The answer to this would be Uterine wall
A girls menstrual cycle is an unfertilized egg sheds on the uterine wall. This lasts for about 5-7 days. When a unfertilized egg reaches the unterine wall it tends to shed which makes it a cycle. This happens every month unless pregnant. It doesnt happen when pregnant due to the egg being used not needing to be released to the uterine wall.
I hope this helps and have a great day dear <3
