The series of cyclic changes that take place simultaneously in the ovaries and uterine wall (endometrium) of the female reproductive tract stimulated by different concentrations of gonadotropins like FSH and LH is called the menstrual cycle. It is mainly made up of 4 phases:
Menstrual phase or Destructive phase -1^st - 4^th day - endometrium degenerate.
Proliferative phase or Follicular phase - 5^th - 13^th day - High F.S.H. level stimulates the primordial follicle to mature into the Graafian follicle.
Ovulatory phase - 14^th day - the release of the ovum.
Luteal phase or secretory phase - 15^th - 28^th day - rise in progesterone levels and the endometrium secretes nutrients for implantation.