Organs of the Female Reproductive System
The organs of the female reproductive system are concentrated in the pelvic cavity. Many of the female reproductive organs are attached to the broad ligament, a sheet of tissue that supports the organs and connects the sides of the uterus to the walls and floor of the pelvis.
The ovaries are two almond-shaped structures approximately 2 inches (5 centimeters) wide, one on each side of the pelvic cavity. They house groups of cells called follicles.
The ovaries are the primary sex organs because they’re the site of oogenesis, the process of oocyte maturation. The ovaries also have a major role in endocrine signaling, especially the production and control of hormones related to sex and reproduction, namely estrogen and progesterone.
Beginning at the female’s puberty, the process of ovulation begins. The primary oocytes that have been dormant in her ovaries since early in her fetal development are hormonally activated, and secondary oocytes are released at a rate of approximately one per month from menarche (the first menstrual period of her life) to menopause (the last) — that is, from her early teen years to her late 40s or early 50s. The human female ovulates about 400 times during her lifetime.
The uterus or womb nourishes and shelters the developing fetus during gestation. It’s a muscular organ about the size and shape of an upside-down pear. The walls of the uterus are thick and capable of stretching as a fetus grows.
The lining of the uterus, called the endometrium, is built and broken down in the menstrual cycle. A portion of the endometrium (deciduas basalis) becomes part of the placenta during pregnancy.
The cervix is a cylindrical muscular structure about 1 inch (2.5 centimeters) long that rests at the bottom of the uterus like a thimble. It controls the movement of biological fluids and other material (not to mention, occasionally, a baby) into and out of the uterus. Normally, the cervix is open ever so slightly to allow sperm to pass into the uterus. During childbirth, the cervix opens wide to allow the fetus to move out of the uterus.
The uterine tubes run from the ovary to the uterus. They are not literally connected to the ovaries; they just kind of hang over them. At the ovary end the uterine tube expands into a funnel shape called the infundibulum. This branches into fingerlike structures called fimbriae, which guide the egg into the uterine tube, which transports it to the uterus. The process of fertilization usually occurs in the uterine tube.
The vagina is the part of the female body that receives the male penis during sexual intercourse and serves as a passageway for sperm to enter into the uterus and uterine tubes. The vagina is about 3 to 4 inches (8 to 10 centimeters) in length. The cervix marks the top of the vagina.
During childbirth, the vagina must accommodate the passage of a fetus weighing on average about 7 pounds (3 kilograms), so the vagina’s walls are made of stretchy tissues — some fibrous, some muscular, and some erectile. In their normal state, the vagina’s walls have many folds, much like the stomach’s lining. When the vagina needs to stretch, the folds flatten out, providing more volume.
In females, the external genitalia comprise the labia majora, labia minora, and the clitoris. Together, these organs are called the vulva. The term labia (singular, labium) means “lips.” The labia of the vulva are loose flaps of flesh, just like the lips of the mouth (called labia mandibulare and labia maxillare, by the way). The labia protect the vagina’s opening and cover the pelvis’s bony structures.
Here are some details about the three parts of the vulva:
- Labia majora: These large folds of skin — one fold on each side — cover the smaller labia minora. The labia majora extend from the mons pubis (pubic mound) back toward the anus. The mons pubis contains fat deposits that cover the pubic bone. Following puberty, pubic hair covers the mons pubis and the labia majora.
- Labia minora: These hairless folds of skin lie underneath the labia majora and cover the opening of the vagina. The labia minora are attached near the vaginal orifice (opening) and extend upward, forming the foreskin that covers the clitoris.
- Clitoris: This part of the vulva located above the vagina’s opening and above the urethra has a shaft and glans tip, just as a penis does, and it’s extremely sensitive to sexual stimulation. The clitoris contains erectile tissues that fill with blood during sexual stimulation. Because the tissue of the labia minora cap the clitoris, the swelling and reddening is also obvious in the labia minora. Stimulation of the clitoris can lead to orgasm in the female. Although females don’t ejaculate, females do experience a building and release of muscular tension. Female orgasm causes the muscle tissue that lines the vagina and uterus to contract, which helps to pull the sperm up through the reproductive tract.
All humans have mammary glands, but only females produce a substance we call milk for the nutrition of relatively helpless infants with high calorie requirements. Besides nutrition, breast milk boosts the infant’s immune system.
The breast contains about two dozen lobules that are filled with alveoli that make and store milk. The milk is released into lactiferous ducts, which merge at the nipple (see figure). During puberty, the lobules and ducts develop, and adipose tissue is deposited under the skin to protect the lobules and ducts and give shape to the breast. During pregnancy, hormones increase the number of milk-producing cells and increase the size of the lobules and ducts.
After the infant is born, the mother’s pituitary gland secretes the hormone prolactin, which causes the milk-producing cells to create milk, and lactation begins. The infant suckles the milk out of the ducts through the nipple. Lactation continues as long as a child nurses regularly.
The hormone oxytocin is strongly involved in milk release (let-down reflex). Stimulation of the nipple prompts the secretion of oxytocin from the mother’s pituitary gland. Oxytocin expels milk from the lobules by causing them to contract, just as it stimulates uterine contractions to expel the fetus. This hormone has also been strongly correlated with neuro-emotional phenomena, such as family bonding.