Figure 2. These blood vessels were spiral arteries (before the uterus became pregnant), but now have been remodeled. Spiral arteries remodeled by pregnancy hormones and by trophoblast are called uteroplacental arteries. Note that the normal vascular media has been replaced by a pinkish material ("fibrinoid"), the lumen calibers are markedly larger, and there are numerous endovascular cells, trophoblast, which have been "caught" in this section, as they were crawling down the margins of the blood vessels en route to remodel these vessels at deeper (myometrial) levels.