Question

Why pulmonary artery and pulmonary vein are considered exceptions in terms of blood they transport!???

Answer 1

 pulmonary artery and pulmonary vein are considered exceptions in terms of blood they transport because
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pulmonary artery carries de-oxygenated blood whereas other arteries carry oxygenated blood
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pulmonary vein carries oxygenated blood to the heart whereas other veins carry de-oxygenated blood
 

Answer 2

Pulmonary Artery:-

All arteries carry oxygenated blood away from the heart to all other parts of the body 

Pulmonary Artery carries de-oxygenated blood from the right ventricle (heart) to the lungs.

Pulmonary Vein:-

All veins are responsible to take back deoxygenated blood to the heart after arteries carry blood out.

Pulmonary Vein is the only vein which carries oxygenated blood from the lungs to the  heart.