The menstrual cycle
During the monthly cycle, the mucous membrane slowly builds up in the uterine cavity. If fertilisation does not take place after ovulation, the mucous membrane is shed at the end of the cycle.
This process results in monthly bleeding, which can be of varying intensity and length, and can be more or less painful.
These diagrams show the structure and shedding of the mucous membrane in the uterus during a cycle.