A small tear in the lining of the artery.

动有个小裂口。

A dissection is where the inner wall, or intima, gets a tear, and blood tracks into a false lumen in the vessel wall.

动或者说产生撕裂，血流随之进入管的假腔中。

When progesterone reaches its lowest level, the spiral arteries collapse, and the functional layer dies off and is eliminated through menstruation, which marks the beginning of a new menstrual cycle.

当孕激素达到最低水平，螺旋动破裂，子宫功落，形成月经，也开启了一个新的月经周期。