The female reproductive system is a network of internal and external organs that work together to produce eggs, make hormones, support pregnancy, and carry out menstruation. It changes dramatically across a lifetime, from puberty through menopause, driven by a precise cycle of hormonal signals.
External Structures: The Vulva
The external part of the female reproductive system is collectively called the vulva. Many people use the word “vagina” to refer to all female anatomy in this area, but the vagina is actually an internal structure. The vulva includes several distinct parts:
- Mons pubis: the rounded pad of fatty tissue over the pubic bone, covered with hair after puberty.
- Labia majora: the larger outer folds of skin that enclose and protect the other external structures.
- Labia minora: smaller inner folds that begin at the clitoris and extend downward, surrounding the openings of the urethra and vagina.
- Clitoris: a small, highly sensitive organ located where the labia minora meet at the front. Its primary role is sensory, and it is the anatomical counterpart to the head of the penis.
- Vaginal opening: the entry to the vaginal canal, typically partially covered by a thin membrane called the hymen.
- Urethral opening: a small opening just in front of the vaginal opening where urine exits the body.
The area between the labia minora is called the vestibule. It also contains small glands that produce lubrication during arousal.
Internal Organs and What They Do
The internal organs are where most of the reproductive work happens: producing eggs, transporting them, supporting a potential pregnancy, and shedding the uterine lining each month if pregnancy doesn’t occur.
Ovaries
The ovaries are two small, oval-shaped glands sitting on either side of the uterus. They serve a dual purpose. First, they store and release eggs. A female embryo develops roughly 7 million egg cells by the seventh month of pregnancy, but that number drops sharply before birth. Of the millions of immature eggs present at birth, only about 400 will fully mature and be released during a woman’s reproductive years. Second, the ovaries produce hormones, primarily estrogen and progesterone, that regulate the menstrual cycle, support pregnancy, and influence bone health, skin, and dozens of other body functions.
Fallopian Tubes
Two narrow tubes connect the upper part of the uterus to the area near each ovary. The end of each tube closest to the ovary has finger-like projections called fimbria that sweep a released egg into the tube. Fertilization, the union of sperm and egg, happens inside the fallopian tube at a specific junction partway along its length. After being released from the ovary, the egg rests at this spot for about 30 hours. If sperm are present, fertilization can occur there. The resulting embryo then travels through the remainder of the tube toward the uterus.
Uterus
The uterus is a hollow, pear-shaped organ made of thick muscle. It has two main parts: the corpus (the larger upper body) and the cervix (the narrow lower neck that opens into the vagina). The inner lining of the corpus, called the endometrium, is the tissue that thickens each month in preparation for a potential pregnancy and sheds during menstruation if no pregnancy occurs.
If a fertilized egg does arrive, it reaches the blastocyst stage about five to six days after fertilization and then implants into the thickened endometrial lining. The corpus expands enormously during pregnancy to accommodate a growing fetus.
Cervix
The cervix acts as a gateway between the uterus and the vagina. It produces mucus that changes in consistency throughout the menstrual cycle. After ovulation, progesterone causes the cervix to produce thick mucus that forms a barrier, while around ovulation the mucus thins to allow sperm to pass through more easily.
Vagina
The vagina is a flexible, muscular canal that connects the cervix to the outside of the body. It serves as the passageway for menstrual blood, the birth canal during delivery, and the receptive organ during intercourse. Its walls are lined with a mucosa that responds to estrogen. When estrogen levels drop, such as during menopause, the vaginal lining thins.
The Menstrual Cycle
The menstrual cycle is the monthly process that prepares the body for pregnancy. A typical cycle lasts about 28 days, though normal cycles can range from 21 to 35 days. It is controlled by hormones released from both the brain and the ovaries, and it involves coordinated changes in the uterine lining, the ovaries, and hormone levels.
Phases of the Cycle
The cycle begins on the first day of menstrual bleeding. During menstruation, the endometrium is thin, measuring just 1 to 4 millimeters. This phase typically lasts three to seven days as the body sheds the uterine lining that built up during the previous cycle.
Overlapping with menstruation is the follicular phase. During this time, the pituitary gland in the brain releases increasing amounts of follicle-stimulating hormone (FSH), which triggers several immature egg-containing follicles in the ovaries to start growing. These growing follicles produce estrogen, which causes the endometrium to thicken and develop a layered structure. By ovulation, around day 14, the lining measures roughly 12 to 13 millimeters.
As estrogen rises sharply around days 7 through 10, it triggers a large surge of luteinizing hormone (LH) from the pituitary. Within 10 to 12 hours of this LH surge, ovulation occurs: a single mature egg is released from its follicle. During this process, the immature egg cell completes its first round of cell division, keeping one set of chromosomes and discarding the other into a tiny structure called a polar body. The released egg enters the fallopian tube, ready for potential fertilization.
After ovulation, the secretory phase begins. The empty follicle transforms into a structure that pumps out progesterone. This hormone further thickens the endometrial lining to 16 to 18 millimeters and stimulates the development of blood vessels and glandular secretions that would nourish an implanted embryo. If fertilization doesn’t happen, progesterone levels drop, and this triggers the lining to break down and shed, starting the next period.
Hormones That Run the System
Four hormones do the bulk of the work. FSH and LH are produced by the pituitary gland in the brain. FSH stimulates egg-containing follicles to grow, while LH triggers ovulation and supports the follicle’s transformation afterward. Estrogen and progesterone are produced mainly by the ovaries and have wide-ranging effects beyond reproduction.
Estrogen thickens the uterine lining during the first half of the cycle, drives the growth spurt during puberty, maintains bone density, and keeps the vaginal lining healthy. Progesterone dominates the second half of the cycle, preparing the lining for implantation, producing thick cervical mucus, and sustaining early pregnancy until the placenta takes over. These hormones operate in a feedback loop with the brain: rising estrogen eventually triggers the LH surge that causes ovulation, and falling progesterone at the end of a cycle signals the brain to start the process over again.
Changes Across a Lifetime
Puberty
Puberty begins when the brain starts sending out pulses of a signaling hormone that activates the pituitary gland. In girls, the first visible sign is breast budding, which typically occurs after age 8. This is followed by pubic hair development, a growth spurt, and eventually the first menstrual period, called menarche. Menarche usually arrives between ages 10 and 16, with an average around age 12.4. It generally occurs two to three years after breast budding begins and about six months after a girl reaches her peak growth rate. Rising estrogen levels during this time drive breast development, bone growth, and the maturation of the reproductive organs.
Menopause
Menopause is the permanent end of menstrual periods, defined as 12 consecutive months without a period. It typically occurs in the late 40s or early 50s. In the years leading up to it, a transitional phase called perimenopause brings increasingly irregular cycles. During perimenopause, estrogen levels actually average 20% to 30% higher than in earlier reproductive years, swinging unpredictably before ultimately declining. As the ovaries stop producing eggs and estrogen drops, FSH levels rise significantly. This hormonal shift affects the entire reproductive system: the endometrium thins, the vaginal lining becomes less robust, and fertility ends.