A woman's menstrual period, which typically occurs approximately once a month, represents the sloughing of proliferated uterine lining tissue. The tissue thickens to provide a place for a fertilized egg to implant. Once it becomes clear that no such egg is implanting, hormonal changes signal the body to lose the uterine lining. Although there are very few natural processes through which cells "stop" a period, aberrant behavior from certain body cells can prevent menstrual periods.
Fertilized Egg
The one cell biologically designed to stop a woman's menstrual period is a fertilized egg. Egg cells contain half of a woman's genetic information, says Dr. Lauralee Sherwood in her book, "Human Physiology." The egg can't develop into a human being on its own. Likewise, sperm cells contain half of a man's genetic information. When a sperm cell combines with an egg, the resulting combination, a fertilized egg or zygote, contains an entire person's worth of genetic information. The fertilized egg travels from the site of fertilization to the uterus, where it implants in the uterine lining and begins to divide, eventually forming a zygote. The dividing egg makes hormones that stop a woman's period from taking place for as long as there's a developing baby in the uterus.
Ovarian Cells
The cells of the ovaries produce hormones, specifically progesterone and estrogen, that are responsible for regulating a woman's menstrual cycle. If these cells malfunction or fail to produce adequate levels of hormones, the uterine lining can't proliferate. The entire menstrual cycle hinges upon fluctuating levels of estrogen and progesterone, Dr. Sherwood says. Rising hormone levels cause the lining of the uterus to proliferate and maintain the lining through the period during which an egg might implant. If the ovarian cells fail to produce adequate levels of estrogen and progesterone, the uterine lining never develops in the first place, and there isn't anything to slough at the end of the cycle. So menstruation never occurs.
Brain Cells
The menstrual cycle is regulated by more hormones than those produced by the ovaries. Follicle-stimulating hormone from the anterior pituitary gland in the brain causes an egg to begin to ripen, which leads to rising levels of estrogen and progesterone, explains Dr. Gary Thibodeau in his book, "Anatomy and Physiology." Luteinizing hormone, also from the anterior pituitary, leads to ovulation and causes large increases in estrogen and progesterone levels. Gonadotropin-releasing hormone from the hypothalamus causes luteinizing hormone and follicle-stimulating hormone to be released. Abnormalities in hypothalamic or anterior pituitary cells lead to low levels of hormones released by these cells, which can stop menstruation.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
