What lining is involved in the menstrual cycle?

The endometrium is the lining of the uterus that plays a crucial role in the menstrual cycle. Its primary function is to provide a suitable environment for a fertilized egg to implant. Each month during the menstrual cycle, hormonal changes cause the endometrium to thicken in preparation for potential pregnancy. If fertilization does not occur, the levels of hormones drop, and the endometrium is shed during menstruation.

The myometrium is the muscular layer of the uterus responsible for contractions during childbirth and menstruation, but it does not directly participate in the cyclical changes that occur in the menstrual cycle. The epithelium refers generally to the outer layer of cells on various organs, while the peritoneum is the membrane that lines the abdominal cavity and does not relate specifically to the menstrual cycle. Thus, the endometrium is the correct answer as it is directly involved in the cyclical changes that define the menstrual cycle.