The rhythmic series of changes that occur in the reproductive organs of female primates...
The rhythmic series of changes that occur in the reproductive organs of female primates (monkeys, apes and human beings) is called menstrual cycle.
It is repeated at an average interval of about 28/29 days.
The first appearance of menstruation at puberty is called menarche.
During pregnancy all events of the menstrual cycle stop and there is no menstruation.
A natural decline or cease of menstrual cycle at the age of 45-50 years is called menopause.
The menstrual cycle has four phases. These are:
The soft tissue of endometrial lining of the uterus disintegrates causing bleeding.
The unfertilised egg and soft tissues are discharged.
It lasts for 3-5 days.
Follicular Phase/Proliferative Phase:
The primary follicles in the ovary grow and become a fully mature Graafian follicle.
The endometrium of the uterus is regenerated due to the secretion of LH and FSH from anterior pituitary and ovarian hormone, estrogen.
It lasts for about 10 to 14 days.
Rapid secretion of LH (LH surge) induces rupture of Graafian follicle, thereby leading to ovulation (release of ovum).
It lasts for only about 48 hours.
Luteal Phase/Secretory Phase:
In this phase the ruptured follicle changes into corpus luteum in the ovary and it begins to secrete the hormone progesterone.
The endometrium thickens further, and their glands secrete a fluid into the uterus.
If ovum is not fertilized, the corpus luteum undergoes degeneration and this causes disintegration of the endometrium leading to menstruation.
Estrogen and progesterone levels rise during this phase.
It lasts for only 1 day.