The period of the first day of starting first menstrual excretion and the first day of the second menstrual excretion is called menstrual cycle. Its period is of 28 days. In each menstrual excretion, there are some changes in the stimulated ova glands and walls of uterus because of the change in the concentration of gonadotrophic hormones of anterior pituitary gland.
There are below mentioned phases in the menstrual cycle-
Endometrium become well on the fifth day of menstrual excretion. All the changes which take place from sixth to fourteenth days come into proliferative phase. In this phase, anterior portion of pituitary gland excretes follicle stimulating hormone FSH whereby ovarian follicle gets matured and the hormone named estrogen starts to excrete from it. The endometrium becomes much thick and conduits because of the influence of estrogen. When the quantity of estrogen reaches on the high level in the blood, the excessive secretion of FSH gets stopped but the anterior pituitary gland starts the secretion of leutinizing hormone LH. There is ovulation on the 14th day and the proliferative phase comes to an end.
After ovulation, cells which unstratified to the ovum gland follicle changes into corpus luteum because of the influence of leutinizing hormone (LH) of which progesterone hormone originates. Endometrium gets developed fully because of the influence of progesterone hormone and excretes glycogen and other enzymes whereby fertilized ovum is nurtured. If the ovum is not fertilized, the premenstrual phase starts before the menstrual excretion.
The period before starting the menstrual excretion is called premenstrual phase. In this phase, the secretion of estrogen and progesterone gets stopped and because of its absence corpus luteum starts to destroy and endometrium starts to contract.
After 28 days, the menstrual excretion phase starts which remains continue from one day to five day. The hormone named oxytocin becomes active because of the deduction in the level of progesterone whereby contraction originates in the uterus and blood contained in it comes out. The endrometium comes out with blood by collapsing. Less level of progesterone stimulates to the anterior pituitary gland to excrete much FSH and this again cycle starts.