The menstrual cycle is the series of changes that occur in the women`s body in anticipation of fertilization and pregnancy. Menarche is first menstrual cycle of a girl. It can happen as early as about age 9 or up to age 15.About once a month, the uterus grows a new lining called endometrium to get ready for reception of fertilized egg.When there is no fertilized egg to start pregnancy the uterus sheds its endometrium. This is monthly menstrual bleeding. There are three phases in menstrual cycle which are controlled by hormones secreted by pitutary gland and ovaries. follicle stimulating hormone (FSH) and luteinizing hormone (LH) and prolactin are hormones secreted by Pitutary gland. Ovaries produce Oestrogen and progesterone hormones
The entire duration of a Menstrual cycle can be divided into four main phases:
- Menstrual phase (From day 1 to 5)
- Follicular phase (From day 1 to 13)
- Ovulation phase (Day 14)
- Luteal phase (From day 15 to 28)
Menstrual phase begins on the first day of menstruation and lasts till the 5th day of the menstrual cycle. The following events occur during this phase.The uterus looses its inner lining of soft endometrial tissue,unfertilized ova, blood vessels and blood in the form of menstrual fluid through vagina.This phenomena is called weeping of uterus.Blood loss of ten ml to eighty ml is considered normal. This fluid may be bright red, light pink or even brown.Women usually feel abdominal discomfort and use of sanitary napkins during this period is common practice to maintain hygienic conditions.
This phase starts from first day and lasts for thirteen days. The pituitary gland secretes FSH hormone that stimulates the egg cells in the ovaries to grow and mature.One of these egg cells begins to mature in a sac like structure called follicle. It takes thirteen days for the egg cell to reach complete maturity. When the egg cell matures, its follicle secretes FSH that stimulates the uterus to develop a lining of blood vessels and soft cushiony tissue called endometrium. The lining of uterus begins to grow thick in response to this increase in estrogen hormone.
The pitutary gland on 14th day secretes LH hormone that causes the ovary to release the matured egg cell. The egg cell is directed into the fallopian tube by the cilia of the fimbriae. Fimbriae are finger like projections present at the end of the fallopian tube close to the ovaries .The increase in LH triggers ovulation. The egg then travels into the uterus. If you have regular 28-day menstrual cycles, ovulation usually occurs on day 14. However, most women have different menstrual cycle lengths. In general, ovulation occurs 11 to 16 days before your upcoming period. As the egg moves down the fallopian tube over several days, the lining of the uterus continues to grow thicker and thicker. It takes about three to four days for the egg to travel toward the uterus. If fertilization is to occur, it must happen within 24 hours of ovulation or the egg degenerates.
This phase begins on the 15th day and lasts till the end of the cycle. The following events occur during this phase.The egg cell released during the ovulation phase stays in the fallopian tube for 24 hours.If a sperm cell does not impregnate the egg cell within that time, the egg cell disintegrates. After ovulation, the graffian follicle becomes a hormone-producing structure called the corpus luteum. The cells of the corpus luteum produce estrogen and large amounts of progesterone, with the latter hormone stimulating the uterine lining development in preparation for implantation of a fertilized egg. If fertilization does not occur, the corpus luteum degenerates about two weeks after ovulation. Because of this, progesterone levels drop and the stimulation for the lining is lost. This causes the lining to shed as a new menstrual cycle starts.
The loss of the corpus luteum can be prevented by fertilization of the egg. If fertilization occur within 24 hours of ovulation. About five days after fertilization, the fertilized egg enters uterus and becomes embedded in the lining. With implantation, cells that will eventually become the placenta begin to produce the “pregnancy hormone” or human chorionic gonadotropin (HCG). It interrupts your menstrual cycle by providing continual stimulation of the corpus luteum to produce progesterone. This prevents the loss of endometrium.