tud jaz sem bila presenečena da je 1ka vseeno kar velika, ampak je super zadeva. Ampak ker še nisem navajena koliko časa traja preden se napolni stalno preverjam

The hole in our cervix is what the blood comes out of. It starts off up in the uterus, but the uterus has to cramp down rather hard, and do a bunch of pushing and squeezing to get that blood through the cervix and eventually, out the vagina. There is also gravity, pulling everything down.
In order for your menstrual blood to go back up into the uterus, it would have to force itself back through the cervix (with no strong muscle such as the uterus to push it though). Then it would have to fight gravity some more, to get all the way up through the uterus.
It takes a lot of muscles contractions for the uterus to squeeze the blood through the tiny cervix hole– it is not an easy task, and there is no force or muscle that would be pushing it back the other way through the cervix.