No, hon - a lot of the pain is in muscle cramps, hence the term “menstrual cramps”. Anything ranging from a mild ache to a knock-you-over charliehorse spasm.
Inflammation is also a factor, yes, but they really are CRAMPS. Uterine wall muscle contracting and all that.
>sigh<
It’s BOTH. It’s uterine lining AND blood, some of which actually can clot into nasty lumps, along with a fair bit of vaginal mucus.
The uterine lining grows into this spongey stuff due to a rich network of small blood vessels. At a certain point, these pinch off, starving the squishy uterine tissue and killing it. Then they re-open and break off, the resulting blood helping the tissue to slough off and leave the vicinity. It’s not usually gushers and geysers, but the uterus really does bleed until the little blood vessels seal off and the cycle starts over.
So, blood thinners or not, the uterus does bleed after the endometrium (you had that correct) falls away. Likewise, the uterus bleeds for some time after childbirth, after the placenta peels away and is expelled. It is rare, but menstrual bleeding can become life-threatening if the volume lost is excessive or the blood refuses to clot at all.