The hormones produced function not only to get the endometrium ready for a potential embryo,But also act on the breast,bone and other tissues to prepare the body for a potential state of pregnancy with subsequent childbirth and the need for breastfeeding.Should fertilization of the egg occur at or about 2 weeks into the cycle (usually in the fallopian tube) the endometrium must be ready for an embryo to implant itself into the endometrium. Ovarian estrogen and progesterone travel in the blood and interact with cellular receptors of the uterus endometrium. Both hormones are produced by cells in the ovaries that surrounds and nourish the eggs of the ovaries. Each hormone will affect the endometrial cells in somewhat different ways.