Why does blood seem blue in your veins but comes out red?



  1. 0 Votes

    Interesting question mercer. When hemoglobin, the iron containing oxygen transport protein in our blood, is bound to oxygen it is bright red. This happens, for example, just after blood leaves the lungs, or if the skin is broken and the blood is exposed to air. When blood is in its deoxygenated stage, for example when it is returning to the lungs, it is dark red.

    The observation that blood in veins appears blue under the skin, however, has more to do with light absorption and reflection. The color we see is determined by what colors (or light wavelengths) are reflected from the surface of an object. In the case of skin, no light is absorbed very well, which gives it a light appearance (depending on how much melanin it contains). However, there is a higher ratio of red light reflected to blue light. On the other hand, with blood, more red light is absorbed by the blood and more blue light is reflected. So the depth of the vein impacts whether the vein appears blue or red. Ones close to the surface of the skin appear red, while those with a depth of at least 0.5mm appear blue, and if the veins are too deep, we don’t see them at all.

    Hope this helps some.

  2. 0 Votes

    Well, there are two states of oxygen that flow through your viens, oxygenated and non-oxygenated. Blood is naturally blue, but when exposed to oxygen through your respiratory and cardiovascular system, or when your skin is lacerated, your blood turns a vibrant red. Hope I helped, and have a green day!

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