Your uterus has 3 layers:
perimetrium (outermost layer)
myometrium (middle, muscular layer)
endometrium (innermost layer)
This endometrium is the one that's the focus of this blog post. The endometrium has a basal layer and a functional layer.
It's this functional layer that ebbs and flows throughout a menstrual cycle. It contains immune cells and lots of blood vessels.
Menstruation is triggered by a drop in progesterone in the previous menstrual cycle. This drop initiated a destabilization and inflammatory response in the endometrium.
This inflammatory response is a bit like what happens if you were to injure yourself: redness, swelling, and immune compounds are present.
During a period, there's more fluid that's drawn into the uterus, there's an increase in blood flow, and prostaglandins and leukotrienes (immune compounds) are produced. And, all of this happens without any scars or loss of function in the uterus (... only if my skin would react this way without any scarring!).
Hopefully, this sheds some light onto this monthly process and helps explain some of the things that you notice in yourself at this time, like fluid retention, discomfort, and softer stools.
If you experience period pain, especially significant period pain, then that might be because you produce a lot more of the inflammatory mediators. We don't necessarily know why, but working on this immune response can be helpful to decrease the pain. You can check out my blog posts on some strategies:
