Girls have periods because their bodies are biologically designed for reproduction. Each month the uterus prepares for a possible pregnancy by thickening its lining to nourish a fertilized egg. If the egg released from the ovary is not fertilized, hormone levels drop, causing the thickened uterine lining to shed and exit the body as menstrual blood. This natural cyclical process is called menstruation or having a period and usually begins around puberty as part of a healthy reproductive system.
Biological Purpose of Periods
The menstrual cycle is regulated by hormones such as estrogen and progesterone. Estrogen helps thicken the uterine lining, and progesterone maintains it if fertilization occurs. Without fertilization, progesterone levels fall, signaling the body to shed the lining. This prepares the uterus for the next cycle, making pregnancy possible if an egg is fertilized.
Evolution and Significance
Menstruation likely evolved to accommodate the unique way human embryos embed into the uterus lining. Shedding the lining monthly helps maintain a healthy uterine environment and may prevent infections or other complications.
In summary, girls have periods as a crucial part of the reproductive system that prepares the body for potential pregnancy, and menstruation is the process of shedding the uterine lining when pregnancy does not occur.
