Why do blood vessels look blue under the skin?

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Veins looking Blue It is an optical illusion caused by light reflecting on and through the skin.

Blood in the arteries is bright red, blood in the veins is dark red mostly from the impurities that are being carried back to the kidneys and liver for disposal that are mixed in and brownish which darkens the red color to more maroon. Blood in veins can look "blue" when viewed through the skin because of light refraction and other factors. But the blood is red and the veins are actually white.

When a person donates blood, it comes from a vein, not an artery. It is also not exposed to air, or it would be contaminated and need to be disposed of. It also happens to be dark red, NOT blue.

The common misconception of "blue" blood is continued due to textbook illustrators use of blue and red to differentiate arteries and veins. Venous blood is actually a burgundy or maroon color.

An Optical Illusion
The reason we see blue is more into the optics side of science. It is really because of how light reflects on our skin, and the way different wavelengths piece through our skin with different effectiveness.

The veins you see through your skin appear blue because red light goes through the skin much more easily (and thus more) than blue light. The red light is absorbed, and the blue is reflected. Optical scientists also believe that the eyes see more of the blue color than the red.

A vein is just a tube blood travels through when returning to the heart and lungs after depleted of nutrients and oxygen, the neutral color of a vein itself doesn't change the color of the blood.

It is not the blood but the veins that "look" blue, and even then it is not the actual color of the vessel. The difference is in the way colored light moves through the tissues, and how the eye perceives those colors of light.

The oxidation state of the iron in the hemoglobin also affects the color but only slightly and not as much as the wastes carried in the veins do.

Some factor of the changes in blood coloration do relate to the respiratory pigment, hemoglobin. Hemoglobin is a topologically complex molecule that very readily binds to oxygen. Once the molecule is fully saturated, it reflects in the crimson red spectrum, and therefore fully oxygenated blood appears to be bright red. After the hemoglobin molecule gives up its oxygen to tissue that needs it, the molecule becomes much less reflective, and with the added wastes the venous blood carries, the returning blood appears very dark red to purple. However, it is more the addition of wastes that impacts the darkened color, not so much the change in oxygen content.

As mentioned above, blue is often used in illustrations in charts and diagrams of the circulatory system and vessels to contrast against red, with usually red representing the arterial system bearing O2 and blue being the "deoxygenated" blood in the venous system. However, this tradition of using these colors is just that: tradition. It is not based on actual blood color. The colors could just as easily be shown as yellow or green for the purposes of the illustrations to show blood flow.

The reason why only veins appear blue to your eye is because they are the most superficial to the skin and therefore seen through the skin. Arteries can not be seen because of how deep they are in the body (a protective mechanism of our bodies). The color blue/violet is the highest frequency of the visible light scale; it therefore has the most penetrating power to be seen through skin, fat, etc. Red is low frequency and is filtered out by skin and fat, which is why it cannot be seen.

Science Project: If you took a red diode light and put it in milk, it would appear blue in color because milk filters the red out much like our fat/skin. Try it and see!
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When does blood look blue?

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Which blood vessels have blue blood?

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Why does blood appear blue under the skin?

Veins are very close to the skin, which allows them to play a role in heat dissipation. Because they are so close to the skin, you are able to easily see them. They appear blue because of the way light diffuses through the skin. It possibly also has to do with the way that subcutaneous fat absorbs l (MORE)

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only the veins are blue because they blood cells have no oxygen so they are heading back to the heart for fresh oxygen and then goes through this progress again. the blood is red because its blood of course.