Endometrium

A specialized tissue that lines the uterus and undergoes changes during the menstrual cycle. It builds up (proliferates) under the influence of estrogen during the follicular phase before ovulation. Following ovulation, under the influence of progesterone as well as estrogen, it becomes more mature (secretory) and ready for egg implantation. Endometrial shedding occurs normally with a decrease in estrogen and progesterone levels but occurs with decreases in estrogen levels in anovulatory cycles and also despite continued high levels of estrogen. Estrogen stimulates and progesterone inhibits the endometrium. OR the inner lining of the uterus that is stimulated by estrogen to become thicker, and is caused by progesterone to become mature and ready to support a fertilized egg.