Female Reproductive System
How does the female reproductive system work?
The female reproductive system provides several functions. The ovaries produce the female egg cells, called the ova or oocytes. The oocytes are then transported to the fallopian tube where fertilization by a sperm may occur. The fertilized egg then moves to the uterus, where the uterine lining has thickened in response to the normal hormones of the reproductive cycle. Once in the uterus the fertilized egg can implant into thickened uterine lining and continue to develop. If fertilization does not take place, the uterine lining is shed as menstrual flow. In addition, the female reproductive system produces female sex hormones that maintain the reproductive cycle.
During menopause the female reproductive system gradually stops making the female hormones necessary for the reproductive cycle to work. At this point, menstrual cycles can become irregular and eventually stop. One year after menstrual cycles stop, the woman is considered to be menopausal.
What parts make-up the female anatomy?
The female reproductive anatomy includes both external and internal structures.
The function of the external female reproductive structures (the genital) is twofold: To enable sperm to enter the body and to protect the internal genital organs from infectious organisms.
The main external structures of the female reproductive system include:
- Labia majora: The labia majora (“large lips”) enclose and protect the other external reproductive organs. During puberty, hair growth occurs and the skin of the labia majora, which also contain sweat and oil-secreting glands.
- Labia minora: The labia minora (“small lips”) can have a variety of sizes and shapes. They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body). This skin is very delicate and can become easily irritated and swollen.
- Bartholin’s glands: These glands are located next to the vaginal opening on each side and produce a fluid (mucus) secretion.
- Clitoris: The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect.
The internal reproductive organs include:
- Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.
- Uterus (womb): The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A canal through the cervix allows sperm to enter and menstrual blood to exit.
- Ovaries: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.
- Fallopian tubes: These are narrow tubes that are attached to the upper part of the uterus and serve as pathways for the ova (egg cells) to travel from the ovaries to the uterus. Fertilization of an egg by a sperm normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants to the uterine lining.
What happens during the menstrual cycle?
Females of reproductive age (beginning anywhere from 11-16 years of age) experience cycles of hormonal activity that repeat at about one-month intervals. Menstru means "monthly"; hence the term menstrual cycle. With every cycle, a woman’s body prepares for a potential pregnancy, whether or not that is the woman’s intention. The term menstruation refers to the periodic shedding of the uterine lining.
The average menstrual cycle takes about 28 days and occurs in phases: the follicular phase (development of the egg), the ovulatory phase (release of the egg), and the luteal phase (hormone levels decrease if the egg is not fertilized).
There are four major hormones (chemicals that stimulate or regulate the activity of cells or organs) involved in the menstrual cycle: follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone.
This phase starts on the first day of your period. During the follicular phase of the menstrual cycle, the following events occur:
- Two hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH) are released from the brain and travel in the blood to the ovaries.
- The hormones stimulate the growth of about 15-20 eggs in the ovaries, each in its own "shell," called a follicle.
- These hormones (FSH and LH) also trigger an increase in the production of the female hormone estrogen.
- As estrogen levels rise, like a switch, it turns off the production of follicle-stimulating hormone. This careful balance of hormones allows the body to limit the number of follicles that will prepare eggs to be released.
- As the follicular phase progresses, one follicle in one ovary becomes dominant and continues to mature. This dominant follicle suppresses all of the other follicles in the group. As a result, they stop growing and die. The dominant follicle continues to produce estrogen.
The ovulatory phase, or ovulation, starts about 14 days after the follicular phase started. The ovulatory phase is the midpoint of the menstrual cycle, with the next menstrual period starting about 2 weeks later. During this phase, the following events occur:
- The rise in estrogen from the dominant follicle triggers a surge in the amount of luteinizing hormone that is produced by the brain.
- This causes the dominant follicle to release its egg from the ovary.
- As the egg is released (a process called ovulation) it is captured by finger-like projections on the end of the fallopian tubes (fimbriae). The fimbriae sweep the egg into the tube.
- Also during this phase, there is an increase in the amount and thickness of mucus produced by the cervix (lower part of the uterus.) If a woman were to have intercourse during this time, the thick mucus captures the man's sperm, nourishes it, and helps it to move towards the egg for fertilization.
The luteal phase begins right after ovulation and involves the following processes:
- Once it releases its egg, the empty ovarian follicle develops into a new structure called the corpus luteum.
- The corpus luteum secretes the hormones estrogen and progesterone. Progesterone prepares the uterus for a fertilized egg to implant.
- If intercourse has taken place and a man's sperm has fertilized the egg (a process called conception), the fertilized egg (embryo) will travel through the fallopian tube to implant in the uterus. The woman is now considered pregnant.
- If the egg is not fertilized, it passes through the uterus. Not needed to support a pregnancy, the lining of the uterus breaks down and sheds, and the next menstrual period begins.
How many eggs does a woman have?
During fetal life, there are about 6 million to 7 million eggs. From this time, no new eggs are produced. At birth, there are approximately 1 million eggs; and by the time of puberty, only about 300,000 remain. Of these, only 300 to 400 will be ovulated during a woman's reproductive lifetime. Fertility can drop as a woman ages due to decreasing number and quality of the remaining eggs.