The endometrium is the mucous membrane that serves as a lining for the inside of the uterus. A woman of child-bearing age generally has two layers of endometrium. The functional layer that grows throughout a woman's menstrual cycle and is shed during menstruation and, beneath that, the basal layer is never shed.
More About Endometrium
The cycle that causes the endometrium to grow and shed is primarily controlled by estrogen and progesterone. The purpose of the endometrium is to provide a hospitable environment for a fertilized ovum.
There are certain circumstances, including menopause or long-term use of certain contraception that can cause endometrial atrophy.