While many of the body’s hormones are shared by men and women, there are some that predominate in females. These are responsible for the unique characteristics and qualities of women, including menstruation, breast function and pregnancy. Women’s bodies develop the ability to produce these hormones during puberty, which leads to many of the changes associated with that stage of life. Hormones are produced until the cessation of reproductive capability, at menopause.
Estrogen
Perhaps the best known of the female hormones, estrogen is responsible for proliferation of the lining of the uterus during the early portion of the menstrual cycle. Notes Dr. Lauralee Sherwood in her text, “Human Physiology,” it’s important that the uterine lining develop in tandem with the ripening of an egg, so that if the egg should be fertilized after ovulation, it will have somewhere to implant. Increasing estrogen concentrations also signal the anterior pituitary, a gland in the brain, to release luteinizing hormone, which causes ovulation.
Progesterone
Progesterone is, like estrogen, associated with maintenance of the menstrual cycle. After ovulation, the ovary that released an egg forms a small cyst, called a corpus luteum, that secretes progesterone for up to 14 days, explains Dr. Sherwood. This maintains the lining of the uterus after ovulation. If a fertilized egg implants, the egg begins secreting human chorionic gonadotropin, another hormone, which keeps the corpus luteum alive and secreting progesterone so that the uterine lining remains. If no egg implants, the corpus luteum dies and stops producing progesterone, which leads to shedding of the uterine lining, or menstruation.
Oxytocin
The hormone oxytocin has multiple functions in women, explains Dr. Gary Thibodeau in his book, “Anatomy and Physiology.” One important role of the hormone is that it produces the uterine contractions that lead to expulsion of a fetus. In fact, a synthetic form of the hormone, called Pitocin, is sometimes administered to women to induce labor. Oxytocin also causes milk letdown from the breasts, such that when a nursing woman sees or hears her infant, oxytocin released in response to that stimulus causes the milk ducts to eject milk. At the same time, the oxytocin continues to have an effect upon the uterus. This is particularly useful shortly after labor—when a new mother nurses her infant for the first time, the oxytocin not only provides the baby with milk, it also causes the mother’s uterus to contract. This helps prevent bleeding after labor and delivery.
Prolactin
The other hormone closely associated with breastfeeding, notes Dr. Thibodeau, is prolactin, which causes the milk-producing cells in the breast to begin making milk for a baby. As long as nursing continues, prolactin secretion remains high, meaning that a mother is able to continue to nurse for as long—and providing as much volume—as her baby requires. Prolactin also interferes with the menstrual cycle, meaning that many women don’t become pregnant while breastfeeding.
References
- “Human Physiology”; Lauralee Sherwood, Ph.D.; 2004
- “Anatomy and Physiology”; Gary Thibodeau, Ph.D.; 2007
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