The Menstrual Cycle

The Menstrual Cycle

What happens during a women's menstrual cycle? Hormone levels fall following the degeneration of the corpus lueteum, the uterine lining sheds because it's not needed to help sustain the fertilized ovum. The shedding of the endomentrial tissue and the bleeding the follows it is a monthly event that happens in a woman's life during puberty and lasts all through menopause. (textbook)

The menstrual cycle is considered to begin with menstruation. The midpoint of the cycle is characterized by ovulation, in which a single egg cell is expelled from the ovary. If the ovum is fertilized by a sperm, it lodges in the uterus and develops into a fetus.(Doria, John J.).

Menstrual cycles normally range from about 25 to 36 days. Menstrual bleeding lasts 3 to 7 days, averaging 5 days and blood loss during a cycle usually ranges from ½ to 2½ ounces. The menstrual cycle is regulated by hormones. Luteinizing hormone and follicle-stimulating hormone, which are produced by the pituitary gland, promote ovulation and stimulate the ovaries to produce estrogen and progesterone. Estrogen and progesterone stimulate the uterus and breasts to prepare for possible fertilization. (Peter L. Rosenblatt)

The menstrual cycle is divided into three phases. The first phase is the menstrual phase: The outer layer of the endometrium becomes detached from the uterine wall and the shedding of the enometrium marks the beginning of the menstrual phase. The endometrial tissue along with mucus and other vaginal secretions and a small amount of blood is expelled through the vagina. The menstrual flow occurs over a period of 3-5 days. Follicle-stimulating hormones and luteinizing hormones increase around day 5, and this marks the end of this phase.

The second phase is the Proliferate Phase. This phase lasts about 9 days and during this time, the endometrium thickens in response to increases estrogen. The proliferative phase ends with ovulation. The third phase is called the secretory phase. During this time, with the help of progesterone, the endometrium begins to prepare for the arrival of a fertilized ovum. Glands within the uterus enlarge and begin secreting glycogen, a cell nutrient. The cervical mucus thickens, and starts forming a plug to seal off the uterus in the event of pregnancy. If pregnancy doesn't occur, the corpus luteum begins to degenerate. Progesterone levels fall and the endometrial cells begin to die. The secretory phase lasts 14 days and ends with the shedding of the endometrium. (textbook)

For some women, menstruation is