If you are a fertile healthy woman, ovulation (egg production) will occur in you every month. One of the two ovaries excretes egg (ovum), which then travels throught the fallopian tube to the uterus; this ”travel” usually lasts for five days. After the intercourse, male sperm (semen) travels through the fallopian tube. If you had an intercourse a day or two before or after egg excretion, the semen can fertilize it. Precisely because of this fertilization possibility, the uterus mucosa begins to thicken, about nine days before ovulation, and begins to swell due to the blood (that is accumulated). Mucosa can then receive the fertilized egg, which will ”sit” in it and begin to develop into the embryo. In that case, you are pregnant.
If the egg is not fertilized, thickened uterine mucosa is unnecessary, so unfertilized eggs and mucosa are discarded about 14 days after the onset of ovulation (even when ovulation does not occur regularly), i.e. they pass through the cervix to the vagina and, from there, are expelled from the body. This epxelling – generally referred to as a menstruation or period – lasts about five days. During the next nine days, a new mucosa develops in the uterus and then ovulation begins again. The whole cycle lasts an average of 28 days. For most women, the duration of the cycle varies – it may be a day or two, and it may be longer.
Each stage of the menstrual cycle is managed by an interrelated system of hormones and other chemical compounds that are secreted by the hypothalamus (part of the brain), the pituitary gland and the ovaries.
Menstruation usually begins at the age of 11 to 14 years. The first menstruation is called menarche. The first year or two menstruations are irregular because often there is no ovulation. For the same reason, menstruation becomes irregular after 45 years of age because it is then close to the end of the fertile period of a woman. After all, menstruation will eventually stop, and the last menstruation is called menopause.