Understanding the Decidua: Functional Layers and Menstrual Cycles

Decidua is the thickened endometrium that lines the uterus, and it is shed during menstruation. The decidua is made up of two layers: the functional layer and the basal layer. The functional layer is the outer layer of the endometrium that responds to hormonal changes and grows in preparation for a potential pregnancy. The basal layer is the inner layer of the endometrium that remains relatively stable and provides a foundation for the functional layer.

During the menstrual cycle, the functional layer of the decidua thickens and becomes more vascular in preparation for a potential pregnancy. If pregnancy does not occur, the functional layer breaks down and is shed as menstrual fluid. The basal layer remains intact and continues to provide a foundation for the next menstrual cycle.

It is important to note that the term "decidua" is often used interchangeably with "endometrium," but they are not exactly the same thing. The endometrium is the entire lining of the uterus, including both the functional and basal layers, while the decidua is only the thickened outer layer that sheds during menstruation.