Endometriosis is a disorder in which tissue resembling the endometrial tissue (that lines the uterus) grows in patches outside of the uterus. These patches or lesions swell and shed in response to the hormones that control the menstrual cycle. Unlike endometrial tissue within the uterus, these lesions cannot shed properly, causing inflammation and pain.

The causes of endometriosis are unclear, but one hypothesis is the stem cell theory.

What are stem cells?

Stem cells are a special type of cells that can develop into many other cell types. In embryos, essentially all cells are stem cells, but as the embryo develops, some stem cells lose the ability to change into other cell types. In most tissues in adults, stem cells are able to help tissue heal and regenerate after injury. However, these cells are more limited in ability than embryonic stem cells — a liver stem cell would not be able to become a muscle cell, for example.

A population of stem cells in the uterus helps the endometrium regenerate after shedding each month during menstruation. These stem cells divide and produce more endometrial tissue to replace what has been lost during menstruation.

What is stem cell theory?

The stem cell theory of endometriosis suggests that the stem cells in the uterus may be able to migrate outside of the uterus. Once outside the uterus, these cells may divide and form endometrial-like tissue that expands into the characteristic endometrial lesions.

What might cause stem cells to migrate out of the uterus is unknown, but some researchers have suggested that this might be the missing piece connecting retrograde menstruation to endometriosis.

Retrograde menstruation is the theory that menstrual discharge can flow up the uterus or fallopian tubes, carrying endometrial cells that might implant outside of the uterus. Retrograde menstruation as a cause of endometriosis does not have much support because evidence suggests that it happens to nearly every woman every month, and yet not every woman develops endometriosis.

Current theories suggest that retrograde menstruation might carry a small number of stem cells and that a certain number of these cells might implant outside of the uterus and form lesions over time.


Last updated: August 2, 2019


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