Dear experts,
If pulmonaryartery and vein carry deoxidised and oxidised blood instead ofoxidised and deoxidisedblood respectively, then why are they named so? What is the criterion to decide whether a blood vessel is an artery or vein?

I had learned in school that the pulmonary artery carries deoxidised blood but is still called an "artery" because of its characteristic thick walls. Meanwhile the pulmonary vein carrying the oxidised blood back to the heart, so due to less pressure, it does not require thick walls and also shows the presence of valves in it like a regular vein.
I hope this answers your question Abhilasha:))