The Menstrual cycle
Once in puberty, menstrual cycles begin. These cycles generally last 28 to 30 days and begin with the onset of menstruation.
with the onset of menstruation.A succession of changes will occur in the ovaries and uterus, orchestrated by specialized molecules produced in cycles, hormones. They ensure communication between all organs of the genital tract but also with the pituitary gland at the base of the brain. We can define three phases in the menstrual cycle-FOLLICULAR phase (phase of maturation of a follicle)Each month, amongst the ovarian reserve fifty oocytes become sensitive to hormonal secretions. With the exception of one, they usually degenerate (atresia). The one which matures is contained in a small bag (follicle) and bathed in a fluid (follicular fluid). The bag inflates slowly to the surface of the ovary, in response to the production of the hormone FSH (follicle stimulating hormone) by the pituitary gland. This bag will be about 2cm in diameter just before ovulation. The oocyte is a large cell which is about one tenth of a millimeter. Unlike all other body cells, the oocyte contains only half the chromosomes (23) which hold all the genetic information that the woman will transmit to her offspring. Chromosomal or genetic capital of the embryo will be formed after addition of 23 chromosomes contained in the sperm. During the follicular phase, the ovaries also secrete hormones, estrogens. These hormones prepare the uterus to receive the eventual embryo.Phase OVULATION Ovulation occurs about 14 days before the onset of menstruation. This means that when the woman has cycles of 28 days, she will ovulate around day 14 of her cycle. If, however the woman has longer cycles, the ovulation will be delayed. It may be in these conditions more difficult to determine. During ovulation, the oocyte is expelled from the follicle of which the lining breaks and is sucked through the fallopian tube. Ovulation is caused by another signal from the pituitary gland (a hormone called LH). The egg then begins its migration to the uterus.-Luteal phase (or phase of preparing the uterus for implantation of a possible embryo) During this phase, the lining of the uterus (endometrium) is preparing for implantation of the embryo resulting from fertilization of the egg by sperm. This process is under hormonal control of the follicle that released the egg: it becomes a corpus luteum and begins to secrete another hormone (progesterone).
Victor Hugo