Assertion: vein's lumen | /r/HasProperty | hollow passageway
Facets:
Source sentences:
text: Each type of vessel has a lumen—a hollow passageway through which blood flows.
text: The lumen is the hollow opening or the space inside the blood vessel.
text: These layers surround the lumen, the hollow interior through which blood flows.
text: Each type of vessel has a lumen—a hollow passageway through which blood flows.