Menstruation occurs as part of the menstrual cycle, which prepares a woman's body for the possibility of pregnancy each month. During the cycle, the lining of the uterus thickens to create an ideal environment for a fertilized egg. If pregnancy does not occur, hormone levels (especially progesterone) fall, leading to the shedding of the thickened uterine lining. This shedding is what causes the bleeding observed during menstruation, known as a period. The menstrual cycle then restarts, preparing the body again for potential pregnancy in the next cycle.
Biological Process of Menstruation
Monthly, the pituitary gland, ovaries, and uterus interact hormonally to regulate the cycle. Estrogen causes the uterine lining to thicken, and ovulation releases an egg from the ovary. If the egg is not fertilized, the drop in progesterone triggers the breakdown and shedding of the uterine lining, which exits the body as menstrual blood.
Evolutionary Purpose
Menstruation is viewed as a mechanism to renew the uterine lining when pregnancy does not occur, ensuring the uterus stays healthy and prepares for a possible future pregnancy. It is a characteristic seen in humans and some other mammals, thought to be linked to the way the embryo implants and maternal-fetal interactions.
In summary, menstruation is the body's natural way of resetting the uterine lining monthly when pregnancy does not take place. This is why it occurs regularly in reproductive-aged individuals as part of the menstrual cycle.
