Genitals, Female

Though the female genitals (or genitalia) are often narrowly defined as only those tissues and organs involved in reproduction that are visible on the outside of the body (the external or primary genitalia), broader definitions include internal (or secondary) sex organs as well. Some definitions include the breasts (mammary tissue) within the scope of female genitals because of their function in lactation following childbirth. External genitalia includes the vulva (pudendum); the labia (Latin for lips) majora and minora; the clitoris (a small and highly sensitive organ composed of erectile tissue that engorges with blood and grows larger upon sexual arousal); the clitoral hood (or prepuce); the mons pubis; and the urethra (the tube that carries urine out of the body). The internal genitalia consist of the ovaries (female gonads); fallopian tubes (or oviducts, uterine tube, or salpinges); uterus (or womb); Skene's glands; Bartholin's glands; and the vagina (or birth canal).

PHYSIOLOGY AND MORPHOLOGY OF THE INTERNAL FEMALE GENITALS

The internal genitals are located within the female pelvis between the bladder and the rectum. The uterus and vagina are situated in the midline of the lower abdomen. One of a pair of ovaries lies on either side of the uterus and connects to it by way of the fallopian tubes. These internal organs are supported by ligaments (notably the broad ligament).

The ovaries are a pair of small, almond-shaped glands with a puckered uneven surface. They are analogous to the testes in males in that they are the sex organ responsible for producing the gametes (or sex cells—the ovum in women and the sperm in men whose union, known as fertilization, is a necessary step for human reproduction). The broad ligament holds the ovary in the pelvis. This ligament is attached to the peritoneum, a membrane that separates the pelvic region from the abdominal organs. Two other ligaments support the ovaries: the suspensory ligaments which attach the ovary to the lateral wall of the pelvic region and the ovarian ligaments which attach it to the top part of the uterus. Veins, arteries, and nerves that supply the ovary travel through the suspensory ligament. The outer layer of the ovaries is made up of a dense connective tissue that contains the ovarian follicles, each of which encloses an oocyte (or egg, the cell that eventually becomes the ovum). Female infants are born with all the oocytes the body will use in a lifetime. These begin developing by dividing at the subcellular level (through meiosis) but will not complete the process until ovulation begins after puberty. These immature (or primary) oocytes and their surrounding tissues (granulosa cells) make up the primary follicle. At birth the ovaries contains roughly 1 million primary follicles. From then until puberty, that number falls to about 300,000 to 400,000. Of this number, only about 400 will continue the maturation process and be released from the ovary during a process called ovulation. All remaining follicles will eventually degenerate.

During childhood the ovaries remain inactive until the age of nine or ten when the anterior pituitary gland in the brain begins secreting hormones that initiate puberty. This is associated with the growth of the ovaries, which then begin secreting feminizing hormones (notably estrogens and progesterones). The dramatic increase in these hormones stimulates the growth and function of the primary sexual characteristics (including the ovaries, fallopian tubes, uterus, and vagina) as well as the secondary sexual characteristics (such as hair distribution and breast development). The external genitalia including the vulva and labia majora and minora also grow to mature size.

After puberty, fluctuations in hormone levels from the anterior pituitary cause one ovarian follicle each month to develop and a consequent increase in hormone secretion by the cells surrounding the follicle. This increase in turn causes the follicle to grow larger until changes in hormonal stimulation cause it to blister and rupture resulting in ovulation. What remains of the follicle becomes the corpus luteum, which secretes hormones that will support a pregnancy (should it occur) through the first three months (after which time its function is replaced by the placenta—a large gland that grows at the site of embryo implantation in the uterus). If no pregnancy occurs, the corpus luteum degenerates causing a subsequent drop in the level of hormones formerly secreted by the now-degenerating tissue. This triggers the start of menstruation—the sloughing of the inner (or endometrial) lining of the uterus. This cycle of hormonal fluctuation, ovulation, and menstruation continues on average every twenty-eight days until menopause (around the age of fifty) when the ovaries stop producing enough hormones to sustain the reproductive cycle.

After ovulation, the oocyte is released into the pelvic cavity adjacent to the end of the fallopian tube. The ovarian end of the tube flairs out, and its opening is fringed by long thin fimbriae that surround the surface of the ovary. Cilia on the fimbriae propel the ovulated oocyte into the fallopian tube where fertilization may occur if sperm is present. (Tubal ligation by surgically cutting away or tying off a portion of the fallopian tubes is an elective method of birth control, which works by preventing the sperm from reaching the egg.) After fertilization, the newly formed embryo continues through the fallopian tube to the uterus. Unfertilized ova also continue through to the uterus where they are expelled with the menstrual fluids.

The uterus is the major reproductive organ in females. In its mature and nonpregnant state, it is roughly the size and shape of a pear—with its upper and larger, rounded end (or body) connected to the fallopian tubes (at the uterine fundus), and its lower aspect, or the cervix, located at the bottom and opening into the vagina. The uterus is composed of three main layers: an outer (or serous) layer made of peritoneal tissue; a middle muscular layer (the myometrium); and an inner endometrium. The uterus' primary function is to provide a protective and nourishing environment for the fertilized ovum. Blood vessels from the endometrium specifically supply the placenta that in turn supports the embryo, which later develops into a fetus. It does this by going through cyclic changes that help improve the chances that an embryo will successfully implant in the lining of the uterine cavity. The inner two linings of the uterus undergo profound changes during the menstrual cycle due to the effects of the hormones estrogen and progesterone. Estrogen stimulates the rapid growth of both the myometrium and endometrium. Progesterone then stimulates the endometrial layer to thicken with an increased supply of blood vessels and to begin secreting a sugar-like substance in order to provide a hospitable and nourishing environment for the implantation of the embryo.

Beneath the uterus is the vagina, a three to four inch fibro-muscular tube that attaches to the lower part of the uterus and extends to the vulvar opening. Its opening is often covered by a thin layer of tissue, the hymen, which generally stretches or tears during a female's first sexual intercourse (coitus), through the use of tampons, or as a result of trauma. The vagina is the female sex organ for intercourse in that it allows the entry of the penis that, when ejaculation occurs, provides a conduit for the sperm to travel up through the uterus and into the fallopian tubes to fertilize the ovum. The vaginal walls are much thinner than those of the uterus, and they are lined with mucous membranes that moisten and provide lubrication for the act of intercourse. The vagina also provides a canal through which the infant travels from the uterus to the outside during childbirth. When pregnancy does not occur, the pathway allows the monthly menstrual flow to exit the body. Though the vaginal walls are usually collapsed upon themselves, the outer muscular layer readily expands to allow the penis to enter into the vaginal canal. These muscles are capable of stretching enough to allow the passage of a full-term infant during childbirth. The presence of estrogen makes the lining of the vagina more resilient to trauma and better able to avoid infection. Inside the anterior (or frontal) aspect of the vaginal wall behind the pubic bone is an area of spongy and highly sensitive tissue known as the Gräfenberg spot (or G-spot, for the German doctor who identified it) that can be a source of sexual arousal when stroked or stimulated. It is associated with the Skene's glands, which open near the vestibule (the space into which the vagina and urethra open) near the urethra. These glands are homologous to the prostate gland in males and may be the source of a female ejaculate (though there is controversy in the medical community about the existence of both the G-spot and female ejaculation).

Another pair of glands, the Bartholin glands, is located just within the entrance and on either side of the vagina. These glands produce a waxy substance that may contribute to vaginal lubrication and may also produce pheromones (natural chemicals emitted to attract members of the same species).

PHYSIOLOGY AND MORPHOLOGY OF THE EXTERNAL FEMALE GENITALS

The vulva is the external and visible part of the female genitalia that lies at the opening of the vagina. It is composed of the vestibule and its associated tissues and structures. The vulvar opening is lined by two thin, skin folds called the labia minora. These inner folds run longitudinally along the vaginal opening and meet at its anterior aspect to form a hood that covers the clitoris. Masters and Johnson (1966) point out that the clitoris is the only organ in humans whose sole purpose is to provide erotic pleasure). The inner labia also meet at the bottom of the vestibule at the fourchette, which is next to the anus. The tissue between the anal opening and the vagina is called the perineum. This tissue is often surgically cut (in an episiotomy) during vaginal childbirth to help prevent tearing during the birth process. Next to the labia minor lie the outermost folds, the labia majora. These are generally larger in size and are usually covered with pubic hair. The labia minora may naturally be completely contained within the folds of the labia majora, or they may extend below. Labiaplasty is a controversial procedure where women surgically alter the appearance of the labia to make them appear more like an "aesthetic ideal."

The mons pubis is a soft mound of flesh made of fatty tissue and located just over the pubic bone. The function of this tissue is to protect the bone beneath it. Like the labia majora, it is usually covered with pubic hair.

The urethra in females functions only to transport urine from the bladder to outside the body. It is located in the vulva between the opening of the vagina and the clitoris. Because it is so close to the anogenital area, the incidence of urinary tract infections (UTI or cystitis) is common in females.

DISEASES OF THE FEMALE GENITALS

Adhesive disease is a condition that is usually the result of an inflammatory process, such as pelvic inflammatory disease (PID) or other intra-abdominal inflammations (such as Crohn's Disease or those resulting post-surgically). Other common causes are endometriosis or history of recurrent ovarian cyst ruptures. Symptoms may include pelvic pain; dysmenorrhea (painful periods); infertility; painful intercourse; and (in severe forms) bowel or urinary obstructions. Treatment is difficult because adhesions often reform after surgical excision.

Benign ovarian cysts are a common gynecologic condition that is generally ovulatory in nature (such as a hemorrhagic [or bleeding] corpus leuteum). Symptoms may include abdominal pain, nausea, vomiting, low-grade fever, and abnormal uterine bleeding. The condition is usually self-limiting with symptoms going away in a day or two. In more persistent cases, it can be treated with hormonal suppression (i.e., birth control pills or Depo-Provera) or surgical excision of the cysts.

Cervical cancer is one of the most common cancers of the reproductive system. The predominate risk factor for contracting this disease is infection with the human papilloma virus (HPV), a sexually transmitted disease (STD). In some women, infection progresses to cervical dysplasia (pre-cancerous cell change). From there it can develop into invasive cancer. The vast majority of cervical dysplasia is diagnosed and treated prior to becoming invasive. Cervical dysplasia is diagnosed during routine Pap tests and further identified with a colposcopy-directed biopsy. Treatment includes cryotherapy (freezing), thermal ablation (burning), or surgical excision. The risk of cervical cancer increases with the number of sexual partners. Consistent and proper use of latex condoms offers only limited protection against developing HPV. A vaccine is available for young girls who have not yet had sex and for young women, even if they are sexually active, to convey immunity against HPV.

Ectopic pregnancy is a condition where the embryo implants outside the uterine cavity. Most commonly this occurs in the fallopian tube (tubal pregnancy), but it can also implant in the cervix, ovary, or abdominal cavity. Because these other sites cannot accommodate the growth of a fetus, left untreated, the site of implantation will eventually rupture and cause intra-abdominal bleeding (very rarely ectopic pregnancies in the abdomen progress to full term and must be delivered by Caesarian section—surgical removal of the baby through an incision in the abdomen). Treatment consists either of medication such as methotrexate (which causes regression of the embryonic tissue) or surgery to excise the ectopic pregnancy (with or without tubal preservation). Up until the end of the nineteenth century, ruptured ectopic pregnancy was a significant cause for the high mortality rate of pregnancy.

Endometriosis is a common condition where endometrial cells (which normally line the uterine cavity) are present in the abdominal/pelvic cavity and other areas of the body. This occurs mostly by regurgitation of menstrual fluid out of the fallopian tubes with subsequent implantation of the endometrial cells in the abdominal cavity. The main treatment is hormonal suppression or surgical excision (with or without removal of the ovaries). A family history of endometriosis is the main risk factor for developing the disease.

Infections may affect all areas of the female genitalia, but most gynecologic infections are limited to the vagina. These may consist of yeast, bacterial, as well as other STDs such as PID, chlamydia, gonorrhea, HPV, and human immunodeficiency virus (HIV). Depending on the causative agent, symptoms may be mild or severe (possibly leading to infertility), and treatments may vary. The most reliable method for prevention of all STDs is abstinence or limiting sexual activity to monogamous, long-term relationships with partners who have been tested and are free of infection. Consistent and correct use of latex condoms may help to prevent the transmission of many STDs but is ineffective in others.

Ovarian cancer is the ninth most common cancer in women and the fifth leading cause of cancer death. Benign disease (which does not spread beyond the ovaries) may be successfully treated by removing the affected ovary (oophorectomy). In more serious cases, surgery to remove the ovaries, fallopian tubes, and the uterus and/or debulking by removing tumors that have spread to other organs (such as the kidneys) is followed by chemotherapy and/or radiation therapy as indicated.

Primary infertility is a condition defined by a one year period during which unprotected intercourse does not result in pregnancy. Common causes are tubal damage or occlusion due to infection, endometriosis, and adhesion, among others. Problems may also arise due to ovulation irregularities (as with hormonal insufficiency), structural abnormalities (such as fibroid in the uterus or congenital defects), and cervical mucous incompatibility (where a woman builds up antibodies to her partner's sperm). Most common infertility problems can be successfully treated with current infertility technology including in-vitro fertilization (IVF) or drug therapy.

Uterine fibroids are not uncommon in women in general, but are more prevalent in African-American women. They may cause dysfunctional uterine bleeding (non-menstrual), pelvic pain, and (to a lesser degree) infertility, miscarriage, and cancer. Treatment includes surgical excision, hormonal suppression, and in some cases vascular embolization (blocking the uterine blood flow to the fibroid to make it shrink).

Vaginal cancer is a less common form of malignancy. Risk factors include age (it is more common in women sixty years and older); exposure to diethylstilbestrol (DES, a hormone that was prescribed between 1940 and 1971 to women with an increased risk of miscarriage); HIV or HPV infection; prior cervical cancer; and smoking. Treatment usually consists of surgery, radiation, and, possibly, chemotherapy in advanced cases.

see also Clitoris; Uterus; Vagina.

BIBLIOGRAPHY

Guyton, Arthur C. 1991. Textbook of Medical Physiology. 8th edition. Philadelphia, PA: Saunders.

Luciano, Dorothy S.; Arthur J. Vander; and James H. Sherman. 1978. Human Function and Structure. New York: McGraw-Hill.

Masters, William H., and Virginia E. Johnson. 1966. Human Sexual Response. Boston: Little Brown.

Seeley, Rod R.; Trent D. Stephens; and Philip Tate. 1991. Essentials of Anatomy and Physiology. St. Louis, MO: Mosby Year Book.

Speroff, Leon; Robert H. Glass; and Nathan G. Kase. 1994. Clinical Gynecologic Endocrinology and Infertility. 5th edition. Baltimore, MD: Williams & Wilkins.

Thibodeau, Gary A. Anatomy and Physiology. 1987. St. Louis, MO: Times Mirror/Mosby College Publishing.

                                          Diane Sue Saylor