Assertion: circulatory system's vein | /r/CapableOf | emphasize the need
Facets:
value: in order to prevent backflow of blood
type: PURPOSE
value: for unidirectional valves
type: PURPOSE
value: inside of the veins
type: LOCATION
Source sentences:
text: The veins are a passive conduit for carrying the blood (controlled by the initial compression and contraction of the heart, arteries and arterioles) emphasizing the need for unidirectional valves inside of the veins in order to prevent backflow of blood.