ABSTRACT
The endometrium is a highly dynamic tissue that undergoes cyclical variation with every estrous or menstrual cycle during the reproductive years. Under the influence of the changing hormonal milieu, cellular proliferation, differentiation, and apoptosis occur in association with changes in extracellular matrix (ECM) composition and leukocyte trafficking. Among species, the changes are the most extreme in women, in whom the entire functional layer (functionalis) of the endometrium is shed at menstruation with subsequent regeneration of the tissue from the remaining basal layer (basalis). In other mammals, such renewal occurs only postpartum. The purpose of the remodeling is to provide an environment that is conducive to implantation of the conceptus, but only a time when the conceptus is appropriately developed.1-3 Because the mechanisms of embryo implantation differ widely between mammalian species, the extent of endometrial preparation or remodeling also varies. Importantly, developmental plasticity that is generally lost in adult tissues is retained in the endometrium since this tissue constantly renews during reproductive life. In this chapter, the focus is on dynamic cyclical changes in women, but comparisons are drawn with mice, the most widely used experimental animals.
