Ultimately, veins and arteries are defined most by: their different shapes.
whether they carry oxygenated blood.
their different sizes.
whether they carry blood to or away from the heart.

whether they carry blood to or away from the heart.  

Explanation: (the last one) hope this helps and have a nice day!:)

my hamster died and my second hamster i got after that one died as well. i also lost two birds named rainbow and kiwi, (they didn't die, they flew off and escaped). i lost a cat named omi, and a dog named snoopie. the best way i got over it is, paying my respects, and just thinking that they were in a happy place. as well as just remembering but not thinking about it all the time, just do fun activities and try not to think about it too much. hope you feel better. i'm sorry about your loss. : (