During the menstrual phase of the menstrual cycle which starts on the 28th day, the endometrial lining of the female genital tract breaks down due to lack of progesterone As a result bleeding occurs. This monthly flow of blood is called menstruation.
During menstrual cycles, the various changes occur in the ovary under the influence of various hormones:-
Menstrual phase:- The levels of hormones LH, FSH estrogen & progesterone is very less which results in the breakdown of the endometrial lining of the uterus.
Follicular phase:- In this phase, the levels of pituitary hormones FSH & LH increase which causes ovarian hormone estrogen to release, FSH controls the follicular phase, it stimulates the growth of follicles. Both FSH & LH reach their peak level in the
middle of the cycle (14th day)
Ovulatory Phase:- The level of LH hormones reaching its peak (called LH swing) induces the ruptures of mature Graffian follicle & thereby release of ovum.
Luteal phase:- The LH & FSH hormones begin to decline. After ovulation, the follicle ruptures & is transformed into the corpus Luteum which secretes large quantities of progesterone.