Female Reproductive Organ Anatomy

The female reproductive system is a complicated but fascinating subject. It has the capability to function intimately with nearly every other body system for the purpose of reproduction.

The female reproductive organs can be subdivided into the internal and external genitalia (see the images below). The internal genitalia are those organs that are within the true pelvis. These include the vagina, uterus, cervix, uterine tubes (oviducts or fallopian tubes), and ovaries. The external genitalia lie outside the true pelvis. These include the perineum, mons pubis, clitoris, urethral (urinary) meatus, labia majora and minora, vestibule, greater vestibular (Bartholin) glands, Skene glands, and periurethral area.

External Genitalia

The vulva, also known as the pudendum, is a term used to describe those external organs that may be visible in the perineal area (see the images below). The vulva consists of the following organs: mons pubis, labia minora and majora, hymen, clitoris, vestibule, urethra, Skene glands, greater vestibular (Bartholin) glands, and vestibular bulbs. ^{[1, 2, 3]} The boundaries include the mons pubis anteriorly, the rectum posteriorly, and the genitocrural folds (thigh folds) laterally.

Mons pubis

The mons pubis is the rounded portion of the vulva where sexual hair development occurs at the time of puberty. This area may be described as directly anterosuperior to the pubic symphysis.

Labia

The labia majora are 2 large, longitudinal folds of adipose and fibrous tissue. They vary in size and distribution from female to female, and the size is dependent upon adipose content. They extend from the mons anteriorly to the perineal body posteriorly. The labia majora have hair follicles.

The labia minora, also known as nymphae, are 2 small cutaneous folds that are found between the labia majora and the introitus or vaginal vestibule. Anteriorly, the labia minora join to form the frenulum of the clitoris.

Hymen

The hymen is a thin membrane found at the entrance to the vaginal orifice. Often, this membrane is perforated before the onset of menstruation, allowing flow of menses. The hymen varies greatly in shape.

Clitoris

The clitoris is an erectile structure found beneath the anterior joining of the labia minora. Its width in an adult female is approximately 1 cm, with an average length of 1.5–2.0 cm. The clitoris is made up of 2 crura, which attach to the periosteum of the ischiopubic rami. It is a very sensitive structure, analogous to the male penis. It is innervated by the dorsal nerve of the clitoris, a terminal branch of the pudendal nerve.

Vestibule and urethra

Between the clitoris and the vaginal introitus (opening) is a triangular area known as the vestibule, which extends to the posterior fourchette. The vestibule is where the urethral (urinary) meatus is found, approximately 1 cm anterior to the vaginal orifice, and it also gives rise to the opening of the Skene glands bilaterally. The urethra is composed of membranous connective tissue and links the urinary bladder to the vestibule externally. A female urethra ranges in length from 3.5 to 5.0 cm.

Skene and Bartholin glands

The Skene glands secrete lubrication at the opening of the urethra. The greater vestibular (Bartholin) glands are also responsible for secreting lubrication to the vagina, with openings just outside the hymen, bilaterally, at the posterior aspect of the vagina. Each gland is small, similar in shape to a kidney bean.

Vestibular bulbs

Finally, the vestibular bulbs are 2 masses of erectile tissue that lie deep to the bulbocavernosus muscles bilaterally.

Internal Genitalia

Vagina

The vagina extends from the vulva externally to the uterine cervix internally. It is located within the pelvis, anterior to the rectum and posterior to the urinary bladder. The vagina lies at a 90º angle in relation to the uterus. The vagina is held in place by endopelvic fascia and ligaments (see the image below).

The vagina is lined by rugae, which are situated in folds throughout. These allow easy distention, especially during child bearing. The structure of the vagina is a network of connective, membranous, and erectile tissues.

The pelvic diaphragm, the sphincter urethrae and transverse peroneus muscles, and the perineal membrane support the vagina. The sphincter urethrae and the transverse peroneus are innervated by perineal branches of the pudendal nerve. The pelvic diaphragm primarily refers to the levator ani and the coccygeus and is innervated by branches of sacral nerves S2-S4.

The vascular supply to the vagina is primarily from the vaginal artery, a branch of the anterior division of the internal iliac artery. Several of these arteries may be found on either side of the pelvis to richly supply the vagina.

The nerve supply to the vagina is primarily from the autonomic nervous system. Sensory fibers to the lower vagina arise from the pudendal nerve, and pain fibers are from sacral nerve roots. Lymphatic drainage of the vagina is generally to the external iliac nodes (upper third of the vagina), the common and internal iliac nodes (middle third), and the superficial inguinal nodes (lower third).

Uterus

The uterus is the inverted pear-shaped female reproductive organ that lies in the midline of the body, within the pelvis between the bladder and the rectum. It is thick-walled and muscular, with a lining that, during reproductive years, changes in response to hormone stimulation throughout a woman’s monthly cycle.

The uterus can be divided into 2 parts: the most inferior aspect is the cervix, and the bulk of the organ is called the body of the uterus (corpus uteri). Between these 2 is the isthmus, a short area of constriction.

The body of the uterus is globe-shaped and is typically situated in an anteverted position, at a 90º angle to the vagina. The upper aspect of the body is dome-shaped and is called the fundus; it is typically the most muscular part of the uterus. The body of the uterus is responsible for holding a pregnancy, and strong uterine wall contractions help to expel the fetus during labor and delivery.

The average weight of a nonpregnant, nulliparous uterus is approximately 40-50 g. A multiparous uterus may weigh slightly more than this, with an upper limit of approximately 110 g. A menopausal uterus is small and atrophied and typically weighs much less.

The cavity of the uterus is flattened and triangular. The uterine tubes enter the uterine cavity bilaterally in the superolateral portion of the cavity.

The uterus is connected to its surrounding structures by a series of ligaments and connective tissue. The pelvic peritoneum is attached to the body and the cervix as the broad ligament, reflecting onto the bladder. The broad ligament attaches the uterus to the lateral pelvic side walls. Within the broad base of the broad ligament, between its anterior and posterior laminae, connective tissue strands associated with the uterine and vaginal vessels help to support the uterus and vagina. Together, these strands are referred to as the cardinal ligament.

Rectouterine ligaments, lying within peritoneal folds, stretch posteriorly from the cervix to reach the sacrum. The round ligaments of the uterus are much denser structures and connect the uterus to the anterolateral abdominal wall at the deep inguinal ring. They lie within the anterior lamina of the broad ligament. Within the round ligament is the artery of Sampson, a small artery that must be ligated during hysterectomy.

The vasculature of the uterus is derived from the uterine arteries and veins. The uterine vessels arise from the anterior division of the internal iliac, and branches of the uterine artery anastomose with the ovarian artery along the uterine tube.

The nerve supply and lymphatic drainage of the uterus are complex. Lymphatic drainage is primarily to the lateral aortic, pelvic, and iliac nodes that surround the iliac vessels. The nerve supply is attained through the sympathetic nervous system (by way of the hypogastric and ovarian plexuses) and the parasympathetic nervous system (by way of the pelvic splanchnic nerves from the second through fourth sacral nerves).

Cervix

The cervix is the inferior portion of the uterus, separating the body of the uterus from the vagina. The cervix is cylindrical in shape, with an endocervical canal located in the midline, allowing passage of semen into the uterus. The external opening into the vagina is termed the external os, and the internal opening into the endometrial cavity is termed the internal os. The internal os is the portion of a female cervix that dilates to allow delivery of the fetus during labor. The average length of the cervix is 3-5 cm.

The vasculature is supplied by descending branches of the uterine artery, which run bilaterally at the 3 o'clock and 9 o’clock position of the cervix. The nerve supply to the cervix is via the parasympathetic nervous system by way of the second through fourth sacral segments. Many pain nerve fibers run alongside these parasympathetics. Lymphatic drainage of the cervix is complex. The obturator, common iliac, internal iliac, external iliac, and visceral parametrial nodes are the main drainage points.

Uterine tubes

The uterine tubes (also referred to as oviducts or fallopian tubes) are uterine appendages located bilaterally at the superior portion of the cavity. Their primary function is to transport sperm toward the egg, which is released by the ovary, and then to allow passage of the fertilized egg back to the uterus for implantation.

The uterine tubes exit the uterus through an area known as the cornua and form a connection between the endometrial and peritoneal cavities. Each tube is approximately 10 cm in length and 1 cm in diameter and is situated within a portion of the broad ligament called the mesosalpinx. The distal portion of the uterine tube ends in an orientation encircling the ovary.

The uterine tube has 3 parts. The first segment, closest to the uterus, is called the isthmus. The second segment is the ampulla, which becomes more dilated in diameter and is the typical place of fertilization. The final segment, furthest from the uterus, is the infundibulum. The infundibulum gives rise to the fimbriae, fingerlike projections that are responsible for catching the egg that is released by the ovary.

The arterial supply to the uterine tubes is from branches of the uterine and ovarian arteries, small vessels that are located within the mesosalpinx. The nerve supply to the uterine tubes is via both sympathetic and parasympathetic fibers. Sensory fibers run from thoracic segments 11-12 and lumbar segment 1. Lymphatic drainage of the uterine tubes is through the iliac and aortic nodes.

Ovaries

The ovaries are paired organs located on either side of the uterus within the mesovarium portion of the broad ligament below the uterine tubes. The ovaries are responsible for housing and releasing the ova, or eggs, necessary for reproduction. At birth, a female has approximately 1-2 million eggs, but only 300 of these eggs ever mature and are released for the purpose of fertilization.

The ovaries are small and oval-shaped, exhibit a grayish color, and have an uneven surface. The actual size of an ovary depends on a woman’s age and hormonal status; the ovaries are approximately 3-5 cm in length during childbearing years and become much smaller and atrophic once menopause occurs. A cross-section of the ovary reveals many cystic structures that vary in size. These structures represent ovarian follicles at different stages of development and degeneration.

Several ligaments support the ovary. The ovarian ligament connects the uterus and ovary. The posterior portion of the broad ligament forms the mesovarium, which supports the ovary and houses the vascular supply. The suspensory ligament of the ovary (infundibular pelvic ligament), a peritoneal fold overlying the ovarian vessels, attaches the ovary to the pelvic side wall.

Blood supply to the ovary is via the ovarian artery; both right and left ovarian arteries originate directly from the descending aorta at the level of the L2 vertebra. The ovarian artery and vein enter and exit the ovary at the hilum. The left ovarian vein drains into the left renal vein, and the right ovarian vein empties directly into the inferior vena cava.

Nerve supply to the ovaries run with the vasculature within the suspensory ligament of the ovary, entering the ovary at the hilum. Supply is through the ovarian, hypogastric, and aortic plexuses. Lymphatic drainage of the ovary is primarily to the lateral aortic nodes; however, the iliac nodes may also be involved.

Histologically, the vulva is predominantly keratinized, stratified squamous epithelium. ^[4] The labia majora are composed of both sebaceous and sweat glands; the labia minora are made up of dense connective tissue with erectile tissue and elastic fibers.

The hymen consists of fibrous tissue with a few small blood vessels and is covered by stratified squamous epithelium. The body of the clitoris is composed of 2 channels of vessels and nerve endings that function as erectile tissue, the corpora cavernosa.

The mucosa of the proximal two-thirds of the urethra is composed of stratified transitional epithelium similar to that of the urinary bladder. The distal one-third is composed of stratified squamous epithelium. The greater vestibular glands are mostly made up of cuboidal epithelium, with the ducts lined by transitional epithelium.

The vagina has 3 layers. The first layer is the mucosa, the epithelium of which is composed of stratified squamous cells that contain a small amount of keratin. The lamina propria is composed of loose connective tissue that has a vast amount of elastic fibers, giving the vagina its capability to distend. The second layer is muscular, mainly smooth muscle. The final layer is the adventitia, which is also rich in elastic fibers. A large plexus of blood vessels is also present. ^[4]

The uterine corpus has 3 layers, from innermost to outermost: endometrium, myometrium, and serosa. The endometrium is composed of cells resembling embryonic connective tissue, with scant amounts of cytoplasm and large nuclei. It can be subdivided into 2 more layers: the inner stratum basale and the outer stratum functionale. The stratum functionale is the layer of the endometrium that responds to hormonal stimulation. The myometrium is composed of 3 layers of smooth muscle. The serosa is a continuation of the visceral peritoneum. ^[4]

Most of the cervix is composed of collagenous connective tissue, smooth muscle, and mucopolysaccharide ground substance. The endocervical canal is rich in mucous glands and is primarily columnar epithelium. The external portion of the cervix that lies within the vagina is composed of stratified squamous epithelium.

The area surrounding the external os is termed the transformation zone, which is the transition point between squamous cells externally and columnar cells of the endocervical canal. The transformation zone is the area where cervical cell changes (ie, dysplasia) can occur. Most cell changes are picked up during a Papanicolaou smear, the screening test for cervical cancer. ^[4]

Internally, the uterine tubes have many folds, or plicae, which are most evident in the ampulla. Within the mucosa of the uterine tubes, 3 different dell types exist: columnar ciliated epithelial cells (25%), secretory cells (60%), and narrow peg cells (< 10%). A muscular layer of smooth muscle surrounds the mucosa. ^[4]

The ovary can be divided into 2 main sections: the outer cortex and the inner medulla. A germinal layer coats the entire ovary, made of cuboidal epithelial cells. The cortex is where the follicles are found at various stages of development and degeneration. The cortex is made of tightly packed connective tissue. The medulla is where the ovarian vasculature is found and is composed primarily of loose stromal tissue. ^[4]

Variations of female reproductive anatomy often stem from dysfunction during development in utero. They can also be caused by genetic changes or teratogenic effects.

Clitoromegaly, imperforate hymen (see the image below), labial fusion, and vaginal agenesis are the most common variants of the external genitalia. Performing a thorough physical examination of newborns to detect these changes is important.

Internally, the most common variants include vaginal septa, arcuate uterus, bicornuate uterus, didelphic uterus (see the image below), unicornuate uterus, and septate uterus. Uterine anomalies are most frequently diagnosed by performing hysterosalpingography, a radiologic study in which dye is injected into the uterine cavity to visualize any abnormalities. Uterine anomalies are often detected during evaluation for infertility. These conditions are commonly diagnosed at the time of cesarean section.

The female reproductive organs are associated with various disorders, including infections, disorders of menstruation, pain, pelvic floor support with or without continence disorders, trauma, iatrogenic outcomes, correction of congenital anomalies, and malignancies.

Briefly, infectious complications associated with female reproductive organs include, but are not limited to, vaginal and vulvar candidiasis, herpes simplex lesions, Neisseria gonorrhoeae infection, Chlamydia trachomatis infection, trichomoniasis, bacterial vaginosis, tubo-ovarian abscesses, and pelvic inflammatory disease.

Much attention is brought to disorders of menstruation because these affect many women at some point in their lives. Such disorders include heavy menses (menorrhagia), painful menses (metrorrhagia), irregular menses (oligomenorrhea), lack of menses (amenorrhea), or frequent menses (hypermenorrhea). Premenstrual disorder and premenstrual dysphoric disorder are also problems associated with the menstrual cycle.

Pain can be a common problem among women, especially those with endometriosis, multiple pelvic surgeries, and history of pelvic inflammatory disease. Women with a history of an ectopic pregnancy (pregnancy outside the uterine cavity) who required surgery may have long-term pain issues.

Malignancies of the female reproductive organs are unfortunately common and often life-threatening. Vaginal cancer, associated with infection by the human papillomavirus (HPV), is rare. Vulvar cancer, also associated with HPV infection, is more common. Cervical cancer, although less common as a result of better screening with Papanicolaou smears, can be devastating if not detected early. Cervical cancer is also associated with infection by HPV.

Malignancy of the uterine corpus is often a disease of postmenopausal women. Uterine cancer is directly associated with unopposed estrogen stimulation of the endometrial tissue. Ovarian cancer is often not detected until it has progressed significantly, because a good screening test for this disease does not exist.

Other changes to consider include the following:

• Changes as a result of gynecologic-oncology procedures (eg, transposition of the ovaries, radiation changes, radical vulvectomy changes)
• Iatrogenic changes secondary to transgender procedures
• Correction of congenital anomalies (eg, vaginoplasty, labial reconstruction)
• Changes seen before and after pelvic floor reconstructive and urinary and anal continence procedures