Endometriosis is a condition in which the endometrium, or the tissue that usually lines the uterus, grows elsewhere in the body.
The endometrium swells during each reproductive cycle in preparation for a potential pregnancy. If no pregnancy occurs, the endometrium is broken down and shed during menstruation. The endometrial tissue that grows outside the uterus also goes through the same changes during the reproductive cycle, but unlike the normal endometrium, it cannot shed and exit the body. This leads to pain and inflammation at the site where the endometriotic tissue has implanted.
The exact cause of endometriosis is not well-understood, and a combination of factors are likely to play a role. It is thought that endometriotic tissue may be spread through the circulatory and lymphatic system, leading to the development of endometriotic lesions at distant sites.
About the circulatory and lymphatic system
The circulatory system transports oxygen, nutrients, and other substances throughout the body. The heart takes a central role in this system by pumping blood through the vessels that supply all tissues and organs in the body.
The lymphatic system is part of the circulatory system and is essential for immune defense and tissue fluid balance. It consists of the lymphatic organs and a network of lymphatic vessels that carry a clear fluid, the lymph, throughout the body. The lymphatic vessels are present in almost all tissues and organs. They connect the lymph nodes, small lymphoid tissues that function as filters for foreign substances, such as bacteria and viruses.
How endometriotic tissue is thought to spread through the circulatory and lymphatic system
The theory about the spread of endometriotic tissue through the circulatory and lymphatic system may explain the occurrence of endometriotic lesions at distant sites, such as the lungs, eyes, and brain.
In women with endometriosis, endometriotic cells are thought to enter the bloodstream through capillary vessels that drain the uterus and pelvis and to travel to distant sites, where they implant and start growing in response to hormonal stimuli.
Endometriotic cells also occur on lymph nodes in the uterus and pelvis. It is thought that these cells may be able to travel from there through the lymphatic circulation to distant sites where they implant to form new endometriotic lesions.
The idea that endometriotic tissue spreads through the lymphatic system is further supported by the fact that endometriotic lesions tend to have a high lymphatic vessel density.
Endometriosis is also associated with an impaired immune function of lymph nodes in the uterus, favoring the survival of endometriotic cells.
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