Menstrual cycle

Now unlike the male sperms, female eggs need not be formed because they are already present in the ovaries at birth. Instead, during puberty, girls will release their eggs in a process known as ovulation during a menstrual cycle which starts at puberty. The process ends at around the age of 51 (termed as menopause) and the woman can no longer reproduce. The average menstrual cycle is 28 days long. The purpose of the menstrual cycle is to prepare the body for pregnancy each month
So, the first part of the cycle is menstruation. Menstruation is the shedding and breaking down of the uterine lining which occurs because estrogen and progesterone levels decreased at the end of the previous cycle. This results in menstrual blood flows from the uterus through the small opening in the cervix, and passing out of the body through the vagina. Most menstrual periods last from three to five days. To contain the blood, many women use tampoons or pads.
About this time, the follicle-stimulating hormone level increases slightly, stimulating the development of several ovarian follicles. Each follicle contains an egg. Later, as the follicle-stimulating hormone level decreases, only one follicle continues to develop. This follicle produces estrogen.
The ovulatory phase begins with a surge in luteinizing hormone and follicle-stimulating hormone levels. Luteinizing hormone stimulates egg release (ovulation) of the dominant follicle that ruptures the ovaries. After the egg has left the ovary it travels through the fallopian tube to the uterus. Hormone levels rise and help prepare the uterine lining for pregnancy. A woman is most likely to get pregnant during the three days before ovulation or on the day of ovulation.
During the luteal phase, luteinizing hormone and follicle-stimulating hormone levels decrease. The ruptured follicle closes after releasing the egg and forms a corpus luteum, which produces progester-one. During most of this phase, the estrogen level is high. Progesterone and estrogen cause the lining of the uterus to thicken more, to prepare for possible fertilization. If the egg is not fertilized, the corpus luteum degenerates and no longer produces progesterone, the estrogen level decreases, the top layers of the lining break down and are shed, and a new menstrual cycle begins.
This is a video on the menstrual cycle

Because of the taxing nature of the mestrual cycle, some women experience pre-menstrual syndrome. The three most prominent symptoms are irritability, tension, and dysphoria. Physical symptoms also include cramps and headaches. Treatment is mostly counselling and recommendations to change lifestyle and diet.
I would like to thank wikipedia and www.merck.com/mmhe/sec22/ch241/ch241e.html for the info.