The endometrium is the mucous membrane that internally lines the uterus. It experiences morphological and functional changes along the woman’s menstrual cycle, with the intent to accomplish its major function: to host the embryo.
The endometrium on its first stage is proliferative, and after the ovulation it becomes secreting, being then a more mucous one and nutrient-richer, and preparing itself for the embryo’s arrival if the fertilization of the egg has taken place.
If there is to be implantation, the embryo at blastocyst stage must mantain a close dialogue with the endometrium, both tissues must synchronise one another and several growth factors must be given. The highest point of endometrial receptivity is known as implantation window and lasts about 4 days.