What is lost during menstruation?

During menstruation, the uterine lining, also known as the endometrium, is shed. This process occurs as a response to hormonal changes in the female reproductive system. When a fertilized egg does not implant in the uterine lining, estrogen and progesterone levels drop, signaling the body to expel the thickened lining that was prepared for potential pregnancy. As a result, blood, mucus, and tissue from the endometrium are lost through the vagina.

While oocytes and eggs (both referring to potential fertilizable female gametes) are indeed present in the ovaries, they are not expelled during menstruation. Rather, the menstruation process primarily involves the loss of the uterine lining. Hormones themselves are not lost; they are part of the regulatory process leading to menstruation but are not physically expelled from the body. Understanding the role of the uterine lining in the menstrual cycle is crucial for grasping women's reproductive health and the consequences of processes such as fertilization or lack thereof.