EXTERNAL STRUCTURES (PUDENDUM MULIEBRE)
The external genital structures include the mons pubis, labia majora, labia minora, clitoris, vestibule of the vagina, ure- thral (urinary) meatus, Skene’s glands, Bartholin’s glands, vaginal introitus (opening), hymen, and the perineum (Fig. 5-1).
The vulva (pudendum femininum) is the portion of the female external genitalia that lies posterior to the mons pubis. It consists of the labia majora, labia minora, clitoris, vestibule of the vagina, vaginal opening, and Bar- tholin’s glands (Venes, 2009).
Mons Pubis
The mons pubis, or mons veneris, is a layer of subcutane- ous tissue anterior to the genitalia in front of the symphy- sis pubis. It is located in the lowest portion of the abdo- men and typically is covered with pubic hair that grows in a transverse pattern. The texture and amount of pubic hair vary ethnically. In Asian women, the hair is fi ne and sparse. In women of African descent, the hair is thick and curly. The mons pubis is essentially a fatty pad that cush- ions and protects the pelvic bones, especially during intercourse.
Labia
The labia majora are the two folds of tissue that lie lateral to the genitalia and serve to protect the delicate tissues between them. The external labia are covered with pubic hair while the medial surfaces, which are moist and pink, are without pubic hair. During pregnancy, the labia majora are highly vascular due to hormonal infl uences.
The labia majora share an extensive lymphatic network with other vulvar structures, leading to an enhanced capacity to spread diseases such as malignant carcinomas.
The labia majora become less prominent after each pregnancy.
The labia minora are two folds of tissue that lie within the labia majora and converge near the anus to form the fourchette (a tense fold of mucous membrane at the pos-
terior opening of the vagina). Similar to but smaller than the labia majora, these structures are moist and absent of hair follicles and resemble mucous membrane. The labia minora contain a number of sebaceous glands that pro- vide lubrication and protective bacteriocidal secretions.
During puberty the labia minora enlarge. After meno- pause they become smaller due to declining hormonal levels. The mons, labia majora, and labia minora all func- tion to protect the clitoris and vestibule.
Clitoris
The clitoris is located at the upper junction of the labia minora. The prepuce, or clitoral hood, is a small fold of skin that partially covers the glans (head) of the clitoris.
Composed of erectile tissue, the clitoris is primarily the organ of sexual pleasure and orgasm in women. The clito- ris contains a rich blood and nerve supply, and is extremely sensitive. Sensory receptors located in the clitoris send information to the sexual response area in the brain. This message prompts the clitoris to secrete a cheese-like fatty substance with a distinctive odor called smegma. It is believed that smegma is a pheromone (chemical signal sent between individuals). Anatomically, the clitoral shape is similar to that of the urinary meatus, and the structural similarity of the two organs sometimes results in mis- guided and painful catheterization attempts. Some cul- tures remove the clitoris and other external genitalia in a ritualistic process called female circumcision.
Vestibule
The vestibule is essentially an oval-shaped space enclosed by the labia minora. It contains openings to the urethra and vagina, the Skene’s glands, and the Bartholin’s glands.
This area of a woman’s anatomy is extremely sensitive to chemical irritants. Nurses should be prepared to educate women about the potential discomforts associated with the use of dyes and perfumes found in soaps, detergents, and feminine hygiene products, and encourage their dis- continuation if symptoms develop.
Urethral (Urinary) Meatus
The urethral or urinary meatus (opening) is located in the midline of the vestibule, approximately 0.4 to 1 inch (1 to 2.5 cm) below the clitoris. The small opening is often shaped like an inverted “V.” The vaginal orifi ce or introitus lies in the lower portion of the vestibule posterior to the urethral meatus. It is essentially a boundary between the internal and external genitals. The hymen, a connec- tive tissue membrane, encircles the vaginal introitus.
Skene’s Glands and Bartholin’s Glands
The Skene’s glands (paraurethral glands), located on each side of the urethra, produce mucus that helps to lubricate the vagina. The Skene’s glands are not readily visible. To facilitate examination, the margins of the urethra are drawn apart and the mucous membrane gently everted to reveal the small glandular opening on each side of the fl oor of the urethra (Venes, 2009).
The Bartholin’s glands, also known as the greater ves- tibular or vulvovaginal glands, are located deep within the posterior portion of the vestibule near the posterior vagi- nal introitus. These glands secrete a clear mucus that moistens and lubricates the vagina during sexual arousal.
Prepuce of clitoris Clitoris Labia majora Labia minora Bartholin's
glands
Perineum
Urethral orifice
Skene's ducts Vaginal
orifice
Hymen Anus
Figure 5-1 Female external genitalia.
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116 unit two The Process of Human Reproduction
Hymen
Surrounding the opening of the vagina is a small portion of tissue called the hymen. The hymen typically forms a border around the entrance of the vagina in premenstrual girls. Hymenal tissue does not completely cover or occlude the vagina. Ultimately the hymen becomes widened, sometimes by tearing, which may be accompanied by bleeding. Widening of the hymen may also occur follow- ing a vulvar injury, tampon insertion, or at the time of the fi rst sexual intercourse. It is a societal myth that the hymen must be intact for a female to be considered a virgin.
Perineum
The perineum, an anatomical landmark, is the skin- covered region between the vagina and the anus. The peri- neal body consists of fi bromuscular tissue located between the lower part of the vagina and the anus. During the labor process, as the fetus descends through the vagina, the perineum stretches and becomes very thin, sometimes tearing as the baby is born. An episiotomy (incision made to enlarge the perineal opening to allow delivery of a fetus) may be performed to widen the external passage (see Chapter 12 for further discussion).
Now Can You— Discuss aspects of development of the reproductive system and identify components of the female reproductive tract?
1. Identify the developmental week when differentiation of the embryo’s reproductive system occurs?
2. Name three structures that arise from the mesonephric ducts?
3. Describe the anatomical locations and functions of the labia, Skene’s glands, and Bartholin’s glands?
PELVIC FLOOR
The bony pelvis contains a pelvic fl oor of soft tissues that provides support and stability for surrounding structures.
Most of the perineal support comes from the pelvic dia- phragm (musculofascial layer forming the lower boundary of the abdominopelvic cavity) and the urogenital diaphragm (musculofascial sheath lying between the ischiopubic rami
surrounding the female vagina). The pelvic diaphragm includes fascia and the levator ani and coccygeus muscles (Cunningham et al., 2005).
Above the pelvic diaphragm lies the pelvic cavity;
below and behind is the perineum. The urogenital dia- phragm includes fascia, deep transverse perineal muscles, and the urethral constrictor (Cunningham et al, 2005).
The muscles of the pelvic fl oor include the levator ani (consists of the iliococcygeal, pubococcygeal [pubovagi- nal], puborectal muscles) and the coccygeus. These struc- tures create a “sling” that provides support for internal pelvic structures and the pelvic fl oor. The ischiocaver- nosus muscle extends from the clitoris to the ischial tuberosities on each side of the lower bony pelvis. Two transverse perineal muscles extend from fi brous tissue of the perineum to the ischial tuberosities to stabilize the perineum (Fig. 5-2).
INTERNAL STRUCTURES
The internal female reproductive structures consist of the ovaries, fallopian tubes (oviducts, or uterine tubes), uterus, adjacent structures (adnexa), and vagina (Figs. 5-3 and 5-4). The ureters, bladder, and urethra are structures of the internal urinary system.
Ovaries
The ovaries are sometimes referred to as the essential female organ because they produce ova (female gametes or eggs) that are required for reproduction. They are a pair of oval structures, each measuring approximately 1.5 inches (4 cm) long, located on each side of the uterus below and behind the fallopian tubes. The ovarian liga- ment extends from the medial side of each ovary to the uterine wall; the broad ligament is a fold of the perito- neum that provides a covering for the ovaries. These two ligaments help to keep the ovaries in place.
The ovaries are responsible for the production of ova and the secretion of female sex hormones. Both of these func- tions become activated at the time of puberty. Oogenesis (the process of meiosis for egg cell formation) results in the formation of mature eggs within the ovary. Oogenesis is a process that occurs at regular (usually monthly) intervals.
The ovaries also secrete the female sex hormones estrogen
Urinary meatus
Pelvic fascia
Gluteus maximus muscle Transverse perineal
muscle
Anus
Ischiocavernosus muscle
Vaginal introitus Pubococcygeal (pubovaginal) muscle Puborectal muscle Iliococcygeal muscle
Levator ani
Figure 5-2 The muscles of the female pelvic fl oor.
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chapter 5 Reproductive Anatomy and Physiology 117
and progesterone. This important endocrine function helps to regulate the menstrual cycle.
A & P review Oogenesis
Oogenesis begins in the ovaries and is regulated by follicle stimulating hormone (FSH), which initiates the growth of ovarian follicles. Each follicle contains an oogonium, or egg-generating cell (Fig. 5-5). FSH also stimulates the fol- licle cells to secrete estrogen, which promotes maturation of the ovum. For each primary oocyte that undergoes the process of meiosis, only one functional egg cell is
produced. The remaining three cells, termed polar bodies, have no function and deteriorate. A mature ovarian folli- cle, also called a graafi an follicle, contains the secondary oocyte and if the egg is fertilized, the second meiotic divi- sion occurs and the ovum nucleus becomes the female pronucleus. ◆
Microscopically, the ovarian surface is termed the ger- minal epithelium. Each ovary has hundreds of thousands of follicles that contain immature female sex cells. All of the follicles in a woman’s ovaries develop in utero and are present at birth. During a postpubertal woman’s monthly
Fallopian tube Ovary Peritoneal cavity
Uterus Bladder Symphysis
pubis
Urethra
Clitoris
Labia minora Labia
majora Vagina Anus
Anterior fornix of vagina
Posterior fornix of
vagina Cervix
Rectum
Figure 5-3 Internal female genitalia and cross section of the rectum.
Body of uterus Fundus of uterus
Vagina Cervical canal Cervix
Broad ligament Ovarian ligament
Ovary
Fallopian tube
Figure 5-4 Internal structures of the adnexa.
Mitosis
Stem cell
Oogonium New stem cell
Figure 5-5 Oogenesis is the processes of mitosis and meiosis. For each primary oocyte that undergoes meiosis, only one functional ovum is formed.
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118 unit two The Process of Human Reproduction
menstrual cycle, one follicle develops and releases a mature ovum. (Please refer to the menstrual cycle discus- sion later in this chapter for additional information.) Throughout a woman’s reproductive years, only 300 to 400 follicles develop into mature ova and are released for potential fertilization by a sperm.
The ovaries are supported in their position in the pelvis by three important ligaments: the mesovarium, the ovar- ian ligament, and the infundibular pelvic ligament or sus- pensory ligament. The ovarian ligament positions the fi mbriae (fi nger-like projections) of the fallopian tube in contact with the lower pole of the ovary to enhance “pick- up” of the ovum following ovulation.
ACCESSORY ORGANS Fallopian Tubes
The (two) fallopian tubes are also called the uterine tubes or oviducts. Measuring approximately 4 inches (10 cm) in length, the lateral end of each fallopian tube encloses an ovary; the medial end opens into the uterus. Anatomi- cally, the fallopian tubes are composed of four layers.
Beginning with the external layer and progressing inward to the internal layer, these include the peritoneal (serous), which is covered by the peritoneum, the subserous (adven- titial), the muscular, and the mucous layers. The blood and nerve supplies are housed in the subserous layer. The muscular layer has an inner circular and an outer longitu- dinal layer of smooth muscle. It provides peristalsis that assists in transporting the ovum toward the uterus for potential implantation. The mucosal layer contains cilia (hairlike projections) that also assist in directing the ovum toward the uterus (Venes, 2009).
The fallopian tubes are attached at the upper outer angles of the uterus, and then extend upward and outward (Fig. 5-6). The diameter of each tube is approximately 6 mm. Anatomically, the tubes consist of three divisions:
infundi bulum, ampulla, and isthmus. The infundibulum is the funnel-shaped portion located at the distal end of the fallopian tube. The ovum enters the fallopian tube through a small opening (ostium) located at the bottom of the infundibulum. Several fi nger-like processes (fi mbriae) sur- round each ostium and extend toward the ovary. The lon- gest fi mbria, the fi mbria ovarica, is attached to the ovary.
The ampulla, which is the second division of the fallopian tube, is two-thirds the length of the tube and is most often
the site of ovum fertilization. The third division of the fal- lopian tube, the isthmus, is nearest the uterus and is typi- cally the site for tubal ligation (permanent sterilization).
A patent fallopian tube is able to convey the ovum from the ovary to the uterus and the spermatozoa from the uterus toward the ovary. Fertilization usually occurs in the outer one third of the fallopian tube, which provides a safe, nourishing environment for the ovum and sperm. If fertilization occurs, the fertilized ovum (termed a zygote until the fi rst cell division) is slowly and gently swept into the uterus by fallopian peristalsis and cilia movement, where implantation takes place. If fertilization does not occur, the ovum dies within 24 to 48 hours and disinte- grates, either in the tube or in the uterus.
Internally, each tube connects laterally with its corre- sponding ovary and medially with the uterus. Thus, there is a continuous route that passes from the vagina into the uterus and then on out to the tubes and ovaries. If the vagina is infected by a pathogen, the potential exists for retrograde transmission to the ovaries. Although most vaginal infections can be readily treated and cured, resid- ual scarring from the infl ammatory process can cause tubal narrowing leading to an increased risk for tubal pregnancies or infertility resulting from blockage.
Uterus
The uterus, centrally located in the pelvic cavity between the bladder (anteriorly) and rectum (posteriorly), is approximately 3 inches long by 2 inches wide (7.5 cm 5 cm). It is a pear-shaped organ with the narrower end positioned closest to the vagina (Fig. 5-7). The uterine interior is hollow and forms a path from the vagina to the fallopian tubes. Because the uterine walls are very thick and collapsed upon each other, the interior cavity is, in actuality, a “potential space.”
Two major functions of the uterus are to permit sperm to ascend toward the fallopian tubes and to provide a nourish- ing environment for the zygote until placental function begins. In addition, it provides a safe environment that pro- tects and nurtures the growing embryo/fetus until the preg- nancy has been completed. In the absence of conception, the uterus sheds the outermost layers of the inside of the endo- metrium (menstruation) in order to prepare for another menstrual cycle by regeneration of the endometrium.
The arteries of the uterus are the uterine, from the hypogastric arteries, and the ovarian, from the abdominal
Round ligament of uterus Fallopian tube
Isthmus Ampulla Infundibulum Fimbriae
Germinal epithelium
Tunica
albuginea Cortex of ovary
Vagina Cervix
Ovary Ovarian vessels Ovarian
ligament Fundus
of uterus Intrauterine part
of fallopian tube
Figure 5-6 Fallopian tube and ovary.
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chapter 5 Reproductive Anatomy and Physiology 119
aorta. This rich blood supply helps to ensure ample oxy- genation and nutrition to facilitate the growing uterus and fetus during pregnancy. The uterine veins drain into the internal iliac veins. The vasculature of the uterus is twisted and tortuous and as the gravid (pregnant) uterus expands, these vessels straighten out, allowing a contin- ued rich blood supply throughout pregnancy.
The uterus receives its nerve supply via the afferent (sen- sory) and efferent (motor) autonomic nervous systems.
These two systems are important in regulating both vaso- constriction and muscle contractions. The uterus also has an innate intrinsic motility as well. Thus, a patient with a spinal cord injury above level T6 may still have adequate enough uterine contractions to deliver a fetus vaginally.
Uterine pain nerve fi bers reach the spinal cord at levels T11 and T12. Because of this location and the presence of other pain receptors there, pain from the ovaries, ureters, and uterus may all be similar and may be reported by a woman who identifi es pain in the fl ank, inguinal, or vulvar areas. Several sensory nerve fi bers that contribute to dys- menorrhea (painful menstruation) are housed in the uterosacral ligaments.