The uterine lining (endometrium) consists of two types of tissue: the stroma and the supporting structure and the glands (buried withing the stroma). During the second half of the menstrual cycle (10-27) the rising progesterone levels STOP proliferation of endometrial cells that happened in the first half of the menstrual cycle due to strogens. Progesterone matures the stroma and glands, turning them into cells that can nourish and support a developing embryo. The blood supply to the uterus increases and the lining thickens with additional fluid and nutrients.