Endometrium

The endometrium is the inner layer of the uterus, and it is the tissue that lines the inside of the uterus and prepares for pregnancy. Every month it thickens and sheds during the menstrual cycle. If a woman becomes pregnant, the endometrium thickens and becomes the site of implantation of the fertilized egg and the nourishment of the developing embryo. If pregnancy does not occur, the endometrium is shed as menstrual flow. The endometrium is a complex tissue composed of three layers: the basalis, functionalis and the stratum compactum. The functionalis layer is the most prominent layer and is mainly responsible for the cyclic changes in the endometrium that occur throughout the menstrual cycle. This layer is composed of glands, stromal cells and blood vessels. The glands secrete hormones and other substances that are necessary for implantation of the fertilized egg. The stromal cells form the connective tissue that supports the endometrium. The stratum compactum is the innermost layer and is composed of tightly packed epithelial cells that form a barrier to prevent bacteria and toxins from entering the uterus. The endometrium undergoes cyclic changes throughout the menstrual cycle in response to hormones released from the ovaries. During the proliferative phase, the endometrium thickens and the glands become longer and more branched. During the secretory phase, the endometrium further thickens, the glands produce more secretions and the uterine lining becomes more receptive to implantation of a fertilized egg. If pregnancy does not occur, the endometrium is shed during the menstrual period. The endometrium is an important tissue for successful pregnancy. It plays a crucial role in implantation of the fertilized egg, the formation of the placenta and the nourishment of the developing embryo. Disorders of the endometrium can cause infertility, recurrent miscarriages and other health problems.