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  • Category: Cardiology

    Why do veins appear blue in colour?

    Wondering why veins appear blue in colour? Find responses from experts on this page.

    Why do veins appear blue in colour when they carry blood which is red in colour?
    One person suffering from anaemia. She often complains of tiredness and lack of energy. Why does she show these symptoms? Also explain about the need of book lungs. What are the functions of book lungs?
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  • Answers

    5 Answers found.
  • There are two blood vessels-1. veins 2. artery. Artery carries the pure blood from heart to different parts of body and supply the oxygen and other nutrients to the cells whereas the veins carry the deoxygenated/ the impure blood to heart for purification. Due to lack of oxygen the veins color appears blue.

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  • Red color of blood is due to a pigment called hemoglobin. This pigment carries oxygen. From heart fresh blood is pumped through arteries which is bright red in color due to oxygenated hemoglobin. Since arteries are deep and light cant cross the skin so usually we dont see red color arteries but the fact is seen where there is abundance of capillaries like lips, ear lobes, tongue etc. (This is the reason why anemia is clinically checked at these places.)
    Veins are carrier of deoxygenated blood to heart, so there is reduced hemoglobin (Here reduced doesnt mean less but reduced means non oxidized) and is present in periphery as well so appears blue.

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  • I think this color variation is learnt in schooling. The colors are always observed in wavelength and they are usually reflected back to us. Veins appear blue because blue light is reflected back to us. As per science blue light will not able to penetrate our human body so it is reflected back, but where as veins are very closer to the skin and thus the red light is absorbed and there is nothing to reflect. That's why veins appear in blue color even when blood is red in color.

  • Veins carry blood which is rich in CO2 and with less haemoglobin. In common parlance, this blood is called 'impure' blood. On the other hand, arteries (except pulmonary artery) carry blood rich in oxygen and haemoglobin. As the veins carry blood with less haemoglobin, they appear bluish.

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    When light falls on the skin surface, it penetrates the skin, is absorbed and re-emitted. The veins present underneath the skin surface re-emit small amounts of red light and high amounts of blue light, which is visible. This is one of the reasons, why veins appear blue.
    When the blood carries oxygen, it is known as oxygenated blood (carried through arteries). After it is supplied to the organs and comes back to the heart, it is known as de-oxygenated blood (carried through veins). And as the oxygen levels falls (de-oxygenated blood), the colour changes from red to dark red, which in turn appears closer to blue.
    when light falls on the skin, this small difference in colour is amplified and veins tend to appear blue and arteries that have smaller diameter and located deep inside the skin look red.
    the visual reception process. For example, if there are red coloured and purple coloured objects, you brain perceives the purple as a shade of blue. So your brain processes whatever you visualise through the retina. So this can be one of the reasons why veins appear blue to you even though they are not.

  • When light falls on the skin, only blue colour is reflected out. due to the presence of veins superficially beneath the skin, only we can see the veins, which also in blue colour. Generally veins carry the deoxygenated blood and there is a difference in concentration of the fluid between the oxygenated and deoxygenated blood, this may be the another reason. The third reason may be the thickness of the blood vessels.The veins are thinner than the arteries hence when light falls on the vessel of vein can easily reflected.

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