What causes endometriosis?
The cause of endometriosis is unknown. While multiple theories exist to its etiology, these should be taken as hypotheses that need further research to be validated. This is why it is so crucial to keeping investing and funding in endometriosis research within the medical community. It is unlikely that there is only one cause for endometriosis, therefore it is useful to understand what each of these theories proposes.
Sampson’s Theory of Retrograde Menstruation
One of the oldest theories explaining the etiology of endometriosis, proposes menstrual blood containing endometrial cells flows backward through the fallopian tubes and into the pelvic cavity rather than out of the body. These endometrial cells that should have been shed during menstruation can then lead to implantation and further spreading of endometriosis lesions.
Mulleriosis & Embryonic Origin Theory
The theory of mulleriosis proposes that the cause of endometriosis lies in developmental abnormalities in the female reproductive system. It proposes that endometriosis occurs due to abnormal differentiation or migration of any component of the mullerian duct system. This system is a channel in the early embryo that goes on to develop into the fallopian tubes, uterus, and cervix.
Stem Cell Theory
Some believe that the cells responsible for regeneration of the endometrial lining during one’s menstrual cycle may also play a role in the development of endometriosis. The spreading of these stem cells to ectopic regions can then lead to the differentiation of endometrial cells and cause endometriosis.
Many scientists agree that there is a genetic component to the cause of endometriosis. Endometriosis has been studied through a micro perspective in the case of changes in gene expression to a more macro level in terms of what it means to have a family history of endometriosis. With one first-degree family member affected (mother, sister, daughter), a woman has an increased risk of having endometriosis. Besides just inheriting the disease itself, a family history of endometriosis can increase the risk of earlier age of symptom onset, similar symptoms or more severe symptoms, and infertility. Researchers are still trying to understand the mechanisms involved in inheritance and the role of genes. Some studies have found that progesterone resistance may play a role in endometriosis development. However, most of this research has ruled inconclusive to whether these genes are associated with endometriosis, and further study is needed.
- Uterine Peristalsis: Uterine peristalsis, the rhythmic contraction and relaxation of tissue muscle, is one of the fundamental functions of the non-pregnant uterus. Contractions of the uterus allow for proper menstruation and are involved in early reproductive processes, such as sperm transportation and egg implantation. Dysfunctional uterine peristalsis may play a part in the development of endometriosis, particularly through the process of retrograde menstruation.
- Hormones: Researchers have proposed that hormones play a role in endometriosis development. Estrogen and progesterone have been a subject of much debate amongst endocrinologists in all sorts of endometriosis theories. More research is needed to fully understand the exact role of estrogen and progesterone in the development of endometriosis.
- Lymphatic System: The lymphatic system is part of the circulatory system and is responsible for carrying and removing fluids from the body’s tissues. This fluid can contain a variety of essential life components, including red blood cells, white blood cells, and plasma. Many have proposed that this system plays a role in transporting endometrial cells to other parts of the body, which explains how endometriosis can spread throughout the body. The lymphatic system also serves as a connection for endometriosis involvement with the immune system.
- Immune System: The immune system is responsible for protecting the body from disease. In endometriosis, the affected areas become excessively red and swollen. Because an inflammatory response typically occurs when the body is fighting an infectious disease, the immune system’s role in endometriosis progression has become a subject of much interest. Researchers suspect that an issue in the immune system may make the body ill-equipped to recognize and destroy endometrial tissue growing outside of the uterus.
- Oxidative Stress: Free radicals are highly reactive molecules of oxygen. Typically, the body will manage these molecules with anti-oxidants. Although some free radicals can be beneficial for the body, an excessive amount can be harmful. The elevation of free radicals in the peritoneum (lining of the abdomen), and lack of anti-oxidants, is suspected to be one of the links in the chain of events causing endometriosis.
- Apoptosis: Apoptosis occurs when the body signals out dysfunctional cells which could be harmful and destroys them. This is a highly regulated mechanism and is key in the body’s maintenance of preventing disease. In fact, the malfunction in the mechanisms regulating apoptosis is a common cause of cancer. As the body cannot rid itself of harmful, damaging cells, these cells grow and spread, causing tumors and cancer. Endometriosis cells have the capacity to avoid apoptosis. The role this plays in the development of the disease is currently being investigated