Question

Why does the pulmonary artery carry deoxygenated blood instead of oxygenated blood? Why does the pulmonary vein carry oxygenated blood instead of deoxygenated blood?

Answer 1

Here we consider the definition of an artery as-"a blood vessel which carries blood AWAY from the heart "
Similarly the definition of a vein is -"a blood vessel which carries blood TOWARDS the heart"

The pulmonary artery carries blood away from the heart and the pulmonary vein carries blood towards the heart. That is why they are called an artery and vein respectively.

True they are exceptions to the definition that we usually follow but when we consider the definition I've mentioned above, it makes sense.
So here we don't consider the nature of blood through the vessel

Hope it helps a bit!!