THE MENSTRUATION, or "flow", (Menses for short) is the presence of blood flowing from the lining of the womb, through the neck of the womb, down the vagina and visible on the outside of the genital area.
Menses is a combination of fresh and clotted blood within the endometrial (lining of the womb) tissue. The initial flow of menarche is usually a brighter color of red than the later, mature menstrual flow. It is often minimal in amount and may be very brief, with just a single occurrence of "spotting".
Within two to three years of reaching menarche, a hormone called estrogen stimulates growth of the womb, breasts, and pelvis. It also helps girls grow taller and it lays down adipose tissue (fat cells).