Question

in a coloured diagram why do we generally show the pulmonary artery in blue and pulmonery vein in red colour.

Answer 1

Because the color red represents the flow of oxygenated blood in a blood vessel, while, mean blue means deoxygenated blood in a blood vessel.This is the reason that all the arteries except the pulmonary artery is represented in red as they carry oxygenated blood. And that's why the pulmonary is colored red as it also carries oxygenated blood. While pulmonary artery and all the other veins are shown blue because of carrying deoxygenated blood.