The menstrual cycle begins on the first day of menstruation (periodic discharge of the blood flow on part of the uterus) and finishes the day before the next one, approximately 28 days later.It is bounded by two important milestones that happen in different stages of a womans life, and they are: the first menstruation or menarchy and menopause.Both moments mark what the womans fertile life will be, from puberty (around 12 years old) until the age of approximately 55. The menstrual-ovarian cycle is directly ruled by hormonal action, which brings on some actions and prepares some structures for the arrival of a possible fertilized embryo. The follicle stimulating hormone (FSH) as well as the luteinizing hormone (LH) both activated from the hypophysis- have a fundamental role in the development of the ovule inside the ovary, as well as in the preparation of the uterine walls, which engorge in order to receive the possible embryo.
During the first days of the cycle, stimulated by FSH, twenty or so follicles housed in the ovaries begin to mature, secreting a higher amount of estrogens at the same time. In a coordinated chain, this female hormone causes the blood vessels of the endometrium to elongate. After 10 or 14 days, some follicles already have a mature ovule; in this stage, the amount of estrogens drops, while the hypophysis begins to secrete LH, hormone that acts directly upon the follicles, swelling them to such a point that only one ovule is released towards the fallopian tube. This is the exact moment of ovulation.
While the follicles that were about to mature atrophy, the one that covered the mature ovule continues evolving until it becomes the corpus luteum (luteum body). This structure is capable of secreting progesterone, hormone that readies the uterus for a possible pregnancy. This way, its mucous layer (endometrium) manufactures some tissues that ease the implantation of the embryo and eventual gestation.The ovule begins its trip through the tubes, having an approximate lifespan of 24 hours, during which it waits to be fertilized. If this happens, the menstrual cycle is interrupted and the embryo travels in order to bind to the uterine wall and begin its development; if the opposite happens, hormone levels drop and the unfertilized ovule leaves the uterus (along with part of this organs internal lining) during menstruation.
Menstruation
Around the age of 12, girls have their first menstruation. It is a standard age as it can come before or later, according to each body.Menstruation is the exit of part of the mucosa that lines the uterus and which, for a few days and under the effect of hormones, develops multiple blood vessels and new glands, doubling its size.If the ovule has not been fertilized, this tissue detaches from the uterus through successive and intense contractions of the muscular uterine wall (myometrium), reaching the vagina and evacuating through the vaginal orifice.
Generally, the secretion presents a viscous and brown appearance; meanwhile, its amount varies in each body. Generally, it is characterized by a light flow during the first day, followed by a more abundant one that goes away little by little. Anatomically, the female body also suffers noticeable modifications during the menstrual period. Days before and during menstruation, the lower abdomen swells and the breasts become more rigid, heavy and sensitive.
Ovogenesis
It is the formation and differentiation process of the female sexual cells or ovules.This process begins in a girls gestational stage (as of the third month of fetal development), a period in which two important cellular modifications take place. In the first of them, the ovules split through mitosis and originate ovogonia (multiplication stage), while in the second instance, the sexual cells grow and transform into first order ovocytes. This way, at birth, each girl already has a considerable number of immature ovules, not qualified for fertilization.Each one of these cells sleeps in the ovaries, waiting for the appearance of puberty. With the arrival of this period, the secondary sexual characteristics show up (physiognomic changes, like the development of breasts and the appearance of hair on the pubis and underarms, among others) and the first menstruation takes place, an indicator that the ovules have begun to mature. The ovules process of maturation occurs in the cortex of the ovaries, where numerous follicles are housed in different degrees of development. The follicles are a series of wrappings that surround the ovule and suffer several changes during its maturation, regarding appearance, composition and size.Finally, the follicle develops alongside the ovocyte until a stage in which the latter already has half of the information required in order to form a new individual: only 23 chromosomes (the spermatozoon has the other half). When the ovule is mature, it is called a Graafian follicle; it breaks, releasing it and giving way to a possible pregnancy.
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