Estrogen thickens the endometrium of the uterus. The FSHR is expressed during the luteal phase in the secretory endometrium of the uterus. Menstruation is the shedding of the uterine lining (endometrium). Estrogen also induces growth of the uterus, proliferation of the endometrium, and menstruation. Endometritis is inflammation of the inner lining of the uterus (endometrium). Placental abruption occurs when the placenta detaches from the endometrium. The cavity of the uterus is lined by the endometrium. Progesterone functions with estrogen by promoting menstrual cycle changes in the endometrium. The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium. Progesterone is a hormone in the endometrium that counteracts estrogen driven growth. Squamous cell carcinoma of the endometrium has a poor prognosis. The trophoblasts adhere by penetrating the endometrium, with protrusions of trophoblast cells. This changes the proliferative pattern of the endometrium to a secretory lining. The decidual cells originate from the stromal cells that are always present in the endometrium. There is an increase of lumican during the proliferative to secretory phase of the endometrium.