Genital Development

September 12, 2011

Female genitalia consist of two main parts, the internal genitalia that includes the uterus, fallopian tubes, and vagina and external genitalia consisting of the vulva. Both internal and external genitalia develop in utero, that is, when the baby is still in the womb. In a series of experiments conducted in the 1950s, Alfred Jost demonstrated that the sex chromosomes (XX or XY) inherited determine whether the fetus will develop male gonads (sex glands) known as testes, or female gonads known as ovaries. In turn, the gonads determine the phenotypic sex (i.e., male versus female sexual/reproductive organs). An undifferentiated gonad develops during the fourth week of gestation, and for the first 2 months of growth, the two sexes develop identically. Starting around the eighth week of pregnancy, sexual differentiation begins when the testes first appear. In contrast, it is hard to observe the first appearance of ovaries and their development is determined based on the absence of testes rather than the presence of ovaries. Around the thirteenth week of pregnancy, however, the ovaries become apparent.

The “XX” sex chromosomes determine the growth of the ovaries. Ovaries produce the hormone estrogen that is essential for the further formation of the ovaries. Unlike in males, hormones are not required for the further genitalia development in females once the ovaries are fully formed. Rather, the internal urogenital tract develops from two sets of ducts present in both sexes: Wolffian and Mullerian ducts. In females, the Mullerian ducts give rise to the internal genitalia: fallopian tubes, uterus, and vagina. In the absence of testes the fetus’ genital tubercle becomes the external genitalia, that is, the clitoris and the vulva. The development of internal and external genitalia is a continuous process starting in utero and continuing through puberty. Parts of the brain become sexually differentiated. One part of the brain secretes the gonadotropin-releasing hormone (GnRH) that is necessary for normal gonadal development. Changes to the structure and functioning of the brain are irreversible and take place during critical windows of human development.

VULVA AND VAGINAL ANATOMY

The word vulva means “covering,” appropriately termed because it covers the openings to the urethra and the vagina. It includes the labia majora, labia minor, and the vestibule. The vulva begins at the top with the mons, or “mountain.” The mons is the pad of fat covered by pubic hair. The first sign of puberty is the growth of pubic hair that grows thicker as girls go through sexual maturation. The pattern of pubic hair, called escutcheon, is an inverted triangle in females. The amount of pubic hair on the mons can vary depending on race; African American girls tend to have thicker and coarser hair compared to Asian women who have sparser growth. Caucasian women tend to be somewhere in between.

The labia majora are the outer folds of the vulva between the thighs and like the mons they contain a fair amount of fat. The labia majora has a large number of sweat glands and other glands that secrete sebum, a wax coating that provides lubrication and prevents friction during sexual intercourse. The labia majora surrounds the labia minora that are the thin flaps of skin without hair. The labia minora is filled with blood vessels that plump up with blood when a woman is sexually aroused. The labia minora and the mons come together at the clitoris. The clitoris has a large number of nerve endings and is easily sexually stimulated. The area between the labia minora is called the vestibule. Like the labia minora, the vestibule is also rich in blood vessels. The blood vessels, also called the bulbs of the vestibule, swell up and become firm when a woman is sexually aroused.

The vagina is a tube that extends from the vestibule to the uterus, also described as the womb. Most of the time the vagina is collapsed, but it stretches when penetrated. The vaginal lining is sturdy because it manages multiple activities including sexual intercourse, childbirth, and menstruation. These activities also create an increased vulnerability to bacterial infections. The cervical canal connects the vagina to the uterus. The uterus and fallopian tubes (also called uterine tubes) play a key role in fertilization and pregnancy. Every month the ovaries release one egg or ovum that travels through the fallopian tubes toward the uterus. Fertilization occurs if the ovum meets a male sperm in the fallopian tubes. The fertilized egg then proceeds down the fallopian tubes until it reaches the uterus, and it embeds itself in the lining of the uterus in preparation for gestation. The fertilized egg develops over the next 40 weeks into a baby. If the ovum remains unfertilized, it dissolves when it reaches the uterus, and the uterine lining plus blood that developed in preparation for nurturing a fertilized egg is shed. The process of discharging the blood and the uterine lining is called menstruation.

CHANGES IN THE VULVA AND VAGINA DURING CHILDHOOD AND PUBERTY

Newborn and Childhood

At birth the labia majora and mons are hairless. The labia majora is plump because of high estrogen levels at birth. However, as the estrogen levels decrease following delivery, the size of the mons and labia majora diminish. Low levels of estrogen cause the vagina in young girls to have a thin lining that lacks protective lactobacilli or “good” bacteria necessary for safeguarding the vagina from other bacteria. Therefore, young girls are often susceptible to irritations from chemicals such as those found in bubble bath or dyes.

Puberty

Girls’ reproductive organs experience a growth spurt during puberty. The vagina doubles in length to about 3-5 in. long and the ovaries and fallopian tubes increase in size to about 3 or 4 in. in length. The uterus also grows in size, and in contrast to its upright position throughout childhood, the uterus begins to tilt during puberty. These changes are accompanied by hormonal shifts. Testosterone, primarily a male hormone but one that exists in females in small quantities, stimulates the growth of pubic and other bodily hair (e.g., armpits, legs). Girls typically develop body odor and acne as a result of increased testosterone during this period. Estrogen levels rise later in puberty giving way to breast development and menarche (see

Menarche). Menarche, or first menstruation, releases acid in the vagina, which in turn helps to fight off bacteria. During puberty, the hymen, which is a thin layer covering the vaginal opening, also undergoes change in preparation for adulthood. The hymen stretches thereby creating additional space for menstrual discharge and sexual activity. In some cases, the hymenal opening may be closed off completely (imperforate hymen) and may need to be surgically opened to allow for menstrual and sexual activity. By the end of puberty, the vagina and vulva are fully developed and girls are capable of sexual reproduction. Pregnancy and menopause bring about further structural changes in the lining of the vulva and vagina. Hormones fluctuate during these times and the stresses of childbirth often reshape the vaginal opening. Additional readings on these changes in later adulthood are provided at the end of the chapter.

GENITAL ABNORMALITIES

Turner Syndrome

Turner syndrome (TS) is characterized by the lack of development of secondary sexual characteristics (i.e., pubic hair and breast development). Other signs include growth retardation (somewhere between 4 ft, 6 in. and 4 ft, 10 in.), webbed neck, a broad chest with broadly spaced nipples, and cognitive difficulties, specifically a nonverbal learning disability. Turner syndrome occurs in approximately 1 out of every 2,000-3,000 births of girls, and is the result of the absence or abnormality in the X chromosome from either parent. Ovarian dysgenesis, the massive loss of egg cells during fetal development and after birth, is implicated in the lack of development of the secondary sexual characteristics. The loss of eggs during development causes the ovaries not to develop in the fetus, and as noted earlier, ovaries are critical to the development of female genitalia during fetal development. Consequently, the absence of ovaries results in infertility in women.

Treatment for Turner syndrome usually includes estrogen replacement therapy to stimulate the development of secondary sexual characteristics and a growth hormone to stimulate growth. If girls receive the treatment early enough in development, they can grow to a normal height. Unfortunately, Turner syndrome is usually not diagnosed until late adolescence when the absence of typical pubertal processes becomes apparent.

Ambiguous Genitalia

Intersex condition or hermaphroditism (46, XX with bilateral ova-testis) is a blending or mix of male and female internal and external genitalia. It is estimated that 0.1-2% of the population have this condition. When infants are born with ambiguous genitalia, doctors typically decide which gender to assign, and then perform surgical procedures and administer hormonal treatments to reinforce that particular gender. Large numbers of infants with ambiguous genitalia are raised female. Genital surgery includes a clitoral reduction and vaginoplasty (reconstructing the vagina).

In some cases the intersex condition is not obvious until puberty. Early signs are ignored, but when the onset of puberty is delayed pediatricians and parents take notice. Even then, some pediatricians may regard delayed pubertal onset as a normal physiological process. Physicians may prescribe oral contraceptives for “girls” to stop virilization (e.g., facial hair growth) and stimulate menstruation and breast growth. The psychological impact of this late diagnosis can be devastating, particularly because it is damaging to adolescents’ already vulnerable sense of self. Adolescents raised as girls may exaggerate their feminine characteristics to meet society’s expectations but at the same time feel like they are living a lie. In addition, adolescents may get little support from family members who find it difficult to accept their offspring’s new sexual status.

GENITAL MUTILATION

Genital mutilation, or female circumcision, involves the removal of external genitalia in women and may include partial or complete elimination of the clitoris, the labia minora, and/or partially stitching the labia majora together. This practice is highly prevalent in African countries. In Egypt, for example, 97% of women aged 15-49 were circumcised in 1995, with minimal variation in the percentage across age groups. Female circumcision is viewed as a universal sign of marriageability in Egyptian culture, and is maintained by people’s fear of family dishonor if they eliminate the practice.

Public outrage in the Western world has spurred some change in the prevalence of female circumcision. A qualitative analysis comparing circumcision histories of women aged 15-54 and their daughters who were at least 5 years old found that educated women were less likely to have their daughters circumcised. One explanation offered was that education about the risks of clitoridectomy, including bleeding, infections, infertility, and urinary problems, served as a deterrent. However, this study also found that maternal decisions not to circumcise their daughters had more to do with women’s resistance to beliefs about circumcision as a marker of purity and femininity, than to her knowledge of health risks. Circumcisions continue to take place in various countries across the world, but they are more likely to be performed by doctors than untrained professionals. Efforts to fully eradicate this practice will require careful attention to the social consequences of being ostracized and suffering family dishonor versus women’s health.

SEE ALSO: Adolescence, Female genital mutilation, Puberty, Sexual organs

Suggested Reading

  • Brooks, N. A. (2001). Sexual differentiation and development of the reproductive organs. In R. Harding & A. D. Bocking (Eds.), Fetal growth and development (pp. 207—223). New York: Guilford.
  • Diamond, M. (1997). Sexual identity and sexual orientation in children with traumatized and ambiguous genitalia. Journal of Sex Research, 34(2), 199-211.
  • Powell, P. M., & Schulte, T. (1999). Turner syndrome. In S. Goldstein & C. R. Reynolds (Eds.), Handbook of neurodevelopmental and genetic disorders in children (pp. 277-297). New York: Cambridge University Press.
  • Stewart, E. G. (2002). The V book: A doctor’s guide to complete vulvovaginal health. New York: Bantam Books.
  • Yount, K. M. (2002). Like mother, like daughter? Female genital cutting in Egypt. Journal of Health and Social Behavior, 43(3), 336-358.

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