During each menstrual cycle, a lining forms on the wall of the uterus, ready to receive an embryo for development. This lining is called the "endometrium." The lining begins to form shortly after the blood flow ends from the previous menstrual cycle and becomes full developed at approximately the time a woman releases an ovum. If an embryo does not imbed itself into the lining, then the lining begins to break down starting about a week after ovation and is shed, creating the next period of blood flood (or menarche).
The cycle is regulated by a complex series of hormones produced by different parts of the female reproductive system. These hormones serve as a communications system telling the various parts of the reproductive system when one part of the cycle is complete and when the next needs to begin.
