during a menstrual cycle, what is the purpose of the uterine lining buildup?

During a menstrual cycle, the purpose of the uterine lining build up IS TO PREPARE THE UTERUS TO RECEIVE A FERTILIZED EGG.
If no egg is fertilized during a menstrual cycle, the uterine build up will be dissolve and this will come out of the body in form of blood. If an egg is fertilized during the menstrual cycle the uterine build up will be further consolidated. 

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