The Menstrual Cycle

Loss of blood through the vagina due to deterioration of the endometrium, occurring at an interval of about a month is called menstrual period. The onset of menstruation marks the beginning of the reproductive life of women.Approximately 130 ml of blood lost per cycle or this loss can be within a range extending from 13 to 300 ml. Usually the bleeding, which does not clot unless it is very abundant, is more plentiful on the second day.The first day of bleeding is considered as the first day of menstrual cycle, which involves several elements including the main hormones produced by the ovaries and pituitary glands like estrogen, progesterone, follicle-stimulating hormones.

The endometrium is the lining of the uterus. It consists of three layers: the first is eliminating the monthly menstruation, and is regenerated in the same period according to the phase of the cycle which it belongs.
Based on the endocrine events, menstrual cycle, which can be between 23 and 35 days, is divided into three phases.
Follicular phase (preovulatory): begins at the first day of bleeding and lasts until the day before the preovulatory rise of luteinizing hormone, which marks the beginning of the ovulatory phase.
ovulatory phase:This is the most variable in duration, as it is considered normal within a range that goes from 12 to 14 days. During this period, endometrial thickening occurs due to elevated estrogen and follicle stimulating hormone, which regenerates itself completely in a period of four to seven days after menstruation. Similarly stimulates the growth of a group of three to 30 follicles (eggs) that are recruited due to its rapid growth during the last days of the previous cycle. As the levels of follicle-stimulating hormone down, one of these follicles is selected to ovulate, and when it matures, the others are eliminated.
Ovulatory phase normally occurs on day 14 of cycle. Given the complex series of hormonal events that take place in it, is considered the ovulatory phase as the fertile menstrual cycle. This is when the follicle or egg enlarges and bulges in the outer layer of the ovary that rupture, leads to ovulation, the release of an egg from the ovary.
Luteal or ovulatory phase occurs during the second half of the menstrual cycle. During this the egg begins to travel along the fallopian tube toward the uterus, resulting in increased levels of progesterone and helps to prepare the uterine lining for possible pregnancy. If a sperm fertilizes the egg and it becomes attached to the wall of the uterus, the woman becomes pregnant. If the egg is not fertilized, it dissolves or is absorbed by the body, pregnancy does not occur, levels of estrogen and progesterone fall, the thickened uterine lining and menstruation is released.This Menstrual Phase last from 5 to 7 days normally.

The reproductive organs and menstrual cycle

The cervix. During the follicular phase there is a progressive increase in vascularization and cervical mucus secretion. The external OS opens to a diameter of 3 mm at ovulation, then reduced to 1 mm. The gradual increase of estrogen increases  ten to 30 times the amount of cervical mucus, whose characteristics are clinically useful to evaluate the cycle stage and hormonal status of the patient.

The elasticity of the mucus increases just before ovulation, while during latency, and the influence of progesterone, it thickens, it becomes less watery and loses elastic.
The vagina. When at the beginning of the follicular phase ovarian estrogen secretion is low, the vaginal epithelium is thin and pale, but as these are beginning to increase, it becomes more elastic, resistant and violet.

In summary, we can say that menstruation is part of the ovarian cycle in the endometrium responds to estrogen stimulation in the preovulatory phase and the elimination of post-ovulatory progesterone when pregnancy does not occur, and as long as the cycles are regular and ovulation occurs.
 

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