Menstrual blood is a natural fluid that is expelled from the uterus during a woman's menstrual cycle. It consists of blood, uterine lining, and vaginal secretions. This process typically occurs once a month and lasts for about three to seven days, depending on the individual. The menstrual cycle is regulated by hormones such as estrogen and progesterone. Menstrual blood can vary in color, ranging from bright red to dark brown, and its consistency may change throughout the cycle. Understanding menstrual blood is important for recognizing normal patterns and identifying potential health issues.