The Endometrium And It's Important Role In Your Reproductive Health

The human uterus, showing the boundary between the endometrial glands and the smooth muscle. (Magnification x100)
Garry DeLong / Getty Images

What Is The Endometrium?

The endometrium is the lining of the inside of your uterus. The uterus is a part of ​your reproductive system along with the fallopian tubes and ovaries. The function of the reproductive system is to reproduce. In other words, make babies.

Your uterus provides a place for a baby to grow. It is made of smooth muscle called the myometrium. The lining of the uterus or the endometrium (also called the endometrial lining) plays a vital role in supporting a pregnancy.

The endometrium can be divided into two layers a functional layer and an underlying basal layer. The surface of the functional layer is made up of specialized epithelial cells. In addition, uterine glands and supporting tissue that contain lots of blood vessels exist in both the functional and the basal layers. 

The lining of the uterus is a dynamic structure. The role of the endometrium is to provide a place for a fertilized egg to implant and to support the development of the placenta. Menstruation happens when the prior ovulation did not result in implantation of a fertilized egg. So, you bleed or menstruate each month because you did not become pregnant..

What Is The Function Of The Endometrium?

The endometrium undergoes cyclic changes in response to the same hormonal changes that cause ovulation.

Every cycle before ovulation happens the endometrium undergoes changes to prepare it for implantation of a fertilized egg.

This is the proliferative phase of the menstrual cycle. During this phase, under the influence of estrogen being secreted by the ovary, the lining of the uterus thickens. The uterine glands grow and blood vessels fill the supporting tissue.

At the time of ovulation, progesterone levels increase. Progesterone causes the now thickened lining to mature.

The glands and arteries come together to get ready to allow for implantation and to prepare the base for the development of the placenta.

If implantation doesn’t happen, hormonal changes cause the shedding of the now thickened endometrial lining.

Menstrual flow is made up of the cells that are shed from the functional layer mixed with blood from the little blood vessels that surrounded the glands that end up exposed when the functional layer sheds. As the next ovulatory cycle starts, the functional layer regrows under the influence of estrogen from the basal layer below it.

How Hormones Affect The Endometrium

Because the endometrium changes in response to the changing hormone levels of an ovulating woman, the endometrium of young girls and menopausal women is relatively thin and doesn’t change.

The endometrium also responds to hormonal medications or excess physiologically produced hormones in the same way that it responds to natural hormone changes.

For instance, obese women because their excess fat cells produce excess estrogen they will often have heavier periods because of an extra build up in the functional layer during the proliferative phase. This chronic extra build-up can also lead to a condition called endometrial hyperplasia.

Another example is what happens to the endometrium in women who are using progesterone only contraception like the Mirena intrauterine device or the contraceptive implant Nexplanon. Both of these methods result in a chronic excess of progesterone that limits then suppresses the build-up of the functional layer of the endometrium. This ultimately results in minimal to no menstrual bleeding because there is very little to no lining to shed.


Updated by Andrea Chisholm, MD


Maybin,JA. Menstrual Physiology:Implications For Endometrial Pathology and Beyond. Human Reprod Update. 2015;21(6):748-761

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