Embryonic implantation.

Embryo implantation is a progressive process which requires a communication between two different organisms, and consists of three consecutive phases: apposition, adhesion and invasion. It must be realized throughout the period called "window of implantation", which is characterized by morphological and biochemical changes in the endometrium, as the plasma membrane transformation and the presence of some specific adhesion molecules, chemokines, cytokines, growth factors, and invasive proteinases. All of then acting in a paracrine/autocrine manner, and drive by endocrine hormones.