endometrium

The endometrium is the tissue that lines the inside of the uterus, also called the womb. It is not a fixed layer that stays the same all the time. Instead, it changes through the menstrual cycle, preparing the uterus for a possible pregnancy. You can think of it as a bed of soil being refreshed again and again, getting ready in case a seed needs a place to take root.

This inner lining has a top part that is shed during menstruation and a deeper part that helps it grow back. Hormones, mainly estrogen and progesterone, control these changes. After menstruation, the lining begins to thicken and build up more blood vessels. If fertilization does not happen, hormone levels fall, and the upper part breaks down and leaves the body as menstrual flow.

If a fertilized egg attaches to this lining, the tissue helps support and nourish the developing embryo. During pregnancy, it continues to change and becomes part of the support system between mother and baby, including the maternal part of the placenta.

The health of the endometrium is important for reproductive health. Problems related to it can include endometriosis, in which tissue similar to this lining grows outside the uterus, adenomyosis, in which this kind of tissue grows into the muscular wall of the uterus, and endometrial hyperplasia, which means the lining becomes too thick. These problems can cause pain, unusual bleeding, trouble becoming pregnant, and other complications. Doctors may take a small sample of the lining in a procedure called an endometrial biopsy to help diagnose problems or check for cancer.

So, the endometrium is much more than a simple inner covering. It is an active tissue that responds to hormones and plays a central role in menstruation, fertility, and pregnancy.