands but no hair follicle. The labia majora are covered with squamous epithelium and contain sweat glands. Beneath the skin, there is dense connective tissue and adipose tissue. The adipose tissue is richly supplied with venous plexus which may produce hematoma, if injured during childbirth. The labia majora are homologous to the scrotum in the male. The round ligament terminates at its upper border.
LABIA MINORA
They are two thin folds of skin, devoid of fat, on either side just within the labia majora. Except in the parous women, they are exposed only when the labia majora are separated. Anteriorly, they divide to enclose the clitoris and unite with each other in front and behind the clitoris to form the prepuce and frenulum respectively. The lower portion of the labia minora fuses across the midline to form a fold of skin known as fourchette. It is usually lacerated during childbirth. Between the fourchette and the vaginal orifice is the fossa navicularis. The labia minora contain no hair follicles or sweat glands. The folds contain connective tissues, numerous sebaceous glands, erectile muscle fibers and numerous vessels and nerve endings. The labia minora are homologous to the penile urethra and part of the skin of penis in males.
CLITORIS
It is a small cylindrical erectile body, measuring about 1.5–2 cm situated in the most anterior part of the vulva. It consists of a glans, a body and two crura. The clitoris consists of two cylindrical corpora cavernosa (erectile tissue). The glans is covered by squamous epithelium and is richly supplied with nerves. The vessels of the clitoris are connected with the vestibular bulb and are liable to be injured during childbirth. Clitoris is homologous to the penis in the male but it differs in being entirely separate from the urethra. It is attached to the undersurface of the symphysis pubis by the suspensory ligament.
VESTIBULE
It is a triangular space bounded anteriorly by the clitoris, posteriorly by the fourchette and on either side by labia minora. There are four openings into the vestibule.
(a) Urethral opening: The opening is situated in the midline just in front of the vaginal orifice about 1–1.5 cm below the pubic arch. The paraurethral ducts open either on the posterior wall of the urethral orifice or directly into the vestibule.
(b) Vaginal orifice and hymen: The vaginal orifice lies in the posterior end of the vestibule and is of varying size and shape. In virgins and nulliparae, the opening is closed by the labia minora, but in parous, it may be exposed. It is incompletely closed by a septum of mucous membrane, called hymen. The membrane varies in shape but is usually circular or crescentic in virgins. The hymen is usually ruptured at the consummation of marriage. During childbirth, the hymen is extremely lacerated and is later represented by cicatrized nodules of varying size, called the carunculae myrtiformes. On both sides it is lined by stratified squamous epithelium.
(c) Opening of Bartholin's ducts: There are two Bartholin glands (greater vestibular gland), one on each side. They are situated in the superficial perineal pouch, close to the posterior end of the vestibular bulb. They are pea-sized and yellowish white in color. During sexual excitement, it secretes abundant alkaline mucus which helps in lubrication. The glands are of compound racemose variety and are lined by cuboidal epithelium. Each gland has got a duct which measures about 2 cm and opens into the vestibule outside the hymen at the junction of the anterior two-thirds and posterior one-third in the groove between the hymen and the labium minus. The duct is lined by columnar epithelium but near its opening by stratified squamous epithelium. Bartholin's glands are homologous to the bulb of the penis in male.
(d) Skene's glands are the largest paraurethral glands. Skene's glands are homologous to the prostate in the male. The two Skene's ducts may open in the vestibule on either side of the external urethral meatus.
VESTIBULAR BULB: These are bilateral elongated masses of erectile tissues situated beneath the mucous membrane of the vestibule. Each bulb lies on either side of the vaginal orifice in front of the Bartholin's gland and is incorporated with the bulbocavernosus muscle.3
They are homologous to the bulb of the penis and corpus spongiosum in the male. They are likely to be injured during childbirth with brisk hemorrhage (Fig. 1.2).
PERINEUM
The details of its anatomy are described later in the chapter.
BLOOD SUPPLY: Arteries: (a) Branches of internal pudendal artery—the chief being labial, transverse perineal, artery to the vestibular bulb and deep and dorsal arteries to the clitoris. (b) Branches of femoral artery—superficial and deep external pudendal.
Veins: The veins form plexuses and drain into—(a) internal pudendal vein, (b) vesical or vaginal venous plexus and (c) long saphenous vein. Varicosities during pregnancy are not uncommon and may rupture spontaneously causing visible bleeding or hematoma formation.
NERVE SUPPLY: The supply is through bilateral spinal somatic nerves—anterosuperior part is supplied by the cutaneous branches from the ilioinguinal and genital branch of genitofemoral nerve (L1 and L2) and the posteroinferior part by the pudendal branches from the posterior cutaneous nerve of thigh (S1,2,3). Between these two groups, the vulva is supplied by the labial and perineal branches of the pudendal nerve (S2,3,4).
LYMPHATICS: Vulval lymphatics have bilateral drainage. Lymphatics drain into—(a) superficial inguinal nodes, (b) intermediate groups of inguinal lymph nodes—gland of Cloquet and (c) external and internal iliac lymph nodes.
DEVELOPMENT: External genitalia is developed in the region of the cranial aspect of ectodermal cloacal fossa; clitoris from the genital tubercle; labia minora from the genital folds; labia majora from the labioscrotal swelling and the vestibule from the urogenital sinus.
INTERNAL GENITALIA
The internal genital organs in female include vagina, uterus, Fallopian tubes and the ovaries. These organs are placed internally and require special instruments for inspection.
VAGINA
The vagina is a fibromusculomembranous sheath communicating the uterine cavity with the exterior at the vulva. It constitutes the excretory channel for the uterine secretion and menstrual blood. It is the organ of copulation and forms the birth canal of parturition. The canal is directed upwards and backwards forming an angle of 45° with the horizontal in erect posture. The long axis of the vagina almost lies parallel to the plane of the pelvic inlet and at right angles to that of the uterus. The diameter of the canal is about 2.5 cm, being widest in the upper part and narrowest at its introitus. It has got enough power of distensibility as evident during childbirth.
WALLS: Vagina has got an anterior, a posterior and two lateral walls. The anterior and posterior walls are opposed together but the lateral walls are comparatively stiffer especially at its middle, as such, it looks ‘H’ shaped on transverse section. The length of the anterior wall is about 7 cm and that of the posterior wall is about 9 cm.4
FORNICES: The fornices are the clefts formed at the top of vagina (vault) due to the projection of the uterine cervix through the anterior vaginal wall where it is blended inseparably with its wall. There are four fornices—one anterior, one posterior and two lateral; the posterior one being deeper and the anterior, most shallow one.
RELATIONS
Anterior: The upper one-third is related with base of the bladder and the lower two-thirds are with the urethra, the lower half of which is firmly embedded with its wall.
Posterior: The upper one-third is related with the pouch of Douglas, the middle-third with the anterior rectal wall separated by rectovaginal septum and the lower-third is separated from the anal canal by the perineal body (Fig. 1.3).
Lateral walls: The upper one-third is related with the pelvic cellular tissue at the base of broad ligament in which the ureter and the uterine artery lie approximately 2 cm from the lateral fornices. The middle-third is blended with the levator ani and the lower-third is related with the bulbocavernosus muscles, vestibular bulbs and Bartholin's glands (Fig. 1.11).
STRUCTURES: Layers from within outwards are—(1) mucous coat which is lined by stratified squamous epithelium without any secreting glands, (2) submucous layer of loose areolar vascular tissues, (3) muscular layer consisting of indistinct inner circular and outer longitudinal muscles and (4) fibrous coat derived from the endopelvic fascia and is highly vascular.
VAGINAL SECRETION: The vaginal pH, from puberty to menopause, is acidic because of the presence of Döderlein's bacilli which produce lactic acid from the glycogen present in the exfoliated cells. The pH varies with the estrogenic activity and ranges between 4 and 5.
BLOOD SUPPLY: The arteries involved are—(1) cervico-vaginal branch of the uterine artery, (2) vaginal artery—a branch of anterior division of internal iliac or in common origin with the uterine, (3) middle rectal and (4) internal pudendal. These anastomose with one another and form two azygos arteries—anterior and posterior.
Veins drain into internal iliac veins and internal pudendal veins.
LYMPHATICS: On each side, the lymphatics drain into—(1) upper one-third—internal iliac group, (2) middle one-third up to hymen—internal iliac group, (3) below the hymen—superficial inguinal group.
NERVE SUPPLY: The vagina is supplied by sympathetic and parasympathetic from the pelvic plexus. The lower part is supplied by the pudendal nerve.
DEVELOPMENT: The vagina is developed from the following sources: (a) Upper four-fifths, above the hymen—the mucous membrane is derived from endoderm of the canalized sinovaginal bulbs. The musculature is developed from the mesoderm of two fused Müllerian ducts. (b) Lower one-fifth, below the hymen is developed from the endoderm of the urogenital sinus. (c) External vaginal orifice is formed from the genital fold ectoderm after rupture of the urogenital membrane.
UTERUS
The uterus is a hollow pyriform muscular organ situated in the pelvis between the bladder in front and the rectum behind.
POSITION: Its normal position is one of the anteversion and anteflexion. The uterus usually inclines to the right (dextrorotation) so that the cervix is directed to the left (levorotation) and comes in close relation with the left ureter.
5MEASUREMENTS AND PARTS: The uterus measures about 8 cm long, 5 cm wide at the fundus and its walls are about 1.25 cm thick. Its weight varies from 50 to 80 g. It has got the following parts:
- Body or corpus ✦ Isthmus ✦ Cervix
(1) Body or corpus: The body is further divided into fundus—the part which lies above the openings of the uterine tubes. The body proper is triangular and lies between the openings of the tubes and the isthmus. The superolateral angles of the body of the uterus project outwards from the junction of the fundus and body and is called the cornua of the uterus. The uterine tube, round ligament and ligament of the ovary are attached to it. (2) Isthmus is a constricted part measuring about 0.5 cm, situated between the body and the cervix. It is limited above by the anatomical internal os and below by the histological internal os (Aschoff). Some consider isthmus as a part of the lower portion of the body of the uterus. (3) Cervix is cylindrical in shape and measures about 2.5 cm. It extends from the isthmus and ends at the external os which opens into the vagina after perforating its anterior wall. The part lying above the vagina is called supravaginal and that which lies within the vagina is called the vaginal part (Fig. 1.4).
CAVITY: The cavity of the uterine body is triangular on coronal section with the base above and the apex below. It measures about 3.5 cm. There is no cavity in the fundus. The cervical canal is fusiform and measures about 2.5 cm. Thus, the normal length of the uterine cavity is usually 6.5–7 cm.
RELATIONS
Anteriorly: Above the internal os, the body forms the posterior wall of the uterovesical pouch. Below the internal os, it is separated from the base of the bladder by loose areolar tissue.
Posteriorly: It is covered with peritoneum and forms the anterior wall of the pouch of Douglas containing coils of intestine.
Laterally: The double fold of peritoneum of the broad ligament are attached between which the uterine artery ascends up. Attachment of the Mackenrodt's ligament extends from the internal os down to the supravaginal cervix and lateral vaginal wall. About 1.5 cm away at the level of internal os, a little nearer on the left side is the crossing of the uterine artery and the ureter. The uterine artery crosses from above and in front of the ureter, soon before the ureter enters the ureteric tunnel (Fig. 1.5).
STRUCTURES
Body: The wall consists of three layers from outside inwards:
- Parametrium: It is the serous coat which invests the entire organ except on the lateral borders. The peritoneum is intimately adherent to the underlying muscles.
- Myometrium: It consists of thick bundles of smooth muscle fibers held by connective tissues and are arranged in various directions. During pregnancy, however, three distinct layers can be identified—outer longitudinal, middle interlacing and the inner circular.
- Endometrium: The mucus lining of the cavity is called endometrium. As there is no submucous layer, the endometrium is directly opposed to the muscle coat. It consists of lamina propria and surface epithelium. The surface epithelium is a single layer of ciliated columnar epithelium. The lamina propria contains stromal cells, endometrial glands, vessels and nerves. The glands are simple tubular and lined by mucus secreting non-ciliated columnar epithelium which penetrate the stroma and sometimes even enter the muscle coat. The endometrium is changed to decidua during pregnancy.
6Cervix—The cervix is composed mainly of fibrous connective tissues. The smooth muscle fibers average 10–15%. Only the posterior surface has got peritoneal coat. Mucous coat lining the endocervix is simple columnar with basal nuclei and that lining the gland is non-ciliated secretory columnar cells. The vaginal part of the cervix is lined by stratified squamous epithelium. The squamocolumnar junction is situated at the external os.
SECRETION: The endometrial secretion is scanty and watery. Secretion of the cervical glands is alkaline and thick, rich in mucoprotein, fructose and sodium chloride.
PERITONEUM IN RELATION TO THE UTERUS: Traced anteriorly: The peritoneum covering the superior surface of the bladder reflects over the anterior surface of the uterus at the level of the internal os. The pouch, so formed, is called uterovesical pouch. The peritoneum thereafter, is firmly attached to the anterior and posterior walls of the uterus and upper one-third of the posterior vaginal wall from where it is reflected over the rectum. The pouch, so formed, is called pouch of Douglas (Fig. 1.3).
Traced laterally: The adherent peritoneum of the anterior and posterior walls of the uterus is continuous laterally forming the broad ligament. Laterally, it extends to the lateral pelvic walls where the layers reflect to cover the anterior and posterior aspects of the pelvic cavity. On its superior free border, lies the Fallopian tube and on the posterior layer, the ovary is attached by mesovarium. The lateral one-fourth of the free border is called infundibulopelvic ligament.
BLOOD SUPPLY: Arterial supply: The blood supply is from the uterine arteries one on each side. The artery arises directly from the anterior division of the internal iliac or in common with superior vesical artery. The other sources are ovarian and vaginal arteries with which the uterine arteries anastomose. The internal supply of the uterus is shown in Figures 1.6A and B.
Veins: The venous channels correspond to the arterial course and drain into internal iliac veins.
LYMPHATICS: Body: (1) From the fundus and upper part of the body of the uterus, the lymphatics drain into preaortic and lateral aortic groups of glands. (2) Cornu drains to superficial inguinal gland along the round ligament. (3) Lower part of the body drains into external iliac groups.
Cervix: On each side, the lymphatics drain into—(1) external iliac, obturator lymph nodes either directly or through paracervical lymph nodes, (2) internal iliac groups and (3) sacral groups.
NERVES: The nerve supply of the uterus is derived principally from the sympathetic system and partly from the parasympathetic system. Sympathetic components are from T5 to T6 (motor) and T10 to L1 spinal segments (sensory). The somatic distribution of uterine pain is that area of the abdomen supplied by T10 to L8. The parasympathetic system is represented on either side by the pelvic nerve which consists of both motor and sensory fibers from S2,3,4 and ends in the ganglia of Frankenhauser. The details are described in Ch. 34.
The cervix is insensitive to touch, heat and also when it is grasped by any instrument. The uterus, too, is insensitive to handling and even to incision over its wall.
DEVELOPMENT: The uterus is developed from the fused vertical part of the two Müllerian ducts.
FALLOPIAN TUBE (Synonyms: Uterine tube, oviduct)
The uterine tubes are paired structures, measuring about 10 cm and are situated in the medial three-fourths of the upper free margin of the broad ligament. Each tube has got two openings, one communicating with the lateral angle of the uterine cavity called uterine opening and measures 1 mm in diameter, the other is on the lateral end of the tube, called pelvic opening or abdominal ostium and measures about 2 mm in diameter.
Figs. 1.6A and B: (A) Showing pattern of basal and spiral arteries in the endometrium; (B) Internal blood supply of uterus.
7PARTS: There are four parts. From medial to lateral are— (1) intramural or interstitial lying in the uterine wall and measures 1.25 cm in length and 1 mm in diameter, (2) isthmus—almost straight and measures about 3–4 cm in length and 2 mm in diameter, (3) ampulla—tortuous part and measures about 5 cm in length which ends in, (4) wide infundibulum measuring about 1.25 cm long with a maximum diameter of 6 mm. The abdominal ostium is surrounded by a number of radiating fimbriae (20–25), one of these is longer than the rest and is attached to the outer pole of the ovary called ovarian fimbria (Fig. 1.7).
STRUCTURES: It consists of three layers—(1) Serous: consists of peritoneum on all sides except along the line of attachment of mesosalpinx, (2) Muscular: arranged in two layers outer longitudinal and inner circular and (3) Mucous membrane has three different cell types and is thrown into longitudinal folds. The epithelium rests on a delicate vascular reticulum of connective tissue. Mucous membrane is lined by: (i) Columnar ciliated epithelial cells that are most predominant near the ovarian end of the tube. These cells compose 25% of the mucosal cells, (ii) Secretory columnar cells are present at the isthmic segment and compose 60% of epithelial cells, (iii) Peg cells are found in between the above two cells. They are the variant of secretory cells.
FUNCTIONS: The important functions of the tubes are—(1) transport of the gametes and (2) to facilitate fertilization and survival of zygote through its secretion.
BLOOD SUPPLY: Arterial supply is from the uterine and ovarian. Venous drainage is through the pampiniform plexus into the ovarian veins.
LYMPHATICS: The lymphatics run along the ovarian vessels to para-aortic nodes.
NERVE SUPPLY: The nerve supply is derived from the uterine and ovarian nerves. The tube is very much sensitive to handling.
DEVELOPMENT: The tube is developed from the upper vertical part of the corresponding Müllerian duct at about 6–10th week.
OVARY
The ovaries are paired sex glands or gonads in female which are concerned for—(i) germ cell maturation, storage and its release and (ii) steroidogenesis. Each gland is oval in shape and pinkish gray in color and the surface is scarred during reproductive period. It measures about 3 cm in length, 2 cm in breadth and 1 cm in thickness. Each ovary presents two ends—tubal and uterine, two borders—mesovarium and free posterior and two surfaces—medial and lateral.
The ovaries are intraperitoneal structures. In nullipara, the ovary lies in the ovarian fossa on the lateral pelvic wall. The ovary is attached to the posterior layer of the broad ligament by the mesovarium, to the lateral pelvic wall by the infundibulopelvic ligament and to the uterus by the ovarian ligament.
RELATIONS: Mesovarium or anterior border: A fold of peritoneum from the posterior leaf of the broad ligament is attached to the anterior border through which the ovarian vessels and nerves enter the hilum of the gland.
Posterior border is free and is related to the tubal ampulla. It is separated by the peritoneum from the ureter and the internal iliac artery.
Medial surface is related to fimbrial part of the tube.
Lateral surface is in contact with the ovarian fossa on the lateral pelvic wall.
The fossa is related superiorly to the external iliac vein, posteriorly to the ureter and internal iliac vessels and laterally to the peritoneum separating the obturator vessels and nerves (Fig. 1.8).
STRUCTURES: The ovary is covered by a single layer of cubical cell known as germinal epithelium. The substance of the gland consists of outer cortex and inner medulla.
Fig. 1.7: Half of uterine cavity and Fallopian tube of one side are cut open to show different parts of the tube. The vestigial structures in the broad ligament are shown.
Cortex: It consists of stromal cells which are thickened beneath the germinal epithelium to form tunica albuginea. During reproductive period (i.e., from puberty to menopause) the cortex is studded with numerous follicular structures, called the functional units of the ovary, in various phases of their development. These are related to sex hormone production and ovulation. The structures include—primordial follicles, maturing follicles, Graafian follicles and corpus luteum. Atresia of the structures results in formation of atretic follicles or corpus albicans (Fig. 1.9).
Medulla: It consists of loose connective tissues, few unstriped muscles, blood vessels and nerves. There is a small collection of cells called ‘hilus cells’ which are homologous to the interstitial cells of the testes.
BLOOD SUPPLY: Arterial supply is from the ovarian artery, a branch of the abdominal aorta. Venous drainage is through pampiniform plexus, to form the ovarian 9veins which drain into inferior vena cava on the right side and left renal vein on the left side. Part of the venous blood from the placental site drains into the ovarian veins and thus may become the site of thrombophlebitis in puerperium.
LYMPHATICS: Through the ovarian vessels drain to the para-aortic lymph nodes.
NERVE SUPPLY: Sympathetic supply comes down along the ovarian artery from T10 segment. Ovaries are sensitive to manual squeezing.
DEVELOPMENT: The ovary is developed from the cortex of the undifferentiated genital ridges by about 9th week; the primary germ cells reaching the site migrating from the dorsal end of yolk sac.
MUSCLES AND FASCIA IN RELATION TO THE PELVIC ORGANS
The most important muscle supporting the pelvic organs is the levator ani which forms the pelvic floor. The small muscles of the perineum also have got some contribution.
PELVIC FLOOR (Synonym: Pelvic diaphragm)
Pelvic floor is a muscular partition which separates the pelvic cavity from the anatomical perineum. It consists of three sets of muscles on either side—pubococcygeus, iliococcygeus and ischiococcygeus and these are collectively called levator ani. Its upper surface is concave and slopes downwards, backwards and medially and is covered by parietal layer of pelvic fascia. The inferior surface is convex and is covered by anal fascia. The muscle with the covering fascia is called the pelvic diaphragm.
ORIGIN: Each levator ani arises from the back of the pubic rami, from the condensed fascia covering the obturator internus (white line) and from the inner surface of the ischial spine.
INSERTION: From this extensive origin, the fibers pass, backwards and medially to be inserted in the midline from before backwards to the vagina (lateral and posterior walls), perineal body and anococcygeal raphe, lateral borders of the coccyx and lower part of the sacrum (Fig. 1.10).
GAPS: There are two gaps in the midline—(1) The anterior one is called hiatus urogenitalis which is bridged by the muscles and fascia of urogenital triangle and pierced by the urethra and vagina. (2) The posterior one is called hiatus rectalis, transmitting the rectum.
STRUCTURES IN RELATION TO PELVIC FLOOR
The superior surface is related with the following:
(1) Pelvic organs from anterior to posterior are bladder, vagina, uterus and rectum. (2) Pelvic cellular tissues between the pelvic peritoneum and upper surface of the levator ani which fill all the available spaces. (3) Ureter lies on the floor in relation to the lateral vaginal fornix. The uterine artery lies above and the vaginal artery lies below it. (4) Pelvic nerves.
The inferior surface is related to the anatomical perineum.
NERVE SUPPLY: It is supplied by the 4th sacral nerve, inferior rectal nerve and a perineal branch of pudendal nerve S2,3,4.
10FUNCTIONS: (1) To support the pelvic organs—the pubovaginalis which forms a ‘U’ shaped sling, supports the vagina which in turn supports the other pelvic organs—bladder and uterus. Weakness or tear of this sling during parturition is responsible for prolapse of the organs concerned. (2) To maintain intra-abdominal pressure by reflexly responding to its changes. (3) Facilitates anterior internal rotation of the presenting part when it presses on the pelvic floor. (4) Puborectalis plays an ancillary role to the action of the external anal sphincter. (5) Ischiococcygeus helps to stabilize the sacroiliac and sacrococcygeal joints. (6) To steady the perineal body.
PELVIC FLOOR DURING PREGNANCY AND PARTURITION: During pregnancy levator muscles undergo hypertrophy, become less rigid and more distensible. Due to water retention, it swells up and sags down. In the second stage, the pubovaginalis and puborectalis relax and the levator ani is drawn up over the advancing presenting part in the second stage. Failure of the levator ani to relax at the crucial moment may lead to extensive damage of the pelvic structures. The effect of such a displacement is to elongate the birth canal which is composed solely of soft parts below the bony outlet. The soft canal has got deep lateral and posterior walls and its axis is in continuation with the axis of the bony pelvis.
PERINEUM
ANATOMICAL PERINEUM: Anatomically, the perineum is bounded above by the inferior surface of the pelvic floor, below by the skin between the buttocks and thighs. Laterally, it is bounded by the ischiopubic ramus, ischial tuberosities and sacrotuberous ligaments and posteriorly, by the coccyx. The diamond-shaped space of the bony pelvic outlet is divided into two triangular spaces with the common base formed by the free border of the urogenital diaphragm. The anterior triangle is called the urogenital triangle which fills up the gap of the hiatus urogenitalis and is important from the obstetric point of view. The posterior one is called the anal triangle.
Urogenital triangle: It is pierced by the terminal part of the vagina and the urethra. The small perineal muscles are situated in two compartments formed by the ill-defined fascia. The compartments are superficial and deep perineal pouch. The superficial pouch is formed by the deep layer of the superficial perineal fascia (Colles fascia) and inferior layer of the urogenital diaphragm (perineal membrane). The contents are (Fig. 1.2) superficial transverse perinei (paired), bulbospongiosus covering the bulb of the vestibule, ischiocavernosus (paired) covering the crura of the clitoris and the Bartholin's gland (paired). The deep perineal pouch is formed by the inferior and superior layer of the urogenital diaphragm—together called urogenital diaphragm or triangular ligament. Between the layers there is a potential space of about 1.25 cm. The contents are the following muscles—deep transverse perinei (paired) and sphincter urethrae membranacea. Both the pouches contain vessels and nerves (Fig. 1.11).
Anal triangle: It has got no obstetric importance. It contains the terminal part of the anal canal with sphincter ani externus, anococcygeal body, ischiorectal fossa, blood vessels, nerves and lymphatics.
Fig. 1.11: Schematic diagram showing the pelvic muscles, fascia and cellular tissue as seen from the front.
11OBSTETRICAL PERINEUM: (Synonyms: Perineal body, central point of the perineum). The pyramidal-shaped tissue where the pelvic floor and the perineal muscles and fascia meet in between the vagina and the anal canal is called the obstetrical perineum. It measures about 4 cm × 4 cm with the base covered by the perineal skin and the apex is pointed and is continuous with the rectovaginal septum.
The musculofascial structures involved are:
- Fasciae—(1) Two layers of superficial perineal fascia-superficial fatty layer and deeper layer called Colles fascia. (2) Inferior and superior layer of urogenital diaphragm, together called triangular ligament.
- Muscles—(1) Superficial and deep transverse perinei (paired). (2) Bulbospongiosus. (3) Levator ani pubococcygeus part (paired), situated at the junction of the upper two-thirds and lower one-third of the vagina. (4) Sphincter ani externus (few fibers).
Importance: (1) It helps to support the levator ani which is placed above it. (2) By supporting the posterior vaginal wall, it indirectly supports the anterior vaginal wall, bladder and the uterus. (3) It is vulnerable to injury during childbirth. (4) Deliberate cutting of the structures during delivery is called episiotomy.
PELVIC FASCIA
For descriptive purpose, the pelvic fascia is grouped under the heading that covers the pelvic wall, the pelvic floor and the pelvic viscera.
Fascia on the pelvic wall: It is very tough and membranous. It covers the obturator internus and piriformis and gets attached to the margins of the bone. The pelvic nerves lie external to the fascia but the vessels lie internal to it.
Fascia on the pelvic floor: It is not tough but loose. The superior and the inferior surfaces are covered by the parietal layer of the pelvic fascia which runs down from the white line to merge with the visceral layer of the pelvic fascia covering the anal canal (Fig. 1.11).
Fascia covering the pelvic viscera: The fascia is not condensed and often contains loose areolar tissue to allow distension of the organs.
PELVIC CELLULAR TISSUE
It lies between the pelvic peritoneum and the pelvic floor and fills up all the available empty spaces. It contains fatty and connective tissues and unstriated muscle fibers. Its distribution around the vaginal vault, supravaginal part of the cervix and into the layers of the broad ligament is called parametrium. Condensation occurs especially near the cervicovaginal junction to form ligaments which extend from the viscera to the pelvic walls on either side. These are Mackenrodt's ligaments, uterosacral ligaments and vesicocervical ligaments (fascia). All these constitute important supports of the uterus to keep it in position (Fig. 1.12).
Importance: (1) To support the pelvic organs. (2) To form protective sheath for the blood vessels and the terminal part of the ureter. (3) Infection spreads along the track, so formed, outside the pelvis to the perinephric region along the ureter, to the buttock along the gluteal vessels, to the thigh along the external iliac vessels and to the groin along the round ligament. (4) Marked hypertrophy occurs during pregnancy to widen up the spaces.
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FEMALE URETHRA
The female urethra extends from the neck of the bladder to the external urethral meatus which opens into the vestibule about 2.5 cm below the clitoris. It measures about 4 cm and has a diameter of 6 mm. Its upper half is separated from the anterior vaginal wall by loose areolar tissue and the lower half is firmly embedded in its wall. Numerous tubular glands called paraurethral glands open into the lumen through ducts. Of these, two are larger called Skene's ducts which open either on the posterior wall just inside the external meatus or into the vestibule. These glands are the sites for harboring infection and occasional development of benign adenoma or malignant changes. While piercing the deep perineal pouch it is surrounded by sphincter urethrae membranacea which acts as an external sphincter.
STRUCTURES: Mucous membrane in the distal one-third is lined by stratified squamous epithelium but in the proximal two-thirds it becomes stratified transitional epithelium. Submucous coat is vascular. Muscle coat is arranged as inner longitudinal and outer circular.
BLOOD SUPPLY: Arterial supply: Proximal parts are supplied by the inferior vesical branch and the distal part by a branch of internal pudendal artery. The veins drain into vesical plexus and into internal pudendal veins.
LYMPHATICS: Ear the meatus, the lymphatics drain into superficial inguinal glands and the rest drain into internal and external iliac group of glands.
NERVE SUPPLY: It is supplied by the pudendal nerve.
DEVELOPMENT: The urethra is developed from the vesicourethral portion of the cloaca.
URINARY BLADDER
The bladder is a hollow muscular organ with considerable power of distension. Its capacity is about 450 mL (15 oz) but can retain as much as 3–4 liters of urine. When distended it is ovoid in shape. It has got—(1) an apex, (2) superior surface, (3) base, (4) two inferolateral surfaces and (5) neck, which is continuous with the urethra. The base and the neck remain fixed even when the bladder is distended.
RELATIONS: The superior surface is related with the peritoneum of the uterovesical pouch. The base is related with the supravaginal cervix and the anterior fornix. The ureters, after crossing the pelvic floor at the sides of the cervix, enter the bladder on its lateral angles. In the interior of bladder, the triangular area marked by three openings—two ureteric and one urethral, is called the trigone. The inferolateral surfaces are related with the space of Retzius. The neck rests on the superior layer of the urogenital diaphragm.
STRUCTURES: From outside inwards—(1) Outer-visceral layer of the pelvic fascia. (2) Muscle layer composed of muscles running in various directions. Near the internal urethral opening the circular muscle fibers provide involuntary sphincter. (3) Mucous coat is lined by transitional epithelium with no gland. There is no submucous coat.
BLOOD SUPPLY: The blood supply is through superior and inferior vesical arteries. The veins drain into vesical and vaginal plexus and thence to internal iliac veins.
LYMPHATICS: Lymphatics drain into external and internal iliac lymph nodes.
NERVE SUPPLY: The sympathetic supply is from the pelvic plexus and the parasympathetic via the pelvic plexus from the nervi erigentes (S2,3,4). The parasympathetic produces contraction of the detrusor muscles and relaxation of the internal sphincter (nerve of evacuation). Sympathetic conveys afferent painful stimuli of overdistension.
DEVELOPMENT: The urinary bladder is developed from the upper part of the urogenital sinus.
PELVIC URETER
It extends from the crossing of the ureter over the pelvic brim up to its opening into the bladder. It measures about 13 cm in length and has a diameter of 5 mm. Ureter is retroperitoneal in course.
COURSE AND RELATIONS: The ureter enters the pelvis in front of the bifurcation of the common iliac artery over the sacroiliac joint behind the root of the mesentery on the right side and the apex of the mesosigmoid on the left side. As it courses downwards in contact with the peritoneum, it lies anterior to the internal iliac artery and behind the ovary and forms the posterior boundary of ovarian fossa (Fig. 1.8). On reaching the ischial spine, it lies over the pelvic floor and as it courses forwards and medially on the base of the broad ligament, it is crossed by the uterine artery anteriorly (Fig. 1.5). Soon, it enters into the ureteric tunnel and lies close to the supravaginal part of the cervix, about 1.5 cm lateral to it. After traversing a short distance on the anterior fornix of the vagina, it courses into the wall of the bladder obliquely for about 2 cm by piercing the lateral angle before it opens into the base of the trigone. In the pelvic portion, the ureter is comparatively constricted—(a) where it crosses the pelvic brim, (b) where crossed by the uterine artery and (c) in the intravesical part.
STRUCTURES: From outside inwards—(1) Fibers derived from the visceral layer of the pelvic fascia. (2) Muscle coat consisting of three layers—outer and inner longitudinal and intermediate circular. (3) Mucous layer lined by transitional epithelium.13
BLOOD SUPPLY: It has got segmental supply from nearly all the visceral branches of the anterior division of the internal iliac (uterine, vaginal, vesical, middle rectal) and superior gluteal arteries. The venous drainage corresponds to the arteries.
LYMPHATICS: The lymphatics from the lower part drain into the external and internal iliac lymph nodes and the upper part into the lumbar lymph nodes.
NERVE SUPPLY: Sympathetic supply is from the hypogastric and pelvic plexus; parasympathetic from the sacral plexus.
DEVELOPMENT: It is developed as an ureteric bud from the caudal end of the mesonephric duct.
BREASTS
The breasts are large, modified sebaceous glands. The breasts are bilateral and in female constitute accessory reproductive organs as the glands are concerned with lactation following childbirth.
The shape of the breast varies in women and also in different periods of life. But the size of the base of the breast is fairly constant. It usually extends from the second to sixth rib in the midclavicular line. It lies in the subcutaneous tissue over the fascia covering the pectoralis major or even beyond that to lie over the serratus anterior and external oblique. A lateral projection of the breast towards the axilla is known as axillary tail of Spence. It lies in the axillary fossa, sometimes deep to the deep fascia. The breast weighs 200–300 g during the childbearing age.
STRUCTURES (Non-lactating breasts): The areola is placed about the center of the breast and is pigmented. It is about 2.5 cm in diameter. Montgomery glands are accessory glands located around the periphery of the areola. They can secrete milk. The nipple is a muscular projection covered by pigmented skin. It is vascular and surrounded by unstriated muscles which make it erectile. It accommodates about 15–20 lactiferous ducts and their openings. Each milk duct (lactiferous duct) dilates to form lactiferous sinus at about 5–10 mm away from its opening in the nipple. When these sinuses are pulled into the teat during nursing, the infants tongue, facial muscles and mouth squeeze the milk from the sinuses into the infant's oropharynx. The whole breast is embedded in the subcutaneous fat. The fat is, however, absent beneath the nipple and areola.
The mature breast consists of about 20% glandular tissue and 80% fat and the rest connective tissue (Figs. 1.13A and B). The breast is composed of 12–20 lobes. Each lobe has one excretory duct (lactiferous duct) that opens at the nipple. Each lobe has about 10–100 lobules. Cooper's ligaments are the fibrous septa, that extend from the skin to the underlying pectoral fascia. These ligaments provide support to the breast. One lactiferous duct drains a lobe. The lining epithelium of the duct is cubical, becomes stratified squamous near the openings. Each alveolus is lined by columnar epithelium where milk secretion occurs. A network of branching longitudinal striated cells called myoepithelial cells surround the alveoli and the smaller ducts. There is a dense network of capillaries surrounding the alveoli. These are situated between the basement membrane and epithelial lining.
Figs. 1.13A and B: (A) Structure of the basic unit of the mammary gland; (B) Structure of adult female breast.
14Contraction of these cells squeezes the alveoli and ejects the milk into the larger duct. Behind the nipple, the main duct (lactiferous) dilates to form ampulla where the milk is stored.
Breast tissue is sensitive to the cyclic changes of hormones estrogen and progesterone. Women often feel breast tenderness and fullness during the luteal phase of the cycle. During the follicular phase, there is proliferation of the ductal system whereas during the luteal phase there is dilatation of the ductal system and differentiation of the alveolar cells into secretory cells. In postmenopausal women, the breast lobules and ducts atrophy. Accessory breasts or nipples can occur along the breast or milk line which extends from the axilla to the groin. Supernumerary nipples (polythelia) are associated with renal abnormalities (10%). Asymmetry of breasts is a normal variation. Massive hypertrophy of the breasts is a rare problem.
BLOOD SUPPLY: Arterial supply: (1) Lateral thoracic—branches of the axillary artery, (2) Internal mammary, (3) Intercostal arteries. Veins—The veins follow the courses of the arteries.
LYMPHATICS: (1) Lateral hemisphere—anterior axillary nodes (75%). (2) Upper convexity—infraclavicular group. (3) Medial convexity—internal mammary chain of nodes (cross connection between the two breasts). There is no contralateral drainage of lymph, until and unless there is ipsilateral obstruction. (4) Inferior convexity—mediastinal glands.
NERVE SUPPLY: The nerve supply is from fourth, fifth and sixth intercostal nerves.
DEVELOPMENT: The parenchyma of the breasts is developed from the ectoderm. The connective tissue stroma is from the mesoderm.
ANATOMY OF THE ANTERIOR ABDOMINAL WALL
Langer lines in the anterior abdominal wall, are arranged transversely. Vertical incisions cause more wider scars due to more lateral tensions during the process of healing. Pfannenstiel incisions (low transverse incisions) follow the Langer's lines, heal much better and have superior cosmetic results. There are total eight layers of the anterior wall from front to backwards. These are: (a) skin; (b) superficial fascia; (c) external oblique aponeurosis; (d) internal oblique aponeurosis; (e) transversus abdominis; (f) fascia transversalis; (g) extraperitoneal fatty tissue and (h) the parietal peritoneum. The subcutaneous layers are: Superficial fatty layer—fascia of Camper and the deep membranous layer—fascia of Scarpa. Scarpa fascia continues inferiorly onto the perineum as Colles fascia (Fig. 1.14).
The transverse muscles in the anterior abdominal wall are—(i) external oblique; (ii) internal oblique and (iii) transversus abdominis.
15The longitudinal muscles are—(a) rectus abdominis and (b) pyramidalis in the lower part. The external and internal oblique aponeuroses split and invest the rectus muscles and reunite in the midline to form linea alba. The transversus abdominis muscle forms the posterior wall of the rectus sheath up to midway between umbilicus and symphysis pubis. In the lower part, it forms a free margin with concavity downwards known as arcuate line. Thereafter it forms the anterior wall of the same sheath.
Blood supply: The skin, subcutaneous tissues of the anterior abdominal wall and the mons pubis are supplied by the superficial epigastric, superficial circumflex iliac and superficial external pudendal artery. These are the branches arising from the femoral artery just below the inguinal ligament within the femoral triangle. These vessels are seen while making the low transverse incision. They run above the fascia Scarpa. These vessels are often ligated or coagulated during surgery. The deep epigastric (inferior epigastric) vessels are the branches of the external iliac vessels and arise just above the inguinal ligament. It runs upwards and medially in the extraperitoneal tissue (fascia transversalis) along the medial margin of the deep inguinal ring. Here it is hooked laterally by the round ligament of the uterus. It enters rectus sheath in front of the arcuate line and at the level of umbilicus it anastomoses with the superior epigastric artery which is a branch of internal thoracic artery. Both supply the rectus muscles.
Inferior epigastric artery may be injured during rectus muscle transection. Clinically this vessel may be lacerated during cesarean section or hysterectomy or during rectus muscle transection. Rupture of this vessels may cause rectus sheath hematoma.
Hesselback triangle in this region is bounded laterally by the inferior epigastric vessels, medially by the lateral border of the rectus abdominis muscle and below by the inguinal ligament. Hernias in this triangle are termed direct inguinal hernia. Hernias through the deep inguinal ring are the indirect inguinal hernias.
Nerve supply: The entire abdominal wall is supplied by the intercostal nerves (T7-T11), subcostal nerve (T12) and the iliohypogastric and the ilioinguinal nerves (L1). The space between the transversus abdominis and internal oblique muscle is used for postcesarean analgesia block as the nerves traverse in the plane. The ilioinguinal and the iliohypogastric nerves can be damaged during a transverse incision or entrapped during suturing the wound. Injury to these nerves causes loss of sensation within the areas supplied. There may be chronic pain also. Analgesia for labor, vaginal birth and cesarean delivery are discussed (Ch. 34).