The menstrual cycle consists of changes in the ovary and the uterus simultaneously. It begins with the menstrual or bleeding phase. This represents the shedding of the endometrium of the uterus and unfertilized secondary oocyte. This occurs because the corpus luteum of the previous cycle is degenerating. Due to this the hormones secreted by corpus luteum also start decreasing. These hormones include estrogen and progesterone. These hormones are responsible for maintaining the uterine lining and since these are decreasing the uterine lining too starts shedding. Thus levels of these hormones are minimum at the beginning of the menstrual cycle. During the follicular phase, FSH is increasing and estrogen and progesterone have started the proliferation of the endometrium. During ovulation LH is at its peak and estrogen is also increasing. The secretory phase in uterus coincides with luteal phase in the ovary and thus because of the formation of corpus luteum, estrogen and progesterone are also high.