Female Reproductive System
Understanding female reproductive anatomy includes the study of the external and internal structures; and the hormonal cycle.
The external genitalia, also called the vulva, includes the mons pubis (a fatty mound which covers the pubic bone), the labia majora (outer lips of the vagina), the labia minora (the inner lips of the vagina), the vaginal opening, the urethral opening (opening of the urethra, a tube which carries urine from the bladder outside of the body), the clitoris (a small structure with sensitive nerve endings located within the labia minora, the sole purpose of which is for sexual arousal and pleasure), and the perineum (the space between the anus (the rectal opening), and the vaginal opening).
Urinary Track Infections: The close proximity of the urethra and the rectum makes women susceptible to urinary tract infections (UTIs) because bacteria from the anus can enter the urethra. Health education about reproductive anatomy includes instructing women to avoid contamination of the urethra by "wiping from front to back" following urination.
The internal reproductive anatomy includes the uterus, two ovaries, two fallopian tubes, the urethra, the pubic bone, and the rectum. The uterus contains an inner lining called the endometrium (which builds ups and sheds monthly in response to hormonal stimulation). The lower portion of the uterus is called the cervix, which contains a small opening called the os. Menstrual blood flows through the os into the vagina during menstruation. Semen travels through the os into the uterus and the fallopian tubes following ejaculation during sexual intercourse. The cervical os dilates (opens) during childbirth.
- The cervix, the lower portion of the uterus, can be visualized during a gynecological examination by inserting a speculum into the vagina. The Pap smear, developed in the 1940's by Dr. George Papaniclaou, is a simple and cost-effective screening test that involves the collection of a sample of cells from the cervix, which are examined microscopically. The Pap smear screens for infections and/or cell changes which, can detect indications of cervical cancer. In the developed world, Pap smear screening has been instrumental in reducing morbidity and mortality associated with cervical cancer. Cervical screening technologies have expanded to include liquid cytology, although the traditional Pap smear is still used.
- Despite the availability of Pap smear screening in the developed world, studies of its use reveal racial, economic and ethnic disparities. In the developing world, programs for screening and treating cervical cancer are rare.
The ovaries, two small almond-shaped structures located on each side of the uterus, are the female gonads (reproductive glands). Female babies are born with over 400,000 ova (the gametes, also referred to as egg cells or oocytes), which are stored in the ovaries. The female body does not produce any additional ova. The ovaries produce estrogen and progesterone. The ovaries are close to, but not actually connected to the fallopian tubes, thin tube-like structures that are the site of fertilization, the fusion of the male and female gametes.
The Menstrual/Hormonal Cycle
The hormonal cycle facilitates maturation and rupture of the ovarian follicle resulting in the release of an ovum (the female reproductive or germ cell). Each month a series of changes take place which prepares the uterus for pregnancy. This cycle (menstrual cycle) is described below:
The first day of menstruation (referred to as Day 1) occurs when levels of estrogen and progesterone are low. In response to these low levels, the hypothalamus secretes gonadotrophin releasing hormone (GnRH) which triggers the anterior pituitary gland to release two hormones: follicle stimulating hormone (FSH), and luteinizing hormone (LH).
FSH stimulates the development of many follicles within the ovary. One dominant follicle takes over. As it continues to grow, it produces increasing amounts of estrogen, which stimulates the release of LH, and inhibits FSH, which suppresses further follicular development.
When LH levels are highest (LH surge), the ovarian follicle "ruptures" and releases one ovum, which is "swept" into the fallopian tube by hair-like projections called cilia that line the fimbriae (the fringe-like end of the fallopian tube that is closest to the ovary). This process is called ovulation. Increasing estrogen levels causes the cervical mucous (vaginal secretions) to become clear and profuse and the os to dilate. These two actions may facilitate the transport of semen (containing sperm) from the vagina, through the uterus, and into the fallopian tube.
Following ovulation, the ruptured follicle is transformed into the corpus luteum, a glandular mass that continues to produce estrogen and high levels of progesterone. The progesterone causes the endometrium to thicken, preparing it for implantation of a fertilized egg. If fertilization takes place during ovulation, hormonal levels remain high, essential for the maintenance of the pregnancy.
If fertilization does not occur, the corpus luteum shrinks and levels of both estrogen and progesterone decrease. The withdrawal of estrogen and progesterone cause the blood vessels of the endometrial (uterine) lining to "break" resulting in vaginal bleeding (menstruation). The average menstrual cycle is 28-35 days, and menstrual flow usually continues for three to seven days, although there are variations among women.
Following menstruation, estrogen and progesterone levels are low, triggering the hypothalamus to once again release GnRH, starting the entire cycle again. If fertilization does take place, menstruation will not reoccur for the duration of the pregnancy
Mechanism of Action for Contraception/Pregnancy
- Most hormonal methods of birth control, including emergency contraception, work by preventing or postponing ovulation, and by thickening the cervical mucous.
- The absence of a menstrual period in a sexually active woman may indicate that pregnancy has occurred. It is a presumptive, although not definitive, sign of pregnancy.
Menopause, the end of menstruation, occurs between the ages of 45 and 55 (with the average age of 51.3). An entirely normal developmental and physiological process, it can be accompanied by symptoms including hot flashes, fatigue, moodiness, insomnia, decreased libido and sexual response, changes in memory, weight gain, and vaginal dryness. Until cessation of ovarian function is confirmed through a blood test, and/or one year of no menses, women may continue to ovulate and therefore require contraception to prevent unintended pregnancy.