Why are veins blue in color?

Answer 1

Contrary to popular belief, the veins are not blue. The color of most blood is a transparent yellow which is due to the majority of blood being comprised of blood plasma (If you have seen blood centrifuged, you know what I am referring to). The hematocrit is the only part of blood that is red: dark red if deoxygenated and bright red if oxygenated. No blood is blue (inside the body or out). Dried blood which has no gaseous oxygen in it is still red (though a brownish red at that) because the iron in the bood is still rusted from oxidation. The red blood cells have iron in them due to the hemoglobin molecule in them. It is the iron in blood which attracts oxygen that gives it its red color. The reason why only veins appear blue is because they are the most superficial to the skin and therefore seen by the eye. 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. 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!

Answer 2

Contrary to popular belief, the veins are not blue. The color of most blood is a transparent yellow which is due to the majority of blood being comprised of blood plasma (If you have seen blood centrifuged, you know what I am referring to). The hematocrit is the only part of blood that is red: dark red if deoxygenated and bright red if oxygenated. No blood is blue (inside the body or out). Dried blood which has no gaseous oxygen in it is still red (though a brownish red at that) because the iron in the bood is still rusted from oxidation. The red blood cells have iron in them due to the hemoglobin molecule in them. It is the iron in blood which attracts oxygen that gives it its red color. The reason why only veins appear blue is because they are the most superficial to the skin and therefore seen by the eye. 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. 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!

and this site is gay and wrong the reason veins are blue is because the blood inside is blue as well and goes red when it touches the air but this is to quick for the human eye

Because your blood is blue into it is in touch with oxygen and then it turns red

Answer 3

The answer is really quite complicated. There is less red light reflected from the shallow area between the surface and the vein than blue light because blue light is scattered more. The surrounding tissue reflects back more red. This does not make the vein blue, however. It only makes it look blue.

If you eliminate the surrounding color the blue effect should go away. I just took a piece of white paper and punched a round hole in it with a three-hole-punch. When placed over a vein, sure enough I don't see blue. Try it yourself.

Answer 4

To begin with, it is not because veins contain blue blood. All human blood is red.

The compound that gives blood its red colour is called haemoglobin, and is the primary "tool" used for oxygen transport in the blood, as it increases the amount of oxygen that can be dissolved by a large factor. It does this by binding oxygen to an iron ion, embedded within the structure of the heamoglobin molecule. These iron ions are the same thing that cause rust to be orangey-red and Mars to have its bloody colour.

When it does this, it causes the oxidation of that iron, to a higher oxidation state. The result is that the compound becomes a deeper, darker red (because of the way light is given out by atoms and ions, and the way this is affected by the presence or absence of cerain electrons). However, when there is no oxygen, the iron is reduced back to the original state. When the compound contains iron in this form, it gives off a much brighter red.

It goes without saying that arteries contain blood with lots of oxygen and therefore much more "dark haemoglobin" - that in the oxidised form - while veins carry blood with little oxygen and therefore much more "lighter haemoglobin" - the reduced or original form. Because of this lighter colour, combined with the colours of the vein itself and the skin and tissues around it, veins appear blue.

Also, blood which has lost all of its oxygen is very sad, and is feeling blue on its way to back to the lungs. When you feel blue, sometimes the emotion leaks out and you actually turn blue. So veins are sad, and arteries are elated (or maybe angry - red).

Answer 5

Your blood in your veins isn't blue honestly. I thought that too. The blood in your veins is deoxygenated (It has no oxygen in it) so it is usually a deep deep red going on purple. The veins appear blue because you are looking at them through your skin.....I suppose it's a trick of the light! Hope I've helped =D

Answer 6

When someone asks the question "why are veins blue?" a likely response is that they're blue because the blood in veins is deoxygenated. While it's true that venous blood vessels carry a lower concentration of oxygen than their arterial counterparts, this isn't the reason for their blue appearance in your skin. Still, when someone invariably responds to the veins-are-blue-because-they're-deoxygenated argument with the observation that "I've never seen blue blood before" one might then hear the slightly more sophisticated-sounding but increasingly far-fetched claim that we don't ever observe blue blood because it is immediately oxidized upon contact with air. (Check out these beauties from Yahoo Answers to witness these arguments yourself.)

Wrong. Blood is never blue. Ever. Period. (And, this is an excellent example of why you should never ingest information from Yahoo Answers uncritically.)

The bright red color of arterial blood stems from a complex that's formed between hemoglobin, iron, and molecular oxygen. This complex mainly absorbs higher energy (shorter wavelength) blue and green light, leaving behind primarily just red wavelengths for our eyes to detect. However, even when blood is largely depleted of oxygen, it is never blue: it's more of a deep maroon color. And, although I have not participated in a surgery myself, those who have (including my girlfriend, a veterinary student) assure me that in surgery, veins within the body do not appear blue either. So, not only is blood not blue, veins on their own aren't either. "Blue veins", then, are a phenomenon unique to the skin.

So, what's going on here?

The most comprehensive answer that I've been able to find comes from a paper by Kienle et al. published over twelve years ago in the journal Applied Optics and entitled "Why do veins appear blue? A new look at an old question". Based on the findings of the authors, three reasons emerge for the blue appearance of veins in skin. The first two are physical and stem directly from the way in which light interacts with blood (how it is absorbed) and with skin (in this case, how light is reflected). The final reason is psychological, dealing with the way in which our brain processes information relatively to generate color perception. (Greg Laden sort of hinted at some of this recently on his blog).

Since the paper in question is a study in optics, it is way outside of my area of expertise. So, just in case you wanted an in depth technical critique of its methodology, you're not going to find it here. However, I can give you a basic summary of the paper's major findings. And then, if you still have the desire (and the ability) to explore the subject in greater depth, you can parse through the paper yourself.

To tackle this problem, the authors measured how much light of various wavelengths was reflected from both real blood vessels in skin and imitation vessels in a skin-like environment, using a sophisticated technique that gave them spatially-resolved measurements. The synthetic vessel (which was a capillary tube filled with blood and placed in a milky substance with optical properties similar to skin) allowed the authors to experiment with a variety of parameters (particularly vessel depth and diameter), and they were then able to validate their results by taking measurements on actual vessels in skin. Using this set-up, they were able to demonstrate that the optical properties of skin and blood (combined with the influence of relative color perception) explain why veins in skin appear blue, despite not actually being blue.

Skin does not absorb much light at any wavelength, making it look white (depending on how much melanin is present, of course-making this discussion only really relevant to people with lighter skin). Blood, on the other hand, absorbs light of all wavelengths (but less in the red part of the spectrum). However, blue light does not penetrate the skin as well as red light. If a vessel is near the surface of the skin, almost all blue light is absorbed by the vessel, so even though only about 1/4 of the red light is reflected, the ratio of red light reflected to blue light reflected is about 10:1. This vessel appears red.

If the vessel is deeper (about 0.5 mm or more), not as much blue or red light will be absorbed. Importantly, this effect will be more pronounced on blue light than on red light since blue light doesn't penetrate skin very well (the ratio of red light reflected to blue light reflected is about 3:2 or less). This is the case for the "blue veins" observed in skin. Once the vessel is deep enough, though, it won't be seen at all, as light of all wavelengths will be reflected before it can interact with the blood.

Perplexingly, this 0.5-mm-deep vessel appears blue despite reflecting slightly more red light than blue light. This is where relative color perception comes into play. The surrounding skin reflects more red light than blue light (by a ratio of about 5:3), and it does not absorb as much of either type of light as a blood vessel does. Since vision is influenced in part by relative perception, if something purple is placed next to something red, the purple object will appear blue.

None of this, however, addresses the question of why veins specifically appear blue. To answer this one, I can fortunately once again rely on the expertise of Meredith, my vet student girlfriend. The reason why only veins appear blue is that veins are the only vessels we actually observe through the skin. This is due to the fact that veins are larger, have thinner walls, and are more superficial than arteries (and, no, I don't meant that veins prefer People or Us Weekly over The New Yorker-"superficial" is just medical speak for closer to the surface). All of these aspects of veins have clear biological rationales. Beyond just carrying blood back to the heart, the primary function of the venous system is as a blood reservoir. In fact, about two-thirds of your blood volume is held in your veins at any given time, hence their larger size. Because the heart has to push blood directly through arteries, their walls are subject to higher pressures than the walls of veins, so they need to be thicker. Finally, veins are located closer to the surface of the skin, because they also play an important role in heat exchange with the outside environment (to help cool the body). Arteries could perform this function just as well, but it's much more advantageous to keep those higher pressure blood conduits deeper in the body and protected from injury.

The take-home message here is that the bluish appearance of veins in the skin has everything to do with where they are located, and nothing to do with the concentration of oxygen within them. In fact, if we could see them through the skin as well, even arteries would look blue.

Answer 7

when the blood isn't touching oxygen, it's blue. But when it touches oxygen, it turned red.

Answer 8

because blood pumped from the heart is blue till oxygen hits it

Answer 9

because they are blue in colour