Component of the menstrual cycle that focuses specifically on the cyclical changes in the endometrium, the inner lining of the uterus. It consists of different phases, including the menstrual phase, the proliferative phase (corresponding to the follicular phase in the ovulation cycle) and the secretory phase (corresponding to the luteal phase of the ovary). Each of these phases can be further subdivided into early, intermediate and late stages, as determined by histological examination of the endometrial tissue. It is also known as uterine cycle.