Dear friends! Please solve my following confusion:

Artery is a blood vessel that carries oxygenated blood from heart to all parts of the human body while vein brings de-oxygenated blood from the body cells to the human heart. The function of both is clearly defined. Now the question is why Pulmonary Artery carries de-oxygenated blood from the heart to the lungs and a pulmonary vein brings oxygenated from the lungs to the heart?
Why both vessels have different functions here or why both have twisted names here?

Knowledgeable members are requested to explain it.

Thanks and regards

Arteries are vessels that take blood away from the heart and veins are vessels that carry blood to the heart. The pulmonary artery carries deoxygenated blood away from the heart to the lungs and the pulmonary vein returns oxygenated blood to the heart from the lungs. Generally, arteries carry oxygenated blood and veins carry deoxygenated blood but that is now how they're defined. The vessels are defined as those that take blood away from the heart and those that return blood to the heart. I could go in deeper if you want. Hope it helps.

The pulmonary artery and the pulmonary vein are just exceptions to the definition.

They're not exceptions to the definition, they're divided into vessels that carry blood to the heart and those that carry blood away from the heart.
Dr. Asad Shafiq

Can anybody tell me why do veins look green (or blue) while the blood is red?

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Mujhe Manzil Ki Talab Hai Na Hi Nakami Ka Dar
Muhjhe Safar Me Acha KHasa Lutf Aata Hai......(hamid)

Deoxygenated blood is generally a dusky or darker red colour. Veins appearing green or blue has more to do with the type of light waves reflected off the skin, thus appearing as green or blue. It varies from skin tone to skin tone.

The color of blood looks green or blue because we're viewing it through a layer of vein wall, skin and hypodermis(subcutaneous tissue). Those tissues bend the light, like the atmosphere bends the light in the sky, turning it blue.

Further, any Doctor will better explain it.

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Left is Right

Couldn't get your point. My point is whereas all the arteries carry oxygenated blood from the heart, and all the veins carry de-oxygenated blood to the heart, the pulmonary artery and the pulmonary vein do exactly opposite. What it means is that the pulmonary artery and the pulmonary vein do not conform to that definition. So they are exceptions.

TS:
You'll never encounter such a question on your paper. Rest assured.

Sorry! Got your point now. They are exceptions when we talk in terms of oxygenated/de-oxygenated blood. Otherwise, all the arteries including the pulmonary artery carry the blood away from the heart. And all the veins including the pulmonary vein carry the blood to the heart. The difference being that the pulmonary artery carries the de-oxygenated blood, unlike other arteries which carry oxygenated blood. The same is the case with the pulmonary vein.

These vessels are 'defined' as those that carry blood to the heart and those that carry blood away from the heart. Their general characteristics include that arteries generally carry oxygenated blood and veins generally carry deoxygenated blood , with the exception of the pulmonary artery and veins. The reversal of function is not an exception to their definition but an exception to their characteristics. You mentioned it being an exception to the definition. It's a minute difference and probably doesn't even matter but i just wanted to clear the concepts of the the person making the enquiry.
An earlier typo may have made my answer somewhat hazy, i typed in 'now' instead of 'not'. Quote correction " The pulmonary artery carries deoxygenated blood away from the heart to the lungs and the pulmonary vein returns oxygenated blood to the heart from the lungs. Generally, arteries carry oxygenated blood and veins carry deoxygenated blood but that is 'NOT' how they're defined.
Again, it's a minor difference but i wanted the person asking to have a clear concept of it.