Tissue layers in the uterus. The outer layer of the uterus, the serosa, consists of a thin layer of epithelial cells. The inner lining of the uterus is the endometrium. The endometrium is comprised primarily of stromal fibroblasts, epithelial cells and immune cells. Proliferation, differentiation and function of the cells in the endometrium varies by the level of reproductive hormones. Then endometrium is the tissue shed in the cyclic process of menstruation. The myometrium is a muscular layer that lies between the serosa and endometrium and is the predominant tissue type in the uterus. In this protocol the anterior or posterior wall of the uterus in each region (lower uterine segment, body and