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Menstruation, commonly called a woman's period, is the approximately monthly shedding of the lining of the uterus; the blood and tissues that have built up throughout the month preparing for fertilization leave the body through the vagina. This bleeding, which can last from 2 to 7 days, is a sign that conception has not taken place and that the woman is not pregnant. Menstruation is a normal, natural cyclic process occurring in all healthy adult women between puberty and menopause. Young women can begin to menstruate at any time between the ages of 8 and 18; mature women might experience menopause sometime between the ages of 40 and 60.
By convention, the onset of menstrual bleeding (menstruation or menses) marks the beginning of the cycle. Menstruation lasts for several days and is caused by the loss of the lining of the uterus. The uterus was ready to accept a fertilized egg ( ovum), but none arrived, and so the lining (called endometrium) is expelled. Therefore, if menstrual bleeding occurs, a woman knows that she is not pregnant.
Then a new egg matures in the ovaries, and about at the middle of the cycle (14 days before beginning of the next menstrual bleeding), ovulation occurs, meaning that the egg is released by the ovary and enters the fallopian tube. In some women, ovulation is accompanied by a characteristic pain called MittelschmerzMittelschmerz ( German: "middle pain") is a medical term for "ovulation pain". Some women have mittelschmerz regularly and can time their ovulation by it but many never experience it. It is characterised by lower abdominal and pelvic pain that occurs roug which lasts for several hours. A characteristic clear and stringy mucusMucus is a slippery secretion of the lining of various membranes in the body ( mucous membranes). Mucus aids in the protection of the lungs by trapping foreign particles that enter the nose during normal breathing. Additionally, it prevents tissues from d develops at the cervixThe cervix (from Latin "neck") is the neck of the uterus. This is the place where the uterus joins with the top end of the vagina. It is normally blocked by a mucosal plug which helps to prevent infection, and which has to be evacuated before the childbir, ready to accept spermacrosome, (2) cell membrane, (3) nucleus, (4) mitochondria, and (5) flagellum (tail) A sperm cell or spermatozoon is the haploid cell that is the male gamete. It is carried in fluid called semen, and is capable of fertilising an egg cell to form a zygote.. The egg (with a diameter of about 0.5 mmTo help compare different orders of magnitude this page lists lengths between 100 µm and 1 mm (10-4 m and 10-3 m). See also lengths of other orders of magnitude. Shorter distances 100 micrometre is equal to 1/10th of a millimetre, 0. 00394 inches. 125 µm,) travels through the fallopian tube to the uterus, pushed along by movements of the lining of the tube. This trip, which is about 7–14 cm long, takes about one day, and the egg is available to be fertilized during this period.
In the meantime, the endometrium has started to grow again. If fertilization occurs, the egg implants in the wall of the uterus and major changes take place, with the menstrual cycle being suspended for the length of the pregnancy. If no fertilization occurs, the endometrium is lost with bleeding and the cycle starts again.
About 50 millilitres of blood are lost during menstruation. The blood is prevented from clotting by an enzyme called plasmin contained in the endometrium. This blood loss is the reason that women have higher dietary requirements for iron than males in order to prevent iron deficiency.
In most women, menstruation is preceded or accompanied by various unpleasant symptoms caused by the involved hormones and by cramping of the uterus. Among these are abdominal pain, migraine headache, depression and irritability. Premenstrual stress syndrome (PMS or premenstrual syndrome), amenorrhea and dysmenorrhea can also occur. The list of symptoms experienced varies from person to person. Furthermore, within an individual, the severity of the symptoms may vary from cycle to cycle.
All of a woman's ova are present in the ovaries at the time of birth; an estimated 250,000 to 400,000 immature eggs reside in each ovary. On average 450 of them develop into mature reproductive cells during a lifetime.
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