How exactly does endo cause pain?
Endometriosis lesions themselves are not believed to cause pain. This may be the reason why some women with endo are symptomless until they run into fertility problems.
It is the inflammatory response of the tissues surrounding endometriotic lesions that causes pain, in addition to the irritant fluid endometriosis lesions can secrete into the pelvis, which irritates the peritoneal lining, nerves and tissues of the pelvic cavity.
Other ways that endometriosis can cause pain include distortion of the normal pelvic anatomy due to adhesions, kissing ovaries etc.
Large endometriomas can leak stale (deoxygenated, brown) blood hence the name "chocolate cysts".
Endometriosis on or near nerves, for example the sciatic nerve, affect the nervous system and cause high levels of pain as well as affecting muscle movement. To read more about sciatic endometriosis check out Professor Marc Possover's blog (Switzerland) and also the work of Shaheen Khazali (U.K).
"Endometriosis is composed of glandular tissue surrounded by tissue called stroma. All glandular tissues secrete substances. For example, sweat glands secrete sweat; saliva glands secrete saliva. We don't know exactly what the glands involved in endometriosis secrete, but it is probably difference from what the endometrial glands of the uterine lining secrete.
This substance leaks out into the surrounding tissue and can be very irritating.
These secretions can destabilize adjacent capillaries, causing them to bleed, which may be part of the pain women with endometriosis experience. Of course, many endometriosis lesions are not associated with any bleeding at all, so the secretions themselves must have the ability to irritate tiny nerves in the peritoneal lining and the surrounding tissues."
"Endometriosis does not slough and shed like the menstruating uterine lining and many lesions of endometriosis are not associated with bleeding."
David B. Redwine, MD via Endo Girls Blog, 2019
"Endometriosis lesions themselves have never been observed to be bleeding at laparoscopy"
Charles E. Miller, Endo Dubai Congress, 2019