what is menstrual cycle? xplain broadly.urgent.
In women, reproductive phase begins with the onset of menses at about the age of 13 years. During this reproductive period, the ovaries and the female reproductive tract undergo a series of cyclic changes which are primarily meant to prepare them for fertilization and pregnancy and collectively form the menstrual cycle.
Menstural cycle, continues for an average of 28 days, after which some blood along with the endometrium are discharged from the uterus as menstural bleeding. This process is called mensuration.
The length of the menstrual cycle varies widely in women, but on an average it extends to about 28 days. Menstraul cycle is not seen during the times of pregnancy and is suppressed for few months at the time of lactation. It completely stops at the menopause stage
The menstrual cycle is divided into 4 phases.
- Follicular phase or Proliferative phase
- Ovulatory phase
- Luteal or Secretory phase
- Menstrual phase
Follicular phase or Proliferative phase
This phase lasts for about 10 - 12 days (from the 5th - 14th day of menstrual cycle). It comprises the following events.
- The anterior lobe of the pituitary secretes the FSH, increasing the level of Follicle Stimulating Hormone in the blood.
- The FSH stimulates the growth of the selected primary ovarian follicle and maturation of the primary oocyte in this follicle.
- The follicular cells of the graafian follicle secrete estrogens.
- The uterine endometrium becomes thick, more vascular and more glandular, due to the rising level of estrogens.
- The lining of the fallopian tubes becomes thickened and its ciliary movement is increased. These changes prepare the fallopian tubes for conveying the ovum into the uterus.
The lutenising hormone induces the mature graafian follicle to burst and eject its egg into the fallopian tube. This is called ovulation. It occurs after about 14 days. The egg at this time is in the secondary oocyte stage with the second meiotic division in progress. The luteinising hormone starts to change the empty graafian follicle into a corpus luteum, and secretion of progesterone from corpus luteum.
It is also called as secretory phase or the post - ovulatory phase. It lasts for about 12 - 14 days and extends from the 16th - 28th day of the menstrual cycle. During this period cells of the ruptured follicle enlarge and form golden colored corpus luteum. It grows for about 7 days and secretes progesterone. As the level of progesterone increases in the blood it decreases the secretion of FSH and LH from the anterior pituitary. So this inhibits future maturation of follicle and ovulation till pregnancy is over.
This phase is called secretory phase because the uterine wall secretes some nutritious fluid in the uterus.
It lasts for about 3 - 5 days and extends from the 1st - 4th day of the menstrual cycle.
When fertilization of ovum does not take place, the corpus luteum starts degenerating. The level of progesterone in the blood starts decreasing. The uterine tissues fail to be maintained. Then the uterine wall (endometrium) is sloughed off. The glands and blood vessels of the endometrium are broken down and lost. This causes discharge of blood and is called menstruation (mensem - month). This occurs monthly. About 50 - 100 ml of blood is discharged out through the vaginal orifice.