The menstrual cycle is the change that the female reproductive organs undergo about every 28 days beginning at puberty, usually between ages 11 and 13. It is the process in which an egg ripens in the |ovaries| and is released for fertilization. At the same time, a change occurs in the lining of the |uterus|, the endometrium, to prepare it for implantation of the fertilized egg. If fertilization does not take place, the endometrium breaks down, producing the menstrual flow, or period, and the cycle begins again. Different stages of the process are triggered by ~hormones~ (chemical messengers), two of which are secreted by the |pituitary gland| and two by the |ovaries|.
The beginning of the cycle, the Proliferative Phase, is triggered by the |hypothalamus|, the body's internal clock, which is part of the |brain|. The |hypothalamus| signals to the |pituitary gland| to release the follicle-stimulating ~hormone~ (FSH) into the bloodstream. Immature follicles, each of which encloses an immature egg (ovum), are stimulated by the FSH. Usually only one egg ripens in each cycle; the rest degenerate. ~Estrogen~ from the |ovaries| stimulates the lining of the |uterus| and acts on the |hypothalamus| which, in addition to controlling the secretion of FSH, triggers the release of luteinizing ~hormone~ (LH) by the |pituitary gland|. ~Estrogen~ also causes thickening of the endometrium (the lining of the |uterus|). This stage of the menstrual cycle lasts approximately 14 days.
During the second phase, the Premenstrual Cycle or Secretory Phase, the LH causes the follicle to rupture and release the ovum. The empty follicle forms the |corpus luteum| and then secretes ~estrogen~ and progesterone to prepare the endometrium for implantation and to stop the flow of FSH and LH Also during this stage, which lasts about 7 days, the mammary |glands| may become slightly swollen and sore, and emotional changes may occur, such as irritability, depression, or nervousness.
If the released ovum is not fertilized, the last phase of the menstrual cycle, called the Destructive Phase, begins. The |corpus luteum| degenerates. The levels of ~estrogen~ and progesterone fall rapidly, causing the outer layer of the endometrium to break down and be shed as the period, or menstrual flow. The actual flow may last 4-5 days; the Destructive Phase lasts a total of 7 days. While menstruation is still going on, the first stage of a new cycle is once again initiated by the |hypothalamus|, which signals the |pituitary gland| to release FSH.
The menstrual cycle usually lasts for one month, but in some women it takes up to six weeks or is irregular. Patterns of menstruation are as unique as each individual. The cycle can also be affected by stress, weight loss, or something as simple as long-distance travel. In the years leading up to |menopause| (which can begin in a woman's mid-40's to early 50's), follicles may develop but fail to ovulate. This can cause irregular or heavy |bleeding| and medical advice should be sought.
Although few women escape some form of discomfort during the menstruation cycle, most symptoms are not permanent nor do they usually indicate any serious underlying condition. Two side effects of menstruation that are most common, however, are dysmenorrhea ("cramps") and premenstrual syndrome (PMS). The cause of dysmenorrhea is uterine spasms, which temporarily deprive the muscle of oxygen, and almost always happens at the beginning of a period lasting up to three days. No specific relief or remedy has been found to be a cure-all; however, use of |aspirin| or |ibuprofen| can be of some help.
PMS has been characterized by tension, increased irritability, breast soreness, weight gain, |headaches|, craving for certain foods, and a feeling of fatigue. Doctors do not agree on what it is, what causes it, how many women suffer from it, or how to treat it. Use of |aspirin| or |ibuprofen| may help (or may not), and reduction of salt intake while increasing water intake may also help. Different things work, or don't work, for different people. Extreme cases of either cramps or PMS should be cause to seek medical attention.
