How does the menstrual cycle work?

How does the menstrual cycle work?-I know that it all starts off with the pituitary gland which release FSH into the blood stream and so on... I just don't understand all the small details. It would be really helpful if you could explain it properly.

I'll try. Let's start where you did, at the secretion of FSH, released from the pituitary about 3-4 days after the menses.This hormone stimulates follicles on the ovary to begin producing eggs through meiosis, but only one follicle (usually) actually reaches maturity to secrete an ovum. While FSH is being secreted, it also stimulates the ovaries to raise the levels of estrogen in the bloodstream, and this increase in estrogen is what causes the uterine lining to develop and thicken its lining, in preparation for implantation if fertilization takes place. However, we're talking about a non-pregnant menstrual cycle, so fertilization and the resulting hormones are not part of this discussion. 

At the peak of estrogen levels in the blood, LH (lutenizing hormone) is released from the pituitary gland and this stimulates the most developed follicle on one of the ovaries to release its ovum in the process called ovulation, which occurs about 13-16 days into the cycle. Every woman is different; these are averages. 

Once released from the ovary, the ovum can only live on its own, or stay viable, for about 24 hours at the most. It not fertilized, it breaks down and is shed along with the uterine lining. 

Around the time of ovulation, the follicle which released the ovum becomes a structure called the corpus luteum on the surface of the ovary. This structure increases both estrogen and progesterone production in preparation for implantation. When implantation of a fertilized ovum does not occur, the levels of estrogen and progesterone drop, and this causes the uterine lining to break down and to be shed in the process of menstruation. 

The abrupt decline of estrogen and progestrone are what give many women "PMS" because mood, sense of well being and physically feeling well can be affected temporarily by the dropping out of these hormones. 

Once menstruation happens, we go back to the FSH stimulation and begin the cycle again.

Source(s): masters in human physiology, many years teaching physiology and AP bio